Note: Descriptions are shown in the official language in which they were submitted.
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POLARIZATION-DIVERSITY OPTICAL POWER SUPPLY
CROSS-REFERENCE TO RELATED APPLICATION
111 This application is a continuation-in-part of and claims priority to
U.S. patent
application 16/888,890, filed on June 1, 2020, the entire content of which is
herein
incorporated by reference. This application claims priority to U.S.
provisional patent
application 63/145,368, filed on February 3, 2021, the entire content of which
is herein
incorporated by reference.
BACKGROUND
Field
[2] Various example embodiments relate to optical communication equipment
and,
more specifically but not exclusively, to optical power supplies.
Description of the Related Art
[3] This section introduces aspects that can help facilitate a better
understanding of the
disclosure. Accordingly, the statements of this section are to be read in this
light and are
not to be understood as admissions about what is in the prior art or what is
not in the prior
art.
[4] As the input/output (I/0) capacities of electronic processing chips
increase, electrical
signals may not provide sufficient I/0 capacity across the limited size of a
practically
viable electronic chip package. A feasible alternative can be to interconnect
electronic
chip packages using optical signals, which can typically be delivered with a
much higher
I/0 capacity per unit area compared to electrical I/0s.
SUMMARY
[5] Disclosed herein are various embodiments of an optical communication
system
comprising a polarization-diversity optical power supply capable of supplying
light over a
non-polarization-maintaining optical fiber to a polarization-sensitive
modulation device.
In an example embodiment, the polarization-diversity optical power supply
operates to
accommodate random polarization fluctuations within the non-polarization-
maintaining
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optical fiber and enables an equal-power split at a passive polarization
splitter preceding
the polarization-sensitive modulation device.
[6] According to one embodiment, provided is an apparatus for communicating
optical
signals modulated at a symbol rate, the apparatus comprising an optical power
supply that
comprises: a light source and an electronic controller connected to the light
source to cause
the light source to generate a first light output having a first optical
frequency and a second
light output having a second optical frequency different from the first
optical frequency,
each of the first and second light outputs being steady during a time interval
that is
significantly longer than one over the symbol rate; and a polarization
combiner connected
to receive the first and second light outputs of the light source at different
respective input
ports thereof, the polarization combiner being configured to generate, at an
output port
thereof, an optical output in which first and second mutually orthogonal
polarization
components carry light of the first and second light outputs, respectively.
[7] In some embodiments of the above apparatus, the electronic controller is
configured to
cause the first light output and the second light output to be mutually
time/frequency
orthogonal.
[8] In some embodiments of any of the above apparatus, a degree to which the
first light
output and the second light output are time/frequency orthogonal is greater
than 0.8.
[9] In some embodiments of any of the above apparatus, the degree is greater
than 0.9.
[10] In some embodiments of any of the above apparatus, the degree is greater
than
0.99.
[11] In some embodiments of any of the above apparatus, the first light output
comprises
a first continuous-wave optical field at the first optical frequency, and the
second light
output comprises a second continuous-wave optical field at the second optical
frequency.
[12] In some embodiments of any of the above apparatus, a difference between
the first
optical frequency and the second optical frequency is greater than five times
the symbol
rate.
[13] In some embodiments of any of the above apparatus, a difference between
the first
optical frequency and the second optical frequency is approximately an integer
multiple of
the symbol rate.
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[14] In some embodiments of any of the above apparatus, the first light output
comprises
a first optical pulse train of a first period, and the second light output
comprises a second
optical pulse train of the first period.
[15] In some embodiments of any of the above apparatus, pulses of the first
and second
optical pulse trains have a same intensity waveform.
[16] In some embodiments of any of the above apparatus, pulses of the first
and second
optical pulse trains have different respective intensity waveforms.
[17] In some embodiments of any of the above apparatus, the first and second
optical
pulse trains are phase-locked with respect to one another.
[18] In some embodiments of any of the above apparatus, centers of pulses of
the first
optical pulse train are temporally aligned with centers of corresponding
pulses of the
second optical pulse train.
[19] In some embodiments of any of the above apparatus, centers of pulses of
the first
optical pulse train are temporally offset from centers of corresponding pulses
of the second
optical pulse train by a nonzero time shift.
[20] In some embodiments of any of the above apparatus, the nonzero time shift
is
smaller than one half the first period.
[21] In some embodiments of any of the above apparatus, the nonzero time shift
is
smaller than one quarter of the first period.
[22] In some embodiments of any of the above apparatus, the difference between
the
first optical frequency and the second optical frequency is twice the pulse
repetition rate.
[23] In some embodiments of any of the above apparatus, the difference between
the
first optical frequency and the second optical frequency is three times the
pulse repetition
rate.
[24] In some embodiments of any of the above apparatus, a spectrum of the
first pulse
train has two first optical frequency tones; and a spectrum of the second
pulse train has two
second optical frequency tones different from the two first optical frequency
tones.
[25] In some embodiments of any of the above apparatus, the first and second
optical
frequency tones are equidistantly spaced by an integer multiple of the symbol
rate.
[26] In some embodiments of any of the above apparatus, the integer multiple
is two.
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[27] In some embodiments of any of the above apparatus, the electronic
controller is
further configured to imprint first control information on the first light
output of the light
source and second control information on the second light output of the light
source.
[28] In some embodiments of any of the above apparatus, the first control
information is
identical to the second control information.
[29] In some embodiments of any of the above apparatus, the electronic
controller
imprints the first and second control information using one or more of: an
intensity, a
phase, a frequency, and a polarization of the first light output and the
second light output.
[30] In some embodiments of any of the above apparatus, the light source
comprises a
first CW laser oscillating at the first optical frequency, and a second CW
laser oscillating
at the second optical frequency.
[31] In some embodiments of any of the above apparatus, the electronic
controller is
configured to control the first CW laser and the second CW laser to
controllably set a
frequency difference between the first and second optical frequencies.
[32] In some embodiments of any of the above apparatus, the polarization
combiner
comprises one or more of: a polarization beam combiner, a polarization-
maintaining
optical power combiner, and a polarization-maintaining wavelength multiplexer.
[33] In some embodiments of any of the above apparatus, the light source
comprises a
CW laser and an optical modulator optically connected to the CW laser, the
optical
modulator configured to generate a first modulation tone at the first optical
frequency.
[34] In some embodiments of any of the above apparatus, the electronic
controller is
configured to control an optical frequency of the first modulation tone.
[35] In some embodiments of any of the above apparatus, the optical modulator
is
further configured to generate a second modulation tone at the second optical
frequency.
[36] In some embodiments of any of the above apparatus, the light source
comprises an
optical amplitude modulator configured to generate an optical pulse train.
[37] In some embodiments of any of the above apparatus, the light source
comprises a
pulsed laser configured to generate an optical pulse train.
[38] In some embodiments of any of the above apparatus, the light source
comprises an
optical delay element configured to delay the first light output with respect
to the second
light output.
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[39] In some embodiments of any of the above apparatus, the optical power
supply
comprises an optical dispersion-compensating element.
[40] In some embodiments of any of the above apparatus, the light source
comprises a
polarization-diversity in-phase/quadrature modulator.
5 [41] In some embodiments of any of the above apparatus: the polarization-
diversity in-
phase/quadrature modulator is configured to generate two tones in a first
polarization and
two tones in a second polarization orthogonal to the first polarization;
wherein frequency
spacing between the two tones in the first polarization and frequency spacing
between the
two tones in the second polarization are equal to one another; and wherein
frequency
spacing between a tone in the first polarization and a tone in the second
polarization is an
integer multiple of said equal frequency spacing.
[42] In some embodiments of any of the above apparatus, the phase difference
between
the two tones in the first polarization is equal to the phase difference
between the two tones
in the second polarization.
[43] In some embodiments of any of the above apparatus, the apparatus further
comprises an optical transmit module optically end-connected to the output
port of the
polarization combiner via one or more sections of optical fiber, the transmit
module
comprising: a polarization splitter having an input port thereof optically
connected to an
end of one of the sections of the optical fiber to receive light of the
optical output; a first
optical data modulator connected to a first output of the polarization
splitter; and a second
optical data modulator connected to a second output of the polarization
splitter.
[44] In some embodiments of any of the above apparatus, at least one of the
first and
second optical data modulators is configured to modulate received light at the
symbol rate.
[45] In some embodiments of any of the above apparatus, at least one of the
one or more
sections of the optical fiber is non-polarization-maintaining.
[46] In some embodiments of any of the above apparatus, the optical fiber is
at least one
meter long.
[47] In some embodiments of any of the above apparatus, the optical fiber is
at least ten
meters long.
[48] According to another embodiment, provided is an apparatus comprising an
optical
transmitter that comprises: a passive polarization splitter having an optical
input port and
first and second optical output ports, the optical input port being optically
connected to
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receive an optical input signal having first and second polarization
components, the first
polarization component carrying light of a first optical frequency, the second
polarization
component carrying light of a second optical frequency different from the
first optical
frequency, the first and second polarization components being mutually
orthogonal and
jointly undergoing a state-of-polarization change during a time interval, the
passive
polarization splitter causing light of a first fixed polarization to be
directed from the optical
input port to the first optical output port and also causing light of a second
fixed
polarization to be directed from the optical input port to the second optical
output port, the
first and second fixed polarizations being orthogonal to one another, the
state-of-
polarization change causing respective spectral compositions of the lights
directed to the
first and second optical ports to change during said time interval; and a
first optical
modulator connected to the first optical output port and configured to
modulate the light of
the first fixed polarization received therefrom in response to a first data
signal.
[49] In some embodiments of the above apparatus, the optical transmitter
further
comprises a second optical modulator connected to the second optical output
port and
configured to modulate the light of the second fixed polarization received
therefrom in
response to a second data signal.
[50] In some embodiments of any of the above apparatus, the first and second
optical
modulators are connected to transmit the respective modulated lights through
different
respective optical fibers.
[51] In some embodiments of any of the above apparatus: at some times of said
time
interval, the first optical modulator receives from the first output port the
first optical
frequency but not the second optical frequency; and at some other times of
said time
interval, the first optical modulator receives from the first output port the
second optical
frequency but not the first optical frequency.
[52] In some embodiments of any of the above apparatus, at yet some other
times of said
time interval, the first optical modulator receives from the first output port
a mix of the
first and second optical frequencies.
[53] In some embodiments of any of the above apparatus, the optical input port
is
optically connected to receive the optical input signal from a proximate end
of a section of
optical fiber, the optical fiber including at least one section that is non-
polarization-
maintaining.
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[54] In some embodiments of any of the above apparatus, the state-of-
polarization
change is due to time-varying polarization rotation in said at least one
section.
[55] In some embodiments of any of the above apparatus, the time-varying
polarization
rotation is random.
[56] In some embodiments of any of the above apparatus, the optical
transmitter further
comprises an optical power supply optically connected to apply the optical
input signal
through the optical fiber to the passive polarization splitter.
[57] In some embodiments of any of the above apparatus, the optical power
supply
comprises: a light source and an electronic controller connected to the light
source to cause
the light source to generate a first light output having the first optical
frequency and a
second light output having the second optical frequency, each of the first and
second light
outputs being steady during said time interval; and a polarization combiner
connected to
receive the first and second light outputs of the light source at different
respective input
ports thereof, the polarization combiner being configured to generate, at an
output port
thereof, an optical output that is coupled into the optical fiber to cause the
optical input
port of the polarization splitter to receive the optical input signal.
[58] In some embodiments of any of the above apparatus, the first optical
modulator is a
polarization-sensitive device designed to modulate optical signals having the
first fixed
polarization.
[59] In some embodiments of any of the above apparatus, the first optical
modulator is
unsuitable for modulating optical signals having the second fixed
polarization.
[60] In some embodiments of any of the above apparatus, the second optical
modulator
is a polarization-sensitive device designed to modulate optical signals having
the second
fixed polarization.
[61] In some embodiments of any of the above apparatus, the second optical
modulator
is unsuitable for modulating optical signals having the first fixed
polarization.
[62] In some embodiments of any of the above apparatus, the difference between
the
first optical frequency and the second optical frequency can be Af, the symbol
rate can be
Rs, and Af can be within 10% of Rs.
[63] In some embodiments of any of the above apparatus, the apparatus can
include: a
transmit module that includes at least one optical modulator configured to
modulate the
optical output signal from the output port of the polarization combiner; and
an optical fiber
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that includes one or more sections of non-polarization-maintaining fiber. The
optical fiber
can be optically coupled between the output port of the polarization combiner
and the
transmit module, and the optical fiber can be configured to transmit the
optical output
signal from the output port of the polarization combiner to the transmit
module.
[64] In some embodiments of any of the above apparatus, the optical fiber
between the
transmit module and the polarization combiner can be at least one meter long.
[65] In some embodiments of any of the above apparatus, the optical fiber
between the
transmit module and the polarization combiner can be at least ten meters long.
[66] In some embodiments of any of the above apparatus, the transmit module
can
include: a passive polarization splitter having an optical input port and
first and second
optical output ports, the optical input port being optically connected to
receive the optical
input signal from the optical power supply having first and second
polarization
components, the first polarization component carrying light of the first
optical frequency,
and the second polarization component carrying light of the second optical
frequency. The
first and second polarization components can be mutually orthogonal and
jointly undergo a
state-of-polarization change during a time interval, the passive polarization
splitter can
cause light of a first fixed polarization to be directed from the optical
input port to the first
optical output port and also cause light of a second fixed polarization to be
directed from
the optical input port to the second optical output port. The first and second
fixed
polarizations can be orthogonal to one another, the state-of-polarization
change can cause
respective spectral compositions of the lights directed to the first and
second optical ports
to change during the time interval. The transmit module can include a first
optical
modulator optically coupled to the first optical output port and configured to
modulate the
light of the first fixed polarization received therefrom in response to a
first data signal.
[67] In some embodiments of any of the above apparatus, the optical
transmitter can
include a second optical modulator optically coupled to the second optical
output port and
configured to modulate the light of the second fixed polarization received
therefrom in
response to a second data signal.
[68] In some embodiments of any of the above apparatus, the first and second
optical
modulators can be optically connected to transmit the respective modulated
lights through
different respective optical fibers.
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[69] In some embodiments of any of the above apparatus, at some times of the
time
interval, the first optical modulator can receive from the first output port
the first optical
frequency but not the second optical frequency; and at some other times of the
time
interval, the first optical modulator can receive from the first output port
the second optical
frequency but not the first optical frequency.
[70] In some embodiments of any of the above apparatus, at yet some other
times of the
time interval the first optical modulator can receive from the first output
port a mix of the
first and second optical frequencies.
[71] In some embodiments of any of the above apparatus, the polarization
combiner can
include at least one of a polarization beam combiner, a polarization-
maintaining optical
power combiner, or a polarization-maintaining wavelength multiplexer.
[72] In some embodiments of any of the above apparatus, the apparatus can
include a
chromatic-dispersion-compensating optical element that is configured to pre-
disperse the
optical output signal from the polarization combiner.
[73] In some embodiments of any of the above apparatus, the light source can
include: a
first laser that is configured to generate first polarized light that has the
first optical
frequency. The first polarized light can form the first light output of the
light source. The
light source can include a second laser that is configured to generate second
polarized light
that has the second optical frequency. The second polarized light can form the
second light
output of the light source.
[74] In some embodiments of any of the above apparatus, the light source can
include: a
laser that is configured to generate first polarized light that has the first
optical frequency;
and an optical splitter that is configured to receive the first polarized
light and output a first
portion of the first polarized light and a second portion of the first
polarized light. The first
portion can form the first light output of the light source. The second
portion can be
transmitted to a frequency shifter that is configured to frequency-shift the
second portion to
generate a frequency-shifted second portion that has the second optical
frequency, and the
frequency-shifted second portion can form the second light output of the light
source.
[75] In some embodiments of any of the above apparatus, the light source can
include: a
laser that is configured to generate first light; a modulator that is
configured to split the
first light into a first spectral tone and a second spectral tone, and
generate second light that
includes the first and second spectral tones; and a frequency splitter that is
configured to
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frequency-split the second light into a first portion and a second portion.
The first portion
can include the first spectral tone, and the second portion can include the
second spectral
tone. The first portion can form the first light output of the light source,
and the second
portion can form the second light output of the light source.
5 [76] In some embodiments of any of the above apparatus, the light source
can include: a
first laser that is configured to emit first polarized light at a first
wavelength; a second laser
that is configured to emit second polarized light at a second wavelength; a
first optical
modulator configured to modulate the first polarized light to generate first
modulated
polarized light; and a second optical modulator configured to modulate the
second
10 polarized light to generate second modulated polarized light. The first
modulated polarized
light can form the first light output of the light source, and the second
modulated polarized
light can form the second light output of the light source.
[77] In some embodiments of any of the above apparatus, the light source can
include an
optical delay element configured to delay the second modulated polarized light
before the
second modulated polarized light is polarization-combined with the first
modulated
polarized light.
[78] In some embodiments of any of the above apparatus, the light source can
include a
signal generator configured to generate electrical signals for driving the
first and second
optical modulators. The first laser, the first modulator, and the signal
generator can be
configured to generate the first modulated polarized light as a first optical
pulse train. The
second laser, the second modulator, and the signal generator can be configured
to generate
the second modulated polarized light as a second optical pulse train.
[79] In some embodiments of any of the above apparatus, the light source can
include a
signal generator configured to generate electrical signals for driving the
first and second
optical modulators. The first laser, the first modulator, the second
modulator, and the
signal generator can be configured to generate the first and second modulated
polarized
light as dispersion pre-distorted optical signals.
[80] In some embodiments of any of the above apparatus, the first and second
modulators can be configured to modulate time stamps onto the first and second
modulated
polarized light.
[81] In some embodiments of any of the above apparatus, the light source can
include: a
first laser that is configured to emit first polarized light at a first
wavelength; a second laser
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that is configured to emit second polarized light at a second wavelength; a
second
polarization combiner configured to polarization-combine the first polarized
light and the
second polarized light to generate first combined light; an optical modulator
configured to
modulate the first combined light to generate a modulated combined light; and
a splitter to
split the modulated combined light into a first portion and a second portion.
The first
portion can form the first light output of the light source, and the second
portion can form
the second light output of the light source.
[82] In some embodiments of any of the above apparatus, the light source can
include an
optical delay element configured to delay the second portion before the second
portion is
polarization-combined with the first portion by the polarization combiner.
[83] In another general aspect, an apparatus for communicating optical
signals
modulated at a symbol rate includes: an optical power supply that includes: a
laser; an
electronic controller electrically coupled to the laser and configured to
cause the laser to
generate a first polarized light output having a first optical frequency; and
an optical
splitter that is configured to receive the first polarized light and output a
first portion of the
first polarized light and a second portion of the first polarized light. The
optical power
supply includes a frequency shifter that is configured to frequency-shift the
second portion
to generate a frequency-shifted second portion that has a second optical
frequency different
from the first optical frequency. Each of the first portion and the frequency-
shifted second
portion is steady during a time interval that is significantly longer than one
over the symbol
rate. The optical power supply includes a polarization combiner configured to
receive the
first portion and the frequency-shifted second portion. The polarization
combiner is
configured to generate, at an output port of the polarization combiner, an
optical output
signal that includes first and second mutually orthogonal polarization
components that
carry light of the first portion and the frequency-shifted second portion,
respectively.
[84] In another general aspect, an apparatus for communicating optical
signals
modulated at a symbol rate includes: an optical power supply that includes: a
laser that is
configured to generate first light; and a modulator that is configured to
split the first light
into a first spectral tone and a second spectral tone, and generate second
light that includes
the first and second spectral tones. The optical power supply includes a
frequency splitter
that is configured to frequency-split the second light into a first portion
and a second
portion. The first portion includes the first spectral tone, and the second
portion includes
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the second spectral tone, and each of the first portion and the second portion
is steady
during a time interval that is significantly longer than one over the symbol
rate. The optical
power supply includes a polarization combiner configured to receive the first
portion and
the second portion. The polarization combiner is configured to generate, at an
output port
of the polarization combiner, an optical output signal that includes first and
second
mutually orthogonal polarization components that carry light of the first
portion and the
second portion, respectively.
[85] In another general aspect, an apparatus for communicating optical
signals
modulated at a symbol rate includes: an optical power supply that includes: a
first laser that
is configured to emit first polarized light at a first wavelength; and a
second laser that is
configured to emit second polarized light at a second wavelength. The optical
power
supply includes a first optical modulator configured to modulate the first
polarized light to
generate first modulated polarized light; and a second optical modulator
configured to
modulate the second polarized light to generate second modulated polarized
light. Each of
the first modulated polarized light and the second modulated polarized light
is steady
during a time interval that is significantly longer than one over the symbol
rate. The optical
power supply includes a polarization combiner configured to receive the first
modulated
polarized light and the second modulated polarized light. The polarization
combiner is
configured to generate, at an output port of the polarization combiner, an
optical output
signal that includes first and second mutually orthogonal polarization
components that
carry light of the first modulated polarized light and the second modulated
polarized light,
respectively.
[86] Implementations can include one or more of the following features. The
optical
power supply can include an optical delay element configured to delay the
second
modulated polarized light before the second modulated polarized light is
polarization-
combined with the first modulated polarized light.
[87] In another general aspect, an apparatus for communicating optical
signals
modulated at a symbol rate includes: an optical power supply that includes: a
first laser that
is configured to emit first polarized light at a first wavelength; and a
second laser that is
configured to emit second polarized light at a second wavelength. The optical
power
supply includes a first polarization combiner configured to polarization-
combine the first
polarized light and the second polarized light to generate first combined
light; and an
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optical modulator configured to modulate the first combined light to generate
a modulated
combined light. The optical power supply includes a splitter to split the
modulated
combined light into a first portion and a second portion, and each of the
first modulated
polarized light and the second modulated polarized light is steady during a
time interval
that is significantly longer than one over the symbol rate. The optical power
supply
includes a polarization combiner configured to receive the first portion and
the second
portion. The polarization combiner is configured to generate, at an output
port of the
polarization combiner, an optical output signal that includes first and second
mutually
orthogonal polarization components that carry light of the first portion and
the second
.. portion, respectively.
[88] Implementations can include one or more of the following features. The
optical
power supply can include an optical delay element configured to delay the
second portion
before the second portion is polarization-combined with the first portion by
the
polarization combiner.
.. [89] In another general aspect, a method of communicating optical signals
modulated at
a symbol rate includes: generating a first light output having a first optical
frequency; and
generating a second light output having a second optical frequency different
from the first
optical frequency, each of the first and second light outputs being steady
during a time
interval that is significantly longer than one over the symbol rate; and
polarization-
.. combining the first and second light outputs and generating an optical
output signal that
includes first and second mutually orthogonal polarization components that
carry light of
the first and second light outputs, respectively. The method includes
propagating the
optical output signal through an optical fiber that includes one or more
sections of non-
polarization-maintaining fiber to a transmit module that includes at least one
optical
.. modulator configured to modulate the optical output signal.
[90] Implementations can include one or more of the following features. The
method
can include configuring the first light output and the second light output to
be mutually
time/frequency orthogonal.
[91] Generating the first light output can include generating a first
continuous-wave
.. optical field at the first optical frequency, and generating the second
light output can
include generating a second continuous-wave optical field at the second
optical frequency.
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[92] A difference between the first optical frequency and the second optical
frequency
can be approximately an integer multiple of the symbol rate.
[93] Generating the first light output can include generating a first
optical pulse train
having a first period, and generating the second light output can include
generating a
second optical pulse train having a second period.
[94] The method can include temporally aligning centers of pulses of the
first optical
pulse train with centers of corresponding pulses of the second optical pulse
train.
[95] The method can include temporally offsetting centers of pulses of the
first optical
pulse train from centers of corresponding pulses of the second optical pulse
train by a
nonzero time shift.
[96] Generating a first optical pulse train can include generating a first
optical pulse
train having a spectrum that includes two first optical frequency tones.
Generating a
second optical pulse train can include generating a second optical pulse train
having a
spectrum that includes two second optical frequency tones different from the
two first
optical frequency tones.
[97] The method can include imprinting first control information on the
first light output
and second control information on the second light output.
[98] The method can include using a polarization-diversity in-
phase/quadrature
modulator to generate two tones in a first polarization and two tones in a
second
polarization orthogonal to the first polarization.
[99] Frequency spacing between the two tones in the first polarization and
frequency
spacing between the two tones in the second polarization can be equal to each
another.
[100] Frequency spacing between a tone in the first polarization and a tone in
the second
polarization can be an integer multiple of the frequency spacing between the
two tones in
the first polarization.
[101] The method can include splitting the optical output signal into a first
portion and a
second portion; modulating the first portion with first data to generate a
first modulated
optical signal; and modulating the second portion with second data to generate
a second
modulated optical signal.
[102] In another general aspect, a system includes: an optical power supply
that includes:
a first light source and an electronic controller connected to the light
source to cause the
light source to generate a first light output having a first optical frequency
and a second
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light output having a second optical frequency different from the first
optical frequency,
each of the first and second light outputs being steady during a time interval
that is
significantly longer than one over a symbol rate. The optical power supply
includes a first
polarization combiner connected to receive the first and second light outputs
of the light
5 source at different respective input ports thereof, the polarization
combiner being
configured to generate, at an output port thereof, a first optical output
signal in which first
and second mutually orthogonal polarization components carry light of the
first and second
light outputs, respectively.
[103] Implementations can include one or more of the following features. The
system can
10 include a first data processing apparatus that includes: a first
housing, a first data processor
disposed in the first housing, and a first co-packaged optical module that is
configured to
convert output electrical signals from the first data processor to output
optical signals that
are provided to a first optical fiber cable optically coupled to the first
data processing
apparatus. The optical power supply can be configured to provide the first
optical output
15 signal to the first co-packaged optical module through a first optical
link.
[104] The optical power supply can include: a second light source configured
to generate
a first light output having a first optical frequency and a second light
output having a
second optical frequency different from the first optical frequency, each of
the first and
second light outputs being steady during a time interval that is significantly
longer than
one over the symbol rate. The optical power supply can include a second
polarization
combiner connected to receive the first and second light outputs of the second
light source
at different respective input ports thereof, the second polarization combiner
being
configured to generate, at an output port thereof, a second optical output
signal in which
first and second mutually orthogonal polarization components carry light of
the first and
second light outputs, respectively. The system can include a second data
processing
apparatus that includes: a second housing, a second data processor disposed in
the second
housing, and a second co-packaged optical module that is configured to convert
output
electrical signals from the second data processor to output optical signals
that are provided
to a second optical fiber cable optically coupled to the second data
processing apparatus,
the first and second optical fiber cables are either the same cable or
different cables. The
optical power supply can be configured to provide the second optical output
signal to the
second co-packaged optical module through a second optical link.
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11051 The first co-packaged optical module can include a transmit module that
includes at
least one optical modulator configured to modulate the first optical output
signal from the
output port of the polarization combiner. The first optical link can include
one or more
sections of non-polarization-maintaining fiber. The first optical link can be
optically
coupled between the output port of the polarization combiner and the transmit
module, and
the first optical link can be configured to transmit the first optical output
signal from the
output port of the polarization combiner to the transmit module.
[106] The system can include a distributed data processing system, the first
data
processing apparatus can include a data server, the data server can include a
circuit board
on which the first data processor is mounted, the circuit board can be
positioned relative to
the housing such that a first main surface of the circuit board is at an angle
relative to a
bottom panel of the housing, and the angle can be in a range from 45 to 90 .
[107] The circuit board can be positioned parallel to the front panel.
[108] The first data processor can include at least one of a network switch, a
central
processor unit, a graphics processor unit, a tensor processing unit, a neural
network
processor, an artificial intelligence accelerator, a digital signal processor,
a
microcontroller, or an application specific integrated circuit (ASIC).
[109] The first co-packaged optical module can include a first photonic
integrated circuit,
a first optical connector part that is configured to be removably coupled to a
second optical
connector part that is attached to the first optical fiber cable, and an
optical power supply
connector that is connected to the first optical link to receive supply light
from the optical
power supply.
[110] The first optical output signal can be modulated with synchronization
information,
the first co-packaged optical module can include an optical splitter that
splits the supply
light and provides a first portion of the supply light to a receiver that is
configured to
extract the synchronization information.
[111] The first co-packaged optical module can include an optical splitter
that splits the
supply light and provides a first portion of the supply light to an
optoelectronic modulator
that is configured to modulate onto the first portion of the supply light the
output electrical
signals from the first data processor to generate modulated light, in which
the modulated
light is output through the first optical fiber cable.
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[112] The first co-packaged optical module can be electrically coupled to the
first circuit
board using electrical contacts that include at least one of spring-loaded
elements,
compression interposers, or land-grid arrays.
[113] The system can include: a transmit module that includes at least one
optical
modulator configured to modulate the optical output signal from the output
port of the
polarization combiner; and an optical fiber that includes one or more sections
of non-
polarization-maintaining fiber. The optical fiber can be optically coupled
between the
output port of the polarization combiner and the transmit module, and the
optical fiber can
be configured to transmit the optical output signal from the output port of
the polarization
combiner to the transmit module.
[114] The system can include an optical cable assembly that includes the first
optical
link. The optical cable assembly can include: a first optical fiber connector
including an
optical power supply fiber port, a transmitter fiber port, and a receiver
fiber port; and a
second optical fiber connector including an optical power supply fiber port.
The optical
power supply fiber port of the first optical fiber connector can be optically
coupled to the
optical power supply fiber port of the second optical fiber connector. The
first optical fiber
connector can be configured to be optically coupled to the first co-packaged
optical
module. The second optical fiber connector can be configured to be optically
coupled to
the optical power supply to receive the first optical output signal from the
output port.
11151 The optical cable assembly can include a first optical fiber optically
coupled to the
optical power supply fiber port of the first optical fiber connector and the
first optical
power supply fiber port of the second optical fiber connector.
[116] The system can include an optical cable assembly that includes the first
optical link
and the second optical link. The optical cable assembly can include: a first
optical fiber
connector including an optical power supply fiber port, a transmitter fiber
port, and a
receiver fiber port; a second optical fiber connector including an optical
power supply fiber
port, a transmitter fiber port, and a receiver fiber port; and a third optical
fiber connector
including a first optical power supply fiber port and a second optical power
supply fiber
port. The optical power supply fiber port of the first optical fiber connector
can be
optically coupled to the first optical power supply fiber port of the third
optical fiber
connector, and the optical power supply fiber port of the second optical fiber
connector can
be optically coupled to the second optical power supply fiber port of the
third optical fiber
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connector. The first optical fiber connector can be configured to be optically
coupled to the
first co-packaged optical module, the second optical fiber connector can be
configured to
be optically coupled to the second co-packaged optical module, and the third
optical fiber
connector can be configured to be optically coupled to the optical power
supply.
[117] The optical cable assembly can include a first optical fiber optically
coupled to the
optical power supply fiber port of the first optical fiber connector and the
first optical
power supply fiber port of the third optical fiber connector.
[118] The optical cable assembly can include a second optical fiber optically
coupled to
the optical power supply fiber port of the second optical fiber connector and
the second
optical power supply fiber port of the third optical fiber connector.
[119] The optical cable assembly can include a third optical fiber optically
coupled to the
transmitter fiber port of the first optical fiber connector and the receiver
fiber port of the
second optical fiber connector.
[120] The optical cable assembly can include a fourth optical fiber optically
coupled to
the receiver fiber port of the first optical fiber connector and the
transmitter fiber port of
the second optical fiber connector.
[121] The optical cable assembly can include an optical fiber guide module
including a
first port, a second port, and a third port. The first optical fiber can
extend through the first
and third ports, the second optical fiber can extend through the second and
third ports, the
third optical fiber can extend through the first and second ports, and the
fourth optical fiber
can extend through the first and second ports.
[122] The first, third, and fourth optical fibers can extend from the first
port of the optical
fiber guide module to the first optical fiber connector.
[123] The second, third, and fourth optical fibers can extend from the second
port of the
optical fiber guide module to the second optical fiber connector.
[124] The first and second optical fibers can extend from the third port of
the optical fiber
guide module to the third optical fiber connector.
[125] The optical fiber guide module can be configured to restrict bending of
the optical
fibers that pass through the optical fiber guide module such that each optical
fiber within
the optical fiber guide module has a bending radius greater than a
predetermined value to
prevent excess optical light loss or damage to the optical fiber due to
bending.
[126] The first co-packaged optical module can include a first photonic
integrated circuit
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optically coupled to the first optical fiber connector and configured to
receive the power
supply light from the first light source through the optical power supply
fiber port of the
first optical fiber connector.
[127] The first photonic integrated circuit can be configured to modulate the
power
supply light to generate a first modulated optical signal, and transmit the
first modulated
optical signal to the transmitter fiber port of the first optical fiber
connector.
[128] The second co-packaged optical module can include a second photonic
integrated
circuit optically coupled to the second optical fiber connector and configured
to receive the
power supply light from the second light source through the optical power
supply fiber
port of the second optical fiber connector.
[129] The second photonic integrated circuit can be configured to modulate the
power
supply light to generate a second modulated optical signal, and transmit the
second
modulated optical signal to the transmitter fiber port of the second optical
fiber connector.
[130] The first photonic integrated circuit can be configured to, through the
receiver fiber
port of the first optical fiber connector, receive the second modulated
optical signal
transmitted from the second photonic integrated circuit.
[131] The second photonic integrated circuit can be configured to, through the
receiver
fiber port of the second optical fiber connector, receive the first modulated
optical signal
transmitted from the first photonic integrated circuit.
[132] The optical power supply can be optically coupled to the third optical
fiber
connector and configured to provide a first sequence of optical frame
templates to the first
optical power supply fiber port and a second sequence of optical frame
templates to the
second optical power supply fiber port.
[133] The first co-packaged optical module can include a first photonic
integrated circuit
optically coupled to the first optical fiber connector and configured to
receive the first
sequence of optical frame templates from the optical power supply through the
optical
power supply fiber port of the first optical fiber connector.
[134] The first photonic integrated circuit can be configured to modulate the
first
sequence of optical frame templates to generate a first sequence of loaded
optical frames,
and transmit the first sequence of loaded optical frames to the transmitter
fiber port of the
first optical fiber connector.
[135] The second co-packaged optical module can include a second photonic
integrated
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circuit optically coupled to the second optical fiber connector and configured
to receive the
second sequence of optical frame templates from the optical power supply
through the
optical power supply fiber port of the second optical fiber connector.
[136] The second photonic integrated circuit can be configured to modulate the
second
5 sequence of optical frame templates to generate a second sequence of
loaded optical
frames, and transmit the second sequence of loaded optical frames to the
transmitter fiber
port of the second optical fiber connector.
[137] The first photonic integrated circuit can be configured to, through the
receiver fiber
port of the first optical fiber connector, receive the second sequence of
loaded optical
10 frames transmitted from the second photonic integrated circuit.
[138] The second photonic integrated circuit can be configured to, through the
receiver
fiber port of the second optical fiber connector, receive the first sequence
of loaded optical
frames transmitted from the first photonic integrated circuit.
[139] In another general aspect, a system includes: a first data processing
apparatus
15 including a first optical transmitter that includes: a passive
polarization splitter having an
optical input port and first and second optical output ports. The optical
input port is
optically connected to receive an optical input signal having first and second
polarization
components, the first polarization component carries light of a first optical
frequency, and
the second polarization component carries light of a second optical frequency
different
20 from the first optical frequency. The first and second polarization
components are mutually
orthogonal and jointly undergo a state-of-polarization change during a time
interval. The
passive polarization splitter causes light of a first fixed polarization to be
directed from the
optical input port to the first optical output port and also causes light of a
second fixed
polarization to be directed from the optical input port to the second optical
output port. The
first and second fixed polarizations are orthogonal to one another. The state-
of-polarization
change causes respective spectral compositions of the lights directed to the
first and second
optical ports to change during said time interval. The first data processing
apparatus
includes a first optical modulator connected to the first optical output port
and configured
to modulate the light of the first fixed polarization received therefrom in
response to a first
data signal. The apparatus includes a first optical link optically connected
between the
optical input port and an optical power supply that provides the optical input
signal.
[140] Implementations can include one or more of the following features. The
first data
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processing apparatus can include a first housing, and the first optical
transmitter can be
disposed in the first housing. The system can include: a second data
processing apparatus
that includes a second housing, and a second optical transmitter disposed in
the second
housing. The system can include a second optical link optically connected
between the
.. second optical transmitter and the optical power supply.
[141] The first optical link can include one or more sections of non-
polarization-
maintaining fiber. The first optical link can be optically coupled between the
output port of
the polarization combiner and the transmit module, and the first optical link
can be
configured to transmit the first optical output signal from the output port of
the polarization
combiner to the transmit module.
[142] The first data processing apparatus can include a circuit board on which
a first
photonic integrated circuit is mounted, the first optical transmitter can be
part of the first
photonic integrated circuit, the circuit board can be positioned relative to
the housing such
that a first main surface of the circuit board is at an angle relative to a
bottom panel of the
housing, and the angle can be in a range from 45 to 90 .
[143] The circuit board can be positioned parallel to a front panel of the
housing.
[144] The first data processing apparatus can include a first data processor
that is
configured to provide the first data signal, and the first data processor can
include at least
one of a network switch, a central processor unit, a graphics processor unit,
a tensor
processing unit, a neural network processor, an artificial intelligence
accelerator, a digital
signal processor, a microcontroller, or an application specific integrated
circuit (ASIC).
[145] The system can include an optical cable assembly that includes the first
optical
link. The optical cable assembly can include: a first optical fiber connector
including an
optical power supply fiber port, a transmitter fiber port, and a receiver
fiber port; and a
second optical fiber connector including an optical power supply fiber port.
The optical
power supply fiber port of the first optical fiber connector can be optically
coupled to the
optical power supply fiber port of the second optical fiber connector. The
first optical fiber
connector can be configured to be optically coupled to the first data
processing apparatus.
The second optical fiber connector can be configured to be optically coupled
to the optical
power supply.
[146] The optical cable assembly can include a first optical fiber optically
coupled to the
optical power supply fiber port of the first optical fiber connector and the
optical power
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supply fiber port of the second optical fiber connector.
[147] The system can include an optical cable assembly that includes the first
optical link
and the second optical link. The optical cable assembly can include: a first
optical fiber
connector including an optical power supply fiber port, a transmitter fiber
port, and a
receiver fiber port; a second optical fiber connector including an optical
power supply fiber
port, a transmitter fiber port, and a receiver fiber port; and a third optical
fiber connector
including a first optical power supply fiber port and a second optical power
supply fiber
port. The optical power supply fiber port of the first optical fiber connector
can be
optically coupled to the first optical power supply fiber port of the third
optical fiber
connector, and the optical power supply fiber port of the second optical fiber
connector can
be optically coupled to the second optical power supply fiber port of the
third optical fiber
connector. The first optical fiber connector can be configured to be optically
coupled to the
first data processing apparatus, the second optical fiber connector can be
configured to be
optically coupled to the second data processing apparatus, and the third
optical fiber
connector can be configured to be optically coupled to the optical power
supply.
[148] The optical cable assembly can include a first optical fiber optically
coupled to the
optical power supply fiber port of the first optical fiber connector and the
first optical
power supply fiber port of the third optical fiber connector.
[149] The optical cable assembly can include a second optical fiber optically
coupled to
the optical power supply fiber port of the second optical fiber connector and
the second
optical power supply fiber port of the third optical fiber connector.
[150] The optical cable assembly can include a third optical fiber optically
coupled to the
transmitter fiber port of the first optical fiber connector and the receiver
fiber port of the
second optical fiber connector.
11511 The optical cable assembly can include a fourth optical fiber optically
coupled to
the receiver fiber port of the first optical fiber connector and the
transmitter fiber port of
the second optical fiber connector.
[152] The optical cable assembly can include an optical fiber guide module
including a
first port, a second port, and a third port. The first optical fiber can
extend through the first
and third ports, the second optical fiber can extend through the second and
third ports, the
third optical fiber can extend through the first and second ports, and the
fourth optical fiber
can extend through the first and second ports.
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[153] The first, third, and fourth optical fibers can extend from the first
port of the optical
fiber guide module to the first optical fiber connector.
[154] The second, third, and fourth optical fibers can extend from the second
port of the
optical fiber guide module to the second optical fiber connector.
[155] The first and second optical fibers can extend from the third port of
the optical fiber
guide module to the third optical fiber connector.
[156] The optical fiber guide module can be configured to restrict bending of
the optical
fibers that pass through the optical fiber guide module such that each optical
fiber within
the optical fiber guide module has a bending radius greater than a
predetermined value to
prevent excess optical light loss or damage to the optical fiber due to
bending.
[157] The first optical transmitter can be configured to receive power supply
light from
the optical power supply through the optical power supply fiber port of the
first optical
fiber connector, modulate the light of the first fixed polarization in
response to the first
data signal to generate a first modulated optical signal, and transmit the
first modulated
optical signal to the transmitter fiber port of the first optical fiber
connector.
[158] The second optical transmitter can be configured to receive power supply
light
from the optical power supply through the optical power supply fiber port of
the second
optical fiber connector, modulate the power supply light to generate a second
modulated
optical signal, and transmit the second modulated optical signal to the
transmitter fiber port
of the second optical fiber connector.
[159] The system can include the optical power supply. The optical power
supply can be
optically coupled to the third optical fiber connector and configured to
provide a first
sequence of optical frame templates to the first optical power supply fiber
port and a
second sequence of optical frame templates to the second optical power supply
fiber port.
[160] The first optical transmitter can be configured to receive the first
sequence of
optical frame templates from the optical power supply through the optical
power supply
fiber port of the first optical fiber connector.
[161] The first optical transmitter can be configured to modulate the first
sequence of
optical frame templates in response to the first data signal to generate a
first sequence of
loaded optical frames, and transmit the first sequence of loaded optical
frames to the
transmitter fiber port of the first optical fiber connector.
[162] The second optical transmitter can be configured to receive the second
sequence of
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optical frame templates from the optical power supply through the optical
power supply
fiber port of the second optical fiber connector.
[163] The second optical transmitter can be configured to modulate the second
sequence
of optical frame templates to generate a second sequence of loaded optical
frames, and
transmit the second sequence of loaded optical frames to the transmitter fiber
port of the
second optical fiber connector.
[164] The first data processing apparatus can be configured to, through the
receiver fiber
port of the first optical fiber connector, receive the second sequence of
loaded optical
frames transmitted from the second photonic integrated circuit.
[165] The second data processing apparatus can be configured to, through the
receiver
fiber port of the second optical fiber connector, receive the first sequence
of loaded optical
frames transmitted from the first photonic integrated circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
.. [166] Other aspects, features, and benefits of various disclosed
embodiments will become
more fully apparent, by way of example, from the following detailed
description and the
accompanying drawings, in which:
[167] FIG. 1 shows a block diagram of an optical communication system in which
at least
some embodiments can be practiced;
[168] FIG. 2 shows a block diagram of an optical power supply module that can
be used
in the optical communication system of FIG. 1 according to an example
embodiment;
[169] FIGs. 3A-3E illustrate some features of the light generated by an
optical power
supply in the optical communication system of FIG. 1 according to some
embodiments;
[170] FIGs. 4A-4F illustrate optical power supplies, one or more of which can
be used in
the optical communication system of FIG. 1 according to some embodiments;
[171] FIG. 5 shows a block diagram of an example distributed optical
transmitter of the
optical communication system of FIG. 1 employing an optical power supply
module of
FIG. 2 according to an embodiment;
[172] FIG. 6 shows a block diagram of an optical transmitter that can be used
in the
optical communication system of FIG. 1 according to an embodiment;
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[173] FIGs. 7A-7D graphically show some example use cases illustrating
polarization-
rotation independent optical-power splitting that can be implemented in the
optical
communication system of FIG. 1 according to some embodiments; and
[174] FIG. 8 graphically illustrates some signals used/generated in the
optical transmitter
5 of FIG. 5 and the corresponding electrical signals recovered by a
corresponding optical
receiver according to an example embodiment.
[175] FIGS. 9 to 13A are diagrams of examples of optical communications
systems.
[176] FIG. 13B is a diagram of an example of an optical cable assembly used in
the
optical communication system of FIG. 13A.
10 [177] FIG. 13C is an enlarged diagram of the optical cable assembly of
FIG. 13B.
[178] FIG. 13D is an enlarged diagram of the upper portion of the optical
cable assembly
of FIG. 13B.
[179] FIG. 13E is an enlarged diagram of the lower portion of the optical
cable assembly
of FIG. 13B.
15 [180] FIGS. 14 and 15A are diagrams of examples of optical communication
systems.
[181] FIG. 15B is a diagram of an example of an optical cable assembly.
[182] FIG. 15C is an enlarged diagram of the optical cable assembly of FIG.
15B.
[183] FIG. 15D is an enlarged diagram of the upper portion of the optical
cable assembly
of FIG. 15B.
20 [184] FIG. 15E is an enlarged diagram of the lower portion of the
optical cable assembly
of FIG. 15B.
[185] FIGS. 16 and 17A are diagrams of examples of optical communication
systems.
[186] FIG. 17B is a diagram of an example of an optical cable assembly.
[187] FIG. 17C is an enlarged diagram of the optical cable assembly of FIG.
17B.
25 [188] FIGS. 18 to 20B are diagrams of examples of data processing
systems.
DETAILED DESCRIPTION
[189] At least some embodiments can benefit from the use of a light source
configured to
supply pulsed light for local optical modulation and/or as a clock reference
within a
corresponding island of synchronicity, e.g., as disclosed in U.S. patent
application
16/847,705, filed on April 14, 2020, which is incorporated herein by reference
in its
entirety.
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[190] Emerging optical interconnects aim to co-package and even co-integrate
optical
transponders with electronic processing chips, which necessitates transponder
solutions
that consume relatively low power and that are sufficiently robust against
significant
temperature variations as can be found within an electronic processing chip
package. Of
significant interest are massively spatially parallel optical interconnect
solutions that
multiplex information onto relatively few wavelengths and use a relatively
large number of
parallel spatial paths for chip-to-chip interconnection. In such systems, it
can be beneficial
to place the light source outside the package housing the corresponding
photonic and
electronic processing chips, and to connect the light source to the package
via one or more
optical fibers. In some such systems, the light source can be placed at a
separate location
optically connected to the package by, e.g., by at least one meter of optical
fiber.
[191] In some such systems, at least some photonic components within the
package can
be polarization sensitive, i.e., can only accept or can only properly process
light of a
certain polarization state. For example, a one-dimensional vertical grating
coupler, which
can serve as a coupling interface to the optical fiber connecting the light
source to the
package, can only couple light of one particular polarization from the fiber
to the photonic
processing chip while rejecting, deflecting, or dissipating other light. In
another example,
an optical modulator integrated within a package can effectively modulate only
light in one
particular polarization state. In such systems, it can therefore be beneficial
to connect the
light source with the corresponding electronic and photonic processing chips
using
polarization-maintaining optical fiber (PMF). However, some systems employing
P1Vif
may be more difficult and/or more expensive to manufacture than systems
employing
standard, non-polarization-maintaining optical fiber (SF), e.g., because PMF
may be more
expensive than SF, and PMF may require rotationally aligned optical fiber
connections.
SF, however, may not preserve the polarization state of the light upon its
transmission
from the light source to the package housing.
[192] Some systems that use SF to connect the light source with a photonic
chip can
therefore require either an active optical polarization control mechanism or a
polarization-
diversity setup. In some such systems, polarization diversity can be
implemented by
doubling the number of data modulators within the package, e.g., as disclosed
in U.S.
Patent No. 5,654,818, which is incorporated herein by reference in its
entirety. In some
such systems, polarization diversity can be implemented by using more-complex
optical
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data modulator structures, e.g., a 4-port optical modulator disclosed in U.S.
Patent No.
10,222,676, which is incorporated herein by reference in its entirety.
[193] U.S. Patent Nos. 6,959,152 and 7,106,970, which are incorporated herein
by
reference in their entirety, disclose some systems configured to use
temporally interleaved
and orthogonally polarized trains of optical pulses at the same optical
wavelength.
However, such temporal interleaving can lead to a significant timing jitter
and/or pulse
broadening at the modulator due to random polarization rotations within the
corresponding
SF.
[194] At least some of the above-indicated problems in the state of the art
can be
addressed by the use of various embodiments employing a polarization-diversity
optical
power supply, e.g., as outlined in this specification. For example, a need for
PMF can
beneficially be circumvented.
[195] FIG. 1 shows a block diagram of a communication system 100 in which at
least
some embodiments can be practiced. As shown, system 100 comprises nodes 1011-
1016,
which in some embodiments can each comprise one or more of: optical
communication
devices, electronic and/or optical switching devices, electronic and/or
optical routing
devices, network control devices, traffic control devices, synchronization
devices,
computing devices, and data storage devices. Nodes 1011-1016 can be suitably
interconnected by optical fiber links 1021-10212 establishing communication
paths between
the communication devices within the nodes. System 100 can also comprise one
or more
optical power supply modules 103 producing one or more light supply outputs.
[196] As used herein, a "light supply" or "supplied light" is light intended
for use as a
modulation carrier in one or more of the optical communication devices of the
nodes 101i-
1016 whose complex optical field amplitude is "steady." Herein, light is
referred to as
being "steady" either if said light comprises one or more continuous-wave (CW)
optical
fields or if said light comprises one or more optical pulse trains of period
Ti (where pulse
repetition rate RI= 1/Ti), each of the pulse trains having a substantially
constant respective
optical-pulse amplitude and a substantially constant respective optical-pulse
duration over
a time interval that is significantly longer (e.g., at least by a factor of
100) than the duration
Ts of a modulation symbol used for optical communication in system 100.
(Hereafter, Rs=
llTsis referred to as the modulation symbol rate.)
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[197] As used herein, light is called "continuous-wave (CW)" if the complex
amplitude
of the optical field of said light is approximately (e.g., to within 20%)
constant over a
duration Tcw that is much longer than a minimum characteristic duration used
by
communication signals within system 100. In some embodiments, light can be
referred to
as being CW light if the complex amplitude of the optical field of said light
is
approximately constant over at least 100 times the duration Ts of a modulation
symbol, i.e.,
Tcw > 100 Ts. In some embodiments, light can be referred to as being CW light
if the
complex amplitude of the optical field of said light is approximately constant
over a at
least Tcw > 1000 Ts. In some embodiments, the term "continuous-wave" (or CW)
can also
be applicable to an optical field affected by random noise, random drifts, or
small analog
dither modulations using one or more sinewave dither tones at frequencies much
lower
than Rs, e.g., at frequencies smaller than Rs/1000, as long as the effect of
noise, drift, or
dither is not so strong as to induce optical intensity variations, e.g.,
exceeding 20% of the
average optical intensity within a duration Tcw.
[198] As used herein, the phrase an "optical pulse train of period Tr" refers
to an optical
field whose optical intensity waveform 1(t) = 1E002 is periodic with the time
period Ti. In
some embodiments, the complex amplitude Eo(t) of the optical field of an
optical pulse
train can be periodic with an integer multiple of Ti, i.e., with a period of n
T1, where n = 1,
2, 3, ... .
[199] As used herein, the term "periodic" refers to a waveform characterized
by a
parameter or feature (or a change of a parameter or feature) that is repeated
every time
period T within a duration of time TD, where TD is significantly larger than
T, e.g., TD >
100 T. In some cases, the term "periodic" can also be applicable to a waveform
affected
by random noise, random drifts, or small analog dither modulations using one
or more
sinewave dither tones at frequencies much lower than 1/T, e.g., at frequencies
smaller than
1/(1000 T), as long as the effect of noise, drift, or dither is not so strong
as to obscure (e.g.,
make substantially undetectable) the waveform periodicity.
[200] In some embodiments, a light supply can also comprise control
information.
Control information can be used by other network elements of system 100, e.g.,
as
described in the above-cited U.S. Patent Application No. 16/847,705. As used
herein, the
term "control information" refers to information imprinted by optical power
supply module
130 onto one or more light supplies for the purpose of controlling, managing,
and/or
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monitoring one or more network elements of system 100, and/or for facilitating
various
synchronization operations within one or more network elements of system 100.
In some
embodiments, control information can comprise one or more of: a clock
frequency, a
clock phase, a synchronization time stamp, a frame delimiter, a frame counter,
status
information, a heartbeat signal, and a command that can be used to control the
behavior of
other network elements, such as a master/slave assignment or a reset command.
[201] For illustration purposes, only one such optical power supply module 103
is shown
in FIG. 1. A person of ordinary skill in the art will understand that some
embodiments can
have more than one optical power supply module 103 appropriately distributed
over
system 100 and that such multiple optical power supply modules can be
synchronized, e.g.,
using some of the techniques disclosed in the above-cited U.S. Patent
Application No.
16/847,705.
[202] Some end-to-end communication paths can pass through an optical power
supply
module 103 (e.g., see the communication path between nodes 1012 and 1016). For
example, the communication path between nodes 1012 and 1016 can be jointly
established
by optical fiber links 1027 and 1028, whereby light supplied by optical power
supply
module 103 is multiplexed onto optical fiber links 1027 and 1028.
[203] Some end-to-end communication paths can pass through one or more optical
multiplexing units 104 (e.g., see the communication path between nodes 1012
and 1016).
For example, the communication path between nodes 1012 and 1016 can be jointly
established by optical fiber links 10249 and 10244. Multiplexing unit 104 is
also connected,
through link 1029, to receive light supplied by optical power supply module
103 and, as
such, can be operated to multiplex said received light supply onto optical
fiber links 10249
and 10244.
[204] Some end-to-end communication paths can pass through one or more optical
switching units 105 (e.g., see the communication path between nodes 10h and
1014). For
example, the communication path between nodes 10h and 1014 can be jointly
established
by optical fiber links 1023 and 10212, whereby light from optical fiber links
1023 and 1024
is either statically or dynamically directed to optical fiber link 10212.
[205] As used herein, the term "network element" refers to any element that
generates,
modulates, processes, or receives light within system 100 for the purpose of
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communication. Example network elements include a node 101, an optical power
supply
module 103, an optical multiplexing unit 104, and an optical switching unit
105.
[206] Some light supply distribution paths can pass through one or more
network
elements. For example, optical power supply module 103 can supply light to
node 1014
5 via optical fiber links 1027, 1024, and 10212, letting the supply light
pass through network
elements 1012 and 105.
[207] FIG. 2 shows a block diagram of an optical power supply 290 that can be
used as
part of optical power supply module 103 to create a light supply for use in
system 100
according to an example embodiment. Optical power supply 290 comprises: (i) a
light
10 source 200 possessing two light outputs 212 and 222, each in a single
state of polarization;
(ii) an electronic controller 230 configured to control light source 200 such
as to establish
time/frequency orthogonality between light output 212 and light output 222;
and a
polarization combiner 240 configured to multiplex light outputs 212 and 222
onto two
orthogonal polarization states at its output 242.
15 [208] Herein, a "polarization combiner" is an optical device having two
input ports (e.g.,
connected to 212 and 222) and at least one output port (e.g. 242) and
configured to
multiplex light in a first polarization state at its first input port onto a
first polarization state
of light on one of its output ports, and light in a second polarization state
at its second input
port onto a second polarization state of light on the same output port, the
second
20 polarization state at output port 242 being approximately orthogonal to
the first
polarization state at output port 242. In some embodiments, the two orthogonal
polarization states at output port 242 can be horizontally and vertically
linearly polarized,
respectively. In some other embodiments, the two orthogonal polarization
states at output
port 242 can be left-handed and right-handed circularly polarized,
respectively. In some
25 other embodiments, the two orthogonal polarization states at output port
242 can be
relatively orthogonally, elliptically polarized states. In some embodiments,
the
polarization states at input ports 212 and 222 can be identical. In some other
embodiments, the polarization states at input ports 212 and 222 can be
orthogonal. In
some embodiments, polarization combiner 240 can include polarization-sensitive
optical
30 elements, e.g., be implemented as a polarization beam combiner. In some
other
embodiments, polarization combiner 240 may not include any polarization-
sensitive
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elements, e.g., be implemented as a polarization-maintaining optical power
combiner or as
a polarization-maintaining wavelength multiplexer.
[209] The concept of "polarization state" is graphically illustrated in FIG.
7A. For
example, light in a linear polarization state can be represented by a complex
electrical field
vector
E(t) = E0(t) exp(j2n- ft)
(1)
wherein the unit vector 4 can maintain its direction along a linear Cartesian
axis (e.g., the
x-axis as defined with respect to the fixed coordinate system of light source
200) to an
accuracy of, e.g., within 20 degrees over a relatively long duration, e.g.,
about one hour.
In some embodiments, the unit vector 4 can maintain its direction along a
linear Cartesian
axis to within an accuracy of, e.g., 20 degrees for the duration of typical
normal operation
of optical power supply 290. In the above expression, Eo(t) is the constant or
time-varying
complex amplitude of the complex electrical field vector, f is the optical
frequency, t
denotes the time variable and j = VTI. In another example, a circular
polarization state
can be represented by a complex electrical field vector
P(t) = E0(0/-,/ exp(j2n- f t) + exp(j7r/2) e'y ,
(2)
wherein the unit vector e'y is orthogonal to 4 and both unit vectors maintain
their
directions along two orthogonal linear Cartesian axis to within an accuracy
of, e.g., 20
degrees over a relatively long duration of, e.g., about one hour. As used
herein, the term
"polarized light" denotes light in some well defined polarization state.
[210] As used herein, two optical fields are said to be "time/frequency
orthogonal" if the
degree of orthogonality t7 of the two optical fields' complex amplitudes Ei(t)
and E2(t),
defined as
= 1 ( itt+T
El ()E2* (x)d-c 12 (rt+T I E(
iT) 12 iftIt+TE2 T. )12 dT)
t t
(3)
is close to 1, e.g., has a value between 0.8 and 1. Herein, the integration
time interval [t, t
+ I] represents the time interval during which time/frequency orthogonality is
to be
determined. If at least one of the optical fields Ei(t) and E2(t) has a non-
periodic complex
amplitude, the integration time interval is chosen to be long compared to a
characteristic
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time duration within system 100, for example, duration T can be chosen to be
at least 10
times a duration Ts of a modulation symbol, at least 10 times a duration of an
information
packet, or at least 10 times a duration of an optical frame template. If both
optical fields
have periodic complex amplitudes Ei(t) or E2(t) with period T, then the time
duration T can
be chosen as the duration over which the above integrals are being taken. In
some
embodiments, two fields can be called time/frequency orthogonal if i is
greater than 0.8.
In some embodiments two fields can be called time/frequency orthogonal if i is
greater
than 0.9. In some embodiments two fields can be called time/frequency
orthogonal if i is
greater than 0.99. The degree of orthogonality //can also be expressed in the
frequency
domain as
, rco ,2 _co co
= 1 ¨ Ei(f)E2*(f)dfl lEi(f)12df f IE2(f)12df).
co _co
(4)
[211] From the above two definitions (see Eqs. (3) and (4)), it can be seen
that two optical
fields are time-frequency orthogonal, e.g., if they are: (i) spectrally
disjoint, i.e., if the
spectral contents of the two fields are primarily located at mutually
exclusive optical
frequencies; and/or (ii) temporally disjoint, i.e., the complex amplitudes of
the two optical
fields differ from zero primarily at mutually exclusive times. In some
embodiments, two
optical fields can be time/frequency orthogonal if they overlap both in time
and in
frequency, provided that their degree of orthogonality is close to 1, e.g., as
indicated by the
example values/ranges of //mentioned above.
[212] In some embodiments, light source 200 produces light of different
respective
optical center frequencies for light outputs 212 and 222. As used herein, the
term "optical
center frequency" refers to the center of mass of the power spectral density
of an optical
field. In some embodiments, controller 230 can operate to control the optical
frequency
separation of light outputs 212 and 222 generated by light source 200, e.g.,
the difference
between the two light sources' optical center frequencies.
[213] In some embodiments, light source 200 can operate to generate two
continuous-
wave (CW) light outputs.
[214] In some embodiments, light source 200 can be configured to let light
outputs 212
and 222 comprise optical pulse trains of approximately (e.g., to within 1%)
the same
period Ti. In some embodiments, the shape of the optical pulses of the pulse
train on light
output 212 can differ from the shape of the optical pulses of the pulse train
on light output
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222. In some embodiments, the shape of the optical pulses of the pulse train
on light
output 212 can be approximately the same as the shape of the optical pulses of
the pulse
train on light output 222. In some embodiments, controller 230 can be
configured to
phase-lock said optical pulse trains with respect to one another. In some
embodiments,
controller 230 can be configured to synchronize said optical pulse trains such
that the
centers of the optical pulses on light output 212 are temporally aligned with
the centers of
the pulses on light output 222. As used herein, the term "center of a pulse"
refers to a time
corresponding to the center of mass of a pulse's intensity waveform. In some
embodiments, controller 230 can be configured to synchronize said optical
pulse trains
such that the centers of the optical pulses on light output 212 are temporally
offset from the
centers of the pulses on light output 222 by a fixed amount AT In some
embodiments, AT
<T1/2. In some embodiments, AT< T1 1 4.
[215] In some embodiments, controller 230 can invoke light outputs 212 and 222
to carry
control information. Control information can be used by other network elements
of system
100, e.g., as described in the above-cited U.S. Patent Application No.
16/847,705. As used
herein, the term "control information" refers to information imprinted by
optical power
supply 290 onto one or both of light outputs 212 and 222 (e.g., equally or
unequally) for
the purpose of controlling, managing, and/or monitoring one or more network
elements of
system 100, and/or for facilitating various synchronization operations within
one or more
network elements of system 100. In some embodiments, control information can
comprise
one or more of: a clock frequency, a clock phase, a synchronization time
stamp, a frame
delimiter, a frame counter, status information, a heartbeat signal, and a
command that can
be used to control the behavior of other network elements, such as a
master/slave
assignment or a reset command. Different types of control information can be
imprinted
equally or unequally onto both light outputs 212 and 222 using different
features thereof.
For example, some types of control information can be imprinted using any
suitable data
modulation equally or unequally imprinted on both light outputs 212 and 222.
In various
embodiments, control information can be imprinted using an approximately equal
change
of intensity, phase, frequency, or polarization of light 212 and 222.
[216] FIGs. 3A-3E illustrate various features of light outputs 212 and 222 of
optical
power supply 290 according to some embodiments. FIG. 3A illustrates intensity-
versus-
time plots of some embodiments of light outputs 212 and 222. In these
particular
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embodiments, light outputs 212 and 222 can be CW at different optical
frequenciesfi =
cal andf2= c/X2, respectively, where Xi and X2 are the wavelengths associated
with optical
frequenciesfi and/2 and c is the speed of light in the medium in which the
wavelengths are
being measured.
[217] FIG. 3B illustrates the optical power-spectral densities (PSDs) of light
outputs 212
and 222. In some embodiments, the optical frequency difference Af = fi
¨f2lbetween light
output 212 and light output 222 can be significantly larger than the symbol
rate Rs used for
communication by a transmitter of node 101 that receives light for modulation
from optical
power supply 290, i.e., Af >> Rs. In some embodiments, Af > 2 Rs. In some
other
embodiments, Af > 5 Rs. In some other embodiments, the frequency difference Af
can be
chosen to be approximately (e.g., to within 10%) an integer multiple of Rs,
i.e., Af n Rs,
with n = 1, 2, 3, ... . In some embodiments, Af Rs. In some embodiments, Af 2
Rs.
[218] FIG. 3C shows intensity-versus-time plots of light outputs 212 and 222
for some
example embodiments. In these embodiments, light outputs 212 and 222 can, each
on a
different respective optical center frequencyfi carry an optical pulse
train of period Ti
and pulse duration Tp. In some embodiments, Tp can be defined as the full-
width-at-half
height of a pulse's optical intensity waveform. In other embodiments, Tp can
be defined as
the reciprocal of the 3-dB bandwidth of the optical pulse spectrum. In some
embodiments,
Tp can be approximately equal to one half of the pulse train period Ti, i.e.,
Tp TI1 2. In
some embodiments, the pulse train of light output 212 can be temporally offset
by an
amount of time AT relative to the pulse train of light output 222. In some
embodiments,
the temporal offset AT can be larger than 1.5 times the full-width-at-half-
height of the
pulses constituting the pulse trains. In some other embodiments, the temporal
offset AT
can be larger than 2 times the full-width-at-half-height of the pulses
constituting the pulse
.. trains. In some embodiments, the temporal offset can be significantly
smaller than TI1 2.
In some embodiments, the two pulse trains can be temporally aligned, i.e., AT
0. In
some embodiments, temporal alignment can imply AT< Tp 110. In some
embodiments,
temporal alignment can imply AT< Tp 1100. In some embodiments, temporal
alignment
can imply AT< Tub. In some embodiments, temporal alignment can imply AT< Ti
1100.
[219] FIGs. 3D and 3E illustrate optical spectra of light outputs 212 and 222
according to
some example embodiments. In some embodiments, the frequency separation Af =
fi ¨1'21
can be significantly larger than the pulse repetition rate RI = i.e., Af >>
RI. In some
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other embodiments, Af > 5 RI. In some other embodiments, the frequency
difference Af
can be chosen to be approximately (e.g., to within 10%) an integer multiple
of RI, i.e., Af
n RI, with n = 2, 3, 4, ... . In some embodiments, Af 2 RI. In some
embodiments, Af
3 RI. In some embodiments, visualized in FIG. 3E, the complex amplitude of
light output
5 212 and light output 222 can each have a sinusoidal time dependence of
period R1/ 2, i.e.,
the spectra of light output 212 and light output 222 each comprise two tones
spaced by RI.
The resulting temporal intensity waveforms are therefore proportional to
5in2(n Ri t) for the
corresponding pulse trains at light outputs 212 and 222. In various
embodiments, the
center frequencies of light outputs 212 and 222 can be spaced by 2 RI, i.e.,
the four tones
10 jointly making up light outputs 212 and 222 are all spaced by RI. In
various embodiments,
the optical phase difference between spectrally adjacent tones is constant,
e.g., the phase
difference between the tone at frequencyfi ¨ Ri I 2 and the tone at
frequencyfi + Ri I 2 is
the same as the phase difference between the tone at frequency/2 ¨ Ri I 2 and
the tone at
frequency/2 + Ri I 2. Such a constant phase progression can ensure that the
temporal skew
15 between pulse trains at light outputs 212 and 222 is approximately zero,
e.g., AT= 0. In
some embodiments, the tone at frequencyfi + Ri I 2 and the tone at frequency/2
¨ Ri I 2 can
also have the same phase difference as the phase difference between the tone
at frequency
fi ¨ I 2 and the tone at frequencyfi + I 2.
[220] FIGs. 4A-4F illustrate various embodiments of optical power supply 290.
Various
20 embodiments corresponding to FIGs. 4A-4C implement some of the schemes
described
above in reference to FIGs. 3A-3B. In the example embodiment shown in FIG. 4A,
two
CW laser sources 410 and 420 operate to emit polarized light (i.e., light in
respective
specific polarization states) at different respective wavelengths Xi and X2
that can be
optically amplified using polarization-maintaining optical amplifiers 413 and
423. The
25 two sources of CW light can be polarization-combined using optical
polarization combiner
440, configured to combine polarized light on its two input ports 412 and 422
onto two
orthogonal polarization states at its output port 441. Spectral
characteristics of optical
polarization combiner 440 are such that light of both wavelengths Xi and X2
can be passed
through with little attenuation. In some embodiments, polarization combiner
440 can be a
30 polarization beam combiner. In some other embodiments, polarization
combiner 440 can
be a polarization-maintaining optical power combiner. In yet some other
embodiments,
polarization combiner 440 can be a polarization-maintaining wavelength
multiplexer.
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Polarization combiner 440 can be followed by a polarization-independent
optical amplifier
443. Lasers 410 and 420 can be wavelength-controlled by a wavelength
controller 430.
[221] In the embodiment of optical power supply 290 shown in FIG. 4B, CW laser
source
410 at wavelength Xi can be free-running or can be wavelength-locked by a
wavelength
controller 431 and configured to emit polarized light. Light generated by
laser source 410
can be amplified by polarization-maintaining optical amplifier 413 before
being split by an
optical splitter 414. In some embodiments, optical splitter 414 can be a
polarization-
maintaining optical power splitter. In some other embodiments, optical
splitter 414 can be
a polarization beam splitter configured to split polarized light incident on
its input 415 into
two orthogonally polarized parts at its two outputs 416 and 426. In some
embodiments,
optical splitter 414 can be a linear polarization splitter oriented at 45
degrees relative to the
linear polarization state of the incident laser light on its input 415. A
portion 416 of the
split light at wavelength X1 can be passed directly to combiner 440, while a
portion 426 of
the split light can be frequency-shifted using an optical frequency shifter
424, driven by,
e.g., a sinusoidal electrical reference signal 432. In some embodiments,
frequency shifter
424 includes one of: an acousto-optic modulator, a single-sideband modulator,
and a
Mach-Zehnder modulator. In some embodiments, frequency shifter 424 can be
followed
by an optional optical bandpass filter 425 that can pass only one of the
several tones that
can be generated by the upstream frequency shifter 424. An additional optical
amplifier
423 can be used to compensate for optical losses. Frequency-shifted light at
port 422 can
be polarization-combined with frequency un-shifted light at port 412 in
combiner 440.
[222] In the embodiment of optical power supply 290 shown in FIG. 4C, CW laser
source
410 can be free-running or wavelength-controlled by wavelength controller 431.
The
output of laser source 410 can be modulated by an optical modulator 417 driven
by an
electrical signal generator 433. Modulator 417 can be configured to split a CW
optical
field at its input into two spectral tones at its output. For example,
modulator 417 can be a
Mach-Zehnder modulator biased at its transmission null and driven by a
sinusoidal
electrical signal whose amplitude is substantially smaller than the
modulator's half-wave
voltage and whose period is T This mode of operation is known to suppress the
incoming
CW tone at optical frequencyfo and to produce two spectral tones atfi,2 =fo T
at the
modulator output. The two tones constituting an optical field 418 can be
frequency-split
by an optical frequency splitter 419 into portions 416 and 426. In some
embodiments,
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optical frequency splitter 419 can be implemented using an optical
(de)interleaver.
Portions 416 and 426 can then be polarization-orthogonally combined using
combiner 440.
In some embodiments, modulator 417 can further be configured to imprint
control
information on optical field 418. For example, modulator 417 can be configured
to
periodically extinguish light of optical field 418 for a brief amount of time.
In some
embodiments, modulator 417 can be configured to extinguish light of optical
field 418 for
a duration of 2 Ts once per period of duration 1000 Ts. In some embodiments,
modulator
417 can be configured to modulate a time stamp onto light 418 for a duration
of 10 Ts once
per period of duration 10000 Ts.
[223] Various embodiments shown in FIGs. 4D-4F implement some of the schemes
described above in reference to FIGs. 3C-3E. In the embodiment of optical
power supply
290 shown in FIG. 4D, two laser sources 410 and 420 can emit polarized light
at different
wavelengths Xi and X2. In some embodiments, wavelengths Xi and X2 and/or their
difference can be controlled by wavelength controller 430. In some
embodiments, lasers
410 and 420 can emit CW light. In some other embodiments, light emitted by one
or both
of lasers 410 and 420 can comprise an optical pulse train. In some
embodiments, light
emitted by lasers 410 and 420 can be modulated using optical modulators 417
and 427,
driven by respective electrical signals generated by signal generator 433. In
some
embodiments, laser 410 and modulator 417, as well as laser 420 and modulator
427,
together with signal generator 433, can be configured such that modulated
optical fields
456 and 457 each comprise an optical pulse train with period Ti. In various
embodiments,
modulators 417 and 427 can be electro-absorption modulators, ring modulators,
Mach-
Zehnder modulators, or in-phase/quadrature (IQ) modulators. In some
embodiments,
modulators 417 and 427 and signal generator 433 can be configured to generate
optical
fields 456 and 457 that are periodically modulated in both amplitude and
phase, including
chirped and arbitrarily pre-distorted optical fields, e.g., dispersion pre-
distorted optical
fields. In some embodiments, the functionalities of light generation and
modulation
provided by laser 410 and modulators 417 as well as by laser 420 and
modulators 427 can
each be implemented using a single direct-modulated laser or a mode-locked
laser. In
some embodiments, the output of modulator 427 can be delayed by an optical
delay
element 419. In some embodiments, delay element 419 can be implemented using a
length
of optical fiber. In some other embodiments, delay element 419 can be a lumped
free-
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space optical delay element. In some embodiments, the delay AT imposed by
delay
element 419 onto optical pulse train 457 relative to optical pulse train 456
can be less than
half the period of the optical pulse train, i.e., AT< T112. In some other
embodiments, the
delay imposed by delay element 419 onto optical pulse train 457 relative to
optical pulse
train 456 can be less than half the period of the optical pulse train modulo
an integer
multiple of Tr, i.e., AT + k Ti, with k = 1, 2, 3, .... In some
embodiments, individual
pulses of optical pulse trains 456 and 457 can have substantially similar
intensity
waveforms. In some other embodiments, individual pulses of optical pulse
trains 456 and
457 can have different intensity waveforms. Optical pulse trains 456 and 457
can be
polarization-combined using combiner 440, configured to combine light on its
two input
ports onto orthogonal polarizations at its output port. In some embodiments, a
chromatic-
dispersion-compensating optical element 470 can pre-disperse polarization-
multiplexed
optical pulse trains. In some embodiments, chromatic-dispersion-compensating
optical
element 470 can be a grating-based or an etalon-based optical dispersion
compensator. In
some other embodiments, chromatic-dispersion-compensating optical element 470
can be
implemented using a length of dispersion-compensating optical fiber. In some
embodiments, modulators 417 and 427 can further be configured to imprint
control
information on optical pulse trains 456 and 457. For example, modulators 417
and 427 can
be configured to periodically extinguish light 456 and 457 for a brief amount
of time. In
some embodiments, modulators 417 and 427 can be configured to extinguish light
456 and
457 for a duration of 2 Ts once per period of duration 1000 Ts. In some
embodiments,
modulators 417 and 427 can be configured to modulate a time stamp onto light
456 and
457 for a duration of 10 Ts once per period of duration 10000 Ts.
[224] In the embodiment of optical power supply 290 shown in FIG. 4E, two
laser
sources 410 and 420 can emit polarized light at different respective
wavelengths Xi and X2.
In some embodiments, wavelengths Xi and X2 and/or their difference can be
controlled by
wavelength controller 430. Light generated by laser 410 and laser 420 can be
combined by
a polarization-maintaining optical combiner 428. In some embodiments,
polarization-
maintaining optical combiner 428 can be a polarization-maintaining optical
power
combiner. In some embodiments, polarization-maintaining optical combiner 428
can be a
polarization-maintaining optical wavelength multiplexer. Combined light can be
modulated by optical modulator 417 driven by electrical signal generator 433
to generate at
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each of wavelengths Xi and X2 an optical pulse train at modulator output 418.
The light
outputted by modulator 417 can be split into two portions 456 and 457 using
splitter 414.
In some embodiments, portion 456 can be passed directly to combiner 440 while
portion
457 of can be optically delayed by delay element 419. Optionally relatively
delayed
.. portions 456 and 457 can be polarization-combined using combiner 440,
configured to
combine light on its two input ports onto orthogonal polarizations at its
output port. In
some embodiments, chromatic-dispersion-compensating optical element 470 can
pre-
disperse polarization-multiplexed optical pulse trains. In some embodiments,
modulator
417 can further be configured to imprint control information on light output
418. For
.. example, modulator 417 can be configured to periodically extinguish light
418 for a brief
amount of time. In some embodiments, modulator 417 can be configured to
extinguish
light 418 for a duration of 2 Ts once per period of duration 1000 Ts. In some
embodiments, modulator 417 can be configured to modulate a time stamp onto
light 418
for a duration of 10 Ts once per period of duration 10000 Ts.
[225] In the embodiment of optical power supply 290 shown in FIG. 4F, CW laser
source
410 can be free-running or wavelength-controlled by wavelength controller 431.
The
output of laser source 410 can be modulated by optical modulator 417 driven by
electrical
signal generator 433. Modulator 417 can be a polarization-diversity in-
phase/quadrature
(IQ) modulator (PDM-IQM), comprising a total of four Mach-Zehnder modulators
(labeled
Ix-MZM, Qx-MZM, Iy-MZM, and Qy-MZM, FIG. 4F) in a nested configuration, with
the
"Q" paths having built-in an optical phase shift of 90 degrees relative to the
"I" paths.
PDM-IQM 417 and signal generator 433 can be configured to produce the spectrum
shown
in FIG. 3E, e.g., as follows: Signals 433li, 433Qx, 4334, and 433Qy are
configured to be
electrical signals with a voltage swing that is not significantly larger than
the half-wave
.. voltage of each Mach-Zehnder modulator, and with a temporal dependence of,
respectively, cos(a t) + cos(3n t), ¨ sin(a t) ¨ sin(3n t), cos(a t) + cos(3n
t),
and sin(a RI t) + sin(3n RI t) . In some embodiments, electrical signals
433li, 433Qx, 4334,
and 433Qy can be generated using digital-to-analog converters (not explicitly
shown in
FIG. 4F). In some embodiments, modulator 417 can further be configured to
imprint
control information on light 456 and 457. For example, modulator 417 can be
configured
to periodically extinguish light 456 and 457 for a brief amount of time. In
some
embodiments, modulator 417 can be configured to extinguish light 456 and 457
for a
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duration of 2 Ts once per period of duration 1000 Ts. In some embodiments,
modulator
417 can be configured to modulate a time stamp onto light 456 and 457 for a
duration of
10 Ts once per period of duration 10000 Ts.
[226] FIG. 5 shows a block diagram of a distributed optical transmitter 500
that can be
5 used in optical communication system 100 of FIG. 1 according to an
embodiment.
Transmitter 500 comprises optical power supply 290 and a transmit module 504.
As
indicated in FIG. 5, optical power supply 290 can be a part of optical power
supply module
103. In operation, optical power supply 290 can generate a light supply on
output 242,
e.g., as described in reference to one or more of FIGs. 3A-3E. Output 242 of
optical
10 power supply 290 is optically coupled to transmit module 504 by way of
an optical fiber
543, which can be a part of, e.g., fiber link 1026. In different embodiments,
transmit
module 504 can be a part of different network elements of system 100. For
illustration
purposes and without any implied limitation, transmit module 504 is described
herein in
reference to an embodiment in which said transmit element is a part of node
10h.
15 [227] In some embodiments, optical fiber 543 can include one or more
sections of non-
polarization-maintaining optical fiber. In such embodiments, light supplied by
optical
power supply module 103 to node 10h can experience random polarization
rotation upon
propagation through optical fiber 543. Owing to this random polarization
rotation, light
supplied by optical fiber 543 can arrive at node 10h such that the two
polarized
20 components of light output 242 are in two random, but relatively
orthogonal states of
polarization when entering transmit module 504 via an optical interface 510
thereof. The
relative orthogonality can be maintained, e.g., because both of the two
polarized
components of light output 242 are subjected to substantially the same (albeit
random)
polarization rotations in the one or more sections of non-polarization-
maintaining optical
25 fiber.
[228] In some embodiments, optical interface 510 can comprise one or more
optical
connectors, one or more edge-coupling mechanisms to a photonic integrated
circuit (PIC),
one or more vertical coupling mechanisms to a PIC, etc. Optical interface 510
is
connected to an optical polarization splitter 515. In some embodiments, the
polarization
30 splitting function of optical polarization splitter 515 can be
integrated into optical interface
510. For example, in some embodiments, a polarization-diversity vertical
grating coupler
can be configured to simultaneously act as a polarization splitter 515 and as
a part of
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optical interface 510. In some other embodiments, an optical connector
comprising a
polarization-diversity arrangement can simultaneously act as an optical
interface 510 and
as a polarization splitter 515.
[229] Owing to the polarization-multiplexed nature as well as the
time/frequency
orthogonality of the light generated by optical power supply 290 on output
242, any
arbitrary polarization rotation within fiber link 1026 results in a
substantially equal optical
power split between output ports 516 and 517 of optical polarization splitter
515 (e.g., see
a detailed description of FIGs. 7A-7D below). Therefore, light on ports 516
and 517 can
be used as a relatively stable optical power supply for optical modulation
within transmit
module 504, which is independent of random polarization rotations that might
be occurring
within link 1026.
[230] Optical modulators 5301 and 5302 receive supply light on respective
polarization
splitter outputs 516 and 517 and modulate data onto said light using one or
more electrical
drive signals 5311 and 5312, thereby producing respective modulated optical
signals on
modulator outputs 5321 and 5312, respectively. In various embodiments,
modulation can
be done in any one or more of intensity, phase, polarization, and frequency.
In some
embodiments, modulation can be done at a modulation symbol rate In some
embodiments, a polarization rotator 506 can be employed to convert orthogonal
output
polarization states at polarization splitter outputs 516 and 517 to equal
polarization states
on ports 516 and 517' for subsequent modulation. For example, polarization
splitter 515
can split light incident on its input port into transversal-magnetic (TM) and
transversal-
electric (TE) polarizations at its two outputs 516 and 517, respectively. If
modulators 530
are both designed for modulating TE-polarized light, then polarization rotator
506 can be
used to rotate TM-polarized light on port 517 to TE-polarized light on port
517'. In some
embodiments, polarization rotator 506 can be a part of polarization splitter
515.
[231] Modulated light on modulator output ports 5321 and 5322 can be passed to
different
respective fibers of link 1021 for communication of information to another
node of system
100, which in the example case shown in FIG. 5 is node 1012. Some example
signals that
can be used and/or generated in transmitter 500 are described below in
reference to FIG. 8.
[232] FIG. 6 shows a block diagram of an optical transmit module 600 that can
be used in
system 100 according to an embodiment. Transmit module 600 can be implemented
using
some of the same elements as transmit module 504, e.g., as indicated by the
corresponding
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matching reference numerals in FIGs. 5 and 6. In different embodiments,
transmit module
600 can be a part of different network elements of system 100. For
illustration purposes
and without any implied limitation, transmit module 600 is described below in
reference to
an embodiment in which said transmit module is a part of node 1011.
[233] In operation, transmit module 600 can receive light from optical port
242 of optical
power supply 290 contained within optical power supply module 103 via optical
interface
510 and optical link 1026 (also see FIGs. 1 and 5). Optical interface 510 is
connected to
optical polarization splitter 515. In some embodiments, the polarization
splitting function
of optical polarization splitter 515 can be integrated into optical interface
510. In some
.. embodiments, optical polarization splitter 515 can further be connected to
one or more
(e.g., cascaded) optical splitters 620, only two of which are shown in FIG. 6
for illustration
purposes. In various embodiments, an optical splitter 620 can be constructed,
e.g., as
known in the pertinent art, using one or more of: optical power splitters,
wavelength
splitters, and spatial-distribution splitters, such as spatial-mode splitters
or multi-core-fiber
.. fanouts.
[234] Optical modulators 530 of transmit module 600 receive light on
respective optical-
splitter outputs 622 and modulate data onto said light using one or more
electrical drive
signals 531, thereby producing respective modulated optical signals on
modulator outputs
532. In various embodiments, modulation can be done in any one or more of
intensity,
phase, polarization, and frequency. In some embodiments, modulation can be
done at a
modulation symbol rate Rs = RI=
[235] In some embodiments, one or more modulators 530 can at times not
modulate
information onto light of outputs 622. Alternatively or in addition, one or
more of the
shown modulators 530 can be omitted from (i.e., not present in) the structure
of transmit
module 600. In such cases, light of the corresponding output(s) 622 can be
passed through
transmit module 600 on to other network elements of system 100, e.g., in
accordance with
the above-provided functional description of certain aspects of system 100
(FIG. 1). In
some embodiments, some of such passed-on light 622 can be used by other
network
elements of system 100 as an optical power supply. In some embodiments, some
of such
passed-on light 622 can be received by other network elements of system 100 to
extract
control information therefrom.
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[236] In some embodiments, some modulators 530 of transmit module 600 can be
configured to use more than one electrical drive signal 531 to modulate light
received from
the corresponding output 622. Examples of such modulators 530 include but are
not
limited to in-phase/quadrature (IQ) modulators and segmented-electrode
modulators. In
various embodiments, opto-electronic modulators 530 can comprise electro-
absorption
modulators, ring modulators, or Mach-Zehnder modulators. In various
embodiments,
opto-electronic modulators 530 can be made of semiconductor materials,
materials used in
Silicon Photonics, polymer materials, or Lithium Niobate. In some embodiments,
opto-
electronic modulators 530 can at least partially be integrated in one or more
PICs (not
explicitly shown in FIG. 6). In various embodiments, electrical drive signals
531 can be
binary or multilevel. In some embodiments, electrical drive signals 531 can be
suitably
pulse-shaped or can be pre-distorted using digital or analog filters, or can
be electrically
amplified using electrical driver amplifiers.
[237] In some embodiments, some of the light on optical splitter outputs 622
can be
detected using one or more optical receivers 680 to extract information
contained therein.
Such information can include, without limitation, one or more frequency
components, one
or more time skew or clock phase values, and one or more pieces of control
information
embedded within the supply light generated by optical power supply module 103.
[238] In some embodiments, information extracted by optical receivers 680 can
be
provided to devices external to transmit module 600 on an output port 681
thereof for
further use within system 100, such as for network traffic
synchronization/arbitration/scheduling, database time-stamping, local clock
synchronization, etc. In some embodiments, information extracted by optical
receiver(s)
680 can be fed into an electronic signal processor 612. In some embodiments,
electronic
signal processor 612 can receive one or more electrical signals 614 and can
pre-process
those electrical signals to generate electrical drive signals 531 for
modulators 530. In some
embodiments, pre-processing can comprise any form of analog, digital, or mixed-
signal
manipulation, including but not limited to retiming, de-skewing, buffering,
bit stuffing, bit
removal, forward error correction coding, line coding, framing, insertion of
pilots and
packet headers, time-stamping, linear and nonlinear pre-compensation, pre-
equalization,
pre-emphasis, and pre-distortion.
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[239] In some embodiments, modulated light on modulator outputs 532 can be
multiplexed in wavelength, polarization, or spatial distribution of the
optical field using
one or more multiplexers 624 to generate one or more optical multiplexed
signals 652.
Multiplexed signals 652 can then be transmitted via one or more output
interfaces 650 to
one or more optical fibers 1021. In some embodiments, output interfaces 650
can be
implemented, e.g., as one or more optical fiber connectors, one or more edge
couplers from
PIC to fibers, or one or more vertical couplers from PIC to fibers. In some
embodiments,
certain multiplexing functions of multiplexer 624 can be integrated into
certain output
interfaces 650. For example, in some embodiments, a polarization-diversity
vertical
grating coupler can simultaneously act as a polarization multiplexer of
multiplexer 624 and
as a part of an output interface 650. In some other embodiments, an optical
connector
comprising a polarization-diversity arrangement can simultaneously act as an
output
interface 650 and as a polarization multiplexer 624.
[240] In some embodiments, each modulator output 532 can be passed directly to
a
corresponding optical fiber or to a corresponding optical fiber core of fiber
link 1021 via a
corresponding output interface 650, i.e., without undergoing any multiplexing
therebetween. In other words, multiplexer 624 or some parts thereof may not be
present in
some embodiments.
[241] FIGs. 7A-7D graphically show some example use cases, e.g., illustrating
the
polarization-rotation independent optical power splitting within transmit
modules 504 and
600, that can be implemented based on embodiments of optical power supply 290
within
optical power supply module 103.
[242] FIG. 7A shows a Poincare sphere, conventionally used to visualize
polarization
states of light. Mutually orthogonal polarization states are found at
diametrically opposed
locations on the sphere. For example, linear polarization states are found on
the equator of
the sphere, with one orthogonal pair including horizontal linear polarization
(HLP) and
vertical linear polarization (VLP), and another orthogonal pair including 45-
degree
(LP 45-deg) linear polarizations being indicated in FIG. 7A. The orthogonal
pair of right-
circular polarization (RCP) and left-circular polarization (LCP) is found on
the two poles
of the Poincare sphere, as is also indicated in FIG. 7A.
[243] FIG. 7B shows intensity-versus-time plots of the light at the two output
ports 516
and 517 of polarization splitter 515 (also see FIGs. 5 and 6) for an example
case, wherein
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optical power supply 103 transmits CW wavelength Xi in HLP and CW wavelength
X2 in
VLP (also see FIGs. 3A-3B). Time intervals (A), (B), and (C), which are
neither implied
to occur in the shown temporal succession nor to be characterized by sharp
transitions
therebetween, correspond to three different example instantiations of random
polarization
5 rotations, wherein: during time interval (A), fiber link 1026 does not
rotate the
polarization; during time interval (B), fiber link 1026 rotates the
polarizations to the
LP 45-deg states; and during time interval (C), fiber link 1026 rotates the
polarizations to
the RCP/LCP states. As optical power supply 290 is configured to transmit two
time/frequency-orthogonal optical fields in two orthogonal polarization
states, the light
10 .. intensities at output ports 516 and 517 of polarization splitter 515
will be approximately
constant, irrespective of random polarization rotations at the polarization
splitter input.
[244] For the time interval (A), polarization splitter 515 operates to: (i)
direct light of
wavelength X1 substantially exclusively to output port 516; and (ii) direct
light of
wavelength X2 substantially exclusively to output port 517. For the time
interval (B),
15 polarization splitter 515 operates to cause each of output ports 516 and
517 to have an
approximately equal amount of light at wavelength X1 and at wavelength X2.
Likewise, for
the time interval (C), polarization splitter 515 operates to cause each of
output ports 516
and 517 to have an approximately equal amount of light at wavelength X1 and at
wavelength X2. Not shown in FIG. 7B, for time intervals (B) and (C), are
possible beat
20 frequency oscillations at the difference frequency Af = i ¨f2 between
the two CW tones at
wavelengths X1 and X2. However, as long as Af is chosen sufficiently large
compared to
the symbol rate Rs, these oscillations can average out within each modulation
symbol of
transmitter 500 and, as such, may not significantly affect the performance.
Choosing Af
smaller than Rs can result in slow fading of the light output at each
individual port 516 and
25 517. More specifically, light incident at polarization splitter 515 can
periodically transition
between appearing entirely on output port 516 (with no light appearing on
output port 517)
and appearing entirely on output port 517 (with no light appearing on output
port 516).
This periodic transition of light between ports 516 and 517 can occur at a
period Af, and if
4/ is significantly smaller than Rs can lead to some modulation time slots on
each
30 polarization splitter output port receiving no or insufficient light to
modulate information
onto. Choosing 4/ to be significantly larger than Rs lets the light
transitions between ports
516 and 517 occur multiple times per symbol period, so that every symbol time
slot always
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receives half the light supplied by optical power supply 103. Choosing Af
equal to Rs can
result in either constant power during the time interval (A) or in 5in2(n Rs
t) shaped pulses
during the time intervals (B) and (C) at ports 516 and 517. This particular
configuration
can be useful for some modes of operation. Similarly, choosing Af equal to an
integer
multiple of Rs (4f= n Rs, n = 1, 2, 3, ...) can be a beneficial mode of
operation.
[245] FIG. 7C shows the optical power at the two output ports 516 and 517 of
polarization splitter 515 for the example use case, wherein optical power
supply 103
operates to transmit temporally partially overlapping pulse trains (i.e., AT<
Tp) at
wavelengths Xi and X2 in HLP and VLP (also see FIG. 3C). Time intervals (A),
(B), and
(C) correspond to the same three instantiations of random polarization
fluctuations as in
FIG. 7B. For the time interval (A), polarization splitter 515 operates to: (i)
direct the
pulse train at wavelength Xi substantially exclusively to output port 516; and
(ii) direct the
pulse train at wavelength X2 substantially exclusively to output port 517. For
the time
interval (B), polarization splitter 515 operates to cause each of output ports
516 and 517 to
have an approximately equal amount of the pulse train at wavelength X1 and the
pulse train
at wavelength X2. Likewise, for the time interval (C), polarization splitter
515 operates to
cause each of output ports 516 and 517 to have an approximately equal amount
of the
pulse train at wavelength X1 and the pulse train at wavelength X2. Not shown
in FIG. 7C,
for time intervals (B) and (C), are possible beat frequency oscillations at
the difference
frequency 4f= tfi ¨f2 during times when pulses at wavelength X1 temporally
overlap with
pulses at wavelength X2. However, as long as Af is chosen sufficiently large
compared to
the symbol rate Rs, these oscillations can average out within each modulation
symbol of
transmitter 500 and, as such, may not significantly affect the performance.
More precisely,
the total optical energy within a time period corresponding to twice the total
optical pulse
.. duration Tp measured at the polarization-splitting interface 515 can remain
approximately
constant, irrespective of the polarization state at the input to polarization
splitter 515.
[246] FIG. 7D shows the optical power at the two output ports 516 and 517 of
polarization
splitter 515 for the example use case, wherein optical power supply 103
operates to
transmit four tones separated by RI, two in HLP and two in VLP (also see FIG.
3E). Time
intervals (A), (B), and (C) correspond to the same three instantiations of
random
polarization fluctuations as in FIG. 7B. For the time interval (A),
polarization splitter 515
operates to: (i) direct the two lower-frequency tones at frequenciesfi ¨ RI /2
andfi + RI /2
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substantially exclusively to output port 516; and (ii) direct the two higher-
frequency tones
at frequencies f2 ¨ RI /2 and f2 + RI /2 substantially exclusively to output
port 517. In the
time domain, output ports 516 and 517 can therefore exhibit time-aligned sin2-
shaped
optical intensity pulses. For the time interval (B), polarization splitter 515
operates to
cause each of output ports 516 and 517 to have an approximately equal amount
of the four
tones shown in FIG. 3E. Likewise, for the time interval (C), polarization
splitter 515
operates to cause each of output ports 516 and 517 to have an approximately
equal amount
of the four tones shown in FIG. 3E. Owing to the close spacing of the two
lower-
frequency tones and the two higher-frequency tones, beat oscillations can be
clearly visible
in (B) and (C). However, due to the specific nature of the four-tone dual-
polarization
optical field, the pulse energy can always stay well confined near a common
center-of-
mass line, e.g., 710, irrespective of polarization rotations. This confinement
of pulse
energies at a specific temporal location within a symbol period irrespective
of polarization
rotations on fiber link 1026 can be beneficial for modulation within transmit
module 504.
[247] As exemplified by the results graphically shown in FIGs. 7B-7D, the use
of various
embodiments of optical power supply module 103 beneficially causes
polarization splitter
515 to passively perform a substantially equal-power split between output
ports 516 and
517 thereof regardless of polarization rotations within one or more sections
of non-
polarization-maintaining optical fiber disposed between optical power supply
module 103
and the host device (e.g., transmit module 504, FIG. 5) of polarization
splitter 515. This
passive, equal-power split in polarization splitter 515 is enabled, e.g., by
the above-
described example configurations of optical power supply module 103, according
to which
the light outputted at output port 242 thereof has two components that are
both
time/frequency orthogonal to one another and polarization-orthogonal. The
latter
characteristic of the received light then causes polarization splitter 515 to
perform the
substantially equal-power split between output ports 516 and 517 thereof
passively, i.e.,
without the use of any tuning or active power-control mechanisms. The light
produced at
output ports 516 and 517 can then advantageously be used, e.g., as an optical
carrier onto
which data information can be modulated by transmit module 504.
[248] As a result of the above-described operation of polarization splitter
515, during
some time intervals (e.g., time interval (A)) optical modulator 5301 can
receive supply
light at a first optical center frequency but not at a second optical center
frequency, and
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modulator 5302 can receive supply light at the second optical center frequency
but not at
the first optical center frequency; during some time intervals (not explicitly
shown in FIG.
7) optical modulator 5301 can receive supply light at the second optical
center frequency
but not at the first optical center frequency, and modulator 5302 can receive
supply light at
the first optical center frequency but not at the second optical center
frequency; during
some time intervals (e.g., time intervals (B) and (C)) optical modulator 5301
can receive
supply light at both the first optical center frequency and the second optical
center
frequency, and modulator 5302 can also receive supply light at both the first
optical center
frequency and the second optical center frequency.
[249] FIG. 8 graphically illustrates some signals used/generated in optical
transmitter 500
(FIG. 5) and the corresponding electrical signals recovered by a corresponding
optical data
receiver according to an example embodiment. More specifically, the following
time-
dependent signals are shown in FIG. 8:
(i) light supply waveforms at ports 516 and 517, respectively, corresponding
to the
embodiment of FIG. 3E. These waveforms are shown for three different
polarization
rotations in optical fiber 543, i.e., for time intervals (A), (B), and (C), as
per FIG. 7D;
(ii) electrical drive signals 5311 and 5312 driving optical modulators 5301
and 5302,
FIG. 5. For illustration purposes, the modulation format imprinted onto the
supply light is
binary on/off keying (00K) in this example embodiment (a person of ordinary
skill in the
art will understand that any other optical modulation format can also be
imprinted onto the
supply light, including multi-level and multi-dimensional formats using any
physical
modulation dimension of the supply light's optical field, such as its
amplitude, phase, in-
phase/quadrature components, frequency, and polarization). The exemplary
binary data
sequence represented by electrical drive signal 5311 is
[01101010...01101010...01101010]. The exemplary binary data sequence
represented by
electrical drive signal 5312 is [01011100...01011100...01011100];
(iii) modulated optical output signals 5321 and 5322 generated by transmit
module
504 in response to the shown electrical drive signals 5311 and 5312,
respectively; and
(iv) electrical signals 801 and 802 generated by a direct-detection optical
receiver in
response to the shown modulated optical output signals 5321 and 5322,
respectively. The
direct-detection optical receiver is modeled to have a first-order Gaussian
low-pass
characteristic of an electrical bandwidth equal to the symbol rate.
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The accurate and substantially jitter-free reconstruction of electrical data
signals 5311 and
5322 by electrical signals 801 and 802 is evident, irrespective of the
polarization rotation
exerted by optical fiber 543.
[250] FIG. 9 shows an optical communications system 900 that includes an
optical power
supply (also referred to as an external photon supply) 902, a first data
processing apparatus
904, and a second data processing apparatus 906. The first data processing
apparatus 904
includes a first chip 905, and the second data processing apparatus 906
includes a second
chip 908. The system 900 enables high-speed communications between the first
chip 905
and the second chip 908 using co-packaged optical interconnect modules 910
similar to
those shown in, e.g., FIGS. 2-5 and 17 of U.S. application 63/145,368. Each of
the first and
second chips 906, 908 can be a high-capacity chip, e.g., a high bandwidth
Ethernet switch
chip.
[251] The first and second chips 906, 908 communicate with each other through
an
optical fiber interconnection cable 912 that includes a plurality of optical
fibers. In some
implementations, the optical fiber interconnection cable 912 can include
optical fiber cores
that transmit data and control signals between the first and second chips 906,
908. The
optical fiber interconnection cable 912 also includes one or more optical
fiber cores that
transmit optical power supply light from the optical power supply or photon
supply 902 to
the photonic integrated circuits in the co-packaged optical interconnect
modules 910 that
provide optoelectronic interfaces for the first and second chips 906, 908.
[252] The optical fiber interconnection cable 912 can include single-core
fibers or multi-
core fibers. Each single-core fiber includes a cladding and a core, typically
made from
glasses of different refractive indices such that the refractive index of the
cladding is lower
than the refractive index of the core to establish a dielectric optical
waveguide. Each multi-
core optical fiber includes a cladding and multiple cores, typically made from
glasses of
different refractive indices such that the refractive index of the cladding is
lower than the
refractive index of the core. More complex refractive index profiles, such as
index
trenches, multi-index profiles, or gradually changing refractive index
profiles can also be
used. More complex geometric structures such as non-circular cores or
claddings, photonic
crystal structures, photonic bandgap structures, or nested antiresonant
nodeless hollow core
structures can also be used.
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[253] The example of FIG. 9 illustrates a switch-to-switch use case. The
external optical
power supply or photon supply 902 provides optical power supply signals, which
can be,
e.g., continuous-wave light, one or more trains of periodic optical pulses, or
one or more
trains of non-periodic optical pulses. The power supply light is provided from
the photon
5 supply 902 to the co-packaged optical interconnect modules 910 through
optical fibers 914
and 916, respectively. For example, the optical power supply 902 can provide
continuous
wave light, or both pulsed light for data modulation and synchronization, as
described in
U.S. patent application 16/847,705. This allows the first chip 905 to be
synchronized with
the second chip 908.
10 [254] For example, the photon supply 902 can correspond to the optical
power supply 103
of FIG. 1. The pulsed light from the photon supply 902 can be provided to the
link 1026 of
the data processing system 200 of FIG. 20 of U.S. application 63/145,368. In
some
implementations, the photon supply 902 can provide a sequence of optical frame
templates, in which each of the optical frame templates includes a respective
frame header
15 and a respective frame body, and the frame body includes a respective
optical pulse train.
The modulators 417 of FIG. 20 of U.S. application 63/145,368 can load data
into the
respective frame bodies to convert the sequence of optical frame templates
into a
corresponding sequence of loaded optical frames that are output through
optical fiber link
1021.
20 [255] FIG. 10 shows an example of an optical communications system 1000
providing
high-speed communications between a high-capacity chip 1002 (e.g., an Ethernet
switch
chip) and multiple lower-capacity chips 1004a, 1004b, 1004c, e.g., multiple
network
interface chips attached to computer servers using co-packaged optical
interconnect
modules 910 similar to those shown in FIG. 9. The high-capacity chip 1002
communicates
25 with the lower-capacity chips 1004a, 1004b, 1004c through a high-
capacity optical fiber
interconnection cable 1008 that later branches out into several lower-capacity
optical fiber
interconnection cables 1010a, 1010b, 1010c that are connected to the lower-
capacity chips
1004a, 1004b, 1004c, respectively. This example illustrates a switch-to-
servers use case.
[256] An external optical power supply or photon supply 1012 provides optical
power
30 supply signals, which can be continuous-wave light, one or more trains
of periodic optical
pulses, or one or more trains of non-periodic optical pulses. The power supply
light is
provided from the photon supply 1012 to the optical interconnect modules 1006
through
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optical fibers 1014, 1016a, 1016b, 1016c, respectively. For example, the
optical power
supply 1012 can provide both pulsed light for data modulation and
synchronization, as
described in U.S. patent application 16/847,705. This allows the high-capacity
chip 1002
to be synchronized with the lower-capacity chips 1004a, 1004b, and 1004c.
[257] FIG. 11 shows an optical communications system 1100 providing high-speed
communications between a high-capacity chip 1102 (e.g., an Ethernet switch
chip) and
multiple lower-capacity chips 1104a, 1104b, e.g., multiple network interface
chips,
attached to computer servers using a mix of co-packaged optical interconnect
modules 901
similar to those shown in FIG. 9 as well as conventional pluggable optical
interconnect
modules 1108.
[258] An external optical power supply or photon supply 1106 provides optical
power
supply signals, which can be continuous-wave light, one or more trains of
periodic optical
pulses, or one or more trains of non-periodic optical pulses. For example, the
optical power
supply 1106 can provide both pulsed light for data modulation and
synchronization, as
described in U.S. patent application 16/847,705. This allows the high-capacity
chip 1102
to be synchronized with the lower-capacity chips 1104a and 1104b.
[259] FIGS. 9 to 11 show examples of optical communications systems 900, 1000,
1100
in which in each system an optical power supply or photon supply provides
optical power
supply light to photonic integrated circuits hosted in multiple communication
devices (e.g.,
optical transponders), and the optical power supply is external to the
communication
devices. The optical power supply can have its own housing, electrical power
supply, and
control circuitry, independent of the housings, electrical power supplies, and
control
circuitry of the communication devices. This allows the optical power supply
to be
serviced, repaired, or replaced independent of the communication devices.
Redundant
optical power supplies can be provided so that a defective external optical
power supply
can be repaired or replaced without taking the communication devices off-line.
The
external optical power supply can be placed at a convenient centralized
location with a
dedicated temperature environment (as opposed to being crammed inside the
communication devices, which can have a high temperature). The external
optical power
supply can be built more efficiently than individual power supply units, as
certain common
parts such as monitoring circuitry and thermal control units can be amortized
over many
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more communication devices. The following describes implementations of the
fiber
cabling for remote optical power supplies.
[260] FIG. 12 is a system functional block diagram of an example of an optical
communication system 1200 that includes a first communication transponder 1202
and a
second communication transponder 1204. Each of the first and second
communication
transponders 1202, 1204 can include one or more co-packaged optical modules
described
above. Each communication transponder can include, e.g., one or more data
processors,
such as network switches, central processing units, graphics processor units,
tensor
processing units, digital signal processors, and/or other application specific
integrated
circuits (ASICs). In this example, the first communication transponder 1202
sends optical
signals to, and receives optical signals from, the second communication
transponder 1204
through a first optical communication link 1206. The one or more data
processors in each
communication transponder 1202, 1204 process the data received from the first
optical
communication link 1206 and outputs processed data to the first optical
communication
link 1206. The optical communication system 1200 can be expanded to include
additional
communication transponders. The optical communication system 1200 can also be
expanded to include additional communication between two or more external
photon
supplies, which can coordinate aspects of the supplied light, such as the
respectively
emitted wavelengths or the relative timing of the respectively emitted optical
pulses.
[261] A first external photon supply 1208 provides optical power supply light
to the first
communication transponder 1202 through a first optical power supply link 1210,
and a
second external photon supply 1212 provides optical power supply light to the
second
communication transponder 1204 through a second optical power supply link
1214. In one
example embodiment, the first external photon supply 1208 and the second
external photon
supply 1212 provide continuous wave laser light at the same optical
wavelength. In
another example embodiment, the first external photon supply 1208 and the
second
external photon supply 1212 provide continuous wave laser light at different
optical
wavelengths. In yet another example embodiment, the first external photon
supply 1208
provides a first sequence of optical frame templates to the first
communication transponder
1202, and the second external photon supply 1212 provides a second sequence of
optical
frame templates to the second communication transponder 1204. For example, as
described
in U.S. patent 16/847,705, each of the optical frame templates can include a
respective
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frame header and a respective frame body, and the frame body includes a
respective optical
pulse train. The first communication transponder 1202 receives the first
sequence of
optical frame templates from the first external photon supply 1208, loads data
into the
respective frame bodies to convert the first sequence of optical frame
templates into a first
sequence of loaded optical frames that are transmitted through the first
optical
communication link 1206 to the second communication transponder 1204.
Similarly, the
second communication transponder 1204 receives the second sequence of optical
frame
templates from the second external photon supply 1212, loads data into the
respective
frame bodies to convert the second sequence of optical frame templates into a
second
sequence of loaded optical frames that are transmitted through the first
optical
communication link 1206 to the first communication transponder 1202.
[262] FIG. 13A is a diagram of an example of an optical communication system
1300 that
includes a first switch box 1302 and a second switch box 1304. Each of the
switch boxes
1302, 1304 can include one or more data processors, such as network switches.
The first
and second switch boxes 1302, 1304 can be separated by a distance greater
than, e.g., 1
foot, 3 feet, 10 feet, 100 feet, or 1000 feet. The figure shows a diagram of a
front panel
1306 of the first switch box 1302 and a front panel 1308 of the second switch
box 1304. In
this example, the first switch box 1302 includes a vertical ASIC mount grid
structure 1310,
similar to the grid structure 870 of FIG. 43 of U.S. application 63/145,368. A
co-packaged
optical module 1312 is attached to a receptor of the grid structure 1310. The
second switch
box 1304 includes a vertical ASIC mount grid structure 1314, similar to the
grid structure
870 of FIG. 43 of U.S. application 63/145,368. A co-packaged optical module
1316 is
attached to a receptor of the grid structure 1314. The first co-packaged
optical module
1312 communicates with the second co-packaged optical module 1316 through an
optical
fiber bundle 1318 that includes multiple optical fibers. Optional fiber
connectors 1320 can
be used along the optical fiber bundle 1318, in which shorter sections of
optical fiber
bundles are connected by the fiber connectors 1320.
[263] In some implementations, each co-packaged optical module (e.g., 1312,
1316)
includes a photonic integrated circuit configured to convert input optical
signals to input
electrical signals that are provided to a data processor, and convert output
electrical signals
from the data processor to output optical signals. The co-packaged optical
module can
include an electronic integrated circuit configured to process the input
electrical signals
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from the photonic integrated circuit before the input electrical signals are
transmitted to the
data processor, and to process the output electrical signals from the data
processor before
the output electrical signals are transmitted to the photonic integrated
circuit. In some
implementations, the electronic integrated circuit can include a plurality of
serializers/deserializers configured to process the input electrical signals
from the photonic
integrated circuit, and to process the output electrical signals transmitted
to the photonic
integrated circuit. The electronic integrated circuit can include a first
serializers/deserializers module having multiple serializer units and
deserializer units, in
which the first serializers/deserializers module is configured to generate a
plurality of sets
.. of first parallel electrical signals based on a plurality of first serial
electrical signals
provided by the photonic integrated circuit, and condition the electrical
signals, in which
each set of first parallel electrical signals is generated based on a
corresponding first serial
electrical signal. The electronic integrated circuit can include a second
serializers/deserializers module having multiple serializer units and
deserializer units, in
.. which the second serializers/deserializers module is configured to generate
a plurality of
second serial electrical signals based on the plurality of sets of first
parallel electrical
signals, and each second serial electrical signal is generated based on a
corresponding set
of first parallel electrical signals. The plurality of second serial
electrical signals can be
transmitted toward the data processor.
[264] The first switch box 1302 includes an external optical power supply 1322
(i.e.,
external to the co-packaged optical module) that provides optical power supply
light
through an optical connector array 1324. In this example, the optical power
supply 1322 is
located internal of the housing of the switch box 1302. Optical fibers 1326
are optically
coupled to an optical connector 1328 (of the optical connector array 1324) and
the co-
.. packaged optical module 1312. The optical power supply 1322 sends optical
power supply
light through the optical connector 1328 and the optical fibers 1326 to the co-
packaged
optical module 1312. For example, the co-packaged optical module 1312 includes
a
photonic integrated circuit that modulates the power supply light based on
data provided
by a data processor to generate a modulated optical signal, and transmits the
modulated
optical signal to the co-packaged optical module 1316 through one of the
optical fibers in
the fiber bundle 1318.
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[265] In some examples, the optical power supply 1322 is configured to provide
optical
power supply light to the co-packaged optical module 1312 through multiple
links that
have built-in redundancy in case of malfunction in some of the optical power
supply
modules. For example, the co-packaged optical module 1312 can be designed to
receive N
5 channels of optical power supply light (e.g., Ni continuous wave light
signals at the same
or at different optical wavelengths, or Ni sequences of optical frame
templates), Ni being
a positive integer, from the optical power supply 1322. The optical power
supply 1322
provides Nl+Ml channels of optical power supply light to the co-packaged
optical module
1312, in which M1 channels of optical power supply light are used for backup
in case of
10 failure of one or more of the Ni channels of optical power supply light,
M1 being a
positive integer.
[266] The second switch box 1304 receives optical power supply light from a co-
located
optical power supply 1330, which is, e.g., external to the second switch box
1304 and
located near the second switch box 1304, e.g., in the same rack as the second
switch box
15 1304 in a data center. The optical power supply 1330 includes an array
of optical
connectors 1332. Optical fibers 1334 are optically coupled to an optical
connector 1336 (of
the optical connectors 1332) and the co-packaged optical module 1316. The
optical power
supply 1330 sends optical power supply light through the optical connector
1336 and the
optical fibers 1334 to the co-packaged optical module 1316. For example, the
co-packaged
20 optical module 1316 includes a photonic integrated circuit that
modulates the power supply
light based on data provided by a data processor to generate a modulated
optical signal,
and transmits the modulated optical signal to the co-packaged optical module
1312 through
one of the optical fibers in the fiber bundle 1318.
[267] In some examples, the optical power supply 1330 is configured to provide
optical
25 power supply light to the co-packaged optical module 1316 through
multiple links that
have built-in redundancy in case of malfunction in some of the optical power
supply
modules. For example, the co-packaged optical module 1316 can be designed to
receive
N2 channels of optical power supply light (e.g., N2 continuous wave light
signals at the
same or at different optical wavelengths, or N2 sequences of optical frame
templates), N2
30 being a positive integer, from the optical power supply 1322. The
optical power supply
1322 provides N2+M2 channels of optical power supply light to the co-packaged
optical
module 1312, in which M2 channels of optical power supply light are used for
backup in
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case of failure of one or more of the N2 channels of optical power supply
light, M2 being a
positive integer.
[268] FIG. 13B is a diagram of an example of an optical cable assembly 1340
that can be
used to enable the first co-packaged optical module 1312 to receive optical
power supply
light from the first optical power supply 1322, enable the second co-packaged
optical
module 1316 to receive optical power supply light from the second optical
power supply
1330, and enable the first co-packaged optical module 1312 to communicate with
the
second co-packaged optical module 1316. FIG. 13C is an enlarged diagram of the
optical
cable assembly 1340 without some of the reference numbers to enhance clarity
of
illustration.
[269] The optical cable assembly 1340 includes a first optical fiber connector
1342, a
second optical fiber connector 1344, a third optical fiber connector 1346, and
a fourth
optical fiber connector 1348. The first optical fiber connector 1342 is
designed and
configured to be optically coupled to the first co-packaged optical module
1312. For
example, the first optical fiber connector 1342 can be configured to mate with
a connector
part of the first co-packaged optical module 1312, or a connector part that is
optically
coupled to the first co-packaged optical module 1312. The first, second,
third, and fourth
optical fiber connectors 1342, 1344, 1346, 1348 can comply with an industry
standard that
defines the specifications for optical fiber interconnection cables that
transmit data and
control signals, and optical power supply light.
[270] The first optical fiber connector 1342 includes optical power supply
(PS) fiber
ports, transmitter (TX) fiber ports, and receiver (RX) fiber ports. The
optical power supply
fiber ports provide optical power supply light to the co-packaged optical
module 1312. The
transmitter fiber ports allow the co-packaged optical module 1312 to transmit
output
optical signals (e.g., data and/or control signals), and the receiver fiber
ports allow the co-
packaged optical module 1312 to receive input optical signals (e.g., data
and/or control
signals). An example of the arrangement of the optical power supply fiber
ports, the
transmitter ports, and the receiver ports in the first optical fiber connector
1342 are shown
in FIG. 13D.
[271] FIG. 13D shows an enlarged upper portion of the diagram of FIG. 13B,
with the
addition of an example of a mapping of fiber ports 1750 of the first optical
fiber connector
1342 and a mapping of fiber ports 1752 of the third optical fiber connector
1346. The
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mapping of fiber ports 1750 shows the positions of the transmitter fiber ports
(e.g., 1753),
receiver fiber ports (e.g., 1755), and power supply fiber ports (e.g., 1751)
of the first
optical fiber connector 1342 when viewed in the direction 1754 into the first
optical fiber
connector 1342. The mapping of fiber ports 1752 shows the positions of the
power supply
fiber ports (e.g., 1757) of the third optical fiber connector 1346 when viewed
in the
direction 1756 into the third optical fiber connector 1346.
[272] The second optical fiber connector 1344 is designed and configured to be
optically
coupled to the second co-packaged optical module 1316. The second optical
fiber
connector 1344 includes optical power supply fiber ports, transmitter fiber
ports, and
receiver fiber ports. The optical power supply fiber ports provide optical
power supply
light to the co-packaged optical module 1316. The transmitter fiber ports
allow the co-
packaged optical module 1316 to transmit output optical signals, and the
receiver fiber
ports allow the co-packaged optical module 1316 to receive input optical
signals. An
examples of the arrangement of the optical power supply fiber ports, the
transmitter ports,
and the receiver ports in the second optical fiber connector 1344 are shown in
FIG. 13E.
[273] FIG. 13E shows an enlarged lower portion of the diagram of FIG. 13B,
with the
addition of an example of a mapping of fiber ports 1760 of the second optical
fiber
connector 1344 and a mapping of fiber ports 1762 of the fourth optical fiber
connector
1348. The mapping of fiber ports 1760 shows the positions of the transmitter
fiber ports
(e.g., 1763), receiver fiber ports (e.g., 1765), and power supply fiber ports
(e.g., 1761) of
the second optical fiber connector 1344 when viewed in the direction 1764 into
the second
optical fiber connector 1344. The mapping of fiber ports 1762 shows the
positions of the
power supply fiber ports (e.g., 1767) of the fourth optical fiber connector
1348 when
viewed in the direction 1766 into the fourth fiber connector 1348.
[274] The third optical connector 1346 is designed and configured to be
optically coupled
to the power supply 1322. The third optical connector 1346 includes optical
power supply
fiber ports (e.g., 1757) through which the power supply 1322 can output the
optical power
supply light. The fourth optical connector 1348 is designed and configured to
be optically
coupled to the power supply 1330. The fourth optical connector 1348 includes
optical
power supply fiber ports (e.g., 1762) through which the power supply 1322 can
output the
optical power supply light.
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[275] In some implementations, the optical power supply fiber ports, the
transmitter fiber
ports, and the receiver fiber ports in the first and second optical fiber
connectors 1342,
1344 are designed to be independent of the communication devices, i.e., the
first optical
fiber connector 1342 can be optically coupled to the second switch box 1304,
and the
second optical fiber connector 1344 can be optically coupled to the first
switch box 1302
without any re-mapping of the fiber ports. Similarly, the optical power supply
fiber ports in
the third and fourth optical fiber connectors 1346, 1348 are designed to be
independent of
the optical power supplies, i.e., if the first optical fiber connector 1342 is
optically coupled
to the second switch box 1304, the third optical fiber connector 1346 can be
optically
coupled to the second optical power supply 1330. If the second optical fiber
connector
1344 is optically coupled to the first switch box 1302, the fourth optical
fiber connector
1348 can be optically coupled to the first optical power supply 1322.
[276] The optical cable assembly 1340 includes a first optical fiber guide
module 1350
and a second optical fiber guide module 1352. The optical fiber guide module
depending
on context is also referred to as an optical fiber coupler or splitter because
the optical fiber
guide module combines multiple bundles of fibers into one bundle of fibers, or
separates
one bundle of fibers into multiple bundles of fibers. The first optical fiber
guide module
1350 includes a first port 1354, a second port 1356, and a third port 1358.
The second
optical fiber guide module 1352 includes a first port 1360, a second port
1362, and a third
port 1364. The fiber bundle 1318 extends from the first optical fiber
connector 1342 to the
second optical fiber connector 1344 through the first port 1354 and the second
port 1356 of
the first optical fiber guide module 1350 and the second port 1362 and the
first port 1360
of the second optical fiber guide module 1352. The optical fibers 1326 extend
from the
third optical fiber connector 1346 to the first optical fiber connector 1342
through the third
port 1358 and the first port 1354 of the first optical fiber guide module
1350. The optical
fibers 1334 extend from the fourth optical fiber connector 1348 to the second
optical fiber
connector 1344 through the third port 1364 and the first port 1360 of the
second optical
fiber guide module 1352.
[277] A portion (or section) of the optical fibers 1318 and a portion of the
optical fibers
1326 extend from the first port 1354 of the first optical fiber guide module
1350 to the first
optical fiber connector 1342. A portion of the optical fibers 1318 extend from
the second
port 1356 of the first optical fiber guide module 1350 to the second port 1362
of the second
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optical fiber guide module 1352, with optional optical connectors (e.g., 1320)
along the
paths of the optical fibers 1318. A portion of the optical fibers 1326 extend
from the third
port 1358 of the first optical fiber connector 1350 to the third optical fiber
connector 1346.
A portion of the optical fibers 1334 extend from the third port 1364 of the
second optical
fiber connector 1352 to the fourth optical fiber connector 1348.
[278] The first optical fiber guide module 1350 is designed to restrict
bending of the
optical fibers such that the bending radius of any optical fiber in the first
optical fiber guide
module 1350 is greater than the minimum bending radius specified by the
optical fiber
manufacturer to avoid excess optical light loss or damage to the optical
fiber. For example,
the minimum bend radii can be 2 cm, 1 cm, 5 mm, or 2.5 mm. Other bend radii
are also
possible. For example, the fibers 1318 and the fibers 1326 extend outward from
the first
port 1354 along a first direction, the fibers 1318 extend outward from the
second port 1356
along a second direction, and the fibers 1326 extend outward from the third
port 1358
along a third direction. A first angle is between the first and second
directions, a second
angle is between the first and third directions, and a third angle is between
the second and
third directions. The first optical fiber guide module 1350 can be designed to
limit the
bending of optical fibers so that each of the first, second, and third angles
is in a range
from, e.g., 30 to 180 .
[279] For example, the portion of the optical fibers 1318 and the portion of
the optical
fibers 1326 between the first optical fiber connector 1342 and the first port
1354 of the first
optical fiber guide module 1350 can be surrounded and protected by a first
common sheath
1366. The optical fibers 1318 between the second port 1356 of the first
optical fiber guide
module 1350 and the second port 1362 of the second optical fiber guide module
1352 can
be surrounded and protected by a second common sheath 1368. The portion of the
optical
fibers 1318 and the portion of the optical fibers 1334 between the second
optical fiber
connector 1344 and the first port 1360 of the second optical fiber guide
module 1352 can
be surrounded and protected by a third common sheath 1369. The optical fibers
1326
between the third optical fiber connector 1346 and the third port 1358 of the
first optical
fiber guide module 1350 can be surrounded and protected by a fourth common
sheath
1367. The optical fibers 1334 between the fourth optical fiber connector 1348
and the third
port 1364 of the second optical fiber guide module 1352 can be surrounded and
protected
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by a fifth common sheath 1370. Each of the common sheaths can be laterally
flexible
and/or laterally stretchable, as described in, e.g., U.S. patent application
16/822,103.
[280] One or more optical cable assemblies 1340 (FIGS. 13B, 13C) and other
optical
cable assemblies (e.g., 1400 of FIG. 15B, 15C, 1490 of FIG. 17B, 17C)
described in this
5 document can be used to optically connect switch boxes that are
configured differently
compared to the switch boxes 1302, 1304 shown in FIG. 13A, in which the switch
boxes
receive optical power supply light from one or more external optical power
supplies. For
example, in some implementations, the optical cable assembly 1340 can be
attached to a
fiber-optic array connector mounted on the outside of the front panel of an
optical switch,
10 and another fiber-optic cable then connects the inside of the fiber
connector to a co-
packaged optical module that is mounted on a circuit board positioned inside
the housing
of the switch box. The co-packaged optical module (which includes, e.g., a
photonic
integrated circuit, optical-to-electrical converters, such as photodetectors,
and electrical-to-
optical converters, such as laser diodes) can be co-packaged with a switch
ASIC and
15 mounted on a circuit board that can be vertically or horizontally
oriented. For example, in
some implementations, the front panel is mounted on hinges and a vertical ASIC
mount is
recessed behind it. See the examples in FIGS. 77A, 77B, and 78 of U.S.
application
63/145,368. The optical cable assembly 1340 provides optical paths for
communication
between the switch boxes, and optical paths for transmitting power supply
light from one
20 or more external optical power supplies to the switch boxes. The switch
boxes can have
any of a variety of configurations regarding how the power supply light and
the data and/or
control signals from the optical fiber connectors are transmitted to or
received from the
photonic integrated circuits, and how the signals are transmitted between the
photonic
integrated circuits and the data processors.
25 [281] One or more optical cable assemblies 1340 and other optical cable
assemblies (e.g.,
1400 of FIG. 15B, 15C, 1490 of FIG. 17B, 17C) described in this document can
be used to
optically connect computing devices other than switch boxes. For example, the
computing
devices can be server computers that provide a variety of services, such as
cloud
computing, database processing, audio/video hosting and streaming, electronic
mail, data
30 storage, web hosting, social network, supercomputing, scientific
research computing,
healthcare data processing, financial transaction processing, logistics
management, weather
forecast, or simulation, to list a few examples. The optical power light
required by the
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optoelectronic modules of the computing devices can be provided using one or
more
external optical power supplies. For example, in some implementations, one or
more
external optical power supplies that are centrally managed can be configured
to provide the
optical power supply light for hundreds or thousands of server computers in a
data center,
and the one or more optical power supplies and the server computers can be
optically
connected using the optical cable assemblies (e.g., 1340, 1400, 1490)
described in this
document and variations of the optical cable assemblies using the principles
described in
this document.
[282] FIG. 14 is a system functional block diagram of an example of an optical
communication system 1380 that includes a first communication transponder 1282
and a
second communication transponder 1284. The first communication transponder
1282 sends
optical signals to, and receives optical signals from, the second
communication
transponder 1284 through a first optical communication link 1290. The optical
communication system 1380 can be expanded to include additional communication
transponders.
[283] An external photon supply 1382 provides optical power supply light to
the first
communication transponder 1282 through a first optical power supply link 1384,
and
provides optical power supply light to the second communication transponder
1284
through a second optical power supply link 1386. In one example, the external
photon
supply 1282 provides continuous wave light to the first communication
transponder 1282
and to the second communication transponder 1284. In one example, the
continuous wave
light can be at the same optical wavelength. In another example, the
continuous wave light
can be at different optical wavelengths. In yet another example, the external
photon supply
1282 provides a first sequence of optical frame templates to the first
communication
transponder 1282, and provides a second sequence of optical frame templates to
the second
communication transponder 1284. Each of the optical frame templates can
include a
respective frame header and a respective frame body, and the frame body
includes a
respective optical pulse train. The first communication transponder 1282
receives the first
sequence of optical frame templates from the external photon supply 1382,
loads data into
.. the respective frame bodies to convert the first sequence of optical frame
templates into a
first sequence of loaded optical frames that are transmitted through the first
optical
communication link 1290 to the second communication transponder 1284.
Similarly, the
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second communication transponder 1284 receives the second sequence of optical
frame
templates from the external photon supply 1382, loads data into the respective
frame
bodies to convert the second sequence of optical frame templates into a second
sequence of
loaded optical frames that are transmitted through the first optical
communication link
1290 to the first communication transponder 1282.
[284] FIG. 15A is a diagram of an example of an optical communication system
1390 that
includes a first switch box 1302 and a second switch box 1304, similar to
those in FIG.
13A. The first switch box 1302 includes a vertical ASIC mount grid structure
1310, and a
co-packaged optical module 1312 is attached to a receptor of the grid
structure 1310. The
second switch box 1304 includes a vertical ASIC mount grid structure 1314, and
a co-
packaged optical module 1316 is attached to a receptor of the grid structure
1314. The first
co-packaged optical module 1312 communicates with the second co-packaged
optical
module 1316 through an optical fiber bundle 1318 that includes multiple
optical fibers.
[285] As discussed above in connection with FIGS. 13A to 13E, the first and
second
switch boxes 1302, 1304 can have other configurations. For example,
horizontally
mounted ASICs can be used. A fiber-optic array connector attached to a front
panel can be
used to optically connect the optical cable assembly 1340 to another fiber-
optic cable that
connects to a co-packaged optical module mounted on a circuit board inside the
switch
box. The front panel can be mounted on hinges and a vertical ASIC mount can be
recessed
behind it. The switch boxes can be replaced by other types of server
computers.
[286] In an example embodiment, the first switch box 1302 includes an external
optical
power supply 1322 that provides optical power supply light to both the co-
packaged
optical module 1312 in the first switch box 1302 and the co-packaged optical
module 1316
in the second switch box 1304. In another example embodiment, the optical
power supply
can be located outside the switch box 1302 (cf. 1330, FIG. 13A). The optical
power supply
1322 provides the optical power supply light through an optical connector
array 1324.
Optical fibers 1392 are optically coupled to an optical connector 1396 and the
co-packaged
optical module 1312. The optical power supply 1322 sends optical power supply
light
through the optical connector 1396 and the optical fibers 1392 to the co-
packaged optical
module 1312 in the first switch box 1302. Optical fibers 1394 are optically
coupled to the
optical connector 1396 and the co-packaged optical module 1316. The optical
power
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supply 1322 sends optical power supply light through the optical connector
1396 and the
optical fibers 1394 to the co-packaged optical module 1316 in the second
switch box 1304.
[287] FIG. 15B shows an example of an optical cable assembly 1400 that can be
used to
enable the first co-packaged optical module 1312 to receive optical power
supply light
from the optical power supply 1322, enable the second co-packaged optical
module 1316
to receive optical power supply light from the optical power supply 1322, and
enable the
first co-packaged optical module 1312 to communicate with the second co-
packaged
optical module 1316. FIG. 15C is an enlarged diagram of the optical cable
assembly 1400
without some of the reference numbers to enhance clarity of illustration.
[288] The optical cable assembly 1400 includes a first optical fiber connector
1402, a
second optical fiber connector 1404, and a third optical fiber connector 1406.
The first
optical fiber connector 1402 is similar to the first optical fiber connector
1342 of FIGS.
13B, 13C, 13D, and is designed and configured to be optically coupled to the
first co-
packaged optical module 1312. The second optical fiber connector 1404 is
similar to the
second optical fiber connector 1344 of FIGS. 13B, 13C, 13E, and is designed
and
configured to be optically coupled to the second co-packaged optical module
1316. The
third optical connector 1406 is designed and configured to be optically
coupled to the
power supply 1322. The third optical connector 1406 includes first optical
power supply
fiber ports (e.g., 1770, FIG. 15D) and second optical power supply fiber ports
(e.g., 1772).
The power supply 1322 outputs optical power supply light through the first
optical power
supply fiber ports to the optical fibers 1392, and outputs optical power
supply light through
the second optical power supply fiber ports to the optical fibers 1394. The
first, second,
and third optical fiber connectors 1402, 1404, 1406 can comply with an
industry standard
that defines the specifications for optical fiber interconnection cables that
transmit data and
control signals, and optical power supply light.
[289] FIG. 15D shows an enlarged upper portion of the diagram of FIG. 15B,
with the
addition of an example of a mapping of fiber ports 1774 of the first optical
fiber connector
1402 and a mapping of fiber ports 1776 of the third optical fiber connector
1406. The
mapping of fiber ports 1774 shows the positions of the transmitter fiber ports
(e.g., 1778),
receiver fiber ports (e.g., 1780), and power supply fiber ports (e.g., 1782)
of the first
optical fiber connector 1402 when viewed in the direction 1784 into the first
optical fiber
connector 1402. The mapping of fiber ports 1776 shows the positions of the
power supply
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fiber ports (e.g., 1770, 1772) of the third optical fiber connector 1406 when
viewed in the
direction 1786 into the third optical fiber connector 1406. In this example,
the third optical
fiber connector 1406 includes 8 optical power supply fiber ports.
[290] In some examples, optical connector array 1324 of the optical power
supply 1322
can include a first type of optical connectors that accept optical fiber
connectors having 4
optical power supply fiber ports, as in the example of FIG. 13D, and a second
type of
optical connectors that accept optical fiber connectors having 8 optical power
supply fiber
ports, as in the example of FIG. 15D. In some examples, if the optical
connector array
1324 of the optical power supply 1322 only accepts optical fiber connectors
having 4
optical power supply fiber ports, then a converter cable can be used to
convert the third
optical fiber connector 1406 of FIG. 15D to two optical fiber connectors, each
having 4
optical power supply fiber ports, that is compatible with the optical
connector array 1324.
[291] FIG. 15E shows an enlarged lower portion of the diagram of FIG. 15B,
with the
addition of an example of a mapping of fiber ports 1790 of the second optical
fiber
connector 1404. The mapping of fiber ports 1790 shows the positions of the
transmitter
fiber ports (e.g., 1792), receiver fiber ports (e.g., 1794), and power supply
fiber ports (e.g.,
1796) of the second optical fiber connector 1404 when viewed in the direction
1798 into
the second optical fiber connector 1404.
[292] The port mappings of the optical fiber connectors shown in FIGS. 13D,
13E, 15D,
and 15E are merely examples. Each optical fiber connector can include a
greater number or
a smaller number of transmitter fiber ports, a greater number or a smaller
number of
receiver fiber ports, and a greater number or a smaller number of optical
power supply
fiber ports, as compared to those shown in FIGS. 13D, 13E, 15D, and 15E. The
arrangement of the relative positions of the transmitter, receiver, and
optical power supply
fiber ports can also be different from those shown in FIGS. 13D, 13E, 15D, and
15E.
[293] The optical cable assembly 1400 includes an optical fiber guide module
1408,
which includes a first port 1410, a second port 1412, and a third port 1414.
The optical
fiber guide module 1408 depending on context is also referred as an optical
fiber coupler
(for combining multiple bundles of optical fibers into one bundle of optical
fiber) or an
optical fiber splitter (for separating a bundle of optical fibers into
multiple bundles of
optical fibers). The fiber bundle 1318 extends from the first optical fiber
connector 1402 to
the second optical fiber connector 1404 through the first port 1410 and the
second port
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1412 of the optical fiber guide module 1408. The optical fibers 1392 extend
from the third
optical fiber connector 1406 to the first optical fiber connector 1402 through
the third port
1414 and the first port 1410 of the optical fiber guide module 1408. The
optical fibers 1394
extend from the third optical fiber connector 1406 to the second optical fiber
connector
5 1404 through the third port 1414 and the second port 1412 of the optical
fiber guide
module 1408.
[294] A portion of the optical fibers 1318 and a portion of the optical fibers
1392 extend
from the first port 1410 of the optical fiber guide module 1408 to the first
optical fiber
connector 1402. A portion of the optical fibers 1318 and a portion of the
optical fibers
10 1394 extend from the second port 1412 of the optical fiber guide module
1408 to the
second optical fiber connector 1404. A portion of the optical fibers 1394
extend from the
third port 1414 of the optical fiber connector 1408 to the third optical fiber
connector 1406.
[295] The optical fiber guide module 1408 is designed to restrict bending of
the optical
fibers such that the radius of curvature of any optical fiber in the optical
fiber guide
15 module 1408 is greater than the minimum radius of curvature specified by
the optical fiber
manufacturer to avoid excess optical light loss or damage to the optical
fiber. For example,
the optical fibers 1318 and the optical fibers 1392 extend outward from the
first port 1410
along a first direction, the optical fibers 1318 and the optical fibers 1394
extend outward
from the second port 1412 along a second direction, and the optical fibers
1392 and the
20 optical fibers 1394 extend outward from the third port 1414 along a
third direction. A first
angle is between the first and second directions, a second angle is between
the first and
third directions, and a third angle is between the second and third
directions. The optical
fiber guide module 1408 is designed to limit the bending of optical fibers so
that each of
the first, second, and third angles is in a range from, e.g., 30 to 180 .
25 [296] For example, the portion of the optical fibers 1318 and the
portion of the optical
fibers 1392 between the first optical fiber connector 1402 and the first port
1410 of the
optical fiber guide module 1408 can be surrounded and protected by a first
common sheath
1416. The optical fibers 1318 and the optical fibers 1394 between the second
optical fiber
connector 1404 and the second port 1412 of the optical fiber guide module 1408
can be
30 surrounded and protected by a second common sheath 1418. The optical
fibers 1392 and
the optical fibers 1394 between the third optical fiber connector 1406 and the
third port
1414 of the optical fiber guide module 1408 can be surrounded and protected by
a third
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common sheath 1420. Each of the common sheaths can be laterally flexible
and/or laterally
stretchable.
[297] FIG. 16 is a system functional block diagram of an example of an optical
communication system 1430 that includes a first communication transponder
1432, a
second communication transponder 1434, a third communication transponder 1436,
and a
fourth communication transponder 1438. Each of the communication transponders
1432,
1434, 1436, 1438 can be similar to the communication transponders 1202, 1204
of FIG.
12. The first communication transponder 1432 communicates with the second
communication transponder 1434 through a first optical link 1440. The first
communication transponder 1432 communicates with the third communication
transponder
1436 through a second optical link 1442. The first communication transponder
1432
communicates with the fourth communication transponder 1438 through a third
optical
link 1444.
[298] An external photon supply 1446 provides optical power supply light to
the first
communication transponder 1432 through a first optical power supply link 1448,
provides
optical power supply light to the second communication transponder 1434
through a
second optical power supply link 1450, provides optical power supply light to
the third
communication transponder 1436 through a third optical power supply link 1452,
and
provides optical power supply light to the fourth communication transponder
1438 through
a fourth optical power supply link 1454.
[299] FIG. 17A is a diagram of an example of an optical communication system
1460 that
includes a first switch box 1462 and a remote server array 1470 that includes
a second
switch box 1464, a third switch box 1466, and a fourth switch box 1468. The
first switch
box 1462 includes a vertical ASIC mount grid structure 1310, and a co-packaged
optical
module 1312 is attached to a receptor of the grid structure 1310. The second
switch box
1464 includes a co-packaged optical module 1472, the third switch box 1466
includes a co-
packaged optical module 1474, and the third switch box 1468 includes a co-
packaged
optical module 1476. The first co-packaged optical module 1312 communicates
with the
co-packaged optical modules 1472, 1474, 1476 through an optical fiber bundle
1478 that
later branches out to the co-packaged optical modules 1472, 1474, 1476.
[300] In one example embodiment, the first switch box 1462 includes an
external optical
power supply 1322 that provides optical power supply light through an optical
connector
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array 1324. In another example embodiment, the optical power supply can be
located
external to switch box 1462 (cf. 1330, FIG. 13A). Optical fibers 1480 are
optically coupled
to an optical connector 1482, and the optical power supply 1322 sends optical
power
supply light through the optical connector 1482 and the optical fibers 1480 to
the co-
packaged optical modules 1312, 1472, 1474, 1476.
[301] FIG. 17B shows an example of an optical cable assembly 1490 that can be
used to
enable the optical power supply 1322 to provide optical power supply light to
the co-
packaged optical modules 1312, 1472, 1474, 1476, and enable the co-packaged
optical
module 1312 to communicate with the co-packaged optical modules 1472, 1474,
1476.
The optical cable assembly 1490 includes a first optical fiber connector 1492,
a second
optical fiber connector 1494, a third optical fiber connector 1496, a fourth
optical fiber
connector 1498, and a fifth optical fiber connector 1500. The first optical
fiber connector
1492 is configured to be optically coupled to the co-packaged optical module
1312. The
second optical fiber connector 1494 is configured to be optically coupled to
the co-
packaged optical module 1472. The third optical fiber connector 1496 is
configured to be
optically coupled to the co-packaged optical module 1474. The fourth optical
fiber
connector 1498 is configured to be optically coupled to the co-packaged
optical module
1476. The fifth optical fiber connector 1500 is configured to be optically
coupled to the
optical power supply 1322. FIG. 17C is an enlarged diagram of the optical
cable assembly
1490.
[302] Optical fibers that are optically coupled to the optical fiber
connectors 1500 and
1492 enable the optical power supply 1322 to provide the optical power supply
light to the
co-packaged optical module 1312. Optical fibers that are optically coupled to
the optical
fiber connectors 1500 and 1494 enable the optical power supply 1322 to provide
the
optical power supply light to the co-packaged optical module 1472. Optical
fibers that are
optically coupled to the optical fiber connectors 1500 and 1496 enable the
optical power
supply 1322 to provide the optical power supply light to the co-packaged
optical module
1474. Optical fibers that are optically coupled to the optical fiber
connectors 1500 and
1498 enable the optical power supply 1322 to provide the optical power supply
light to the
co-packaged optical module 1476.
[303] Optical fiber guide modules 1502, 1504, 1506, and common sheaths are
provided to
organize the optical fibers so that they can be easily deployed and managed.
The optical
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fiber guide module 1502 is similar to the optical fiber guide module 1408 of
FIG. 15B. The
optical fiber guide modules 1504, 1506 are similar to the optical fiber guide
module 1350
of FIG. 13B. The common sheaths gather the optical fibers in a bundle so that
they can be
more easily handled, and the optical fiber guide modules guide the optical
fibers so that
they extend in various directions toward the devices that need to be optically
coupled by
the optical cable assembly 1490. The optical fiber guide modules restrict
bending of the
optical fibers such that the bending radiuses are greater than minimum values
specified by
the optical fiber manufacturers to prevent excess optical light loss or damage
to the optical
fibers.
[304] The optical fibers 1480 that extend from the include optical fibers that
extend from
the optical 1482 are surrounded and protected by a common sheath 1508. At the
optical
fiber guide module 1502, the optical fibers 1480 separate into a first group
of optical fibers
1510 and a second group of optical fibers 1512. The first group of optical
fibers 1510
extend to the first optical fiber connector 1492. The second group of optical
fibers 1512
extend toward the optical fiber guide modules 1504, 1506, which together
function as a 1:3
splitter that separates the optical fibers 1512 into a third group of optical
fibers 1514, a
fourth group of optical fibers 1516, and a fifth group of optical fibers 1518.
The group of
optical fibers 1514 extend to the optical fiber connector 1494, the group of
optical fibers
1516 extend to the optical fiber connector 1496, and the group of optical
fibers 1518
.. extend to the optical fiber connector 1498. In some examples, instead of
using two 1:2 split
optical fiber guide modules 1504, 1506, it is also possible to use a 1:3 split
optical fiber
guide module that has four ports, e.g., one input port and three output ports.
In general,
separating the optical fibers in a 1:N split (N being an integer greater than
2) can occur in
one step or multiple steps.
[305] FIG. 18 is a diagram of an example of a data processing system (e.g.,
data center)
1520 that includes N servers 1522 spread across K racks 1524. In this example,
there are 6
racks 1524, and each rack 1524 includes 15 servers 1522. Each server 1522
directly
communicates with a tier 1 switch 1526. The left portion of the figure shows
an enlarged
view of a portion 1528 of the system 1520. A server 1522a directly
communicates with a
tier 1 switch 1526a through a communication link 1530a. Similarly, servers
1522b, 1522c
directly communicate with the tier 1 switch 1526a through communication links
1530b,
1530c, respectively. The server 1522a directly communicates with a tier 1
switch 1526b
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through a communication link 1532a. Similarly, servers 1522b, 1522c directly
communicate with the tier 1 switch 1526b through communication links 1532b,
1532c,
respectively. Each communication link can include a pair of optical fibers to
allow bi-
directional communication. The system 1520 bypasses the conventional top-of-
rack switch
and can have the advantage of higher data throughput. The system 1520 includes
a point-
to-point connection between every server 1522 and every tier 1 switch 1526. In
this
example, there are 4 tier 1 switches 1526, and 4 fiber pairs are used per
server 1522 for
communicating with the tier 1 switches 1526. Each tier-1 switch 1526 is
connected to N
servers, so there are N fiber pairs connected to each tier-1 switch 1526.
[306] Referring to FIG. 19, in some implementations, a data processing system
(e.g., data
center) 1540 includes tier-1 switches 1526 that are co-located in a rack 1540
separate from
the N servers 1522 that are spread across K racks 1524. Each server 1522 has a
direct link
to each of the tier-1 switches 1526. In some implementations, there is one
fiber cable 1542
(or a small number <<N/K of fiber cables) from the tier-1 switch rack 1540 to
each of the
K server racks 1524.
[307] FIG. 20A is a diagram of an example of a data processing system 1550
that
includes N=1024 servers 1552 spread across K=32 racks 1554, in which each rack
1554
includes N/K=1024/32=32 servers 1552. There are 4 tier-1 switches 1556 and an
optical
power supply 1558 that is co-located in a rack 1560.
[308] Optical fibers connect the servers 1552 to the tier-1 switches 1556 and
the optical
power supply 1558. In this example, a bundle of 9 optical fibers is optically
coupled to a
co-packaged optical module 1564 of a server 1552, in which 1 optical fiber
provides the
optical power supply light, and 4 pairs of (a total of 8) optical fibers
provide 4 bi-
directional communication channels, each channel having a 100 Gbps bandwidth,
for a
total of 4 x 100 Gbps bandwidth in each direction. Because there are 32
servers 1552 in
each rack 1554, there are a total of 256 + 32 = 288 optical fibers that extend
from each
rack 1554 of servers 1552, in which 32 optical fibers provide the optical
power supply
light, and 256 optical fibers provide 128 bi-directional communication
channels, each
channel having a 100 Gbps bandwidth.
[309] For example, at the server rack side, optical fibers 1566 (that are
connected to the
servers 1552 of a rack 1554) terminate at a server rack connector 1568. At the
switch rack
side, optical fibers 1578 (that are connected to the switch boxes 1556 and the
optical power
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supply 1558) terminate at a switch rack connector 1576. An optical fiber
extension cable
1572 is optically coupled to the server rack side and the switch rack side.
The optical fiber
extension cable 1572 includes 256 + 32 = 288 optical fibers. The optical fiber
extension
cable 1572 includes a first optical fiber connector 1570 and a second optical
fiber
5 connector 1574. The first optical fiber connector 1570 is connected to
the server rack
connector 1568, and the second optical fiber connector 1574 is connected to
the switch
rack connector 1576. At the switch rack side, the optical fibers 1578 include
288 optical
fibers, of which 32 optical fibers 1580 are optically coupled to the optical
power supply
1558. The 256 optical fibers that carry 128 bi-directional communication
channels (each
10 channel having a 100 Gbps bandwidth in each direction) are separated
into four groups of
64 optical fibers, in which each group of 64 optical fibers is optically
coupled to a co-
packaged optical module 1582 in one of the switch boxes 1556. The co-packaged
optical
module 1582 is configured to have a bandwidth of 32 x 100 Gbps = 3.2 Tbps in
each
direction (input and output). Each switch box 1556 is connected to each server
1552 of the
15 rack 1554 through a pair of optical fibers that carry a bandwidth of 100
Gbps in each
direction.
[310] The optical power supply 1558 provides optical power supply light to co-
packaged
optical modules 1582 at the switch boxes 1556. In this example, the optical
power supply
1558 provides optical power supply light through 4 optical fibers to each co-
packaged
20 optical module 1582, so that a total of 16 optical fibers are used to
provide the optical
power supply light to the 4 switch boxes 1556. A bundle of optical fibers 1584
is optically
coupled to the co-packaged optical module 1582 of the switch box 1556. The
bundle of
optical fibers 1584 includes 64 + 16 = 80 fibers. In some examples, the
optical power
supply 1558 can provide additional optical power supply light to the co-
packaged optical
25 module 1582 using additional optical fibers. For example, the optical
power supply 1558
can provide optical power supply light to the co-packaged optical module 1582
using 32
optical fibers with built-in redundancy.
[311] Referring to FIG. 20B, the data processing system 1550 includes an
optical fiber
guide module 1590 that helps organize the optical fibers so that they are
directed to the
30 appropriate directions. The optical fiber guide module 1590 also
restricts bending of the
optical fibers to be within the specified limits to prevent excess optical
light loss or damage
to the optical fibers. The optical fiber guide module 1590 includes a first
port 1592, a
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second port 1594, and a third port 1596. The optical fibers that extend
outward from the
first port 1592 are optically coupled to the switch rack connector 1576. The
optical fibers
that extend outward from the second port 1594 are optically coupled to the
switch boxes.
The optical fibers that extend outward from the third port 1596 are optically
coupled to the
optical power supply 1558.
[312] In some implementations, each of the optical power supply or external
photon
supply 902 of FIG. 9, 1012 of FIG. 10, 1106 of FIG. 11, 1208, 1212 of FIG. 12,
1322,
1330 of FIG. 13A, 1382 of FIG. 14, 1322 of FIG. 15A, 1446 of FIG. 16, 1322 of
FIG.
17A, and 1558 of FIGS. 20A and 20B can have a configuration similar to any one
of the
optical power supplies shown in FIGS. 2 and 4A to 4F. In some implementations,
each of
the optical fibers 914 and 916 of FIG. 9, 1014, 1016a, 1016b, 1016c of FIG.
10, 1210 and
1214 of FIG. 12, 1384 and 1386 of FIG. 14, 1394 of FIG. 15A, 1448, 1450, 1452,
1454 of
FIG. 16, and 1580 of FIG. 20A that is optically coupled to the optical power
supply can
include one or more sections of non-polarization-maintaining optical fiber.
Light supplied
by optical power supply module can experience random polarization rotation
upon
propagation through the optical fiber.
[313] In some implementations, each of the co-packaged optical interconnect
modules
910 of FIGS. 9 to 11, the communication transponders 1202 and 1204 of FIG. 12,
the co-
packaged optical modules 1312 and 1316 of FIG. 13A, the communication
transponders
1282 and 1284 of FIG. 14, the co-packaged optical modules 1312 and 1316 of
FIG. 15A,
the communication transponders 1432, 1434, 1436, and 1438 of FIG. 16, the co-
packaged
optical modules 1312, 1472, 1474, and 1476 of FIG. 17A, the co-packaged
optical module
1564 and 1582 of FIG. 20A, can have one or more optical transmit modules
similar to the
optical transmit module 504 of FIG. 5 or 600 of FIG. 6.
[314] Additional details of the fiber cables that can be used to transmit
light from the
optical power supplies to photonic integrated circuits that include modulators
that can
modulate the light, and fiber-to-photonic integrated circuit connects that can
be used to
couple the light from the fibers to the photonic integrated circuits, can be
found in, e.g.,
U.S. patent application 16/816,171, filed on March 11, 2020, and PCT
application
PCT/U52021/021953, filed on March 11, 2021, U.S. patent application
16/822,103, filed
on March 18, 2020, PCT application PCT/U52021/022730, filed on March 17, 2021,
and
PCT application PCT/U52021/027306, filed on April 14, 2021. The entire
contents of
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application 16/816,171, application PCT/US2021/021953, application 16/822,103,
application PCT/US2021/022730, and application PCT/US2021/027306 are herein
incorporated by reference. Additional details related to the photonic
integrated circuits that
include modulators that can modulate the light provided by the optical power
supplies can
be found in, e.g., U.S. provisional patent application 63/080,528, filed on
September 18,
2020, the entire content of which is herein incorporated by reference.
Additional details for
fiber connectors that can assist in the connection of optical fiber cables to
the optical power
supplies and the photonic integrated circuits can be found in, e.g., U.S.
provisional patent
application 63/088,914, filed on October 7, 2020, the entire content of which
is herein
incorporated by reference.
[315] According to an example embodiment disclosed above, e.g., in the summary
section and/or in reference to any one or any combination of some or all of
FIGs. 1-8,
provided is an apparatus (e.g., 100, FIG. 1) for communicating optical signals
modulated at
a symbol rate (e.g., Rs), the apparatus comprising an optical power supply
(e.g., 290, FIG.
2) that comprises: a light source (e.g., 200, FIG. 2) and an electronic
controller (e.g., 230,
FIG. 2) connected to the light source to cause the light source to generate a
first light
output having a first optical frequency (e.g., 212, FIGs. 2 and 3) and a
second light output
having a second optical frequency (e.g., 222, FIGs. 2 and 3) different from
the first optical
frequency, each of the first and second light outputs being steady during a
time interval
that is significantly longer (e.g., by a factor of 100) than one over the
symbol rate; and a
polarization combiner (e.g., 240, FIG. 2) connected to receive the first and
second light
outputs of the light source at different respective input ports thereof, the
polarization
combiner being configured to generate, at an output port thereof, an optical
output in
which first and second mutually orthogonal polarization components carry light
of the first
and second light outputs, respectively.
[316] In some embodiments of the above apparatus, the electronic controller is
configured
to cause the first light output and the second light output to be mutually
time/frequency
orthogonal (e.g., as per Eqs. (3) and (4)).
[317] In some embodiments of any of the above apparatus, a degree to which the
first
light output and the second light output are time/frequency orthogonal is
greater than 0.8.
[318] In some embodiments of any of the above apparatus, the degree is greater
than 0.9.
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[319] In some embodiments of any of the above apparatus, the degree is greater
than
0.99.
[320] In some embodiments of any of the above apparatus, the first light
output comprises
a first continuous-wave optical field at the first optical frequency, and the
second light
output comprises a second continuous-wave optical field at the second optical
frequency.
[321] In some embodiments of any of the above apparatus, a difference between
the first
optical frequency and the second optical frequency is greater than five times
the symbol
rate (e.g., Af = 1f1¨f21> 5 RI, 212, 222, FIG. 3D).
[322] In some embodiments of any of the above apparatus, a difference between
the first
optical frequency and the second optical frequency is approximately an integer
multiple of
the symbol rate (i.e., Af n RI, with n = 2,3,4,...).
[323] In some embodiments of any of the above apparatus, the first light
output comprises
a first optical pulse train of a first period, and the second light output
comprises a second
optical pulse train of the first period.
[324] In some embodiments of any of the above apparatus, pulses of the first
and second
optical pulse trains have a same intensity waveform (e.g., 212, 222, FIG. 3C).
[325] In some embodiments of any of the above apparatus, pulses of the first
and second
optical pulse trains have different respective intensity waveforms.
[326] In some embodiments of any of the above apparatus, the first and second
optical
pulse trains are phase-locked with respect to one another.
[327] In some embodiments of any of the above apparatus, centers of pulses of
the first
optical pulse train are temporally aligned with centers of corresponding
pulses of the
second optical pulse train (e.g., AT 0, 212, 222, FIG. 3C).
[328] In some embodiments of any of the above apparatus, centers of pulses of
the first
optical pulse train are temporally offset from centers of corresponding pulses
of the second
optical pulse train by a nonzero time shift (e.g., AT, 212, 222, FIG. 3C).
[329] In some embodiments of any of the above apparatus, the nonzero time
shift is
smaller than one half the first period (e.g., AT< Ti /2, 212, 222, FIG. 3C).
[330] In some embodiments of any of the above apparatus, the nonzero time
shift is
smaller than one quarter of the first period (e.g., AT< Ti /4, 212, 222, FIG.
3C).
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[331] In some embodiments of any of the above apparatus, the difference
between the
first optical frequency and the second optical frequency is twice the pulse
repetition rate
(i.e., Af 2 RI, 212, 222, FIG. 3E).
[332] In some embodiments of any of the above apparatus, the difference
between the
first optical frequency and the second optical frequency is three times the
pulse repetition
rate (i.e., Af 3 RI).
[333] In some embodiments of any of the above apparatus (e.g., 212, 222, FIG.
3E; 516,
517, FIG. 6D) a spectrum of the first pulse train has two first optical
frequency tones; and a
spectrum of the second pulse train has two second optical frequency tones
different from
the two first optical frequency tones.
[334] In some embodiments of any of the above apparatus, the first and second
optical
frequency tones are equidistantly spaced by an integer multiple of the symbol
rate.
[335] In some embodiments of any of the above apparatus, the integer multiple
is two.
[336] In some embodiments of any of the above apparatus, the electronic
controller is
further configured to imprint first control information on the first light
output of the light
source and second control information on the second light output of the light
source.
[337] In some embodiments of any of the above apparatus, the first control
information is
identical to the second control information.
[338] In some embodiments of any of the above apparatus, the electronic
controller
imprints the first and second control information using one or more of: an
intensity, a
phase, a frequency, and a polarization of the first light output and the
second light output.
[339] In some embodiments of any of the above apparatus, the light source
comprises a
first CW laser oscillating at the first optical frequency (e.g., 410, FIG.
4A), and a second
CW laser oscillating at the second optical frequency (e.g., 420, FIG. 4A).
[340] In some embodiments of any of the above apparatus, the electronic
controller is
configured to control the first CW laser and the second CW laser (e.g., 430,
FIG. 4A) to
controllably set a frequency difference between the first and second optical
frequencies.
[341] In some embodiments of any of the above apparatus, the polarization
combiner
comprises one or more of: a polarization beam combiner, a polarization-
maintaining
optical power combiner, and a polarization-maintaining wavelength multiplexer.
[342] In some embodiments of any of the above apparatus, the light source
comprises a
CW laser and an optical modulator optically connected to the CW laser, the
optical
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modulator configured to generate a first modulation tone at the first optical
frequency (e.g.,
424, FIG. 4B; 417, FIG. 4C).
[343] In some embodiments of any of the above apparatus, the electronic
controller (e.g.,
432, FIG. 4B; 433, FIG. 4C) is configured to control an optical frequency of
the first
5 modulation tone.
[344] In some embodiments of any of the above apparatus, the optical modulator
is
further configured to generate a second modulation tone at the second optical
frequency
(e.g., 417, FIG. 4B).
[345] In some embodiments of any of the above apparatus, the light source
comprises an
10 .. optical amplitude modulator configured to generate an optical pulse
train (e.g., 417, 427,
FIG. 4D; 417, FIG. 4E).
[346] In some embodiments of any of the above apparatus, the light source
comprises a
pulsed laser configured to generate an optical pulse train (e.g., 410 and 417,
420 and 427,
FIG. 4C).
15 [347] In some embodiments of any of the above apparatus, the light
source comprises an
optical delay element configured to delay the first light output with respect
to the second
light output (e.g., 419, FIGs. 4D and 4E).
[348] In some embodiments of any of the above apparatus, the optical power
supply
comprises an optical dispersion-compensating element (e.g., 470, FIGs. 4D and
4E).
20 [349] In some embodiments of any of the above apparatus, the light
source comprises a
polarization-diversity in-phase/quadrature modulator (e.g., 417, FIG. 4F).
[350] In some embodiments of any of the above apparatus (e.g., 212, 222, FIG.
3E): the
polarization-diversity in-phase/quadrature modulator is configured to generate
two tones in
a first polarization and two tones in a second polarization orthogonal to the
first
25 polarization; wherein frequency spacing between the two tones in the
first polarization and
frequency spacing between the two tones in the second polarization are equal
to one
another; and wherein frequency spacing between a tone in the first
polarization and a tone
in the second polarization is an integer multiple of said equal frequency
spacing.
[351] In some embodiments of any of the above apparatus, the phase difference
between
30 the two tones in the first polarization is equal to the phase difference
between the two tones
in the second polarization.
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[352] In some embodiments of any of the above apparatus, the apparatus further
comprises an optical transmit module (e.g., 504, FIG. 5; 600, FIG. 6)
optically end-
connected to the output port of the polarization combiner (e.g., 242, FIG. 2)
via one or
more sections of optical fiber (e.g., 1026, 543, FIG. 5), the transmit module
comprising: a
polarization splitter (e.g., 515, FIG. 5) having an input port thereof
optically connected to
an end of one of the sections of the optical fiber to receive light of the
optical output; a first
optical data modulator (e.g., 5301, FIG. 5) connected to a first output of the
polarization
splitter; and a second optical data modulator (e.g., 5302, FIG. 5) connected
to a second
output of the polarization splitter.
[353] In some embodiments of any of the above apparatus, at least one of the
first and
second optical data modulators is configured to modulate received light at the
symbol rate.
[354] In some embodiments of any of the above apparatus, at least one of the
one or more
sections of the optical fiber is non-polarization-maintaining.
[355] In some embodiments of any of the above apparatus, the optical fiber is
at least one
meter long.
[356] In some embodiments of any of the above apparatus, the optical fiber is
at least ten
meters long.
[357] According to another example embodiment disclosed above, e.g., in the
summary
section and/or in reference to any one or any combination of some or all of
FIGs. 1-8,
provided is an apparatus comprising an optical transmitter (e.g., 500, FIG. 5)
that
comprises: a passive polarization splitter (e.g., 515, FIG. 5) having an
optical input port
and first (e.g., 516, FIG. 5) and second (e.g., 517, FIG. 5) optical output
ports, the optical
input port being optically connected to receive an optical input signal having
first and
second polarization components (e.g., FIGs. 3A-3E), the first polarization
component
carrying light of a first optical frequency, the second polarization component
carrying light
of a second optical frequency different from the first optical frequency, the
first and second
polarization components being mutually orthogonal and jointly undergoing a
state-of-
polarization change during a time interval (e.g., intervals (A), (B), (C),
FIGs. 7B-7D), the
passive polarization splitter causing light of a first fixed polarization to
be directed from
the optical input port to the first optical output port and also causing light
of a second fixed
polarization to be directed from the optical input port to the second optical
output port, the
first and second fixed polarizations being orthogonal to one another, the
state-of-
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polarization change causing respective spectral compositions of the lights
directed to the
first and second optical ports to change during said time interval (e.g.,
FIGs. 7B-7D); and a
first optical modulator (e.g., 5301, FIG. 5) connected to the first optical
output port and
configured to modulate the light of the first fixed polarization received
therefrom (e.g.,
516, FIG. 5) in response to a first data signal (e.g., Data 1, FIG. 5).
[358] In some embodiments of the above apparatus, the optical transmitter
further
comprises a second optical modulator (e.g., 5302, FIG. 5) connected to the
second optical
output port and configured to modulate the light of the second fixed
polarization received
therefrom (e.g., 517, FIG. 5) in response to a second data signal (e.g., Data
2, FIG. 5).
[359] In some embodiments of any of the above apparatus, the first and second
optical
modulators are connected to transmit the respective modulated lights (e.g., on
ports 5321
and 5322, FIG. 5) through different respective optical fibers.
[360] In some embodiments of any of the above apparatus, at some times of said
time
interval (e.g., interval (A), FIGs. 7B-7D), the first optical modulator
receives from the first
output port the first optical frequency but not the second optical frequency;
and at some
other times of said time interval, the first optical modulator receives from
the first output
port the second optical frequency but not the first optical frequency.
[361] In some embodiments of any of the above apparatus, at yet some other
times of said
time interval, the first optical modulator receives from the first output port
a mix of the
.. first and second optical frequencies (e.g., intervals (B), (C), FIGs. 7B-
7D).
[362] In some embodiments of any of the above apparatus, the optical input
port is
optically connected to receive the optical input signal from a proximate end
of a section of
optical fiber (e.g., 543, FIG. 5), the optical fiber including at least one
section that is non-
polarization-maintaining.
[363] In some embodiments of any of the above apparatus, the state-of-
polarization
change is due to time-varying polarization rotation in said at least one
section.
[364] In some embodiments of any of the above apparatus, the time-varying
polarization
rotation is random.
[365] In some embodiments of any of the above apparatus, the optical
transmitter further
comprises an optical power supply (e.g., 290, FIG. 5) optically connected to
apply the
optical input signal through the optical fiber to the passive polarization
splitter.
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[366] In some embodiments of any of the above apparatus, the optical power
supply
comprises: a light source (e.g., 200, FIG. 2) and an electronic controller
(e.g., 230, FIG. 2)
connected to the light source to cause the light source to generate a first
light output having
the first optical frequency (e.g., 212, FIGs. 2 and 3) and a second light
output having the
second optical frequency (e.g., 222, FIGs. 2 and 3), each of the first and
second light
outputs being steady during said time interval; and a polarization combiner
(e.g., 240, FIG.
2) connected to receive the first and second light outputs of the light source
at different
respective input ports thereof, the polarization combiner being configured to
generate, at
an output port thereof, an optical output that is coupled into the optical
fiber to cause the
optical input port of the polarization splitter to receive the optical input
signal.
[367] In some embodiments of any of the above apparatus, the first optical
modulator is a
polarization-sensitive device designed to modulate optical signals having the
first fixed
polarization.
[368] In some embodiments of any of the above apparatus, the first optical
modulator is
unsuitable for modulating optical signals having the second fixed
polarization.
[369] In some embodiments of any of the above apparatus, the second optical
modulator
is a polarization-sensitive device designed to modulate optical signals having
the second
fixed polarization.
[370] In some embodiments of any of the above apparatus, the second optical
modulator
is unsuitable for modulating optical signals having the first fixed
polarization.
[371] While this disclosure includes references to illustrative embodiments,
this
specification is not intended to be construed in a limiting sense. Various
modifications of
the described embodiments, as well as other embodiments within the scope of
the
disclosure, which are apparent to persons skilled in the art to which the
disclosure pertains
are deemed to lie within the principle and scope of the disclosure, e.g., as
expressed in the
following claims.
[372] Some embodiments can be implemented as circuit-based processes,
including
possible implementation on a single integrated circuit.
[373] Unless explicitly stated otherwise, each numerical value and range
should be
interpreted as being approximate as if the word "about" or "approximately"
preceded the
value or range.
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[374] It will be further understood that various changes in the details,
materials, and
arrangements of the parts which have been described and illustrated in order
to explain the
nature of this disclosure can be made by those skilled in the art without
departing from the
scope of the disclosure, e.g., as expressed in the following claims.
[375] The use of figure numbers and/or figure reference labels in the claims
is intended to
identify one or more possible embodiments of the claimed subject matter in
order to
facilitate the interpretation of the claims. Such use is not to be construed
as necessarily
limiting the scope of those claims to the embodiments shown in the
corresponding figures.
[376] Although the elements in the following method claims, if any, are
recited in a
particular sequence with corresponding labeling, unless the claim recitations
otherwise
imply a particular sequence for implementing some or all of those elements,
those
elements are not necessarily intended to be limited to being implemented in
that particular
sequence.
[377] Reference herein to "one embodiment" or "an embodiment" means that a
particular
feature, structure, or characteristic described in connection with the
embodiment can be
included in at least one embodiment of the disclosure. The appearances of the
phrase "in
one embodiment" in various places in the specification are not necessarily all
referring to
the same embodiment, nor are separate or alternative embodiments necessarily
mutually
exclusive of other embodiments. The same applies to the term "implementation."
.. [378] Unless otherwise specified herein, the use of the ordinal adjectives
"first,"
"second," "third," etc., to refer to an object of a plurality of like objects
merely indicates
that different instances of such like objects are being referred to, and is
not intended to
imply that the like objects so referred-to have to be in a corresponding order
or sequence,
either temporally, spatially, in ranking, or in any other manner.
[379] Also for purposes of this description, the terms "couple," "coupling,"
"coupled,"
"connect," "connecting," or "connected" refer to any manner known in the art
or later
developed in which energy is allowed to be transferred between two or more
elements, and
the interposition of one or more additional elements is contemplated, although
not
required. Conversely, the terms "directly coupled," "directly connected,"
etc., imply the
absence of such additional elements.
[380] As used herein in reference to an element and a standard, the term
compatible
means that the element communicates with other elements in a manner wholly or
partially
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specified by the standard, and would be recognized by other elements as
sufficiently
capable of communicating with the other elements in the manner specified by
the standard.
The compatible element does not need to operate internally in a manner
specified by the
standard.
5 [381] The described embodiments are to be considered in all respects as
only illustrative
and not restrictive. In particular, the scope of the disclosure is indicated
by the appended
claims rather than by the description and figures herein. All changes that
come within the
meaning and range of equivalency of the claims are to be embraced within their
scope.
[382] The description and drawings merely illustrate the principles of the
disclosure. It
10 will thus be appreciated that those of ordinary skill in the art will be
able to devise various
arrangements that, although not explicitly described or shown herein, embody
the
principles of the disclosure and are included within its spirit and scope.
Furthermore, all
examples recited herein are principally intended expressly to be only for
pedagogical
purposes to aid the reader in understanding the principles of the disclosure
and the
15 concepts contributed by the inventor(s) to furthering the art, and are
to be construed as
being without limitation to such specifically recited examples and conditions.
Moreover,
all statements herein reciting principles, aspects, and embodiments of the
disclosure, as
well as specific examples thereof, are intended to encompass equivalents
thereof
[383] The functions of the various elements shown in the figures, including
any
20 functional blocks labeled or referred to as "processors" and/or
"controllers," can be
provided through the use of dedicated hardware as well as hardware capable of
executing
software in association with appropriate software. When provided by a
processor, the
functions can be provided by a single dedicated processor, by a single shared
processor, or
by a plurality of individual processors, some of which can be shared.
Moreover, explicit
25 use of the term "processor" or "controller" should not be construed to
refer exclusively to
hardware capable of executing software, and can implicitly include, without
limitation,
digital signal processor (DSP) hardware, network processor, application
specific integrated
circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM)
for
storing software, random access memory (RAM), and non-volatile storage. Other
30 hardware, conventional and/or custom, can also be included. Similarly,
any switches
shown in the figures are conceptual only. Their function can be carried out
through the
operation of program logic, through dedicated logic, through the interaction
of program
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control and dedicated logic, or even manually, the particular technique being
selectable by
the implementer as more specifically understood from the context.
[384] As used in this application, the term "circuitry" can refer to one or
more or all of
the following: (a) hardware-only circuit implementations (such as
implementations in only
.. analog and/or digital circuitry); (b) combinations of hardware circuits and
software, such
as (as applicable): (i) a combination of analog and/or digital hardware
circuit(s) with
software/firmware and (ii) any portions of hardware processor(s) with software
(including
digital signal processor(s)), software, and memory(ies) that work together to
cause an
apparatus, such as a mobile phone or server, to perform various functions);
and (c)
hardware circuit(s) and or processor(s), such as a microprocessor(s) or a
portion of a
microprocessor(s), that requires software (e.g., firmware) for operation, but
the software
may not be present when it is not needed for operation." This definition of
circuitry
applies to all uses of this term in this application, including in any claims.
As a further
example, as used in this application, the term circuitry also covers an
implementation of
merely a hardware circuit or processor (or multiple processors) or portion of
a hardware
circuit or processor and its (or their) accompanying software and/or firmware.
The term
circuitry also covers, for example and if applicable to the particular claim
element, a
baseband integrated circuit or processor integrated circuit for a mobile
device or a similar
integrated circuit in server, a cellular network device, or other computing or
network
.. device.
[385] It should be appreciated by those of ordinary skill in the art that any
block diagrams
herein represent conceptual views of illustrative circuitry embodying the
principles of the
disclosure.
