Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02363627 2001-11-20
Doc. No. 10-462 CA Patent
WAVELENGTH-DEPENDENT OPTICAL SIGNAL PROCESSING USING
AN ANGLE-TO-OFFSET MODULE
MICROFICHE APPENDIX
[0001] Not Applicable.
TECHNICAL FIELD
[0002] The present invention relates to optical signal processing devices, and
in particular to
wavelength-dependent optical signal processing devices incorporating an angle-
to-offset module.
BACKGROUND OF THE INVENTION
[0003] In the modern communications network space, the use of wavelength
division
multiplexed (WDM) and dense wavelength division multiplexed (DWDM) optical
signals are
becoming increasingly popular. As is well known in the art, wavelength
division multiplexing
involves the transmission of multiple light beams through a single waveguide
or optical fiber. Each
light beam (which is commonly referred to as a channel) generally has a narrow
range of wavelengths
centered on a nominal channel or center wavelength, and normally conveys a
respective stream of
data traffic.
[0004] At a minimum, practical implementation of wavelength division
multiplexing requires
optical components capable of optically multiplexing each channel into a
single waveguide, and then
optically demultiplexing each of the channels from that waveguide.
Conventionally, other
channel-specific signal processing, such as signal regeneration; Add-Drop
Multiplexing (ADM);
channel equalization; gain equalization; and channel switching, have been
performed electronically.
That is, each channel is converted into an electronic signal, processed using
conventional electronic
means, and then converted back into optical signals for transmission. At lower
data rates (e.g.,
approx. 2.5GHz), such electronic processing systems can be cost effective.
However, as data rates
increase (e.g., beyond about 10GHz), electronic signal processing systems
become increasingly
expensive, because of physical limitations inherent to electronic systems.
Thus optical signal
processing systems capable of performing complex channel-specific signal
processing functions
entirely in the optical domain are increasingly in demand.
[0005] Optical signal processing modules (e.g., Add-Drop Multiplexers (ADMs);
Dynamic
Channel Equalizers (DCEs); and switches) are known. These modules
conventionally require
complex opto-mechanical layouts (in which the involved optical components are
not located on a
common optical axis) in order to achieve the spatial separations needed to
perform the desired
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function. The physical size and complexity of these modules increases the
difficulty of maintaining
adequate precision during manufacture. This inevitably results in increased
costs.
[0006] Accordingly, an optical signal processing module, in which channel-
specific optical
signal processing can be accomplished using a simple component layout and
small physical size,
remains highly desirable.
SUMMARY OF THE INVENTION
[0007] Accordingly, an object of the present invention is to provide an
optical signal processing
module capable of channel-specific optical signal processing using a simple,
physically compact
component layout.
[0008] Accordingly, an aspect of the present invention provides an optical
device for
wavelength dependent processing of optical signals. The optical device
comprises a dispersion
element, a reflector, and an angle-to-offset (ATO) element. The angle-to-
offset (ATO) element has at
least one focal plane having a focal length approximately equal to a near zone
length or Rayleigh
range of the beam of light incident on the ATO element. The dispersion element
is adapted to separate
an input wavelength division multiplexed (WDM) light beam received from an
input port of the
optical device into two or more channel light beams. The reflector is arranged
to receive the channel
light beams from the dispersion element via the ATO element. The reflector is
designed to reflect at
least one of the channel light beams toward a respective output port of the
optical device. With this
arrangement, the dispersion element, reflector and ATO element cooperate to
demultiplex the input
WDM light beam optically. Additional optical elements arranged in the
propagation path between the
reflector and the output port(s) and/or between the input port and the
dispersion element can be used
to provide further optical signal processing functionality, as well, the
reflector can be modified to
change functionality.
[0009] The dispersion element may be provided as a diffraction grating
disposed in or near a
focal plane of the ATO element.
[0010] The ATO element may be either a curved mirror having a focal plane, or
a refractive
lens. In the case of a mirror, both the dispersion element and the reflector
are disposed in or near the
focal plane. In the case of a lens, the dispersion element and the deflector
are disposed in or near
respective opposite focal planes of the lens.
[0011] In some embodiments, the reflector comprises an array of two or more
reflective
elements disposed in or near a focal plane of the ATO element. Each reflective
element can be
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arranged in a propagation path of a respective channel light beam from the
dispersion element, via the
ATO element.
[0012] In some embodiments, each reflective element is fixed. The reflective
elements may be
oriented at a common angle, or at a respective unique angles with respect to
the dispersion plane of
the dispersion element. In other embodiments, each reflective element is
independently movable,
either under analog control or bi-stable. In either case, each reflective
element may be provided as
either a mirror or a total internal reflection (TIR) element. In some
embodiments, each TIR element
may be independently controllable to selectively frustrate (or otherwise
inhibit) reflection of light.
[0013] In some embodiments, an optical switch is provided for switching each
channel light
beam to a selected output waveguide. The optical switch preferably includes
first and second MEMS
arrays, each of which are disposed in or near a focal plane of the ATO
element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Further features and advantages of the present invention will become
apparent from the
following detailed description, taken in combination with the appended
drawings, in which:
[0015] Fig. 1 is a schematic illustration showing principle elements and
operation of a first
embodiment of the present invention implemented as a wavelength demultiplexer;
[0016] Fig. 2 is a schematic illustration showing principle elements and
operation of a second
embodiment of the present invention implemented as a wavelength demultiplexer;
[0017] FIG. 3a-c show principle elements and characteristics of alternative
reflectors usable in
embodiments of the present invention;
[0018] FIGs. 4a-4d are schematic illustrations showing principle elements and
operation of
respective alternative embodiments of the present invention implemented as a
dynamic channel
equalizer (DCE);
[0019] FIG. 5 is a schematic illustration showing principle elements and
operation of an
embodiment of the present invention implemented as a wavelength channel
blocker;
[0020] FIGs. 6a and 6b are schematic illustrations showing principle elements
and operation of
respective alternative embodiments of the present invention implemented as an
Add-Drop Multiplexer
(ADM); and
[0021] FIGs. 7a and 7b are schematic illustrations showing principle elements
and operation of
respective alternative embodiments of the present invention implemented as a
channel switch.
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[0022] It will be noted that throughout the appended drawings, like features
are identified by
like reference numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] The present invention provides a structurally simple and compact
optical signal processor
that can be readily adapted to perform multiple optical signal processing
functions. FIG. 1 illustrates
principle elements of an embodiment of the present invention implemented as a
wavelength
multiplexer/demultiplexer (Mux/Demux).
[0024] As shown in FIG.1, a wavelength Mux/Demux 2 in accordance with the
present
invention includes an optical core 4 defined by a dispersion element 6 and a
reflector 8 separated by
an optical element 10 having optical power. Both the dispersion element 6 and
the reflector 8 are
conveniently disposed in or near a focal plane of the optical element 10.
[0025] The dispersion element 6 can be provided as a conventional diffraction
grating, and is
arranged to receive a WDM light beam 12 from an input waveguide 14. In all
figures, the dispersion
element 6 is shown perpendicular to the optical axis for simplicity only. As
is well known in the art,
the position can be different. The dispersion element 6 operates to reflect
light of the WDM light
beam 12 through an angle that is a function of wavelength, in a manner well
known in the art. Thus
the dispersion element 6 causes a spatial (angular) separation of the channels
multiplexed within the
WDM light beam 12.
[0026] As may be seen in FIG. 1, the reflector 8 operates to reflect
diffracted channel light
beams 16 received from the dispersion element 6 toward one or more output
waveguides 18. As will
be described in greater detail below, the design of the reflector 8 can be
suitably selected in
accordance with the desired signal processing functionality. Additional
optical elements (e.g.,
dispersion elements, reflectors and MEMS arrays) can also be inserted into the
optical path between
the reflector 8 and the output waveguide(s) 18, as will also be described in
greater detail below.
[0027] The Optical element 10 having optical power may be either a curved
(focusing) mirror or
a refractive lens. In the illustrated embodiments, the optical element 10 is
shown as a refractive lens
for ease of illustration only. In embodiments in which the optical element 10
is a mirror, the optical
paths illustrated in the appended figures are "folded" about the plane of the
ATO element, but are
otherwise closely similar to those illustrated in the figures. The use of a
mirror as the optical element
10 may have an advantage over a lens, in that a mirror enables folding of
optical paths, and thereby
perrnits a more compact design.
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While not essential for the purposes of the present invention, the optical
element 10 is preferably a
"true" Angle-To-Offset (ATO) element whose focal length approximately
corresponds to the near
zone length (multi mode) or Rayleigh range (single mode) of the beam of light
incident on the ATO
element. The use of a true ATO element means that the size (i.e., the
diameter) of a light beam routed
through the optical core 4 is substantially the same at both input and output
optical bypass 24a, 24b
of the optical core 4. Assuming optically identical optics 26a and 26b, and
identical input micro-
collimators at A and I, the beam sizes will also be the same at the waveguides
14 and 18. This feature
is useful for optimizing coupling of the beam between input and output
waveguides 14 and 18.
However, it is not strictly necessary for optical signal processing in
accordance with the present
invention.
[0028] On the other hand, in all cases, the element 10 operates to redirect
any beam propagating
at a given angle at the front focal plane to a fixed offset at the back focal
plane and vice versa. This is
also a characteristic of a true ATO element. Accordingly, for the purposes of
the present invention,
the term "ATO" will be used in describing the element 10, even though true ATO
functionality is not
strictly required. As illustrated, lenses 26 and 10 serve as a telecentric
relay to image the input
waveguides to the dispersion element. As well lens 10 provides switching
functionality. It should be
noted that other optical systems could be used to image the input to the
dispersion element. This also
follows for the output imaging system.
[0029] In general, the input and output waveguides 14 and 18 are arranged in
respective fiber
bundles 20 arranged along a common optical axis 22 on opposite sides of the
optical core 4. Each
fiber bundle 20 includes an array of waveguides, each of which may terminate
in a microlens, or other
convenient lens that operates to guide a light beam into (and/or out of) the
associated waveguide.
[0030] Each fiber bundle 20 is associated with a respective optical bypass 24
(e.g., a hole or
optically transparent region) of the optical core 4, through which light beams
propagating to/from
each waveguide can enter/leave the optical core 4. The propagation paths of
light beams emerging
from each waveguide of a bundle 20 are made to converge within the optical
bypass 24. In the
embodiment of FIG. 1, this is accomplished by means of a relay lens 26
positioned between each fiber
bundle 20 and its associated optical bypass 24, and separated from the optical
bypass 24 by a distance
that approximately corresponds with the focal length of the relay lens 26.
This arrangement facilitates
a compact design of the optical core 4.
[0031] Operation of the embodiment of FIG. 1 to demultiplex a received WDM
light beam 12 is
shown by the solid and dashed lines of FIG. 1. For ease of illustration, the
multiple WDM light beam
12 is illustrated by a solid line, while demultiplexed channel light beams 16
are shown as dashed
lines. Similarly, for ease of illustration, the WDM light beam 12 is
considered to be composed of two
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channels. It will be appreciated, however, that more than two channels can be
readily accommodated
by the present invention. Thus, a WDM light beam 12 enters the demuxer 2
through a respective
input waveguide 14 (at A), is deflected by the relay lens 26a (at B), and
enters the optical core 4
through optical bypass 24a (at C). As the input WDM light beam 12 propagates
through the optical
core 4, it is deflected by the ATO element 10 (at D), and made incident upon
the dispersion element 6
(at E). As mentioned previously, the dispersion element 6 operates to reflect
light of the WDM light
beam 12 through an angle that is a function of wavelength, and thus causes
spatial separation of the
channels of the WDM light beam 12. Thus, each channel light beam 16 propagates
away from the
dispersion element 6 at a unique angle, and passes through the ATO element 10
(at F and F') which
deflects the channels toward the reflector 8. As may be seen in FIG. 1, the
ATO element 10 operates
to convert the angular separation of each channel light beam 16 into a lateral
offset at the focal planes,
so that all of the channel light beams 16 are parallel when they hit the
reflector 8 (at G and G').
[0032] In the embodiment of FIG. 1, the reflector 8 may be provided as a
simple fixed mirror
(having one or more fixed reflective surfaces) designed to reflect incident
channel light beams 16
through a common angle. Thus the channel light beams 16 are reflected by the
reflector 8 (at G and
G') and remain parallel until they pass through the ATO element 10 (at H and
H'), which deflects the
parallel channel light beams 16 to respective output waveguides 18 (at I and
I') via their associated
optical bypass 24b and output relay lens 26b.
[0033] Thus it will be seen that the embodiment of FIG. 1 will operate to
demultiplex an input
WDM light beam 12, and output the demultiplexed channel light beams 16 through
respective output
waveguides 18. As will be appreciated, reversing the propagation direction of
the light beams will
perform the reciprocal operation (that is, the demuxer becomes a muxer). Thus,
channel light beams
16 entering the optical core at I and I' will be multiplexed into a single WDM
light beam 12, which
leaves the muxer 2 through the "input" waveguide 14 at A.
[0034] In practice, the channel light beams 16 are not truly mono-chromatic.
Typically, each
channel light beam 16 has a range of wavelengths. Because the dispersion
element 6 causes
wavelength-dependent reflection of light, the channel light beams 16 will be
slightly dispersed by the
dispersion element 6. Because of this, coupling of light into the output
waveguides 18 will involve
wavelength dependent insertion losses. FIG. 2 illustrates a variation of the
embodiment of FIG. 1, in
which the dispersion of each channel light beam 16 is corrected, to yield so-
called "flat-top"
performance.
[0035] As described above, dispersion of each channel light beam 16 is caused
by
wavelength-dependent reflection of light by the dispersion element 6. Thus it
will be apparent that
this dispersion can be corrected by directing the parallel channel light beams
16 back through the
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ATO element 10 to the dispersion element 6, which recombines the channel light
beams 16. Thus in
the embodiment of FIG. 2, the reflector 8 is arranged to deflect the parallel
channel beams 16 (at G
and G') through the ATO element 10 (at J and J') to the dispersion element 6a
(at K).
[0036] In order to prevent multiplexing of the channel light beams 16 at K
(which would clearly
negate the demultiplexing operation of the device), the reflector 8 is
designed to cause a lateral offset
of each of the channel light beams 16 hitting the dispersion element 6a. As a
result, each of the
channel light beams 16 falls on the dispersion element 6a at K arrayed along
an x axis perpendicular
to the page (in FIG. 2) so that spatial separation of the channel light beams
16 is preserved. The plane
of the page is defined as y-z, y being the "vertical" orientation of the
drawing and z being the
"horizontal" orientation of the drawing. This can be accomplished using a
reflector 8 similar to that
illustrated in FIG. 3a. As may be seen in FIG. 3a, the reflector 8 is divided
into a plurality of facets
28 (nominally one facet for each channel light beam). All of the facets 28 are
fixed at a common
angle with respect to the dispersion plane of the dispersion element 6a, eg.
Ox (theta x) so that all of
the channel light beams 16 will be focused by the ATO element 10 onto the
dispersion element 6a at a
common height. The dispersion plane is defined as the plane perpendicular to a
grating surface and
perpendicular to the grating lines. However, each facet is also arranged at a
unique angle Oy (theta y)
(perpendicular to the plane of the page in FIG. 2), so that each channel light
beam 16 will be projected
out of the plane of the page of FIG. 2, and thus be targeted to a different
horizontal position of the
dispersion element 6a.
[0037] Following reflection of the channel light beams 16 from the dispersion
element 6a (at K)
the now horizontally separated light beams 16 pass through the ATO element 10
(at L), and are
imaged onto a horizontal array of output waveguides 18 (shown schematically at
M).
[0038] In the embodiment of FIG. 2, the dispersion element 6 is enlarged
(relative to that of
FIG. 1) in order to accommodate the second reflection of the channel light
beams 16 at K. However,
it will be appreciated that a separate diffraction grating element could
equally be used for this
purpose.
[0039] FIGs. 4a and 4b illustrate respective embodiments of the present
invention implemented
as dynamic channel equalizers (DCEs) 30. As is well known in the art, minimum
insertion loss is
obtained when a channel light beam 16 follows an ideal propagation path
between the reflector 8 and
a respective output waveguide 18. Small-scale "errors" in reflector position
cause lateral and/or
angular offsets in the propagation path of each light beam 16, with
corresponding increases in
insertion loss. In the embodiments of FIGs. 4a and 4b, this phenomenon is
exploited to obtain
dynamic channel equalization, by enabling channel-specific control of
insertion loss. Thus the
embodiments of FIGs. 4a and 4b are obtained by replacing the fixed reflectors
8 of FIGs. 1 and 2,
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respectively, with a Micro-Electromechanical (MEMs) array 32 of independently
controllable
micro-mirrors (not shown). Each micro-mirror is controlled in a known manner
to provide
small-scale analog adjustment of mirror position. This arrangement enables
higher-power channel
light beams (which may be detected in a conventional manner) to be
individually "walked off' their
respective output waveguides 18 (as illustrated by the fine line in FIGs. 4a
and 4b)either by angular
displacement in Fig. 4a, or lateral displacement in Fig. 4b, to increase their
insertion loss and thereby
equalize channel power of each channel of the WDM light beam 12 to that of the
weakest channel.
[0040] It will be appreciated that the DCEs 30 of FIGs. 4a and 4b are closely
similar to the
demuxers 2 of FIGs. 1 and 2, in that they provide non-flat top and flat top
performance, respectively.
[0041] FIG. 4c illustrates a multiplexed version of a flat top DCE 30, in
which the micro-
mirrors of the MEMS array 32 are positioned to reflect each channel light beam
back along its
incident propagation path toward the input waveguide 14. A conventional
optical circulator 38 is
coupled between the optical core 4 and the input and output waveguides 14,18.
The optical circulator
38 operates in a conventional manner to direct the inbound WDM light beam 12
from the input
waveguide 14 into the optical core 4, and direct the outbound WDM light beam
12 from the optical
core 4 into the output waveguide 18. As in the embodiments of FIGs. 4a and 4b,
dynamic channel
equalization is obtained by adjusting each micro-mirror of the MEMS array 32
to control the insertion
loss of their respective channel light beam into the circulator 38 and output
waveguide 18.
[0042] FIG. 4d illustrates a still further variation of the multiplexed flat
top DCE 30. This
embodiment is closely similar to that of FIG. 4c, except that a polarization
beam splitter/combiner is
inserted between the circulator 38 and the optical core 4. The polarization
beam splitter/combiner 39
operates to split the input WDM light beam 12 into a pair of orthogonally
polarized light beams which
are redirected to propagate in parallel (e.g. horizontally separated), with
one beam passed through a
polarization rotator, so that both beams pass through the optical core 4
having a same polarization
state. The dispersion element 6 diffracts each of the orthogonally polarized
light beams into respective
sets of channel light beams. Each channel light beam is then made incident on
a respective micro-
mirror of the MEMS array. Thus, for each channel, a pair of orthogonally
polarized channel light
beams are diffracted by the dispersion element 6, and are subsequently
received a respective pair of
micro-mirrors of the MEMS array 36. With this arrangement, the insertion loss
of each orthogonally
polarized channel light beam into the circulator 38 and output waveguide 18
can be independently
controlled. As a result, in addition to the channel-specific DCE functionality
of the embodiments of
FIGs. 4a-4c, the embodiment of FIG. 4d is also capable of actively
compensating Polarization
Dependent Loss (PDL), on a per-channel basis.
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[0043] As described above, dynamic channel equalization can be obtained by
small-scale analog
adjustment of MEMS mirror position to yield corresponding fine control of
insertion loss. Insertion
losses increase with increasing excursions in micro-mirror position, until the
insertion loss is
sufficient. At the maximum extinction, the DCEs 30 of FIGs. 4a and 4b will
operate as controllable
channel blockers.
[0044] As may be appreciated, in situations where only the channel-blocker
functionality is
required, the analog MEMS array 32 can be replaced by a less expensive array
of bi-stable micro-
mirrors. An alternative embodiment of the invention, implemented as a single-
purpose channel
blocker 34, is illustrated in FIG. 5.
[0045] In the embodiment of FIG. 5, the (analog or bi-stable) MEMS array
reflector 32 is
replaced by a controllable retro-reflector 36. As is known in the art, a retro-
reflector operates (by
either reflection or total internal reflection(TIR)) to reflect a light beam
back along its incident
propagation path. FIG. 3b is a cross-sectional view showing principle
components and operation of a
total internal reflection(TIR) retro-i-eflector 36. As shown in FIG. 3b, the
TIR retro-reflector 36
comprises a prism 56 (having a refractive index n2) bounded by a region 58 of
lower refractive index
n, (thus ni<nz). A fixed mirror 60 covers a portion of the prism 56, leaving a
window 62 for ingress
and egress of light. With this arrangement, a channel light beam 16 enters the
prism through the
window 62; is reflected at the n4n, interfaces 64 and hits the mirror 60. The
channel light beam 16
will then retrace the same route back out of the retro-reflector 36.
[0046] In the embodiment of FIG. 5, this functionality is used to reflect the
channel light beams
16 back toward the input waveguide 14. A conventional optical circulator 38 is
coupled between the
optical core 4 and the input and output waveguides 14,18. The optical
circulator 38 operates in a
conventional manner to direct the inbound WDM light beam 12 from the input
waveguide 14 into the
optical core 4, and direct the outbound WDM light beam 12 from the optical
core 4 into the output
waveguide 18. Channel blocking functionality is obtained by controlling the
retro-reflector 36 to
frustrate reflection of one or more channel light beams 16. Controllable retro-
reflectors 36 capable of
this type of operation are known, such as, for example "Fiberkey" (Tradename),
an optical switch
manufactured by Optical Switch Corp. An array of bi-stable micro-mirrors can
also be used, if
desired.
[0047] As is known in the art, total internal reflection of a light beam at an
interface 64 (FIG.
3b) between high and low regions of refractive index causes a relative phase
shift in orthogonal
polarizations of the light beam. As shown in FIG. 3c, the degree of phase
shift (referred to as
retardance) is generally a function of the difference in refractive index
across the interface. Thus the
retardance can be modulated by changing the refractive index of the media on
one (or both) sides of
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the interface. Various known methods of modulating refractive index may be
used for this purpose
(such as, for example, differential heating; electric fields; or bringing a
material close to, but not
touching, the interface). Modulating the retardance changes the state of
polarization of the channel
light beam, and may be used for such purposes as switching, control of
polarization mode dispersion
(PMD), etc.
[0048] FIGs. 6a and 6b illustrated principle elements of respective
embodiments of the present
invention deployed as Add Drop Multiplexers (ADMs) 40. As with the embodiments
of FIGs. 4a and
4b, the embodiments of FIGs. 6a and 6b are similar to the embodiments of FIGs.
1 and 2 in that they
provide non-flat top and flat top performance, respectively. In order to
implement an ADM 40, a first
optical circulator 38 is provided to couple an inbound WDM light beam 12
between an "input"
waveguide 14 and the optical core 4, and couple an out-bound WDM light beam 12
between the
switch core 4 and a "through" (or output) waveguide 18. On the opposite side
of the core 4, one or
more respective channel circulators 42 are used to couple a channel light beam
16 being dropped from
the WDM light beam into a respective "drop" waveguide 44; while simultaneously
coupling a new
channel light beam 16' being added to the WDM light beam 12 from a respective
"add" waveguide 46
and into the optical core 4.
[0049] As may be appreciated, light beams will thus be propagating bi-
directionally through the
optical core 4. An inbound multi-channel WDM light beam 12 is received through
the input and add
waveguides 14 and 46, while the outbound WDM light beam exits the device 40
via the through and
drop waveguides 18 and 44. Both the inbound and outbound WDM light beams may
well have the
same channel schedule (i.e., number of channels, and wavelength of each
channel). However, the add
and drop function enables optical signal traffic in each channel of the
outbound WDM light beam to
be arbitrarily different from that of the inbound WDM light beam.
[0050] FIGs. 7a and 7b illustrate principle elements of respective embodiments
of the present
invention deployed as a wavelength switch 48. As with the previously described
embodiments of
FIGs. 1, 4a and 6a, the embodiment of FIG. 7a includes a single reflection
from the dispersion
element 6, and so provides non-flat top performance. Conversely, the
embodiment of FIG. 7b uses a
second reflection from the dispersion element 6 (as per the embodiments of
FIGs. 2, 4b and 6b) to
correct dispersion of channel light beams 16, and so achieve flat-top
performance.
[0051] As may be appreciated, full wavelength switching functionality requires
the ability to
switch any channel light beam 16 from an input waveguide 14 to any one of M
output waveguides 18.
Preferably, this functionality can be provided, in parallel, for up to N input
waveguides 14, to yield
NxM switching. For ease of illustration, the path traced by a single channel
light beam 16 switched
through the wavelength switch 48 between respective input and output
waveguides 14,18 is shown. It
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will be understood, however, that each channel light beam 16 will follow its
own path through the
switch 48 between the input waveguide 14, and any one of a plurality of output
waveguides 18.
[0052] Referring now to FIG. 7a, the demultiplexing wavelength switch 48 is
composed of a
wavelength demultiplexer 50 (positioned below the optical axis 22 in FIG. 7a,
and closely similar to
that described above with reference to FIG. 1), in combination with an optical
switch 52 (positioned
above the optical axis 22 in FIG. 7a) composed of a pair of arrays 54 of
independently controllable
deflectors, such as MEMs mirrors disposed in or near opposite focal planes of
the ATO element 10.
[0053] Operation of the embodiment of FIG. 7a to switch each channel of a
received WDM light
beam 12 is shown by the solid and dashed lines of FIG. 7a. For ease of
illustration, the multiplexed
WDM light beam 12 is illustrated by a solid line, while demultiplexed channel
light beams 16 are
shown as dashed lines. Similarly, for ease of illustration, the WDM light beam
12 is considered to be
composed of two channels, only one of which is traced through the wavelength
switch 48 to a selected
output waveguide 18. It will be appreciated, however, that more than two
channels per WDM light
beam 12 can be readily accommodated by the present invention. Thus, the WDM
light beam 12
enters the wavelength switch 48 through a respective input waveguide 14 (at A)
and propagates
through the optical core 4 to the dispersion element 6 (at E). Each channel
light beam 16 propagates
away from the dispersion element 6 at a unique angle, and passes through the
ATO element 10 (at F
and F') which deflects the channel light beams toward the reflector 8.
[0054] As in the embodiment of FIG. 2, the reflector 8 may be provided as a
simple fixed mirror
(having one or more fixed reflective surfaces) designed to reflect incident
channel light beams 16
through a common angle in (0y) out of the dispersion plane of the dispersion
element 6, and at unique
angles for each wavelength in the dispersion plane (Ox) in order to maintain
the wavelength
separation. Thus a channel light beam 16 is reflected by the reflector (at G
and G') and passes
through the ATO element 10 (at H), which images one channel light beam 16 onto
a predetermined
mirror M1 (at I) within a first MEMS array 54a. Since all of the optical
elements between the input
waveguide 14 and mirror Ml are fixed, mirror M1 will be associated with one
channel of the input
waveguide 14, and receives only that one channel light beam 16. However,
mirror M1 is also
independently movable to deflect the channel light beam 16 to any one of the
mirrors of the second
MEMS array 54b on the opposite side of the ATO element 10. Each mirror of this
second MEMS
array 54b is associated with one respective output waveguide 18, and is
independently movable to
deflect a light beam received from any mirror of the first MEMS array 54a into
that output waveguide
18. Thus in the embodiment of FIG. 7a, the channel light beam 16 can be
switched into any output
waveguide 18 by controlling mirror Ml to deflect the channel light beam 16
through the ATO
element 10 (at J) to the associated mirror (M2 at K) associated with the
selected output waveguide 18.
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Mirror M2 is then controlled to deflect the channel light beam 16 to the
output waveguide 18 (at L)
via the ATO element 10, output optical bypass 24b and output relay lens 26b.
[0055] As mentioned previously, each channel light beam 16 is made incident on
a unique single
mirror M1 of the first MEMS array 54a. Thus it will be apparent that multiple
input waveguides 14,
and multiple channels per WDM light beam 12 can readily be accommodated by
providing the first
and second MEMS array 54a,54b with a total number of mirrors that at least
equals the total number
of input channels (that is, the number of input waveguides 14 multiplied by
the number of channels
per waveguide). Each channel light beam 16 can then be switched to a selected
mirror within the
second MEMS array 54b, which then deflects the channel light beam 16 to its
respective output
waveguide 18.
[0056] The embodiment of FIG. 7b is similar to that of FIG. 7a, with the
exception that the
propagation path of each channel light beam 16 includes a second reflection
from the dispersion
element 6 to achieve flat-top performance and to remultiplex the outputs. Thus
mirror M2 deflects the
channel light beam 16 to a third mirror (M3 at M) within the first MEMS array
54a. Mirror M3 then
deflects the channel light beam 16 back through the ATO element 10 to the
reflector 8 (at G), which
then reflects the channel light beam 16 to the dispersion element 6(at N). The
channel light beam 16
is reflected by the dispersion element 6, and then passes through the ATO
element 10, optical bypass
24a, and relay lens 26b before reaching the selected output waveguide 18.
[0057] In this embodiment, the first MEMS array 54a must include at least two
mirrors (M1 and
M3) for each channel. In this case, mirror M1 is associated with one input
waveguide 14 (as
described above), while mirror M3 is associated with one output waveguide 18.
Mirror M2 is
associated with mirror MI, and is used to switch the channel light beam
received from M1 to M3 in
order to select the desired output waveguide 18.
[0058] As may be seen in FIG. 7b, between mirror M3 and the output waveguide
18, each
channel light beam follows a "reverse" path through the demultiplexer section
50 of the wavelength
switch 48'. As mentioned previously, such a reverse path yields a multiplexing
function, so that
multiple channel light beams 16 can be multiplexed into the output waveguide
18. This contrasts with
the embodiment of FIG. 7a, in which each channel light beam 16 exits the
wavelength switch 48 via a
respective output waveguide 18.
[0059] Thus it will be seen that the present invention provides a simple,
compact and efficient
design for implementing a variety of optical signal processing devices. All of
these devices are built
upon a "base" of an optical demultiplexer provided by a dispersion element and
a reflector disposed in
or near opposite focal planes of an optical element having optical power.
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[0060] The embodiment(s) of the invention described above is(are) intended to
be exemplary
= only. The scope of the invention is therefore intended to be limited solely
by the scope of the
appended claims.
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