Note: Descriptions are shown in the official language in which they were submitted.
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Specification
OPTICAL WAVEFORM SHAPING DEVICE
Technical Field
[00011
The present invention relates to an optical waveform shaping device
and so on.
Background Art
[0002]
The waveform of an optical signal transmitted in an optical
transmission system degrades by ASE noise, non-linear characteristics of an
optical fiber, etc., resulting in degradation of transmission quality. In such
a
case, the degraded waveform of the optical signal is recovered by an optical
waveform shaping device for shaping the waveform an optical signal.
Furthermore, an optical waveform shaping device is used in an observation
device using a femtosecond laser etc., for example, as it is important to
shape a
laser waveform.
[0003]
For example, JP-A 2001-42274 discloses an optical waveform
shaping device with a spatial light modulator for phase modulation and a
spatial phase modulator for intensity modulation. However, the optical
waveform shaping device disclosed in the publication uses two modulators
each having a glass substrate, which inevitably leads to the expansion of the
diameter of a beam. Thus, there is a problem of low resolution.
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Patent document 1: JP-A 2003-90926
Patent document 2: JP-A 2002-1317 10
Brief Description of the Drawings
Fig. 1 is a conceptual diagram showing a configuration example of an
optical waveform shaping device of the present invention.
Fig. 2 is a conceptual diagram of a spatial optical modulator having a
phase modulation part and an intensity modulation part.
Fig. 3 is a conceptual diagram showing the orientation of an intensity
modulation part and a phase modulation part.
Figs. 4 are conceptual diagrams for explaining polarization control,
intensity control, and phase control.
Fig. 5 is a diagram showing an example of an optical waveform
shaping device which uses a prism as a folded reflector.
Figs. 6 are figures showing a beam incident on cells. Fig. 6(a) shows
a light beam on the short wavelength side incident on cells, while Fig. 6(b)
shows a light beam on the long wavelength side incident on cells.
Figs. 7 are figures showing an optical waveform shaping device of
the present invention capable of phase shift compensation. Fig. 7(a) shows an
example using an existing driver, while Fig. 7(b) shows an example
performing DIO direct control.
Fig. 8 is a comprehensive diagram of the optical waveform shaping
device according to Embodiment 1.
Figs. 9 are schematic diagrams of the optical system according to
Embodiment 1. Fig. 9(a) is a top view, while Fig. 9(b) is a side view.
Fig. 10 is a schematic diagram of a simulation determining the
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position of an optical element.
Figs. 11 are figures showing an example of a liquid crystal spatial
light modulator. Fig. 11(a) through Fig. 11(c) are figures showing an overview
of the actually manufactured spatial light modulator.
Figs. 12 are graphs replaced with drawings showing the optical
intensity control characteristic of an optical waveform shaping device. Fig.
12(a) shows a graph of measurement of the optical intensity control
characteristic when an ASE light source is used and all the channels are
controlled collectively. Fig. 12(b) shows a graph of measurement of the
optical
intensity control characteristic when all the channels are intermediately
controlled. Fig. 12(c) shows a graph of measurement of the optical intensity
control characteristic when all the channels are OFF controlled
Figs. 13 are graphs replaced with drawings showing frequency
spacing of an optical waveform shaping device. The wavelength of a
wavelength variable LD light source was swept at a 0.01nm step, and the
power of each wavelength with optical intensity controlled was measured with
a power meter. The optical intensity control was set for every 1CH, and the
frequency spacing was checked. Fig. 13(a) shows a frequency spacing in case
of one ON, Fig 13(b) shows a frequency spacing in case of two adjacent ON,
Fig. 13(c) shows a frequency spacing in case of three ON, and Fig. 13(d)
shows a frequency spacing in case of two separate ON.
Fig. 14 shows a graph replaced with a drawing showing the spatial
resolution of an optical waveform shaping device.
Fig. 15 is a schematic diagram showing the device configuration for
measuring an insertion loss.
Fig. 16 is an example of the grating part using a prism.
Fig. 17 is a conceptual diagram showing an example of a prism.
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Fig. 18 is a figure showing the relation between the lattice cycle of a
VPH grating part and the incidence angle of a grating.
Fig. 19 is a figure showing a modified prism.
Disclosure of the Invention
Problems to be Solved by the Invention
[0004]
It is an object of the present invention to provide an optical waveform
shaping device of high resolution.
[0005]
It is an object of the present invention to provide an optical waveform
shaping device of high resolution which is capable of phase shift compensation
associated with optical intensity modulation.
[0006]
It is an object of the present invention to provide an optical waveform
shaping device with a passband generally rectangular in shape. It is an object
of the present invention to provide an optical waveform shaping device which
is capable of ultrafast optical clock generation of the terahertz order.
[0007]
It is an object of the present invention to provide a band variable
optical waveform shaping device which is capable of miniaturization.
Means for Solving Problems
[0008]
The present invention is basically based on knowledge that the use of
a spatial light modulator having a phase modulation part and an intensity
modulation part can provide an optical waveform shaping device of high
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resolution, resulting in a new applied technology including ultrafast optical
clock generation of the terahertz order. That is, the present specification
discloses the following embodiment of the invention:
An optical waveform shaping device (10) comprising:
a branching filter (1) for branching the light beam from a light source
into light beams of each frequency;
a condensing part (2) for condensing a plurality of light beams
branched by the branching filter (1);
a polarizing plate (3) for adjusting the polarization planes of the light
beams having passed through the condensing part (2); and
a spatial light modulator (4) having a phase modulation part and an intensity
modulation part where the light beams having passed through the polarizing
plate (3) are incident.
[0009]
According to another embodiment, the branching filter (1) comprises
a high-dispersion element.
[0010]
According to a further embodiment,,
the spatial light modulator (4) comprises:
an intensity modulation part (22) having a plurality of liquid crystal
cells (21) formed in a line or in a matrix; and
a phase modulation part (24) having a plurality of liquid crystal cells
(23) corresponding to the liquid crystal cells (21) of the intensity
modulation
part,
and wherein the orientation of liquid crystals of the intensity
modulation part is 45 degrees offset from the orientation of liquid crystals
of
the phase modulation part.
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[0011]
According to still another embodiment,
the spatial light modulator (4) comprises:
an intensity modulation part (22) having a plurality of liquid crystal
cells (21) formed in a line or in a matrix; and
a phase modulation part (24) having a plurality of liquid crystal cells
(23) corresponding to the liquid crystal cells (21) of the intensity
modulation
part,
wherein each of the liquid crystal (21) of the intensity modulation
part (22) and the liquid crystal (23) of the phase modulation part (24)
comprises liquid crystal substances and electrodes which exist holding the
liquid crystal substances therebetween,
and wherein the optical waveform shaping device comprises:
a detection part (31) for detecting output light from the optical
waveform shaping device (21) when the intensity modulation by the intensity
modulation part (22) is performed;
a control device (32) for receiving information on the optical phase
shifting of each frequency detected by the detection part (31) and controlling
the voltage applied to the electrodes of each liquid crystal cell (23) of the
phase modulation part (24);
a voltage adjustment part (33) for each liquid crystal cell of the phase
modulation part (24) which outputs the voltage applied to the electrodes of
each liquid crystal cell (23) of the phase modulator (24) in accordance with
the
control instructions from the control device (32).
[0012]
According to other embodiments, the optical waveform shaping
device (10) further comprises a reflective part (5) where the light beams
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having passed through the spatial light modulator (4) are incident.
[0013] According to some embodiment, the optical waveform shaping device
(10) further comprises a second condensing lens (11) where the light beams
having passed through the spatial light modulator (4), and an optical
multiplexer (12) where the light beams having passed through the second
condensing lens (11) are incident to multiplex the light beams separated into
a
plurality of frequencies.
[0014] An optical waveform shaping device (10) according to still a further
embodiment comprises:
a grating (1) for branching the light beam from a light source into
light beams of each frequency;
a condensing lens (2) for condensing the plurality of light beams
branched by the grating (1);
a polarizing plate(3) for adjusting the polarization planes of the light
beams having passed through the condensing lens (2);
a spatial light modulator (4) having a phase modulation part and an
intensity modulation part where the light beams having passed through the
polarizing plate (3) are incident, wherein the orientation of liquid crystals
of
the phase modulation part is parallel to the polarization planes adjusted by
the
polarizing plate (3), the phase modulation part and the intensity modulation
part each having a plurality of liquid crystal cells in a line or in a matrix
existing in corresponding spatial positions, and the orientation of liquid
crystals of the intensity modulation part is 45 degrees offset from the
orientation of the liquid crystal of the phase modulation part; and
a folded reflector where the light beams having passed through the
spatial light modulator (4) are incident,
wherein the light beam from a light source is frequency separated and
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is dispersed spatially by the grating (1),
wherein the frequency separated and spatially dispersed light beams
are condensed by the condensing lens (2),
wherein the polarization planes of the condensed light beams are
adjusted by the polarizing plate (3),
and wherein the light beams with the polarization planes adjusted
separately are subjected to separately controlled phase modulation and
intensity modulation by the spatial light modulator (4), the light beams
folded
by the folded reflector (5), condensed through the condensing lens (2), and
the frequency separated light beams multiplexed by the grating (1).
Effect of the Invention
[0015]
The optical waveform shaping device of the present invention uses
one spatial light modulator (4) having a phase modulation part and an
intensity
modulation part, and the phase modulation part and the intensity modulation
part have a glass substrate in common, which prevents the expansion of the
diameter of a beam, thereby providing high resolution.
[0016]
The optical waveform shaping device of the present invention further
feedbacks the phase shift associated with optical intensity modulation to the
control voltage of liquid crystals, or adjusts the orientation of a polarizer
and
the liquid crystals in the phase modulation part of the spatial light
modulator
to compensate the phase shift associated with intensity modulation, which
compensates the phase shift associated with the optical intensity modulation.
[0017]
The optical waveform shaping device of the present invention can
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provide an optical waveform shaping device with a passband generally
rectangular in shape as was confirmed in an actual device.
[0018]
The optical waveform shaping device of the present invention can be
used as a band variable optical waveform shaping device as the passbands of
adjacent bands form continuous passbands.
[0019]
The optical waveform shaping device of the present invention can be
miniaturized precisely as optical elements can be omitted and the influences
such as dispersion can be compensated in case it is a reflection type.
Best Mode for Carrying Out the Invention
[0020]
Fig. 1 is a conceptual diagram showing an example of a configuration
of an optical waveform shaping device of the present invention. As shown in
Fig. 1, the optical waveform shaping device of the present invention comprises
a branching filter (1) such as a grating, a condensing lens (2), a polarizing
plate (3), a spatial light modulator (4) having a phase modulation part and an
intensity modulation part, and a folded reflector (5). In Fig. 1, numeral 6
indicates a collimating lens.
[0021]
The branching filter (1) is an element for branching the light from a
light source into light beams of each frequency. As a branching filter, a
grating,
a prism, or a high-dispersion element such as a grism may be used.
Alternatively, an AWG may be used. As a light source, white light or light
containing a plurality of wavelengths of light, for example, may be used.
Alternatively, pulsed light with a wavelength of approximately 1550nm may be
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used. As for the light beam from a light source, the polarizing plane may be
adjusted with a polarization adjuster, a polarizing plate, etc. Furthermore,
the
light beam from a light source may be polarized and separated into two kinds
of light beams having mutually-perpendicular polarization planes, for example.
[0022]
The condensing lens (2) serves as a condensing part for condensing a
plurality of light beams condensed by the branching filter (1). A well-known
condensing lens can preferably be used as a condensing lens. The condensing
lens (2) may be provided in the spatial position where the light beams
spatially
dispersed by the grating (1) can be condensed and can be guided to a
predetermined cells of the spatial light modulator (4).
[0023]
A polarizing plate (3) is an optical element for adjusting the
polarization plane of incident light having passed through the condensing lens
(2). As a polarizing plate, a well-known polarizing plate or a polarizer can
preferably be used. An interference film type polarizer is more preferable as
the polarizing plate. The use of such an interference film type polarizer
indicates the use of a polarizer with a large diameter, which leads to
improvement of convenience.
[0024]
The spatial light modulator (4) where the light beams having passed
through the polarizing plate (3) is incident has a phase modulation part and
an
intensity modulation part each having a plurality of liquid crystal cells in a
line or in a matrix existing in the corresponding spatial positions. For
example,
in the above Patent document 1, a spatial phase modulation part and a spatial
intensity modulation part are separated from each other. On the other hand, in
the present invention, a phase modulation part and an intensity modulation
part
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are joined together and are arranged on a glass substrate. This can reduce the
number of glass substrates used in a spatial light modulator to one, which can
prevent the expansion of the diameter of a beam, thereby providing high
resolution. In order to control unnecessary reflection, the phase modulation
part and the intensity modulation part are preferably joined together so that
each refractive index is matched. A plurality of liquid crystal cells in a
line
means a plurality of liquid crystal cells arranged in a straight line, while a
plurality of liquid crystal cells in a matrix means a plurality of liquid
crystal
cells arranged in good order vertically and horizontally. The plurality of
liquid
crystal cells arranged in a straight line is more preferable. And the
orientation
of liquid crystals of the phase modulation part is parallel to the
polarization
plane adjusted with the polarizing plate (3), for example, while the
orientation
of liquid crystals of the intensity modulation part is offset from the
orientation
of liquid crystals of the phase modulation part. A specific offset in the
orientation of the intensity modulation part is preferably in the range of 30
degrees-60 degrees, more preferably 40 degrees-50 degrees, most preferably
45 degrees. The liquid crystal spatial phase modulation part may exist in the
front (polarizing plate side) of the liquid crystal spatial intensity
modulation
part, or the liquid crystal spatial intensity modulation part may exist in the
front.
[0025]
Fig. 2 is a conceptual diagram of a spatial light modulator having a
phase modulation part and an intensity modulation part. As shown in Fig. 2, a
spatial light modulator (4) comprises an intensity modulation part (22) having
a plurality of liquid crystal cells (21) formed in a line or in a matrix, and
a
phase modulation part (24) having a plurality of liquid crystal cells (23)
corresponding to the liquid crystal cells (21) of the intensity modulation
part.
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The liquid crystal cells (21) of the intensity modulation part (22) and the
liquid
crystal cells (23) of the phase modulation part (24) each comprise liquid
crystal substances as well as electrodes holding the liquid crystal substances
therebetween. This electrode may be a transparent electrode or a metal
electrode existing anywhere in the circumference of the cells. An example of a
specific configuration is such that two liquid crystal elements with a lattice
pitch of 10 m-40 m are joined together and are mounted on a glass substrate.
The lattice pitch is a factor determining the width of each cell. As shown in
Fig. 2, a gap may be provided between the adjacent liquid crystal cells (21,
23).
[0026]
Fig. 3 is a conceptual diagram showing the orientation of an intensity
modulation part and a phase modulation part. As shown in Fig. 3, the
orientation of the intensity modulation part is 45 degrees offset from that of
the phase modulation part, for example. In order for phase modulation and
intensity modulation to be performed with these liquid crystal elements, the
polarization plane by the polarizing plate may be parallel to the orientation
of
liquid crystals of the phase modulation part, and the orientation of liquid
crystals of the intensity modulation part may be 45 degrees offset from the
polarization plane by the polarizing plate. The offset angle in the intensity
modulation part may be any value except 0 degree. However, 45 degrees is
preferable from a viewpoint of controlling intensity easily.
[0027]
Figs. 4 are conceptual diagrams for explaining polarization control,
intensity control, and phase control. Fig. 4(a) is a diagram showing the
intensity modulation and the phase modulation of the present invention. Fig.
4(b) is a diagram showing the optical phase shift when only the intensity
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modulation is performed. As shown in Fig. 4(b), when only the intensity
modulation is performed, intensity is adjusted with an intensity modulator,
and
linear polarization is changed to circular polarization. Then, circular
polarization is changed back to linear polarization with a polarizer. The
intensity modulation is performed in this way. However, as shown in Fig. 4(b),
though the optical phase is back to liner polarization, the phase state is
changed. On the other hand, as shown in Fig. 4(a), in a system having both
intensity modulation and phase modulation, the phase modulation compensates
the phase shift by the intensity modulation, which allows the phase of output
light to be matched with the phase of input light.
[0028]
A smaller condensing diameter of the liquid crystal cells on the
condensing lens side is more preferable as it reduces the width of the
obtained
bandpass. From this viewpoint, the condensing diameter may be in the range of
20 m-80 m, preferably 30 m-70 m. And the size of the liquid crystal cells
may be 10 m-40 m, preferably 15 m-30 m, or it may be 15 m-25 m. The use
of such microscopic cells enables the passbands of a 10GHz interval.
Furthermore, as a wavelength becomes larger, the condensing diameter
becomes larger, and thus one light beam on the short wavelength side may be
received by two liquid crystal cells while one light beam on the long
wavelength side may be received by three liquid crystal cells. The condensing
diameter refers to the diameter of the light beam derived from the image
formed on the liquid crystal cells by a plurality of light beams condensed by
the condensing lens.
[0029]
A folded reflector (5) is an optical element where the light beams
having passed through a spatial light modulator (4) having a phase modulation
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part and an intensity modulation part are incident and shift the traveling
direction. A well-known optical element such as a mirror and a prism can
preferably be used as the folded reflector. This adoption of reflection type
enables the overlapped use of optical elements and also enables compensating
for the influences of dispersion etc., resulting in precise miniaturization of
an
optical waveform shaping device.
[0030]
Fig. 5 is a diagram showing an example of an optical waveform
shaping device which uses a prism as a folded reflector. As shown in Fig. 5,
the use of a prism (26) can ensure vertical or horizontal optical paths. As a
result, two kinds of light beams can follow symmetrical optical paths, thereby
equalizing the influences such as a noise derived from the optical paths.
[0031]
Lightwaves are dispersed spatially for each frequency by a grating (1).
The spatially-dispersed lightwaves are condensed with a condensing lens (2),
and are incident on a spatial light modulator (4) through a polarizing plate
(3),
where the lightwaves are subjected to separately-controlled phase modulation
and intensity modulation. At the spatial light modulator (4), the lightwaves
are
incident on different cells for each dispersed frequency. Figs. 6 are figures
showing a beam incident on cells. Fig. 6(a) shows a light beam on the short
wavelength side incident on cells, while Fig. 6(b) shows a light beam on the
long wavelength side incident on cells. The cell size is, for example, a 20 m
interval, and the light beam on the short wavelength side may be incident on
two cells, while the light beam on the long wavelength side may be incident on
three cells. Thus, the light beams in real time can be resolved into
frequencies
and can be expanded in real space. Furthermore, the number of cells to a
certain beam can be adjusted according to the wavelength dispersion
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characteristic of a grating. Light beams are folded by a folded reflector (5).
The folded light beams are condensed with the condensing lens (2), and the
spatially-dispersed light beams are multiplexed by a grating (1). Thus, each
spatially-dispersed light beam is multiplexed with its phase and intensity
adjusted.
[0032]
The invention has been explained in the above with reference to a
reflection type optical waveform shaping device. However, the optical
waveform shaping device of the present invention may be a transmission type.
Specifically, a transmission type optical waveform shaping device may
comprise a grating, a first condensing lens, a polarizing plate, a spatial
light
modulator having a phase modulation part and an intensity modulation part, a
second condensing lens, and an optical multiplexer. The same lens as the first
condensing lens may be used as the second condensing lens. The same thing as
the grating may be used as the optical multiplexer.
[0033]
Figs. 7 are figures showing an optical waveform shaping device of
the present invention capable of phase shift compensation. Fig. 7(a) shows an
example using an existing driver, while Fig. 7(b) shows an example
performing DIO direct control. In Fig. 7(a), a control device such as a PC is
connected with a voltage control part (32), and the voltage control part has a
SLM driver 1 and a SLM driver 2 which control the driving voltage applied to
a spatial phase modulation part and a spatial intensity modulation part. On
the
other hand, in the case of DIO direct control as shown in Fig. 7(b), the
driving
voltage applied to the spatial phase modulation part and the spatial intensity
modulation part is directly controlled in accordance with the instructions
from
the control device. As shown in Fig. 7, this optical waveform shaping device
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comprises a spatial light modulator (4), a detection part (31), a control
device
(32), and a voltage adjustment part (33). And the control device outputs
control signals for instructing the voltage adjustment part based on the phase
shift detected by the detection part. On the other hand, the voltage
adjustment
part outputs predetermined voltage to the electrode of each cell according to
the received controlled signals. Thus, according to the optical waveform
shaping device of the present invention, the phase shift accompanied with
intensity modulation can be compensated.
[0034]
The detection part (31) is an element for detecting output light from
the optical waveform shaping device when intensity modulation is performed
by an intensity modulation part (22). As the detection part, a well-known
detection device such as a photodiode can arbitrarily be employed. The
detection part (31) is preferably provided within the chassis of the optical
waveform shaping device. Furthermore, the detection part preferably monitors
the controlled variable relating to both optical intensity and optical phase.
[0035]
The control device (32) is a device for receiving information relating
to the phase shift of each frequency detected by the detection part (31) and
controlling the voltage applied to the electrode of each liquid crystal cell
(23)
of the phase modulation part (24). Specifically, a computer serves as the
control device. The control device may be provided as a unit with the optical
waveform shaping device or may be provided externally. In terms of
downsizing the device, the control device is preferably provided within the
chassis of the optical waveform shaping device. When the detection part
monitors the controlled variable relating to both optical intensity and
optical
phase, such control is preferably performed by a closed loop so that optical
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intensity and optical phase come closer to a set value following a comparison
of measured optical intensity and optical phase with the set value. This
control
of optical intensity and optical phase can increase the stability of the
device.
[0036]
The voltage adjustment part (33) outputs the voltage applied to the
electrodes of each liquid crystal cell (23) of the phase modulation part (24)
to
each liquid crystal cell of the phase modulator (24) in accordance with the
control instructions from the control device (32). Furthermore, instead of
feedback control, the orientation direction of a polarizer and the phase
modulation part (24) may be adjusted so that phase modulation can be
performed to compensate the phase shift by intensity modulation. That is, it
is
a preferable mode of the present invention to use the orientation direction of
liquid crystals of a polarizing plane of the polarizer and the phase
modulation
part (24) so that phase modulation can be performed to compensate the phase
shift by intensity modulation. The intensity modulation part may have a
similar
configuration so that the intensity variation accompanied with phase
modulation.
[0037]
The optical waveform shaping device of the present invention can be
used as a light source for WDM etc. Furthermore, the optical waveform
shaping device of the present invention can be used as an optical transmission
device for EDFA etc.
[0038]
As mentioned above, the optical waveform shaping device of the
present invention basically employs the configuration comprising a grating
part such as an optical multiplexer for multiplexing light beams and a spatial
light modulator for controlling the light beams multiplexed in the grating
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for every microscopic wavelength zone. In addition to a grating and a prism as
mentioned above, a grism can be used in the grating part. Fig. 16 is an
example
of the grating part using a grism. In this case, the grism is a dispersive
element
consisting of a combination of a prism and a grating. In the figure, the grism
is
shown as a "volume phase holographic grating" (VPHG). Light beams from a
fiber are collimated by a first collimating lens and are incident on the
grism.
The light beams incident on the grism are dispersed according to the
wavelengths. The dispersed light beams are collimated with a second
collimating lens and are output to a fiber through an amplitude shutter and a
condensing lens. The grism itself is well-known. Examples of a grism are
described in JP-B 3576538, JP-A 2004-130806, etc.
[0039]
Fig. 17 is a conceptual diagram showing an example of a grism. As
shown in Fig. 17, one example of a grism comprises a VPH grating part with a
refractive index of n2, glass substrates with a refractive index of no at both
sides of the VPH grating part, and a first prism and a second prism with a
refractive index of nI provided outside the two glass substrates.
[0040]
Fig. 18 is a figure showing the relation between the lattice cycle of
the VPH grating part and the incidence angle of the grating.
[00411
Fig. 19 is a figure showing a modified grism. That is, a grism having
three prisms and two volume phase holographic gratings provided in the
connecting positions of the three prisms may be used.
Embodiment 1
[0042]
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Fig. 8 is a comprehensive diagram of the optical waveform shaping
device according to Embodiment 1. Figs. 9 are schematic diagrams of the
optical system according to Embodiment 1. Fig. 9(a) is a top view, while Fig.
9(b) is a side view. In the figures, PBS indicates a polarizing beam splitter,
FR
indicates a Faraday rotator, SMF indicates a single mode fiber, and 2-PMF
indicates a 2-axis polarization-preserving fiber. As shown in Figs. 9, this
optical system comprises a 2-axis polarization-preserving fiber (2-PMF), a
collimating lens with a diameter of 15cm and a focal length of 6cm, a grating
having a surface center position at 6cm from the collimating lens, a
condensing lens (fl5cm) positioned at 15cm from the surface center position
of the grating, a polarizing plate, a liquid crystal spatial intensity
adjustment
part, a liquid crystal spatial phase modulation part, and a folded reflector.
The
position of the folded reflector (prism) was set at 15cm from the condensing
lens. The width of the control part of each liquid cell was set 17 m, and the
size of the gap part was set 3 m. That is, one cell size was 20 m. The
distance
between the collimating lens and the grating and the distance between the
collimating lens and the condensing lens were calculated by doing simulation
as shown in Fig. 10.
[0043]
Phases fluctuate sensitively to the changes such as tension or
temperature of a fiber. As this embodiment employs the above configuration,
when the two optical paths of fibers are replaced with each other, the outward
path and the return path will receive the same phase shift in total. As a
result,
though fibers etc. lack phase stability, an optical waveform shaping device
with high phase stability can be provided.
[0044]
Figs. 11 are figures showing an example of a liquid crystal spatial
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light modulator. Fig. 11(a) through Fig. 11(c) are figures showing an overview
of the actually manufactured spatial light modulator. The spatial optical
modulator shown in Fig. 11(a) used a glass substrate with a width of 65mm x
48mm and a thickness of 0.5mm. The size of a liquid crystal cell gap located
between glass substrates having a common electrode and a pattern electrode
respectively was set 8 m. The width of a liquid crystal lattice was 14 x 14mm,
and it was installed near the center of the glass substrates. The pitch of the
liquid crystal lattice was 20 m (specifically, the control area was 17 m and
the gap was 3 m). As for the orientation of liquid crystals, the orientation
direction was set 45 degrees in case of intensity control, and it was set 0
degree in case of phase control. The liquid crystal spatial light modulator
for
intensity control and the liquid crystal spatial light modulator for phase
control
were prepared separately.
[0045]
In Fig. 11(b), the glass substrate with a width of 65 x up to 30mm and
a thickness of 0.3mm was used. The size of a liquid crystal cell gap located
between glass substrates having a common electrode and a pattern electrode
respectively was set 8 m. The liquid crystal lattice with a size of 10mm x up
to 5mm was used. In Fig. 11(b), the liquid crystal spatial light modulator was
put to either the left or the right of the glass substrate. This intentional
arrangement of the liquid crystal light modulator away from the center enabled
easier preparation. As a pitch of the liquid crystal lattice, the following
three
patterns were manufactured:
(i) Pitch of liquid crystal lattice: 20 m (control area: 17 m, gap: 3 m)
(ii) Pitch of liquid crystal lattice: 20 m (control area: 18 m, gap: 2 m)
(iii) Pitch of liquid crystal lattice: 10 m (control area: 8 m, gap: 2 m)
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As for the orientation of liquid crystals, the orientation direction was
set 45 degrees in case of intensity control, and it was set 0 degree in case
of
phase control. The liquid crystal spatial light modulator for intensity
control
and the liquid crystal spatial light modulator for phase control were prepared
separately. When connecting the two liquid crystal elements, a marker for
positioning the lattices was provided. Furthermore, control ICs were
collectively arranged on one side of the glass substrate.
[0046]
In the spatial light modulator as shown in Fig. 11(c), a liquid crystal
spatial light modulator for intensity control and a liquid crystal spatial
light
modulator for phase control are provided on each of the surface and the rear
surface respectively of the glass substrate having a pattern electrode. These
were prepared with the potion of the lattices aligned. As shown in Fig. 11(c),
this liquid crystal spatial light modulator has the configuration where the
glass
substrate having the pattern electrode is put between two substrates having a
common electrode. The size of a liquid crystal cell gap located between glass
substrates each having a common electrode and a pattern electrode was set
8 m. The liquid crystal lattice with a size of up to 20mm x up to 5mm was
used. In Fig. 11(c), the liquid crystal spatial light modulator was put to
either
the left or the right of the glass substrate. This intentional arrangement of
the
liquid crystal light modulator away from the center enabled easier
preparation.
As a pitch of the liquid crystal lattice, the following three patterns were
manufactured:
(i) Pitch of liquid crystal lattice: 20 m (control area: 17 m, gap: 3 m)
(ii) Pitch of liquid crystal lattice: 20 m (control area: 18 m, gap: 2 m)
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CA 02690852 2009-12-15
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(iii) Pitch of liquid crystal lattice: 10 m (control area: 8 m, gap: 2 m)
As for the orientation of liquid crystals, the orientation direction was
set 45 degrees in case of intensity control, and it was set 0 degree in case
of
phase control. The liquid crystal spatial light modulator for intensity
control
and the liquid crystal spatial light modulator for phase control were prepared
as a unit with the glass substrate having a pattern electrode in common.
[0047]
Figs. 12 are graphs replaced with drawings showing the optical
intensity control characteristic of an optical waveform shaping device. Fig.
12(a) shows a graph of measurement of the optical intensity control
characteristic when an ASE light source is used and all the channels are
controlled collectively. Fig. 12(b) shows a graph of measurement of the
optical
intensity control characteristic when all the channels are intermediately
controlled. Fig. 12(c) shows a graph of measurement of the optical intensity
control characteristic when all the channels are OFF controlled. Fig 12(a)
shows that the passbands of adjacent bands forms continuous passbands in the
optical waveform shaping device of the present invention. On the other hand,
Fig .12(b) shows that the intensity control variable can be set arbitrarily
within
the control range. Fig. 12(c) shows that output can be suppressed in case of
OFF control.
[0048]
Figs. 13 are graphs replaced with drawings showing frequency
spacing of an optical waveform shaping device. The wavelength of a
wavelength variable LD light source was swept at a 0.01nm step, and the
power of each wavelength with optical intensity controlled was measured with
a power meter. The optical intensity control was set for every 1CH, and the
CA 02690852 2009-12-15
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frequency spacing was checked. Fig. 13(a) shows a frequency spacing in case
of one ON, Fig 13(b) shows a frequency spacing in case of two adjacent ON,
Fig. 13(c) shows a frequency spacing in case of three ON, and Fig. 13(d)
shows a frequency spacing in case of two separate ON.
[0049]
Fig. 14 is a graph replaced with a drawing showing the spatial
resolution of an optical waveform shaping device. An ASE light source was
used and the optical intensity was controlled for every 48CH (ON as a whole;
OFF control for every 48CH). The spatial resolution per PAL-SLM cell in each
wavelength band was measured from the control wavelength difference. As a
result, the spatial resolution was 12.1GHz/cell at a wavelength of 1535nm, the
spatial resolution was 10.7GHz/cell at a wavelength of 1550nm, and the spatial
resolution was 9.2GHz/cell at a wavelength of 1565nm.
[0050]
Fig. 15 is a schematic diagram showing a device configuration for
measuring an insertion loss. As a result, the insertion loss was 6.5dB at a
wavelength of 1535nm, the insertion loss was 5.0dB at a wavelength of
1550nm, and the insertion loss was 7.5dB at wavelength of 1565nm.
[00511
Table 1 is a table showing the dispersion characteristic of a grating.
[Table 1]
Wavelength Incident angle Diffraction angle Diffraction efficiency
1540nm 50deg 68.9deg 87.0%
1550nm 50deg 70.Odeg 88.2%
1560nm 50deg 71.2deg 89.1%
[0052]
Table 2 is a table showing the diameter of a PAL-SLM incident beam.
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[Table 2]
Wavelength Condensing diameter (x-axis) Condensing diameter (y-axis)
1530nm Dx-40 m (Dx - 74pm
1550nm (Dx - 38pm (Dx - 65pm
1570nm (Dx - 45 m (Dx - 86pm
Industrial Applicability
[0053]
The optical waveform shaping device of the present invention is
preferably used in the fields such as optical information and communication.
Description of the Numerals
[0054]
1 Branching filter
2 Condensing part
3 Polarizing plate
4 Spatial light modulator
10 Optical waveform shaping device
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example using an existing driver, while Fig. 7(b) shows an example
performing DIO direct control.
Fig. 8 is a comprehensive diagram of the optical waveform shaping
device according to Embodiment 1.
Figs. 9 are schematic diagrams of the optical system according to
Embodiment 1. Fig. 9(a) is a top view, while Fig. 9(b) is a side view.
Fig. 10 is a schematic diagram of a simulation determining the
position of an optical element.
Figs. 11 are figures showing an example of a liquid crystal spatial
light modulator. Fig. 11(a) through Fig. 11(c) are figures showing an overview
of the actually manufactured spatial light modulator.
Figs. 12 are graphs replaced with drawings showing the optical
intensity control characteristic of an optical waveform shaping device. Fig.
12(a) shows a graph of measurement of the optical intensity control
characteristic when an ASE light source is used and all the channels are
controlled collectively. Fig. 12(b) shows a graph of measurement of the
optical
intensity control characteristic when all the channels are intermediately
controlled. Fig. 12(c) shows a graph of measurement of the optical intensity
control characteristic when all the channels are OFF controlled
Figs. 13 are graphs replaced with drawings showing frequency
spacing of an optical waveform shaping device. The wavelength of a
wavelength variable LD light source was swept at a 0.01nm step, and the
power of each wavelength with optical intensity controlled was measured with
a power meter. The optical intensity control was set for every 1CH, and the
frequency spacing was checked. Fig. 13(a) shows a frequency spacing in case
of one ON, Fig 13(b) shows a frequency spacing in case of two adjacent ON,
Fig. 13(c) shows a frequency spacing in case of three ON, and Fig. 13(d)
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shows a frequency spacing in case of two separate ON.
Fig. 14 shows a graph replaced with a drawing showing the spatial
resolution of an optical waveform shaping device.
Fig. 15 is a schematic diagram showing the device configuration for
measuring an insertion loss.
Fig. 16 is an example of the grating part using a grism.
Fig. 17 is a conceptual diagram showing an example of a grism.
Fig. 18 is a figure showing the relation between the lattice cycle of a
VPH grating part and the incidence angle of a grating.
Fig. 19 is a figure showing a modified grism.
Description of the Numerals
[0055]
1 Branching filter
2 Condensing part
3 Polarizing plate
4 Spatial light modulator
10 Optical waveform shaping device
24
