JP2003172913A - Variable gain equalizing filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable gain equalizing filter having high spectrum resolution and low power consumption. <P>SOLUTION: Since a phase controlling means 22 utilizes a phase change due to an electrooptical effect of a liquid crystal 29 in the variable gain equalizing filter, conventional heaters 14 and 14ab are not needed and thermal influence of a channel waveguide 13 being an controlling object on a channel waveguide 13 adjacent thereto is eliminated. As a result, isolation between channels can be enhanced and not only the spectrum resolution can be enhanced, but also power consumption can be reduced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength multiplexing communication filter in optical communication, and more particularly to a variable gain equalization filter.

[0002]

2. Description of the Related Art A conventional variable gain equalization filter (DGE)
Some of F) include a circulator, a channel waveguide, a slab waveguide, an arrayed waveguide, a total reflection mirror, and a phase controller waveguide. A thermo-optical effect by a heater is used for this phase control unit.

FIG. 5 (a) is a plan view of a conventional variable gain equalizing filter, and FIG. 5 (b) is an enlarged view of a region 5b in FIG. 5 (a).

When the wavelength-multiplexed signal light L1 is incident on the first port P1 of the circulator 1, the second port P1
Emit from 2. The signal light emitted from the second port P2 propagates through the optical fiber 2 through the channel waveguide 4 formed on the substrate 3 and is branched by the Y branch waveguide 5. The branched signal light propagates through the channel waveguides 6 and 7. The signal light propagating through the channel waveguide 6 is reflected by the total reflection mirror 8 provided on the substrate 3 and propagates in the returning direction through the channel waveguide 6.

On the other hand, the signal light branched to the channel waveguide 7 enters the slab waveguide 10 of the arrayed waveguide diffraction grating 9 as a demultiplexer connected to the channel waveguide 7. The signal light incident on the slab waveguide 10 propagates through channel waveguides (waveguide array) 11 having different lengths, and enters the slab waveguide 12. The signal light incident on the slab waveguide 12 propagates through the slab waveguide 12 and is condensed at a position corresponding to the wavelength. One end of each of the plurality of channel waveguides 13 is connected to the focusing position. The signal light incident on each channel waveguide 13 is reflected by the total reflection mirror 8 connected to the other end of each channel waveguide 13, and the optical path is reversed and propagates through the channel waveguide 13 and the arrayed waveguide diffraction grating 9. .

The signal lights returning to the channel waveguides 6 and 7 respectively enter the Y branch waveguide 5 and interfere with each other. At this time, paying attention to each wavelength, it can be seen that a Michelson interferometer is configured for each wavelength between the path of the channel waveguide 6 and the paths after the channel waveguide 7.

Therefore, if the phase difference is controlled for each wavelength, the power of the signal light incident on the channel waveguide 4 at each wavelength can be controlled. It is possible to control the phase of the signal light for each wavelength by the plurality of heaters 14 provided on each channel waveguide 13. as a result,
The spectral response of the signal light that enters the channel waveguide 4 from the Y-branch waveguide 5 can be arbitrarily controlled. The signal light emitted from the channel waveguide 4 enters the second port P2 of the three-terminal circulator 1 connected to the waveguide and is emitted from the third port P3 of the three-terminal circulator 1 (L2).

FIG. 6A is a plan view showing a conventional example of a transmission type variable gain equalizing filter, and FIG. 6B is a plan view.
It is an enlarged view of the area | region 6ab of (a).

In this transmission type variable gain equalization filter, the interferometer section of the variable gain equalization filter shown in FIGS. 5A and 5B is replaced with a Mach-Zehnder interferometer from a Michelson interferometer. Is equivalent to

This variable gain equalization filter has a structure in which the first channel waveguide 4, Y shown in FIG.
The branch waveguide 5, the second channel waveguide 6, the third channel waveguide 7, the array waveguide diffraction grating 9, and the fourth channel waveguide 13 are orthogonal to the second channel waveguide 6 and the fourth channel waveguide 13. The channel waveguides 4a, 4b, 6a, 6b, 13a, 13b, so as to be axisymmetric with respect to the line,
Y branch waveguides 5a, 5b and arrayed waveguide diffraction grating 9
a and 9b are formed, and each fourth channel waveguide 13 is formed.
A heater 14ab is formed on each of a and 13b. Incidentally, 16 and 17 are optical fibers.

This variable gain type equalizing filter is shown in FIG.
The interferometer section of the variable gain equalization filter shown in (a) and (b) is replaced with a Mach-Zehnder interferometer, and the variable gain equalization filter shown in FIGS. Do the same.

[0012]

[Problems to be Solved by the Invention]
In the conventional examples shown in (a), (b) and FIGS. 6 (a), (b), since the heaters 14 and 14ab are used for the phase control of the signal light, the target phase control section waveguide is used. The adjacent phase control section waveguide is affected by heat and changes the phase. That is, even when it is desired to control the loss in a certain wavelength range, the loss in the wavelength range adjacent to the wavelength range also changes. Therefore, it is necessary to construct a system that performs control considering the influence of heat applied to the adjacent waveguide.

Further, in order to improve the spectral resolution, it is necessary to increase the number of waveguides of the phase control section, and the waveguide spacing becomes narrow because the waveguides are arranged in a limited space. As a result, the influence of the heater of the adjacent waveguide becomes stronger, and it becomes impossible to control only the target wavelength range.

Furthermore, an increase in power consumption due to an increase in the number of channels in the phase control unit cannot be avoided.

That is, in the conventional variable gain equalization filter, (1) it is not easy to simplify the control system because the inter-channel isolation of the phase controller is poor. (2) Spectral resolution cannot be increased. (3) It is not easy to reduce power consumption. There was a problem.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to solve the above problems and provide a variable gain equalization filter having high spectral resolution and low power consumption.

[0017]

In order to achieve the above object, the invention according to claim 1 is a demultiplexer for demultiplexing wavelength-multiplexed signal light input on a substrate for each wavelength, and In a variable gain equalizing filter having phase control means for controlling the phase of each signal light demultiplexed by the demultiplexer, the phase control means includes a liquid crystal to which each signal light is input, and a refractive index of the liquid crystal. Is selectively changed to control the phase of each signal light.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the wavelength-multiplexed signal light is input to the first port and the phase-controlled wavelength-multiplexed signal light is output from the third port. Of the three-terminal circulator, the first channel waveguide formed on the substrate, and one end of which is connected to the second port of the three-terminal circulator through one end face of the substrate, and the multiplexing-side waveguide is the first channel waveguide. A Y-branch waveguide connected to the other end of the waveguide, and a second channel conductor formed so that one end is connected to one branch-side waveguide of the Y-branch waveguide and the other end is exposed at the other end face of the substrate. A waveguide, a total reflection mirror connected to the other end of the second channel waveguide, a third channel waveguide whose one end is connected to the other branch side waveguide of the Y branch waveguide, and a third channel waveguide Connected to the other end, from the third channel waveguide A demultiplexer for demultiplexing the wavelength-multiplexed signal light for each wavelength; a plurality of fourth channel waveguides formed so that one end is connected to the demultiplexer and the other end is exposed at the other end face of the substrate; In the variable gain equalization filter having the phase control means for controlling the phase of the demultiplexed signal light provided on the other end side of the fourth channel waveguide, the phase control means is the other end of each fourth channel waveguide. The liquid crystal phase shifter cell that controls the phase of each optical signal from the liquid crystal by selectively changing the refractive index of the liquid crystal, and after changing the polarization state of the optical signal that has passed through the liquid crystal phase shifter cell, Each 4th
And a Faraday mirror that reflects on each of the channel waveguides.

In addition to the structure described in claim 1 or 2, the liquid crystal phase shifter cell of the variable gain equalizing filter of the present invention comprises:
A transparent substrate provided on the other end face of the substrate, a transparent electrode piece provided on the end face of the fourth channel waveguide of the transparent substrate, an alignment film covering the transparent electrode piece, and arranged in parallel with the transparent substrate. Other transparent substrate, a transparent electrode plate provided inside the other transparent substrate, another alignment film covering the transparent electrode plate, and a liquid crystal filled between the both transparent substrates. .

The liquid crystal phase shifter cell of the variable gain equalizing filter according to the present invention, in addition to the constitution described in claim 1 or 2,
A transparent substrate provided on the other end face of the substrate, a transparent electrode piece provided on the end face of the fourth channel waveguide of the transparent substrate, an alignment film covering the transparent electrode piece, and arranged in parallel with the transparent substrate. It may have a transparent electrode plate formed directly inside the formed Faraday mirror, another alignment film covering the transparent electrode plate, and liquid crystal filled between both transparent substrates.

According to a fifth aspect of the present invention, a first substrate and a first channel waveguide formed on the first substrate such that one end of the first substrate is exposed to one end face of the first substrate and on which wavelength-multiplexed signal light is incident. And a first Y-branch waveguide in which the combining-side waveguide is connected to the other end of the first channel waveguide, and one end is connected to one branch-side waveguide in the first Y-branch waveguide and the other end is the first substrate. A second channel waveguide formed on the first substrate so as to be exposed at the other end surface of the first channel, a third channel waveguide having one end connected to the other branch waveguide of the first Y branch waveguide, and a third channel A demultiplexer connected to the other end of the waveguide for demultiplexing the wavelength-multiplexed signal light from the third channel waveguide for each wavelength, and one end connected to the demultiplexer and the other end of the first substrate A plurality of fourth channel waveguides formed on the first substrate so as to be exposed at the end face of the second substrate; A fifth channel waveguide formed on the second substrate such that one end is exposed on one end surface of the second substrate and faces the other end of the second channel waveguide, and one branch waveguide is formed on the fifth channel waveguide. Second connected to the other end of the waveguide
A Y-branch waveguide, and a sixth channel waveguide formed on the second substrate so that one end is connected to the combining side of the second Y-branch waveguide and the other end is exposed at the other end face of the second substrate, A plurality of seventh channel waveguides formed on the second substrate such that one end is exposed on one end surface of the second substrate and faces the fourth channel waveguide, and is connected to the other end of the seventh channel waveguide. A multiplexer for multiplexing signal lights of different wavelengths, an eighth channel waveguide having one end connected to the multiplexer and the other end connected to the other branch waveguide of the second Y branch waveguide, and a first substrate Between the second channel waveguide and the fifth channel waveguide and between the fourth channel waveguide and the seventh channel waveguide that are provided between the other end surface of the second substrate and the one end surface of the second substrate. Phase control means for controlling the phase of the generated signal light is provided.

In addition to the structure described in claim 5, the variable gain equalizing filter of the present invention has one end of the first channel waveguide and the sixth channel waveguide.
The other end of the channel waveguide is connected to the two terminals of the polarization beam splitter using a polarization maintaining optical fiber so that the polarization directions of light incident on these channel waveguides are the same. A three-terminal circulator into which wavelength-multiplexed signal light is incident may be connected to the remaining terminals of the splitter.

According to the variable gain equalization filter of the present invention, in addition to the structure described in claim 5 or 6, the phase control means includes a transparent electrode plate covering one end face of the second substrate and the other end face of the first substrate. A plurality of transparent electrode pieces that cover the end faces of the second channel waveguide and the fourth channel waveguides exposed to each other, an alignment film that covers the other end face of the first substrate and one end face of the second substrate, respectively. A sealing member that covers the other end face side of the first substrate and one end face side of the second substrate so that a sealed space is formed between the substrate and the second substrate, and a liquid crystal filled in the sealed space are provided. You may.

According to the present invention, since the phase control means utilizes the phase change due to the electro-optical effect of the liquid crystal, a heater is not required, and the thermal influence of the channel waveguide to be controlled on the adjacent channel waveguide is eliminated. Disappear. As a result, it is possible to improve the inter-channel isolation, improve not only the spectral resolution, but also the power consumption.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 5 (a), (b),
The same reference numerals are used for the same members as in the conventional example shown in FIGS. 6 (a) and 6 (b).

FIG. 1A is a plan view of the variable gain equalizing filter of the present invention, and FIG. 1B is an enlarged schematic view of the phase control means 22 of the variable gain equalizing filter shown in FIG. 1A. It is a figure.

The difference between the variable gain equalization filter shown in FIG. 5A and the conventional example shown in FIGS. 5A and 5B is that the heater 14 constituting the phase control means of the variable gain equalization filter is different.
, There is no total reflection mirror 8 that directly covers the end faces of the plurality of channel waveguides 13, and a liquid crystal phase shifter cell (here, the orientation and operation mode of the liquid crystal cells are horizontal electric field control A birefringent type "ECB cell") 20 and a phase control means 22 including a Faraday mirror 21 are provided.

As shown in FIG. 1A, the first channel waveguide 4 is formed on the substrate 3 so that one end surface (the left side in the drawing) of the substrate 3 is exposed. The other side of the first channel waveguide 4 is connected to the wave-combining side waveguide of the Y-branch waveguide 5. One side (upper side in the drawing) of the Y-branching waveguide 5 has a second channel waveguide 6 formed so that one end surface is exposed at the other end side (right side in the drawing) of the substrate 3. The other end is connected. A total reflection mirror 8a is provided on the other end surface (right side in the figure) of the substrate 3 so as to cover the other end surface of the second channel waveguide 6.

The other branch side waveguide (lower side in the figure) of the Y branch waveguide 5 has a third channel conductor whose one end is connected to the first slab waveguide 10 of the arrayed waveguide diffraction grating 9 as a demultiplexer. The other end of the waveguide 7 is connected. The second slab waveguide 12 of the arrayed waveguide diffraction grating 9 is connected to the other ends of a plurality of fourth channel waveguides 13 formed so that one end is exposed at the other end face of the substrate 3.

Here, the arrayed-waveguide diffraction grating 9 includes the first
A plurality of arrayed waveguides 1 that are connected between the slab waveguide 10, the second slab waveguide 12, and the first slab waveguide 10 and the second slab waveguide 12 and that differ in length by a predetermined length.
It is composed of 1 and 1.

Phase control means 22 is provided on the other end face of the substrate 3 so as to cover the other ends of all the fourth channel waveguides 13.

An optical fiber is provided between the second port P2 of the three-terminal circulator 1 on which the wavelength-multiplexed signal light L1 is incident on the first port P1 and the end face of the first channel waveguide 4 exposed on one end face of the substrate 3. Connected with 2.

The phase control means shown in FIG. 1B controls the phase of each optical signal from the other end of the fourth channel waveguide 13 by the liquid crystal 2.
9. A liquid crystal phase shifter cell 20 for controlling by selectively changing the refractive index of the liquid crystal phase shifter cell 20, and a liquid crystal phase shifter cell 20.
And a Faraday mirror 21 that changes the polarization state of the optical signal that has passed through and is reflected by each of the fourth channel waveguides 13.

The liquid crystal phase shifter cell 20 has a transparent substrate 23 whose one surface (left side in the drawing) is joined to the other end surface of the substrate 3 and a fourth transparent substrate 23 on the other surface (right side in the drawing). A plurality of transparent electrode pieces 24 arranged to face the end faces of the channel waveguides 13, an alignment film 25 covering the other surface of the transparent substrate 23, and another transparent substrate 26 arranged in parallel with the transparent substrate 23. A transparent electrode plate 27 disposed on one surface (left side in the figure) of the transparent substrate 26;
A sealing member (not shown) that holds the alignment film 28 that covers 7 and both transparent substrates 23 and 26 and forms a sealed space.
And a liquid crystal 29 filled in the closed space.

The operation mode of the liquid crystal uses the electric field control birefringence effect (ECB mode). By independently controlling the voltage applied between each transparent electrode piece 24 and the transparent electrode plate 27, the phase of the signal light propagating through the fourth channel waveguide 13 can be independently controlled. Also, EC
Since the B mode has polarization dependence, the Faraday mirror changes the polarization state by 90 ° to eliminate the polarization dependence.

The Faraday mirror 21 includes a Faraday element (for example, a 45 ° rotating Faraday element) 30 provided on the other surface of the transparent substrate 26, a total reflection mirror 31 provided outside the Faraday element 30, and a transparent substrate 26. And a magnet 32 which is provided on the outer side of the magnetic field and forms a magnetic field in a direction parallel to the optical axis of the fourth channel waveguide 13.

Next, the operation of the variable gain equalizing filter shown in FIG. 1A will be described with reference to FIG.

When the WDM signal light L1 enters the first port P1 of the three-terminal circulator 1, the second port P2
From the optical fiber 2, enters the first channel waveguide 4 through the optical fiber 2, and enters the Y-branch waveguide 5. The wavelength-division-multiplexed signal light incident on the Y-branch waveguide 5 is branched into two directions,
The WDM signal light that has proceeded to the channel waveguide 6 is reflected by the total reflection mirror 8 a and returns to the first channel waveguide 4.

On the other hand, the wavelength-multiplexed signal light that has proceeded to the third channel waveguide 7 enters the first slab waveguide 10 of the arrayed waveguide diffraction grating 9. The wavelength-multiplexed signal light that has entered the first slab waveguide 10 propagates through the first slab waveguide 10 and enters the arrayed waveguide 11. The wavelength-multiplexed signal lights incident on the arrayed waveguides are arrayed waveguides 1 having different lengths.
1 and is incident on the second slab waveguide 12. The wavelength-multiplexed signal light incident on the second slab waveguide 12 propagates through the second slab waveguide 12 and is condensed at a position corresponding to the wavelength. The signal lights with different wavelengths demultiplexed in this way are
Each of the fourth channel waveguides 1 arranged at the condensing position of the signal light
Propagate 3 respectively.

The signal light propagating through each of the fourth channel waveguides 13 is emitted from the other end face of the substrate 3 and is incident on the liquid crystal phase shifter cell 20. The signal light transmitted through the liquid crystal phase shifter cell 20 is reflected by the Faraday mirror 21, and at the same time, the polarization state is rotated by 90 °. The signal light returns to the original optical path, and propagates through the third channel waveguide 7.

The signal lights returning to the second channel waveguide 6 and the third channel waveguide 7 enter the Y branch waveguide 5 and interfere with each other. At this time, when the signal light is focused on each wavelength, a Michelson interferometer is configured for each wavelength between (the path of the second channel waveguide 6) and (the path of the third channel waveguide 7 and thereafter). I understand that. Therefore, by controlling the phase difference of the signal light for each wavelength, it becomes possible to control the power of the signal light incident on the first channel waveguide 4 at each wavelength.

The liquid crystal phase shifter cell 20 makes it possible to control the phase of the signal light for each wavelength, and as a result, the spectral response of the signal light incident on the first channel waveguide 4 from the Y branch waveguide 5 can be arbitrarily set. Can be controlled. The signal light emitted from the first channel waveguide 4 propagates through the optical fiber 2, enters the second port P2 of the three-terminal circulator 1, and is emitted from the third port P3 (arrow L2).

As described above, a variable gain equalizing filter having high spectral resolution and low power consumption can be obtained.

Next, optimum conditions will be described.

The phase control width of the liquid crystal phase shifter cell 20 must be at least 2π in the used wavelength range. When the birefringence difference Δn of the liquid crystal 29 used is 0.11, and the liquid crystal 29 operates in the ECB mode, the thickness of the liquid crystal 29 is at least 2.
6 μm is required. Further, since the operation required for the liquid crystal phase shifter cell 20 is a change in the refractive index due to the electro-optical effect, the same effect can be obtained even if the operation mode of the liquid crystal 29 uses twisted nematic (TN) orientation.

Here, by integrating the liquid crystal phase shifter and the Faraday mirror of the variable gain equalizing filter shown in FIG. 1A, the fabrication becomes easy, the total optical path length can be shortened, and the diffraction loss can be reduced. Can be reduced.

FIG. 4 shows a phase control means in which the liquid crystal phase shifter shown in FIG. 1B and the Faraday mirror are integrated.

This phase control means is one in which the transparent electrode plate 27 is directly provided on the Faraday element 30a without using the transparent substrate 26 used in the variable gain equalization filter shown in FIG. 1 (b).

That is, the transparent electrode piece 24 covering the end face of each fourth channel waveguide 13 of the liquid crystal phase shifter cell 20a.
The transparent electrode plate 27a facing the Faraday element 30a.
By directly providing the liquid crystal phase shifter cell 20a.
And the Faraday mirror 21a are integrated. Since it is not necessary to use the transparent substrate (see FIG. 1B) 26, the number of steps is reduced accordingly.

Even if such a phase control means is used, there is no substitute for the phase control function and the polarization dependence compensation function.

The present invention is not limited to the above embodiment, but may be applied to the transmissive element shown in FIG. However, some changes will be made to the polarization dependence compensation mechanism. Here, an example is shown in which the polarization dependence is eliminated by using polarization diversity using a polarization beam splitter (PBS) and a polarization maintaining fiber.

FIG. 2 (a) is a plan view showing another embodiment of the variable gain equalization filter of the present invention, and FIG. 2 (b) shows the variable gain equalization filter shown in FIG. 2 (a). It is a partially expanded schematic diagram of a control means.

In the first substrate 15a shown in FIG. 9A, the first channel waveguide 4 is formed so that one end is exposed at one end surface (left side in the figure) of the first substrate (left side in the figure) 15a.
a is formed. The first Y-branch waveguide 5a in which the multiplexing side waveguide is connected to the other end of the first channel waveguide 4a is the first
It is formed on the substrate 15a.

The second channel waveguide 6a is formed on one branch side waveguide (upper side in the figure) of the first Y branching waveguide 5a so that the other end is exposed at the other end face (center in the figure) of the first substrate 15a. It is formed on the first substrate 15a.

A third channel waveguide 7a whose one end is connected to the other (lower side in the figure) of the first Y-branch waveguide 5a is formed on the first substrate 15a, and the other third channel waveguide 7a is formed. A first arrayed waveguide diffraction grating 9a as a demultiplexer having the end connected to the first slab waveguide 10a is formed on the first substrate 15a.

One end is connected to the second slab waveguide 12a of the first arrayed waveguide diffraction grating 9a, and a plurality of fourth channel waveguides 13a are formed so that the other end is exposed at the other end face of the first substrate 15a. It is formed on one substrate 15a.

On the other hand, one end of the second substrate 15b is exposed at one end face (the center in the drawing) of the second substrate 15b, and the other end of the second substrate 15b is opposed to the other end of the second channel waveguide 6a of the first substrate 15a. A 5-channel waveguide 6b is formed.

A second Y-branch waveguide 5b, to which one (upper side in the figure) branch waveguide is connected to the other end of the fifth channel waveguide 6b, is formed on the second substrate 15b.

The sixth channel waveguide 4b is connected to the multiplexing side of the second Y-branch waveguide 5b, and the sixth channel waveguide 4b is exposed so that the other end is exposed on the other (right side in the figure) end face of the second substrate 15b. It is formed in 15b.

The same number of seventh channel waveguides 13b are provided so that one end is exposed at one end surface of the second substrate 15b and faces the plurality of fourth channel waveguides 13a exposed at the other end surface of the first substrate 15a. It is formed on the second substrate 15b.

A second arrayed waveguide diffraction grating 9b as a multiplexer, in which the third slab waveguide 12b is connected to the other end of the seventh channel waveguide 13b, is formed on the second substrate 15b.

An eighth channel waveguide 7b having one end connected to the fourth slab waveguide 10b of the second arrayed waveguide diffraction grating 9b and the other end connected to the other branch waveguide of the second Y branch waveguide 5b is formed. It is formed on the second substrate 15b.

The other end face of the first substrate 15a and the second substrate 1
The second channel waveguide 6a is provided between the second channel waveguide 6a and one of the end faces of 5b.
And the fifth channel waveguide 6b, and between the fourth channel waveguide 13a and the seventh channel waveguide 13b, the refractive index of the liquid crystal 29 is selectively changed, so that the respective demultiplexed signal lights are generated. Phase control means 33 for controlling the phase of is provided.

The phase control means 33 includes a transparent electrode plate 27 that covers one end surface of the second substrate 15b, a second channel waveguide 6a exposed at the other end surface of the first substrate 15a, and each fourth electrode.
A plurality of transparent electrode pieces 2 covering the end face of the channel waveguide 13a
4, the other end surface of the first substrate 15a and the second substrate 15b
Alignment films 25 and 28 respectively covering one end surface of the
The other end face side of the first substrate 15a and the second substrate 1 so that a sealed space is formed between the substrate 15a and the second substrate 15b.
5b, and a liquid crystal 29 filled in the hermetically sealed space.

FIG. 3 is a block diagram for eliminating the polarization dependence of the variable gain equalization filter shown in FIG.

This variable gain equalizing filter is the first channel waveguide 4a of the variable gain equalizing filter shown in FIG. 2 (a).
And the other end of the sixth channel waveguide 4b using the polarization maintaining optical fibers 35 and 36.
The second port P2 of the 3-terminal circulator 1 into which the wavelength multiplexed signal light L1 is incident on the first port P1 is connected to the remaining terminals of the polarization beam splitter 37. Single mode optical fiber (SM
F) 38 to the first port P1 of the 3-terminal circulator 1
The wavelength-multiplexed signal light incident on is emitted to the SMF 39 and is incident on the polarization beam splitter 37. The signal lights split into TE-polarized light and TM-polarized light by the polarization beam splitter 37 enter polarization-maintaining optical fibers 35 and 36, respectively,
It is incident on a transmission type variable gain equalization filter. When the signal light enters the variable gain equalization filter, one polarization-maintaining optical fiber 35 is twisted by 90 ° and connected to the first channel waveguide 4a.
Only E-polarized light will enter from the right and left directions, respectively. The signal lights that have entered from both sides enter the polarization maintaining optical fibers 35 and 36, respectively, after passing through the first substrate 15a and the second substrate 15b. Polarizing beam splitter 3
By 7, the respective signal lights are multiplexed into the SMF 39,
From the third port P3 of the 3-terminal circulator 1 to the SMF4
The light is emitted to 0 (arrow L2).

With such an operation, only the TE polarized light is transmitted through the variable gain equalization filter, and the polarization dependency due to the use of the liquid crystal phase shifter can be eliminated. With this configuration, the polarization independent variable is obtained as a whole. Operates as a gain equalization filter. Further, it has the same effect as that of the variable gain equalizing filter shown in FIG.

In the above, by utilizing the phase change due to the electrochemical effect of the liquid crystal in the phase control means to improve the inter-channel isolation, the control system of the variable gain equalization filter is simplified and the spectral resolution is improved. A reduction in power consumption can be achieved.

[0069]

In summary, according to the present invention, it is possible to provide a variable gain equalization filter having high spectral resolution and low power consumption.

[Brief description of drawings]

FIG. 1A is a plan view of a variable gain equalization filter of the present invention, and FIG. 1B is an enlarged schematic view of a phase control unit of the variable gain equalization filter shown in FIG.

2A is a plan view showing another embodiment of the variable gain equalization filter of the present invention, and FIG. 2B is a partial enlargement of the control means of the variable gain equalization filter shown in FIG. It is a schematic diagram.

FIG. 3 is a configuration diagram for eliminating the polarization dependence of the variable gain equalization filter shown in FIG.

FIG. 4 is a phase control unit in which the liquid crystal phase shifter shown in FIG. 1B and a Faraday mirror are integrated.

5A is a plan view of a conventional variable gain equalization filter, and FIG. 5B is an enlarged view of a region 5b in FIG. 5A.

6A is a plan view showing a conventional example of a transmission type variable gain equalization filter, and FIG. 6B is an enlarged view of a region 6ab in FIG. 6A.

[Explanation of symbols]

1 3 terminal circulator 3 substrates 4 First channel waveguide 5 Y-branch waveguide 6 Second channel waveguide 7 Third channel waveguide 8a total reflection mirror 9 Array waveguide diffraction grating (demultiplexer) 10 First slab waveguide 11 Array waveguide 12 Second slab waveguide 13 Fourth Channel Waveguide 20 Liquid crystal phase shifter cell 21 Faraday mirror 22 Phase control means 23, 26 Transparent substrate 24 Transparent electrode piece 25, 28 Alignment film 29 LCD 30 Faraday element 31 total reflection mirror 32 magnets

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoto Uezuka             1-6-1, Otemachi, Chiyoda-ku, Tokyo             Standing Wire Co., Ltd. F term (reference) 2H049 AA51 AA59 AA62 AA64                 2H079 AA02 AA03 AA12 BA02 BA03                       CA24 DA08 EA13 EA28 EB15                       EB17 GA03 KA08                 2H088 EA46 EA47 HA10 HA20 HA21                       HA30 JA05 JA09 MA20

Claims (7)

[Claims] 1. A demultiplexer that demultiplexes wavelength-multiplexed signal light that is formed on a substrate and that is input, and a phase control that controls the phase of each of the signal lights demultiplexed by the demultiplexer. And a variable gain equalization filter having means,
The phase control means includes a liquid crystal to which each of the signal lights is input, and selectively changes the refractive index of the liquid crystal to control the phase of each of the signal lights. filter. 2. A three-terminal circulator for inputting wavelength-multiplexed signal light to the first port and outputting phase-controlled wavelength-multiplexed signal light from the third port, and one terminal formed on the substrate and having one end. A first channel waveguide connected to the second port of the three-terminal circulator via the end face of the Y-branch waveguide having the coupling side waveguide connected to the other end of the first channel waveguide, and one end A second channel waveguide which is connected to one branch side waveguide of the Y branch waveguide and is formed so that the other end is exposed at the other end face of the substrate;
A total reflection mirror connected to the other end of the channel waveguide, a third channel waveguide whose one end is connected to the other branch side waveguide of the Y branch waveguide, and a other end of the third channel waveguide And a demultiplexer for demultiplexing the wavelength-multiplexed signal light from the third channel waveguide for each wavelength, and one end connected to the demultiplexer and the other end exposed on the other end face of the substrate. In the variable gain equalization filter having a plurality of fourth channel waveguides and phase control means for controlling the phase of the demultiplexed signal light provided on the other end side of all the fourth channel waveguides, the phase control The means controls a phase of each optical signal from the other end of each fourth channel waveguide by selectively changing the refractive index of the liquid crystal, and an optical signal transmitted through the liquid crystal phase shifter cell. After changing the polarization state of each optical signal Variable gain equalizing filter, characterized in that a Faraday mirror for reflecting each of the fourth channel waveguide. 3. The liquid crystal phase shifter cell comprises: a transparent substrate provided on the other end face of the substrate; transparent electrode pieces provided respectively on the end faces of the fourth channel waveguides of the transparent substrate; An alignment film covering the electrode piece, another transparent substrate arranged in parallel with the transparent substrate, a transparent electrode plate provided inside the other transparent substrate, another alignment film covering the transparent electrode plate, and The variable gain equalization filter according to claim 1, further comprising a liquid crystal filled between the transparent substrates. 4. The liquid crystal phase shifter cell comprises: a transparent substrate provided on the other end face of the substrate; transparent electrode pieces provided respectively on the end faces of the fourth channel waveguides of the transparent substrate; An alignment film covering the electrode piece, a transparent electrode plate formed directly inside the Faraday mirror arranged in parallel with the transparent substrate, another alignment film covering the transparent electrode plate, and a space between the transparent substrates. The variable gain equalization filter according to claim 1, further comprising a liquid crystal. 5. A first substrate, a first channel waveguide formed on the first substrate such that one end is exposed at one end face of the first substrate, and on which wavelength-multiplexed signal light is incident, and a multiplexing side waveguide. Is connected to the other end of the first channel waveguide, and one end is connected to one branch side waveguide of the first Y branch waveguide, and the other end is exposed to the other end face of the first substrate. The second channel waveguide formed on the first substrate, and one end of the first waveguide
A third channel waveguide connected to the other branch waveguide of the Y branch waveguide, and connected to the other end of the third channel waveguide,
A demultiplexer for demultiplexing the wavelength-multiplexed signal light from the third channel waveguide for each wavelength and a first demultiplexer having one end connected to the demultiplexer and the other end exposed at the other end face of the first substrate. A plurality of fourth channel waveguides formed on the substrate, a second substrate, and formed on the second substrate so that one end is exposed at one end face of the second substrate and faces the other end of the second channel waveguide. And a second Y-branch waveguide in which one branch waveguide is connected to the other end of the fifth channel waveguide, one end is connected to the combining side of the second Y-branch waveguide, and the other A sixth channel waveguide formed on the second substrate so that its end is exposed at the other end face of the second substrate, and one end is exposed at one end face of the second substrate and faces the fourth channel waveguide. To the second
A plurality of seventh channel waveguides formed on the substrate, a multiplexer connected to the other end of the seventh channel waveguide to combine signal lights of different wavelengths, and one end connected to the multiplexer and the other end Is the second
An eighth channel waveguide connected to the other branch waveguide of the Y branch waveguide, a second channel waveguide provided between the other end surface of the first substrate and one end surface of the second substrate, and a fifth channel waveguide A variable gain equalizing filter comprising phase control means for controlling the phase of the demultiplexed signal light between the channel waveguide and between the fourth channel waveguide and the seventh channel waveguide. 6. A polarization-maintaining optical fiber is used so that one end of the first channel waveguide and the other end of the sixth channel waveguide have the same polarization direction of light incident on these channel waveguides. Connect it to the two terminals of the polarizing beam splitter,
The variable gain equalization filter according to claim 5, wherein a three-terminal circulator into which wavelength-multiplexed signal light is incident is connected to the remaining terminals of the polarization beam splitter. 7. The phase control means includes a transparent electrode plate covering one end surface of the second substrate, and a second channel waveguide and an end surface of each fourth channel waveguide exposed on the other end surface of the first substrate. A plurality of transparent electrode pieces for covering, an alignment film for covering the other end surface of the first substrate and one end surface of the second substrate, respectively,
A sealing member that covers the other end face side of the first substrate and one end face side of the second substrate so that a sealed space is formed between the substrate and the second substrate, and a liquid crystal filled in the sealed space. 7. The variable gain equalization filter according to claim 5, which has.