JP2011059588A - Optical waveguide - Google Patents

Abstract

The object of the present invention is to provide a grooved ridge structure type optical waveguide in which the birefringence does not fluctuate even in a high temperature and high humidity test (85 ° C., 85%), and the polarization dependent frequency difference (PDf) is long-term. A highly reliable optical waveguide that does not fluctuate at the same time is provided.
An optical waveguide according to the present invention is a part of an optical waveguide manufactured on a substrate, wherein a part of the optical waveguide is provided with a pair of grooves on both sides of the optical waveguide, and the groove is provided. When the groove interval at which the birefringence value of the optical waveguide is minimized is W, the groove interval is W or when the groove depth distance is H, The interval is equal to H.
[Selection] Figure 1

Description

  The present invention relates to an optical waveguide in which a change in birefringence with time is suppressed and a Mach-Zehnder interferometer using the same.

  In an optical waveguide component used for optical communication, a Mach-Zehnder interferometer circuit (hereinafter referred to as MZI) is widely used as an optical attenuator and a DPSK signal receiving circuit, and is an important circuit. This consists of two couplers, an arm waveguide connecting them, and a thin film heater formed on the arm waveguide. FIG. 11 shows a Mach-Zehnder interferometer circuit 1100 when a multimode interferometer (MMI) is used for the coupler. In FIG. 11, the Mach-Zehnder interferometer circuit 1100 includes an optical waveguide 1101, a multimode interferometer 1102, and a heater 1103.

In the following, the operating principle of the Mach-Zehnder interferometer and its polarization dependence will be briefly described.
When the input I1 → output O1 is defined as a through path, and the input I1 → output O2 is defined as a cross path, their optical outputs (O ^THROUGH , O ^CROSS ) can be described by the following equations according to a known interference principle. (Here, the coupling rate of the coupler is 50%.)

Here, I ₀ is the light intensity of the input light, n is the effective refractive index, ΔL is the difference in length between the two arm waveguides, f is the optical frequency, and c is the speed of light.

  For example, in the case of a DPSK receiving circuit, after being separated by a coupler at the front stage, the optical signal propagating through one arm waveguide is compared with the other signal, delayed by 1 bit, and then interfered by a coupler at the rear stage. , Phase detection. At this time, in order to give a 1-bit delay, it is necessary to set a difference in length (ΔL) between the two arm waveguides. In addition, the heater 1103 is used to correct a shift in the delay amount.

  As a method for manufacturing an optical waveguide used in such a device, for example, the following method is available.

  Using a flame deposition method, a lower under cladding layer mainly composed of quartz glass and a core layer obtained by adding germanium to quartz glass are deposited on a silicon substrate. Then, the core layer is patterned by photolithography and reactive ion etching, and an overcladding layer is deposited again using a flame deposition method to produce a buried optical waveguide.

Usually, such an optical waveguide has birefringence due to the difference in the shape of the core and the thermal expansion coefficient between the substrate and the clad. That is, the effective refractive index (n _TE , n _TM ) of the TM polarized wave having the electric field direction perpendicular to the substrate and the TE polarized wave having the electric field direction parallel to the substrate is different, and the birefringence is B = n _TE −. n _TM . Due to the difference (ΔL) between the birefringence and the lengths of the two arm waveguides, a difference in delay amount depending on the polarization occurs, and polarization dependency occurs. Here, this polarization dependency can be expressed by the following equation as an optical path length difference Δ (BL) depending on the polarization.

Here, l ₁ and l ₂ are line coordinates along two arm waveguides, respectively. Further, ∫Bdl ₁ and ∫Bdl ₂ are line integrals along the birefringence arm waveguide.

  Since the optical path length difference Δ (BL) depending on the polarization has a finite value, it causes a polarization dependent loss (PDL) and a polarization dependent frequency difference (PDf), and the signal quality is greatly deteriorated. Here, PDf is an amount defined by BΔL / λ · FSR and indicates a difference in optical frequency having the same phase.

  In order to eliminate these polarization dependencies, a DQPSK receiving circuit in which grooves are formed on both sides of a waveguide and birefringence control is performed has been proposed (see Non-Patent Document 1). The schematic is shown in FIG. This is a DQPSK receiving circuit, which has a configuration in which an optical signal is branched into two and each is connected to an MZI having an FSR of 21.5 GHz. In FIG. 12, the DQPSK receiving circuit 1200 that has performed birefringence control includes an optical waveguide 1201, a multimode interferometer 1202, a Y branch 1203, a heater 1204, a groove 1205, and a half-wave plate 1206.

Next, a method for eliminating polarization dependence using a groove will be briefly described. Δ (BL) where B _{0 is} the birefringence of a normal waveguide without a groove, B _{1 is} the length of the groove, and B ₁ is the birefringence of a waveguide having a groove (ridge structure type optical waveguide). Is given by:

  By designing the groove interval (ridge width) and the length of the heat insulating groove so that the above equation becomes zero, polarization independence can be achieved. In addition, a heater 1204 is formed between these grooves, and is also used as a heat insulating groove for efficiently transmitting heat generated by heating the heater to the waveguide. In general, the power consumption when phase control is performed via a thermo-optic effect by heating a heater requires, for example, several hundred mW to move the phase of π, and a heat insulating groove is formed in the vicinity of the heater By doing so, low power consumption can be realized.

2009 IEICE General Conference C-3-46 "Integrated polarization beam splitter using waveguide birefringencedependence on waveguide core width", Electronics Letters, Volume 37, Issue 25, pp. 1517-1518

  However, the MZI having a ridge structure type optical waveguide having grooves as described above has the following problems.

  In the DPSK receiving circuit, the birefringence of a ridge structure type optical waveguide having a groove changes when a high temperature and high humidity test (85 ° C. and 85%) is performed. As a result, in the MZI type DPSK receiving circuit or the MZI type DQPSK receiving circuit, the polarization dependent frequency difference (PDf) fluctuates over a long period of time, which causes a problem in reliability.

  In order to solve the above problems, an optical waveguide according to the present invention is an optical waveguide manufactured on a substrate, wherein a pair of grooves are provided on both sides of the optical waveguide in a part of the optical waveguide, The groove interval is W, where W is the groove interval at which the birefringence value of the optical waveguide in the provided portion is minimized.

  In order to solve the above problems, an optical waveguide according to the present invention is an optical waveguide manufactured on a substrate, wherein a pair of grooves are provided on both sides of the optical waveguide in a part of the optical waveguide. When the depth distance is H, the groove interval is equal to H.

  Further, a heater is provided on a portion of the optical waveguide where the pair of grooves are provided on both sides.

  In order to solve the above-described problem, the Mach-Zehnder interferometer circuit of the present invention is connected to an optical branching portion that receives input light and outputs 2N (N: natural number) branching output light, and the optical branching portion. N first arm waveguides through which the N first branch output lights propagate respectively and the N second branch output lights that are connected to the optical branch portion and through which each of the N second branch output lights propagates. Propagating through the second arm waveguide, one of the N first branch output lights propagating through the N first arm waveguides, and the N second arm waveguides, N optical multiplexing circuits that respectively combine and interfere with one of the N second branched output lights corresponding to the one of the N first branched output lights. Each of the optical multiplexing portions includes the optical branching portion, one of the N first arm waveguides, An interferometer is formed with each of the second arm waveguides corresponding to one of the first arm waveguides, and the optical waveguide according to any one of claims 1 to 3 includes the N interferences. It is arranged in at least one of the first arm waveguide and the second arm waveguide constituting the meter.

  According to the present invention, in a ridge structure type optical waveguide in which grooves are formed, birefringence does not fluctuate even in a high temperature and high humidity test (85 ° C., 85%), and the polarization dependent frequency difference (PDf) does not fluctuate over a long period of time. A highly reliable optical waveguide can be provided. In addition, the birefringence fluctuation is smaller than the other ridge widths with respect to the ridge width deviation caused by the process error, and as a result, an optical waveguide having a high ridge width tolerance of the characteristics of the optical circuit can be provided.

1 is a schematic diagram of a DSPK receiving circuit as a first embodiment of the present invention. It is sectional drawing in line segment AA 'shown in FIG. It is a figure which shows PDf fluctuation | variation after the high temperature high humidity test (85 degreeC85%) 2000 hours of the 1st Example of this invention. It is a figure which shows the relationship between the birefringence of 1st Example of this invention, and a ridge width | variety. It is an example of a sectional view of a ridge structure type optical waveguide of the present invention. It is an example of a sectional view of a ridge structure type optical waveguide of the present invention. FIG. 7 is a schematic top view of a DPSK receiving circuit as a second embodiment of the present invention. FIG. 5 is a schematic top view of an optical attenuator as a third embodiment of the present invention. It is a figure which shows the PDL fluctuation | variation after 2000 hours of high temperature high humidity (85 degreeC85%) of this invention. It is a top schematic diagram of an attenuator as a 4th example of the present invention. 1 is a schematic diagram of a Mach-Zehnder interferometer circuit according to the prior art. It is a figure of the DQPSK receiving circuit which performed birefringence control by a prior art.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Example 1]
FIG. 1 is a schematic diagram of a DPSK receiving circuit 100 as a first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA ′ in FIG.

First, a specific configuration will be described.
In FIG. 1, the DPSK receiving circuit 100 includes two multimode interferometer couplers 102, two arm waveguides 101 sandwiched between the multimode interferometer couplers 102, and an arm waveguide 101. It comprises a polyimide wave plate 103 inserted into a groove 106 formed so as to be divided. This polyimide wave plate 103 has an optical principal axis orthogonal to the propagation direction and inclined by 45 degrees from the horizontal direction of the substrate, and the polarized wave propagating along the slow axis and the fast axis is a phase difference corresponding to a half wavelength of the design wavelength. Is given. The half-wave plate 103 functions as a polarization rotator that performs polarization conversion of TM polarization (or TE polarization) to TE polarization (or TM polarization). Since the MZI 100 has an FSR of 40 GHz, the length difference (ΔL) between the two arm waveguides 101 is 5.06 mm. Further, grooves 105 are formed on both sides of a part of the longer one of the two arm waveguides 101. The ridge width, which is the distance from the groove 105, was 40 μm. A thin film heater 104 is formed on the upper surface of the optical waveguide sandwiched between the grooves 105. This thin film heater is used to add a function as a phase shifter utilizing the thermo-optic effect, and is used for phase adjustment. Further, by forming the groove, the heating region is limited and low power consumption is realized. Next, the optimum length (L ₁ ) of the ridge structure type optical waveguide 101 will be described. The birefringence of the ridge width 40 μm is −8 × 10 ⁻⁴ (B ₁ ), and the birefringence of the normal buried optical waveguide 101 is 5.5 × 10 ⁻⁴ (B ₀ ). The difference is 5.11 mm (ΔL). Here, the optical path length difference Δ (BL) depending on the polarization can be expressed by the following equation.

Next, the polarization dependence can be suppressed by setting the above equation to zero. In other words, by designing L ₁ that satisfies Equation (6), the optical path length difference Δ (BL) depending on the polarization expressed by Equation (3) can be eliminated.

From the above, the design parameters are summarized as follows: B ₁ = −8e−4, ΔL = 5.11 mm, B = 5.5e−4, L ₁ = 2.08 mm.

Next, the reason why the ridge width is 40 μm will be described.
The buried optical waveguide 101 used in the present example includes an under cladding layer 501 mainly composed of SiO ₂ using a flame deposition method on a silicon substrate 201 and a core layer 203 in which GeO ₂ is added to SiO ₂ . After the core is processed, the core is processed into a desired shape, and then the over clad layer 502 is deposited. The relative refractive index difference between the core 203 and the clad 202 is 1.5%. Further, the thickness of the clad 202 composed of the under clad 501, the core 203 and the over clad 502 is 40 μm. In this, a groove 105 for forming a ridge structure is formed until the silicon substrate is exposed. That is, the depth of the groove 105 is 40 μm, which is the same as the thickness of the clad 202. Further, like the thickness of the clad 202, the ridge width was set to 40 μm. Here, the dependency of birefringence on the ridge width is shown in FIG. 4, and the differential value of the birefringence with respect to the ridge width is zero and minimal when the ridge width is 40 μm. At this time, the birefringence fluctuation is extremely insensitive to the ridge width fluctuation.

The mechanism of the birefringence behavior related to the ridge width dependence will be briefly described.
Stress is strongly involved in birefringence. The occurrence of birefringence is due to the fact that stress on the core 203 gives different refractive indexes to TE polarized light and TM polarized light through the photoelastic effect (stress birefringence). At that time, the main factors of the stress are the lateral compressive stress due to the difference in thermal expansion coefficient between the silicon substrate and the glass, and the longitudinal compressive stress due to the difference in thermal expansion coefficient between the over clad 502 and the core 203. In the quartz waveguide on the silicon substrate of the present invention, the lateral compressive stress is larger than the longitudinal compressive stress, and birefringence and polarization dependency occur. On the other hand, in the case of the ridge structure type optical waveguide 101 in which the groove 105 is provided in the vicinity of these optical waveguides, the stress in the vertical direction and the horizontal direction increases or decreases depending on the ridge width, and the birefringence obtains a minimum value at a certain ridge width.

Next, the relationship between high temperature and high humidity fluctuations and birefringence fluctuations will be briefly described.
When the ridge structure type optical waveguide is subjected to a humidity resistance test such as a high-temperature and high-humidity test, the etched surface such as the wall surface of the ridge structure is in a state where the glass is altered and the stress is released. In other words, only the glass on the wall surface is altered, showing birefringence fluctuations as if the ridge width was narrowed. The direction of increase / decrease in birefringence can be estimated from the characteristics shown in FIG. 4, and the sign is the same as that obtained by exchanging the sign of the differential value with respect to the ridge width of birefringence. In other words, the ridge structure having a ridge width of 40 μm in which the differential value with respect to the ridge width of the birefringence is zero can be said to be in a very stable state because the birefringence fluctuation due to the test becomes zero at a certain test time.

  This stable state is structurally equivalent to when the ridge width and the depth of the groove 105 are equal.

  As shown in FIG. 2, the clad 202 and the core 203 are formed on substrates having different thermal expansion coefficients, and the aspect ratio of the clad 202 and the core 203 is 1: 1. In order to fabricate this structure, the thickness of the clad 202, the depth of the groove 105, and the ridge width must all match. However, as shown in FIG. 5 and FIG. 6, even if the groove depth is deviated from the thickness of the clad 202, the effect of this patent can be obtained if the ridge width and the groove 105 depth are equal. . Further, if the ridge width is shifted by about 10% with respect to the depth of the groove 105, the same effect can be obtained. In this regard, with further explanation, this patent aims to use a ridge width that minimizes the variation of the birefringence with respect to the ridge width by forming a structure in which the ridge width and the depth of the groove 105 are equal. Yes. That is, even if the ridge width and the depth of the groove 105 are not equal, the same effect can be obtained by using a parameter that can obtain a minute value of birefringence as a result of changing the structural parameter such as the ridge width. It is clear.

  In this embodiment, the clad 202 is composed of the under clad 501, the core 103, and the over clad 502. However, when glass having the same composition as that of the over clad 502 is separately deposited on the upper surface of the over clad 502, It is important that the depth of the groove 105 including the ridge width is equal.

  FIG. 3 shows the time-dependent change of the polarization dependent frequency difference (PDf) after leaving the DPSK receiving circuit 100 of this example in a constant temperature bath at 85 ° C. and 85% for 2000 hours. The circuit with a ridge width of 40 μm had a PDf variation of about 50 MHz. On the other hand, in a circuit with a ridge width of 80 μm, the PDf variation is 500 MHz, and it can be confirmed that the PDf variation is suppressed at 40 μm.

  Another effect of this patent is that the birefringence fluctuation is smaller than the other ridge widths with respect to the ridge width shift caused by the process error. As a result, it can be said that the ridge width tolerance of the characteristics of the optical circuit is high.

[Example 2]
FIG. 7 is a schematic diagram of a DPSK receiving circuit 700 as a second embodiment of the present invention.
Since the configuration is similar to that of the first embodiment, only differences will be described.
The difference is that the ridge structure type optical waveguide 701 is composed of two different ridge widths. One ridge width is 20 μm, and the other ridge width is 80 μm. The thickness of the clad 202 is 40 μm, and the depths of the grooves 705 and 706 are also 40 μm. One ridge width is shorter than the depth of the grooves 705 and 706, and the other ridge width is longer than the depth of the grooves 705 and 706. The birefringence is −5.7 × 10 ⁻⁴ for ridge widths of 20 μm and 80 μm. Here, B _n and B _w are birefringence with a ridge width of 20 μm and 80 μm, and L _n and L _w are waveguide lengths with a ridge width of 20 μm and 80 μm. Next, when the difference in length between the two arms 701 is ΔL and the birefringence of a normal waveguide that is not a ridge structure is B ₀ , the optical path length difference depending on the polarization is satisfied by satisfying Equation (7). (Δ (BL)) can be eliminated.

The birefringence fluctuation after 2000 hours at a high temperature and high humidity test (85 ° C. and 85%) is 5 × 10 ⁻⁵ (ΔB _n ) when the ridge width is 20 μm, and −1 × 10 ⁻⁵ (ΔB _w when the ridge width is 80 μm. Therefore, the birefringence fluctuation can be suppressed by determining each length so as to satisfy the following expression. That is, the birefringence fluctuation can be eliminated as a whole by canceling one birefringence fluctuation with the other birefringence fluctuation.

  Equation (8) can be paraphrased as a value obtained by integrating the birefringence fluctuation after the test in the propagation direction of the waveguide, and it is important that it becomes zero.

  From the above equations (7) and (8), the length of the ridge width of 20 μm was set to 0.42 mm, and the length of the ridge width of 80 μm was set to 2.09 mm. By selecting this length, initial PDf is suppressed, and PDf fluctuation is also suppressed at the same time.

  The fluctuation amount of the polarization dependent frequency difference (PDf) after leaving the DPSK receiving circuit 700 of this example in a constant temperature bath at 85 ° C. and 85% for 2000 hours was about 55 MHz. For example, when the ridge width is 80 μm, the PDf fluctuation is 500 MHz. Compared with this, it can be confirmed that the PDf fluctuation is suppressed in this embodiment.

  The characteristics of this configuration are shown below. This configuration is capable of extremely narrowing one ridge width. By forming the heater 704 in a narrow ridge width and functioning as a phase shifter, it is possible to achieve much lower power consumption than the phase shifter having a ridge width of 40 μm as used in the first embodiment.

  Another effect of this patent is that the birefringence fluctuation is small with respect to the ridge width shift caused by the process error. Specifically, in the etching process for forming the ridge structure, a process error occurs in the width of the groove. In this patent, ridge widths of 20 μm and 80 μm are used in which the sign of birefringence fluctuation with respect to the ridge width is reversed, and there is an effect of canceling out birefringence due to groove width shift.

  In Examples 1 and 2 described above, MZI having an FSR of 40 GHz was used. In addition, it is obvious that the same effect can be expected with other FSRs such as 20 GHz and 100 GHz.

[Example 3]
FIG. 8 is a schematic diagram of a variable optical attenuator 800 manufactured as the third embodiment of the present invention.
First, a specific configuration will be described.
In FIG. 8, the variable optical attenuator 800 is formed on two directional couplers 802, two arm waveguides 801 sandwiched between the directional couplers 802, and the arm waveguides 801. It consists of a thin film heater 803 and grooves 804 formed on both sides of the arm waveguide 801. The variable optical attenuator 800 is designed with an optical path length difference (ΔL) of 0.52 μm, which corresponds to half of the signal wavelength. The thin film heater 803 has a function as a phase shifter using a thermo-optic effect. Further, by forming the groove, the heating region is limited and low power consumption is realized.

Next, the structure of a ridge type optical waveguide composed of grooves formed in this will be described.
As in the first embodiment, the buried optical waveguide used in this embodiment includes an under clad 501, a core 203, and an over clad 502 using silicon as a substrate 201. The thickness of the clad 202 was 40 μm, and the ridge width was also 40 μm.

  FIG. 9 shows a change with time in polarization dependent loss (PDL) at 25 dB attenuation after the variable optical attenuator 800 of this example is left in a constant temperature bath at 85 ° C. and 85% for 2000 hours. Even after 2000 hours, the PDL fluctuation was 0.1 dB or less. On the other hand, when the ridge width is 20 μm, the PDL variation is 0.45 dB, and when the ridge width is 40 μm, it can be confirmed that the PDL variation is suppressed.

This is because the birefringence fluctuation is suppressed. The mechanism will be explained briefly.
Polarization coupling occurs in the directional coupler 802, and the PDL varies depending on the birefringent waveguide integral value between the directional couplers 802. That is, when the birefringence of the ridge-type optical waveguide in which the grooves 804 are formed on both sides is changed, the waveguide integral value of the birefringence described above changes and appears as PDL fluctuation. Further, by making the ridge width the same as the depth of the groove 804 by the same mechanism as in the first embodiment, birefringence fluctuations are suppressed and PDL fluctuations are suppressed.

[Example 4]
FIG. 10 is a schematic diagram of a variable optical attenuator 1000 as a fourth embodiment of the present invention.
The configuration is almost the same as that of the third embodiment, but the difference is that the ridge structure type optical waveguide 1001 is constituted by two different ridge widths. The thickness of the clad 202 is 40 μm, and the depth of the groove 804 is 40 μm. One ridge width is 20 μm and the other ridge width is 80 μm. One is shorter than the depth of 40 μm of the groove 804 and the other is longer. The birefringence is −5.7e-4 for both ridge widths of 20 μm and 80 μm. The birefringence fluctuation after 2000 hours at a high temperature and high humidity test (85 ° C. and 85%) is 5e-5 (ΔB _n ) when the ridge width is 20 μm, and −1e-5 (ΔB when the ridge width is 80 μm. since a _w), the length of each of the ridge structure-type optical waveguide, and L _n at the ridge width 20 [mu] m, when the L _w in ridge width 80 [mu] m, was set to satisfy equation (9). Thus, the birefringence fluctuation can be eliminated as a whole by canceling out one birefringence fluctuation with the other birefringence fluctuation.

That is, 0.3 mm when the ridge width is 20 μm and 1.7 mm when the ridge width is 80 μm.
After the variable optical attenuator of this example was left in a constant temperature bath at 85 ° C. and 85% for 2000 hours, the fluctuation amount of the polarization dependent loss difference (PDL) was 0.1 dB or less. For example, when the ridge width is 20 μm, the PDL fluctuation is 0.45 dB, and it can be confirmed that the PDL fluctuation of this embodiment is suppressed as compared with it.

  A feature of this configuration is that one ridge width can be extremely narrow. By forming the heater 1003 in a ridge structure type waveguide having a narrow ridge width and functioning as a phase shifter, the power consumption is much lower than that of the phase shifter having a ridge width of 40 μm as used in the fourth embodiment. Can be realized.

  As another application circuit, a polarization separation / synthesis circuit (PBS / PBC) as shown in Non-Patent Document 2 can be considered. This realizes the function as a polarization separation / synthesis circuit (PBS / PBC) by designing the birefringence of the arm waveguide 1001 of the Mach-Zehnder interferometer 1002 to a desired value. Since the birefringence can be set to a desired value also in the ridge structure type optical waveguide, a similar circuit can be realized. Furthermore, by applying this patent to this, it is possible to suppress or eliminate fluctuations of birefringence at high temperature and high humidity (85 ° C. 85%), so that long-term fluctuations in the polarization extinction ratio of PBS / PBC can be suppressed or eliminated. Can be easily inferred.

101, 701, 801, 1001 Optical waveguide 102, 702, 802, 1002 Multimode interferometer 103, 703 Half-wave plate 104, 704, 803, 1003 Heater 105, 705, 706, 804, 1004, 1005 Groove 201 Silicon substrate 202 Grad 203 core 501 under clad 502 over clad

Claims (4)

In an optical waveguide fabricated on a substrate,
A part of the optical waveguide is provided with a pair of grooves on both sides of the optical waveguide,
When the interval between the grooves is such that the value of the birefringence of the optical waveguide in the portion where the grooves are provided is minimized, W
An optical waveguide characterized in that an interval between the grooves is W. In an optical waveguide fabricated on a substrate,
A part of the optical waveguide is provided with a pair of grooves on both sides of the optical waveguide,
When the distance of the depth of the groove is H,
An optical waveguide, wherein an interval between the grooves is equal to H.   The optical waveguide according to claim 1, wherein a heater is provided on a portion of the optical waveguide where the pair of grooves are provided on both sides. An optical branching unit that receives input light and outputs 2N (N: natural number) branching output light;
N first arm waveguides that are connected to the optical branching portion and through which each of the N first branched output lights propagates,
N second arm waveguides that are connected to the optical branching part and through which the N second branched output lights respectively propagate;
One of the N first branch output lights propagating through the N first arm waveguides, and the N second arm waveguides propagating through the N second arm waveguides. N optical combining circuits that respectively combine and interfere with one of the N second branched output lights corresponding to the one of the light,
Each of the N optical multiplexing portions includes the optical branching portion, one of the N first arm waveguides, and the second arm corresponding to one of the first arm waveguides. Each interferometer is configured with one of the waveguides,
4. The optical waveguide according to claim 1, wherein the optical waveguide is disposed in at least one of the first arm waveguide and the second arm waveguide constituting the N interferometers. A Mach-Zehnder interferometer circuit.

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