JP2020194092A - Wavelength multiplex/demultiplexer, optical transmitter, and optical receiver - Google Patents

Abstract

To provide a wavelength multiplexer/demultiplexer, an optical transmitter and an optical receiver with which it is possible to further expand an effective wavelength band.SOLUTION: The wavelength multiplexer/demultiplexer includes three delay interferometer 110, in which two delay interferometers in a second stage are respectively connected to one delay interferometer in a first stage. The delay interferometers include a pair of optical couplers 130, 140 equipped with input/output ports, a first arm waveguide 121 and a second arm waveguide 122 which are connected between the pair of optical couplers and has different optical path length one another, and a phase collection area 123 provided in either of the first or second arm waveguide. The difference between the optical path lengths of the first and second arm waveguides of a delay interferometer in the (k+1)th stage is 1/2 of the difference between the optical path lengths of the first and second arm waveguides of a delay interferometer in the k-th stage. The phase change amount of the phase correction area of a delay interferometer in each stage is large enough to cancel out a phase change due to an optical coupler in each stage.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to a wavelength combiner / demultiplexer, an optical transmitter and an optical receiver.

In recent years, as a promising technology for large-capacity interconnects, the introduction of wavelength division multiplexing (WDM) technology into the silicon (Si) photonics platform has greatly improved the transmission capacity per optical wiring. Is attracting attention. In order to transmit and receive the WDM optical signal in the Si chip, a Si thin line waveguide type wavelength division multiplexing / demultiplexing element that causes the WDM optical signal to combine (MUX) and demultiplex (DeMUX) as necessary is provided.

In addition to low loss and low crosstalk, expansion of the operating wavelength band is important as a condition required for a wavelength combining / demultiplexing element. That is, in order to relax the wavelength accuracy of the light source, it is strongly required to expand the wavelength interval (channel interval) Δν in the WDM signal. As a result, it is required to expand the wavelength band that operates as a wavelength combination / demultiplexing element. The expansion of the effective wavelength band includes not only the expansion of the bandwidth corresponding to the number of WDM wavelengths but also the securing of the further bandwidth to the short wavelength side and the long wavelength side. The expansion of the effective wavelength band enables further expansion of fabrication tolerance.

So far, as silicon waveguide type wavelength junction gratings, ring resonators (MRR), delay Mach-Zehnder interferometers (DMZI), and arrayed waveguide gratings (AWG) have been used. ) Based devices have been reported.

However, it is difficult for conventional wavelength combined / demultiplexing devices to sufficiently respond to the further expansion of the effective wavelength band in recent years.

Japanese Unexamined Patent Publication No. 2016-212173

D. W. Kim, A. Barkai, R. Jones, N. Elek, H. Nguyen, and A. Liu, “Silicon-on-insulator eight-channel optical multiplexer based on a cascade of asymmetric Mach-Zehnder interferometers,” Optics Letters 33 (5), 530-532 (2008) J. Van Campenhout, W. M. J. Green, S. Assefa, and Y. A. Vlasov, “Low-power, 2 × 2 silicon electro-optic switch with 110-nm bandwidth for broadband reconfigurable optical networks,” Optics Express 17, 24020-24029 (2009) F. Horst, W. M. J. Green, S. Assefa, S.M. M. Shank, Y. A. Vlasov and Bert Jan Offrein, “Cascaded Mach-Zehnder wavelength filters in silicon photonics for low loss and flat pass-band WDM (De-) Multiplexing,” Optics Express 21, 11652-11658 (2013) S. -H. Jeong, S. Tanaka, T. Akiyama, S. Sekiguchi, Y. Tanaka, and K. Morito, “Flat-topped and low loss silicon-nanowire-type optical MUX / DeMUX multiplexing multi-stage microring resonator assisted delayed Mach-Zehnder interferometers,” Optics Express 20, 26000-26011 (2012)

An object of the present disclosure is to provide a wavelength combining / demultiplexing element, an optical transmitter, and an optical receiver capable of further expanding the effective wavelength band.

According to one form of the present disclosure, there are (2 ^N- 1) delay interferometers in the N stage (N is a natural number of 2 or more), and 2 ^k-1 units in the kth stage (k <N). to the delay interferometer, ^(k + 1) 2 k pieces of the delay interferometer stage is vertical connection, the delay interferometer includes a pair of optical couplers having input and output ports, said pair of optical couplers A phase correction region provided in one of a first arm waveguide and a second arm waveguide having different optical path lengths and different optical path lengths, and one of the first arm waveguide and the second arm waveguide. And, the optical coupler comprises a pair of directional couplers, a third arm waveguide and a fourth arm waveguide connected between the pair of directional couplers, and the above. It has a phase shifter provided on one of the third arm waveguide and the fourth arm waveguide, and has the optical path length of the first arm waveguide in the delay interferometer in the (k + 1) stage. The difference from the optical path length of the second arm waveguide is one of the difference between the optical path length of the first arm waveguide and the optical path length of the second arm waveguide in the k-th stage delay interferometer. A wavelength junction demultiplexing element is provided, which is / 2, and the phase change amount in the phase correction region of the delay interferometer in each stage is a value that cancels the phase fluctuation caused by the optical coupler in each stage.

According to the present disclosure, the effective wavelength band can be further expanded.

It is a figure which shows the structure of the wavelength compound demultiplexing element of the 1st reference example. It is a figure which shows the spectral characteristic of the wavelength combined / demultiplexing element of the 1st reference example. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-1 in the 1st reference example. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-2 in the 1st reference example. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-3 in the 1st reference example. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-4 in the 1st reference example. It is a figure which shows the structure of the wavelength compound demultiplexing element which concerns on 1st Embodiment. It is a figure which shows the structure of the wavelength compound demultiplexing element which concerns on 2nd Embodiment. It is sectional drawing (the 1) which shows the structure of the optical waveguide which constitutes the wavelength combined / demultiplexing element which concerns on 2nd Embodiment. FIG. 2 is a cross-sectional view (No. 2) showing a structure of an optical waveguide constituting a wavelength combination / demultiplexing element according to a second embodiment. FIG. 3 is a cross-sectional view (No. 3) showing a structure of an optical waveguide constituting a wavelength combination / demultiplexing element according to a second embodiment. It is sectional drawing which shows the modification of the structure of an optical waveguide. It is a figure which shows the spectral characteristic of the wavelength combined / demultiplexing element which concerns on 2nd Embodiment. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-1 in the 2nd Embodiment. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-2 in the 2nd Embodiment. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-3 in the 2nd Embodiment. It is a figure which shows the spectral characteristic of the light wavelength component emitted from the output channel Ch-4 in the 2nd Embodiment. It is a figure which shows the structure of the wavelength compound demultiplexing element which concerns on 3rd Embodiment. It is a figure which shows the structure of the wavelength compound demultiplexing element which concerns on 4th Embodiment. It is a figure which shows the structure of the wavelength compound demultiplexing element which concerns on 5th Embodiment. It is a figure which shows the relationship between the spectral characteristic of the delay interferometer and the spectral characteristic of a ring resonator in the fifth embodiment. It is a figure which shows the structure of the wavelength compound demultiplexing element of the 2nd reference example. It is a figure which shows the relationship of the band R1 to R3. It is a figure which shows the spectral characteristic of the band R1 of the 2nd reference example. It is a figure which shows the spectral characteristic of the band R2 of the 2nd reference example. It is a figure which shows the spectral characteristic of the band R3 of the 2nd reference example. It is a figure which shows the spectral characteristic of the band R1 of the 3rd reference example. It is a figure which shows the spectral characteristic of the band R2 of the 3rd reference example. It is a figure which shows the spectral characteristic of the band R3 of the 3rd reference example. It is a figure which shows the spectral characteristic of the band R1 of 5th Embodiment. It is a figure which shows the spectral characteristic of the band R2 of 5th Embodiment. It is a figure which shows the spectral characteristic of the band R3 of 5th Embodiment. It is a figure which shows the continuous wavelength spectrum characteristic of the wavelength combination demultiplexing element of the 2nd reference example. It is a figure which shows the continuous wavelength spectrum characteristic of the wavelength compound demultiplexing element which concerns on 5th Embodiment. It is a figure which shows the structure of the optical transmission device which concerns on 6th Embodiment. It is a figure which shows the structure of the optical transmission device which concerns on the modification of 6th Embodiment. It is a figure which shows the structure of the optical receiver device which concerns on 7th Embodiment. It is a figure which shows the structure of the optical receiver device which concerns on the modification of 7th Embodiment.

(First reference example)
First, the first reference example will be described. FIG. 1 is a diagram showing a configuration of a wavelength combining / demultiplexing element of the first reference example. The wavelength merging / demultiplexing element of the reference example is a 1 × 4 Ch delayed Mach-Zehnder interferometer (DMZI) type wavelength merging / demultiplexing element.

As shown in FIG. 1, the wavelength merging / demultiplexing element 900 of the reference example has three delay interferometers 910 in two stages and four output channels Ch-1 to Ch-4. Two delay interferometers 910 (910B, 910C) of the second stage are vertically connected to one delay interferometer 910 (910A) of the first stage.

The delay interferometer 910 has a pair of wavelength insensitive couplers (WINCs) 930 and 940 with input / output ports and a delay line 920 connected between the pair of WINS 930 and 940. .. The delay line 920 has a first arm waveguide 921 and a second arm waveguide 922 having different optical path lengths, and a phase correction region 923 is provided in the second arm waveguide 922.

The WINC 930 has a pair of directional couplers (DCs) 931, 935 and two arm waveguides 932, 933 connected between the pair of DC 931, 935. The WNC940 has a pair of DC941 and 945 and two arm waveguides 942 and 943 connected between the pair of DC941 and 945. The arm waveguide 933 is provided with a phase shifter 934, and the arm waveguide 943 is provided with a phase shifter 944. The phase shift amount of the phase shifters 934 and 944 is +0.45π [rad] to +0.50π [rad].

For the second-stage delay interferometer 910 (910A, 910B), the description of the code is omitted.

The difference (delay length) ΔL ₂ between the optical path length of the first arm waveguide 921 and the optical path length of the second arm waveguide 922 in the _second- stage delay interferometer 910 is that in the first-stage delay interferometer 910. the first optical path length of the arm waveguide 921 and the difference between the optical path length of the second arm waveguide 922 (delay length) is 1/2 of the [Delta] L _1. Neither the delay lengths ΔL ₁ and ΔL ₂ include a delay amount corresponding to the phase change amount due to the phase correction region 923.

The phase change amount (δφ _z1 ) of the phase correction region 923 of the first-stage delay interferometer 910A is + 1.0π [rad]. Of the two delay interferometers 910 in the second stage, the phase change amount (δφ _z2 ) of the phase correction region 923 of the delay interferometer 910B connected to the output channels Ch-1 to Ch-2 is 0 [rad]. Of the two delay interferometers 910 in the second stage, the phase change amount (δφ _z3 ) of the phase correction region 923 of the delay interferometers 910B connected to the output channels Ch-3 to Ch-4 is + 0.5π [rad]. is there. Hereinafter, the delay length corresponding to the phase change amount (δφ _X ) is referred to as δL (δφ _X ).

The delay length L _{1 on} the delay line 920 of the delay interferometer 910A, the delay length L _{2 on} the delay line 920 of the delay interferometer 910B, and the delay length L _{3 on} the delay line 920 of the delay interferometer 910C, including the phase correction region 923, are , Expressed by the following formulas (1) to (5).
L ₁ = ΔL ₁ + δL (δφ _z1 ) = ΔL ₁ + δL (+ 1.0π) ... (1)
L ₂ = ΔL ₂ + δL (δφ _z2 ) = ΔL ₂ + δL (0) ・ ・ ・ (2)
L ₃ = ΔL ₂ + δL (δφ _z3 ) = ΔL ₂ + δL (+ 0.5π) ・ ・ ・ (3)
_{ΔL 2 = ΔL 1/2 ···} (4)
ΔL ₁ = (λ _DMZI × m) / N _eq ... (5)

Here, λ _DMZI, m and _{N eq} is the central wavelength, the diffraction effective refractive index of the order and Si wire waveguide of the delay interference section. Further, the wavelength interval (channel interval) Δν is determined by the following mathematical formula (6).
Δν = λ _DMZI ² / (2 × N _Gr × ΔL ₁ ) ・ ・ ・ (6)

Here, N _Gr is a group refractive index defined by the group velocity of propagating light.

FIG. 2 shows the spectral characteristics of the wavelength division multiplexing element 900 of the first reference example assuming a WDM signal having a wavelength interval Δν (about 6.4 nm in the 1.5 μm band) corresponding to a frequency of 800 GHz. The horizontal axis of FIG. 2 shows the deviation from the center wavelength. As shown in FIG. 2, the peak transmission loss can be suppressed to 1 dB or less and the wavelength crosstalk can be suppressed to -15 dB or less in the wavelength range of approximately 100 nm. If the width of the wavelength band having a peak transmission loss of 1 dB or less and a wavelength crosstalk of −15 dB or less is defined as an effective wavelength bandwidth, the effective wavelength bandwidth W of the first reference example is about 100 nm. That is, according to the first reference example, the transmission characteristics of all output channels can be kept substantially constant while suppressing excessive loss in the wavelength range of approximately 100 nm.

However, the effective wavelength bandwidth of 100 nm cannot sufficiently respond to the further expansion of the effective wavelength bandwidth in recent years. Therefore, the inventor of the present application has conducted diligent studies in order to clarify the reason why the effective wavelength bandwidth is limited to 100 nm in the structure of the first reference example.

In the wavelength combination / demultiplexing element 900 of the first reference example, as shown in FIG. 2, λ ₁ , λ ₂ , λ ₃ , and λ ₄ are arranged from the short wavelength side to the long wavelength side with respect to the light wavelength component. By definition, the four output channels Ch-1 to Ch-4 emit in the order of λ ₂ , λ ₃ , λ ₁ , and λ ₄ . Analysis of the spectral characteristics of the light wavelength components emitted from each of these output channels Ch-1 to Ch-4 revealed that there is a large distortion in these spectral characteristics. FIG. 3A is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-1. FIG. 3B is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-2. FIG. 3C is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-3. FIG. 3D is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-4. As shown in FIGS. 3A to 3D, when the wavelength exceeds ± 50 nm from the center wavelength, the spectral characteristics include a large distortion. The inventor of the present application has conducted further diligent studies in order to eliminate such distortion of spectral characteristics, and has arrived at the following embodiment.

Hereinafter, embodiments will be specifically described with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration may be designated by the same reference numerals to omit duplicate explanations.

(First Embodiment)
The first embodiment will be described. FIG. 4 is a diagram showing a configuration of a wavelength combining / demultiplexing element according to the first embodiment. The wavelength merging / demultiplexing element according to the first embodiment is a 1 × 4 Ch wavelength merging / demultiplexing element.

As shown in FIG. 4, the wavelength combining / demultiplexing element 100 according to the first embodiment has (2 ^N -1) number of delay interferometers 110 (N is a natural number of 2 or more) in N stages. The 2 ^k-1 delay interferometers 110 in the kth stage (k <N) are vertically connected to the 2 ^k delay interferometers 110 in the (k + 1) stage. Here, a two-stage 1 × 4 Ch wavelength combined / demultiplexing element 100 is configured by using three delay interferometers 110.

The delay interferometer 110 has a pair of optical couplers 130, 140 provided with input / output ports and a delay line 120 connected between the pair of optical couplers 130, 140. The delay line 120 has a first arm waveguide 121 and a second arm waveguide 122 having different optical path lengths, and one of the first arm waveguide 121 and the second arm waveguide 122, here, A phase correction region 123 is provided in the second arm waveguide 122.

The optical coupler 130 has a pair of DC 131, 135 and two arm waveguides 132, 133 connected between the pair of DC 131, 135. The optical coupler has a pair of DCs 141 and 145 and two arm waveguides 142 and 143 connected between the pair of DCs 141 and 145. A phase shifter 134 is provided on one of the two arm waveguides 132 and 133, here on the arm waveguide 133, and on one of the two arm waveguides 142 and 143, here on the arm waveguide 143. A shifter 144 is provided. The phase shift amount (δφ _Coup ) of the phase shifters 134 and 144 is, for example, +0.45π [rad] to +0.50π [rad].

For the second-stage delay interferometer 110, the entry of the code is omitted.

The difference between the optical path length of the first arm waveguide 121 and the optical path length of the second arm waveguide 122 in the delay interferometer 110 of the (k + 1) stage, here the second stage, ΔL _{k + 1} is the kth stage. The difference between the optical path length of the first arm waveguide 121 and the optical path length of the second arm waveguide 122 in the delay interferometer 110 is 1/2 of ΔL _k . The delay lengths ΔL _k and ΔL _{k + 1} do not include the delay amount corresponding to the phase change amount due to the phase correction region 223.

The amount of phase change in the phase correction region 123 of the delay interferometer 110 in each stage is set to a value that cancels the phase fluctuation caused by the optical couplers 130 and 140 in each stage.

The wavelength combined / demultiplexing element 100 according to the first embodiment is, for example, a single crystal silicon provided on an embedded oxide layer (BOX layer) using an SOI (silicon on insulator) substrate by applying silicon photonics technology. A typical form is to process and form a layer.

An optical transmitter can be configured by using the wavelength combiner / demultiplexer 100 as a wavelength combiner and combining it with ^2N semiconductor lasers and ^2N light modulators.

Further, when the wavelength combined demultiplexing element 100 is used as a wavelength demultiplexing element and combined with ^2N light receiving elements, an optical receiving element can be configured. In this case, in order to prevent the influence of the polarization state of the wavelength division multiplexing (WDM) signal light, the light is divided into TE light and TM light by the polarizing beam splitter, and the TM light is TE by the polarizing rotator. It suffices to receive light after converting it into light. In that case, for example, 2 × ^2N light receiving elements are used.

According to the present disclosure, it is possible to realize a wavelength combined / demultiplexing device that reduces the wavelength dependence of the optical coupling rate, secures low loss property, and operates in a wide wavelength band of, for example, 160 nm or more.

(Second Embodiment)
A second embodiment will be described. FIG. 5 is a diagram showing a configuration of a wavelength combining / demultiplexing element according to the second embodiment. The wavelength demultiplexing element according to the second embodiment is a 1 × 4 Ch DMZI type wavelength demultiplexing element.

As shown in FIG. 5, the wavelength combining / demultiplexing element 200 according to the second embodiment has three delay interferometers 210 in two stages and four output channels Ch-1 to Ch-4. .. Two delay interferometers 210 (210B, 210C) in the second stage are vertically connected to one delay interferometer 210 (210A) in the first stage.

The delay interferometer 210 has a pair of WINS 230, 240 with input / output ports and a delay line 220 connected between the pair of WNC 230, 240. The delay line 220 has a first arm waveguide 221 and a second arm waveguide 222 having different optical path lengths, and one of the first arm waveguide 221 and the second arm waveguide 222, in this case, the first arm waveguide 222. A phase correction region 223 is provided in the arm waveguide 222 of 2.

The WINC 230 has a pair of DC 231 and 235 and two arm waveguides 232 and 233 connected between the pair of DC 231 and 235. The WINC 240 has a pair of DCs 241 and 245 and two arm waveguides 242 and 243 connected between the pair of DCs 241 and 245. A phase shifter 234 is provided on one of the two arm waveguides 232 and 233, here on the arm waveguide 233, and on one of the two arm waveguides 242 and 243, here on the arm waveguide 243, in phase. A shifter 244 is provided. The phase shift amount (δφ _Coup ) of the phase shifters 234 and 244 is, for example, +0.45π [rad] to +0.50π [rad].

For the second-stage delay interferometer 210 (210A, 210B), the description of the reference numeral is omitted.

The difference (delay length) ΔL ₂ between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 in the _second- stage delay interferometer 210 is that in the first-stage delay interferometer 210. the first optical path length of the arm waveguide 221 and the difference between the optical path length of the second arm waveguide 222 (delay length) is 1/2 of the [Delta] L _1. Neither the delay lengths ΔL ₁ and ΔL ₂ include the delay length corresponding to the amount of phase change due to the phase correction region 223.

The amount of phase change in the phase correction region 223 of the delay interferometer 210 in each stage is a value that cancels the phase fluctuation due to WNC 230 and 240 in each stage. For example, the phase change amount (δφ _a1 ) of the phase correction region 223 of the first-stage delay interferometer 210A is + δφ _PT [rad]. Of the two delay interferometers 210 in the second stage, the phase change amount (δφ _a2 ) of the phase correction region 223 of the delay interferometer 210B connected to the output channels Ch-1 to Ch-2 is + δφ _PT [rad]. .. Of the two delay interferometers 210 in the second stage, the phase change amount (δφ _a3 ) of the phase correction region 123 of the delay interferometers 210C connected to the output channels Ch-3 to Ch-4 is + 0.5π + δφ _PT [rad]. Is.

The delay length L _{1 on} the delay line 220 of the delay interferometer 210A, the delay length L _{2 on} the delay line 120 of the delay interferometer 210B, and the delay length L _{3 on} the delay line 120 of the delay interferometer 210C, including the phase correction region 223, are , It is expressed by the following formulas (7) to (9).
L ₁ = ΔL ₁ + δL (δφ _a1 ) = ΔL ₁ + δL (+ δφ _PT ) ・ ・ ・ (7)
L ₂ = ΔL ₂ + δL (δφ _a2 ) = ΔL ₂ + δL (+ δφ _PT ) ・ ・ ・ (8)
L ₃ = ΔL ₃ + δL (δφ _a3 ) = ΔL ₂ + δL (+ δφ _PT + 0.5π) ・ ・ ・ (9)

Note that δφ _PT is a correction value for suppressing phase fluctuations inside WINC 230 and 240 located before and after the delay interferometer 210, and as a result of simulation by the inventor of the present application, δφ _PT is the following mathematical formula. It can be represented by (10).
δφ _PT = (-δφ _Coup x 2)-{(0.5π-δφ _Coup ) x 2}
= -1.0π [rad] ・ ・ ・ (10)

Next, the structure of the optical waveguide constituting the wavelength combining and demultiplexing element 200 according to the second embodiment will be described. Here, the structure of the optical waveguide will be described together with a method for manufacturing the wavelength combining and demultiplexing element 200. 6A to 6C are cross-sectional views showing a structure of an optical waveguide constituting the wavelength combining / demultiplexing element 200 according to the second embodiment. In this method, the wavelength merging / demultiplexing element 200 is formed on the SOI substrate by using the Si photonics technique, but here, it will be described with reference to the cross-sectional structure of one waveguide section.

First, as shown in FIG. 6A, an SOI substrate in which a single crystal silicon layer 53 having a thickness of 220 nm is provided on a silicon substrate 51 via a SiO ₂ film 52 as a lower clad layer is prepared.

Next, as shown in FIG. 6B, a resist pattern 54 having a waveguide stripe structure having a width of 450 nm is formed by an exposure process, and dry etching is performed to form a core layer 55 to form a channel waveguide structure.

Next, as shown in FIG. 6C, after removing the resist pattern 54, the SiO ₂ film 56 is deposited on the entire surface to form an upper clad layer.

As shown in FIG. 7, when the core layer 55 is formed, a rib waveguide structure may be formed by leaving a slab portion 57 having a height of 50 nm. By forming the slab portions 57 on both sides of the core layer 55 in this way, the refractive index of the waveguide can be changed by injecting a current.

According to the wavelength combination / demultiplexing element 200 configured in this way, the phase fluctuations generated by the two WINS 230 and 240 are corrected, distortion of the spectral characteristics is suppressed, and a wide effective wavelength bandwidth can be obtained.

Here, the relationship between the delay lengths of the delay interferometers 210 and 910 at the delay lines 220 and 920 will be described with reference to the first reference example. Table 1 below summarizes the delay lengths of the delay lines 120 and 920 including the phase correction regions 223 and 923.

Assuming a WDM signal with a wavelength interval of Δν (about 6.4 nm in the 1.5 μm band) corresponding to a frequency of 800 GHz, ΔL ₁ is about 44 μm and ΔL ₂ is about 22 μm from equations (4) to (6). .. The delay length corresponding to + 1.0π [rad] is about 0.33 μm, and the delay length corresponding to + 0.5π [rad] is about 0.16 μm. Further, assuming that the phase shift amount (δφ _Coup ) of the phase shifters 234 and 244 is, for example, + 0.46π [rad], the correction value (+ δφ _PT ) in the first embodiment is + 1.0π [rad]. The corresponding delay length is about 0.33 μm.

Therefore, in the first reference example, the delay lengths L ₁ , L ₂ , and L ₃ are about 44.33 μm, about 22 μm, and about 22.16 μm, respectively. Further, in the first embodiment, the delay lengths L ₁ , L ₂ , and L ₃ are about 44.33 μm, about 22.33 μm, and about 22.49 μm, respectively.

FIG. 8 shows the spectral characteristics of the wavelength division multiplexing / demultiplexing element 100 when a WDM signal having a wavelength interval Δν (about 6.4 nm in a 1.5 μm band) corresponding to a frequency of 800 GHz is assumed. The horizontal axis of FIG. 8 shows the deviation from the center wavelength. Further, FIGS. 9A to 9D show the spectral characteristics of the light wavelength components emitted from the output channels Ch-1 to Ch-4. FIG. 9A is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-1. FIG. 9B is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-2. FIG. 9C is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-3. FIG. 9D is a diagram showing the spectral characteristics of the light wavelength component emitted from the output channel Ch-4. As shown in FIGS. 9A to 9D, the distortion of the spectral characteristics is small at least in the range of ± 80 nm from the center wavelength. Then, as shown in FIG. 8, the peak transmission loss can be suppressed to 1 dB or less and the wavelength crosstalk can be suppressed to -15 dB or less in the wavelength range of approximately 160 nm. That is, according to the second embodiment, the transmission characteristics of all output channels can be kept substantially constant while suppressing excessive loss in the wavelength range of approximately 160 nm.

In this way, according to the second embodiment, the effective wavelength bandwidth W can be expanded.

(Third Embodiment)
A third embodiment will be described. The third embodiment has the same basic configuration as the second embodiment described above, except that the delay interferometer 210 is configured in three stages and eight WDM signals are combined. FIG. 10 is a diagram showing a configuration of a wavelength combining / demultiplexing element according to the third embodiment. The wavelength demultiplexing element according to the third embodiment is a 1 × 8 Ch DMZI type wavelength demultiplexing element.

As shown in FIG. 10, the wavelength combining / demultiplexing element 300 according to the third embodiment has seven delay interferometers 210 in three stages and has eight output channels Ch-1 to Ch-8. .. The difference (delay length) ΔL ₃ between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 in the _third- stage delay interferometer 210 is that in the second-stage delay interferometer 210. The difference (delay length) between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 is 1/2 of ΔL ₂ . The difference (delay length) ΔL ₂ between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 in the _second- stage delay interferometer 210 is that in the first-stage delay interferometer 210. the first optical path length of the arm waveguide 221 and the difference between the optical path length of the second arm waveguide 222 (delay length) is 1/2 of the [Delta] L _1. The delay lengths ΔL ₁ , ΔL ₂ and ΔL ₃ do not include the delay length corresponding to the amount of phase change due to the phase correction region 223.

The amount of phase change in the phase correction region 223 of the delay interferometer 210 in each stage is a value that cancels the phase fluctuation due to WNC 230 and 240 in each stage. For example, the phase shift amount of the phase correction region 223 included in the first-stage delay interferometer 210A is δφ _b1 . Of the two delay interferometers 210 in the second stage, the phase change amount of the phase correction region 223 included in the delay interferometers 210B connected to the output channels Ch-1 to Ch-4 is δφ _b2 . Of the two delay interferometers 210 in the second stage, the phase change amount of the phase correction region 223 included in the delay interferometer 210C connected to the output channels Ch-5 to Ch-8 is δφ _b3 . Of the four delay interferometers 210 in the third stage, the phase change amount of the phase correction region 223 included in the delay interferometer 210D connected to the output channels Ch-1 to Ch-2 is δφ _b4 . Of the four delay interferometers 210 in the third stage, the phase change amount of the phase correction region 223 included in the delay interferometers 210E connected to the output channels Ch-3 to Ch-4 is δφ _b5 . Of the four delay interferometers 210 in the third stage, the phase change amount of the phase correction region 223 included in the delay interferometer 210F connected to the output channels Ch-5 to Ch-6 is δφ _b6 . Of the four delay interferometers 210 in the third stage, the phase change amount of the phase correction region 223 included in the delay interferometers 210G connected to the output channels C-7 to Ch-8 is δφ _b7 . Table 2 below shows an example of the phase change amounts δφ _{b1 to} δφ _b7 in each phase correction region 223.

Further, Table 3 below shows the delay lengths L _{1 to} L ₇ on the delay line 220 including the phase correction regions 223 of δφ _{b1 to} δφ _b7 whose phase change amounts are shown in Table 2.

According to the wavelength merging / demultiplexing element 300 configured in this way, the phase fluctuations generated in the two WINC 230 and 240 are corrected as in the wavelength merging / demultiplexing element 200, the distortion of the spectral characteristics is suppressed, and a wide range of effectiveness is achieved. Wavelength bandwidth can be obtained.

(Fourth Embodiment)
A fourth embodiment will be described. The fourth embodiment is the same as the first embodiment described above, except that the delay interferometer 210 is configured in four stages and 16 WDM signals are combined. FIG. 11 is a diagram showing a configuration of a wavelength combining / demultiplexing element according to a fourth embodiment. The wavelength demultiplexing element according to the fourth embodiment is a 1 × 16 Ch DMZI type wavelength demultiplexing element.

As shown in FIG. 11, the wavelength combining / demultiplexing element 400 according to the fourth embodiment has 15 delay interferometers 210 in 4 stages and 16 output channels Ch-1 to Ch-16. .. The difference (delay length) ΔL ₄ between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 in the _fourth- stage delay interferometer 210 is that in the third-stage delay interferometer 210. the first optical path length of the arm waveguide 221 and the difference between the optical path length of the second arm waveguide 222 (delay length) is 1/2 of the [Delta] L _3. The difference (delay length) ΔL ₃ between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 in the _third- stage delay interferometer 210 is that in the second-stage delay interferometer 210. The difference (delay length) between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 is 1/2 of ΔL ₂ . The difference (delay length) ΔL ₂ between the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 in the _second- stage delay interferometer 210 is that in the first-stage delay interferometer 210. the first optical path length of the arm waveguide 221 and the difference between the optical path length of the second arm waveguide 222 (delay length) is 1/2 of the [Delta] L _1. The delay lengths ΔL ₁ , ΔL ₂ , ΔL ₃ and ΔL ₄ do not include the delay length corresponding to the amount of phase change due to the phase correction region 223.

The amount of phase change in the phase correction region 223 of the delay interferometer 210 in each stage is a value that cancels the phase fluctuation due to WNC 230 and 240 in each stage. For example, the phase shift amount of the phase correction region 223 included in the first-stage delay interferometer 210A is δφ _c1 . Of the two delay interferometers 210 in the second stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210B connected to the output channels Ch-1 to Ch-8 is δφ _c2 . Of the two delay interferometers 210 in the second stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210C connected to the output channels Ch-9 to Ch-16 is δφ _c3 . Of the four delay interferometers 210 in the third stage, the phase shift amount of the phase correction region 223 included in the delay interferometer 210D connected to the output channels Ch-1 to Ch-4 is δφ _c4 . Of the four delay interferometers 210 in the third stage, the phase shift amount of the phase correction region 223 included in the delay interferometer 210E connected to the output channels Ch-5 to Ch-8 is δφ _c5 . Of the four delay interferometers 210 in the third stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210F connected to the output channels Ch-9 to Ch-12 is δφ _c6 . Of the four delay interferometers 210 in the third stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210G connected to the output channels Ch-13 to Ch-16 is δφ _c7 .

Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210H connected to the output channels Ch-1 to Ch-2 is δφ _c8 . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210I connected to the output channels Ch-3 to Ch-4 is δφ _c9 . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometer 210J connected to the output channels Ch-5 to Ch-6 is δφ _c10 . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210K connected to the output channels Ch-7 to Ch-8 is δφ _c11 . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210L connected to the output channels Ch-9 to Ch-10 is δφ _c12 . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometer 210M connected to the output channels Ch-11 to Ch-12 is _{δφ c13} . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometers 210N connected to the output channels Ch-13 to Ch-14 is _{δφ c14} . Of the eight delay interferometers 210 in the fourth stage, the phase shift amount of the phase correction region 223 included in the delay interferometer 210O connected to the output channels Ch-15 to Ch-16 is δφ _c15 . Table 4 below shows an example of the phase shift amounts δφ _{c1 to} δφ _c15 in each phase correction region 223.

Further, Table 5 below shows the delay lengths L _{1 to} L ₁₅ in the delay line 220 including the phase correction regions 223 having phase shift amounts of δφ _{c1 to} δφ _c15 shown in Table 4, respectively.

According to the wavelength merging / demultiplexing element 400 configured in this way, the phase fluctuations generated in the two WINC 230 and 240 are corrected as in the wavelength merging / demultiplexing element 200, the distortion of the spectral characteristics is suppressed, and a wide range of effectiveness is achieved. Wavelength bandwidth can be obtained.

(Fifth Embodiment)
A fifth embodiment will be described. The fifth embodiment differs from the first embodiment in that it includes a ring resonator. Spectral characteristics can be flattened by including an appropriate ring resonator. FIG. 12 is a diagram showing a configuration of a wavelength combining / demultiplexing element according to a fifth embodiment. The wavelength demultiplexing element according to the fifth embodiment is a 1 × 4 Ch DMZI type wavelength demultiplexing element.

As shown in FIG. 12, in the wavelength combining / demultiplexing element 500 according to the fifth embodiment, the delay interferometer 210 is the shorter of the first arm waveguide 221 and the second arm waveguide 222. It has a loop interferometer 224 close to the arm interferometer 221 of 1. The loop waveguide 224 and the first arm waveguide 221 form a ring resonator 225. The first-stage delay interferometer 210A is provided with a loop waveguide 224A and constitutes a ring resonator 225A. The second-stage delay interferometer 210B is provided with a loop waveguide 224B and constitutes a ring resonator 225B. A loop waveguide 224C is provided in the second-stage delay interferometer 210C, and a ring resonator 225C is configured.

In each delay interferometer 210, the orbital length of the loop waveguide 224 is about twice the difference (delay length) in the optical path length between the first arm waveguide 211 and the second arm waveguide. For example, by adjusting the orbital length of the loop waveguide 224, the difference in optical path length (delay length) between the first arm waveguide 211 and the second arm waveguide can be made about twice. ..

Further, in each delay interferometer 210, the optical path length of the first arm waveguide 221 and the optical path length of the second arm waveguide 222 and the circumferential length of the loop waveguide 224 are input to and output from the WNC 130 and 140. The transmission spectrum characteristics of the ring resonator 225 satisfy the non-resonance condition with respect to the transmission spectrum characteristics of the delay interferometer 210 according to the wavelengths and channel intervals of the plurality of optical signals.

For example, in the delay interferometer 210A, the center wavelength λ _MRRA of the ring resonator 225A _deviates from the channel interval (channel grid) of the delay interferometer 210A by +1.0π [rad] or −1.0π [rad]. In the delay interferometer 210B, the center wavelength λ _MRRB of the ring resonator 225B _deviates from the channel interval (channel grid) of the delay interferometer 210B by +1.0π [rad] or −1.0π [rad]. In the delay interferometer 210C, the central wavelength lambda _MRRC ring resonator 225C is offset by the channel spacing of the delay interferometer 210C (channel grid) + 1.0π [rad] or -1.0π [rad]. Since the delay length ΔL ₂ is 1/2 of the delay length ΔL ₁ , in the delay interferometers 210B and 210C, the free spectral range (FSR) of the spectrum is twice the FSR of the spectrum in the delay interferometer 210A. ing. FIG. 13 shows an outline of these relationships. The CG in FIG. 13 shows the channel grid, the solid line in the spectrum in the delay interferometer 210A shows the spectrum of the light output to the waveguide connected to the delay interferometer 210B, and the broken line shows the spectrum connected to the delay interferometer 210C. The spectrum of the output light is shown.

For example, round-trip length _{L 224A} of the loop waveguide 224A is _{ΔL 1 × 2 + δL (+} 1.0π). The circumference length L _224B of the loop waveguide 224B is ΔL ₂ × 2 + δL (+ 1.0π). The circumference length L _224C of the loop waveguide 224C is ΔL ₂ × 2 + δL (−0.5π).

The optical coupling ratio between the loop waveguide 224 and the first arm waveguide 221 is preferably 80% or more. This optical coupler may be 90% or less. The optical coupling ratio between the loop waveguide 224 and the first arm waveguide 221 adjusts, for example, the distance between the loop waveguide 224 and the first arm waveguide 221 and the length of the adjacent portion. Therefore, it can be easily set to 80% or more and 90% or less.

Here, the effect of the fifth embodiment will be described with reference to the second reference example and the third reference example. FIG. 14 is a diagram showing a configuration of a wavelength combining / demultiplexing element of the second reference example.

As shown in FIG. 14, in the wavelength merging / demultiplexing element 800 of the second reference example, DC830 and 840 are provided in place of the WINS 930 and 940 of the wavelength merging / demultiplexing element 900 of the first reference example. The photocoupling rate of DC830 and 840 is about 50%. A loop waveguide 824 that is close to the first arm waveguide 921 and constitutes a ring resonator 825 together with the first arm waveguide 921 is provided. The FSR in the ring resonator 825 matches the channel spacing of the delay interferometer 910. Further, the center wavelength of the ring resonator 825 deviates from the channel spacing of the delay interferometer 910 by about π / 2 radians. The phase correction region 923 is not provided.

In the wavelength merging / demultiplexing element of the third reference example, WNC930 and 940 are provided in place of the DC830 and 840 of the wavelength merging / demultiplexing element 800 of the second reference example, and the wavelength merging / demultiplexing element 800 is provided with the first It has a structure to which the phase correction region 923 of the reference example is added.

The spectral characteristics of the fifth embodiment, the second reference example, and the third reference example when assuming a WDM signal having a wavelength interval Δν (about 3.2 nm in the 1.55 μm band) corresponding to a frequency of 400 GHz are It looks like this: Here, the spectral characteristics of the three bands R1, R2, and R3 within the wavelength band within ± 100 nm from the center wavelength λ ₀ shown in FIG. 15 are shown. The band R1 is a band in which the deviation from the center wavelength λ ₀ is −10 nm to +10 nm. The band R2 is a band having a deviation of +30 nm to +50 nm. The band R3 is a band having a deviation of +70 nm to +90 nm. In the band of −50 nm to −30 nm, a spectral characteristic symmetrical to the band R2 is obtained, and in the band of −90 nm to −70 nm, a spectral characteristic symmetrical to the band R3 is obtained.

FIG. 16A is a diagram showing the spectral characteristics of the band R1 of the second reference example. FIG. 16B is a diagram showing the spectral characteristics of the band R2 of the second reference example. FIG. 16C is a diagram showing the spectral characteristics of the band R3 of the second reference example. As shown in FIGS. 16A to 16C, in the second reference example, the wavelength crosstalk is significantly deteriorated in the band R2. Therefore, in the second reference example, the effective wavelength bandwidth is limited to about 40 nm even when the symmetry of the spectral characteristics is taken into consideration.

FIG. 17A is a diagram showing the spectral characteristics of the band R1 of the third reference example. FIG. 17B is a diagram showing the spectral characteristics of the band R2 of the third reference example. FIG. 17C is a diagram showing the spectral characteristics of the band R3 of the third reference example. As shown in FIGS. 17A to 17C, the wavelength crosstalk deteriorates in the band R2 also in the third reference example. Further, in the third reference example, the peak transmission loss increases in the band R2, and the shape of the spectral characteristics deteriorates distortedly.

FIG. 18A is a diagram showing the spectral characteristics of the band R1 of the fifth embodiment. FIG. 18B is a diagram showing the spectral characteristics of the band R2 of the fifth embodiment. FIG. 18C is a diagram showing the spectral characteristics of the band R3 of the fifth embodiment. As shown in FIGS. 18A to 18C, peak transmission loss and wavelength crosstalk are suppressed also in the band R2. In band R3, some wavelength crosstalk occurs, but the flatness of the spectrum is maintained.

FIG. 19 shows the continuous wavelength spectral characteristics of the second reference example, and FIG. 20 shows the continuous wavelength spectral characteristics of the fifth embodiment. As shown in FIG. 19, the effective wavelength bandwidth of the second reference example is about 40 nm. On the other hand, according to the fifth embodiment, it is possible to obtain an effective wavelength bandwidth of at least 120 nm while obtaining spectral characteristics with good flatness. That is, according to the fifth embodiment, it is possible to obtain an effective wavelength bandwidth about three times that of the second reference example while obtaining spectral characteristics with good flatness.

The delay interferometer 210 included in the third and fourth embodiments may include the ring resonator 225 as in the fifth embodiment.

(Sixth Embodiment)
A sixth embodiment will be described. A sixth embodiment relates to an optical transmission device including the wavelength combining and demultiplexing element 100 of the first embodiment. FIG. 21 is a diagram showing a configuration of an optical transmission device according to a sixth embodiment.

As shown in FIG. 21, the optical transmitter 600 according to the sixth embodiment includes four semiconductor lasers (LD) 81 to 84 having different oscillation wavelengths and a modulator (MOD) 91 to 94. And a DMZI type wavelength combiner element 601. The LD81-84 are arranged side by side, and the MODs 91-94 modulate the laser beam emitted by the LD81-84, respectively. The DMZI type wavelength combiner element 601 is the wavelength combiner / demultiplexer element 100 according to the first embodiment, and combines the light after modulation by MOD 91 to 94.

In the optical transmitter 600, the wavelength combiner / demultiplexer element 100 is used as the DMZI type wavelength combiner element 601. Therefore, even if Δν is widened or the number of wavelengths (number of channels) is increased so as to have excellent resistance to wavelength deviations and temperature fluctuations in the light source, deterioration of characteristics as a wavelength division multiplexing element is minimized. Therefore, optical transmission of wavelength division multiplexing signals can be performed stably and inexpensively. In addition, instead of the wavelength merging / demultiplexing element 100, the wavelength merging / demultiplexing elements 200, 300, 400 according to the second to fourth embodiments may be used. When the WDM optical signal has 8 channels or the like, the number of channels of the DMZI type wavelength division multiplexing element 601 may be changed according to the number of channels.

(Variation example of the sixth embodiment)
A modified example of the sixth embodiment will be described. FIG. 22 is a diagram showing a configuration of an optical transmission device according to a modified example of the sixth embodiment.

As shown in FIG. 22, the optical transmission device 610 according to the modified example of the sixth embodiment has a DMZI type wavelength wave combiner element 611 instead of the DMZI type wavelength wave wave combiner element 601. The DMZI type wavelength combiner / demultiplexer element 611 is the wavelength combiner / demultiplexer element 500 according to the fifth embodiment, and combines the light after modulation by MOD 91 to 94.

In the optical transmitter 610, the wavelength combiner / demultiplexer element 500 is used as the DMZI type wavelength combiner element 611. Therefore, the spectral characteristics can be flattened, the wavelength accuracy of the light source and the resistance to deterioration of the characteristics due to environmental temperature fluctuations can be improved, and the optical transmission of wavelength division multiplexing signals can be performed stably and inexpensively.

(7th Embodiment)
A seventh embodiment will be described. A seventh embodiment relates to an optical receiver including the wavelength combining and demultiplexing element 100 of the first embodiment. FIG. 23 is a diagram showing a configuration of an optical receiver according to a seventh embodiment.

As shown in FIG. 23, the optical receiver 700 according to the seventh embodiment includes an optical interface (OI) 61, a polarization beam splitter (PBS) 62, and a polarization rotator (polarization rotator). It has PR) 63. The photodetector 700 further includes a first optical waveguide 64, a second optical waveguide 65, a DMZI type wavelength demultiplexing element 701A, a DMZI type wavelength demultiplexing element 701B, and four photodetectors (photo detectors: PD) 71A to 74A and four PD71B to 74B.

The OI61 couples a WDM optical signal to a silicon waveguide. As the OI61, for example, a spot size conversion unit, a grating coupler, or the like can be used. PBS62 separates into the polarization component of TE / TM mode.

The TE mode optical signal separated by the PBS 62 is input to the DMZI type wavelength demultiplexing element 701A via the first optical waveguide 64. The TM mode optical signal separated by the PBS 62 is input to the PR63 via the second optical waveguide 65, the PR63 is converted to the TE mode, and the converted optical signal is input to the DMZI type wavelength demultiplexer 701B. ..

The DMZI type wavelength demultiplexing elements 701A and 701B are both wavelength combined demultiplexing elements 100 according to the first embodiment, and demultiplex each wavelength signal. Then, the 4-channel optical signal demultiplexed by the DMZI type wavelength demultiplexing element 701A is detected by PD71A to 74A, and the 4-channel optical signal demultiplexed by the DMZI type wavelength demultiplexing element 701B is detected by PD71B to 74B. Will be done. In the present embodiment, each wavelength component is detected by eight PDs 71A to 74A and 71B to 74B, but the signal light of the same wavelength component is one PD each having two opposing surfaces as light receiving surfaces. You may try to detect with.

In the optical receiver 700, the wavelength combined / demultiplexing element 100 is used as the DMZI type wavelength demultiplexing elements 701A and 701B. Therefore, even if Δν is widened or the number of wavelengths (number of channels) is increased so as to have excellent resistance to wavelength deviations and temperature fluctuations in the light source, the deterioration of the characteristics as a wavelength combined demultiplexing element is minimized. It can be suppressed. As a result, the power penalty in the optical link can be minimized when the WDM optical signal is detected by the receiver. In addition, instead of the wavelength merging / demultiplexing element 100, the wavelength merging / demultiplexing elements 200, 300, 400 according to the second to fourth embodiments may be used. When the WDM optical signal has 8 channels or the like, the number of channels of the DMZI type wavelength division multiplexing elements 701A and 701B may be changed according to the number of channels. Here, only TE light is detected by using a polarization rotator so as not to be affected by the polarization state of light, but if the operation of the wavelength division multiplexing element is made polarization independent, WDM light is detected. The signal may be directly incident on the wavelength division multiplexing element. In that case, only one wavelength combined / demultiplexing element may be used.

(Modified example of the seventh embodiment)
A modified example of the seventh embodiment will be described. FIG. 24 is a diagram showing a configuration of an optical receiver according to a modified example of the seventh embodiment.

As shown in FIG. 24, the optical receiver 710 according to the modified example of the seventh embodiment has DMZI type wavelength demultiplexing elements 711A and 711B instead of DMZI type wavelength demultiplexing elements 701A and 701B. The DMZI type wavelength demultiplexing elements 711A and 711B are wavelength combined demultiplexing elements 500 according to the fifth embodiment, and demultiplex each wavelength signal.

In the optical receiver 710, the wavelength combined demultiplexing element 500 is used as the DMZI type wavelength demultiplexing elements 711A and 711B. Therefore, the spectral characteristics can be flattened, the wavelength accuracy of the light source and the resistance to deterioration of the characteristics due to environmental temperature fluctuations can be improved, and the optical transmission of wavelength division multiplexing signals can be performed stably and inexpensively.

Although the preferred embodiments and the like have been described in detail above, the embodiments are not limited to the above-described embodiments and the like, and various embodiments and the like described above are used without departing from the scope of the claims. Modifications and substitutions can be added.

Hereinafter, various aspects of the present disclosure will be described together as an appendix.

(Appendix 1)
It has (2 ^N -1) number of delay interferometers (N is a natural number of 2 or more) in N stages.
The 2 ^k-1 delay interferometers in the kth stage (k <N) are vertically connected to the 2 ^k delay interferometers in the (k + 1) stage.
The delay interferometer
A pair of optical couplers with input / output ports and
A first arm waveguide and a second arm waveguide connected between the pair of optical couplers and having different optical path lengths.
A phase correction region provided on one of the first arm waveguide and the second arm waveguide,
Have,
The optical coupler
With a pair of directional couplers,
A third arm waveguide and a fourth arm waveguide connected between the pair of directional couplers,
A phase shifter provided on one of the third arm waveguide and the fourth arm waveguide,
Have,
The difference between the optical path length of the first arm waveguide and the optical path length of the second arm waveguide in the delay interferometer of the (k + 1) stage is the first difference in the delay interferometer of the kth stage. It is 1/2 of the difference between the optical path length of the arm waveguide and the optical path length of the second arm waveguide.
A wavelength merging / demultiplexing element, wherein the amount of phase change in the phase correction region of the delay interferometer in each stage is a value that cancels the phase fluctuation caused by the optical coupler in each stage.
(Appendix 2)
The number of the delay interferometers is three.
When the phase shift amount of the phase shifter is δφ _Coup ,
The amount of phase change in the phase correction region of the delay interferometer in the first stage is "+ δφ _PT " radians.
The amount of phase change in the phase correction region of one of the two delay interferometers in the second stage is "+ δφ _PT " radians, and the amount of phase change in the phase correction region of the other delay interferometer is It is a "+ δφ _PT + 0.5π" radian or a "+ δφ _PT -0.5π" radian.
The wavelength merging / demultiplexing element according to Appendix 1, wherein the δφ _PT is “(−δφ _Coup × 2) − {(0.5π−δφ _Coup ) × 2}”.
(Appendix 3)
The number of the delay interferometers is 7,
When the phase shift amount of the phase shifter is δφ _Coup ,
The amount of phase change in the phase correction region of the delay interferometer in the first stage is "+ δφ _PT " radians.
The amount of phase change in the phase correction region of one of the two delay interferometers in the second stage is "+ δφ _PT " radians, and the amount of phase change in the phase correction region of the other delay interferometer is It is a "+ δφ _PT + 0.5π" radian or a "+ δφ _PT -0.5π" radian.
The amount of phase change in the phase correction region of one of the four delay interferometers in the third stage is "+ δφ _PT " radians, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radians.
The wavelength merging / demultiplexing element according to Appendix 1, wherein the δφ _PT is “(−δφ _Coup × 2) − {(0.5π−δφ _Coup ) × 2}”.
(Appendix 4)
The number of the delay interferometers is eight.
When the phase shift amount of the phase shifter is δφ _Coup ,
The amount of phase change in the phase correction region of the delay interferometer in the first stage is "+ δφ _PT " radians.
The amount of phase change in the phase correction region of one of the two delay interferometers in the second stage is "+ δφ _PT " radians, and the amount of phase change in the phase correction region of the other delay interferometer is It is a "+ δφ _PT + 0.5π" radian or a "+ δφ _PT -0.5π" radian.
The amount of phase change in the phase correction region of one of the four delay interferometers in the third stage is "+ δφ _PT " radians, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radians.
The amount of phase change in the phase correction region of one of the eight delay interferometers in the fourth stage is "+ δφ _PT " radian, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT + 0.125π" radian. The amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT + 0.625π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT- 0". It is .125π "radian, and the amount of phase change in the phase correction region of the other delay interferometer is" + δφ _PT + 0.375π "radian.
The wavelength merging / demultiplexing device according to Appendix 1, wherein the δφ _PT is “(−δφ _Coup × 2) − {(0.5π−δφ _Coup ) × 2}”.
(Appendix 5)
The optical path length of the first arm waveguide is shorter than the optical path length of the second arm waveguide.
The delay interferometer has a loop waveguide that constitutes a ring resonator together with the first arm waveguide.
In each of the delay interferometers, the optical path length of the first arm waveguide, the optical path length of the second arm waveguide, and the circumferential length of the loop waveguide are input to and output from the optical coupler. Any of Appendix 1 to 4, wherein the transmission spectrum characteristic of the ring resonator satisfies the non-resonance condition with respect to the transmission spectrum characteristic of the delay interferometer according to the wavelength and the channel interval of the plurality of optical signals. The wavelength interferometric element according to item 1.
(Appendix 6)
The wavelength combination / demultiplexing device according to Appendix 5, wherein the optical coupling ratio between the first arm waveguide and the loop waveguide is 80% or more.
(Appendix 7)
The one wavelength compounding / demultiplexing element according to any one of Supplementary note 1 to 6 and the
^2N semiconductor laser devices that oscillate at different wavelengths,
2 and ^N optical modulator for modulating the 2 ^N light of each wavelength from the semiconductor laser element,
Have,
The ^2N optical modulators are connected to ^2N input / output ports on the open end side of the optical coupler of the Nth stage delay interferometer of the wavelength junction / demultiplexing element. apparatus.
(Appendix 8)
An input optical waveguide that propagates wavelength division multiplexing optical signals including multiple optical signals having different wavelengths from each other.
A polarizing beam splitter connected to one end of the input optical waveguide,
A first optical waveguide connected to the other end of the polarization beam splitter to which TE mode light is input and a second optical waveguide to which TM mode light is input.
A polarizing rotator inserted in the middle of the second optical waveguide,
The two wavelength combined / demultiplexing elements according to any one of Supplementary note 1 to 6 and
Wherein two of the one wavelength mux of wavelength mux N-th stage of the delay interferometer 2 ^N pieces of which are connected to the 2 ^N output ports of the open end side of the optical coupler of With the receiver
Two of said other wavelength mux of wavelength mux N-th stage of the delay interferometer 2 ^N pieces of which are connected to the 2 ^N output ports of the open end side of the optical coupler of With the receiver
Have,
The first optical waveguide is connected to one input / output port on the open end side of the optical coupler of the first-stage delay interferometer of one of the wavelength junction / demultiplexing elements, and the first optical waveguide is connected.
The second optical waveguide is connected to one input / output port on the open end side of the optical coupler of the first-stage delay interferometer of the other wavelength-coupling / demultiplexing element. A featured optical receiver.

100, 200, 300, 400, 500, 601 73B, 74A, 74B: Receiver 81, 82, 83, 84: Semiconductor laser 91, 92, 93, 94: Modulator 110, 210: Delay interferometer 120, 220: Delay line 121, 221: First arm guide Wavelength 122, 222: Second arm Wavelength path 123, 223: Phase correction region 130, 140: Optical coupler 131, 135, 141, 145: Directional coupler 132, 133, 142, 143, 232, 233, 242, 243: Arm waveguide 134, 144, 234, 244: Phase shifter 224: Loop waveguide 225: Ring resonator 230, 240: Wavelength-independent optical coupler 600, 610: Optical transmitter 700, 710: Optical receiver

Claims (7)

It has (2 ^N -1) number of delay interferometers (N is a natural number of 2 or more) in N stages.
The 2 ^k-1 delay interferometers in the kth stage (k <N) are vertically connected to the 2 ^k delay interferometers in the (k + 1) stage.
The delay interferometer
A pair of optical couplers with input / output ports and
A first arm waveguide and a second arm waveguide connected between the pair of optical couplers and having different optical path lengths.
A phase correction region provided on one of the first arm waveguide and the second arm waveguide,
Have,
The optical coupler
With a pair of directional couplers,
A third arm waveguide and a fourth arm waveguide connected between the pair of directional couplers,
A phase shifter provided on one of the third arm waveguide and the fourth arm waveguide,
Have,
The difference between the optical path length of the first arm waveguide and the optical path length of the second arm waveguide in the delay interferometer of the (k + 1) stage is the first difference in the delay interferometer of the kth stage. It is 1/2 of the difference between the optical path length of the arm waveguide and the optical path length of the second arm waveguide.
A wavelength merging / demultiplexing element, wherein the amount of phase change in the phase correction region of the delay interferometer in each stage is a value that cancels the phase fluctuation caused by the optical coupler in each stage. The number of the delay interferometers is three.
When the phase shift amount of the phase shifter is δφ _Coup ,
The amount of phase change in the phase correction region of the delay interferometer in the first stage is "+ δφ _PT " radians.
The amount of phase change in the phase correction region of one of the two delay interferometers in the second stage is "+ δφ _PT " radians, and the amount of phase change in the phase correction region of the other delay interferometer is It is a "+ δφ _PT + 0.5π" radian or a "+ δφ _PT -0.5π" radian.
The wavelength combination / demultiplexing element according to claim 1, wherein the δφ _PT is “(−δφ _Coup × 2) − {(0.5π−δφ _Coup ) × 2}”. The number of the delay interferometers is 7,
When the phase shift amount of the phase shifter is δφ _Coup ,
The amount of phase change in the phase correction region of the delay interferometer in the first stage is "+ δφ _PT " radians.
The amount of phase change in the phase correction region of one of the two delay interferometers in the second stage is "+ δφ _PT " radians, and the amount of phase change in the phase correction region of the other delay interferometer is It is a "+ δφ _PT + 0.5π" radian or a "+ δφ _PT -0.5π" radian.
The amount of phase change in the phase correction region of one of the four delay interferometers in the third stage is "+ δφ _PT " radians, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radians.
The wavelength combination / demultiplexing element according to claim 1, wherein the δφ _PT is “(−δφ _Coup × 2) − {(0.5π−δφ _Coup ) × 2}”. The number of the delay interferometers is eight.
When the phase shift amount of the phase shifter is δφ _Coup ,
The amount of phase change in the phase correction region of the delay interferometer in the first stage is "+ δφ _PT " radians.
The amount of phase change in the phase correction region of one of the two delay interferometers in the second stage is "+ δφ _PT " radians, and the amount of phase change in the phase correction region of the other delay interferometer is It is a "+ δφ _PT + 0.5π" radian or a "+ δφ _PT -0.5π" radian.
The amount of phase change in the phase correction region of one of the four delay interferometers in the third stage is "+ δφ _PT " radians, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radians.
The amount of phase change in the phase correction region of one of the four delay interferometers in the third stage is "+ δφ _PT " radians, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radians.
The amount of phase change in the phase correction region of one of the eight delay interferometers in the fourth stage is "+ δφ _PT " radian, and the phase change amount of the phase correction region of the other delay interferometer is The amount of phase change is "+ δφ _PT + 0.5π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT -0.25π" radian, and the other one delay. The amount of phase change in the phase correction region of the interferometer is "+ δφ _PT + 0.25π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT + 0.125π" radian. The amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT + 0.625π" radian, and the amount of phase change in the phase correction region of the other delay interferometer is "+ δφ _PT- 0". It is .125π "radian, and the amount of phase change in the phase correction region of the other delay interferometer is" + δφ _PT + 0.375π "radian.
The wavelength combination / demultiplexing element according to claim 1, wherein the δφ _PT is “(−δφ _Coup × 2) − {(0.5π−δφ _Coup ) × 2}”. The optical path length of the first arm waveguide is shorter than the optical path length of the second arm waveguide.
The delay interferometer has a loop waveguide that constitutes a ring resonator together with the first arm waveguide.
In each of the delay interferometers, the optical path length of the first arm waveguide, the optical path length of the second arm waveguide, and the circumferential length of the loop waveguide are input to and output from the optical coupler. Claims 1 to 4, wherein the transmission spectrum characteristics of the ring resonator satisfy a non-resonance condition with respect to the transmission spectrum characteristics of the delay interferometer according to the wavelengths and channel intervals of the plurality of optical signals. The wavelength interferometric element according to any one item. The single wavelength combiner / demultiplexer according to any one of claims 1 to 5.
^2N semiconductor laser devices that oscillate at different wavelengths,
2 and ^N optical modulator for modulating the 2 ^N light of each wavelength from the semiconductor laser element,
Have,
The ^2N optical modulators are connected to ^2N input / output ports on the open end side of the optical coupler of the Nth stage delay interferometer of the wavelength duplexing / demultiplexing element. apparatus. An input optical waveguide that propagates wavelength division multiplexing optical signals including multiple optical signals having different wavelengths from each other.
A polarizing beam splitter connected to one end of the input optical waveguide,
A first optical waveguide connected to the other end of the polarization beam splitter to which TE mode light is input and a second optical waveguide to which TM mode light is input.
A polarizing rotator inserted in the middle of the second optical waveguide,
The two wavelength combined / demultiplexing elements according to any one of claims 1 to 5.
Wherein two of the one wavelength mux of wavelength mux N-th stage of the delay interferometer 2 ^N pieces of which are connected to the 2 ^N output ports of the open end side of the optical coupler of With the receiver
Two of said other wavelength mux of wavelength mux N-th stage of the delay interferometer 2 ^N pieces of which are connected to the 2 ^N output ports of the open end side of the optical coupler of With the receiver
Have,
The first optical waveguide is connected to one input / output port on the open end side of the optical coupler of the first-stage delay interferometer of one of the wavelength junction / demultiplexing elements, and the first optical waveguide is connected.
The second optical waveguide is connected to one input / output port on the open end side of the optical coupler of the first-stage delay interferometer of the other wavelength-coupling / demultiplexing element. A featured optical receiver.

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