Planar light wave circuit-type lattice filter and optical transmission module using same

Abstract

An embodiment of the present disclosure provides a planar light wave circuit-type filter (213) having a small loss and a high rectangularity in a filter shape. The planar light wave circuit-type filter (213) for multiplexing a plurality of optical signals of different wavelengths comprises a plurality of input waveguides (111), a multiplexing circuit (303), and at least one output waveguide (112). The multiplexing circuit (303) has asymmetric MZI circuits (331) that are connected in cascade to a plurality of stages, and the asymmetric MZI circuit (331) includes an input-side coupler, an output-side coupler, and two waveguides that connect the output of the input-side coupler and the input of the output-side coupler and has an optical path length difference. A plurality of input waveguides are connected in pairs to an input (321) of the input-side coupler of the MZI circuit (331) disposed in a first stage. An optical signal, in which the plurality of optical signals, output from the output-side coupler of the MZI circuit (331) disposed in the last stage, are multiplexed, is configured to be coupled to the output waveguide (112).

Description

[Technical field]

[0001] The present disclosure relates to a planar lightwave circuit type filter and an optical transmission module using the same. [Background technology]

[0002] As data communication speeds and volumes increase, optical communication devices and optical interconnection technologies are becoming more advanced. Optical communication devices do not use single-function elements such as conventional laser diodes (LD), photodiodes (PD), and optical waveguide filters, but combine these elements into one package (i.e., integrate multiple elements into one module) to realize multi-channel, multi-function, and high-performance devices.

[0003] These modules are required to be smaller and less expensive, as well as to have a longer transmission distance. For example, the 4ch optical transmission module described in Non-Patent Document 1 and Non-Patent Document 2 has been used for communications with a transmission distance of about 10 km, but there is an increasing demand for it to be used for communications with a transmission distance of about 40 km.

[0004] To extend transmission distances, modules are required to have higher signal output, which in turn requires lower loss in the components and optical coupling parts mounted inside the modules.

[0005] In addition, as the transmission distance becomes longer, it becomes more susceptible to the effects of chromatic dispersion, so it becomes necessary to use propagation light in a wavelength band that is less susceptible to the effects of dispersion wavelengths. In that case, it is necessary to narrow the wavelength intervals of the four signal lights, so the multiplexing filter integrated in the module is required to have a highly rectangular transmission spectrum characteristic.

[0006] A multi-channel optical transmission module is equipped with a MUX filter for multiplexing the signal light output from each LD. As this multiplexing filter, a multilayer crystal type thin film filter (TFF) (see Non-Patent Document 1) and a structure using a planar lightwave circuit AWG (see Non-Patent Document 2) have been reported. Considering that the number of channels to be implemented in a multi-channel optical transmission module will increase in the future, a planar lightwave circuit type with small variation in loss among each signal channel is advantageous.

[0007] FIG. 1 shows a schematic configuration of a 4-channel optical transmission module using a conventional planar lightwave circuit filter. (a) is a top view, and (b) is a teeth 1 is a cross-sectional view. As shown in Fig. 1, in the optical transmission module 100, four LDs 102 and a planar lightwave circuit (PLC) 110 are arranged on the upper surface side of the main surface (XY plane) of a base 101, and are housed in a package 107 (for example, an airtight ceramic butterfly package). A thermoelectric controller (TEC) 109 is arranged between the lower surface of the base 101 and the package 107. A sleeve 121 having an optical fiber 120 and a lens 122 is connected to the package 107.

[0008] The LD 102 is placed on an electric circuit 108 that is placed on the upper surface of the base 101. The electric circuit 108 is a circuit that drives the LD 102. The central wavelengths λ0 to λ3 of the four LDs 102-0 to 102-3 are different from one another, and for example, an optical transmission module for an access system uses the S-band wavelength band.

[0009] Four pairs of lenses 103a and 103b corresponding to the four LDs 102 are disposed between the LDs 102 and the PLC 110. The light from the LDs 102 is converted into collimated light by the lens 103a, and then collected by the lens 103b and coupled to the input waveguide 111. In other words, the LDs 102 and the PLC 110 are optically coupled using a parallel beam system.

[0010] A beam splitter 104 is disposed between the lens 103a and the lens 103b. A monitor PD (MPD) 105 for monitoring the light from the LD 102 is disposed on the upper surface of the beam splitter 104. A part of the light from the LD 102 is split by the beam splitter 104 disposed between the lens 103a and the lens 103b and is received by the monitor PD 105.

[0011] The PLC 110 includes an input waveguide 111, an arrayed waveguide grating (AWG) 113, and an output waveguide 112, and functions as an AWG-type planar lightwave circuit multiplexer (MUX) filter. hand For example, the light having wavelengths λ0, λ1, λ2, and λ3 from the LDs 102-0, 102-1, 102-2, and 102-3, which are input to the planar lightwave circuit from the input waveguides 111-0, 111-1, 111-2, and 111-3, are multiplexed by passing through the AWG 113 and are output from one output waveguide 112 located near the output end face of the PLC 110.

[0012] A lens 103c is provided at the output end face of the PLC 110, and an isolator 106 is disposed beyond the lens 103c. The multiplexed light is guided through the output waveguide 112 and optically coupled to the optical fiber 120 via the lens 103c, the isolator 106, and a lens 122 provided at the end face of the PLC 110. The lens 103c and the lens 122 also optically couple the PLC 110 and the optical fiber 120 in a parallel beam system. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2014-59542 A [Non-patent literature]

[0014] [Non-Patent Document 1] S. Kanazawa et al., "High Output Power and Compact LAN-WDM EADFB Laser TOSA for 4 × 100-Gbit / s / λ 40-km Fiber-Amplifier-Less Transmission," 2020 Optical Fiber Communications Conference and Exhibition (OFC), 2020, pp. 1-3 [Non-Patent Document 2] J. Liu, Q. Huang and J. Xia, "High Assembly Tolerance and Cost-Effective 100-Gb / s TOSA With Silica-PLC AWG Multiplexer," in IEEE Photonics Journal, vol. 11, no. 4, pp. 1-9, Aug. 2019, Art no. 7904909, doi: 10.1109 / JPHOT.2019.2924035 Summary of the Invention

[0015] The optical transmission module using the planar lightwave circuit filter described above with reference to FIG. 1 has the following three main problems. Issue 1: To extend the transmission distance, there is a demand for low loss AWG-type planar lightwave circuit filters mounted inside optical transmission modules. In addition, as the wavelength arrangement of each signal is becoming narrower, there is a demand for highly rectangular transmission spectrum shapes (hereafter referred to as filter shapes) that indicate the characteristics of the filter. Planar lightwave circuit filters equipped with a single AWG have issues of high loss and low rectangularity.

[0016] Issue 2: In order to miniaturize optical transmission modules, the chip (PLC) mounted inside is also required to be miniaturized. However, the AWG, which has multiple waveguides of different lengths between two slab waveguides, occupies a large area in the PLC, which limits the miniaturization of the chip. In addition, if a Mach-Zehnder interferometer (MZI) type circuit connected to the AWG is placed on the PLC to achieve a highly rectangular filter shape, the size of the chip (PLC) will become even larger.

[0017] Issue 3: In order to reduce costs and simplify the mounting process, there is a demand for reducing the number of parts mounted inside the optical transmission module. For example, as described above with reference to FIG. 1, a beam splitter 104 is disposed to monitor the intensity of light from the LD 103. By mounting the beam splitter 104, the number of parts mounted inside the optical transmission module increases, which increases costs and makes the mounting process more difficult. Furthermore, the optical length between the LD 102 and the PLC 110 must also be increased, which is disadvantageous in miniaturizing the optical transmission module.

[0018] The present disclosure has been made in view of such problems, and an object of the present disclosure is to provide a planar lightwave circuit type filter having a small loss and a high degree of rectangularity of the filter shape. filter The present disclosure also provides a compact planar lightwave circuit type filter Furthermore, the present disclosure provides a planar lightwave circuit type optical amplifier that can reduce the number of parts. filter The purpose of this invention is to provide

[0019] One embodiment of the present disclosure is a planar lightwave circuit type lattice filter for multiplexing a plurality of signal lights having different wavelengths, the filter comprising a plurality of input waveguides for inputting the plurality of signal lights, a multiplexing circuit for multiplexing the plurality of signal lights, and at least one output waveguide for outputting the multiplexed signal, the multiplexing circuit being arranged in a plurality of stages. Cascade ConnectionThe asymmetric MZI circuit includes an input coupler, an output coupler, and two waveguides with an optical path length difference that connect the output of the input coupler and the input of the output coupler, and each of the multiple input waveguides is connected in pairs to the input of the input coupler of the asymmetric MZI circuit arranged in the first stage, and a signal light obtained by multiplexing multiple signal lights output from the output coupler of one asymmetric MZI circuit arranged in the final stage is configured to be coupled to the output waveguide.

[0020] According to an embodiment of the present disclosure, it is possible to provide a planar lightwave circuit type lattice filter having low loss and high rectangular filter performance compared to an AWG type planar lightwave circuit type filter. Also, according to an embodiment of the present disclosure, it is possible to provide a planar lightwave circuit type lattice filter that allows for miniaturization of the chip (PLC). Furthermore, according to an embodiment of the present disclosure, Department It is possible to provide a planar lightwave circuit type lattice filter that allows the number of parts to be reduced. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows a schematic configuration of a 4-channel optical transmission module using a conventional arrayed waveguide grating type planar lightwave circuit filter, where (a) is a top view and (b) is a cross-sectional view. [Diagram 2] 1A and 1B are diagrams showing a schematic configuration of a 4-ch optical transmission module using a planar lightwave circuit type lattice filter according to an embodiment of the present disclosure, where (a) is a top view and (b) is a cross-sectional view. [Diagram 3] FIG. 1 is a diagram showing a schematic configuration of a planar lightwave circuit type lattice filter according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a diagram showing a schematic configuration of a planar lightwave circuit type lattice filter according to an embodiment of the present disclosure. [Diagram 5] FIG. 1 is a diagram showing a schematic configuration of a planar lightwave circuit type lattice filter according to an embodiment of the present disclosure. [Figure 6] FIG. 1 is a diagram showing a schematic configuration of a planar lightwave circuit type lattice filter according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The same or similar reference numerals indicate the same or similar elements, and repeated explanations may be omitted. The numerical values ​​in the following description are examples, and the present disclosure may be implemented using other numerical values ​​without departing from the gist of the present disclosure.

[0023] The planar lightwave circuit type lattice filter of various embodiments described below is a planar lightwave circuit type lattice filter for multiplexing N signal lights with different wavelengths, where N is an integer of 2 or more, and may include N input waveguides for inputting the N signal lights, a multiplexing circuit for multiplexing the N signal lights, and at least one output waveguide for outputting the multiplexed signal. Cascade Connection The asymmetric MZI circuit may include at least N-1 asymmetric MZI circuits each having one or two inputs and two outputs. The asymmetric MZI circuit may include an input coupler having one or two inputs and two outputs, an output coupler having two inputs and one or two outputs, and two waveguides having an optical path length difference that connect the two outputs of the input coupler and the two inputs of the output coupler. Two of the N input waveguides may be connected to two inputs of the input coupler of the asymmetric MZI circuit arranged in the first stage. The signal light obtained by multiplexing the N signal lights output from the output coupler of one asymmetric MZI circuit arranged in the final stage may be configured to be coupled to the output waveguide.

[0024] (First embodiment) A planar lightwave circuit type lattice filter and an optical transmission module according to a first embodiment of the present disclosure will be described with reference to Figures 2-4. Here, a 4ch TOSA (Transmitter optical sub-assembly) module using a quartz PLC lattice filter will be described as an example of an optical transmission module using a planar lightwave circuit type lattice filter. Here, an optical transmission module with a 4-channel (ch) configuration, that is, an optical transmission module that multiplexes and transmits four signal lights with different wavelengths, is illustrated, but the number of signal lights or the number of ch is not limited to 4 and can be any number.

[0025] (Configuration of optical transmission module) FIG. 2 shows a schematic configuration of an optical transmission module according to an embodiment of the present disclosure. FIG. 2(a) is a top view, and FIG. 2(b) is a cross-sectional view. As shown in FIG. 2, in the optical transmission module 200, four LDs 102 and a PLC 210 are arranged on the upper surface side of the main surface (XY plane) of a base 101, and are housed and hermetically sealed in a package 107 (for example, a hermetic ceramic butterfly package). A temperature controller (TEC) 109 is arranged between the lower surface of the base 101 and the package 107. A sleeve 121 having an optical fiber 120 and a lens 122 is connected to the package 107.

[0026] The LD 102 is placed on an electric circuit 108 that is placed on the upper surface of the base 101. The electric circuit 108 is a circuit that drives the LD 102. The four LDs 102-0 to 102-3 are configured to have different emission wavelengths. hand As described above, the LD outputs light of different wavelengths λ0 to λ3 corresponding to Lane0 to Lane3.

[0027] Between the LD 102 and the PLC 110, four pairs of lenses 103a and 103b corresponding to the four LDs 102 are arranged. The light from the LD 102 is converted into collimated light by the lens 103a, and then collected by the lens 103b and coupled to the input waveguide 111. That is, the LD 102 and the PLC 110 are optically coupled by a parallel beam system. Unlike the optical transmission module 100 of FIG. 1, the beam splitter 104 is not arranged between the lens 103a and the lens 103b. Therefore, it is possible to shorten the optical length between the LD 102 and the PLC 210. Note that a spot size converter may be arranged in the PLC 210 to match the diameter of the light collected by the lens 103b to the input waveguide 111. The optical coupling between each LD 102 and the input waveguide 111 of the PLC 110 may be optically coupled by a parallel beam system using two lenses as described above, or may be optically coupled by one lens.

[0028] In the optical transmission module 200, four monitor PDs 205-0 to 205-3 are arranged on the side end face of the PLC 210. In this respect, it differs from the optical transmission module 100 in FIG.

[0029] The PLC 210 is a quartz planar lightwave circuit, and includes an input waveguide 111, a lattice filter 213 formed by a waveguide, and an output waveguide 112. The configuration of the lattice filter 213 will be described later. It is configured such that light of wavelength λ0 from the LD 102-0 is coupled to the input waveguide 111-0, light of wavelength λ2 from the LD 102-2 is coupled to the input waveguide 111-1, light of wavelength λ1 from the LD 102-1 is coupled to the input waveguide 111-2, and light of wavelength λ3 from the LD 102-3 is coupled to the input waveguide 111-3. In this embodiment, the light of wavelengths λ0, λ1, λ2, and λ3 input to the lattice filter 213 is multiplexed and coupled to the output waveguide 112, and is output from the end face on the output side of the PLC 210. In this embodiment, the arrangement order of the four LDs 102-0 to 102-3 shown in FIG. 1 is changed to the arrangement order shown in FIG. 2. If the arrangement order of the four LDs 102-0 to 102-3 shown in FIG. 1 is maintained, a crossing waveguide may be used in the PLC 210 to couple the input waveguide 111 and the lattice filter 213 together.

[0030] A lens 103c is provided on the end face of the output side of the PLC 210, and an isolator 106 is disposed beyond the lens 103c. The multiplexed light is guided through the output waveguide 112 and optically coupled to the optical fiber 120 via the lens 103c, the isolator 106, and a lens 122 provided on the end face of the PLC 110. The lenses 103c and 122 also optically couple the PLC 110 and the optical fiber 120 in a parallel beam system. The isolator 106 may be omitted. In order to match the diameter of the light emitted from the PLC 210 to the diameter of the optical fiber 120, a spot size converter may be disposed instead of the lenses 103c and 122. In order to reduce reflected light generated at the end face of PLC210, a PLC210 with an end face cut at an angle may be used in place of isolator 106 or in addition to isolator 106 (for example, the end face of PLC210 may be cut at an angle of about 10 degrees), or a PLC210 with an anti-reflection AR coating on the end face may be used.

[0031] (Lattice filter configuration) Next, a planar lightwave circuit type lattice filter will be described with reference to Fig. 3. Fig. 3 is a diagram showing a schematic configuration of a lattice filter 213 composed of waveguides formed on a PLC 210. As shown in Fig. 3, the lattice filter 213 includes a multiplexing circuit 303 connected to four waveguides 321. Waveguides 321-0 to 321-3 are connected to input waveguides 111-0 to 111-3, respectively.

[0032] The multiplexing circuit 303 is a multi-stage Cascade Connection The optical fiber optics 100 includes four Mach-Zehnder Interferometer (MZI) type circuits 331a, 332a, 341a, and 351a arranged in a matrix. Each of the MZI type circuits includes two 2-input and 2-output couplers and two waveguides coupling the two couplers.

[0033] The MZI type circuit 331a and the MZI type circuit 332a are arranged in parallel. The MZI type circuit 331a and the MZI type circuit 332a are connected to the MZI type circuit 341a. Cascade Connection The MZI circuit 341a is connected to the MZI circuit 351a. Cascade Connection The MZI type circuits 331a and 332a arranged in parallel are the first stage, the MZI type circuit 341a is the second stage, and the MZI type circuit 351a is the third stage. teeth , are arranged in order to make the filter shape more rectangular by passing through them.

[0034] In each MZI circuit, the two waveguides that connect the two couplers have an optical path difference ΔL. An MZI circuit having an optical path difference is also called an asymmetric MZI circuit.

[0035] The signal light λ0 input from the LD 102-0 corresponding to Lane 0 to the waveguide 321-0 is split into two by the coupler on the input side of the first-stage MZI circuit 331a, passes through the two waveguides, and is combined by the coupler on the output side into two ofThe signal light λ2 input from the LD 102-2 corresponding to Lane 2 to the waveguide 321-1 is split into two by the coupler on the input side of the MZI 331a in the first stage, and is output from the lower output of the two waveguides. of The signal light λ0 and the signal light λ2 are input to the second-stage MZI circuit 341a. The signal light λ0 is split into two by the input coupler of the MZI circuit 341a and is output from the lower of the two outputs. of The two are then multiplexed and split by the output coupler. of The signal light λ2 is also output from the output of the second-stage MZI circuit 341a in the same manner as the signal light λ0. of The signal light λ0 and the signal light λ2 are each input to the third-stage MZI circuit 351a. The signal light λ0 is split into two by the input coupler of the third-stage MZI circuit 351a, and is output from two waveguides. of The two are then combined by the output coupler. of The signal light λ2 is also split into two by the coupler on the input side of the third-stage MZI circuit 351a, like the signal light λ0, and is output from the upper output. of The two are then combined by the output coupler. of The signal is output from the upper output.

[0036] The signal light λ1 input from the LD 102-1 corresponding to Lane 1 to the waveguide 321-2 is split into two by the coupler on the input side of the first-stage MZI circuit 332a, passes through the two waveguides, and is combined by the coupler on the output side into two of The signal light λ3 input from the LD 102-3 corresponding to Lane 3 to the waveguide 321-3 is split into two by the coupler on the input side of the MZI 332a in the first stage, and is output from the upper one of the outputs. of The two are then combined by the output coupler. ofThe signal light λ1 and the signal light λ3 are output from the upper output. The signal light λ1 and the signal light λ3 are input to the second-stage MZI circuit 341a. The signal light λ1 is split into two by a coupler on the input side of the MZI circuit 341a, and is output to two waveguides. of The two are then multiplexed and split by the output coupler. of The signal light λ3 is also output from the output of the second-stage MZI circuit 341a in the same manner as the signal light λ1. of The two are then multiplexed and split by the output coupler. of The signal light λ1 and the signal light λ3 are output from the output. Furthermore, the signal light λ1 and the signal light λ3 are each input to the third-stage MZI circuit 351a. The signal light λ1 is split into two by a coupler on the input side of the third-stage MZI circuit 351a, and is output to two waveguides. of The two are then combined by the output coupler. of The signal light λ3 is also split into two by the coupler on the input side of the third-stage MZI circuit 351a, like the signal light λ1, and is output from the upper output. of The two are then combined by the output coupler. of The signal is output from the upper output.

[0037] In this way, the signal lights λ0 to λ3 input to the multiplexing circuit 303 are multiplexed and output by two couplers on the output side of the third-stage MZI circuit 351a. of In this embodiment, a part of the signal light multiplexed by the multiplexing circuit 303 in the coupler 371 is branched off for a power monitor, and the remainder is coupled to the output waveguide 112 through the waveguide 361.

[0038] The lattice filter 213 shown in FIG. 3 includes a demultiplexing circuit 370 connected to the multiplexing circuit 303 via a coupler 371. The demultiplexing circuit 370 is provided to separate a part of the light multiplexed by the multiplexing circuit 303 into four wavelengths again so that the power can be measured by a monitor PD. The configuration of the demultiplexing circuit 370 is the same as that of the multiplexing circuit 303. The demultiplexing circuit 370 is arranged point-symmetrically with the multiplexing circuit 303 with the coupler 371 at the center. By arranging the demultiplexing circuit 370 in this way, the light once multiplexed can be separated again into signals of λ0, λ1, λ2, and λ3, and the signals can be taken out from the end face of the PLC (chip) via output waveguides 381-0 to 381-3 connected to the couplers on the output side of the MZI circuit 331b and the couplers on the output side of the MZI circuit 332b (corresponding to the couplers on the input side of the MZI circuit 331a and the couplers on the input side of the MZI circuit 332a, respectively). To change the arrangement of monitors PD205-0 to 205-3: 、 A cross waveguide may be used to couple between the waveguide 381 of the lattice filter 213 and the monitor PD 205 .

[0039] Since the monitor PD205 is intended to read the power fluctuations of the signal light emitted by the LD102, the branching ratio of the coupler 371 may be set, for example, so that the power of the signal light transmitted to the MPD295 is a very small portion (e.g., 2%) of the power of the multiplexed signal light.

[0040] FIG. 4 is a diagram showing a schematic configuration of a planar lightwave circuit type lattice filter according to an embodiment of the present disclosure. FIG. 4 shows an example of the arrangement of a lattice filter 213 including a multiplexing circuit 303 described with reference to FIG. 3 and a demultiplexing circuit 370 connected via a coupler 371. If a plurality of MZI type circuits that are cascaded in multiple stages and that constitute the lattice filter 213 are arranged in a straight line, the overall circuit length becomes long. As shown in FIG. 4, by arranging them in a coiled manner, they can be accommodated in a small space, and the chip (PLC) can be made smaller. Note that when at least one of the multiplexing circuit 303 and the demultiplexing circuit 370 is arranged in a coiled manner, the overall circuit length can be shortened compared to when they are arranged in a straight line, and the chip can be made smaller.

[0041] In the above-mentioned 4-channel optical transmission module, the multiplexing circuit 303 that multiplexes 4-channel signal lights (λ0 to λ3) with different wavelengths must have at least three MZI type circuits connected in tandem in at least two stages. When multiplexing N (2 or more)-channel signal lights (λ0, . . . λ(N-1)) with different wavelengths, the multiplexing circuit 303 is 1 As proposed in

[2013] , a lattice filter can be constructed by cascading at least N-1 MZI circuits in multiple stages. In addition, the rectangularity of the filter shape can be increased by further cascading the MZI circuits of the lattice filter.

[0042] Second Embodiment A planar lightwave circuit type lattice filter and an optical transmission module according to a second embodiment of the present disclosure will be described with reference to Fig. 5. Fig. 5 is a diagram showing a schematic configuration of a lattice filter 513. The optical transmission module 200 shown in Fig. 2 can be configured using the lattice filter 513 as a substitute for the lattice filter 213 shown in Figs. 3 and 4.

[0043] Lattice filter 513 shown in FIG. 5 includes multiplexing circuit 503 and demultiplexing circuit 570 connected via coupler 371. Multiplexing circuit 503 differs from multiplexing circuit 303 shown in FIG. 3 in that it does not have MZI circuit 351a. Demultiplexing circuit 570 differs from demultiplexing circuit 370 shown in FIG. 3 in that it does not have MZI circuit 351b. The configuration of the MZI circuit constituting lattice filter 513 is similar to that of demultiplexing circuit 370 shown in FIG. 3, so a detailed description will be omitted. Lattice filter 513 shown in FIG. 5 can also be accommodated in a small space by arranging it in a coiled manner as shown in FIG. 4, making it possible to miniaturize the chip (PLC).

[0044] The lattice filter 513 includes an MZI circuit 351a and an MZI circuit 351b. Cascade Connection Since the filter shape is not rectangular, it is less rectangular than the lattice filter 213. Cascade Connection Since the number of MZI circuits required is reduced, it is possible to reduce loss and shorten the circuit length.

[0045] (Third embodiment) A planar lightwave circuit type lattice filter and an optical transmission module according to a third embodiment of the present disclosure will be described with reference to Fig. 6. Fig. 6 is a diagram showing a schematic configuration of a lattice filter 613. The optical transmission module 200 shown in Fig. 2 can be configured using the lattice filter 613 as a substitute for the lattice filter 213 shown in Figs. 3 and 4.

[0046] The lattice filter 613 shown in FIG. 6 includes a multiplexing circuit 603 and a demultiplexing circuit 670 connected via a coupler 371. The multiplexing circuit 603 is connected to the MZI circuit 351a. Cascade Connection 3 in that it has a fourth-stage MZI circuit 661a connected to the MZI circuit 351b. Cascade Connection 3 in that it has an MZI circuit 661b connected thereto.

[0047] In the multiplexing circuit 603 of the lattice filter 613, the signal light λ0 is split into two by a coupler on the input side of the third-stage MZI circuit 351a, and is fed into two waveguides. of The two are then multiplexed and split by the output coupler. of The signal light λ2 is also split into two by the coupler on the input side of the third-stage MZI circuit 351a, like the signal light λ0, and is output from the output. of The two are then multiplexed and split by the output coupler. From the output of Furthermore, the signal light λ0 and the signal light λ2 are each input to the fourth-stage MZI circuit 661a. The signal light λ0 is split into two by a coupler on the input side of the fourth-stage MZI circuit 661a, and is output to two waveguides. of The two are then combined by the output coupler. of The signal light λ2 is also split into two by the input coupler of the fourth-stage MZI circuit 661a, like the signal light λ0, and is output from the upper output. of The two are then combined by the output coupler. of The signal is output from the upper output.

[0048] In the multiplexing circuit 603 of the lattice filter 613, the signal light λ1 is split into two by a coupler on the input side of the third-stage MZI circuit 351a, and is fed into two waveguides. of The two are then multiplexed and split by the output coupler. of The signal light λ3 is also split into two by the coupler on the input side of the third-stage MZI circuit 351a, like the signal light λ1, and is output from the output. of The two are then multiplexed and split by the output coupler. From the output of Furthermore, the signal light λ1 and the signal light λ3 are each input to the fourth-stage MZI circuit 661a. The signal light λ1 is split into two by a coupler on the input side of the fourth-stage MZI circuit 661a, and is output to two waveguides. of The two are then combined by the output coupler. of The signal light λ3 is also split into two by the input coupler of the fourth-stage MZI circuit 661a, like the signal light λ1, and is output from the upper output. ofThe two are then combined by the output coupler. of The signal is output from the upper output.

[0049] In this way, the signal lights λ0 to λ3 input to the multiplexing circuit 603 are multiplexed and output by two couplers on the output side of the fourth-stage MZI circuit 661a. of In this embodiment, a part of the signal light multiplexed by the multiplexing circuit 603 in the coupler 371 is branched off for a power monitor, and the remainder is coupled to the output waveguide 112 through the waveguide 361.

[0050] The lattice filter 613 shown in Fig. 6 includes a demultiplexing circuit 670 connected to the multiplexing circuit 603 via a coupler 371. The demultiplexing circuit 670 is provided to separate a part of the light multiplexed by the multiplexing circuit 303 into four wavelengths again so that the power can be measured by a monitor PD. The configuration of the demultiplexing circuit 670 is the same as that of the multiplexing circuit 603. The demultiplexing circuit 370 is arranged point-symmetrically with the multiplexing circuit 303 with the coupler 371 at the center. This point has been described above with reference to Fig. 3, so a description thereof will be omitted.

[0051] Lattice filter 613 shown in FIG. 6 can also be accommodated in a small space by arranging it in a coiled shape as shown in FIG. 4, making it possible to miniaturize the chip (PLC).

[0052] 6 has a wider spectral transmission width than lattice filter 213 shown in FIG. 3 and lattice filter 413 shown in FIG. 4, and can relax manufacturing margins of the optical transmission module, such as margins for wavelength accuracy. In the multiplexing circuit 603 of the lattice filter 613, an MZI type circuit is used. Cascade Connection It is possible to increase the rectangularity of the filter by increasing the number of stages. [Industrial Applicability]

[0053] This disclosure ToAccording to the present disclosure, it is possible to provide a planar lightwave circuit type having small loss and a high degree of rectangularity of the filter shape. Alternatively, according to the present disclosure, it is possible to provide a compact planar lightwave circuit type. Alternatively, according to the present disclosure, it is possible to provide a planar lightwave circuit type capable of reducing the number of parts. [Explanation of symbols]

[0054] 100, 200 Optical Transmitter Module 101 Pedestal 102 Laser Diode 103, 122 Lens 104 Beam splitter 105, 205 Monitor PD 106 Isolator 107 Packages 108 Electrical Circuit 109 TEC 110, 210 PLC 111 Input waveguide 112 Output waveguide 113 Arrayed Waveguide Grating 120 Optical Fiber 121 Sleeve 213, 513, 613 Lattice Filter 303, 503, 603 multiplexing circuit 370, 570, 670 branching circuit 321, 361, 381 Waveguide 331, 332, 341, 351 MZI type circuit 371 Coupler

Claims

1. A planar lightwave circuit type lattice filter for multiplexing a plurality of signal lights having different wavelengths, comprising: a plurality of input waveguides for receiving the plurality of signal lights; a multiplexing circuit for multiplexing the plurality of signal lights; at least one output waveguide for outputting the combined signal; Equipped with The multiplexing circuit has asymmetric MZI type circuits cascaded in a plurality of stages, The asymmetric MZI type circuit is An input coupler; An output coupler; two waveguides having an optical path length difference, which connect the output of the input side coupler and the input of the output side coupler; Including, Two of the plurality of input waveguides are connected to the inputs of the input-side couplers of the asymmetric MZI circuit arranged in the first stage, A planar lightwave circuit type lattice filter configured such that a signal light obtained by multiplexing the multiple signal lights output from an output coupler of an asymmetric MZI type circuit arranged in a final stage is coupled to the output waveguide.

2. 2. The planar lightwave circuit type lattice filter according to claim 1, wherein the input of the input side coupler of one asymmetric MZI type circuit arranged in the final stage is connected to the output of the output side coupler of one asymmetric MZI type circuit arranged in the stage before the final stage.

3. a coupler having one input and two outputs; Splitter circuit and Further equipped with One input of the coupler is connected to one of two outputs of an output-side coupler of one asymmetric MZI circuit arranged in the final stage of the multiplexing circuit, one of the two outputs of the coupler is connected to the output waveguide, and the other output is connected to the splitter circuit; the branching circuit is configured point-symmetrically with the multiplexing circuit centered on the coupler, 3. The planar lightwave circuit type lattice filter according to claim 1, wherein said demultiplexing circuit demultiplexes the signal multiplexed by said multiplexing circuit into the plurality of signal lights having different wavelengths and outputs the demultiplexed signal lights.

4. 4. The planar lightwave circuit type lattice filter according to claim 3, wherein at least one of the asymmetric MZI type circuits cascaded in multiple stages of the multiplexing circuit and the asymmetric MZI type circuits cascaded in multiple stages of the demultiplexing circuit is arranged in a coiled shape.

5. 5. The planar lightwave circuit type lattice filter according to claim 4, which is a quartz planar lightwave circuit.

6. An optical transmission module for use in optical communications, comprising: A planar lightwave circuit type lattice filter according to claim 3; a plurality of light sources outputting a plurality of signal lights having different wavelengths; Optical fiber and Equipped with an optical transmission module configured so that a signal light obtained by multiplexing the plurality of signal lights guided through the output waveguide is coupled to the optical fiber;

7. a plurality of waveguides to which the plurality of signal lights having different wavelengths demultiplexed from the signal multiplexed by the multiplexing circuit are coupled by the demultiplexing circuit; a plurality of light receiving elements for receiving the plurality of signal lights having different wavelengths; Further equipped with 7. The optical transmission module according to claim 6, wherein the plurality of light receiving elements are arranged on an end face of a substrate on which the multiplexing circuit is formed, and receive the plurality of signal lights having different wavelengths via the plurality of waveguides.