Wavelength filter, wavelength division multiplexing light source, wavelength division multiplexing optical receiver, and wavelength filter production method

Abstract

In a wavelength filter (13) according to the present invention, a single waveguide is connected to one end surface, a plurality of waveguides are connected to the other end surface, the plurality of waveguides respectively input light having a plurality of wavelengths, and light in which the light having a plurality of wavelengths has been multiplexed is output by the single waveguide. The wavelength filter comprises a first substance (131), a second substance (132) that has a lower refractive index than the first substance, and a plurality of aggregates in which the first substance is contiguous in an irregular shape within the second substance. One portion of the aggregates among the plurality of aggregates is disposed so as to be contiguous between the single waveguide and each of the plurality of waveguides. Another portion of the aggregates among the plurality of aggregates is not contiguous with the one portion of aggregates and is disposed surrounding the one portion of aggregates. Input light is multi-scattered, undergoes interference, and is output by the plurality of aggregates.　Thus, the present invention can provide a compact wavelength filter with an excellent modulation characteristic.

Description

Wavelength filter, wavelength multiplexing light source, wavelength multiplexing optical receiver, and method for manufacturing wavelength filter

[0001] The present invention relates to a wavelength filter, a wavelength multiplexing light source, a wavelength multiplexing optical receiver, and a method for manufacturing a wavelength filter.

[0002] With the explosive increase in communication traffic, optical transceivers are required to have higher speeds and larger capacities, lower power consumption, smaller size, and lower cost. To expand communication capacity, optical transceivers for wavelength division multiplexing, polarization multiplexing, multi-channelization, and multi-level modulation have been put into practical use.

[0003] As components of an optical transmitter / receiver for WDM communications, light sources with different wavelengths and a wavelength multiplexer for guiding these multiple wavelength lights into a single optical waveguide are required.

[0004] Conventionally, semiconductor lasers and wavelength multiplexers are manufactured separately, and the laser's oscillation wavelength and the wavelength multiplexer's transmission wavelength are inspected before integration. Good products are selected, and then the good products are hybrid-integrated.

[0005] In recent years, efforts have been made to integrate semiconductor lasers and wavelength multiplexers on a silicon substrate in order to reduce the size and cost of optical transmitters and receivers. In this case, it is not possible to select non-defective products before integrating the semiconductor lasers and wavelength multiplexers. In particular, the oscillation wavelength of the semiconductor laser (e.g., a distributed feedback laser) or the transmission wavelength of the wavelength multiplexer deviates from the design wavelength due to processing errors, resulting in increased optical loss or crosstalk during wavelength multiplexing. Furthermore, the rate of wavelength change (the amount of wavelength change relative to temperature) with substrate temperature differs for the oscillation wavelength of the semiconductor laser and the transmission wavelength of the wavelength multiplexer, resulting in increased optical loss or crosstalk when the substrate temperature changes.

[0006] Therefore, as shown in Non-Patent Document 1, a configuration has been reported in which an arrayed waveguide grating (AWG) filter is inserted into the optical resonator of a semiconductor laser. In this configuration, the oscillation wavelength of the semiconductor laser is determined by the transmission wavelength of the AWG. Therefore, it is not necessary to match the oscillation wavelength of the semiconductor laser with the transmission wavelength of the wavelength multiplexer, and an increase in optical loss due to a difference between these wavelengths does not occur.

[0007] S.Keyvaninia et al., “III-V-on-silicon multi-frequency lasers”, Optics Express Vol.21, Issue 11, pp.13675-13683 (2013), https: / / doi.org / 10.1364 / OE.21.013675

[0008] However, in the above-described configuration in which an AWG filter is inserted into the optical resonator of a semiconductor laser, the size of the AWG filter is large, about several hundred μm square, making it difficult to miniaturize the element.

[0009] Furthermore, an increase in the optical path length of the entire resonator increases the photon lifetime τp and decreases the optical confinement factor Γz of the active layer, which reduces the relaxation oscillation frequency fr to around several GHz, making high-speed direct modulation difficult. Therefore, when optical modulation is performed using an external modulator for high-speed modulation, a discrepancy occurs between the optimal operating wavelength of the modulator and the oscillation wavelength of the laser, which causes a problem of deterioration in modulation efficiency.

[0010] In order to solve the above-mentioned problems, a wavelength filter according to the present invention has a single waveguide connected to one end face and a plurality of waveguides connected to the other end face, light of a plurality of wavelengths input through the plurality of waveguides for each wavelength, and light obtained by combining the light of the plurality of wavelengths is output through the single waveguide, the wavelength filter comprising a first material and a second material having a refractive index lower than that of the first material, the first material comprising a plurality of aggregates that are connected in an irregular shape within the second material, some of the plurality of aggregates being arranged in connection between the single waveguide and each of the plurality of waveguides, and other of the plurality of aggregates being arranged around the some of the aggregates without being connected to the some of the aggregates, and the input light is multiplexed by the plurality of aggregates, interferes, and is output.

[0011] Furthermore, a wavelength filter according to the present invention is a wavelength filter having a single waveguide connected to one end face and a plurality of waveguides connected to the other end face, wherein light obtained by combining light of a plurality of wavelengths is input through the single waveguide and light of the plurality of wavelengths is output through the plurality of waveguides for each wavelength, the wavelength filter comprising a first material and a second material having a refractive index lower than that of the first material, wherein the first material comprises a plurality of aggregates that are connected in an irregular shape within the second material, some of the plurality of aggregates are arranged in connection between the single waveguide and each of the plurality of waveguides, and other some of the plurality of aggregates are arranged around the some of the aggregates without being connected to the some of the aggregates, and the input light is multiplexed by the plurality of aggregates, interferes, and is output.

[0012] Furthermore, a method for manufacturing a wavelength filter according to the present invention is a method for manufacturing a wavelength filter having a topology composed of a first material and a second material having a refractive index lower than that of the first material, and includes the steps of setting the first material, the second material, the size of the topology, and the spectra of input light and output light of the wavelength filter; calculating the spectrum of output light when the set broad light is input for the topology configuration consisting of the first material and the second material and having the size; comparing the spectrum of output light obtained by the calculation with the spectrum of output light set; and forming the topology of the wavelength filter based on the topology when the spectrum of output light obtained by the calculation and the spectrum of output light set approximately match.

[0013] According to the present invention, it is possible to provide a small wavelength filter, a wavelength multiplexing light source, a wavelength multiplexing optical receiver, and a method for manufacturing a wavelength filter, all of which have excellent modulation characteristics.

[0014] FIG. 1 is a schematic diagram showing the configuration of a wavelength-multiplexed light source according to a first embodiment of the present invention. FIG. 2A is a diagram for explaining a wavelength filter according to the first embodiment of the present invention. FIG. 2B is a diagram for explaining a wavelength filter according to the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional diagram showing the configuration of a gain waveguide in a wavelength-multiplexed light source according to the first embodiment of the present invention. FIG. 4A is a diagram for explaining a high-reflectivity mirror in a wavelength-multiplexed light source according to the first embodiment of the present invention. FIG. 4B is a diagram for explaining an example of a high-reflectivity mirror in a wavelength-multiplexed light source according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining a low-reflectivity mirror in a wavelength-multiplexed light source according to the first embodiment of the present invention. FIG. 6 is a flowchart for explaining a method for manufacturing a wavelength filter according to the first embodiment of the present invention. FIG. 7 is a diagram for explaining the effect of a wavelength-multiplexed light source according to the first embodiment of the present invention. FIG. 8 is a schematic cross-sectional diagram showing the configuration of a wavelength-multiplexed light source according to a second embodiment of the present invention. FIG. 9 is a schematic cross-sectional diagram showing the configuration of an electroabsorption modulator in a wavelength-multiplexed light source according to the second embodiment of the present invention. FIG. 10A is a diagram for explaining the effect of a wavelength-multiplexed light source according to the second embodiment of the present invention. Fig. 10B is a diagram for explaining the effect of the wavelength multiplexed light source according to the second embodiment of the present invention. Fig. 11 is a schematic diagram showing an example of the configuration of the wavelength multiplexed light source according to the second embodiment of the present invention. Fig. 12 is a schematic diagram showing the configuration of a wavelength multiplexed optical receiver according to a third embodiment of the present invention.

[0015] First Embodiment A wavelength filter, a wavelength multiplexing light source, and a method for manufacturing a wavelength filter according to a first embodiment of the present invention will be described with reference to FIGS.

[0016] 1, a wavelength-multiplexed light source 10 according to this embodiment includes, in order, a plurality of high-reflectivity mirrors 11, a plurality of gain waveguides 12, a wavelength filter 13, a low-reflectivity mirror 14, and a spot-size converter 15. The plurality of high-reflectivity mirrors 11 and the plurality of gain waveguides 12 are optically connected to each other via optical waveguides 16. The plurality of gain waveguides 12, the wavelength filters 13, and the low-reflectivity mirrors 14 are optically connected to each other via optical waveguides 16.

[0017] The wavelength filter 13 according to this embodiment has a basic configuration in which the topology of its rectangular structure is changed so that multiplexed light of multiple wavelengths enters one end face, is demultiplexed, and light of the desired wavelength is output to each of the multiple waveguides (S. Molesky et al., “Outlook for inverse design in nanophotonics”, Nature Photonics, January 2018, DOI:10.1038 / s41566-018-0246-9).

[0018] Here, the topology is a structure of a first material (e.g., Si) 131 and a second material (e.g., SiO ２ ) 132. The topology size is small, about 1 μm to 10 μm square.

[0019] In the topology of the wavelength filter 13, fine cells (e.g., 1 nm) of a material 131 with a high refractive index are formed. ２ , layer thickness 220 nm) are arranged two-dimensionally irregularly in a substance 132 having a low refractive index so that a plurality of lights of different wavelengths are multiplexed.

[0020] 2A and 2B show an example of the topology of the wavelength filter 13. The rectangular structure of 6 μm square (made of Si, surrounded by SiO ２A single waveguide is connected to one end (left side in the figure) of the optical fiber, and four waveguides are connected to the other end (right side in the figure). The optical fiber is inversely designed so that when light is input from the waveguide at one end, light of a specified wavelength is transmitted from each waveguide at the other end. The transmitted wavelength output from each port has an FSR of 20 nm.

[0021] 2A shows the inverse designed topology obtained by calculation. The light-colored area indicates the area of ​​a substance with a high refractive index (hereinafter also referred to as the "first substance") 131, and the dark-colored area indicates the area of ​​a substance with a low refractive index (hereinafter also referred to as the "second substance") 132. Here, as an example, Si is used for the first substance 131 and SiO is used for the second substance 132. ２ The fine Si of the high refractive index material 131 is mixed with the SiO of the low refractive index material 132. ２ The Si aggregates (input / output aggregates) of the plurality of aggregates are connected in a two-dimensional irregular shape within the substrate, forming a plurality of aggregates. Some Si aggregates (input / output aggregates) of the plurality of aggregates are connected from the light input position to the respective output positions. Other Si aggregates (peripheral aggregates) of the plurality of aggregates are arranged around the input / output aggregates without being connected to them. In the above topology, the propagating light is multiple-scattered and interferes in the plurality of aggregates of the first material (Si) 131, resulting in the light having wavelengths λ １ ~λ ４ The signal is split into two and output.

[0022] Figure 2B shows the transmission spectrum of the topology shown in Figure 2A. Light with a wavelength of 1.27 μm (solid line) is transmitted through the waveguide at port 1 (P1), light with a wavelength of 1.29 μm (dotted line) is transmitted through the waveguide at port 2 (P2), light with a wavelength of 1.31 μm (dashed line) is transmitted through the waveguide at port 3 (P3), and light with a wavelength of 1.33 μm (dashed line) is transmitted through the waveguide at port 4 (P4).

[0023] In the wavelength multiplexed light source 10, the wavelength filter 13 has a configuration in which the input and output of the above-mentioned topology ( FIG. 2 ) are reversed. That is, the wavelength filter 13 is a wavelength multiplexer, and multiple waveguides are connected to one end of a rectangular structure, and a single waveguide is connected to the other end. The topology of the rectangular structure is changed so that light of different wavelengths incident from each of the multiple waveguides is multiplexed in the wavelength multiplexer 13.

[0024] The wavelength multiplexer 13 is made of SiO ２ On the layer, Si and SiO ２ The waveguide layer has a topology (thickness: 220 nm) consisting of:

[0025] In this way, in the wavelength multiplexing light source 10, a conventional AWG filter (for example, 500 μm ２ By using a wavelength multiplexer 13 (approximately 5 μm to 10 μm square) which can be made smaller than a conventional wavelength multiplexer (approximately 5 μm to 10 μm square), the optical path length of the resonator can be reduced, and an increase in the photon lifetime τp and a decrease in the optical confinement factor Γz of the active layer can be suppressed, so that the relaxation oscillation frequency fr can be improved to approximately several tens of GHz. This enables high-speed modulation.

[0026] As shown in FIG. 3, the gain waveguide 12 is formed by sequentially forming a second core (e.g., Si) 1203 and a second clad (e.g., SiO ２ and a second optical waveguide consisting of a first core (e.g., an InP-based multiple quantum well, MQW) 1205 and a first cladding (e.g., InP) 1204, 1206 (see, for example, T. Aihara et al., “Membrane III-V / Si DFB Laser Using Uniform Grating and Width-Modulated Si Waveguide”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 38, NO. 11 (2020)).

[0027] In the gain waveguide 12, a p-type semiconductor layer 1207 is provided on one of the side surfaces of the first optical waveguide, and an n-type semiconductor layer 1208 is provided on the other side surface. Here, the "side surface of the optical waveguide" refers to the end face of the first optical waveguide that is parallel to the propagation direction of light and perpendicular to the surface of the substrate. Also, a p-type modulator electrode 1209 is provided on the surface of the p-type semiconductor layer 1207, and an n-type modulator electrode 1210 is provided on the surface of the n-type semiconductor layer 1208. This allows current to be injected laterally into the first optical waveguide. Also, a dielectric film (e.g., SiO ２ ) 1211 is placed.

[0028] Each of the multiple gain waveguides 12 has a different wavelength λ １ ~λ ４ and each of the gain waveguides 12 has a first core (e.g., MQW) having a composition corresponding to a different wavelength λ １ ~λ ４ It emits light.

[0029] In the second optical waveguide, the second core (Si) 1203 is connected to the second clad (SiO ２ ) 1202, and a supermode is formed between the first core 1205 and the second core 1203.

[0030] The above structure allows for a small, low-loss optical connection between the silicon waveguide 16 and the gain waveguide 12 over a short length (several micrometers). The gain waveguide 12 and the wavelength multiplexer 13 are optically connected via the silicon waveguide 16.

[0031] 4A, the high-reflectivity mirror 11 is, for example, a DBR mirror in which a DBR 111 having a periodic refractive index change is formed in a silicon waveguide 112. In this configuration, light having a wavelength in the stop band of the DBR mirror 11 is reflected with a high reflectivity.

[0032] 4B, the high-reflectivity mirror 11 may be configured by combining a 1×2 multimode interferometer 113 and a ring resonator 114. In this configuration, light having a resonant wavelength of the ring resonator 114 is reflected with a high reflectivity.

[0033] 5, the low-reflectivity mirror 14 has a configuration in which two outputs of a 2×2 multimode interferometer or a directional coupler are connected. For example, input light (solid arrow in the figure) propagates through one waveguide 141, couples to two waveguides (one waveguide and the other waveguide) 141, 142 via a loop waveguide 143, and is output as reflected light (dotted arrow in the figure) from the one waveguide 141. The reflectivity in this configuration can be controlled by the branching ratio of the two waveguides (one waveguide and the other waveguide) 141, 142.

[0034] The spot size converter 15 has a SiOx waveguide structure that narrows toward the tip (see, for example, Non-Patent Document 4). The SiOx waveguide and the Si waveguide are optically coupled. This SiOx waveguide enables low-loss and low-reflection fiber coupling.

[0035] <Method of Manufacturing Wavelength Filter> An example of a method of manufacturing the wavelength filter 13 according to this embodiment will be described below. Fig. 6 is a flowchart illustrating a method of manufacturing the wavelength filter 13.

[0036] The topology of the wavelength filter 13 is designed by inverse design using electromagnetic field analysis based on the finite difference time domain method.

[0037] First, the first material 131 and the second material 132 that make up the topology are selected, and their refractive indices are set. Here, Si (refractive index: 3.48) is used as the first material 131, and SiO 2 is used as the second material 132. ２ (refractive index: 1.44) was set.

[0038] The size of the topology is also set. If the topology is too small, it will not be possible to multiplex or demultiplex light, and if it is too large, optical loss will increase. Here, the size of the topology is set to 6 μm x 6 μm. The size of the topology may be 5 μm x 5 μm to 10 μm x 10 μm. The size of the topology depends on the material that makes up the topology. If SiN is used instead of Si, the size is two to three times larger.

[0039] In addition, the spectrum of the input light and the output light is set (step S1). For example, the input light has a plurality of wavelengths λ １ ~λ４ The output light is a multiplexed light having a peak at a wavelength of 1.3 μm and a broad wavelength range of 1.2 μm to 1.3 μm, as shown in FIG. １ ~λ ４ Let λ be the four spectra. １ = 1.27 μm, λ ２ = 1.29 μm, λ ３ = 1.31 μm, λ ４ = 1.33 μm.

[0040] Next, a predetermined topology (Si and SiO) based on the above setting is created. ２ The spectrum of the output light is calculated assuming that a set broad light is input to the optical fiber (the refractive index distribution between the optical fiber and the optical fiber) (step S2).

[0041] Next, the spectrum of the output light obtained by calculation is compared with the set spectrum of the output light (step S3).

[0042] If the calculated spectrum of the output light and the set spectrum of the output light substantially match, the calculation is terminated. The topology at this time is determined as the topology of the wavelength filter 13.

[0043] If the calculated spectrum of the output light does not substantially match the set spectrum of the output light, the calculation is repeated.

[0044] Here, "substantially match" includes a perfect match, and also includes a case where the difference between the calculated output light spectrum and the set output light spectrum is within a predetermined range. The predetermined range may be a wavelength error of 0.001 μm or less for each peak in the spectrum. Alternatively, the wavelength error of all peaks may be 0.005 μm or less.

[0045] Based on the topology determined above, the topology is formed by semiconductor processing processes such as ordinary photolithography and etching techniques (step S4), thereby manufacturing the wavelength filter 13.

[0046] <Effects> The effects of the wavelength multiplexed light source 10 according to this embodiment will be described with reference to FIG.

[0047] In wavelength-multiplexed light source 10, a resonator is formed between high-reflectivity mirror 11 and low-reflectivity mirror 14. As a result, each of multiple gain waveguides 12 emits light of a different wavelength, and the light of the different wavelengths resonates between high-reflectivity mirror 11 and low-reflectivity mirror 14, resulting in laser oscillation.

[0048] In other words, as shown in FIG. 6, one of the multiple Fabry-Perot modes 171 of the resonator is transmitted through the transmission wavelength (for example, λ １ ) 172, laser oscillation 173 at a single wavelength is obtained. Therefore, this oscillation wavelength is determined by the transmission wavelength of the wavelength multiplexer 13. As a result, even if the transmission wavelength of the wavelength multiplexer 13 changes due to processing errors or temperature fluctuations, laser oscillation occurs at this transmission wavelength, so there is no need to match the oscillation wavelength of the laser with the transmission wavelength of the wavelength multiplexer 13 as in the conventional configuration.

[0049] Since the light guided through each port of the wavelength multiplexer 13 has a different transmission wavelength, the wavelength multiplexed light source 10 oscillates as a laser at a wavelength corresponding to each transmission wavelength. The multi-wavelength laser light from the wavelength multiplexed light source 10 is multiplexed into a single waveguide and output.

[0050] In the wavelength multiplexed light source 10, the intensity of the output light is modulated when the amount of current injected into the gain waveguide 12 is modulated. At this time, the modulation speed is determined by the relaxation oscillation frequency fr.

[0051] In conventional wavelength-multiplexed light sources, the AWG filter is large and the optical coupling length between the gain waveguide 12 and the silicon waveguide is long, resulting in a long overall cavity. As a result, the photon lifetime increases and the optical confinement factor Γz of the active layer decreases, causing the relaxation oscillation frequency fr to drop to around several GHz, making high-speed direct modulation difficult.

[0052] On the other hand, in the wavelength-multiplexed light source 10, the cavity length can be reduced, so the relaxation oscillation frequency fr can be increased to approximately several tens of GHz, enabling high-speed direct optical modulation. The relaxation oscillation frequency of this wavelength-multiplexed light source 10 is equivalent to that of a configuration with mirrors on both ends of the SOA (i.e., a Fabry-Perot laser). This is because the filter is small and the cavity length of the wavelength-multiplexed light source 10 is short.

[0053] Furthermore, as mentioned above, high-speed direct modulation is difficult with conventional wavelength-multiplexed light sources, so an external modulator is required for high-speed modulation. As a result, a deviation occurs between the optimal operating wavelength of the modulator and the laser oscillation wavelength due to processing errors and fluctuations in substrate temperature, resulting in a deterioration of modulation efficiency.

[0054] On the other hand, the wavelength multiplexing light source 10 is capable of high-speed direct modulation and does not require an external modulator for high-speed modulation, so that the degradation of modulation efficiency caused by wavelength shifts in conventional wavelength multiplexing light sources does not occur.

[0055] In this way, with the wavelength multiplexed light source 10, there is no need to adjust the oscillation wavelength of the semiconductor laser, the transmission wavelength of the wavelength multiplexer 13, and the optimal operating wavelength of the modulator, and a compact wavelength multiplexed light source is realized in which the effects of processing errors and temperature changes are suppressed.

[0056] According to this embodiment, it is possible to provide a compact wavelength multiplexed light source capable of high-speed modulation.

[0057] Second Embodiment A multiple wavelength light source according to a second embodiment of the present invention will be described with reference to FIGS.

[0058] 8, a wavelength-multiplexed light source 20 according to this embodiment differs from that of the first embodiment in that it includes an electroabsorption modulator 21 between the gain waveguide 12 and the wavelength multiplexer 13. The other configurations are the same as those of the first embodiment.

[0059] As shown in FIG. 9, the electroabsorption modulator 21 is configured by sequentially stacking a dielectric film (e.g., SiO ２ ) 2102 , and a third optical waveguide consisting of a third core (for example, 1.55 μm wavelength composition InP-based multiple quantum well, MQW) 2105 and third cladding (for example, InP) 2104 , 2106 .

[0060] In the electroabsorption modulator 21, a p-type semiconductor layer 2107 is provided on one of the side surfaces of the third optical waveguide, and an n-type semiconductor layer 2108 is provided on the other side surface. A p-type modulator electrode 2109 is provided on the surface of the p-type semiconductor layer 2107, and an n-type modulator electrode 2110 is provided on the surface of the n-type semiconductor layer 2108. This allows a voltage to be applied laterally to the third optical waveguide. A dielectric film (e.g., SiO ２ ) 2111 is placed.

[0061] In the electroabsorption modulator 21, the second waveguide core (Si core) is not disposed in order to enhance light confinement in the active layer and increase modulation efficiency.

[0062] The gain waveguide 12 and the electroabsorption modulator 21 are optically connected via a Si waveguide.

[0063] In this configuration, the intensity of the output light is modulated by modulating the voltage applied to the electroabsorption modulator 21, thereby modulating the loss within the resonator. Compared to the configuration in which the amount of injected current into the gain waveguide 12 is modulated as in the first embodiment, the degradation of response at frequencies higher than the relaxation oscillation frequency is suppressed (S. Mieda et al., "Ultra-Wide-Bandwidth Optically Controlled DFB Laser With External Cavity," IEEE Journal of Quantum Electronics, Vol. 52, Issue 6, 2200107, (2016)). As a result, a wide modulation bandwidth is obtained.

[0064] In the wavelength multiplexed light source 20, there is no need to match the oscillation wavelength of the semiconductor laser, the transmission wavelength of the wavelength multiplexer 13, and the optimal operating wavelength of the modulator, and a compact wavelength multiplexed light source can be realized in which the effects of processing errors and temperature modulation are suppressed.

[0065] <Effects> The effects of the multiple wavelength light source 20 according to this embodiment will be described with reference to FIGS. 10A and 10B.

[0066] In the wavelength division multiplexed light source 20, the intensity of the output light is modulated when the amount of current injected into the gain waveguide 12 is modulated. At this time, the modulation speed is determined by the relaxation oscillation frequency.

[0067] 10A and 10B show the calculation results (solid lines in the figures) of the relaxation oscillation frequency of the wavelength-multiplexed light source 20. For comparison, the calculation results (dashed lines in the figures) of the relaxation oscillation frequency of an element composed only of an SOA are also shown. The calculation was performed based on a rate equation. The parameters used in the calculation are as follows:

[0068] Length L of the gain waveguide 12 (SOA) ＳＯＡ = 100 μm EA modulator length L ＥＡ = 50 μm Length L of multimode interference waveguide (MMI) ＭＭＩ = 10 μm Absorption coefficient α of SOA ｉ＿ＳＯＡ = 10 cm －１ ・EA absorption coefficient α ｉ＿ＥＡ = 20 cm －１ (Applied voltage V of EA modulator ＥＡ = 0 V) ​​Absorption coefficient α of MMI ｉ＿ＭＭＩ = 20 cm －１ Optical confinement ratio Γxy = 20% Linear gain g = dN × (N - Ntr), where dN = 1145e-22m －２ , Ntr=1.45e24m －３ High-reflection mirror reflectance R1 = 99% Low-reflection mirror reflectance R2 = 1% Internal quantum efficiency η ｉ =0.5 ・Electron lifetime τ ｅ = 1 ns · n ｇ = 4.2 w = 0.6 μm Quantum well thickness d ＱＷ = 6.2 nm Number of quantum wells N ＱＷ = 6

[0069] The calculation results show that the relaxation oscillation frequency of the wavelength-multiplexed light source 20 is about 25 GHz at an injection current Ib of 30 mA, which is not significantly different from a configuration with only an SOA. Thus, the wavelength-multiplexed light source 20, even with a configuration in which an SOA is connected to an EA modulator and a wavelength multiplexer 13, has a relaxation oscillation frequency equivalent to that of a configuration with only an SOA.

[0070] The above calculation results are for the configuration of the second embodiment, which includes an SOA, an EA modulator, and a wavelength multiplexer 13. The wavelength multiplexed light source according to the first embodiment includes an SOA and a wavelength multiplexer 13, and can have the same or shorter overall resonator length as the configuration of the second embodiment, so that the same results as those of the second embodiment can be obtained.

[0071] In conventional wavelength multiplexed light sources, as described above, the entire resonator is long, which increases the photon lifetime and reduces the optical confinement factor Γz of the active layer, thereby reducing the relaxation oscillation frequency fr and making high-speed direct modulation difficult.

[0072] On the other hand, in the wavelength-multiplexed light source 20, the cavity length can be reduced, so the relaxation oscillation frequency can be increased to approximately several tens of GHz, enabling high-speed direct optical modulation. As shown in the above calculation results, the relaxation oscillation frequency of this wavelength-multiplexed light source 20 is equivalent to that of a configuration with mirrors on both ends of the SOA (i.e., a Fabry-Perot laser). This is because the filter is small and the cavity length of the wavelength-multiplexed light source 20 is short.

[0073] Furthermore, as mentioned above, high-speed direct modulation is difficult with conventional wavelength-multiplexed light sources, so an external modulator is required for high-speed modulation. As a result, a deviation occurs between the optimal operating wavelength of the modulator and the laser oscillation wavelength due to processing errors and fluctuations in substrate temperature, resulting in a deterioration of modulation efficiency.

[0074] On the other hand, the wavelength multiplexing light source 20 is capable of high-speed direct modulation and does not require an external modulator for high-speed modulation, so that the degradation of modulation efficiency caused by wavelength shifts in conventional wavelength multiplexing light sources does not occur.

[0075] In this way, in the wavelength multiplexed light source 20, there is no need to adjust the oscillation wavelength of the semiconductor laser, the transmission wavelength of the wavelength multiplexer 13, and the optimal operating wavelength of the modulator, and a compact wavelength multiplexed light source is realized in which the effects of processing errors and temperature changes are suppressed.

[0076] According to this embodiment, it is possible to provide a compact wavelength multiplexed light source capable of high-speed modulation.

[0077] 11, the wavelength multiplexed light source according to this embodiment may be configured as a DFB laser by providing a distributed feedback diffraction grating in the gain waveguide 12. Also, a low reflectance mirror 14 may be provided in front of the wavelength multiplexer 13, and a resonator structure without the wavelength multiplexer 13 may be used.

[0078] In this configuration, the oscillation wavelength of the laser does not depend on the characteristics of the wavelength multiplexer 13 but is determined by the Bragg wavelength of the diffraction grating, and it is necessary to match the oscillation wavelength of the DFB laser 12 with the transmission wavelength of the wavelength multiplexer 13. On the other hand, the photon-photon resonance phenomenon can be used, enabling a wider bandwidth direct modulation operation.

[0079] Third Embodiment A wavelength division multiplexing optical receiver according to a third embodiment of the present invention will be described with reference to FIG.

[0080] 12, a wavelength multiplexed optical receiver 30 according to a third embodiment of the present invention includes a wavelength filter 32 and a plurality of photodetectors 33. A spot size converter 31 is provided at the incident end of the wavelength filter 32. The receiver also includes a microheater 35 and a feedback mechanism.

[0081] The multiple-wavelength multiplexed light (optical modulation signal) is input to a wavelength filter 32 via a spot size converter 31 .

[0082] The wavelength filter 32 is a wavelength demultiplexer and has a configuration similar to the basic configuration of the topology described above. The wavelength demultiplexer 32 has a configuration in which the topology of a rectangular structure is changed so that light of a desired wavelength is output to each waveguide. The topology of the wavelength demultiplexer 32 is designed similarly to the topology of the wavelength multiplexer in the first embodiment.

[0083] The wavelength demultiplexer 32 is made of SiO ２ On the layer, Si and SiO ２ The waveguide layer has a topology (thickness: 220 nm) consisting of:

[0084] In this way, the wavelength demultiplexer 32 demultiplexes the input light into light of a plurality of wavelengths and outputs the demultiplexed light to each of the plurality of photodetectors 33 .

[0085] In the wavelength division multiplexing optical receiver 30, the transmission wavelength of the wavelength demultiplexer 32 and the wavelength of the input multi-wavelength multiplexed optical modulated signal do not necessarily match due to temperature changes and processing errors. Therefore, a microheater 35 and a feedback mechanism are used.

[0086] The feedback mechanism includes a monitor photodetector (PD) 37 and a monitor waveguide 36 for inputting a portion of the input light to the compact wavelength demultiplexer (for example, about 1% of the input light) to the monitor photodetector. Here, the topology of the wavelength demultiplexer 32 is inversely designed so that a portion (about 1%) of the input light is output to the monitor waveguide 36.

[0087] When the multi-wavelength multiplexed light (optically modulated signal) is input to the wavelength demultiplexer 32, the wavelength demultiplexer 32 is heated by the microheater 35 to change the refractive index of the topology of the wavelength demultiplexer 32 and adjust the wavelength of the light transmitted through the wavelength demultiplexer 32 so that the light intensity input to the monitor photodetector 37 is maximized. The transmission characteristics of the wavelength demultiplexer 32 shift overall to the shorter wavelength side when the power of the microheater 35 is reduced, and to the longer wavelength side when the power of the microheater 35 is increased. This allows the transmission wavelength of the wavelength demultiplexer 32 to approximately match the wavelength of the input multi-wavelength multiplexed optically modulated signal, and the light intensity input to each photodetector 33 can be increased.

[0088] This allows the power of the microheater 35 to be adjusted so as to maximize the transmission intensity to the photodetector 33. In this way, the wavelength division multiplexed optical receiver 30 can receive high-speed modulated signals with high efficiency.

[0089] According to this embodiment, it is possible to provide a compact wavelength division multiplexing optical receiver that is compatible with high-speed modulation.

[0090] The wavelength filter according to the embodiment of the present invention can be used as a wavelength demultiplexer or a wavelength multiplexer. When used as a wavelength demultiplexer, multiplexed light of multiple wavelengths is input from one end face, and multiple light of different wavelengths is output from the other end face. When used as a wavelength multiplexer, multiple light of different wavelengths is input from the other end face, and multiplexed light of multiple wavelengths is output from one end face.

[0091] In the embodiment of the present invention, a wavelength filter that inputs and outputs four wavelengths has been shown as an example, but the wavelength filter is not limited to four wavelengths and may be a wavelength filter that inputs and outputs a plurality of wavelengths.

[0092] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configurations of the wavelength filter, wavelength multiplexing light source, and wavelength multiplexing optical receiver, and the manufacturing method of the wavelength filter, etc. are shown, but the present invention is not limited to these. Anything that can exhibit the functions and effects of the wavelength filter, wavelength multiplexing light source, and wavelength multiplexing optical receiver may be used.

[0093] It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0094] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0095] (Supplementary Note 1) A wavelength filter having a single waveguide connected to one end face and a plurality of waveguides connected to the other end face, in which light of a plurality of wavelengths is input through the plurality of waveguides for each wavelength, and light obtained by combining the light of the plurality of wavelengths is output through the single waveguide, the wavelength filter comprising: a first material and a second material having a refractive index lower than that of the first material; the first material comprising a plurality of aggregates that are connected in an irregular shape within the second material; some of the plurality of aggregates are arranged in connection between the single waveguide and each of the plurality of waveguides; other some of the plurality of aggregates are arranged around the some of the aggregates without being connected to the some of the aggregates; the input light is multiplexed by the plurality of aggregates, interferes, and is output.

[0096] (Supplementary Note 2) A wavelength filter having a single waveguide connected to one end face and a plurality of waveguides connected to the other end face, wherein light obtained by combining light of a plurality of wavelengths is input through the single waveguide and light of the plurality of wavelengths is output through the plurality of waveguides for each wavelength, the wavelength filter comprising: a first material and a second material having a refractive index lower than that of the first material; the first material comprising a plurality of aggregates that are connected in an irregular shape within the second material; some of the plurality of aggregates are arranged in connection between the single waveguide and each of the plurality of waveguides; other some of the plurality of aggregates are arranged around the some of the aggregates without being connected to the some of the aggregates; the input light is multiple-scattered by the plurality of aggregates, interferes, and is output.

[0097] (Supplementary Note 3) A wavelength multiplexed light source comprising, in order, a plurality of high-reflection mirrors, a plurality of gain waveguides optically connected to the plurality of high-reflection mirrors, a wavelength filter according to Supplementary Note 1 or Supplementary Note 9 that is optically connected to the plurality of gain waveguides, and a plurality of low-reflection mirrors that are optically connected to the wavelength filter, wherein each of the plurality of gain waveguides emits light of a different wavelength, the emitted light resonates between the high-reflection mirror and the low-reflection mirror, and the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths.

[0098] (Supplementary Note 4) The wavelength multiplexed light source according to Supplementary Note 3, further comprising an optical modulator between the gain waveguide and the wavelength filter.

[0099] (Supplementary Note 5) A wavelength multiplexed light source comprising, in order, a plurality of high-reflection mirrors, a plurality of gain waveguides optically connected to the plurality of high-reflection mirrors, respectively, a plurality of optical modulators optically connected to the plurality of gain waveguides, a plurality of low-reflection mirrors optically connected to the plurality of optical modulators, and a wavelength filter according to Supplementary Note 1 or Supplementary Note 9 optically connected to the plurality of low-reflection mirrors, wherein each of the plurality of gain waveguides emits light of a different wavelength, and the emitted light resonates between the high-reflection mirror and the low-reflection mirror, and the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths.

[0100] (Supplementary Note 6) A wavelength multiplexing optical receiver to which light obtained by multiplexing light of the plurality of wavelengths is input, the wavelength multiplexing optical receiver comprising: a wavelength filter according to Supplementary Note 1; and a plurality of photodetectors optically connected to the wavelength filter, wherein the wavelength filter is a wavelength demultiplexer that demultiplexes the light into the plurality of wavelengths and outputs the demultiplexed light to each of the plurality of photodetectors.

[0101] (Supplementary Note 7) A wavelength multiplexed optical receiver according to Supplementary Note 6 or Supplementary Note 9, comprising a micro-heater that heats the wavelength filter, a monitor optical waveguide connected to the wavelength filter, and a monitor photodetector connected to the monitor optical waveguide, wherein a portion of the light obtained by combining light of the plurality of wavelengths is input to the monitor photodetector via the monitor optical waveguide, and the wavelength filter is heated by the micro-heater so that the intensity of the light input to the monitor photodetector is maximized, thereby changing the refractive indexes of the first material and the second material of the wavelength filter and feeding back the change.

[0102] (Supplementary Note 8) A method for manufacturing a wavelength filter having a topology composed of a first material and a second material having a lower refractive index than the first material, comprising the steps of: setting the first material, the second material, the size of the topology, and the spectra of input light and output light of the wavelength filter; calculating the spectrum of output light when the set broad light is input to the topology configuration consisting of the first material and the second material and having the size; comparing the spectrum of output light obtained by the calculation with the spectrum of output light set; and forming the topology of the wavelength filter based on the topology when the spectrum of output light obtained by the calculation and the spectrum of output light set approximately match.

[0103] (Supplementary Note 9) The first substance is Si and the second substance is SiO ２ and the area of ​​the wavelength filter is 5 to 10 μm × 5 to 10 μm.

[0104] The present invention relates to a wavelength filter, a wavelength multiplexing light source, a wavelength multiplexing optical receiver, and a method for manufacturing a wavelength filter, and can be applied to an optical transmitter / receiver used in an optical communication system.

[0105] 13 wavelength filter 131 first substance 132 second substance

Claims

1. A wavelength filter having a single waveguide connected to one end face and multiple waveguides connected to the other end face, in which light of multiple wavelengths is input through the multiple waveguides for each wavelength, and light obtained by combining the light of the multiple wavelengths is output through the single waveguide, the wavelength filter comprising: a first material; and a second material having a lower refractive index than the first material; the first material comprises multiple aggregates that are connected in an irregular shape within the second material; some of the multiple aggregates are arranged in connection between the single waveguide and each of the multiple waveguides; and other aggregates of the multiple aggregates are arranged around the some of the aggregates without being connected to them; and the input light is multiplexed by the multiple aggregates, interferes, and is output.

2. A wavelength filter having a single waveguide connected to one end face and multiple waveguides connected to the other end face, wherein light composed of multiple wavelengths enters the single waveguide and the multiple wavelengths are output from the multiple waveguides for each wavelength, the wavelength filter comprising: a first material; and a second material having a refractive index lower than that of the first material; the first material comprises multiple aggregates that are connected in an irregular shape within the second material; some of the multiple aggregates are arranged in connection between the single waveguide and each of the multiple waveguides; and other aggregates of the multiple aggregates are arranged around the some of the aggregates without being connected to the some of the aggregates; and the input light is multiple-scattered by the multiple aggregates, interferes, and is output.

3. A wavelength multiplexed light source comprising, in order, a plurality of high-reflection mirrors; a plurality of gain waveguides optically connected to each of the plurality of high-reflection mirrors; a wavelength filter as claimed in claim 1 optically connected to the plurality of gain waveguides; and a plurality of low-reflection mirrors optically connected to the wavelength filter, wherein each of the plurality of gain waveguides emits light of a different wavelength, the emitted light resonates between the high-reflection mirror and the low-reflection mirror, and the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths.

4. The wavelength multiplexed light source according to claim 3, further comprising an optical modulator between the gain waveguide and the wavelength filter.

5. A wavelength multiplexed light source comprising, in order, a plurality of high-reflection mirrors; a plurality of gain waveguides optically connected to each of the plurality of high-reflection mirrors; a plurality of optical modulators optically connected to each of the plurality of gain waveguides; a plurality of low-reflection mirrors optically connected to each of the plurality of optical modulators; and a wavelength filter according to claim 1 optically connected to the plurality of low-reflection mirrors, wherein each of the plurality of gain waveguides emits light of a different wavelength, the emitted light resonates between the high-reflection mirror and the low-reflection mirror, and the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths.

6. A wavelength multiplexing optical receiver to which light obtained by multiplexing light of the plurality of wavelengths is input, comprising: the wavelength filter according to claim 2; and a plurality of photodetectors optically connected to the wavelength filter, wherein the wavelength filter is a wavelength demultiplexer that demultiplexes the light into the plurality of wavelengths and outputs the demultiplexed light to each of the plurality of photodetectors.

7. A wavelength multiplexed optical receiver according to claim 6, comprising: a micro-heater that heats the wavelength filter; a monitor optical waveguide connected to the wavelength filter; and a monitor photodetector connected to the monitor optical waveguide, wherein a portion of the light obtained by combining light of the plurality of wavelengths is input to the monitor photodetector via the monitor optical waveguide, and the wavelength filter is heated by the micro-heater to change the refractive indexes of the first material and the second material of the wavelength filter so that the intensity of the light input to the monitor photodetector is maximized, and feedback is provided.

8. A method for manufacturing a wavelength filter having a topology composed of a first material and a second material having a refractive index lower than that of the first material, comprising the steps of: setting the first material, the second material, the size of the topology, and the spectra of input light and output light of the wavelength filter; calculating the spectrum of output light when the set broad light is input to the topology configuration composed of the first material and the second material and having the size; comparing the spectrum of output light obtained by the calculation with the spectrum of output light set; and forming the topology of the wavelength filter based on the topology when the spectrum of output light obtained by the calculation and the spectrum of output light set are approximately the same.

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