WO2026003908A1 - Wavelength filter, wavelength division multiplexing light source, wavelength division multiplexing optical receiver, and wavelength filter production method - Google Patents

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

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.

With the explosive growth in communications traffic, there is a demand for optical transceivers that are faster, have larger capacities, consume less power, are smaller, and are less costly. To expand communications capacity, optical transceivers that support wavelength division multiplexing, polarization multiplexing, multi-channelization, and multi-level modulation are now in practical use.

The components of an optical transceiver for WDM communications require light sources with different wavelengths and a wavelength multiplexer to guide these multiple wavelengths of light into a single optical waveguide.

In the past, semiconductor lasers and wavelength multiplexers were manufactured separately, and the laser's oscillation wavelength and the wavelength multiplexer's transmission wavelength were inspected before integration. Good products were selected, and then the good products were hybrid-integrated.

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, because 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, optical loss or crosstalk increases during wavelength multiplexing. Furthermore, because the rate of wavelength change due to substrate temperature (the amount of wavelength change relative to temperature) differs for the oscillation wavelength of the semiconductor laser and the transmission wavelength of the wavelength multiplexer, optical loss or crosstalk increases when the substrate temperature changes.

As a result, as shown in Non-Patent Document 1, a configuration has been reported in which an AWG (Arrayed Waveguide Grating) 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, there is no need to match the oscillation wavelength of the semiconductor laser with the transmission wavelength of the wavelength multiplexer, and there is no increase in optical loss due to a mismatch between these wavelengths.

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

However, in the configuration in which an AWG filter is inserted into the optical resonator of the above-mentioned semiconductor laser, the size of the AWG filter is large, at several hundred micrometers square, making it difficult to miniaturize the device.

Furthermore, as the optical path length of the entire resonator increases, the photon lifetime τp increases and the optical confinement factor Γz of the active layer decreases, causing the relaxation oscillation frequency fr to drop to around a few GHz, making high-speed direct modulation difficult. Therefore, when optical modulation is performed using an external modulator to achieve high-speed modulation, a discrepancy occurs between the modulator's optimal operating wavelength and the laser's oscillation wavelength, resulting in a problem of degraded modulation efficiency.

In order to solve the above-mentioned problems, the wavelength filter of the present invention has a single waveguide connected to one end face and multiple waveguides connected to the other end face, light of multiple wavelengths 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 comprises a first material and a second material having a lower refractive index than the first material, and the first material comprises multiple aggregates that are connected in an irregular shape within the second material, some of the multiple aggregates are connected 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.

Furthermore, the wavelength filter according to the present invention has a single waveguide connected to one end face and multiple waveguides connected to the other end face, and light composed of multiple wavelengths is input through the single waveguide, and light of the multiple wavelengths is output from the multiple waveguides for each wavelength. The wavelength filter comprises a first material and a second material having a lower refractive index than the first material, and the first material comprises multiple aggregates that are connected in an irregular shape within the second material, some of the multiple aggregates are connected 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 multiplexed by the multiple aggregates, interferes, and is output.

Furthermore, the 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 lower refractive index than 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 to the topology configuration composed of the first material and the second material and having the set 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.

The present invention provides a compact wavelength filter, wavelength multiplexing light source, wavelength multiplexing optical receiver, and method for manufacturing a wavelength filter that has excellent modulation characteristics.

FIG. 1 is a schematic diagram showing the configuration of a wavelength multiplexing light source according to a first embodiment of the present invention. FIG. 2A is a diagram for explaining a wavelength filter according to a first embodiment of the present invention. FIG. 2B is a diagram for explaining the wavelength filter according to the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view 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 the wavelength multiplexing 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 the wavelength multiplexing light source according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining a low-reflectance mirror in a wavelength multiplexing light source according to the first embodiment of the present invention. FIG. 6 is a flow chart illustrating 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 the wavelength multiplexed light source according to the first embodiment of the present invention. FIG. 8 is a schematic diagram showing the configuration of a wavelength multiplexing light source according to the second embodiment of the present invention. FIG. 9 is a schematic cross-sectional view showing the configuration of an electroabsorption modulator in a wavelength multiplexing light source according to a second embodiment of the present invention. FIG. 10A is a diagram for explaining the effect of the 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 a wavelength multiplexing light source according to the second embodiment of the present invention. FIG. 12 is a schematic diagram showing the configuration of a wavelength division multiplexing optical receiver according to the third embodiment of the present invention.

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.

<Configuration of wavelength multiplexed light source>
1, the 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.

The basic configuration of the wavelength filter 13 according to this embodiment is such that multiplexed light of multiple wavelengths enters from one end face, is demultiplexed, and the topology of the rectangular structure changes so that 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).

Here, the topology is a shape (configuration) of a material that is a combination of a first material (e.g., Si) 131 and a second material (e.g., SiO ₂ ) 132 that has a lower refractive index than the first material. The size of the topology is small, about 1 μm to 10 μm square.

In the topology of the wavelength filter 13, minute cells (e.g., 1 ^nm2 , layer thickness 220 nm) of a high refractive index material 131 are irregularly arranged two-dimensionally within a low refractive index material 132 so that multiple light beams of different wavelengths are multiplexed.

2A and 2B show an example of the topology of the wavelength filter 13. A single waveguide is connected to one end (left side in the figure) of a 6 μm square rectangular structure (made of Si surrounded by SiO ₂ ), and four waveguides are connected to the other end (right side in the figure). The inverse design is such 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.

FIG. 2A shows the inverse designed topology obtained by calculation. The light-colored areas indicate regions of a high-refractive-index material (hereinafter also referred to as the "first material") 131, and the dark-colored areas indicate regions of a low-refractive-index material (hereinafter also referred to as the "second material") 132. Here, as an example, Si is used as the first material 131, and SiO ₂ is used as the second material _132. Fine Si particles of the high-refractive-index material 131 are connected in two-dimensional irregular shapes within the SiO 2 of the low-refractive-index material 132, forming multiple aggregates. Some of the multiple aggregates (input/output aggregates) are connected from the light input position to the respective output positions. Other Si aggregates (peripheral aggregates) of the multiple 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 aggregate of the plurality of first materials (Si) 131, and is split into the respective wavelengths λ ₁ to λ ₄ and output.

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).

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 (Figure 2) are reversed. In other words, the wavelength filter 13 is a wavelength multiplexer, with multiple waveguides connected to one end of its rectangular structure and a single waveguide 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.

The wavelength multiplexer 13 includes a waveguide layer having a topology (thickness: 220 nm) made of Si and SiO ₂ on a SiO ₂ layer.

In this way, by using the wavelength multiplexer 13 (approximately 5 μm to 10 μm square) which can be made smaller than a conventional AWG filter (for example, ^{approximately} 500 μm square) in the wavelength multiplexing light source 10, 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.

As shown in FIG. 3, the gain waveguide 12 includes, on a substrate (e.g., Si) 1201, a second optical waveguide consisting of a second core (e.g., Si) 1203 and a second cladding (e.g., SiO ₂ ) 1202, and a first optical waveguide consisting of a first core (e.g., 1.55 μm wavelength composition InP-based multiple quantum well, MQW) 1205 and 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)).

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 disposed on the surface of the gain waveguide 12 (excluding the electrode portion).

The plurality of gain waveguides 12 each have a first core (eg, MQW) with a composition corresponding to a different wavelength λ ₁ to λ ₄ , and each gain waveguide 12 emits light of a different wavelength λ ₁ to λ ₄ .

In the second optical waveguide, a second core (Si) 1203 is embedded in a second cladding (SiO ₂ ) 1202 , and a supermode is formed between the first core 1205 and the second core 1203 .

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

The high-reflectivity mirror 11 is, for example, a DBR mirror in which a DBR 111 with periodic refractive index changes is formed in a silicon waveguide 112, as shown in Figure 4A. In this configuration, light with wavelengths in the stop band of the DBR mirror 11 is reflected with high reflectivity.

Alternatively, the high-reflectivity mirror 11 may be configured to combine a 1x2 multimode interferometer 113 and a ring resonator 114, as shown in Figure 4B. In this configuration, light at the resonant wavelength of the ring resonator 114 is reflected with a high reflectivity.

As shown in Figure 5, the low-reflectivity mirror 14 has a configuration in which the two outputs of a 2x2 multimode interferometer or directional coupler are connected. For example, input light (solid arrow in the figure) propagates through one waveguide 141 and couples to two waveguides (one waveguide and the other waveguide) 141, 142 via loop waveguide 143, and is output as reflected light (dotted arrow in the figure) from 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.

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 Si waveguide are optically coupled. This SiOx waveguide enables low-loss and low-reflection fiber coupling.

<Wavelength filter manufacturing method>
An example of a method for manufacturing the wavelength filter 13 according to this embodiment will be described below. A flow chart for explaining the method for manufacturing the wavelength filter 13 is shown in FIG.

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

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 set as the first material 131, and SiO ₂ (refractive index: 1.44) is set as the second material 132.

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 topology size was set to 6 μm x 6 μm. The topology size can also 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 will be 2 to 3 times larger.

The spectra of the input light and the output light are set (step S1). For example, the input light is a multiplexed light of multiple wavelengths _λ1 to _λ4 , and is a broad light having a peak at a wavelength of 1.3 μm and extending from 1.2 μm to 1.3 μm. The output light has four spectra of different wavelengths _λ1 to _λ4 , as shown in FIG. 2B. Let _λ1 = 1.27 μm, _λ2 = 1.29 μm, _λ3 = 1.31 μm, and _λ4 = 1.33 μm.

Next, assuming that a set broad light is input to a predetermined topology (distribution of refractive indexes of Si and _SiO2 ) based on the above settings, the spectrum of the output light is calculated (step S2).

Next, the calculated output light spectrum is compared with the set output light spectrum (step S3).

If the calculated spectrum of the output light substantially matches the set spectrum of the output light, the calculation ends. The topology at this point is determined as the topology of the wavelength filter 13.

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

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

Based on the topology determined above, the topology is formed using semiconductor processing processes such as standard photolithography and etching techniques (step S4). This produces the wavelength filter 13.

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

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

6, one of the multiple Fabry-Perot modes 171 of the resonator is selected by the transmission wavelength (e.g., λ ₁ ) 172 of each port of the wavelength multiplexer 13, and 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 laser oscillation wavelength with the transmission wavelength of the wavelength multiplexer 13 as in the conventional configuration.

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.

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

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 active layer optical confinement ratio Γz decreases, causing the relaxation oscillation frequency fr to drop to around several GHz, making high-speed direct modulation difficult.

On the other hand, with the wavelength-multiplexed light source 10, the resonator length can be reduced, so the relaxation oscillation frequency fr can be increased to around 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 resonator length of the wavelength-multiplexed light source 10 is short.

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 discrepancy occurs between the modulator's optimal operating wavelength and the laser's oscillation wavelength due to processing errors and fluctuations in substrate temperature, resulting in a deterioration in modulation efficiency.

On the other hand, the wavelength-multiplexed light source 10 is capable of high-speed direct modulation, so no external modulator is required for high-speed modulation. As a result, there is no degradation in modulation efficiency caused by wavelength shifts in conventional wavelength-multiplexed light sources.

In this way, with the wavelength multiplexed light source 10, there is no need to match the oscillation wavelength of the semiconductor laser, the transmission wavelength of the wavelength multiplexer 13, or the optimal operating wavelength of the modulator, resulting in a compact wavelength multiplexed light source that is less susceptible to the effects of processing errors and temperature changes.

This embodiment provides a compact wavelength multiplexed light source capable of high-speed modulation.

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

<Configuration of wavelength multiplexed light source>
8, the wavelength multiplexed light source 20 according to this embodiment differs from 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.

As shown in FIG. 9 , the electroabsorption modulator 21 includes, on a substrate (e.g., Si) 2101, a dielectric film (e.g., SiO ₂ ) 2102, a third optical waveguide consisting of a third core (e.g., 1.55 μm wavelength composition InP-based multiple quantum well, MQW) 2105, and third claddings (e.g., InP) 2104 and 2106, in that order.

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., _SiO2 ) 2111 is also disposed on the surface of the electroabsorption modulator 21 (excluding the electrode portion).

In the electroabsorption modulator 21, a second waveguide core (Si core) is not provided in order to increase light confinement in the active layer and improve modulation efficiency.

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

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, 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.

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, or the optimal operating wavelength of the modulator, making it possible to realize a compact wavelength multiplexed light source that is less susceptible to the effects of processing errors and temperature modulation.

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

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

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

Length L _SOA of gain waveguide 12 (SOA) = 100 μm
Length of EA modulator L _EA =50 μm
Length of multimode interference waveguide (MMI) L _MMI =10 μm
Absorption coefficient of SOA α _{i_SOA} =10 cm ⁻¹
Absorption coefficient of EA α _{i — EA} =20 cmcm ⁻¹ (applied voltage V _EA of the EA modulator =0 V)
Absorption coefficient of MMI α _{i_MMI} = 20 cm ⁻¹
Optical confinement ratio Γxy = 20%
When linear gain g=dN×(N−Ntr), dN=1145e−22m ⁻² , Ntr=1.45e24m ⁻³
- High reflectivity mirror R1 = 99%
- Reflectance of low-reflection mirror R2 = 1%
Internal quantum efficiency η _i =0.5
・Electron lifetime τ _e = 1ns
・_ng = 4.2
w = 0.6 μm
Quantum well thickness d _QW = 6.2 nm
Number of quantum wells N _QW = 6

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

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 of the first embodiment includes an SOA and a wavelength multiplexer 13, and can achieve the same or shorter overall resonator length compared to the configuration of the second embodiment, thereby achieving results similar to those of the second embodiment.

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

On the other hand, with the wavelength-multiplexed light source 20, the cavity length can be reduced, allowing the relaxation oscillation frequency to be increased to around several tens of GHz, making high-speed direct optical modulation possible. As shown in the calculation results above, 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.

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 discrepancy occurs between the modulator's optimal operating wavelength and the laser's oscillation wavelength due to processing errors and fluctuations in substrate temperature, resulting in a deterioration in modulation efficiency.

On the other hand, the wavelength-multiplexed light source 20 is capable of high-speed direct modulation, so no external modulator is required for high-speed modulation. As a result, there is no degradation in modulation efficiency caused by wavelength shifts in conventional wavelength-multiplexed light sources.

In this way, with 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, or the optimal operating wavelength of the modulator, resulting in a compact wavelength multiplexed light source that is less susceptible to the effects of processing errors and temperature changes.

This embodiment provides a compact wavelength multiplexed light source capable of high-speed modulation.

In the wavelength multiplexed light source according to this embodiment, as shown in FIG. 11, a distributed feedback diffraction grating may be provided in the gain waveguide 12 to form a DFB laser. Also, a low-reflectivity mirror 14 may be provided in front of the wavelength multiplexer 13, resulting in a resonator structure that does not include the wavelength multiplexer 13.

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

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

<Configuration of wavelength division multiplexing optical receiver>
12, a wavelength multiplexed optical receiver 30 according to the 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.

The multi-wavelength multiplexed light (optical modulation signal) is input to the wavelength filter 32 via the spot size converter 31.

The wavelength filter 32 is a wavelength demultiplexer and has a configuration similar to the basic topology described above. The wavelength demultiplexer 32 has a configuration in which the topology of a rectangular structure is changed so that light of the 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.

The wavelength demultiplexer 32 includes a waveguide layer having a topology (thickness: 220 nm) made of Si and SiO ₂ on a SiO ₂ layer.

In this way, the wavelength demultiplexer 32 demultiplexes the input light into light of multiple wavelengths and outputs them to each of the multiple photodetectors 33.

In the wavelength 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.

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, approximately 1% of the input light) to the monitor photodetector. Here, the topology of the wavelength demultiplexer 32 is inversely designed so that a portion (approximately 1%) of the input light is output to the monitor waveguide 36.

When 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 wavelength demultiplexer 32 topology 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 short wavelength side when the power to the microheater 35 is reduced, and to the long wavelength side when the power to the microheater 35 is increased. This allows the transmission wavelength of the wavelength demultiplexer 32 to roughly match the wavelength of the input multi-wavelength multiplexed optically modulated signal, and increases the light intensity input to each photodetector 33.

This allows the power to the microheater 35 to be adjusted so that the transmission intensity to the photodetector 33 is maximized. In this way, the wavelength multiplexed optical receiver 30 can receive high-speed modulated signals with high efficiency.

This embodiment makes it possible to provide a compact wavelength division multiplexing optical receiver that is capable of high-speed modulation.

A wavelength filter according to an embodiment of the present invention can be used as a wavelength demultiplexer or a wavelength multiplexer. When used as a wavelength demultiplexer, multiple wavelengths of light combined together are input from one end face, and multiple wavelengths of light are output from the other end face. When used as a wavelength multiplexer, multiple wavelengths of light are input from the other end face, and multiple wavelengths of light are output from one end face.

In the implementation of the present invention, a wavelength filter that inputs and outputs four wavelengths has been shown as an example, but this is not limited to four wavelengths, and wavelength filters that input and output multiple wavelengths are also acceptable.

In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration of the wavelength filter, wavelength multiplexed light source, and wavelength multiplexed optical receiver, as well as the manufacturing method of the wavelength filter, are shown, but this is not limiting. Anything that can fulfill the functions and effects of the wavelength filter, wavelength multiplexed light source, and wavelength multiplexed optical receiver will suffice.

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 those skilled in the art within the technical spirit of the present invention.

The above-described embodiment or example thereof, in whole or in part, may also be described as, but is not limited to, the following notes.

(Appendix 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 resulting from the multiple wavelengths being combined 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 comprising multiple aggregates that are connected in an irregular shape within the second material, some of the multiple aggregates being connected between the single waveguide and each of the multiple waveguides, and other aggregates of the multiple aggregates being arranged around the some of the aggregates without being connected to the some of the aggregates, the input light undergoing multiple scattering and interference by the multiple aggregates and output.

(Appendix 2) A wavelength filter having a single waveguide connected to one end face and multiple waveguides connected to the other end face, where light composed of multiple wavelengths is input through the single waveguide and light of the multiple wavelengths is output through the multiple waveguides for each wavelength, the wavelength filter comprising a first material and a second material having a lower refractive index than the first material, the first material comprising multiple aggregates arranged in an irregular pattern within the second material, some of the multiple aggregates being arranged in a continuous pattern between the single waveguide and each of the multiple waveguides, and other of the multiple aggregates being arranged around the some of the aggregates without being connected to the some of the aggregates, whereby the input light is multiplexed by the multiple aggregates, interferes, and is output.

(Appendix 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 according to appendix 1 or appendix 9 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.

(Appendix 4) The wavelength-multiplexed light source described in Appendix 3, further comprising an optical modulator between the gain waveguide and the wavelength filter.

(Appendix 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 appendix 1 or appendix 9 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 mirrors and the low-reflection mirrors, and the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths.

(Appendix 6) A wavelength-multiplexed optical receiver to which light obtained by multiplexing light of the plurality of wavelengths is input, the wavelength-multiplexed optical receiver comprising the wavelength filter described in Appendix 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.

(Appendix 7) A wavelength-multiplexed optical receiver as described in Appendix 6 or Appendix 9, comprising a microheater 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 enters the monitor photodetector via the monitor optical waveguide, and the wavelength filter is heated by the microheater to change the refractive index of the first material and the second material of the wavelength filter so that the intensity of the light entering the monitor photodetector is maximized, and feedback is performed.

(Appendix 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 composed of the first material and the second material and having the set 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.

(Appendix 9) The wavelength filter according to appendix 1 or appendix 2, wherein the first substance is Si, the second substance is SiO ₂ , and the area of the wavelength filter is 5 to 10 μm × 5 to 10 μm.

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 optical transmitters and receivers used in optical communication systems.

13 Wavelength filter 131 First substance 132 Second substance

Claims (8)

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 to the plurality of waveguides for each wavelength, and light obtained by combining the light of the plurality of wavelengths is output from the single waveguide,
a first substance; and
a second material having a lower refractive index than the first material;
the first material comprises a plurality of irregularly shaped clusters interconnected within the second material;
some of the plurality of assemblies are arranged in series between the single waveguide and each of the plurality of waveguides;
another part of the plurality of assemblies is not connected to the part of the assemblies but is arranged around the part of the assemblies,
A wavelength filter in which the input light is multiply scattered by the plurality of aggregates, interferes, and is output. 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 to the single waveguide and light of the plurality of wavelengths is output from the plurality of waveguides for each wavelength,
a first substance; and
a second material having a lower refractive index than the first material;
the first material comprises a plurality of irregularly shaped clusters interconnected within the second material;
some of the plurality of assemblies are arranged in series between the single waveguide and each of the plurality of waveguides;
another part of the plurality of assemblies is not connected to the part of the assemblies but is arranged around the part of the assemblies,
A wavelength filter in which the input light is multiply scattered by the plurality of aggregates, interferes, and is output. In turn, a plurality of highly reflective mirrors;
a plurality of gain waveguides optically connected to the plurality of high-reflection mirrors, respectively;
a wavelength filter according to claim 1 optically connected to the plurality of gain waveguides;
a plurality of low-reflection mirrors optically connected to the wavelength filter;
each of the plurality of gain waveguides emitting light of a different wavelength;
the emitted light resonates between the high-reflection mirror and the low-reflection mirror,
A wavelength multiplexing light source, wherein the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths. 4. The optical modulator according to claim 3, further comprising: an optical modulator between the gain waveguide and the wavelength filter.
The wavelength multiplexed light source according to claim 1. In turn, a plurality of highly reflective 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, respectively;
a plurality of low-reflection mirrors optically connected to the plurality of optical modulators, respectively; and the wavelength filter according to claim 1 optically connected to the plurality of low-reflection mirrors,
each of the plurality of gain waveguides emitting light of a different wavelength;
the emitted light resonates between the high-reflection mirror and the low-reflection mirror,
A wavelength multiplexing light source, wherein the wavelength filter is a wavelength multiplexer that multiplexes and outputs the resonating light of different wavelengths. a wavelength division multiplexing optical receiver to which light obtained by multiplexing light of the plurality of wavelengths is input,
The wavelength filter according to claim 2;
a plurality of photodetectors in optical communication with the wavelength filters;
The wavelength multiplexing optical receiver, 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. a microheater that heats the wavelength filter;
a monitor optical waveguide connected to the wavelength filter;
a monitor photodetector connected to the monitor optical waveguide,
a part of the light obtained by combining the light beams of the plurality of wavelengths is input to the monitor photodetector via the monitor optical waveguide;
7. The wavelength division multiplexing optical receiver according to claim 6, wherein the wavelength filter is heated by the microheater 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 the change is fed back. A method for manufacturing a wavelength filter having a topology made of a first material and a second material having a refractive index lower than that of the first material, comprising:
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 a spectrum of output light when the set broad light is input to the topology configuration that is made of the first material and the second material and has the size;
a step of comparing the spectrum of the output light obtained by the calculation with the spectrum of the set output light;
forming a topology of the wavelength filter based on the topology when the spectrum of the output light obtained by the calculation and the spectrum of the set output light approximately match.