Optical device, optical receiver, and optical transmitter

Abstract

To provide an optical device and the like capable of performing high-order conversion while performing space transition of signal light between different waveguides.SOLUTION: An optical device comprises: a board; a taper waveguide that is disposed in a first layer of the board while the waveguide width becomes wider gradually from the input to the output; and a rib waveguide that is disposed on a second layer on the board that differs from the first layer and is overlapped with the taper waveguide in a face direction. The rib waveguide has: a rib in which the core width becomes wider gradually from the input to the output; and a slab that is disposed in both the sides of the rib while the slab width becomes wider gradually from the input to the output.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical device, an optical receiver, and an optical transmitter. [Background technology]

[0002] The optical input section of the optical device that uses silicon photonics technology has an edge coupler for inputting light from an optical fiber, and a PR (Polarization Rotator) / PBS (Polarization Beam Splitter) that separates the path according to the polarization of the light input from the edge coupler. There are planar optical waveguide elements that use this technology. Edge couplers input light from an optical fiber while matching the mode field with the optical fiber. Then, PR / PBS can separate the light input from the edge coupler into paths according to the polarization. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2017-536572 [Patent Document 2] Japanese Patent Publication No. 2023-110383 [Patent Document 3] US Patent Application Publication No. 2019 / 0369333 [Patent Document 4] US Patent Application Publication No. 2009 / 0297093 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-090449 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional optical devices have, for example, an edge coupler configured with a SiN waveguide such as Si3N4 (hereinafter simply referred to as SiN (Silicon Nitride)) and a PR / PBS configured with a Si waveguide. Optical devices are required to perform high-order conversion while spatially transferring signal light between different waveguides, i.e., the SiN waveguide and the Si waveguide.

[0005] In one aspect, an object is to provide an optical device or the like that can perform high-order conversion while spatially transferring signal light between different waveguides. [Means for solving the problem]

[0006] An optical device according to one embodiment includes a substrate, a tapered waveguide disposed on a first layer on the substrate, the tapered waveguide having a width gradually increasing from the input to the output, and a rib waveguide disposed on a second layer on the substrate different from the first layer and overlapping the tapered waveguide in a planar direction. The rib waveguide includes ribs whose core width gradually increases from the input to the output, and slabs disposed on both sides of the rib, the slab width gradually increasing from the input to the output. [Effects of the Invention]

[0007] According to one aspect, higher-order conversion can be performed while spatially transferring signal light between different waveguides. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic plan view showing an example of an optical device according to a first embodiment. [Figure 2A] FIG. 2A is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line AA shown in FIG. [Figure 2B] FIG. 2B is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line BB shown in FIG. [Figure 2C] FIG. 2C is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line CC shown in FIG. [Figure 3] FIG. 3 is a plan view schematically illustrating an example of an optical device according to a second embodiment. [Figure 4A] FIG. 4A is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line AA shown in FIG. [Figure 4B] FIG. 4B is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line BB shown in FIG. [Figure 4C] FIG. 4C is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line CC shown in FIG. [Figure 4D] FIG. 4D is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line DD shown in FIG. [Figure 5] FIG. 5 is a plan view schematically illustrating an example of an optical device according to a third embodiment. [Figure 6A] FIG. 6A is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line AA shown in FIG. [Figure 6B] FIG. 6B is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line BB shown in FIG. [Figure 6C] FIG. 6C is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line CC shown in FIG. [Figure 6D] FIG. 6D is a cross-sectional view showing an example of the cross section taken along line DD shown in FIG. [Figure 7] FIG. 7 is an explanatory diagram illustrating an example of an optical transceiver according to this embodiment. [Figure 8] FIG. 8 is a schematic plan view showing an example of an optical device of the comparative example. [Figure 9A] FIG. 9A is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line AA shown in FIG. [Figure 9B] FIG. 9B is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line BB shown in FIG. [Figure 9C] FIG. 9C is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line CC shown in FIG. [Figure 9D] FIG. 9D is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line DD shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Comparative Example> An optical device 100 of the comparative example will be described, which is capable of high-order conversion while spatially transitioning signal light between different waveguides, for example, between a SiN waveguide and a Si waveguide. Fig. 8 is a schematic plan view showing an example of the optical device 100 of the comparative example. The optical device 100 shown in Fig. 8 is a planar optical waveguide element having an optical input section for optically connecting to an optical fiber F.

[0010] The optical device 100 has an edge coupler 200 that is optically connected to a core FC of an optical fiber F, and a polarization beam splitter (PBS) 300 that is optically connected to the edge coupler 200 and that polarizes and splits the light from the edge coupler 200. The edge coupler 200 is a coupler that is disposed on a chip end face 100E of the optical device 100. The edge coupler 200 has a SiN waveguide 210 with a channel structure formed in a first layer, and a Si waveguide 310 (311) with a channel structure formed in a second layer different from the first layer.

[0011] The PBS 300 is a polarization multiplexer / demultiplexer that separates the signal light input from the edge coupler 200 into signal light with two orthogonal polarization states, for example, an X-polarized component which is TE (Transverse Electric) polarization and a Y-polarized component which is TM (Transverse Magnetic) polarization. The PBS 300 has a Si waveguide 310 with a rib structure. The SiN waveguide 210 has a lower refractive index than the Si waveguide 310, so the mode field of the light can be increased, and also has less polarization dependency than the Si waveguide 310, so the coupling loss of both the TE light and the TM light with the core FC of the optical fiber F can be reduced.

[0012] The SiN waveguide 210 has an inverse tapered waveguide 211 and a tapered waveguide 212 that is optically coupled to the inverse tapered waveguide 211. The inverse tapered waveguide 211 has a tapered structure in which the core width gradually increases from the chip end face 100E toward the tapered waveguide 212. The tapered waveguide 212 has a tapered structure in which the core width gradually decreases from the output of the inverse tapered waveguide 211 toward the Si waveguide 310.

[0013] The Si waveguide 310 includes a channel waveguide 311 and a rib waveguide 312 optically coupled to the channel waveguide 311. The channel waveguide 311 has an inverted tapered structure in which the core width gradually narrows from the rib waveguide 312 toward the chip end face 100E. The rib waveguide 312 includes a first rib waveguide 312A whose slab width gradually increases with increasing distance from the channel waveguide 311, and a second rib waveguide 312B whose slab width is constant and optically coupled to the first rib waveguide 312A. The rib waveguide 312 further includes a third rib waveguide 312C that is optically coupled to the second rib waveguide 312B and optically connected to the first output port 100A and the second output port 100B of the optical device 100.

[0014] The first rib waveguide 312A has a rib 312A1 and slabs 312A2 formed on both sides of the rib 312A1. The rib 312A1 is a rib whose core width gradually increases from the channel waveguide 311 to the second rib waveguide 312B. The slab 312A2 is a slab whose slab width increases on both sides of the rib 312A1 from the channel waveguide 311 to the second rib waveguide 312B.

[0015] The second rib waveguide 312B has a first rib 312B1, slabs 312B3 formed on both sides of the first rib 312B1, and a second rib 312B2 formed on one of the slabs 312B3. The first rib 312B1 has a constant core width from the first rib waveguide 312A to the third rib waveguide 312C. The slab 312B3 has a constant slab width on both sides of the first rib 312B1 from the first rib waveguide 312A to the third rib waveguide 312C. The second rib 312B2 is formed on one of the slabs 312B3 and is arranged in parallel with the first rib 312B1. The second rib 312B2 has a constant core width from the first rib waveguide 312A to the third rib waveguide 312C.

[0016] The third rib waveguide 312C has a first rib 312C1, slabs 312C3 formed on both sides of the first rib 312C1, and a second rib 312C2 formed on one of the slabs 312C3. The first rib 312C1 is optically connected to the first rib 312B1 of the second rib waveguide 312B and outputs light from the second rib waveguide 312B to the first output port 100A, which is the end of the optical input section. The second rib 312C2 is optically connected to the second rib 312B2 of the second rib waveguide 312B and outputs light from the second rib waveguide 312B to the second output port 100B, which is the end of the optical input section.

[0017] The optical device 100 has an inverse tapered portion 110, an adiabatic conversion portion 120, a high-order conversion portion 130, and a directional coupling portion 140. The inverse tapered portion 110 is configured as an inverse tapered waveguide 211 of a SiN waveguide 210. FIG. 9A is a cross-sectional schematic diagram showing an example of the cross section taken along line AA shown in FIG. 8. The cross-sectional portion shown in FIG. 9A is a cross-sectional portion of the inverse tapered portion 110. The optical device 100 shown in FIG. 9A has a Si substrate 111, a cladding layer 112 made of, for example, SiO2, stacked on the Si substrate 111, and an inverse tapered waveguide 211 of the SiN waveguide 210 formed in a first layer in the cladding layer 112. Since the mode fields of the Si waveguide 310 and the core FC of the optical fiber F are different, the inverted taper portion 110 has the function of matching the mode fields between the Si waveguide 310 and the core FC of the optical fiber F, thereby reducing the coupling loss with the core FC of the optical fiber F.

[0018] 9B is a cross-sectional schematic diagram showing an example of the cross section taken along line BB in FIG. 8. The cross-sectional portion shown in FIG. 9B is a cross-sectional portion of the adiabatic conversion section 120. The optical device 100 has a Si substrate 111, a cladding layer 112, a tapered waveguide 212 of a SiN waveguide 210 formed in a first layer in the cladding layer 112, and a channel waveguide 311 of a Si waveguide 310 formed in a second layer in the cladding layer 112. The optical device 100 configures the adiabatic conversion section 120 with the tapered waveguide 212 and the channel waveguide 311 overlapping in the planar direction. In the adiabatic conversion section 120, light gradually transits spatially from the tapered waveguide 212 of the SiN waveguide 210 toward the channel waveguide 311 of the Si waveguide 310. The adiabatic conversion unit 120 spatially transitions the X-polarized TE light to the X-polarized TE0 light and the Y-polarized TM light to the Y-polarized TM0 light from the tapered waveguide 212 toward the channel waveguide 311.

[0019] Fig. 9C is a schematic cross-sectional view showing an example of the cross section taken along line CC shown in Fig. 8. The optical device 100 shown in Fig. 9C has a Si substrate 111, a cladding layer 112, and a channel waveguide 311 of a Si waveguide 310 formed in a second layer in the cladding layer 112.

[0020] The high-order conversion section 130 is configured with a first rib waveguide 312A of the Si waveguide 310, and performs high-order conversion on the light from the channel waveguide 311 in the first rib waveguide 312A. The rib 312A1 of the first rib waveguide 312A transmits and outputs the X-polarized TE0 light input from the channel waveguide 311 to the first rib 312B1 of the second rib waveguide 312B. The rib 312A1 performs high-order conversion on the Y-polarized TM0 light input from the channel waveguide 311 to the Y-polarized TE1 light, and outputs the Y-polarized TE1 light to the first rib 312B1 in the second rib waveguide 312B.

[0021] The directional coupling unit 140 is composed of a first rib 312B1 of the second rib waveguide 312B and a second rib 312B2 within the second rib waveguide 312B. FIG. 9D is a cross-sectional schematic diagram showing an example of the cross section taken along the line DD shown in FIG. 8. The cross-sectional portion shown in FIG. 9D is a cross-sectional portion of the directional coupling unit 140. The optical device 100 shown in FIG. 9D has a Si substrate 111, a cladding layer 112, and a second rib waveguide 312B of the Si waveguide 310 formed in a second layer within the cladding layer 112. The first rib 312B1 of the second rib waveguide 312B transmits and outputs the X-polarized TE0 light input from the first rib waveguide 312A to the first rib 312C1 of the third rib waveguide 312C. The first rib 312B1 converts the Y-polarized TE1 light input from the first rib waveguide 312A into Y-polarized TE0 light, and spatially transitions the converted light to the second rib 312B2 in the second rib waveguide 312B.

[0022] The first rib 312C1 in the third rib waveguide 312C transmits and outputs the X-polarized TE0 light from the first rib 312B1 in the second rib waveguide 312B to the first output port 100A. The second rib 312C2 in the third rib waveguide 312C transmits and outputs the Y-polarized TE0 light from the second rib 312B2 in the second rib waveguide 312B to the second output port 100B. In other words, the PBS 300 separates and outputs the X-polarized TE0 light to the first output port 100A and the Y-polarized TE0 light to the second output port 100B.

[0023] Next, a description will be given of the operation of the optical device 100 of the comparative example. When X-polarized TE light from the optical fiber F is input through the inverse tapered portion 110 to the adiabatic conversion portion 120 of the optical device 100 of the comparative example, the X-polarized TE light undergoes spatial transition from the tapered waveguide 212 toward the channel waveguide 311 as X-polarized TE0 light.

[0024] The first rib waveguide 312A in the high-order conversion unit 130 outputs the X-polarized TE0 light after spatial transition from the channel waveguide 311 to the first rib 312B1 of the second rib waveguide 312B. The first rib 312B1 in the second rib waveguide 312B in the directional coupling unit 140 outputs the X-polarized TE0 light from the first rib 312B1 to the first output port 100A via the first rib 312C1 of the third rib waveguide 312C.

[0025] Furthermore, when Y-polarized TM light from the optical fiber F is input through the inverse taper section 110 of the adiabatic conversion section 120 of the optical device 100, the Y-polarized TM light undergoes spatial transition from the tapered waveguide 212 toward the channel waveguide 311 as Y-polarized TM0 light.

[0026] The first rib waveguide 312A in the high-order conversion unit 130 high-order converts the Y-polarized TM0 light after spatial transition from the channel waveguide 311 into Y-polarized TE1 light and outputs the Y-polarized TE1 light after high-order conversion to the first rib 312B1 of the second rib waveguide 312B. The second rib 312B2 in the second rib waveguide 312B in the directional coupling unit 140 spatially transitions the Y-polarized TE1 light from the first rib 312B1 while converting it into Y-polarized TE0 light. The second rib 312B2 in the second rib waveguide 312B then outputs the Y-polarized TE0 light after spatial transition to the second output port 100B via the second rib 312C2 in the third rib waveguide 312C.

[0027] That is, the optical device 100 can separate and output the X-polarized TE0 light to the first output port 100A and the Y-polarized TE0 light to the second output port 100B according to the polarization state of the light input from the edge coupler 200.

[0028] However, in the optical device 100 of the comparative example, the Si waveguide 310 of the adiabatic conversion portion 120 is a channel waveguide 311, and therefore sidewall roughness occurs due to etching during the creation of the waveguide. As a result, the sidewall roughness of the channel waveguide 311 causes light scattering, resulting in increased light loss and light reflection. Moreover, although the effect of sidewall roughness is small when the core width of the channel waveguide 311 is narrow, the effect becomes greater as the core width of the channel waveguide 311 increases.

[0029] Furthermore, optical connection with the PBS 300 is made after the edge coupler 200, and the adiabatic conversion section 120 and the high-order conversion section 130 are connected in multiple stages, which increases the waveguide length and makes the optical device 100 larger. [Example]

[0030] Therefore, in this embodiment, an embodiment of an optical device that can not only perform high-order conversion while spatially transitioning signal light between different waveguides, but also contribute to miniaturization while achieving low loss and low reflection at the optical input section will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Furthermore, the embodiments shown below may be combined as appropriate within the scope of not causing any contradiction.

[0031] FIG. 1 is a planar schematic diagram showing an example of an optical device 1 according to a first embodiment. The optical device 1 shown in FIG. 1 is a planar optical waveguide element having an optical input portion optically connected to an optical fiber F. The optical device 1 includes an edge coupler 2 disposed on a chip end face 10 of the optical device 1 and optically connected to a core FC of the optical fiber F, and a polarization beam splitter (PBS) 3 optically connected to the edge coupler 2 and performing polarization splitting of light from the edge coupler 2. The edge coupler 2 includes a SiN waveguide 21 with a channel structure formed in a first layer, and a Si waveguide 31 with a rib structure formed in a second layer different from the first layer.

[0032] The PBS 3 is a polarization multiplexer / demultiplexer that separates the signal light input from the edge coupler 200 into signal light of two orthogonal polarization states, for example, an X-polarized component which is TE polarization and a Y-polarized component which is TM polarization. The PBS 3 has a Si waveguide 31 with a rib structure formed on the second layer. The SiN waveguide 21 has a lower refractive index than the Si waveguide 31, so it can increase the mode field of the light, and also has less polarization dependency than the Si waveguide 31, so it can reduce the coupling loss of both the TE light and the TM light with the core FC of the optical fiber F.

[0033] The SiN waveguide 21 has an inverse tapered waveguide 21A and a tapered waveguide 21B that is optically coupled to the inverse tapered waveguide 21A. The inverse tapered waveguide 21A has a tapered structure in which the core width gradually increases from the chip end face 10 toward the tapered waveguide 21B. The tapered waveguide 21B has a tapered structure in which the core width gradually decreases from the output of the inverse tapered waveguide 21A toward the Si waveguide 31.

[0034] The Si waveguide 31 has a first rib waveguide 31A whose slab width gradually increases with increasing distance from the tapered waveguide 21B, and a second rib waveguide 31B whose slab width is constant and optically coupled to the first rib waveguide 31A. The Si waveguide 31 has a third rib waveguide 31C that is optically coupled to the second rib waveguide 31B and optically connected to the first output port 10A and the second output port 10B of the optical device 1.

[0035] The first rib waveguide 31A has a rib 31A1 and slabs 31A2 formed on both sides of the rib 31A1. The rib 31A1 is a rib whose core width gradually increases from the first rib waveguide 31A to the second rib waveguide 31B. The slab 31A2 is a slab whose slab width on both sides of the rib 31A1 increases from the first rib waveguide 31A to the second rib waveguide 31B.

[0036] The second rib waveguide 31B has a first rib 31B1, slabs 31B3 formed on both sides of the first rib 31B1, and a second rib 31B2 formed on one of the slabs 31B3. The first rib 31B1 is a rib whose core width is constant from the first rib waveguide 31A to the third rib waveguide 31C. The slab 31B3 is a slab whose slab width is constant on both sides of the first rib 31B1 from the first rib waveguide 31A to the third rib waveguide 31C. The second rib 31B2 is formed on one of the slabs 31B3 and is arranged in parallel with the first rib 31B1. The second rib 31B2 is a rib whose core width is constant from the first rib waveguide 31A to the third rib waveguide 31C.

[0037] The third rib waveguide 31C has a first rib 31C1, slabs 31C3 formed on both sides of the first rib 31C1, and a second rib 31C2 formed on one of the slabs 31C3. The first rib 31C1 is optically connected to the first rib 31B1 of the second rib waveguide 31B and outputs light from the second rib waveguide 31B to the first output port 10A, which is the terminal end of the optical input section. The second rib 31C2 is optically connected to the second rib 31B2 of the second rib waveguide 31B and outputs light from the second rib waveguide 31B to the second output port 10B, which is the terminal end of the optical input section.

[0038] The optical device 1 has an inverse tapered portion 51, a conversion portion 52, and a directional coupling portion 53. The inverse tapered portion 51 is configured as an inverse tapered waveguide 21A of the SiN waveguide 21. FIG. 2A is a cross-sectional schematic diagram showing an example of the cross section taken along line AA shown in FIG. 1. The cross-sectional portion shown in FIG. 2A is a cross-sectional portion of the inverse tapered portion 51. The optical device 1 shown in FIG. 2A has a Si substrate 11, a cladding layer 12 made of, for example, SiO2, stacked on the Si substrate 11, and an inverse tapered waveguide 21A of the SiN waveguide 21 formed on a first layer in the cladding layer 12. The inverse tapered portion 51 has the function of matching the mode fields between the Si waveguide 31 and the core FC of the optical fiber F, since the mode fields of the Si waveguide 31 and the core FC of the optical fiber F are different. This reduces the coupling loss with the core FC of the optical fiber F.

[0039] FIG. 2B is a schematic cross-sectional view showing an example of the cross section taken along line BB in FIG. 1. The cross-sectional portion shown in FIG. 2B is a cross-sectional portion of a conversion section 52. The optical device 1 shown in FIG. 2B includes a Si substrate 11 and a cladding layer 12 stacked on the Si substrate 11. The optical device 1 includes a tapered waveguide 21B of a SiN waveguide 21 formed in a first layer in the cladding layer 12, and a first rib waveguide 31A of a Si waveguide 31 formed in a second layer in the cladding layer 12. The optical device 1 includes a conversion section 52 formed by the tapered waveguide 21B and the first rib waveguide 31A overlapping in the planar direction. In the conversion section 52, light undergoes spatial transition from the tapered waveguide 21B of the SiN waveguide 21 toward the first rib waveguide 31A of the Si waveguide 31 while gradually undergoing high-order conversion. The conversion section 52 spatially transitions the X-polarized TE light into X-polarized TE0 light and spatially transitions the Y-polarized TM light into Y-polarized TE1 light while performing high-order conversion from the tapered waveguide 21B toward the first rib waveguide 31A.

[0040] The directional coupling section 53 is composed of a first rib 31B1 of the second rib waveguide 31B and a second rib 31B2 within the second rib waveguide 31B. FIG. 2C is a cross-sectional schematic diagram showing an example of a cross section taken along the line CC shown in FIG. 1. The cross-sectional portion shown in FIG. 2C is a cross-sectional portion of the directional coupling section 53. The optical device 1 shown in FIG. 2C includes a Si substrate 11, a cladding layer 12 stacked on the Si substrate 11, and a second rib waveguide 31B of the Si waveguide 31 formed in a second layer within the cladding layer 12. The first rib 31B1 of the second rib waveguide 31B transmits and outputs the X-polarized TE0 light input from the first rib waveguide 31A to the first rib 31C1 of the third rib waveguide 31C. In the first rib 31B1, Y-polarized TE1 light input from the first rib waveguide 31A spatially transitions to Y-polarized TE0 light in the second rib 31B2 in the second rib waveguide 31B.

[0041] The first rib 31C1 in the third rib waveguide 31C transmits and outputs the X-polarized TE0 light from the first rib 31B1 in the second rib waveguide 31B to the first output port 10A. The second rib 31C2 in the third rib waveguide 31C transmits and outputs the Y-polarized TE0 light from the second rib 31B2 in the second rib waveguide 31B to the second output port 10B. In other words, the PBS 3 separates and outputs the X-polarized TE0 light to the first output port 10A and the Y-polarized TE0 light to the second output port 10B.

[0042] Next, a description will be given of the operation of the optical device 1 of Example 1. When X-polarized TE light from the optical fiber F is input through the inverse tapered portion 51, the conversion portion 52 of the optical device 1 spatially transitions the X-polarized TE light from the tapered waveguide 21B toward the first rib waveguide 31A while undergoing high-order conversion as X-polarized TE0 light.

[0043] The first rib waveguide 31A in the conversion unit 52 transmits and outputs the X-polarized TE0 light after spatial transition to the first rib 31B1 of the second rib waveguide 31B. The first rib 31B1 in the second rib waveguide 31B in the directional coupling unit 53 outputs the X-polarized TE0 light from the first rib 31B1 to the first output port 10A via the first rib 31C1 of the third rib waveguide 31C.

[0044] Furthermore, when Y-polarized TM light from the optical fiber F is input through the inverse taper portion 51, the conversion portion 52 of the optical device 1 spatially transitions the Y-polarized TM light from the tapered waveguide 21B toward the first rib waveguide 31A while undergoing high-order conversion from Y-polarized TM light to Y-polarized TE1 light.

[0045] The first rib waveguide 31A in the conversion unit 52 outputs the spatially transitioned Y-polarized TE1 light to the first rib 31B1 of the second rib waveguide 31B. The second rib 31B2 in the second rib waveguide 31B in the directional coupling unit 53 spatially transitions the Y-polarized TE1 light from the first rib 31B1 while converting it into Y-polarized TE0 light. The second rib 31B2 in the second rib waveguide 31B then outputs the spatially transitioned Y-polarized TE0 light to the second output port 10B via the second rib 31C2 in the third rib waveguide 31C.

[0046] That is, the optical device 1 can separate and output X-polarized TE0 light and Y-polarized TE0 light according to the polarization state of light input through the edge coupler 2. Furthermore, in the optical device 1, the tapered waveguide 21B of the SiN waveguide 21 and the first rib waveguide 31A of the Si waveguide 31 form the conversion section 52. The first rib waveguide 31A has ribs 31A1 whose core width gradually increases from the input to the output, and slabs 31A2 arranged on both sides of the rib 31A1 whose slab width gradually increases from the input to the output. The conversion section 52 also performs the functions of adiabatic conversion and high-order conversion. As a result, the length of the waveguides used for adiabatic conversion and high-order conversion can be shortened, significantly contributing to the miniaturization of the optical device 1.

[0047] The conversion unit 52 adiabatically spatially transitions light from the tapered waveguide 21B of the SiN waveguide 21 to the first rib waveguide 31A of the Si waveguide 31, and performs high-order conversion, for example, of TM light to TE1 light. Moreover, by making the Si waveguide 31 of the conversion unit 52 have a rib structure rather than a channel structure, sidewall roughness caused by a conventional channel structure is eliminated, thereby reducing light loss and reflection in the conversion unit 52. Moreover, because the conversion unit 52 performs both the functions of adiabatic conversion and high-order conversion, the length of the waveguide used for adiabatic conversion and high-order conversion can be shortened, thereby enabling the optical device 1 to be made more compact.

[0048] In the first rib waveguide 31A of the conversion unit 52, the TE0 light passes through as is, whereas the effective refractive index of the TM0 light is closer to the effective refractive index of TE1, so the TM0 light is converted to TE1 light. Furthermore, in the directional coupling unit 53, the optical confinement of the TE1 light in the first rib 31B1 is smaller than that of the TE0 light, so the Y-polarized light spatially transitions from the first rib 31B1 to the second rib 31B2 as TE0 light. As a result, only the TE1 light transitions to the second rib 31B2, so it can be spatially separated from the TE0 light.

[0049] In addition, the first rib waveguide 31A of the conversion portion 52 in the optical device 1 of Example 1 has a tendency to strongly confine TE light, making it difficult for the TE light to be optically coupled, and it is conceivable that the efficiency of adiabatic conversion may be deteriorated. Therefore, an embodiment that addresses such a situation will be described below as Example 2. [Example]

[0050] 3 is a schematic plan view showing an example of an optical device 1A of Example 2. Note that the same components as those in the optical device 1 of Example 1 are denoted by the same reference numerals, and explanations of the overlapping components and operations will be omitted. The optical device 1 of Example 1 differs from the optical device 1A of Example 2 in that it has a conversion section 52A that is composed of a tapered waveguide 21B of the SiN waveguide 21, and a channel waveguide 32 and a first rib waveguide 31A of the Si waveguide 31.

[0051] The optical device 1A has an inverse tapered portion 51, a conversion portion 52A, and a directional coupling portion 53. The inverse tapered portion 51 is configured as an inverse tapered waveguide 21A of the SiN waveguide 21. FIG. 4A is a cross-sectional schematic diagram showing an example of the cross section taken along line AA shown in FIG. 3. The cross-sectional portion shown in FIG. 4A is a cross-sectional portion of the inverse tapered portion 51. The optical device 1A shown in FIG. 2A has a Si substrate 11, a cladding layer 12 stacked on the Si substrate 11, and an inverse tapered waveguide 21A of the SiN waveguide 21 formed in a first layer in the cladding layer 12.

[0052] 4B is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line BB in FIG. 3. The cross-sectional portion shown in FIG. 4B is a cross-sectional portion of the input stage of the conversion unit 52A. The optical device 1A shown in FIG. 4B has a Si substrate 11 and a cladding layer 12 stacked on the Si substrate 11. The optical device 1A has a tapered waveguide 21B of a SiN waveguide 21 formed in a first layer in the cladding layer 12, and a channel waveguide 32 of a Si waveguide 31 formed in a second layer in the cladding layer 12.

[0053] 4C is a schematic cross-sectional view showing an example of the cross section taken along line CC shown in FIG. 3. The cross-sectional portion shown in FIG. 4C is a cross-sectional portion of the output stage of the conversion unit 52A. The optical device 1A shown in FIG. 4C includes a Si substrate 11 and a cladding layer 12 stacked on the Si substrate 11. The optical device 1A includes a tapered waveguide 21B of a SiN waveguide 21 formed in a first layer within the cladding layer 12, and a first rib waveguide 31A of a Si waveguide 31 formed in a second layer within the cladding layer 12. The first rib waveguide 31A includes ribs 31A11 optically connected to a channel waveguide 32, and slabs 31A12 arranged on both sides of the rib 31A11, the waveguide width of which gradually increases from the channel waveguide 32 toward the second rib waveguide 31B. The rib 31A11 of the first rib waveguide 31A is optically connected to the first rib 31B1 of the second rib waveguide 31B. The slab 31A12 of the first rib waveguide 31A is connected to the slab 31B3 of the second rib waveguide 31B. The optical device 1A configures a conversion section 52A by overlapping the tapered waveguide 21B, the channel waveguide 32, and the first rib waveguide 31A in the planar direction.

[0054] In the conversion unit 52A, light travels from the tapered waveguide 21B of the SiN waveguide 21 through the channel waveguide 32 of the Si waveguide 31 toward the first rib waveguide 31A while gradually undergoing high-order conversion. In the conversion unit 52A, X-polarized TE light travels from the tapered waveguide 21B toward the first rib waveguide 31A while spatially transitioning to X-polarized TE0 light and Y-polarized TM light while spatially transitioning to Y-polarized TE1 light.

[0055] The directional coupling section 53 is composed of a first rib 31B1 of the second rib waveguide 31B and a second rib 31B2 within the second rib waveguide 31B. FIG. 4D is a cross-sectional schematic diagram showing an example of the cross section taken along the line DD shown in FIG. 3. The cross-sectional portion shown in FIG. 4C is a cross-sectional portion of the directional coupling section 53. The optical device 1A shown in FIG. 4C includes a Si substrate 11, a cladding layer 12 stacked on the Si substrate 11, and a second rib waveguide 31B of the Si waveguide 31 formed in a second layer within the cladding layer 12. The first rib 31B1 of the second rib waveguide 31B transmits and outputs the X-polarized TE0 light input from the first rib waveguide 31A to the first rib 31C1 of the third rib waveguide 31C. In the first rib 31B1, Y-polarized TE1 light input from the first rib waveguide 31A spatially transitions to Y-polarized TE0 light in the second rib 31B2 in the second rib waveguide 31B.

[0056] The first rib 31C1 in the third rib waveguide 31C transmits and outputs the X-polarized TE0 light from the first rib 31B1 in the second rib waveguide 31B to the first output port 10A. The second rib 31C2 in the third rib waveguide 31C transmits and outputs the Y-polarized TE0 light from the second rib 31B2 in the second rib waveguide 31B to the second output port 10B. In other words, the PBS 3 separates and outputs the X-polarized TE0 light to the first output port 10A and the Y-polarized TE0 light to the second output port 10B.

[0057] Next, a description will be given of the operation of the optical device 1A of Example 2. When X-polarized TE light from the optical fiber F is input through the inverse tapered portion 51, the conversion portion 52A of the optical device 1A performs high-order conversion while spatially transitioning the X-polarized TE light from the tapered waveguide 21B through the channel waveguide 32 toward the first rib waveguide 31A to an X-polarized TE0 light.

[0058] The first rib waveguide 31A in the conversion unit 52A transmits and outputs the X-polarized TE0 light after spatial transition to the first rib 31B1 of the second rib waveguide 31B. The first rib 31B1 in the second rib waveguide 31B in the directional coupling unit 53 outputs the X-polarized TE0 light from the first rib 31B1 to the first output port 10A via the first rib 31C1 of the third rib waveguide 31C.

[0059] When Y-polarized TM light from the optical fiber F is input through the inverse taper section 51, the conversion section 52A of the optical device 1A performs high-order conversion while spatially transitioning the Y-polarized TM light from the tapered waveguide 21B through the channel waveguide 32 toward the first rib waveguide 31A to Y-polarized TE1 light.

[0060] The first rib waveguide 31A in the conversion unit 52A outputs the spatially transitioned Y-polarized TE1 light to the first rib 31B1 of the second rib waveguide 31B. The second rib 31B2 in the second rib waveguide 31B in the directional coupling unit 53 spatially transitions the Y-polarized TE1 light from the first rib 31B1 to Y-polarized TE0 light while performing high-order conversion. The second rib 31B2 in the second rib waveguide 31B then outputs the spatially transitioned Y-polarized TE0 light to the second output port 10B via the second rib 31C2 in the third rib waveguide 31C.

[0061] That is, in the optical device 1A, light input to the optical device 1A through the edge coupler 2 can be separated and output as X-polarized TE0 light and Y-polarized TE0 light according to the polarization state of the light input by the PBS 3. Moreover, the optical device 1A has a conversion section 52A that is made up of the tapered waveguide 21B of the SiN waveguide 21 and the channel waveguide 32 and first rib waveguide 31A of the Si waveguide 31. The conversion section 52A combines the functions of adiabatic conversion and high-order conversion, thereby shortening the length of the waveguides used for adiabatic conversion and high-order conversion, which can greatly contribute to the miniaturization of the optical device 1A.

[0062] In the conversion section 52A, the tip of the Si waveguide 31 is the channel waveguide 32, which weakens the confinement of light and improves the efficiency of adiabatic conversion from the SiN waveguide 21 to the Si waveguide 31 (efficiency of optical transition).

[0063] Furthermore, in the conversion section 52A, a sudden change in the mode field between the channel waveguide 32 and the first rib waveguide 31A may occur, resulting in radiation loss. However, the slab 31A2 of the first rib waveguide 31A is designed so that the slab width gradually increases from the channel waveguide 32 toward the second rib waveguide 31B. As a result, a sudden change in the mode field between the channel waveguide 32 and the first rib waveguide 31A in the conversion section 52A is avoided, thereby suppressing the occurrence of radiation loss.

[0064] In the optical device 1A of Example 2, the core widths of the first rib 31B1 and the second rib 31B2 of the second rib waveguide 31B constituting the directional coupling portion 53 are set constant. However, the present invention is not limited to this, and an embodiment thereof will be described below as Example 3. [Example]

[0065] 5 is a schematic plan view showing an example of an optical device 1B according to a third embodiment. The same components as those in the optical device 1A according to the second embodiment are denoted by the same reference numerals, and explanations of the overlapping components and operations will be omitted. The optical device 1A according to the second embodiment differs from the optical device 1B according to the third embodiment in that the optical device 1B according to the third embodiment has a directional coupling portion 53A in which the waveguide widths of the first rib 31B11 and the second rib 31B12 in the second rib waveguide 31B are tapered so as to continuously change.

[0066] The second rib waveguide 31B has a first rib 31B11, slabs 31B13 arranged on both sides of the first rib 31B11, and a second rib 31B12. The first rib 31B11 in the second rib waveguide 31B is a rib whose core width narrows from the channel waveguide 32 toward the first rib 31C1 of the third rib waveguide 31C. The second rib 31B12 in the second rib waveguide 31B is a rib whose core width gradually widens from the first rib waveguide 31A toward the second rib 31C2 of the third rib waveguide 31C.

[0067] The optical device 1B has an inverse tapered portion 51, a conversion portion 52A, and a directional coupling portion 53A. The inverse tapered portion 51 is configured as an inverse tapered waveguide 21A of the SiN waveguide 21. FIG. 6A is a cross-sectional schematic diagram showing an example of the cross section taken along line AA shown in FIG. 5. The cross-sectional portion shown in FIG. 6A is a cross-sectional portion of the inverse tapered portion 51. The optical device 1B shown in FIG. 6A has a Si substrate 11, a cladding layer 12, and an inverse tapered waveguide 21A of the SiN waveguide 21 formed in a first layer in the cladding layer 12.

[0068] Fig. 6B is a cross-sectional schematic diagram showing an example of the cross-sectional portion taken along line BB shown in Fig. 5. The cross-sectional portion shown in Fig. 6B is a cross-sectional portion of the input stage of conversion section 52A. Optical device 1B shown in Fig. 6B has Si substrate 11, cladding layer 12, tapered waveguide 21B of SiN waveguide 21 formed in a first layer in cladding layer 12, and channel waveguide 32 of Si waveguide 31 formed in a second layer in cladding layer 12.

[0069] FIG. 6C is a schematic cross-sectional view showing an example of the cross section taken along line CC shown in FIG. 5. The cross-sectional portion shown in FIG. 6C is a cross-sectional portion of the output stage of the conversion section 52A. The optical device 1B shown in FIG. 6C includes a Si substrate 11, a cladding layer 12, a tapered waveguide 21B of a SiN waveguide 21 formed in a first layer within the cladding layer 12, and a first rib waveguide 31A of a Si waveguide 31 formed in a second layer within the cladding layer 12. The first rib waveguide 31A includes ribs 31A11 optically connected to a channel waveguide 32 and slabs 31A12 disposed on both sides of the rib 31A11, the waveguide width of which gradually increases from the channel waveguide 32 toward the second rib waveguide 31B. The ribs 31A11 of the first rib waveguide 31A are optically connected to first ribs 31B1 of the second rib waveguide 31B. The slab 31A12 of the first rib waveguide 31A is connected to the slab 31B3 of the second rib waveguide 31B. In the conversion unit 52A, light travels from the tapered waveguide 21B of the SiN waveguide 21 through the channel waveguide 32 of the Si waveguide 31 toward the first rib waveguide 31A while gradually undergoing high-order conversion and spatial transition. The conversion unit 52A spatially transitions the X-polarized TE light from the tapered waveguide 21B toward the first rib waveguide 31A to the X-polarized TE0 light and spatially transitions the Y-polarized TM light to the Y-polarized TE1 light while performing high-order conversion.

[0070] The directional coupling unit 53A is composed of a first rib 31B11 of the second rib waveguide 31B and a second rib 31B12 within the second rib waveguide 31B. FIG. 6D is a cross-sectional schematic diagram showing an example of the cross section taken along the line DD shown in FIG. 5. The cross-sectional portion shown in FIG. 6D is a cross-sectional portion of the directional coupling unit 53A. The optical device 1B shown in FIG. 6D has a Si substrate 11, a cladding layer 12, and a second rib waveguide 31B of the Si waveguide 31 formed in a second layer within the cladding layer 12. The first rib 31B11 of the second rib waveguide 31B transmits and outputs the X-polarized TE0 light input from the first rib waveguide 31A to the first rib 31C1 of the third rib waveguide 31C. The first rib 31B11 spatially transitions the Y-polarized TE1 light input from the first rib waveguide 31A to the second rib 31B12 in the second rib waveguide 31B as Y-polarized TE0 light.

[0071] The first rib 31C1 in the third rib waveguide 31C transmits and outputs the X-polarized TE0 light from the first rib 31B11 in the second rib waveguide 31B to the first output port 10A. The second rib 31C2 in the third rib waveguide 31C transmits and outputs the Y-polarized TE0 light from the second rib 31B12 in the second rib waveguide 31B to the second output port 10B. In other words, the PBS 3 separates and outputs the X-polarized TE0 light to the first output port 10A and the Y-polarized TE0 light to the second output port 10B.

[0072] Next, the operation of the optical device 1B of Example 3 will be described. When X-polarized TE light from the optical fiber F is input through the inverse tapered portion 51, the conversion portion 52A of the optical device 1B performs high-order conversion while spatially transitioning the X-polarized TE light from the tapered waveguide 21B through the channel waveguide 32 toward the first rib waveguide 31A to an X-polarized TE0 light.

[0073] The first rib waveguide 31A in the conversion unit 52A transmits and outputs the X-polarized TE0 light after spatial transition to the first rib 31B11 of the second rib waveguide 31B. The first rib 31B11 in the second rib waveguide 31B in the directional coupling unit 53 outputs the X-polarized TE0 light from the first rib 31B11 to the first output port 10A via the first rib 31C1 of the third rib waveguide 31C.

[0074] When Y-polarized TM light from the optical fiber F is input through the inverse taper section 51, the conversion section 52A of the optical device 1B performs high-order conversion while spatially transitioning the Y-polarized TM light from the tapered waveguide 21B through the channel waveguide 32 toward the first rib waveguide 31A to Y-polarized TE1 light.

[0075] The first rib waveguide 31A in the conversion unit 52A outputs the spatially transitioned Y-polarized TE1 light to the first rib 31B11 of the second rib waveguide 31B. The second rib 31B12 in the second rib waveguide 31B in the directional coupling unit 53A spatially transitions the Y-polarized TE1 light from the first rib 31B11 to Y-polarized TE0 light while performing high-order conversion. The second rib 31B12 in the second rib waveguide 31B then outputs the spatially transitioned Y-polarized TE0 light to the second output port 10B via the second rib 31C2 in the third rib waveguide 31C.

[0076] That is, in the optical device 1B, light input to the optical device 1B through the edge coupler 2 can be separated and output as X-polarized TE0 light and Y-polarized TE0 light according to the polarization state of the light input by the PBS 3. Moreover, in the optical device 1B, the tapered waveguide 21B of the SiN waveguide 21 and the channel waveguide 32 and first rib waveguide 31A of the Si waveguide 31 form the conversion section 52A. The conversion section 52A combines the functions of adiabatic conversion and high-order conversion, thereby shortening the length of the waveguides used for adiabatic conversion and high-order conversion, which can greatly contribute to the miniaturization of the optical device 1B.

[0077] In the directional coupling unit 53A, the first rib 31B11 and the second rib 31B12 in the second rib waveguide 31B have a tapered shape in which the core widths change continuously. As a result, by tapering the core width of the directional coupling unit 53A and changing it continuously, the efficiency of light transition increases, improving the coupling efficiency of the directional coupling unit 53A and shortening the waveguide length of the directional coupling unit 53A.

[0078] In the optical device 1 (1A, 1B) of this embodiment, an example is shown in which the edge coupler 2 and the PBS 3 optically connected to the edge coupler 2 are included, but a PR (Polarization Rotator) that rotates the polarization of the signal light may be disposed instead of the PBS 3, and modifications can be made as appropriate. Also, in the optical device 1 (1A, 1B), instead of the edge coupler 2, a crossing waveguide in which a SiN waveguide and a Si waveguide intersect may be disposed, and modifications can be made as appropriate.

[0079] FIG. 7 is an explanatory diagram illustrating an example of an optical transceiver 70 according to this embodiment. The optical transceiver 70 shown in FIG. 7 is connected to an output optical fiber and an input optical fiber. The optical transceiver 70 includes a DSP (Digital Signal Processor) 72 and an optical transmitter / receiver 73. The optical transmitter / receiver 73 includes an optical transmitter 73A and an optical receiver 73B. The DSP 72 is an electrical component that performs digital signal processing. For example, the DSP 72 performs processing such as encoding transmission data, generates an electrical signal containing the transmission data, and outputs the generated electrical signal to the optical transmitter 73A. The DSP 72 also acquires an electrical signal containing reception data from the optical receiver 73B and performs processing such as decoding the acquired electrical signal to obtain the reception data.

[0080] The light source (not shown) includes, for example, a laser diode, and generates light of a predetermined wavelength and supplies it to the optical transmitter 73A and the optical receiver 73B. The optical transmitter 73A modulates the light supplied from the light source using an electrical signal output from the DSP 72, and outputs the resulting transmission light to an optical fiber. The optical transmitter 73A has an optical modulator element 73A1 that generates transmission light by modulating the light supplied from the light source using an electrical signal input to the optical modulator as the light propagates through the waveguide.

[0081] The optical receiver 73B has an optical receiver element 73B1 that receives an optical signal from an optical fiber and demodulates the received light using light supplied from a light source. The optical receiver 73B then converts the demodulated received light into an electrical signal and outputs the converted electrical signal to the DSP 72. The optical receiver 73B incorporates an optical device that is a planar optical waveguide element that guides light.

[0082] For convenience of explanation, the optical transceiver 70 has been illustrated as having an optical transmitter 73A and an optical receiver 73B built in, but the optical transceiver 70 may have either the optical transmitter 73A or the optical receiver 73B built in. For example, an optical device may be applied to the optical transceiver 70 having the optical receiver 73B built in, and modifications can be made as appropriate.

[0083] Furthermore, the components of each unit shown in the figure do not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each unit is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0084] Furthermore, the various processing functions performed by each device may be executed in whole or in part on a CPU (Central Processing Unit) (or a microcomputer such as an MPU (Micro Processing Unit) or MCU (Micro Controller Unit)). Needless to say, the various processing functions may be executed in whole or in part on a program analyzed and executed by a CPU (or a microcomputer such as an MPU or MCU), or on hardware using wired logic. [Explanation of symbols]

[0085] 1 Optical Devices 11. Si substrate 21 SiN waveguide 21B Tapered waveguide 31 Si waveguide 31A First Rib Waveguide 31A1, 31A11 Rib 31A2, 31A12 slabs 31B Second rib waveguide 31B1, 31B11 First rib 31B2, 31B12 Second rib 31B3 Slab 32 Channel Waveguide 52 Conversion unit 53 Directional joint

Claims

1. A substrate; a tapered waveguide disposed on a first layer on the substrate, the waveguide width gradually increasing from the input to the output; a rib waveguide disposed on a second layer on the substrate different from the first layer and overlapping the tapered waveguide in a planar direction; The rib waveguide comprises: a rib whose core width gradually increases from the input to the output; slabs arranged on both sides of the rib, the slab width gradually increasing from the input to the output; An optical device comprising:

2. The rib waveguide comprises: a channel waveguide; the rib is optically connected to an output end of the channel waveguide, and the core width of the rib gradually increases from the input to the output; The slabs are arranged on both sides of the rib, and the slab width gradually increases from the input to the output; 2. The optical device according to claim 1, wherein:

3. The tapered waveguide is Constructed of a material containing SiN, The rib waveguide comprises:

2. The optical device according to claim 1, wherein the optical device is made of a material containing Si.

4. another rib waveguide disposed on the second layer and optically connecting to the rib waveguide; The other rib waveguide is a first rib optically connected to the rib; other slabs disposed on either side of the first rib; a second rib disposed in one of the other slabs and arranged in parallel with the first rib; 2. The optical device according to claim 1, wherein:

5. 5. The optical device according to claim 4, wherein the core widths of the first rib and the second rib in the other rib waveguide are constant.

6. 5. The optical device according to claim 4, wherein the core widths of the first rib and the second rib in the other rib waveguide vary continuously.

7. An optical receiver including an optical receiver element that converts received signal light into an electrical signal, The optical receiver element comprises: A substrate; a tapered waveguide disposed on a first layer on the substrate, the waveguide width gradually increasing from the input to the output; a rib waveguide disposed on a second layer on the substrate, the second layer being different from the first layer, and overlapping the tapered waveguide in a planar direction; The rib waveguide comprises: a rib whose core width gradually increases from the input to the output; slabs arranged on both sides of the rib, the slab width gradually increasing from the input to the output; An optical receiver comprising:

8. An optical transmitter including an optical modulator element that modulates guided light in response to an electrical signal, The optical modulator element comprises: A substrate; a tapered waveguide disposed on a first layer on the substrate, the waveguide width gradually increasing from the input to the output; a rib waveguide disposed on a second layer on the substrate, the second layer being different from the first layer, and overlapping the tapered waveguide in a planar direction; The rib waveguide comprises: a rib whose core width gradually increases from the input to the output; slabs arranged on both sides of the rib, the slab width gradually increasing from the input to the output; An optical transmitter comprising:

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