Optical device, optical receiver, and optical transmitter

Abstract

To provide an optical device capable of reducing optical coupling loss and optical reflection.SOLUTION: The optical device includes: a channel waveguide having a waveguide width expanding in a tapered shape; and a rib waveguide connected to a side of the channel waveguide where the waveguide width is expanded and including a rib part and a slab part. The rib waveguide includes a tapered waveguide having a rib part where the rib width expands in a tapered shape with increasing distance from a portion connected to the channel waveguide.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] Fig. 12 is a schematic plan view showing an example of a conventional EC (Edge Coupler) 200. The EC 200 shown in Fig. 12 is a planar optical waveguide element that is disposed near a chip end face D1 and optically coupled to a core C of an optical fiber F. The EC 200 is also a spot size converter that, for example, brings the spot size of the signal light or the local light closer to the mode field diameter of the optical fiber F.

[0003] The EC 200 has a cladding 222 made of, for example, SiO2, and an optical waveguide 210 made of, for example, Si, which is covered with the cladding 222. The optical waveguide 210 is, for example, an optical waveguide with a channel structure. The optical waveguide 210 has a tapered waveguide 211 and a straight waveguide 212 connected to the tapered waveguide 211. The tapered waveguide 211 has a structure in which the waveguide width gradually increases with increasing distance from the starting point of the tapered waveguide 211. The straight waveguide 212 is a waveguide connected to the side of the tapered waveguide 211 where the waveguide width is wider. The straight waveguide 212 and the tapered waveguide 211 have the same waveguide thickness.

[0004] Fig. 13 is a cross-sectional schematic diagram showing an example of a cross-sectional portion taken along line AA of the EC 200 shown in Fig. 12. The EC 200 shown in Fig. 13 has a Si substrate 221, a cladding 222, and an assembly layer 223 arranged on the Si substrate 221. The cross-sectional portion taken along line AA shown in Fig. 13 is a cross-sectional portion of the EC 200 in which a straight waveguide 212 is arranged. The straight waveguide 212 and tapered waveguide 211 of the optical waveguide 210 are arranged in the assembly layer 223. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2017-534926 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-251218 [Patent Document 3] US Patent Application Publication No. 2019 / 0170941 [Patent Document 4] U.S. Patent No. 10,162,133 Summary of the Invention [Problem to be solved by the invention]

[0006] However, because the conventional EC 200 is configured with the optical waveguide 210 having a channel structure, sidewall roughness occurs due to etching during the formation of the optical waveguide 210, and the sidewall roughness causes light scattering, resulting in increased coupling loss and light reflection. Moreover, the effect of sidewall roughness is significant in the portion of the optical waveguide 210 where the waveguide is thick.

[0007] One aspect of the present invention is to provide an optical device or the like that can improve coupling loss and optical reflection. [Means for solving the problem]

[0008] An optical device according to one embodiment includes a channel waveguide whose waveguide width increases in a tapered manner, and a rib waveguide connected to the side of the channel waveguide where the waveguide width increases, the rib waveguide having a rib portion and a slab portion, wherein the rib waveguide has a tapered waveguide in which the rib width of the rib portion increases in a tapered manner with increasing distance from the side connected to the channel waveguide. [Effects of the Invention]

[0009] According to one aspect, an optical device or the like capable of improving coupling loss and optical reflection can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic plan view showing an example of the EC of the first embodiment. [Figure 2A]FIG. 2A is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC shown in FIG. 1 taken along line AA. [Figure 2B] FIG. 2B is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC 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 of EC taken along line CC shown in FIG. [Figure 3] FIG. 3 is a schematic plan view showing an example of the EC of the second embodiment. [Figure 4A] FIG. 4A is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC shown in FIG. 3 taken along the line AA. [Figure 4B] 4B is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC 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 of EC shown in FIG. [Figure 4D] FIG. 4D is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC taken along line DD shown in FIG. [Figure 5] FIG. 5 is a schematic plan view showing an example of the EC of the third embodiment. [Figure 6A] FIG. 6A is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC shown in FIG. 5 taken along the line AA. [Figure 6B] FIG. 6B is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC 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 of EC shown in FIG. [Figure 6D] FIG. 6D is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC taken along line DD shown in FIG. [Figure 7] FIG. 7 is a schematic plan view showing an example of the EC of the fourth embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC shown in FIG. 7 taken along the line AA. [Figure 9] FIG. 9 is an explanatory diagram illustrating an example of an optical transceiver according to this embodiment. [Figure 10]FIG. 10 is a schematic plan view showing an example of an EC of a comparative example. [Figure 11] FIG. 11 is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC shown in FIG. 10 taken along the line AA. [Figure 12] FIG. 12 is a schematic plan view showing an example of a conventional EC. [Figure 13] FIG. 13 is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC shown in FIG. 12 taken along the line AA. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the conventional EC 200, the optical waveguide 210 has a channel structure, which causes light scattering due to rough sidewalls. Therefore, the present applicant has proposed a comparative example, the EC 100, which can deal with such a situation.

[0012] <Comparative Example> Fig. 10 is a schematic plan view showing an example of an EC 100 of a comparative example. The EC 100 shown in Fig. 10 is a portion of a planar optical waveguide device that is arranged near a chip end face D1 and optically coupled to a core C of an optical fiber F. The EC 100 is, for example, a spot size converter that changes the spot size of the signal light or the local light to approximate the mode field diameter of the optical fiber F.

[0013] The EC 100 includes a cladding 122 made of, for example, SiO2, and an optical waveguide 110 made of, for example, Si, and coated with the cladding 122. The optical waveguide 110 is, for example, a rib waveguide having a rib portion 110A and slab portions 110B formed on both sides of the rib portion 110A and thinner than the rib portion 110A. The optical waveguide 110 includes a tapered waveguide 111 and a straight waveguide 112 connected to the tapered waveguide 111. The tapered waveguide 111 has a structure in which the waveguide width gradually increases with increasing distance from the starting point of the tapered waveguide 111. The straight waveguide 112 is connected to the wider-width side of the tapered waveguide 111 and is a waveguide with a constant waveguide width. The straight waveguide 112 and the tapered waveguide 111 have the same waveguide thickness.

[0014] Fig. 11 is a cross-sectional schematic diagram showing an example of a cross-sectional portion taken along line AA of the EC 100 shown in Fig. 10. The EC 100 shown in Fig. 11 has a Si substrate 121, a cladding 122, and an assembly layer 123 arranged on the Si substrate 121. The cross-sectional portion taken along line AA shown in Fig. 11 is a cross-sectional portion of the EC 100 in which a straight waveguide 112 is arranged. The straight waveguide 112 of the optical waveguide 110 is arranged in the assembly layer 123. Furthermore, the tapered waveguide 111 of the optical waveguide 110 is arranged in the assembly layer 123.

[0015] In the EC 100 of the comparative example, the optical waveguide 110 has a rib structure, so there is no roughness on the sidewall, and optical coupling loss and optical reflection due to light scattering caused by the roughness on the sidewall can be suppressed.

[0016] However, the EC 100 of the comparative example has an optical waveguide 110 with a rib structure, and the tapered waveguide 111 of the optical waveguide 110 strongly confines light, making it impossible to expand the mode field.

[0017] Therefore, an embodiment that can deal with such a situation will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment. Furthermore, the examples shown below may be combined as appropriate within the scope that does not cause contradictions. [Example]

[0018] Fig. 1 is a planar schematic diagram showing an example of EC1 of Example 1. EC1 shown in Fig. 1 is a portion of a planar optical waveguide element that is arranged near a chip end face D1 and optically coupled to a core C of an optical fiber F. EC1 is, for example, a spot size converter that changes the spot size of signal light or local light to approximate the mode field diameter of the optical fiber F.

[0019] EC1 has a cladding 22 made of, for example, SiO2 or the like, and an optical waveguide 10 made of, for example, Si or the like, coated with the cladding 22. The optical waveguide 10 has a channel waveguide 11 whose waveguide width increases in a tapered manner from the vicinity of the chip end face D1, and a rib waveguide 12 connected to the side of the channel waveguide 11 where the width increases, and having a rib portion 12A and a slab portion 12B. The channel waveguide 11 is configured as a tapered waveguide whose waveguide width gradually increases with increasing distance from the vicinity of the chip end face D1.

[0020] The rib waveguide 12 has a rib portion 12A and slab portions 12B formed on both sides of the rib portion 12A and thinner than the rib portion 12A. The rib waveguide 12 has a tapered waveguide 13 and a straight waveguide 14 connected to the tapered waveguide 13. The tapered waveguide 13 is connected to the side of the channel waveguide 11 where the waveguide width is wider, and has a structure in which the waveguide width gradually widens with increasing distance from the starting point of the tapered waveguide 13. The straight waveguide 14 is connected to the side of the tapered waveguide 13 where the waveguide width is wider, and is a linear waveguide with a constant waveguide width. The straight waveguide 14 and the tapered waveguide 13 have the same waveguide thickness. In other words, the rib width of the rib portion 12A of the rib waveguide 12 increases in a tapered manner with increasing distance from the portion where it is connected to the channel waveguide 11.

[0021] Fig. 2A is a schematic cross-sectional view showing an example of the approximate cross section of EC1 shown in Fig. 1 taken along line AA. EC1 shown in Fig. 2A has a Si substrate 21, a cladding 22, and a first assembly layer 23 disposed on the Si substrate 21. The approximate cross section of line AA shown in Fig. 2A is a cross-sectional portion of EC1 in which the straight waveguide 14 in the rib waveguide 12 is disposed. The straight waveguide 14 of the rib waveguide 12 is disposed in the first assembly layer 23.

[0022] Fig. 2B is a schematic cross-sectional view showing an example of a schematic cross-sectional portion along line BB of EC1 shown in Fig. 1. EC1 shown in Fig. 2B has a Si substrate 21, a cladding 22, and a first assembly layer 23. The schematic cross-sectional portion along line BB shown in Fig. 2B is a cross-sectional portion of EC1 in which a tapered waveguide 13 is arranged within a rib waveguide 12. The tapered waveguide 13 within the rib waveguide 12 is arranged in the first assembly layer 23.

[0023] Fig. 2C is a schematic cross-sectional view showing an example of a schematic cross-sectional portion of the CC line of EC1 shown in Fig. 1. EC1 shown in Fig. 2C has a Si substrate 21, a cladding 22, and a first assembly layer 23. The schematic cross-sectional portion of the CC line shown in Fig. 2C is a cross-sectional portion of EC1 in which a channel waveguide 11 is arranged. The channel waveguide 11 is arranged in the first assembly layer 23.

[0024] In EC1 of Example 1, a rib waveguide 12 is used in a portion of the optical waveguide 10, so there is no rough sidewall, and optical coupling loss and optical reflection due to light scattering caused by rough sidewalls can be suppressed. Furthermore, EC1 uses a channel waveguide 11 in the portion of the optical waveguide 10 that is optically coupled to the optical fiber F, so light confinement is weak and the mode field can be expanded. Furthermore, EC1 enables low-loss spot size conversion. Furthermore, even though the portion optically coupled to the optical fiber F is a channel waveguide 11, the core width is narrowed, so the effects of rough sidewalls can be suppressed.

[0025] In the example shown in Example 1, the slab width of each slab portion 12B of the tapered waveguide 13 of the rib waveguide 12 is constant. However, this is not limiting, and the slab width of the tapered waveguide 13 of the rib waveguide 12 may be gradually narrowed from the connection portion with the slab portion 12B of the straight waveguide 14 toward the channel waveguide 11, and can be changed as appropriate. In this case, the slab width of the tapered waveguide 13 gradually approaches the channel waveguide 11, thereby making it possible to make the change in the mode field gentler.

[0026] Furthermore, in EC1 of Example 1, a spot size converter having a Si optical waveguide 10 including a channel waveguide 11 and a rib waveguide 12 is exemplified, but it may be possible that the mode field cannot be sufficiently expanded using only the Si optical waveguide 10. Therefore, an embodiment that addresses such a situation will be described below as Example 2. [Example]

[0027] Fig. 3 is a schematic plan view showing an example of an EC5 according to a second embodiment. The same components as those of the EC1 according to the first embodiment are designated by the same reference numerals, and explanations of the overlapping components and operations will be omitted. The EC5 shown in Fig. 3 includes a first EC1A and a second EC3. The first EC1A is the EC1 according to the first embodiment, which includes a channel waveguide 11 and a rib waveguide 12 connected to the channel waveguide 11.

[0028] The second EC3 has a cladding 22 made of SiO2 or the like, and a SiN waveguide 30 made of, for example, Si3N4 (hereinafter simply referred to as SiN (Silicon Nitride)) or the like, coated with the cladding 22. The SiN waveguide 30 has a first tapered waveguide 31 and a second tapered waveguide 32 connected to the first tapered waveguide 31. The first tapered waveguide 31 has a structure in which the waveguide width gradually increases from the optical input / output portion near the chip end face D1 toward the second tapered waveguide 32. The second tapered waveguide 32 has a structure in which the waveguide width gradually decreases from the point where it connects to the first tapered waveguide 31 as it moves away from the first tapered waveguide 31. The second tapered waveguide 32 is another tapered waveguide.

[0029] EC5 has a transition section 33 where light adiabatically transitions between the channel waveguide 11 in the first EC1A and the second tapered waveguide 32 in the SiN waveguide 30 in the second EC3, and an inverted tapered section 34 where the waveguide width to the chip end face D1 gradually narrows. The inverted tapered section 34 is located near the chip end face D1 and is the first tapered waveguide 31 of the SiN waveguide 30 that guides the signal light from the optical fiber F1.

[0030] The transition section 33 has a part of the tapered waveguide 13, the channel waveguide 11, and the second tapered waveguide 32, and light transitions between the part of the tapered waveguide 13, the channel waveguide 11, and the second tapered waveguide 32. That is, in the transition section 33, signal light from the second tapered waveguide 32 transitions to the straight waveguide 14 via the channel waveguide 11 and the tapered waveguide 13 with a rib structure.

[0031] Fig. 4A is a schematic cross-sectional view showing an example of the approximate cross section of the EC5 shown in Fig. 3 taken along line AA. The EC5 shown in Fig. 4A has a Si substrate 21, a cladding 22, a first assembly layer 23 arranged closer to the Si substrate 21, and a second assembly layer 24 arranged farther from the Si substrate 21. The approximate cross section taken along line AA shown in Fig. 4A is a cross-sectional portion of the first EC1A in which the straight waveguide 14 in the rib waveguide 12 is arranged. The straight waveguide 14 of the rib waveguide 12 is arranged in the first assembly layer 23.

[0032] 4B is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC5 shown in FIG. 3 along line BB. The EC5 shown in FIG. 4B includes a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The cross-sectional portion of line BB shown in FIG. 4B is a cross-sectional portion of a transition section 33 where the tapered waveguide 13 in the rib waveguide 12 is disposed. The tapered waveguide 13 in the rib waveguide 12 is disposed in the first assembly layer 23. The second tapered waveguide 32 of the SiN waveguide 30 is disposed in the second assembly layer 24. That is, the second tapered waveguide 32 of the SiN waveguide 30 is disposed in a layer different from the rib waveguide 12, at a position where it overlaps with the tapered waveguide 13 of the rib waveguide 12 in the planar direction.

[0033] 4C is a schematic cross-sectional view showing an example of a schematic cross-sectional portion of the CC line of the EC5 shown in FIG. 3. The EC5 shown in FIG. 4C has a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The schematic cross-sectional portion of the CC line shown in FIG. 4C is a cross-sectional portion of a transition section 33 in which a channel waveguide 11 is disposed. The channel waveguide 11 is disposed in the first assembly layer 23. The second tapered waveguide 32 in the second EC3 is disposed in the second assembly layer 24. That is, the second tapered waveguide 32 of the SiN waveguide 30 is disposed in a layer different from the channel waveguide 11, at a position overlapping the channel waveguide 11 in the planar direction.

[0034] Fig. 4D is a schematic cross-sectional view showing an example of a schematic cross-sectional portion of the DD line of the EC5 shown in Fig. 3. The EC5 shown in Fig. 4D has a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The schematic cross-sectional portion of the DD line shown in Fig. 4D is a cross-sectional portion of an inverted tapered portion 34 in which a first tapered waveguide 31 is arranged. The first tapered waveguide 31 is arranged in the second assembly layer 24.

[0035] The transition section 33 is configured with the Si channel waveguide 11, which has the effect of weakening light confinement compared to a configuration configured with only a Si rib waveguide. This effect is particularly pronounced when the guided light is TE light. Therefore, the transition section 33 expands the mode field of the TE light transitioning from the channel waveguide 11 to the second tapered waveguide 32 of the SiN waveguide 30, and the efficiency of the transition of the TE light from the channel waveguide 11 to the SiN waveguide 30 increases. As a result, the efficiency of adiabatic conversion of the TE light in the transition section 33 can be improved.

[0036] In the EC5 of Example 2, a rib waveguide 12 is used as part of the optical waveguide 10 of the first EC1A, so there is no rough sidewall, and optical coupling loss and optical reflection due to light scattering caused by rough sidewalls can be suppressed. The first EC1A uses a channel waveguide 11 at the transition point between the SiN waveguide 30 and the second tapered waveguide 32, so light confinement is weak and the mode field can be expanded. Moreover, in the first EC1A, even if the transition point between the SiN waveguide 30 and the second tapered waveguide 32 is the channel waveguide 11, the core width is narrowed, so the effects of rough sidewalls can be suppressed.

[0037] For example, when the transition section uses a rib waveguide instead of the channel waveguide 11 and TE light transitions from the rib waveguide to the second tapered waveguide 32, the rib waveguide has strong light confinement, which reduces the efficiency of the transition of the TE light and increases the loss of the TE light. In contrast, the transition section 33 of this embodiment expands the mode field of the TE light transitioning from the channel waveguide 11 to the second tapered waveguide 32 of the SiN waveguide 30. Moreover, the channel waveguide 11 has weak light confinement, which significantly improves the efficiency of the transition of the TE light from the channel waveguide 11 to the SiN waveguide 30. As a result, the efficiency of adiabatic conversion of the TE light in the transition section 33 can be increased, thereby improving the loss of the TE light.

[0038] The EC5 uses the inverse tapered portion 34 to propagate the signal light from the optical fiber F to the transition portion 33. In the transition portion 33, the waveguide widths of the Si channel waveguide 11 and the SiN second tapered waveguide 32 change in a tapered shape. The SiN second tapered waveguide 32 has a lower refractive index than the Si channel waveguide 11, so it sufficiently expands the mode field of the signal light, and moreover, has little polarization dependency, so it is possible to reduce the coupling loss of the TE light and TM light with the optical fiber F and improve the coupling efficiency.

[0039] In the rib waveguide 12 of the first EC1A of Example 2, the width of the slab portion 12B is constant. Therefore, in the transition portion 33 including the tapered waveguide 13 and the channel waveguide 11, a sudden change in the slab width between the tapered waveguide 13 and the channel waveguide 11 may cause a sudden change in the mode field, resulting in radiation loss. Therefore, an embodiment that addresses this situation will be described below as Example 3. [Example]

[0040] 5 is a schematic plan view showing an example of EC5A of Example 3. Note that the same components as those of EC5 of Example 2 are denoted by the same reference numerals, and explanations of the overlapping components and operations will be omitted. EC5 of Example 2 differs from EC5A of Example 3 in that the slab width of the slab portion 12B1 of the straight waveguide 14 of the rib waveguide 12 is constant, but the slab width of the slab portion 12B2 of the tapered waveguide 13A of the rib waveguide 12 changes continuously.

[0041] The slab width of each slab portion 12B2 of the tapered waveguide 13A of the rib waveguide 12 continuously changes so as to gradually narrow from the connection portion with the slab portion 12B1 of the straight waveguide 14 toward the channel waveguide 11. In the transition portion 33A, light adiabatically transitions between the Si tapered waveguide 13A and channel waveguide 11 and the SiN second tapered waveguide 32. As a result, the slab width of the slab portion 12B2 of the tapered waveguide 13A gradually approaches the channel waveguide 11, thereby preventing a sudden change in the mode field.

[0042] Fig. 6A is a schematic cross-sectional view showing an example of a schematic cross-sectional portion taken along line AA of EC5A shown in Fig. 5. EC5A shown in Fig. 6A has a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The schematic cross-sectional portion taken along line AA shown in Fig. 6A is a cross-sectional portion of a first EC1B in which a straight waveguide 14 is arranged in a rib waveguide 12. The straight waveguide 14 of the rib waveguide 12 is arranged in the first assembly layer 23.

[0043] 6B is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC5A shown in FIG. 5 taken along line BB. The EC5A shown in FIG. 6B includes a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The cross-sectional portion of line BB shown in FIG. 6B is a cross-sectional portion of a transition section 33A where a tapered waveguide 13A in a rib waveguide 12 is disposed. The tapered waveguide 13A in the rib waveguide 12 is disposed in the first assembly layer 23. The second tapered waveguide 32 in a SiN waveguide 30 is disposed in the second assembly layer 24. That is, the second tapered waveguide 32 of the SiN waveguide 30 is disposed in a layer different from the rib waveguide 12, at a position where it overlaps with the tapered waveguide 13A of the rib waveguide 12 in the planar direction.

[0044] 6C is a schematic cross-sectional view showing an example of a schematic cross-sectional portion of the CC line of the EC5A shown in FIG. 5. The EC5A shown in FIG. 6C has a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The schematic cross-sectional portion of the CC line shown in FIG. 6C is a cross-sectional portion of a transition section 33A in which a channel waveguide 11 is disposed. The channel waveguide 11 is disposed in the first assembly layer 23. The second tapered waveguide 32 in the SiN waveguide 30 is disposed in the second assembly layer 24. That is, the second tapered waveguide 32 of the SiN waveguide 30 is disposed in a layer different from the rib waveguide 12, at a position overlapping the channel waveguide 11 in the planar direction.

[0045] Fig. 6D is a schematic cross-sectional view showing an example of a schematic cross-sectional portion of the DD line of the EC5A shown in Fig. 5. The EC5A shown in Fig. 6D has a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The schematic cross-sectional portion of the DD line shown in Fig. 6D is a cross-sectional portion of the inverted tapered portion 34 in which the first tapered waveguide 31 is arranged. The first tapered waveguide 31 is arranged in the second assembly layer 24.

[0046] In the EC5A of the third embodiment, the slab width of each slab portion 12B2 of the tapered waveguide 13A of the rib waveguide 12 gradually narrows from the connection portion with the slab portion 12B1 of the straight waveguide 14 toward the channel waveguide 11. That is, the slab width of the slab portion 12B2 of the tapered waveguide 13A gradually approaches the channel waveguide 11, so that the change in the slab width becomes gentler. As a result, the change in the mode field between the tapered waveguide 13A and the channel waveguide 11 becomes gentler, thereby suppressing the occurrence of radiation loss.

[0047] Moreover, EC5A employs a rib waveguide 12 in part of the optical waveguide 10, eliminating sidewall roughness and suppressing optical coupling loss and optical reflection due to light scattering caused by sidewall roughness. The first EC1B employs a channel waveguide 11 at the transition point between the SiN waveguide 30 and the second tapered waveguide 32, resulting in weaker optical confinement and an expanded mode field.

[0048] The EC5A uses the inverse tapered portion 34 to propagate the signal light from the optical fiber F to the transition portion 33A. In the transition portion 33A, the waveguide widths of the Si channel waveguide 11 and the SiN second tapered waveguide 32 change in a tapered shape. The SiN second tapered waveguide 32 has a lower refractive index than the Si channel waveguide 11, so it sufficiently expands the mode field of the signal light, and moreover, has little polarization dependency, so it is possible to reduce the coupling loss of the TE light and TM light with the optical fiber F and improve the coupling efficiency.

[0049] In the EC5A of Example 3, a tapered channel waveguide 11 is exemplified, but if the waveguide width of the channel waveguide 11 is too wide, it is conceivable that coupling loss and optical reflection will increase. Therefore, an embodiment that can improve such a situation will be described below as Example 4. [Example]

[0050] FIG. 7 is a schematic plan view showing an example of EC5B of Example 4. The same components as those of EC5A of Example 3 are denoted by the same reference numerals, and the description of the overlapping components and operations is omitted. The difference between EC5A of Example 3 and EC5B of Example 4 lies in that it has a tapered channel waveguide 11A that is narrower than the waveguide width of the tapered channel waveguide 11.

[0051] In FIG. 7, let the waveguide length of the channel waveguide 11A of the transition portion 33A1 be Lch, and the waveguide length of the tapered waveguide 13A of the transition portion 33A1 be Lrib. Further, let the waveguide width of the channel waveguide 11A at the starting point of the transition portion 33A1 be w1, and the waveguide width of the channel waveguide 11A at the portion connecting to the tapered waveguide 13A of the transition portion 33A1 be w2. Further, let the waveguide width of the tapered waveguide 13A at the portion connecting to the straight waveguide 14 at the end point of the transition portion 33A1 be w3.

[0052] The waveguide length Lch of the channel waveguide 11A is set to a length at which light can be completely transferred between the tapered waveguide 13A and the second tapered waveguide 32 in the transition portion 33A1. Further, the waveguide width w2 of the channel waveguide 11A is set to a width that can suppress coupling loss and light reflection. And the relationship of the waveguide widths is w1 < w2 < w3. And the taper angle α1 of the channel waveguide 11A is ((w2 - w1) / Lch). Further, the taper angle α2 of the tapered waveguide 13A of the rib waveguide 12 is ((w3 - w2) / Lrib). The taper angle α1 of the channel waveguide 11A is different from the taper angle α2 of the tapered waveguide 13A.

[0053] FIG. 8 is a schematic cross-sectional view showing an example of a cross-sectional portion of the EC5B shown in FIG. 7 taken along line AA. The EC5B shown in FIG. 8 includes a Si substrate 21, a cladding 22, a first assembly layer 23, and a second assembly layer 24. The cross-sectional portion of line AA shown in FIG. 8 is a cross-sectional portion of a transition section 33A1 in which a channel waveguide 11A is disposed. The channel waveguide 11A is disposed in the first assembly layer 23. The second tapered waveguide 32 in the second EC3 is disposed in the second assembly layer 24. That is, the second tapered waveguide 32 of the SiN waveguide 30 is disposed in a layer different from the channel waveguide 11A, at a position overlapping the channel waveguide 11A in the planar direction.

[0054] In the transition section 33A1 in the EC5B of the fourth embodiment, the waveguide length Lch of the channel waveguide 11A is set to a length necessary for adiabatic conversion, and the waveguide width w2 of the channel waveguide 11A is set to a width that can suppress coupling loss and optical reflection, thereby making it possible to suppress coupling loss and optical reflection at the transition section 33A1.

[0055] FIG. 9 is an explanatory diagram illustrating an example of an optical transceiver 70 according to this embodiment. The optical transceiver 70 shown in FIG. 9 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.

[0056] The optical transmitter 73A has an optical modulator element 73A1 that modulates supplied light with an electrical signal output from the DSP 72, and outputs the transmitted light modulated by the electrical signal to an optical fiber. The optical modulator element 73A1 incorporates an optical device that is a planar optical waveguide element that guides the light to be output to the optical fiber.

[0057] The optical receiver 73B has an optical receiver element 73B1 that receives an optical signal from an optical fiber, demodulates the received light using the supplied light, converts the demodulated received light into an electrical signal, and outputs the converted electrical signal to the DSP 72. The optical receiver element 73B1 has a built-in optical device that is a planar optical waveguide element that guides the light received from the optical fiber.

[0058] The optical device in the optical transceiver 70 has a channel waveguide whose waveguide width increases in a tapered manner, and a rib waveguide connected to the side of the channel waveguide whose width increases and having a rib portion and a slab portion. The rib waveguide has a tapered waveguide in which the rib width increases in a tapered manner with increasing distance from the side connected to the channel waveguide. As a result, an optical device or the like that can improve optical coupling loss and optical reflection can be provided.

[0059] 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.

[0060] 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.

[0061] 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]

[0062] 1 EC 11 Channel Waveguide 12 Rib waveguide 12A Rib section 12B slab section 13 Tapered waveguide 30 SiN waveguide 31 First tapered waveguide 32 Second tapered waveguide 33 Transition part 34 Reverse tapered section 70 Optical Transceiver 72 DSP 73A Optical Transmitter 73A1 Optical modulator element 73B Optical Receiver 73B1 Optical receiver element

Claims

1. a channel waveguide whose waveguide width expands in a tapered manner; a rib waveguide connected to the side of the channel waveguide where the waveguide width is expanded, the rib waveguide having a rib portion and a slab portion, The rib waveguide comprises: An optical device comprising a tapered waveguide, the rib width of which increases in a tapered shape with increasing distance from a portion on the side connected to the channel waveguide.

2. The slab portion of the tapered waveguide is 2. The optical device according to claim 1, wherein the slab width decreases as it approaches the portion connected to the channel waveguide.

3. 3. The optical device according to claim 1, further comprising: another tapered waveguide, which is disposed in a layer different from that of the tapered waveguide and the channel waveguide, at a position overlapping a part of the tapered waveguide and the channel waveguide in a planar direction, and whose waveguide width increases in a tapered manner from the tapered waveguide toward the channel waveguide.

4. 4. The optical device according to claim 3, further comprising a transition section where light transitions between a part of the tapered waveguide and the channel waveguide and the other tapered waveguide.

5. 5. The optical device according to claim 4, further comprising an inverse tapered waveguide connected to the side of the other tapered waveguide where the waveguide width is enlarged, the waveguide width of which tapers down as it moves away from the other tapered waveguide.

6. The channel waveguide and the rib waveguide are Formed by a Si waveguide, The other tapered waveguide and the inverse tapered waveguide are 6. The optical device according to claim 5, wherein the optical device is formed of a SiN waveguide.

7. An optical receiver including an optical receiver element that converts received signal light into an electrical signal, The optical receiver element comprises: a channel waveguide whose waveguide width expands in a tapered manner; a rib waveguide connected to the side of the channel waveguide where the waveguide width is expanded, the rib waveguide having a rib portion and a slab portion, The rib waveguide comprises:

1. An optical receiver comprising a tapered waveguide in which the rib width of the rib portion increases in a tapered shape with increasing distance from a portion connected to the channel waveguide.

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 channel waveguide whose waveguide width expands in a tapered manner; a rib waveguide connected to the side of the channel waveguide where the waveguide width is expanded, the rib waveguide having a rib portion and a slab portion, The rib waveguide comprises: An optical transmitter comprising a tapered waveguide in which the rib width of the rib portion increases in a tapered shape with increasing distance from a portion on the side connected to the channel waveguide.

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