Optical device, optical receiver, and optical transmitter

Abstract

To provide an optical device which can improve the light connection loss.SOLUTION: An optical device includes: a substrate with a port; and an edge coupler connected to the port. The edge coupler includes: a reverse tapered part connected to the port, the width of a waveguide in the reverse tapered part becoming larger as becoming more distant from the port; and a rib waveguide connected to the reverse tapered part, the largest film thickness of the rib waveguide being larger than that of the reverse tapered part.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] FIG. 18 is an explanatory diagram showing an example of a conventional optical chip 100. The optical chip 100 shown in FIG. 18 is, for example, an optical IC chip having an optical receiver 110 with a digital coherent function. The optical receiver 110 has a first EC (Edge Coupler) 111 arranged at a first port 101 for inputting a signal light, a second EC 112 arranged at a second port 102 for inputting a local light, and a PBS (Polarization Beam Splitter) 113. The optical receiver 110 has a PR (Polarization Rotator) 114, a 1×2 branching coupler 118, a first optical hybrid circuit 115A, and a second optical hybrid circuit 115B. The optical receiver 110 has first to fourth PDs (Photo Diodes) 116A to 116D and first to fourth output ports 117A to 117D. For example, the second EC 112 and the first optical hybrid circuit 115A, the second EC 112 and the second optical hybrid circuit 115B, and the first EC 111 and the PBS 113 are connected by optical waveguides such as Si waveguides.

[0003] The first EC 111 of the first port 101 is formed on a chip end face D11, which is a side end in the optical chip 100, and is, for example, an EC of a port that connects to a first optical fiber F11 that inputs signal light. The first port 101 is exposed to the chip end face D11 of the optical chip 100 by forming the wafer into chips. The second EC 112 of the second port 102 is formed on the chip end face D11 in the optical chip 100, and is, for example, an EC of a port that connects to a second optical fiber F12 that inputs local light from a light source. The second port 102 is exposed to the chip end face D11 of the optical chip 100 by forming the wafer into chips.

[0004] The PBS 113 separates the received light, which is the signal light input from the first EC 111, into 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 113 outputs the received light of the X-polarized component to the first optical hybrid circuit 115A. Furthermore, the PR 114 rotates the polarization of the received light of the Y-polarized component from the PBS 113 by 90 degrees, converts it into the received light of the Y-polarized component after the polarization rotation, and outputs it to the second optical hybrid circuit 115B.

[0005] The branching coupler 118 branches and outputs the local light from the second EC 112 to the first optical hybrid circuit 115A and the second optical hybrid circuit 115B. The first optical hybrid circuit 115A causes the local light to interfere with the received light of the X-polarized component to obtain I-component and Q-component signal light. The I-component is an in-phase axis component, and the Q-component is an orthogonal axis component. The first optical hybrid circuit 115A outputs the I-component signal light of the received light of the X-polarized component to the first PD 116A. The first optical hybrid circuit 115A outputs the Q-component signal light of the received light of the X-polarized component to the second PD 116B.

[0006] The second optical hybrid circuit 115B causes the local light to interfere with the Y-polarized component received light to obtain I-component and Q-component signal light. The second optical hybrid circuit 115B outputs the I-component signal light of the Y-polarized component received light to the third PD 116C. The second optical hybrid circuit 115B outputs the Q-component signal light of the Y-polarized component received light to the fourth PD 116D.

[0007] The first PD 116A electrically converts and gain-adjusts the I-component signal light of the X-polarized component from the first optical hybrid circuit 115A, and outputs the gain-adjusted electrical signal to the first output port 117A. The second PD 116B electrically converts and gain-adjusts the Q-component signal light of the X-polarized component from the first optical hybrid circuit 115A, and outputs the gain-adjusted electrical signal to the second output port 117B.

[0008] The third PD 116C electrically converts and gain-adjusts the I-component signal light of the Y-polarized component from the second optical hybrid circuit 115B, and outputs the gain-adjusted electrical signal to the third output port 117C. The fourth PD 116D electrically converts and gain-adjusts the Q-component signal light of the Y-polarized component from the second optical hybrid circuit 115B, and outputs the gain-adjusted electrical signal to the fourth output port 117D.

[0009] FIG. 19 is a schematic plan view showing an example of an EC part in a conventional optical chip 100. The EC part shown in FIG. 19 is a part of a substrate-type optical waveguide element optically coupled to a core C of a first optical fiber F11 and a second optical fiber F12. The EC part has a first EC 111 at a first port 101 and a second EC 112 at a second port 102. Since the received light includes TE light and TM light, the first EC 111 propagates the TE light and the TM light. Since the local light is TE light, the second EC 112 propagates the TE light. Since the second EC 112 has the same configuration as the first EC 111, the same reference numerals are used to omit explanations of the overlapping configurations and operations.

[0010] The first EC111 is SiO 2 The clad 121 is made of, for example, Si. 3 N 4 The first EC 111 has a first waveguide 122 made of, for example, Si (hereinafter simply referred to as SiN (Silicon Nitride)). The first EC 111 has a second waveguide 123 covered with a cladding 121 and made of, for example, Si, and a transition section 124 where light adiabatically transitions between the first waveguide 122 and the second waveguide 123. Furthermore, the first EC 111 has an inverted taper section 125 having a structure in which the waveguide width to a chip end face D11 of the first waveguide 122 gradually narrows.

[0011] The first waveguide 122 has a first tapered waveguide 122A and a second tapered waveguide 122B connected to the first tapered waveguide 122A. The first tapered waveguide 122A has a structure in which the waveguide width gradually increases from the optical input / output portion near the chip end face D11 toward the second tapered waveguide 122B. The second tapered waveguide 122B has a structure in which the waveguide width gradually decreases from the point where it connects to the first tapered waveguide 122A as it moves away from the first tapered waveguide 122A.

[0012] The second waveguide 123 has a third tapered waveguide 123A arranged at a position where at least a part of the second tapered waveguide 122B overlaps in the planar direction, and a straight waveguide 123B connected to the third tapered waveguide 123A. The third tapered waveguide 123A has a structure in which the waveguide width gradually increases with increasing distance from the starting point of the second tapered waveguide 122B. The straight waveguide 123B is a waveguide connected to the side of the third tapered waveguide 123A where the waveguide width is wider.

[0013] Fig. 20A is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 112 shown in Fig. 19 along the line AA. The second EC 112 shown in Fig. 20A has a Si substrate 131, a clad 121, a first assembly layer 141A arranged on the side farther from the Si substrate 131, and a second assembly layer 141B arranged on the side closer to the Si substrate 131. The schematic cross-sectional portion of the line AA shown in Fig. 20A is a cross-sectional portion of the second EC 112 in which the straight waveguide 123B is arranged. The straight waveguide 123B in the second waveguide 123 is arranged in the second assembly layer 141B.

[0014] FIG. 20B is an explanatory diagram showing an example of a schematic cross-sectional portion of the BB line of the second EC 112 shown in FIG. 19. The second EC 112 shown in FIG. 20B has a Si substrate 131, a clad 121, a first assembly layer 141A, and a second assembly layer 141B. The schematic cross-sectional portion of the BB line shown in FIG. 20B is a cross-sectional portion of the second EC 112 where the transition portion 124 is arranged. The third tapered waveguide 123A in the second waveguide 123 is arranged in the second assembly layer 141B. The second tapered waveguide 122B in the first waveguide 122 is arranged in the first assembly layer 141A.

[0015] 20C is an explanatory diagram showing an example of a schematic cross-sectional portion of the CC line of the second EC 112 shown in FIG. 19. The second EC 112 shown in FIG. 20C has a Si substrate 131 and a clad 121 laminated on the Si substrate 131. The schematic cross-sectional portion of the CC line shown in FIG. 20C is a cross-sectional portion of the second EC 112 in which the reverse taper portion 125 is arranged. Furthermore, the second EC 112 has a first assembly layer 141A and a second assembly layer 141B. The first tapered waveguide 122A in the first waveguide 122 is arranged in the first assembly layer 141A.

[0016] The configuration of the transition section 124 and the reverse taper section 125 of the first EC 111 is the same as that of the transition section 124 and the reverse taper section 125 of the second EC 112, and the waveguide width, the waveguide length and the waveguide thickness are the same.

[0017] 19 uses an inverse taper section 125 to propagate received light from a first optical fiber F11 to a transition section 124. In the transition section 124, the waveguide widths of the first waveguide 122 and the second waveguide 123 change in a tapered shape. The first waveguide 122 has a lower refractive index than the second waveguide 123, so that the mode field of the received light can be increased, and furthermore, the polarization dependency is small, so that the coupling loss of the TE light and the TM light with the first optical fiber F11 can be reduced.

[0018] Moreover, the second EC 112 uses the inverse taper section 125 to propagate the local light from the second optical fiber F12 to the transition section 124. In the transition section 124, the waveguide widths of the first waveguide 122 and the second waveguide 123 change in a tapered shape. Since the first waveguide 122 has a lower refractive index than the second waveguide 123, the mode field of the local light can be increased, and further, since the polarization dependency is small, the coupling loss of the TE light with the second optical fiber F12 can be reduced. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] Special Publication No. 2019-518987 [Patent Document 2] JP 2011-123094 A [Patent Document 3] US Patent Application Publication No. 2014 / 003765 Summary of the Invention [Problem to be solved by the invention]

[0020] In the second EC 112, local light having a higher level than the received light is input from the second optical fiber F12. However, in the second EC 112, the first waveguide 122 is formed of SiN, and therefore when local light is input, the first waveguide 122 is damaged, resulting in a large coupling loss with the second optical fiber F12. Therefore, there is a demand for an EC that can improve the optical coupling loss without using SiN.

[0021] One object of the present invention is to provide an optical device or the like capable of improving optical coupling loss. [Means for solving the problem]

[0022] An optical device according to one embodiment includes a substrate having a port, and an edge coupler connected to the port. The edge coupler includes an inverted tapered portion connected to the port and having a waveguide width that increases with distance from the port, and a rib waveguide connected to the inverted tapered portion and having a maximum thickness greater than that of the inverted tapered portion. Effect of the Invention

[0023] According to one aspect, it is possible to provide an optical device or the like capable of improving optical coupling loss. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is an explanatory diagram showing an example of an optical chip according to this embodiment. [Diagram 2] FIG. 2 is a schematic plan view showing an example of an EC portion in the optical chip according to the first embodiment. [Figure 3A] FIG. 3A is an explanatory diagram showing an example of a schematic cross-sectional portion of the first EC shown in FIG. 2 taken along line A1-A1. [Figure 3B] 3B is an explanatory diagram showing an example of a schematic cross-sectional portion of the first EC shown in FIG. 2 taken along line B1-B1. [Figure 3C] 3C is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line C1-C1 of the first EC shown in FIG. 2. FIG. [Figure 4A] 4A is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 2 taken along line A2-A2. [Figure 4B] 2. FIG. 4B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 2 taken along line B2-B2. [Figure 4C] 2. FIG. 4C is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line C2-C2 of the second EC shown in FIG. [Diagram 5] FIG. 5 is a schematic plan view showing an example of an EC portion in the optical chip according to the second embodiment. [Figure 6A] FIG. 6A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the second EC shown in FIG. [Figure 6B]6B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 5 taken along the line BB. [Figure 6C] 6C is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line CC of the second EC shown in FIG. 5. FIG. [Figure 7] FIG. 7 is a schematic plan view showing an example of an EC portion in the optical chip according to the third embodiment. [Figure 8A] FIG. 8A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the second EC shown in FIG. [Figure 8B] 8B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 7 taken along the line BB. [Figure 9] FIG. 9 is a schematic plan view showing an example of an EC portion in the optical chip according to the fourth embodiment. [Figure 10A] FIG. 10A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the second EC shown in FIG. [Figure 10B] 10B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 9 taken along the line BB. [Figure 11] FIG. 11 is a schematic plan view showing an example of an EC portion in the optical chip according to the fifth embodiment. [Figure 12A] FIG. 12A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the second EC shown in FIG. [Figure 12B] 12B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 11 taken along the line BB. [Figure 13] FIG. 13 is a schematic plan view showing an example of an EC portion in the optical chip according to the sixth embodiment. [Figure 14A] FIG. 14A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the second EC shown in FIG. [Figure 14B] 14B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 13 taken along the line BB. [Figure 15] FIG. 15 is an explanatory diagram illustrating an example of an optical transceiver according to this embodiment. [Figure 16] FIG. 16 is a schematic plan view showing an example of an EC portion in an optical chip of the comparative example. [Figure 17A] FIG. 17A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the second EC shown in FIG. [Figure 17B] 17B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC shown in FIG. 16 taken along the line BB. [Figure 17C] 17C is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line CC of the second EC shown in FIG. [Figure 18] FIG. 18 is an explanatory diagram showing an example of a conventional optical chip. [Figure 19] FIG. 19 is a schematic plan view showing an example of an EC portion in a conventional optical chip. [Figure 20A] FIG. 20A is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line AA of the first EC shown in FIG. [Figure 20B] 20B is an explanatory diagram showing an example of a schematic cross-sectional portion of the first EC shown in FIG. 19 along the line BB. [Figure 20C] 20C is an explanatory diagram showing an example of a schematic cross-sectional portion taken along line CC of the first EC shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The optical chip has a first EC that inputs the received light and a second EC that inputs the local light, and since the level of the local light is stronger than the received light, the first waveguide of the second EC is required to have a higher optical input resistance than the first EC. Therefore, there is an optical chip of a comparative example that can deal with such a situation. <Comparative Example>

[0026] Fig. 16 is a schematic plan view showing an example of an EC part in an optical chip 200 of a comparative example. The EC part shown in Fig. 16 is a part of a substrate-type optical waveguide element optically coupled to the cores C of the first optical fiber F21 and the second optical fiber F22. The EC part has a first EC211 of the first port 201 and a second EC212 of the second port 202. Since the received light includes TE light and TM light, the first EC211 propagates the TE light and the TM light. Since the local light is TE light, the second EC212 propagates the TE light. Since the second EC212 has the same configuration as the first EC211, the same reference numerals are used to omit explanations of the overlapping configurations and operations.

[0027] The first EC211 is SiO 2 The clad 221 is made of, for example, Si. 3 N 4 The first EC 211 has a first waveguide 222 formed of, for example, Si (hereinafter simply referred to as SiN (Silicon Nitride)). The first EC 211 has a second waveguide 223 covered with a cladding 221 and formed of, for example, Si, and a transition section 224 where light adiabatically transitions between the first waveguide 222 and the second waveguide 223. Furthermore, the first EC 211 has an inverted taper section 225 having a structure in which the waveguide width to a chip end face D21 of the first waveguide 222 gradually narrows.

[0028] The first waveguide 222 has a first tapered waveguide 222A and a second tapered waveguide 222B connected to the first tapered waveguide 222A. The first tapered waveguide 222A has a structure in which the waveguide width gradually increases from the optical input / output portion near the chip end face D21 toward the second tapered waveguide 222B. The second tapered waveguide 222B has a structure in which the waveguide width gradually decreases from the point where it connects to the first tapered waveguide 222A as it moves away from the first tapered waveguide 222A.

[0029] The second waveguide 223 includes a third tapered waveguide 223A arranged at a position where at least a part of the second tapered waveguide 222B overlaps in the planar direction, and a straight waveguide 223B connected to the third tapered waveguide 223A. The third tapered waveguide 223A has a structure in which the waveguide width gradually increases with increasing distance from the starting point of the second tapered waveguide 222B. The straight waveguide 223B is a waveguide connected to the side of the third tapered waveguide 223A where the waveguide width is wider.

[0030] The second EC212 is SiO 2 The semiconductor device has a cladding 221 formed of, for example, Si or the like, and a waveguide 233 covered with the cladding 221 and formed of, for example, Si or the like. The waveguide 233 has an inverted taper portion 233A and a straight waveguide 233B connected to the inverted taper portion 233A. The inverted taper portion 233A is a tapered waveguide whose waveguide width gradually increases with increasing distance from the chip end face D21. The straight waveguide 233B is a waveguide connected to the side of the inverted taper portion 233A where the waveguide width is wider.

[0031] Fig. 17A is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 212 shown in Fig. 16 along the line AA. The second EC 212 shown in Fig. 17A has a Si substrate 241, a clad 221, a first assembly layer 251A arranged on the side farther from the Si substrate 241, and a second assembly layer 251B arranged on the side closer to the Si substrate 241. The schematic cross-sectional portion of the line AA shown in Fig. 17A is a cross-sectional portion of the second EC 212 in which the straight waveguide 233B is arranged. The Si straight waveguide 233B is arranged in the second assembly layer 251B.

[0032] Fig. 17B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 212 shown in Fig. 16 along the line BB. The second EC 212 shown in Fig. 17B has a Si substrate 241, a cladding 221, a first assembly layer 251A, and a second assembly layer 251B. The schematic cross-sectional portion of the line BB shown in Fig. 17B is a cross-sectional portion of the second EC 212 in which the reverse taper portion 233A is arranged. The Si reverse taper portion 233A is arranged in the second assembly layer 251B.

[0033] Fig. 17C is an explanatory diagram showing an example of a schematic cross-sectional portion of the CC line of the second EC 212 shown in Fig. 16. The second EC 212 shown in Fig. 17C has a Si substrate 241 and a clad 221 laminated on the Si substrate 241. The schematic cross-sectional portion of the CC line shown in Fig. 17C is a cross-sectional portion of the second EC 212 in which the reverse taper portion 233A is arranged. Furthermore, the second EC 212 has a first assembly layer 251A and a second assembly layer 251B. The Si reverse taper portion 233A is arranged in the second assembly layer 251B.

[0034] Since the second EC 212 connects the second optical fiber F22 and the straight waveguide 233B with the Si inverted taper portion 233A, damage to the inverted taper portion 233A can be suppressed even when a high-level local light is input. As a result, the second EC 212 with high optical input resistance can be ensured.

[0035] However, since the waveguide 233 in the second EC 212 is a Si waveguide, the optical confinement is strong and the optical mode field is smaller than that in the second optical fiber F22, resulting in a large optical coupling loss. Therefore, an embodiment that can deal with such a situation will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Also, the following examples may be appropriately combined within a range that does not cause contradictions. EXAMPLES

[0036] FIG. 1 is an explanatory diagram showing an example of an optical chip 1 of the present embodiment. The optical chip 1 shown in FIG. 1 is, for example, an optical IC chip having an optical receiver 10 with a digital coherent function. The optical receiver 10 has a first EC (Edge Coupler) 11 arranged at a first port 10A for inputting a signal light, a second EC 12 arranged at a second port 10B for inputting a local light, and a PBS (Polarization Beam Splitter) 13. The optical receiver 10 has a PR (Polarization Rotator) 14, a 1×2 branch coupler 18, a first optical hybrid circuit 15A, a second optical hybrid circuit 15B, first to fourth PDs (Photo Diodes) 16A to 16D, and first to fourth output ports 17A to 17D. For example, the second EC 12 and the first optical hybrid circuit 15A, the second EC 12 and the second optical hybrid circuit 15B, and the first EC 11 and the PBS 13 are connected by optical waveguides such as Si waveguides.

[0037] The first EC 11 of the first port 10A is formed on the chip end face D1, which is a side end in the optical chip 1, and is, for example, an EC of a port that connects to a first optical fiber F1 that inputs a received light that is a signal light. The first port 10A is exposed to the chip end face D1 of the optical chip 1 by forming the wafer into a chip. The second EC 12 of the second port 10B is formed on the chip end face D1 in the optical chip 1, and is, for example, an EC of a port that connects to a second optical fiber F2 that inputs a local light from a light source. The second port 10B is exposed to the chip end face D1 of the optical chip 1 by forming the wafer into a chip.

[0038] The PBS 13 is a polarization multiplexer / demultiplexer that separates the received light input from the first EC 11 into 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 13 outputs the X-polarized component of the received light to the first optical hybrid circuit 15A. Furthermore, the PR 14 rotates the Y-polarized component of the received light from the PBS 13 by 90 degrees, converts it into a Y-polarized component of the received light after polarization rotation, and outputs it to the second optical hybrid circuit 15B.

[0039] The branching coupler 18 branches and outputs the local light from the second EC 12 to the first optical hybrid circuit 15A and the second optical hybrid circuit 15B. The first optical hybrid circuit 15A causes the local light to interfere with the received light of the X-polarized component to obtain optical signals of I and Q components. The I component is an in-phase axis component, and the Q component is an orthogonal axis component. The first optical hybrid circuit 15A outputs the I component signal light of the received light of the X-polarized component to the first PD 16A. The first optical hybrid circuit 15A outputs the Q component signal light of the received light of the X-polarized component to the second PD 16B.

[0040] The second optical hybrid circuit 15B causes the local light to interfere with the Y-polarized received light to obtain I- and Q-component signal light. The second optical hybrid circuit 15B outputs the I-component signal light of the Y-polarized received light to the third PD 16C. The second optical hybrid circuit 15B outputs the Q-component signal light of the Y-polarized received light to the fourth PD 16D.

[0041] The first PD 16A electrically converts and gain-adjusts the I-component signal light of the X-polarized component from the first optical hybrid circuit 15A, and outputs the gain-adjusted electrical signal to the first output port 17A. The second PD 16B electrically converts and gain-adjusts the Q-component signal light of the X-polarized component from the first optical hybrid circuit 15A, and outputs the gain-adjusted electrical signal to the second output port 17B.

[0042] The third PD 16C electrically converts and gain-adjusts the I-component signal light of the Y-polarized component from the second optical hybrid circuit 15B, and outputs the gain-adjusted electrical signal to the third output port 17C. The fourth PD 16D electrically converts and gain-adjusts the Q-component signal light of the Y-polarized component from the second optical hybrid circuit 15B, and outputs the gain-adjusted electrical signal to the fourth output port 17D.

[0043] Fig. 2 is a schematic plan view showing an example of an EC section in the optical chip 1 of the first embodiment. The EC section shown in Fig. 2 is an EC such as a substrate-type optical waveguide element optically coupled to the cores C of the first optical fiber F1 and the second optical fiber F2. The EC section has a first EC 11 at the first port 10A and a second EC 12 at the second port 10B. Since the received light includes TE light and TM light, the first EC 11 propagates the TE light and the TM light. Since the local light is TE light, the second EC 12 propagates the TE light.

[0044] The first EC11 is SiO 2 The clad 21 is made of, for example, Si. 3 N 4 The first EC 11 has a first waveguide 22 made of, for example, Si (hereinafter, simply referred to as SiN (Silicon Nitride)). The first EC 11 has a second waveguide 23 covered with a cladding 21 and made of, for example, Si, and a transition section 24 where light undergoes adiabatic optical transition between the first waveguide 22 and the second waveguide 23. Furthermore, the first EC 11 has a first inverse taper section 25 having a structure in which the waveguide width of the first waveguide 22 to the chip end face D1 gradually narrows. The first inverse taper section 25 is a waveguide included in the first EC 11 that propagates received light from a first optical fiber F1 connected to the chip end face D1.

[0045] The first waveguide 22 has a first tapered waveguide 22A and a second tapered waveguide 22B connected to the first tapered waveguide 22A. The first tapered waveguide 22A 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 22B. The second tapered waveguide 22B has a structure in which the waveguide width gradually decreases from the point where it connects to the first tapered waveguide 22A as it moves away from the first tapered waveguide 22A.

[0046] The second waveguide 23 has a third tapered waveguide 23A arranged at a position where at least a part of the second tapered waveguide 22B overlaps in the planar direction, and a straight waveguide 23B connected to the third tapered waveguide 23A. The third tapered waveguide 23A has a structure in which the waveguide width gradually increases with increasing distance from the starting point of the second tapered waveguide 22B. The straight waveguide 23B is a waveguide connected to the side of the third tapered waveguide 23A where the waveguide width is wider.

[0047] The second EC12 is SiO 2 The second EC 12 has a cladding 21 formed of, for example, Si or the like and a second inverse taper portion 32 covered with the cladding 21. The second EC 12 has a waveguide 33 formed of, for example, Si or the like and covered with the cladding 21. Furthermore, the second EC 12 is a tapered waveguide in which the waveguide width to the chip end face D1 of the second inverse taper portion 32 gradually narrows. The second inverse taper portion 32 is a waveguide included in the second EC 12 that propagates local light from a second optical fiber F2 connected to the second port 10B of the chip end face D1.

[0048] The waveguide 33 has a rib waveguide 33A and a straight waveguide 33B. The rib waveguide 33A is connected to the second inverse taper portion 32 and is a waveguide whose maximum film thickness is thicker than that of the second inverse taper portion 32. The rib waveguide 33A has a rib portion 41 and slab portions 42 formed on both sides of the rib portion 41, and the waveguide width of the rib portion 41 gradually increases with increasing distance from the second inverse taper portion 32. The maximum film thickness is the maximum waveguide thickness corresponding to the rib portion 41 of the rib waveguide 33A.

[0049] The straight waveguide 33B is, for example, a channel-type waveguide that is connected to the side of the rib portion 41 of the rib waveguide 33A where the waveguide width is wider.

[0050] Fig. 3A is an explanatory diagram showing an example of a schematic cross-sectional portion of the first EC 11 shown in Fig. 2 taken along the line A1-A1. The first EC 11 shown in Fig. 3A has a Si substrate 51, a clad 21, a first assembly layer 51A arranged on the side farther from the Si substrate 51, and a second assembly layer 51B arranged on the side closer to the Si substrate 51. The schematic cross-sectional portion taken along the line A1-A1 shown in Fig. 3A is a cross-sectional portion of the first EC 11 in which the straight waveguide 23B is arranged. The Si straight waveguide 23B in the second waveguide 23 is arranged in the second assembly layer 51B.

[0051] 3B is an explanatory diagram showing an example of a schematic cross-sectional portion of the first EC 11 shown in FIG. 2 along the line B1-B1. The first EC 11 shown in FIG. 3B has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion of the line B1-B1 shown in FIG. 3B is a cross-sectional portion of the first EC 11 in which the transition portion 24 is disposed. The second assembly layer 51B is provided with a third tapered waveguide 23A made of Si in the second waveguide 23. The first assembly layer 51A is provided with a second tapered waveguide 22B made of SiN in the first waveguide 22.

[0052] 3C is an explanatory diagram showing an example of a schematic cross-sectional portion along the C1-C1 line of the first EC 11 shown in FIG. 2. The first EC 11 shown in FIG. 3C has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion along the C1-C1 line shown in FIG. 3C is a cross-sectional portion of the first EC 11 in which the first reverse taper portion 25 is arranged. Furthermore, the first EC 11 has a first assembly layer 51A and a second assembly layer 51B. The first tapered waveguide 22A in the first waveguide 22 is arranged in the first assembly layer 51A.

[0053] The first EC 11 uses the first inverse taper section 25 to propagate the received light from the first optical fiber F1 to the transition section 24. In the transition section 24, the waveguide widths of the first waveguide 22 and the second waveguide 23 change in a tapered shape. Since the first waveguide 22 has a lower refractive index than the second waveguide 23, the mode field of the received light can be increased, and further, since the polarization dependency is small, the coupling loss of the TE light and the TM light with the first optical fiber F1 can be reduced.

[0054] Fig. 4A is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 12 taken along the line A2-A2 shown in Fig. 2. The second EC 12 shown in Fig. 4A has a Si substrate 51, a clad 21, a first assembly layer 51A arranged on the side farther from the Si substrate 51, and a second assembly layer 51B arranged on the side closer to the Si substrate 51. The schematic cross-sectional portion taken along the line A2-A2 shown in Fig. 4A is a cross-sectional portion of the second EC 12 in which the straight waveguide 33B is arranged. The Si straight waveguide 33B in the waveguide 33 is arranged in the second assembly layer 51B.

[0055] Fig. 4B is an explanatory diagram showing an example of a schematic cross-sectional portion along the line B2-B2 of the second EC 12 shown in Fig. 2. The second EC 12 shown in Fig. 4B has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along the line B2-B2 shown in Fig. 4B is a cross-sectional portion of the second EC 12 in which the rib waveguide 33A is arranged. The Si rib waveguide 33A in the waveguide 33 is arranged in the second assembly layer 51B.

[0056] 4C is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 12 along the line C2-C2 shown in FIG. 2. The second EC 12 shown in FIG. 4C has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion along the line C2-C2 shown in FIG. 4C is a cross-sectional portion of the second EC 12 in which the second reverse taper portion 32 is arranged. Furthermore, the second EC 12 has a first assembly layer 51A and a second assembly layer 51B. The second assembly layer 51B has the second reverse taper portion 32 arranged therein. The waveguide thickness of the second reverse taper portion 32 is made thinner than the waveguide thicknesses of the rib waveguide 33A and the straight waveguide 33B.

[0057] The rib portion 41 of the rib waveguide 33A has a structure in which the rib width of the rib portion 41 gradually increases from the second inverse tapered portion 32 toward the straight waveguide 33B. The slab width of the rib waveguide 33A is constant.

[0058] The second EC 12 has a second inverse taper section 32 whose waveguide width increases with increasing distance from the second port 10B, and a rib waveguide 33A connected to the second inverse taper section 32 and having a maximum film thickness greater than that of the second inverse taper section 32. In the second EC 12, the waveguide thickness of the second inverse taper section 32 is made thinner than that of the rib waveguide 33A, and the waveguide width of the second inverse taper section 32 is made wider, so that the mode field of light can be widened and the coupling loss with the second optical fiber F2 can be reduced. Furthermore, the rib width of the rib waveguide 33A is continuously changed, so that the conversion from the thin Si second inverse taper section 32 to the thick Si straight waveguide 33B can be realized with low loss. Moreover, the second EC 12 has a second inverted taper portion 32 made of Si disposed at the second port 10B that connects to the second optical fiber F2. As a result, even if a high-level local light is input, the second EC 12 is not damaged by the high-level local light, and therefore the coupling loss with the second optical fiber F2 can be suppressed. As a result, an EC with high optical input resistance can be realized.

[0059] In the second EC12 of the first embodiment, the waveguide thickness of the second inverted taper portion 32 is made thinner than the waveguide thickness of the rib waveguide 33A, and the waveguide width of the second inverted taper portion 32 is made wider, so that the mode field of the light can be widened and the coupling loss with the second optical fiber F2 can be reduced.

[0060] The rib waveguide 33A of the second EC 12 has a rib width that changes continuously, so that the conversion from the thin Si second inverted tapered portion 32 to the thick Si straight waveguide 33B can be achieved with low loss.

[0061] In the second EC 12, the rib width of the rib waveguide 33A is gradually increased from the second inverted taper portion 32 toward the straight waveguide 33B, which suppresses light scattering caused by a sudden change in the waveguide width and suppresses optical coupling loss. Furthermore, the mode field at the chip end face D1 is increased, improving the coupling efficiency with the second optical fiber F2.

[0062] In the second EC 12 of the first embodiment, the waveguide width of the second reverse taper portion 32 is monotonically increased, but the present invention is not limited to this. The second EC 12 may include a region where the waveguide width of the second reverse taper portion 32 is constant or narrows, and the same effect can be obtained as long as the waveguide width of the second reverse taper portion 32 at the position connected to the rib waveguide 33A is wider than the waveguide width of the second reverse taper portion 32 at the chip end face D1.

[0063] In the second EC 12 of Example 1, one end of the rib portion 41 and one end of the slab portion 42 in the rib waveguide 33A are connected to a portion of the second inverse taper portion 32 where the waveguide width is wider. However, the present invention is not limited to this, and an embodiment in which the tip of the rib portion 41 in the rib waveguide 33A overlaps in the planar direction with a portion of the portion of the second inverse taper portion 32 where the waveguide width is wider will be described below as Example 2. EXAMPLES

[0064] 5 is a schematic plan view showing an example of an EC part in the optical chip 1A of the second embodiment. The same components as those in the optical chip 1 of the first embodiment are given the same reference numerals, and the description of the overlapping components and operations is omitted. The optical chip 1A of the second embodiment differs from the optical chip 1 of the first embodiment in that the tip of the rib portion 41 in the rib waveguide 33A1 in the second EC 12A is arranged to overlap in the planar direction with a part of the part of the second inverted tapered portion 32 on the side where the waveguide width becomes wider. The rib portion 41 of the rib waveguide 33A1 has a structure in which the rib width of the rib portion 41 gradually narrows from the straight waveguide 33B toward the second inverted tapered portion 32. The slab width of the rib waveguide 33A1 is constant.

[0065] Fig. 6A is an explanatory diagram showing an example of a schematic cross-sectional portion along line AA of the second EC 12A shown in Fig. 5. The second EC 12A shown in Fig. 6A has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along line AA shown in Fig. 6A is a cross-sectional portion of the second EC 12A in which the rib waveguide 33A1 is arranged. The Si rib waveguide 33A1 is arranged in the second assembly layer 51B.

[0066] Fig. 6B is an explanatory diagram showing an example of a schematic cross-sectional portion of the BB line of the second EC 12A shown in Fig. 5. The second EC 12A shown in Fig. 6B has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion of the BB line shown in Fig. 6B is a cross-sectional portion of the second EC 12A in which the second reverse taper portion 32 is arranged. Furthermore, the second EC 12A has a first assembly layer 51A and a second assembly layer 51B. The rib portion 41 and the second reverse taper portion 32 of the rib waveguide 33A1 are arranged in the second assembly layer 51B.

[0067] Fig. 6C is an explanatory diagram showing an example of a schematic cross-sectional portion of the CC line of the second EC 12A shown in Fig. 5. The second EC 12A shown in Fig. 6C has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion of the CC line shown in Fig. 6C is a cross-sectional portion of the second EC 12A in which the second reverse taper portion 32 is arranged. Furthermore, the second EC 12A has a first assembly layer 51A and a second assembly layer 51B. The second reverse taper portion 32 is arranged in the second assembly layer 51B.

[0068] The second EC 12A of the second embodiment is arranged such that the tip of the rib portion 41 of the rib waveguide 33A1 overlaps in the planar direction with a part of the second inverted taper portion 32. As a result, the taper angle is reduced by increasing the waveguide length of the rib portion 41, and loss due to MFD (Mode Field Diameter) conversion can be suppressed.

[0069] In the second EC 12, the second inverted tapered portion 32 of Si and the slab portion 42 of the rib waveguide 33A may be formed in the same manufacturing process, and can be appropriately changed. Therefore, such an embodiment will be described below as Example 3. EXAMPLES

[0070] FIG. 7 is a schematic plan view showing an example of an EC part in the optical chip 1B of the third embodiment. The same components as those in the optical chip 1 of the first embodiment are denoted by the same reference numerals, and the description of the overlapping components and operations is omitted. The optical chip 1B of the third embodiment is different from the optical chip 1 of the first embodiment in that the second inverted taper portion 32B in the second EC 12B and the slab portion 42D in the rib waveguide 33A4 are formed of the same material, Si, with the same thickness. The rib portion 41 of the rib waveguide 33A4 has a structure in which the rib width of the rib portion 41 gradually narrows from the straight waveguide 33B toward the second inverted taper portion 32B. The slab width of the slab portion 42D of the rib waveguide 33A4 is constant. The waveguide width of the rib waveguide 33A4 is the same as the waveguide width of the second inverted taper portion 32B on the wider side.

[0071] Fig. 8A is an explanatory diagram showing an example of a schematic cross-sectional portion along line AA of the second EC 12B shown in Fig. 7. The second EC 12B shown in Fig. 8A has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along line AA shown in Fig. 8A is a cross-sectional portion of the second EC 12B in which the rib waveguide 33A4 is arranged. The Si rib waveguide 33A4 is arranged in the second assembly layer 51B.

[0072] FIG. 8B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 12B shown in FIG. 7 along the line BB. The second EC 12B shown in FIG. 8B has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion of the line BB shown in FIG. 8B is a cross-sectional portion of the second EC 12B in which the second reverse taper portion 32B is arranged. Furthermore, the second EC 12B has a first assembly layer 51A and a second assembly layer 51B. The second assembly layer 51B has the second reverse taper portion 32B arranged therein. In the slab portion 42D of the rib waveguide 33A4, the thickness of the second reverse taper portion 32B is the same.

[0073] Since the slab portion 42D and the second inverted taper portion 32B of the rib waveguide 33A4 in Example 3 are formed in the same layer (second assembly layer 51B) to the same thickness and from the same material, that is, Si, the rib waveguide 33A4 and the second inverted taper portion 32B can be formed by the same process, such as etching.

[0074] In the third embodiment, the rib waveguide 33A4 of the second EC 12B has a constant waveguide width, but the present invention is not limited to this and can be modified as appropriate. This embodiment will be described below as a fourth embodiment. EXAMPLES

[0075] 9 is a schematic plan view showing an example of an EC part in the optical chip 1C of the fourth embodiment. The same components as those in the optical chip 1B of the third embodiment are given the same reference numerals, and the description of the overlapping components and operations is omitted. The optical chip 1C of the fourth embodiment differs from the optical chip 1B of the third embodiment in that the width (slab width) of the slab portion 42A in the rib waveguide 33A2 in the second EC 12C is gradually narrowed from the second reverse taper portion 32B toward the straight waveguide 33B. The rib portion 41 of the rib waveguide 33A2 has a structure in which the rib width of the rib portion 41 gradually increases from the second reverse taper portion 32B toward the straight waveguide 33B.

[0076] The second reverse taper portion 32B and the slab portion 42A in the rib waveguide 33A2 are formed of the same material (Si) and have the same thickness in the second assembly layer 51B. The waveguide width of the rib waveguide 33A2 connected to the second reverse taper portion 32B is the same as the waveguide width on the wider side of the second reverse taper portion 32B.

[0077] Fig. 10A is an explanatory diagram showing an example of a schematic cross-sectional portion along line AA of the second EC 12C shown in Fig. 9. The second EC 12C shown in Fig. 10A has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along line AA shown in Fig. 10A is a cross-sectional portion of the second EC 12C in which a rib waveguide 33A2 is arranged. The Si rib waveguide 33A2 is arranged in the second assembly layer 51B.

[0078] FIG. 10B is an explanatory diagram showing an example of a schematic cross-sectional portion of the BB line of the second EC 12C shown in FIG. 9. The second EC 12C shown in FIG. 10B has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion of the BB line shown in FIG. 10B is a cross-sectional portion of the second EC 12C in which the second reverse taper portion 32B is arranged. Furthermore, the second EC 12C has a first assembly layer 51A and a second assembly layer 51B. The second reverse taper portion 32B is arranged in the second assembly layer 51B. The slab portion 42A and the second reverse taper portion 32B of the rib waveguide 33A2 have the same thickness.

[0079] In the second EC12C of the fourth embodiment, the slab width of the rib waveguide 33A2 is gradually narrowed from the second inverse tapered portion 32B toward the straight waveguide 33B. As a result, the loss during mode field conversion in the rib waveguide 33A2 can be reduced.

[0080] In Example 3, since the slab width of the rib waveguide 33A4 is constant, the change in the mode field becomes abrupt when light propagates from the rib portion 41D of the rib waveguide 33A4 to the channel-type straight waveguide 33B, resulting in coupling loss. In contrast, in Example 4, the width of the slab portion 42 gradually narrows from the second inverse tapered portion 32B toward the straight waveguide 33B, so the change in the mode field becomes gentle when light propagates from the rib waveguide 33A2 to the straight waveguide 33B, thereby suppressing coupling loss.

[0081] In the second EC12C of Example 4, the straight waveguide 33B and the rib waveguide 33A2 are directly connected to each other, but the present invention is not limited to this. An embodiment of the present invention will be described below as Example 5. EXAMPLES

[0082] FIG. 11 is a schematic plan view showing an example of an EC part in the optical chip 1D of the fifth embodiment. The same components as those in the optical chip 1C of the fourth embodiment are given the same reference numerals, and the description of the overlapping components and operations is omitted. The optical chip 1C of the fourth embodiment differs from the optical chip 1D of the fifth embodiment in that the optical chip 1C of the fourth embodiment has a tapered portion 33C between the rib waveguide 33A3 and the straight waveguide 33B in the second EC 12D, the tapered portion 33C gradually narrowing from the straight waveguide 33B toward the rib waveguide 33A3. The tapered portion 33C is a channel-type tapered waveguide connected to the rib portion 41A in the rib waveguide 33A3. The rib portion 41A of the rib waveguide 33A3 has a structure in which the rib width of the rib portion 41A gradually narrows from the straight waveguide 33B toward the second inverse tapered portion 32B.

[0083] In the fourth embodiment, the slab portion 42A of the rib waveguide 33A2 is gradually narrowed from the second inverted tapered portion 32B toward the straight waveguide 33B, but the gradual narrowing may increase the waveguide length of the rib waveguide 33A2. Therefore, a Si tapered portion 33C that gradually widens from the rib waveguide 33A3 toward the straight waveguide 33B is disposed between the rib waveguide 33A3 and the straight waveguide 33B. In this case, it is not necessary to increase the waveguide length of the rib waveguide 33A3.

[0084] The second reverse taper portion 32B and the slab portion 42A in the rib waveguide 33A3 are formed of the same material (Si) and have the same thickness in the second assembly layer 51B. The waveguide width of the rib waveguide 33A3 connected to the second reverse taper portion 32B is the same as the waveguide width on the wider side of the second reverse taper portion 32B.

[0085] Fig. 12A is an explanatory diagram showing an example of a schematic cross-sectional portion along line AA of the second EC 12D shown in Fig. 11. The second EC 12D shown in Fig. 12A has a Si substrate 51, a cladding 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along line AA shown in Fig. 12A is a cross-sectional portion of the second EC 12D in which the straight waveguide 33B is arranged. The straight waveguide 33B is arranged in the second assembly layer 51B.

[0086] Fig. 12B is an explanatory diagram showing an example of a schematic cross-sectional portion along line BB of the second EC 12D shown in Fig. 11. The second EC 12D shown in Fig. 12B has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along line BB shown in Fig. 12B is a cross-sectional portion of the second EC 12D in which the rib waveguide 33A3 is arranged. The rib waveguide 33A3 is arranged in the second assembly layer 51B.

[0087] In the second EC 12D of the fifth embodiment, the straight waveguide 33B and the rib portion 41A of the rib waveguide 33A3 are connected by a tapered portion 33C that gradually becomes larger from the rib waveguide 33A3 toward the straight waveguide 33B. As a result, the length of the rib waveguide 33A3 can be shortened, and the overall length of the second EC 12D can be shortened.

[0088] In the optical chip 1D of the fifth embodiment, the waveguide length of the second inverse taper portion 32B of the second EC 12D is the same as the waveguide length of the first inverse taper portion 25 of the first EC 11A. However, the present invention is not limited to this, and an embodiment of the present invention will be described below as a sixth embodiment. EXAMPLES

[0089] 13 is a schematic plan view showing an example of an EC portion in the optical chip 1E of the sixth embodiment. The same components as those in the optical chip 1D of the fifth embodiment are given the same reference numerals, and the description of the overlapping components and operations is omitted. The optical chip 1D of the fifth embodiment differs from the optical chip 1E of the sixth embodiment in that the waveguide length of the first inverse taper portion 25 in the first EC 11 and the waveguide length of the second inverse taper portion 32B1 in the second EC 12E are different.

[0090] The waveguide length of the second inverse taper portion 32B1 in the second EC 12E is set shorter than the waveguide length of the first inverse taper portion 25 in the first EC 11.

[0091] Fig. 14A is an explanatory diagram showing an example of a schematic cross-sectional portion along line AA of the second EC 12E shown in Fig. 13. The second EC 12E shown in Fig. 14A has a Si substrate 51, a clad 21, a first assembly layer 51A, and a second assembly layer 51B. The schematic cross-sectional portion along line AA shown in Fig. 14A is a cross-sectional portion of the second EC 12E in which the rib waveguide 33A3 is arranged. The rib waveguide 33A3 is arranged in the second assembly layer 51B.

[0092] FIG. 14B is an explanatory diagram showing an example of a schematic cross-sectional portion of the second EC 12E shown in FIG. 13 along the line BB. The second EC 12E shown in FIG. 14B has a Si substrate 51 and a clad 21 laminated on the Si substrate 51. The schematic cross-sectional portion of the line BB shown in FIG. 14B is a cross-sectional portion of the second EC 12E in which the second reverse taper portion 32B1 is arranged. Furthermore, the second EC 12E has a first assembly layer 51A and a second assembly layer 51B. The second reverse taper portion 32B1 is arranged in the second assembly layer 51B. The slab portion 42 of the rib waveguide 33A3 and the second reverse taper portion 32B1 have the same thickness.

[0093] In the second EC12E of the sixth embodiment, the waveguide length of the first reverse taper portion 25 in the first EC11 is different from the waveguide length of the second reverse taper portion 32B1 in the second EC12E. Moreover, the cross-sectional shape of the first reverse taper portion 25 in the first EC11 is different from the cross-sectional shape of the second reverse taper portion 32B1 in the second EC12E. As a result, it is possible to sequentially accommodate a wide variety of designs.

[0094] In addition, the first waveguide 22, the second waveguide 23, the second inverted taper portion 32B and the straight waveguide 33B are shown as channel-type waveguides in the above example, but are not limited thereto. For example, they may be rib waveguides, ridge waveguides, slab waveguides, or the like, and can be modified as appropriate.

[0095] FIG. 15 is an explanatory diagram showing an example of an optical transceiver 70 according to the present embodiment. The optical transceiver 70 shown in FIG. 15 is connected to an output optical fiber and an input optical fiber. The optical transceiver 70 includes a light source 71, a DSP (Digital Signal Processor) 72, and an optical transceiver 73. The optical transceiver 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 including the transmission data, and outputs the generated electrical signal to the optical transmitter 73A. The DSP 72 also obtains an electrical signal including reception data from the optical receiver 73B, and obtains reception data by performing processing such as decoding the obtained electrical signal.

[0096] The light source 71 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 71 with an electrical signal output from the DSP 72, and outputs the obtained 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 71 with an electrical signal input to the optical modulator when the light propagates through the waveguide. The optical modulator element 73A1 incorporates an optical device that is a substrate-type optical waveguide element that guides light.

[0097] 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 the light source 71. 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 element 73B1 incorporates an optical device that is a planar optical waveguide element that guides light.

[0098] The optical device in the optical transceiver 70 includes a substrate having a port and an edge coupler connected to the port. The edge coupler includes an inverted taper section connected to the port, the width of the waveguide increasing with increasing distance from the port, and a rib waveguide connected to the inverted taper section, the maximum film thickness of which is thicker than that of the inverted taper section. As a result, an optical device or the like capable of improving optical coupling loss can be provided.

[0099] For convenience of explanation, the optical transceiver 70 has been illustrated as having the optical transmitter 73A and the 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.

[0100] Furthermore, each component of each unit shown in the figure does 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.

[0101] 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 an MCU (Micro Controller Unit)). It goes without saying that 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 an MCU), or on hardware using wired logic. [Explanation of symbols]

[0102] 1 Optical chip 10A 1st port 10B Second Port 11 The First EC 12 The Second EC 32 Second inverted taper section 33A Rib Waveguide 41 Rib section 42 Slab section 51 Silicon substrate 70 Optical Transceiver 72 DSP 73A1 Optical modulator element 73B Optical Receiver 73B1 Optical receiver element

Claims

1. a substrate having a port; In an optical device having an edge coupler connected to the port, The edge coupler includes: an inverted tapered portion connected to the port, the inverted tapered portion having a waveguide width that increases with increasing distance from the port; a rib waveguide connected to the inverse tapered portion and having a maximum thickness greater than that of the inverse tapered portion; An optical device comprising:

2. The rib waveguide comprises: A rib portion; and a slab portion formed on both sides of the rib portion, The rib portion is 2. The optical device according to claim 1, wherein the rib width increases with increasing distance from the inverse tapered portion.

3. One end of the rib portion of the rib waveguide is The optical device according to claim 2 , wherein the inverted tapered portion is disposed so as to overlap with a part of the inverted tapered portion in a planar direction.

4. The slab portion of the rib waveguide comprises:

3. The optical device according to claim 2, wherein the inverted tapered portion is formed in the same layer, with the same thickness and of the same material as the inverted tapered portion.

5. The slab portion of the rib waveguide comprises:

3. The optical device according to claim 2, wherein the waveguide width decreases with increasing distance from the inverse tapered portion.

6. The waveguide connected to the rib waveguide is A straight waveguide; a tapered portion disposed between the straight waveguide and the rib waveguide, the tapered portion having a waveguide width increasing from the rib waveguide toward the straight waveguide; 2. The optical device according to claim 1, further comprising:

7. The inverted taper portion and the rib waveguide are Made of Si, The inverse tapered portion is 2. The optical device according to claim 1, wherein a local light beam is input from the port.

8. a substrate having a first port for inputting a signal light and a second port for inputting a local light; a first edge coupler connected to the first port and guiding the signal light; a second edge coupler connected to the second port and guiding the local light, The first edge coupler comprises: a first inverted tapered portion connected to the first port, the first inverted tapered portion having a waveguide width that increases with increasing distance from the first port; a waveguide connected to the first inverted tapered portion, The second edge coupler comprises: a second inverted tapered portion connected to the second port, the second inverted tapered portion having a waveguide width that increases with increasing distance from the second port; a rib waveguide connected to the second inverse tapered portion and having a maximum film thickness greater than that of the second inverse tapered portion; An optical device, wherein the waveguide length of said first inverse tapered portion is different from the waveguide length of said second inverse tapered portion.

9. An optical receiver including an optical receiver element that converts a received signal light into an electrical signal, The optical receiver element comprises: a substrate having a port; an edge coupler connected to the port; The edge coupler includes: an inverted tapered portion connected to the port, the inverted tapered portion having a waveguide width that increases with increasing distance from the port; a rib waveguide connected to the inverse tapered portion and having a maximum thickness greater than that of the inverse tapered portion; 1. An optical receiver comprising:

10. 1. An optical transmitter including an optical modulator element that modulates guided light in response to an electrical signal, The optical modulator element includes: a substrate having a port; an edge coupler connected to the port; The edge coupler includes: an inverted tapered portion connected to the port, the inverted tapered portion having a waveguide width that increases with increasing distance from the port; a rib waveguide connected to the inverse tapered portion and having a maximum thickness greater than that of the inverse tapered portion; 1. An optical transmitter comprising:

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