Grating coupler

Abstract

The grating coupler (1) includes a first optical waveguide chip (20), a second optical waveguide chip (30), and a transparent component (40). The first optical waveguide chip (20) includes a first substrate (21), a first waveguide grating (25), and a first chip end face (20c). The second optical waveguide chip (30) includes a second waveguide grating (35) and a second chip top face (30a). The optical path of light in the wavelength range used by the grating coupler (1) is filled by the transparent component (40) between the first light incident and exit surface (20i) of the first optical waveguide chip (20) and the second light incident and exit surface (30i) of the second optical waveguide chip (30).

Description

Technical Field

[0001] This disclosure relates to grating couplers. Background Technology

[0002] Japanese Patent Publication No. 2019-500753 (Patent Document 1) discloses a surface coupling system comprising a faceted light-emitting laser and an optical integrated circuit. The faceted light-emitting laser includes an active portion and a first surface grating. The optical integrated circuit includes a second surface grating. Light emitted from the active portion is diffracted through the first surface grating and coupled to the second surface grating.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2019-500753 Summary of the Invention

[0006] However, in the surface coupling system disclosed in Patent Document 1, even a slight alignment error between the end-face laser and the opto-integrated circuit results in a sharp decrease in the optical coupling efficiency between the first and second surface gratings. This disclosure addresses the aforementioned problem and aims to provide a grating coupler with a wider tolerance for alignment errors.

[0007] The disclosed grating coupler includes a first optical waveguide chip, a second optical waveguide chip, and a transparent component. The first optical waveguide chip includes: a first substrate including a top surface of a first substrate, a first optical waveguide, a first waveguide grating, a bottom surface of a first chip, a top surface of a first chip opposite to the bottom surface of the first chip, and a first chip end surface connected to the top surface and the bottom surface of the first chip. The first optical waveguide is formed on the top surface of the first substrate. The first waveguide grating is formed on the top surface of the first substrate. The first waveguide grating is connected to the first optical waveguide and is closer to the first chip end surface than the first optical waveguide. The second optical waveguide chip includes: a second substrate including a top surface of a second substrate, a second optical waveguide, a second waveguide grating, and a top surface of a second chip. The second optical waveguide is formed on the top surface of the second substrate. The second waveguide grating is formed on the top surface of the second substrate. The second waveguide grating is connected to the second optical waveguide and is closer to the first chip end surface than the second optical waveguide. The second waveguide grating is disposed on one side of the first substrate in a direction that separates the top and bottom surfaces of the first chip from each other. Light incident on the grating coupler of this disclosure is coupled between the first and second waveguide gratings via a first light incident / exit surface of the first optical waveguide chip extending along the end face of the first chip and a second light incident / exit surface of the second optical waveguide chip extending along the top surface of the second chip. The optical path of light within the wavelength range used by the grating coupler is filled between the first and second light incident / exit surfaces by a transparent component.

[0008] The transparent component reduces the variation in the incident position of light towards the first or second waveguide grating due to changes in the relative positions of the first and second waveguide chips. This reduces variations in the optical coupling efficiency of the first or second waveguide grating relative to light. Therefore, the grating coupler of this disclosure has a wider tolerance for alignment errors. Attached Figure Description

[0009] Figure 1 This is a schematic cross-sectional view of the grating coupler in Embodiment 1.

[0010] Figure 2 This is a schematic top view of the grating coupler in Embodiment 1.

[0011] Figure 3 This is a schematic enlarged cross-sectional view of the first waveguide grating in the grating coupler of Embodiment 1.

[0012] Figure 4 This is a schematic enlarged cross-sectional view of the second waveguide grating in the grating coupler of Embodiment 1.

[0013] Figure 5 This is a schematic cross-sectional view of the grating coupler in Embodiment 1.

[0014] Figure 6 This is a schematic cross-sectional view of the grating coupler in Embodiment 1.

[0015] Figure 7 This is a schematic enlarged cross-sectional view of the second optical waveguide chip in the grating coupler of Embodiment 1.

[0016] Figure 8 This is a schematic enlarged cross-sectional view of the first waveguide grating in the grating coupler of the first variation of Embodiment 1.

[0017] Figure 9 This is a schematic enlarged cross-sectional view of the first waveguide grating in the grating coupler of the second variation of Embodiment 1.

[0018] Figure 10 This is a schematic cross-sectional view of the grating coupler of the third variation of Embodiment 1.

[0019] Figure 11 This is a schematic cross-sectional view of the grating coupler in Embodiment 2.

[0020] Figure 12 This is a schematic cross-sectional view of the grating coupler in Embodiment 3.

[0021] Figure 13 This is a schematic cross-sectional view of the grating coupler in Embodiment 4.

[0022] Figure 14 This is a schematic cross-sectional view of the grating coupler in Embodiment 5.

[0023] (Symbol Explanation)

[0024] 1, 1b, 1c, 1d, 1e: Grating couplers; 10: Mount; 10a: Main surface; 11: First sub-mount; 11a: Top surface; 11b: Bottom surface; 12: Second sub-mount; 12a: Top surface; 12b: Bottom surface; 20: First optical waveguide chip; 20a: Top surface of the first chip; 20b: Bottom surface of the first chip; 20c: End surface of the first chip; 20i: First light incident / exit surface; 20n: Normal; 21: First substrate; 21a: Top surface of the first substrate; 21b: Bottom surface of the first substrate; 21c: End surface of the substrate; 22: First optical waveguide; 23: Core layer; 24: Upper cladding; 25: First waveguide grating; 26: First grating; 27: Upper cladding; 30: Second optical waveguide... 30a: Second chip top surface; 30b: Second chip bottom surface; 30c: Second chip end surface; 30i: Second light incident / exit surface; 31: Second substrate; 31a: Second substrate top surface; 31b: Second substrate bottom surface; 32: Second optical waveguide; 33: Core layer; 34a: Lower cladding; 34b: Upper cladding; 35: Second waveguide grating; 36: Second grating; 36a, 36b: Grating ends; 36c: Grating center; 36r: Region; 40: Transparent component; 41: Transparent adhesive layer; 42: Transparent block; 48: Bonding component; 50: Laser structure; 51: Active region; 52: Upper cladding; 53: Contact layer; 54: Upper electrode; 55: Lower electrode; 57: Anti-reflective film. Detailed Implementation

[0025] The embodiments of this disclosure will now be described. Furthermore, the same reference numerals will be used for the same structures, and their descriptions will not be repeated.

[0026] Implementation method 1.

[0027] Reference Figures 1 to 10 The following describes the grating coupler 1 according to Embodiment 1. The grating coupler 1 mainly includes a first optical waveguide chip 20, a second optical waveguide chip 30, and a transparent component 40. The grating coupler 1 may also include a first sub-pattern 11 and a second sub-pattern 12.

[0028] A grating coupler 1 is mounted on a patch 10. The patch 10 is formed, for example, of a metal material with high thermal conductivity, such as a copper-tungsten alloy. Specifically, the patch 10 has a main surface 10a. A first sub-patch 11 and a second sub-patch 12 are mounted on the main surface 10a of the patch 10. The first sub-patch 11 and the second sub-patch 12 are fixed to the main surface 10a of the patch 10 using an adhesive (not shown), such as a conductive adhesive. The first sub-patch 11 and the second sub-patch 12 are formed, for example, of an electrically insulating material with high thermal conductivity, such as aluminum oxide or aluminum nitride.

[0029] The height h2 of the second sub-pattern 12 is lower than the height h1 of the first sub-pattern 11. The height h1 of the first sub-pattern 11 is defined as the distance between the bottom surface 11b of the first sub-pattern 11 facing the main surface 10a of the patch 10 and the top surface 11a of the first sub-pattern 11 on the opposite side of the bottom surface 11b. The height h2 of the second sub-pattern 12 is defined as the distance between the bottom surface 12b of the second sub-pattern 12 facing the main surface 10a of the patch 10 and the top surface 12a of the second sub-pattern 12 on the opposite side of the bottom surface 12b. The first optical waveguide chip 20 is mounted on the first sub-pattern 11. The first optical waveguide chip 20 is fixed to the top surface 11a of the first sub-pattern 11 using an adhesive (not shown), such as a conductive adhesive. The second optical waveguide chip 30 is mounted on the second sub-pattern 12. The second optical waveguide chip 30 is fixed to the top surface 12a of the second sub-pattern 12 using an adhesive (not shown) such as a conductive adhesive.

[0030] The first optical waveguide chip 20 includes a first substrate 21, a first optical waveguide 22, and a first waveguide grating 25. The first optical waveguide chip 20 includes a first chip bottom surface 20b, a first chip top surface 20a opposite to the first chip bottom surface 20b, and a first chip end surface 20c connected to the first chip top surface 20a and the first chip bottom surface 20b. The first chip bottom surface 20b faces the main surface 10a of the patch 10.

[0031] The first substrate 21 is formed, for example, of a compound semiconductor material such as InP or GaAs. The first substrate 21 includes a first substrate bottom surface 21b, a first substrate top surface 21a opposite to the first substrate bottom surface 21b, and a substrate end surface 21c connected to the first substrate top surface 21a and the first substrate bottom surface 21b. The first substrate bottom surface 21b faces the top surface 11a of the first sub-patch 11. The first chip top surface 20a is close to the first substrate top surface 21a and away from the first substrate bottom surface 21b. The first chip bottom surface 20b is close to the first substrate bottom surface 21b and away from the first substrate top surface 21a. The first chip bottom surface 20b being close to the first substrate bottom surface 21b also includes the first chip bottom surface 20b being the first substrate bottom surface 21b. In this embodiment, the first chip bottom surface 20b is the first substrate bottom surface 21b. The first chip end surface 20c includes the substrate end surface 21c. The substrate end face 21c is a part of the first chip end face 20c.

[0032] A first optical waveguide 22 is formed on the top surface 21a of a first substrate. The first optical waveguide 22 includes, for example, a core layer 23 and an upper cladding layer 24. The core layer 23 is formed on the top surface 21a of the first substrate. The core layer 23 is formed, for example, of an InGaAsP-based or AlGaInAs-based compound semiconductor material. When the wavelength of light traveling in the core layer 23 is 1.55 μm, the core layer 23 has, for example, a bandgap of 1.20 μm or more, up to 1.40 μm. The upper cladding layer 24 is formed on the core layer 23. The upper cladding layer 24 is formed, for example, of a compound semiconductor material such as InP or GaAs. The first optical waveguide 22 may also include an upper cladding layer 27, described later. The upper cladding layer 27 is formed on the upper cladding layer 24.

[0033] A first waveguide grating 25 is formed on the top surface 21a of a first substrate. The first waveguide grating 25 includes, for example, a core layer 23, a first grating 26, and an upper cladding layer 27. The first grating 26 is formed, for example, on the core layer 23. The upper cladding layer 27 is formed on the core layer 23 and the first grating 26. The upper cladding layer 27 is close to the top surface 20a of the first chip relative to the core layer 23. In this embodiment, the surface of the upper cladding layer 27 on the side opposite to the core layer 23 is part of the top surface 20a of the first chip. The upper cladding layer 27 is, for example, a dielectric film such as a silicon oxide film or a silicon nitride film.

[0034] The first waveguide grating 25 is connected to the first optical waveguide 22 and is closer to the first chip end face 20c than the first optical waveguide 22. For example, light is incident on the first optical waveguide 22 and then on the first waveguide grating 25. The light is diffracted in the first waveguide grating 25 (first grating 26) toward one side of the first substrate 21. The light is refracted as it exits the first optical waveguide chip 20 toward the second waveguide grating 35.

[0035] Reference Figure 3The first waveguide grating 25 has a first grating pitch Λ1 and a first grating width w1. The first grating width w1 is the width of the recess of the first grating 26 along the length of the core layer 23. In order to diffract the light incident on the first optical waveguide 22 to one side of the first substrate 21, the first grating pitch Λ1 of the first waveguide grating 25 (first grating 26) is more than three times the wavelength of the light. That is, the first grating 26 is a long-period grating.

[0036] The first grating spacing Λ1 of the first waveguide grating 25 can also decrease as it moves away from the first optical waveguide 22. For example, the first grating spacing Λ1 decreases by 0.1 μm for each spacing of the first grating 26 as it moves away from the first optical waveguide 22. Therefore, the light diffracted by the first waveguide grating 25 can be focused in the second waveguide grating 35 along the length of the core layer 33.

[0037] The width w1 of the first grating is more than 0.4 times and less than 0.6 times the first grating spacing Λ1. Furthermore, as the first grating spacing Λ1 decreases with distance from the first optical waveguide 22, the width w1 of the first grating is more than 0.4 times and less than 0.6 times the average value of the first grating spacing Λ1. Therefore, the diffraction efficiency of the first diffracted light in the first waveguide grating 25 (first grating 26) increases, and the diffraction efficiency of the higher-order diffracted light in the first waveguide grating 25 (first grating 26) decreases.

[0038] The first waveguide grating 25 has a grating depth d. The grating depth d is the depth of the recess of the first grating 26 in the thickness direction of the first waveguide grating 25. The grating depth d is, for example, more than 100 nm and less than 250 nm. By increasing the grating depth d, the diffraction efficiency in the first waveguide grating 25 (first grating 26) increases.

[0039] like Figure 8 as well as Figure 9 As shown, the first waveguide grating 25 can also be a stepped grating with multiple steps. Therefore, the diffraction efficiency of higher-order diffracted light in the first waveguide grating 25 decreases, while the diffraction efficiency of first-order diffracted light in the first waveguide grating 25 increases. Figure 9 As shown, the multiple steps can also be inclined steps, and the first waveguide grating 25 can also be a stepped grating with multiple inclined steps. Therefore, the diffraction efficiency of the higher-order diffracted light in the first waveguide grating 25 is further reduced, and the diffraction efficiency of the first-order diffracted light in the first waveguide grating 25 is further increased.

[0040] In such Figure 8 as well as Figure 9In the stepped grating shown, the width w1 of the first grating is provided by S / d. Here, S represents the cross-sectional area of ​​the recess in one pitch of the stepped grating. d represents the depth of the recess in one pitch of the stepped grating, which is the grating depth of the stepped grating.

[0041] Reference Figure 2 When viewed from above the top surface 20a of the first chip, the first waveguide grating 25 (first grating 26) can also have an elliptical arc shape that expands towards the end surface 20c of the first chip. Therefore, light diffracted by the first waveguide grating 25 can be focused in the second waveguide grating 35 along the width of the core layer 33. Furthermore, the first waveguide grating 25 can receive light focused by the second waveguide grating 35 with higher optical coupling efficiency.

[0042] When viewed from above the top surface 20a of the first chip, the width of the core layer 23 of the first waveguide grating 25 can also gradually increase from the first optical waveguide 22 toward the end surface 20c of the first chip. The core layer 23 of the first waveguide grating 25 can also be a tapered waveguide with a width that gradually increases from the first optical waveguide 22 toward the end surface 20c of the first chip.

[0043] Reference Figure 1 The second optical waveguide chip 30 includes a second substrate 31, a second optical waveguide 32, and a second waveguide grating 35. The second optical waveguide chip 30 includes a second chip bottom surface 30b, a second chip top surface 30a on the side opposite to the second chip bottom surface 30b, and a second chip end surface 30c connected to the second chip top surface 30a and the second chip bottom surface 30b.

[0044] The bottom surface 30b of the second chip is opposite to the main surface 10a of the surface mount 10. The bottom surface 30b of the second chip is closer to the main surface 10a of the surface mount 10 than the bottom surface 20b of the first chip. The bottom surface 30b of the second chip faces the same direction as the bottom surface 20b of the first chip. Figure 1 (The direction below the paper). The top surface 30a of the second chip is located on one side of the first substrate 21 relative to the top surface 20a of the first chip 20a and the bottom surface 20b of the first chip, in the direction in which the top surface 20a and the bottom surface 20b of the first chip are separated from each other. The top surface 30a of the second chip is closer to the main surface 10a of the patch 10 than the top surface 20a of the first chip 10 in the direction in which the top surface 20a and the bottom surface 20b of the first chip are separated from each other. The top surface 30a of the second chip faces the same direction as the top surface 20a of the first chip ( Figure 1 (The orientation on the paper).

[0045] The second substrate 31 may also be formed of a different material than the first substrate 21. The second substrate 31 is formed, for example, of a semiconductor material such as Si. The second substrate 31 includes a second substrate bottom surface 31b and a second substrate top surface 31a opposite to the second substrate bottom surface 31b. The second substrate bottom surface 31b faces the top surface 12a of the second sub-patch 12. The second chip top surface 30a is close to the second substrate top surface 31a and away from the second substrate bottom surface 31b. The second chip bottom surface 30b is close to the second substrate bottom surface 31b and away from the second substrate top surface 31a. The second chip bottom surface 30b being close to the second substrate bottom surface 31b also includes the second chip bottom surface 30b being the second substrate bottom surface 31b. In this embodiment, the second chip bottom surface 30b is the second substrate bottom surface 31b. The normal 20n of the second chip end surface 30c on the first chip end surface 20c (refer to...) Figure 5 as well as Figure 6 The second grating 36 is closer to the first chip end face 20c in the direction relative to the second waveguide grating 35. The second chip end face 30c can also face the first chip end face 20c (substrate end face 21c).

[0046] A second optical waveguide 32 is formed on the top surface 31a of the second substrate. The second optical waveguide 32 includes, for example, a core layer 33, a lower cladding layer 34a, and an upper cladding layer 34b. The lower cladding layer 34a is formed on the top surface 31a of the second substrate. The lower cladding layer 34a is closer to the bottom surface 30b of the second chip than the core layer 33. The lower cladding layer 34a is formed, for example, of a dielectric material such as silicon oxide. The core layer 33 is formed on the lower cladding layer 34a. The core layer 33 is formed, for example, of a material different from the core layer 23. The core layer 33 is formed, for example, of a semiconductor material such as Si. The upper cladding layer 34b is formed on the core layer 33. The upper cladding layer 34b is closer to the top surface 30a of the second chip than the core layer 33. The upper cladding layer 34b is formed, for example, of a dielectric material such as silicon oxide. In this embodiment, the surface of the upper cladding 34b on the side opposite to the core layer 33 is part of the top surface 30a of the second chip.

[0047] A second waveguide grating 35 is formed on the top surface 31a of the second substrate. The second waveguide grating 35 includes, for example, a core layer 33, a second grating 36, a lower cladding layer 34a, and an upper cladding layer 34b. The second grating 36 is formed, for example, on the core layer 33. The upper cladding layer 34b is formed on the core layer 33 and the first grating 26. The second grating 36 may also be formed in the portion of the upper cladding layer 34b that is connected to the core layer 33.

[0048] The second waveguide grating 35 is connected to the second optical waveguide 32 and is closer to the first chip end face 20c than the second optical waveguide 32. The second waveguide grating 35 is closer to the second chip end face 30c than the second optical waveguide 32. The second waveguide grating 35 is disposed on one side of the first substrate 21 relative to the first waveguide grating 25 in the direction in which the top surface 20a and the bottom surface 20b of the first chip are separated from each other. The second waveguide grating 35 is closer to the main surface 10a of the patch 10 than the first waveguide grating 25 in the direction in which the top surface 20a and the bottom surface 20b of the first chip are separated from each other.

[0049] The second waveguide grating 35 includes a grating end 36a adjacent to the second optical waveguide 32 and a grating end 36b on the opposite side of the grating end 36a. The grating end 36b is adjacent to the first chip end face 20c (or the second chip end face 30c) in the length direction of the core layer 33.

[0050] Reference Figure 4 The second waveguide grating 35 has a second grating spacing Λ2 and a second grating width w2. The second grating width w2 is the width of the recess of the second grating 36 in the length direction of the core layer 33.

[0051] Region 36r (see reference) near the grating end 36a in the second waveguide grating 35 Figure 7 The width w2 of the second grating in the second waveguide grating 35 can also be greater than 0% and less than or equal to 30% of the second grating spacing Λ2, or greater than 70% and less than 100% of the second grating spacing Λ2. The region 36r in the second waveguide grating 35 near the grating end 36a means the grating center 36c in the second waveguide grating 35 between the grating ends 36a and 36b (see reference). Figure 7 The region between the second waveguide grating 35 and the grating end 36a. Therefore, the intensity distribution of diffracted light from the second waveguide grating 35 relative to its position can be made gentler. Light can be diffracted with higher diffraction efficiency over a wider area of ​​the second waveguide grating 35.

[0052] The core layer 33 can also be formed of silicon nitride, for example. Silicon nitride has a lower refractive index than Si. Therefore, the intensity distribution of diffracted light relative to the position of the second waveguide grating 35 can be made smoother. Light can be diffracted with higher diffraction efficiency over a wider area of ​​the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error.

[0053] Reference Figure 2The second waveguide grating 35 (second grating 36) can also have an elliptical arc shape that expands towards the end face 20c of the first chip when viewed from above the top surface 30a of the second chip (or when viewed from above the top surface 20a of the first chip). Therefore, the second waveguide grating 35 can receive light converged through the first waveguide grating 25 with higher optical coupling efficiency. In addition, the light diffracted through the second waveguide grating 35 can be converged in the width direction of the core layer 23 in the first waveguide grating 25.

[0054] When viewed from above the top surface 30a of the second chip (or from above the top surface 20a of the first chip), the width of the core layer 33 of the second waveguide grating 35 can also gradually increase from the second optical waveguide 32 toward the end surface 20c of the first chip. The core layer 33 of the second waveguide grating 35 can also be a tapered waveguide with a width that gradually increases from the second optical waveguide 32 toward the end surface 20c of the first chip.

[0055] A transparent component 40 is disposed on the first light incident / exit surface 20i and the second light incident / exit surface 30i. The transparent component 40 is transparent within the wavelength range used in the grating coupler 1. The transparent component 40 is formed, for example, of a thermosetting resin or an ultraviolet-curing resin. The transparent component 40 is, for example, a transparent resin component formed of a transparent resin such as a fluorinated epoxy resin, an acrylic resin, or a bromine-containing epoxy resin. The refractive index of the transparent component 40 is greater than the refractive index of air. The refractive index of the transparent component 40 can be, for example, 1.37 or higher, 1.40 or higher, or 1.45 or higher. The refractive index of the transparent component 40 can be, for example, 1.70 or lower, 1.65 or lower, or 1.60 or lower.

[0056] The difference between the refractive index of the transparent component 40 and the refractive index of the uppermost part (upper cladding 34b in this embodiment) of the second optical waveguide chip 30, including the second light incident / exit surface 30i, can also be 0.20 or less. Therefore, the reflection of light in the second light incident / exit surface 30i can be reduced. The difference between the refractive index of the transparent component 40 and the refractive index of the upper cladding 34b can be 0.15 or less, 0.10 or less, or 0.05 or less.

[0057] The first light incident / exit surface 20i means either the light exit surface for light diffracted by the first waveguide grating 25 and traveling towards the second waveguide grating 35, or the light incident surface for light diffracted by the second waveguide grating 35 and traveling towards the first waveguide grating 25. In this embodiment, the first light incident / exit surface 20i is the first chip end face 20c. The second light incident / exit surface 30i means either the light exit surface for light diffracted by the second waveguide grating 35 and traveling towards the first waveguide grating 25, or the light incident surface for light diffracted by the first waveguide grating 25 and traveling towards the second waveguide grating 35. In this embodiment, the second light incident / exit surface 30i is the second chip top surface 30a.

[0058] Light incident on the grating coupler 1 is coupled between the first waveguide grating 25 and the second waveguide grating 35 through the first light incident / exit surface 20i of the first optical waveguide chip 20 and the second light incident / exit surface 30i of the second optical waveguide chip 30. The first light incident / exit surface 20i extends along the end face 20c of the first chip. The second light incident / exit surface 30i extends along the top face 30a of the second chip.

[0059] Specifically, light incident on the first optical waveguide 22 is diffracted in the first waveguide grating 25 (first grating 26) to one side of the first substrate 21 and then incident on the second waveguide grating 35. The light is diffracted in the second waveguide grating 35 (second grating 36) and coupled to the core layer 33. Light from the second waveguide grating 35 is incident on the second optical waveguide 32 and exits from the second waveguide 32 to the outside of the grating coupler 1. Light diffracted by the first waveguide grating 25 and traveling towards the second waveguide grating 35 is coupled, for example, to a region 36r in the second waveguide grating 35 near the grating end 36a (see reference). Figure 7 ).

[0060] Light incident on the second optical waveguide 32 is diffracted at the second waveguide grating 35 (second grating 36) and then incident on the first waveguide grating 25. The light is further diffracted at the first waveguide grating 25 (first grating 26) and coupled to the core layer 23. Light then travels from the first waveguide grating 25 to the first optical waveguide 22 and exits from the first optical waveguide 22 to the outside of the grating coupler 1.

[0061] The light incident on the grating coupler 1 (first optical waveguide chip 20 or second optical waveguide chip 30) has any wavelength within the wavelength range of the grating coupler 1 (hereinafter referred to as the "wavelength range of the grating coupler 1" or simply the "wavelength range"). For example, if the light incident on the grating coupler 1 is laser light emitted from a fixed-wavelength laser, the wavelength range of the grating coupler 1 is the fixed wavelength of the fixed-wavelength laser. If the light incident on the grating coupler 1 is laser light emitted from a wavelength-variable laser, the wavelength range of the grating coupler 1 is the variable wavelength range of the wavelength-variable laser. The wavelength range of the grating coupler 1 is, for example, the C-band (wavelength band of 1.530 μm and above to 1.565 μm and below) or the O-band (wavelength band of 1.260 μm and above to 1.360 μm). The diffraction angle (direction of travel) of the light diffracted by the first waveguide grating 25 or the second waveguide grating 35 varies depending on the wavelength of the light.

[0062] The optical path of light within the operating wavelength range of the grating coupler 1 is filled by the transparent component 40 between the first light incident / exit surface 20i and the second light incident / exit surface 30i. The light within the operating wavelength range of the grating coupler 1 travels only within the transparent component 40 between the first light incident / exit surface 20i and the second light incident / exit surface 30i. That is, the optical paths of light having the minimum wavelength λ1 of the operating wavelength range, the center wavelength λ2 of the operating wavelength range, and the maximum wavelength λ3 of the operating wavelength range are filled by the transparent component 40 between the first light incident / exit surface 20i and the second light incident / exit surface 30i. The light having the minimum wavelength λ1 of the operating wavelength range, the center wavelength λ2 of the operating wavelength range, and the maximum wavelength λ3 of the operating wavelength range travel only within the transparent component 40 between the first light incident / exit surface 20i and the second light incident / exit surface 30i.

[0063] The exit angle θ2 of the first light incident on the first light exit surface 20i of the first optical waveguide chip 20 (refer to) Figure 5 For example, it is 33° or higher. In this embodiment, the first light incident exit surface 20i is the first chip end surface 20c (substrate end surface 21c). The exit angle θ2 is defined as the distance between the direction of light traveled from the first light incident exit surface 20i and the normal 20n of the first light incident exit surface 20i (refer to...). Figure 5 The angle between the first waveguide grating 25 and the second waveguide grating 35 is such that the optical coupling efficiency between them can be prevented from being excessively reduced. For example, by adjusting the diffraction angle θ1 of the first waveguide grating 25 (refer to...) Figure 5 The angle can be increased to 15° or more, making the exit angle θ2 33° or more. For example, the exit angle θ2 can be adjusted by the first grating spacing Λ1 of the first waveguide grating 25.

[0064] Angle of departure θ2 (reference) Figure 5 For example, it is 60° or less. Therefore, it is possible to prevent the light reflectivity in the first light incident and exit surface 20i from becoming excessively high. For example, by making the diffraction angle θ1 of the first waveguide grating 25 (refer to...) Figure 5 By making the first grating spacing Λ1 of the first waveguide grating 25 to be more than 2.7 times and less than 5.4 times the wavelength of light (or the center wavelength of the wavelength range used by the grating coupler 1), the emission angle θ2 can be made to be more than 33° and less than 60°.

[0065] Here is an example illustrating the manufacturing method of the grating coupler 1 in this embodiment.

[0066] The method for manufacturing the grating coupler 1 includes a step of fabricating a first optical waveguide chip 20. Specifically, a core layer 23 and an upper cladding layer 24 are formed on a first substrate 21 using a metal-organic chemical vapor deposition (MOCVD) method or the like. A first grating 26 is formed by etching a portion of the upper cladding layer 24 and a portion of the core layer 23. An upper cladding layer 27 is formed on the core layer 23, the first grating 26, and the upper cladding layer 24 using chemical vapor deposition (CVD). In this way, the first optical waveguide chip 20 can be obtained.

[0067] The manufacturing method of the grating coupler 1 includes a step of fabricating a second optical waveguide chip 30. Specifically, a silicon-on-insulator (SOI) substrate is prepared. The SOI substrate includes a second substrate 31 (silicon substrate), a lower cladding layer 34a (silicon oxide layer), and a silicon layer disposed on the lower cladding layer 34a. A core layer 33 is formed by etching a portion of the silicon layer. A second grating 36 is formed by etching a portion of the core layer 33. An upper cladding layer 34b is formed on the core layer 33, the second grating 36, and the lower cladding layer 34a using a chemical vapor deposition (CVD) method. In this way, the second optical waveguide chip 30 can be obtained.

[0068] Next, a first optical waveguide chip 20 is fixed on the first sub-pattern 11 (top surface 11a). A second optical waveguide chip 30 is fixed on the second sub-pattern 12 (top surface 12a). The first sub-pattern 11 and the second sub-pattern 12 are fixed on the main surface 10a of the patch 10. Transparent components 40 are formed on the first light incident / exit surface 20i and the second light incident / exit surface 30i. In this way, the grating coupler 1 can be obtained.

[0069] By comparing the grating coupler 1 of this embodiment, which is an example of the grating coupler 1 of this embodiment, with the grating coupler of the comparative example, the function of the grating coupler 1 of this embodiment will be explained.

[0070] Reference Figure 5The study investigates the variation of the incident position L1 of the light towards the second waveguide grating 35 when light is coupled from the first waveguide grating 25 to the second waveguide grating 35 in the grating coupler 1 of the embodiment. This variation occurs between light with the minimum wavelength λ1 of the wavelength range used by the grating coupler 1 and light with the maximum wavelength λ3 of the wavelength range used. The incident position L1 is defined as the distance in the direction of the normal 20n of the first light incident exit surface 20i from the first light incident exit surface 20i to the incident position of the light in the second chip top surface 30a of the second waveguide grating 35.

[0071] Light is incident on the core layer 23 of the first optical waveguide 22 and diffracted in the first waveguide grating 25. The diffraction angle θ1 in the first waveguide grating 25 (first grating 26) is provided by the following equation (1).

[0072] [Mathematical Expression 1]

[0073]

[0074] n wg1 λ represents the refractive index of core layer 23. n1 represents the refractive index of the first substrate 21. Λ1 represents the first grating spacing of the first waveguide grating 25. λ represents the wavelength of light. m represents the diffraction order. The diffracted light of the first order (m=1) is coupled between the first waveguide grating 25 and the second waveguide grating 35.

[0075] The light diffracted by the first waveguide grating 25 is refracted when it exits from the first optical waveguide chip 20. The exit angle θ2 of the light diffracted by the first waveguide grating 25 from the first light incident exit surface 20i (first chip end face 20c, substrate end face 21c) is provided by the following equation (2).

[0076] [Mathematical Expression 2]

[0077]

[0078] n2 represents the refractive index of the transparent component 40.

[0079] In this embodiment, the first optical waveguide chip 20 is an InGaAsP-based optical waveguide chip. Specifically, the first substrate 21 is an InP substrate, and n1 is 3.16. The core layer 23 is formed of InGaAsP, and n... wg1 It is 3.238. The first grating spacing Λ1 of the first waveguide grating 25 is 5.39 μm. The light incident on the core layer 23 has any wavelength within the usable wavelength range of 1.53 μm or greater and 1.57 μm. The light with the smallest wavelength λ1 in the usable wavelength range has a wavelength of 1.53 μm. The light with the center wavelength λ2 in the usable wavelength range has a wavelength of 1.55 μm. The light with the largest wavelength λ3 in the usable wavelength range has a wavelength of 1.57 μm.

[0080] The transparent component 40 is formed of epoxy resin, and n2 is 1.50. The second optical waveguide chip 30 is a Si-based optical waveguide chip. Specifically, the second substrate 31 is a silicon substrate. The lower cladding layer 34a is a silicon oxide layer. The core layer 33 is a silicon layer. The upper cladding layer 34b is a silicon oxide layer.

[0081] As shown in Table 1, in this embodiment, the diffraction angle θ1 and exit angle θ2 of light having a center wavelength λ2 (1.55 μm) in the wavelength range of use are 21.00° and 49.00°, respectively. Table 1 shows the diffraction angle θ1, exit angle θ2, and incident position L1 of light having the smallest wavelength λ1 (1.53 μm) in the wavelength range of use and light having the largest wavelength λ3 (1.57 μm) in the wavelength range of use in this embodiment.

[0082] [Table 1]

[0083] Wavelength (μm) <![CDATA[θ1 (°)]]> <![CDATA[θ2 (°)]]> <![CDATA[L1 (μm)]]> 1.53 20.76 48.31 36.26 1.55 21.00 49.00 1.57 21.17 49.53 33.83

[0084] In the embodiment, the incident position L1 varies by 2.43 μm (=36.26 μm-33.83 μm) between light with the minimum wavelength λ1 of the used wavelength range and light with the maximum wavelength λ3 of the used wavelength range.

[0085] The comparative example grating coupler has the same structure as the grating coupler 1 of the embodiment, but differs in the following aspects. The comparative example grating coupler does not have a transparent component 40. In the comparative example, the first chip end face 20c (substrate end face 21c) and the second chip top face 30a are exposed to air, and n2 (refer to the above formula (2)) is 1.00.

[0086] As shown in Table 2, the exit angle θ2 of the comparative example is made equal to the exit angle θ2 of the embodiment. Therefore, in the comparative example, the first grating spacing Λ1 of the first waveguide grating 25 is set to 9.15 μm. In the comparative example, the diffraction angle θ1 of light having a center wavelength λ2 (1.55 μm) in the wavelength range of use is 13.80°. Table 2 shows the respective diffraction angle θ1, exit angle θ2, and incident position L1 of light having the smallest wavelength λ1 (1.53 μm) in the wavelength range of use and light having the largest wavelength λ3 (1.57 μm) in the wavelength range of use in the comparative example.

[0087] [Table 2]

[0088] Wavelength (μm) <![CDATA[θ1 (°)]]> <![CDATA[θ2 (°)]]> <![CDATA[L1 (μm)]]> 1.53 13.65 48.56 37.04 1.55 13.80 49.00 1.57 13.98 49.79 34.03

[0089] In the comparative example, the incident position L1 changes by 3.01 μm (=37.04 μm-34.033 μm) between light with the minimum wavelength λ1 of the range of usable wavelengths and light with the maximum wavelength λ3 of the range of usable wavelengths.

[0090] Therefore, when light is coupled from the first waveguide grating 25 to the second waveguide grating 35, the transparent component 40 can reduce the variation of the incident position L1 of the light toward the second waveguide grating 35.

[0091] Reference Figure 6 The study investigates the variation of the incident position L2 of the light towards the first waveguide grating 25 between light having the minimum wavelength λ1 of the used wavelength range and light having the maximum wavelength λ3 of the used wavelength range, when light is coupled from the second waveguide grating 35 to the first waveguide grating 25 in the grating coupler 1 of the embodiment. The incident position L2 of the light is defined as the distance from the first light incident surface 20i to the incident position of the light in the first grating 26 of the first waveguide grating 25 in the direction of the normal 20n of the first light incident exit surface 20i.

[0092] Light is incident on the core layer 33 of the second optical waveguide 32 and diffracted in the second waveguide grating 35. The diffraction angle θ3 in the second waveguide grating 35 (second grating 36) is provided by the following equation (3).

[0093] [Mathematical Expression 3]

[0094]

[0095] n wg2 n3 represents the refractive index of the core layer 33. n3 represents the refractive index of the upper cladding layer 34b. Λ2 represents the second grating spacing of the second waveguide grating 35. λ represents the wavelength of the light. m represents the diffraction order. The diffracted light of the first order (m=1) is coupled between the first waveguide grating 25 and the second waveguide grating 35.

[0096] The light diffracted by the second waveguide grating 35 is refracted in the second light incident exit surface 30i (the interface between the top surface 30a of the second chip or the upper cladding 34b and the transparent component 40). Furthermore, in this embodiment, the second light incident exit surface 30i is perpendicular to the first light incident exit surface 20i (the end surface 20c of the first chip and the end surface 21c of the substrate). Therefore, the incident angle θ4 of the light towards the first light incident exit surface 20i (the end surface 20c of the first chip and the end surface 21c of the substrate) is provided by the following equation (4).

[0097] [Mathematical Expression 4]

[0098] .

[0099] n3 represents the refractive index of the upper cladding layer 34b. As mentioned above, n2 represents the refractive index of the transparent component 40.

[0100] The light refracted in the second light incident and exit surface 30i (the interface between the top surface 30a of the second chip or the upper cladding layer 34b and the transparent component 40) is refracted in the first light incident and exit surface 20i (the end surface 20c of the first chip and the end surface 21c of the substrate). Therefore, the incident angle θ5 of the light toward the core layer 23 is provided by the following equation (5).

[0101] [Mathematical Expression 5]

[0102] .

[0103] As mentioned above, n1 represents the refractive index of the first substrate 21.

[0104] In this embodiment, the second optical waveguide chip 30 is a Si-based optical waveguide chip. The core layer 33 is a silicon layer, n wg2 The value is 2.797. The upper cladding 34b is a silicon oxide layer, and n3 is 1.50. Referring to Tables 1 and 3, the incident angle θ4 of the embodiment is made equal to the exit angle θ2 of the embodiment. Therefore, the second grating pitch Λ2 of the second waveguide grating 35 is set to 0.855 μm. The transparent component 40 is formed of epoxy resin, and n2 is 1.50. The first substrate 21 is an InP substrate, and n1 is 3.16.

[0105] As shown in Table 3, in this embodiment, the incident angles θ4 and θ5 of light having a center wavelength λ2 (1.55 μm) within the wavelength range of use are 49.00° and 21.00°, respectively. Table 3 shows the respective incident angles θ4, θ5, and incident position L2 of light having the minimum wavelength λ1 (1.53 μm) within the wavelength range of use and light having the maximum wavelength λ3 (1.57 μm) within the wavelength range of use in this embodiment.

[0106] [Table 3]

[0107] Wavelength (μm) <![CDATA[θ4 (°)]]> <![CDATA[θ5 (°)]]> <![CDATA[L2 (μm)]]> 1.53 47.80 20.59 140.92 1.55 49.00 21.00 1.57 50.17 21.38 126.98

[0108] In the embodiment, the incident position L2 varies by 13.94 μm (=140.92 μm-126.98 μm) between light with the minimum wavelength λ1 of the used wavelength range and light with the maximum wavelength λ3 of the used wavelength range.

[0109] The comparative example grating coupler has the same structure as the grating coupler 1 of the embodiment, but differs in the following aspects. The comparative example grating coupler does not have a transparent component 40. In the comparative example, the first chip end face 20c (substrate end face 21c) and the second chip top face 30a are exposed to air, and n2 (refer to formula (4) and formula (5) above) is 1.00.

[0110] As shown in Table 4, the incident angle θ4 of the comparative example is made equal to the incident angle θ4 of the embodiment. Therefore, in the comparative example, the second grating spacing Λ2 of the second waveguide grating 35 is set to 0.720 μm. In the comparative example, the diffraction angle θ1 of light having a center wavelength λ2 (1.55 μm) in the wavelength range of use is 13.80°. Table 4 shows the incident angle θ4, incident angle θ5, and incident position L2 of light having the minimum wavelength λ1 (1.53 μm) in the wavelength range of use and light having the maximum wavelength λ3 (1.57 μm) in the wavelength range of use in the comparative example.

[0111] [Table 4]

[0112] Wavelength (μm) <![CDATA[θ4 (°)]]> <![CDATA[θ5 (°)]]> <![CDATA[L2 (μm)]]> 1.53 47.77 13.55 219.83 1.55 49.00 13.80 1.57 51.93 14.43 183.04

[0113] In the comparative example, the incident position L2 changes by 36.79 μm (=219.83 μm-183.04 μm) between light with the minimum wavelength λ1 of the range of usable wavelengths and light with the maximum wavelength λ3 of the range of usable wavelengths.

[0114] Therefore, when light is coupled from the second waveguide grating 35 to the first waveguide grating 25, the transparent component 40 can reduce the variation of the incident position L2 of the light toward the first waveguide grating 25.

[0115] In this way, the transparent component 40 can reduce the variation in the incident position L1 of light toward the second waveguide grating 35 and the variation in the incident position L2 of light toward the first waveguide grating 25. Similarly, the transparent component 40 can also reduce the variation in the incident position (incident position L1, incident position L2) of light relative to the change in the relative position between the first optical waveguide chip 20 and the second optical waveguide chip 30.

[0116] The reason for the increased permissible alignment error between the first optical waveguide chip 20 and the second optical waveguide chip 30 in the grating coupler 1 is as follows.

[0117] Reference Figure 7 The second waveguide grating 35 diffracts light incident from the second optical waveguide 32. The intensity distribution of the diffracted light from the second waveguide grating 35 is non-uniform relative to its position x. The intensity of the diffracted light from the second waveguide grating 35 varies depending on the position x where the light is diffracted. Specifically, the intensity of the diffracted light from the second waveguide grating 35 is maximized between the grating end 36a and the grating center 36c (the region 36r in the second grating 36 near the grating end 36a). The maximum diffracted light intensity from the second waveguide grating 35 is achieved at the maximum diffraction position x, which is further away from the second waveguide grating 35. max However, the intensity of the diffracted light decreases monotonically. In contrast, the intensity distribution of the diffracted light of the second waveguide grating 35 remains almost unchanged depending on the wavelength of the light.

[0118] Furthermore, generally speaking, gratings are reversible with respect to the direction of light propagation. Therefore, the optical coupling efficiency distribution of the second waveguide grating 35 relative to the incident light is also non-uniform. The optical coupling efficiency of the second waveguide grating 35 varies depending on the incident position L1 of the light towards the second waveguide grating 35 (refer to...). Figure 5 The optical coupling efficiency of the second waveguide grating 35 varies. Specifically, the optical coupling efficiency becomes maximum between the grating end 36a and the grating center 36c (the region 36r in the second grating 36 near the grating end 36a). The optical coupling efficiency of the second waveguide grating 35 increases with increasing distance from the maximum diffraction position x. max However, it decreases monotonically. In contrast, the optical coupling efficiency distribution of the second waveguide grating 35 hardly changes according to the wavelength of light.

[0119] Therefore, when the relative positions of the first optical waveguide chip 20 and the second optical waveguide chip 30 change, the light incident from the first waveguide grating 25 to the second waveguide grating 35 at position L1 (refer to...) Figure 5 The light coupling efficiency of the second waveguide grating 35 changes as the light changes. The transparent component 40, as described above, directs light towards the incident position L1 (refer to...) of the second waveguide grating 35. Figure 5 The change in the light coupling efficiency of the second waveguide grating 35 is reduced, thus reducing the change in the light coupling efficiency of the light.

[0120] Similarly, when the relative positions of the first optical waveguide chip 20 and the second optical waveguide chip 30 change, the light travels from the second waveguide grating 35 to the incident position L2 of the first waveguide grating 25 (refer to...). Figure 6 The light coupling efficiency of the first waveguide grating 25 changes as the light changes. The transparent component 40 directs the light towards the incident position L2 of the first waveguide grating 25 (refer to...). Figure 6 The change in the light coupling efficiency of the first waveguide grating 25 relative to the light decreases as the change in the light decreases.

[0121] In this way, the transparent component 40 enables the grating coupler 1 to have a wider tolerance for alignment error. In addition, the transparent component 40 can expand the wavelength range of light coupled with the minimum allowable optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0122] Reference Figure 10 In the modified example of the grating coupler 1 in this embodiment, the transparent component 40 may also be disposed on the top surface 20a of the first chip.

[0123] The effect of the grating coupler 1 in this embodiment is explained.

[0124] The grating coupler 1 of this embodiment includes a first optical waveguide chip 20, a second optical waveguide chip 30, and a transparent component 40. The first optical waveguide chip 20 includes: a first substrate 21 including a first substrate top surface 21a, a first optical waveguide 22, a first waveguide grating 25, a first chip bottom surface 20b, a first chip top surface 20a opposite to the first chip bottom surface 20b, and a first chip end surface 20c connected to the first chip top surface 20a and the first chip bottom surface 20b. The first optical waveguide 22 is formed on the first substrate top surface 21a. The first waveguide grating 25 is formed on the first substrate top surface 21a. The first waveguide grating 25 is connected to the first optical waveguide 22 and is closer to the first chip end surface 20c than the first optical waveguide 22.

[0125] The second optical waveguide chip 30 includes a second substrate 31 containing a second substrate top surface 31a, a second optical waveguide 32, a second waveguide grating 35, and a second chip top surface 30a. The second optical waveguide 32 is formed on the second substrate top surface 31a. The second waveguide grating 35 is formed on the second substrate top surface 31a. The second waveguide grating 35 is connected to the second optical waveguide 32 and is closer to the first chip end surface 20c than the second optical waveguide 32. The second waveguide grating 35 is disposed on one side of the first substrate 21 relative to the first waveguide grating 25 in a direction in which the first chip top surface 20a and the first chip bottom surface 20b are separated from each other. Light incident on the grating coupler 1 is coupled between the first waveguide grating 25 and the second waveguide grating 35 via the first light incident / exit surface 20i of the first optical waveguide chip 20 extending along the end face 20c of the first chip and the second light incident / exit surface 30i of the second optical waveguide chip 30 extending along the top face 30a of the second chip. The optical path of light within the wavelength range of the grating coupler 1 is filled by the transparent component 40 between the first light incident / exit surface 20i and the second light incident / exit surface 30i.

[0126] The transparent component 40 reduces the variation in the incident position (incident position L1, incident position L2) of light toward the first waveguide grating 25 or the second waveguide grating 35 due to changes in the relative positions between the first waveguide chip 20 and the second waveguide chip 30. This reduces variations in the optical coupling efficiency of the first waveguide grating 25 or the second waveguide grating 35 relative to light. Therefore, the grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0127] In the grating coupler 1 of this embodiment, the exit angle θ2 of the light diffracted by the first waveguide grating 25 and directed toward the second waveguide grating 35 from the first light incident exit surface 20i (first chip end face 20c, substrate end face 21c) of the first optical waveguide chip 20 is 33° or more and 60° or less.

[0128] Therefore, it is possible to prevent a decrease in the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35, and to prevent an excessive increase in the light reflectivity in the first light incident / exit surface 20i. The optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35 can be increased. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0129] In the grating coupler 1 of this embodiment, the transparent component 40 is formed of a thermosetting resin or an ultraviolet-curing resin.

[0130] Therefore, the grating coupler 1 has a wider tolerance for alignment error. In addition, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0131] In the grating coupler 1 of this embodiment, the second waveguide grating 35 includes a first grating end (grating end 36a) near the second optical waveguide 32 and a second grating end (grating end 36b) near the first chip end face 20c. Light diffracted by the first waveguide grating 25 and traveling towards the second waveguide grating 35 is coupled to a region 36r in the second waveguide grating 35 near the first grating end.

[0132] The region 36r near the first grating end (grating end 36a) has a relatively high optical coupling efficiency in the second waveguide grating 35. Therefore, the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35 can be increased. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0133] In the grating coupler 1 of this embodiment, the second waveguide grating 35 has a second grating pitch Λ2 and a second grating width w2. The second waveguide grating 35 includes a first grating end (grating end 36a) near the second optical waveguide 32 and a second grating end (grating end 36b) near the first chip end face 20c. The second grating width w2 in the region 36r near the first grating end of the second waveguide grating 35 is greater than 0% and less than or equal to 30% of the second grating pitch Λ2, or greater than 70% and less than 100% of the second grating pitch Λ2.

[0134] Therefore, the intensity distribution of diffracted light from the second waveguide grating 35 relative to its position can be made smoother. Light can be diffracted with higher diffraction efficiency over a wider area of ​​the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0135] In the grating coupler 1 of this embodiment, the first waveguide grating 25 has a first grating pitch Λ1 and a first grating width w1. The first grating width w1 is more than 0.4 times and less than 0.6 times the first grating pitch Λ1.

[0136] Therefore, the diffraction efficiency of the first diffracted light in the first waveguide grating 25 increases, while the diffraction efficiency of the higher-order diffracted light in the first waveguide grating 25 decreases. This increases the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0137] In the grating coupler 1 of this embodiment, the first grating pitch Λ1 of the first waveguide grating 25 decreases as it moves away from the first optical waveguide 22.

[0138] Therefore, the light diffracted by the first waveguide grating 25 can converge in the second waveguide grating 35. This increases the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error. In addition, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0139] In the grating coupler 1 of this embodiment, the first waveguide grating 25 is a stepped grating with multiple steps.

[0140] Therefore, the diffraction efficiency of higher-order diffracted light in the first waveguide grating 25 decreases, while the diffraction efficiency of first-order diffracted light in the first waveguide grating 25 increases. This increases the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0141] In the grating coupler 1 of this embodiment, the multiple steps are inclined steps.

[0142] Therefore, the diffraction efficiency of higher-order diffracted light in the first waveguide grating 25 is further reduced, and the diffraction efficiency of first-order diffracted light in the first waveguide grating 25 is further increased. This allows for a further increase in the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0143] In the grating coupler 1 of this embodiment, the first grating 26 of the first waveguide grating 25, when viewed from above the top surface 20a of the first chip, has an elliptical arc shape that expands toward the end surface 20c of the first chip. The second grating 36 of the second waveguide grating 35, when viewed from above the top surface 30a of the second chip, has an elliptical arc shape that expands toward the end surface 20c of the first chip.

[0144] Therefore, light diffracted by the first waveguide grating 25 can converge in the second waveguide grating 35. The second waveguide grating 35 can receive the light converged by the first waveguide grating 25 with higher optical coupling efficiency. Alternatively, light diffracted by the second waveguide grating 35 can converge in the first waveguide grating 25. The first waveguide grating 25 can receive the light converged by the second waveguide grating 35 with higher optical coupling efficiency. This increases the optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35. The grating coupler 1 has a wider tolerance for alignment error. Furthermore, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0145] In the grating coupler 1 of this embodiment, the first waveguide grating 25 includes a first core layer (core layer 23) formed of a compound semiconductor material. The second waveguide grating 35 includes a second core layer (core layer 33) formed of silicon.

[0146] Therefore, even though the first optical waveguide chip 20 and the second optical waveguide chip 30 are formed of different materials, the grating coupler 1 has a wider tolerance for alignment error. Furthermore, even though the first optical waveguide chip 20 and the second optical waveguide chip 30 are formed of different materials, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0147] The grating coupler 1 in this embodiment further includes a first patch (first sub-patch 11) on which the first optical waveguide chip 20 is mounted and a second patch (second sub-patch 12) on which the second optical waveguide chip 30 is mounted. The second height (height h2) of the second patch is lower than the first height (height h1) of the first patch.

[0148] Therefore, the first patch (first sub-patch 11) and the second patch (second sub-patch 12) can be used to arrange the second waveguide grating 35 on one side of the first substrate 21 relative to the first waveguide grating 25 in a direction in which the top surface 20a and the bottom surface 20b of the first chip are separated from each other.

[0149] In the grating coupler 1 of this embodiment, the difference between the first refractive index of the transparent component 40 and the second refractive index of the uppermost part (e.g., the upper cladding 34b) of the second optical waveguide chip 30 including the second light incident and exit surface 30i is 0.20 or less.

[0150] Therefore, the reflection of light in the second light incident and exit surface 30i can be reduced. The optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35 is increased. The grating coupler 1 has a wider tolerance for alignment error. In addition, the grating coupler 1 can expand the wavelength range of light coupled with the minimum allowable optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0151] Implementation method 2.

[0152] Reference Figure 11 This describes the grating coupler 1b of Embodiment 2. The grating coupler 1b of this embodiment includes the grating coupler 1 of the variant of Embodiment 1 (see [reference]). Figure 10 The same structure, but different in the following aspects.

[0153] The grating coupler 1b does not have a first sub-pattern 11 and a second sub-pattern 12 (see reference). Figure 10The second optical waveguide chip is fixed to the main surface 10a of the patch 10. The first optical waveguide chip 20 is placed on the top surface 30a of the second chip. Specifically, a bonding member 48, such as solder or adhesive, is disposed between the bottom surface 20b of the first optical waveguide chip 20 and the top surface 30a of the second optical waveguide chip 30. The first optical waveguide chip 20 is fixed to the top surface 30a of the second chip using the bonding member 48.

[0154] In addition to the effects of the grating coupler 1 in Embodiment 1, the grating coupler 1b of this embodiment also has the following effects.

[0155] In the grating coupler 1b of this embodiment, the first optical waveguide chip 20 is mounted on the top surface 30a of the second chip.

[0156] No need to use sub-patch 11 and sub-patch 12 (see reference) Figure 10 The second waveguide grating 35 can be disposed on one side of the first substrate 21 relative to the first waveguide grating 25 in a direction in which the top surface 20a and the bottom surface 20b of the first chip are separated from each other. The first sub-pattern 11 and the second sub-pattern 12 are not required (see reference). Figure 10 Therefore, it is possible to miniaturize the grating coupler 1b and reduce its cost.

[0157] Implementation method 3.

[0158] Reference Figure 12 The grating coupler 1c of Embodiment 3 is described below. The grating coupler 1c of this embodiment has the same structure as the grating coupler 1b of Embodiment 2, but differs mainly in the following aspects.

[0159] In the grating coupler 1c, the entire first optical waveguide chip 20 and the entire second optical waveguide chip 30 are covered by a transparent component 40. The first optical waveguide chip 20 and the second optical waveguide chip 30 are sealed by the transparent component 40.

[0160] In addition to the effects of the grating coupler 1b in embodiment 2, the grating coupler 1c of this embodiment also has the following effects.

[0161] In the grating coupler 1c of this embodiment, the entire first optical waveguide chip 20 and the entire second optical waveguide chip 30 are covered by a transparent component 40. Therefore, the transparent component 40 can protect the first optical waveguide chip 20 and the second optical waveguide chip 30 from humidity or mechanical impact, thus extending the lifespan of the grating coupler 1c.

[0162] Implementation method 4.

[0163] Reference Figure 13The grating coupler 1d of Embodiment 4 is described below. The grating coupler 1d of this embodiment has the same structure as the grating coupler 1 of Embodiment 1, but differs mainly in the following aspects.

[0164] In the grating coupler 1d, the transparent component 40 includes a transparent adhesive layer 41 and a transparent block 42. The transparent block 42 is transparent within the operating wavelength range of the grating coupler 1d. The transparent block 42 is formed, for example, of glass or transparent plastic. The transparent block 42 is bonded to the first light incident / exit surface 20i (first chip end face 20c) and the second light incident / exit surface 30i (second chip top face 30a) via the transparent adhesive layer 41. The transparent adhesive layer 41 is transparent within the operating wavelength range of the grating coupler 1d. The transparent adhesive layer 41 is formed, for example, of a thermosetting resin or a photocurable resin. The transparent adhesive layer 41 is formed, for example, of an epoxy resin or an acrylic resin.

[0165] The difference between the refractive index of the transparent adhesive layer 41 and the refractive index of the uppermost part (upper cladding layer 34b in this embodiment) of the second optical waveguide chip 30, including the second light incident / exit surface 30i, can also be 0.20 or less. Therefore, the reflection of light in the second light incident / exit surface 30i can be reduced. The difference between the refractive index of the transparent component 40 and the refractive index of the upper cladding layer 34b can be 0.15 or less, 0.10 or less, or 0.05 or less.

[0166] The difference between the refractive index of the transparent adhesive layer 41 and the refractive index of the transparent block 42 can also be less than 0.10. Therefore, light reflection at the interface between the transparent adhesive layer 41 and the transparent block 42 can be reduced. The difference between the refractive index of the transparent adhesive layer 41 and the refractive index of the transparent block 42 can also be less than 0.05. Alternatively, the refractive indices of the transparent adhesive layer 41 and the transparent block 42 can be equal.

[0167] In addition to the effects of the grating coupler 1 in Embodiment 1, the grating coupler 1d in this embodiment also has the following effects.

[0168] In the grating coupler 1d of this embodiment, the transparent component 40 includes a transparent adhesive layer 41 and a transparent block 42. The transparent block 42 is bonded to the first light incident / exit surface 20i and the second light incident / exit surface 30i through the transparent adhesive layer 41.

[0169] Even if the space between the first light incident / exit surface 20i and the second light incident / exit surface 30i is large, this space can be easily filled by the transparent component 40, which includes the transparent block 42. The grating coupler 1 has a wider tolerance for alignment error. In addition, the grating coupler 1 can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0170] Implementation method 5.

[0171] Reference Figure 14 The grating coupler 1e of Embodiment 5 is described below. The grating coupler 1e of this embodiment has the same structure as the grating coupler 1 of Embodiment 1, but differs mainly in the following aspects.

[0172] In the grating coupler 1e, the first optical waveguide chip 20 also includes a laser structure 50. In this specification, the laser structure 50 means a structure capable of amplifying light through stimulated emission. The laser structure 50 is, for example, a laser source or an optical amplifier. Specifically, the laser structure 50 is, for example, a semiconductor laser source or a semiconductor optical amplifier. A first optical waveguide 22 is disposed between the laser structure 50 and the first waveguide grating 25. The first optical waveguide 22 couples light emitted from the laser structure 50 to the first waveguide grating 25.

[0173] The laser structure 50 includes an active region 51 optically coupled to the first optical waveguide 22. The active region 51 is formed, for example, of an InGaAsP-based or AlGaAs-based compound semiconductor material. The active region 51 may also have a multiple quantum well (MQW) structure. The active region 51 is formed, for example, on the first substrate 21 (top surface 21a of the first substrate). The active region 51 can also be directly connected to the first optical waveguide 22 via a mating connector or the like.

[0174] The laser structure 50 also includes an upper cladding layer 52, a contact layer 53, an upper electrode 54, and a lower electrode 55. The first substrate 21 is, for example, an n-type InP substrate. The upper cladding layer 52 is formed on the active region 51. The upper cladding layer 52 is, for example, a p-type InP layer. The contact layer 53 is, for example, a p-type InGaAs layer. The upper electrode 54 is formed on the contact layer 53. The lower electrode 55 is disposed on the bottom surface 21b of the first substrate 21. The surface of the lower electrode 55 on the side opposite to the bottom surface 21b of the first substrate is the bottom surface 20b of the first chip.

[0175] The first optical waveguide chip 20 also includes an anti-reflective film 57 disposed on the first chip end face 20c (substrate end face 21c). The anti-reflective film 57 reduces light reflection in the first chip end face 20c (substrate end face 21c). The anti-reflective film 57 may be formed, for example, of a material having a higher refractive index than the transparent component 40, such as silicon nitride or tantalum oxide. The anti-reflective film 57 may also be, for example, a dielectric multilayer film in which low refractive index dielectric layers such as silicon oxide and high refractive index dielectric layers such as silicon nitride or tantalum oxide are alternately stacked. In this embodiment, the first light incident and exit surface 20i is the surface of the anti-reflective film 57 on the side opposite to the first chip end face 20c.

[0176] In the first example of this embodiment, the first optical waveguide chip 20 may also be a semiconductor laser source, the second optical waveguide chip 30 may also be an optical modulator, and the grating coupler 1e may also be an optical transmitter. In the second example of this embodiment, the first optical waveguide chip 20 may also be a semiconductor optical amplifier (SOA), and the second optical waveguide chip 30 may also be part of an external resonator.

[0177] In addition to the effects of the grating coupler 1 in Embodiment 1, the grating coupler 1e in this embodiment also has the following effects.

[0178] In the grating coupler 1e of this embodiment, the first optical waveguide chip 20 further includes an anti-reflection film 57 disposed on the end face 20c of the first chip.

[0179] Therefore, the reflection of light in the first light incident and exit surface 20i can be reduced. The optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35 is increased. The grating coupler 1e has a wider tolerance for alignment error. In addition, the grating coupler 1e can expand the wavelength range of light coupled with the minimum permissible optical coupling efficiency between the first waveguide grating 25 and the second waveguide grating 35.

[0180] In the grating coupler 1e of this embodiment, the first optical waveguide chip 20 further includes a laser structure 50. The first optical waveguide 22 is disposed between the laser structure 50 and the first waveguide grating 25. The laser structure 50 includes an active region 51 optically coupled to the first optical waveguide 22.

[0181] The laser structure 50 is integrated into the first optical waveguide chip 20 of the grating coupler 1e. Since the laser structure 50 does not need to be set up separately from the grating coupler 1e, the optical system including the grating coupler 1e and the laser structure 50 can be miniaturized. The grating coupler 1e can be used as an optical transmitter or an optical amplifier.

[0182] The embodiments 1 to 5 and their variations disclosed herein should be considered illustrative rather than restrictive in all respects. At least two of embodiments 1 to 5 and their variations may be combined, provided there is no contradiction. The scope of this disclosure is set forth in the claims rather than in the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A grating coupler, comprising: First optical waveguide chip; The second optical waveguide chip; and Transparent components, among which, The first optical waveguide chip includes: a first substrate including a top surface of a first substrate, a first optical waveguide formed on the top surface of the first substrate, a first waveguide grating formed on the top surface of the first substrate, a bottom surface of the first chip, a top surface of the first chip on the side opposite to the bottom surface of the first chip, and a first chip end face connected to the top surface and the bottom surface of the first chip. The first waveguide grating is connected to the first optical waveguide and is closer to the end face of the first chip than the first optical waveguide. The second optical waveguide chip includes: a second substrate including a top surface of a second substrate, a second optical waveguide formed on the top surface of the second substrate, a second waveguide grating formed on the top surface of the second substrate, and a top surface of the second chip. The second waveguide grating is connected to the second optical waveguide and is closer to the end face of the first chip than the second optical waveguide. The second waveguide grating is disposed on one side of the first substrate relative to the first waveguide grating in a direction in which the top surface and the bottom surface of the first chip are separated from each other. Light incident on the grating coupler is coupled between the first waveguide grating and the second waveguide grating via a first light incident / exit surface of the first optical waveguide chip extending along the end face of the first chip and a second light incident / exit surface of the second optical waveguide chip extending along the top face of the second chip. The optical path of the light within the operating wavelength range of the grating coupler is filled by the transparent component between the first light incident and exit surface and the second light incident and exit surface. Compared to the absence of the transparent component, the transparent component is configured to reduce the variation in the incident position of light incident on the grating coupler within the wavelength range of use.

2. The grating coupler according to claim 1, wherein, The exit angle of the light diffracted by the first waveguide grating and directed toward the second waveguide grating from the first light incident and exit surface of the first optical waveguide chip is greater than 33° and less than 60°.

3. The grating coupler according to claim 1 or 2, wherein, The transparent component is formed of a thermosetting resin or an ultraviolet-curing resin.

4. The grating coupler according to claim 1 or 2, wherein, The transparent component includes a transparent adhesive layer and a transparent block. The transparent block is bonded to the first light incident and exit surface and the second light incident and exit surface through the transparent adhesive layer.

5. The grating coupler according to claim 1 or 2, wherein, The entire first optical waveguide chip and the entire second optical waveguide chip are covered by the transparent component.

6. The grating coupler according to claim 1 or 2, wherein, The second waveguide grating includes a first grating end near the second optical waveguide and a second grating end near the end face of the first chip. The light diffracted by the first waveguide grating and traveling toward the second waveguide grating is coupled to a region in the second waveguide grating near the end of the first grating.

7. The grating coupler according to claim 1 or 2, wherein, The second waveguide grating has a second grating spacing and a second grating width. The second waveguide grating includes a first grating end near the second optical waveguide and a second grating end near the end face of the first chip. The width of the second grating in the region near the end of the first grating in the second waveguide grating is greater than 0% and less than or equal to 30% of the second grating spacing, or greater than 70% and less than 100% of the second grating spacing.

8. The grating coupler according to claim 1 or 2, wherein, The first waveguide grating has a first grating spacing and a first grating width. The width of the first grating is more than 0.4 times and less than 0.6 times the pitch of the first grating.

9. The grating coupler according to claim 1 or 2, wherein, The spacing of the first grating of the first waveguide grating decreases as it moves away from the first optical waveguide.

10. The grating coupler according to claim 1 or 2, wherein, The first waveguide grating is a stepped grating with multiple steps.

11. The grating coupler according to claim 10, wherein, The aforementioned steps are inclined steps.

12. The grating coupler according to claim 1 or 2, wherein, The first waveguide grating has an elliptical arc shape that expands toward the end face of the first chip when viewed from above the top surface of the first chip. The second waveguide grating has an elliptical arc shape that expands toward the end face of the first chip when viewed from above.

13. The grating coupler according to claim 1 or 2, wherein, The first waveguide grating includes a first core layer formed of a compound semiconductor material. The second waveguide grating includes a second core layer formed of silicon.

14. The grating coupler according to claim 1 or 2, wherein, The first optical waveguide chip also includes an anti-reflective film disposed on the end face of the first chip.

15. The grating coupler according to claim 1 or 2, wherein, The first optical waveguide chip also includes a laser structure. The first optical waveguide is disposed between the laser structure and the first waveguide grating. The laser structure includes an active region optically coupled to the first optical waveguide.

16. The grating coupler according to claim 1 or 2, wherein, It also has: The first patch, on which the first optical waveguide chip is mounted; and The second patch carries the second optical waveguide chip. The second height of the second patch is lower than the first height of the first patch.

17. The grating coupler according to claim 1 or 2, wherein, The first optical waveguide chip is mounted on the top surface of the second chip.

18. The grating coupler according to claim 1 or 2, wherein, The difference between the first refractive index of the transparent component and the second refractive index of the uppermost part of the second optical waveguide chip, which includes the second light incident and exit surface, is less than 0.20.

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