Optical circuit and method for manufacturing the same

Abstract

The present invention provides an optical circuit capable of efficiently coupling multiple optical waveguides. [Solution] The optical circuit comprises a first optical waveguide 20A including a first cladding layer 22, a second cladding layer 24, and a first core layer disposed between the first and second cladding layers; a second optical waveguide 20B including a third cladding layer, a fourth cladding layer 26, and a second core layer disposed between the third and fourth cladding layers; and a third optical waveguide 30 including a fifth cladding layer, a sixth cladding layer 34, and a third core layer disposed between the fifth and sixth cladding layers. The first and third cladding layers are provided on a first substrate, and the fifth cladding layer is provided on a second substrate made of a material different from the material of the first substrate. In a second direction different from the first direction in which the first and second optical waveguides are aligned, the third optical waveguide optically couples with the first and second optical waveguides.

Description

[Technical Field]

[0001] This disclosure relates to optical circuits and methods for manufacturing the same. [Background technology]

[0002] Optical circuits, which integrate semiconductor optical elements and optical waveguides on a substrate, are in high demand in the fields of optical communication and optical sensors. In optical circuits, multiple active optical waveguides, such as a laser light source, an optical modulator, and a photodetector, are optically coupled using a passive optical waveguide. A configuration has been proposed in which a laser diode, an optical modulator, and a passive optical waveguide are provided on a support substrate having a cladding layer on its surface (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-046258 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, forming multiple active optical waveguides, such as laser diodes and optical modulators, and passive optical waveguides on a common cladding layer is often difficult because the materials used for the active and passive optical waveguides are different. Therefore, efficiently optically coupling multiple active optical waveguides via passive optical waveguides is challenging.

[0005] The purpose of this disclosure is to provide an optical circuit and a method for manufacturing the same that can efficiently couple multiple optical waveguides. [Means for solving the problem]

[0006] According to embodiments of the present disclosure, the optical circuit comprises: a first optical waveguide including a first cladding layer, a second cladding layer, and a first core layer disposed between the first and second cladding layers; a second optical waveguide including a third cladding layer, a fourth cladding layer, and a second core layer disposed between the third and fourth cladding layers; and a third optical waveguide including a fifth cladding layer, a sixth cladding layer, and a third core layer disposed between the fifth and sixth cladding layers, wherein the first and third cladding layers are provided on a first substrate, and the fifth cladding layer is provided on a second substrate made of a material different from the material of the first substrate, and the third optical waveguide optically couples with the first and second optical waveguides in a second direction different from the first direction in which the first and second optical waveguides are aligned.

[0007] According to embodiments of the present disclosure, a method for manufacturing an optical circuit involves preparing a first laminate on a first substrate, having a first portion having a first cladding layer, a first core layer, and a second cladding layer in that order, and a second portion having a third cladding layer, a second core layer, and a fourth cladding layer in that order; preparing a second laminate on a second substrate, having a fifth cladding layer and a third core layer in that order; arranging the first and second laminates so that the first core layer and the second core layer face the third core layer; and bonding the second cladding layer, the fourth cladding layer, and the third core layer to a temporary substrate. The process includes: joining the first substrate and the second substrate to a common substrate; removing the temporary substrate after joining the first substrate and the second substrate to the common substrate; processing the first laminate to obtain a first optical waveguide including the first cladding layer, the first core layer, and the second cladding layer, and a second optical waveguide including the third cladding layer, the second core layer, and the fourth cladding layer; and processing the second laminate to obtain a third optical waveguide including at least the fifth cladding layer and the third core layer, which optically couples to the first optical waveguide and the second optical waveguide. [Effects of the Invention]

[0008] According to the present disclosure, a plurality of optical waveguides can be efficiently coupled. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [Figure 1] FIG. 1 is a plan view of an optical circuit according to a first embodiment. [Figure 2A] FIG. 2A is a cross-sectional view taken along line IIA-IIA in FIG. 1. [Figure 2B] FIG. 2B is a cross-sectional view taken along line IIB-IIB in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view of an optical circuit according to a comparative structure. [Figure 5A] FIG. 5A is a cross-sectional view of an optical circuit according to a first modification of the first embodiment. [Figure 5B] FIG. 5B is a cross-sectional view of an optical circuit according to a first modification of the first embodiment. [Figure 6] FIG. 6 is a plan view of an optical circuit according to a second modification of the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 6. [Figure 8] FIG. 8 is a plan view of an optical circuit according to a second embodiment. [Figure 9A] FIG. 9A is a cross-sectional view illustrating a method for manufacturing an optical circuit according to a second embodiment. [Figure 9B] FIG. 9B is a cross-sectional view illustrating a method for manufacturing an optical circuit according to a second embodiment. [Figure 9C] FIG. 9C is a cross-sectional view illustrating a method for manufacturing an optical circuit according to a second embodiment. [Figure 10A] FIG. 10A is a cross-sectional view illustrating a method for manufacturing an optical circuit according to a second embodiment. [Figure 10B] FIG. 10B is a cross-sectional view illustrating a method for manufacturing an optical circuit according to a second embodiment. [Figure 10C] FIG. 10C is a cross-sectional view illustrating a method for manufacturing an optical circuit according to a second embodiment. [Figure 11A]Figure 11A is a plan view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 11B] Figure 11B is a plan view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 12A] Figure 12A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 12B] Figure 12B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 13A] Figure 13A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 13B] Figure 13B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 14A] Figure 14A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 14B] Figure 14B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 15A] Figure 15A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 15B] Figure 15B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 16A] Figure 16A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 16B] Figure 16B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 17A] Figure 17A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 17B] Figure 17B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 18A] Figure 18A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 18B] Figure 18B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 19A] Figure 19A is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 19B]Figure 19B is a cross-sectional view showing a method for manufacturing an optical circuit according to the second embodiment. [Figure 20] Figure 20 is a plan view of the optical circuit according to the third embodiment. [Figure 21] Figure 21 is a plan view of an optical circuit according to a first modified example of the third embodiment. [Figure 22] Figure 22 is a plan view of an optical circuit according to a second modified example of the third embodiment. [Figure 23] Figure 23 is a plan view of an optical circuit according to a third modified example of the third embodiment. [Modes for carrying out the invention]

[0010] The embodiments for implementing this disclosure will be described in detail below with reference to the drawings. The embodiments described below are examples for embodying the technical concept of the invention and do not limit this disclosure to the configurations and numerical values ​​described. In each drawing, the same reference numerals are used for the same components, and redundant explanations may be omitted as appropriate. The size, positional relationships, etc., of each component shown in each drawing may be exaggerated to facilitate understanding of the invention.

[0011] (First Embodiment) Figure 1 is a plan view of the optical circuit according to the first embodiment. Figure 2A is a cross-sectional view along the line IIA-IIA in Figure 1. Figure 2B is a cross-sectional view along the line IIB-IIB in Figure 1. Figure 3 is a cross-sectional view along the line III-III in Figure 1. In the thickness direction of the substrate 10, the stacking direction of each layer is the Z direction, the direction in which the optical waveguides 20A and 20B are aligned is the Y direction, and the direction perpendicular to the Y direction and the Z direction is the X direction. Figure 3 shows the optical waveguides 20A and 20B in a cross-section in the XZ plane, and the optical waveguides 30 and 30A in a cross-section along the core layer 33.

[0012] As shown in Figures 1 to 3, the optical circuit 100 comprises a substrate 10 and optical waveguides 20A, 20B, 30, and 30A. The optical waveguides 20A, 20B, 30, and 30A are arranged on the substrate 10. The optical waveguide 20A (i.e., the first optical waveguide) has a substrate 21 (i.e., the first substrate), a cladding layer 22 (i.e., the first cladding layer), a core layer 23 (i.e., the first core layer), and a cladding layer 24 (i.e., the second cladding layer). The core layer 23 is located between the cladding layers 22 and 24. The cladding layer 22 is closer to the substrate 21 than the cladding layer 24. The optical axis of the optical waveguide 20A is in the X direction.

[0013] The optical waveguide 20B (second optical waveguide) has a substrate 21, a cladding layer 22 (i.e., a third cladding layer), a core layer 25 (i.e., a second core layer), and a cladding layer 26 (i.e., a fourth cladding layer). The core layer 25 is located between the cladding layers 22 and 26. The cladding layer 22 is closer to the substrate 21 than the cladding layer 26. The optical axis of the optical waveguide 20B is in the X direction.

[0014] The substrate 21 and the cladding layer 22 are shared in optical waveguides 20A and 20B. That is, the cladding layer 22 of optical waveguide 20A and the cladding layer 22 of optical waveguide 20B are arranged on the same substrate 21. Furthermore, the cladding layer 22 of optical waveguide 20A and the cladding layer 22 of optical waveguide 20B are the same cladding layer. Note that the cladding layer 22 of optical waveguide 20A and the cladding layer 22 of optical waveguide 20B may contain different cladding layers. The substrate 21 may also function as a cladding layer together with the cladding layer 22. Although optical waveguides 20A and 20B are illustrated as examples of optical waveguides having a ridge structure, optical waveguides 20A and 20B may be other refractive index waveguides or gain waveguides. In Figure 2A, the ridge in optical waveguide 20A refers to the convex portion formed in the cladding layer 24. Furthermore, in optical waveguide 20B, the ridge refers to the convex portion including the cladding layer 22, core layer 25, and cladding layer 26. Thus, the ridge represents the convex portion that contributes to the lateral confinement of optical waveguides 20A and 20B. In other words, it represents the portion where the channel protrudes more than the rest.

[0015] The optical waveguide 30 (third optical waveguide) has a substrate 31 (i.e., second substrate), a cladding layer 32 (i.e., fifth cladding layer), a core layer 33 (i.e., third core layer), and a cladding layer 34 (i.e., sixth cladding layer). The core layer 33 is located between the cladding layers 32 and 34. The cladding layer 32 is closer to the substrate 31 than the cladding layer 34.

[0016] The optical waveguide 30A (the fourth optical waveguide) has a substrate 31A (i.e., the third substrate), a cladding layer 32A (i.e., the seventh cladding layer), a core layer 33A (i.e., the fourth core layer), and a cladding layer 34A (i.e., the eighth cladding layer). The core layer 33A is located between the cladding layers 32A and 34A. The cladding layer 32A is closer to the substrate 31A than the cladding layer 34A.

[0017] Substrate 21 and substrates 31 and 31A are made of different materials, for example. Substrates 31 and 31A may be made of the same material or different materials. In Figures 2B and 3, the lower ends of the ridges of the optical waveguides 30 and 30A are shown as coinciding with the lower ends of the core layers 33 and 33A, but the lower ends of the ridges do not have to coincide with the lower ends of the core layers 33 and 33A. Preferably, the lower ends of the ridges coincide with the lower ends of the core layers 33 and 33A or are located within the cladding layers 32 and 32A. This reduces bending loss.

[0018] The optical waveguides 20A and 20B are, for example, nitride semiconductor devices, and at least a portion of the substrate 21, cladding layers 22, 24, 26, and core layers 23 and 25 includes a nitride semiconductor. The nitride semiconductor is, for example, GaN, AlN, InN, and mixed crystals thereof AlGaN, InGaN, AlInN, and AlInGaN. The core layers 23 and 25 are, for example, single-crystal nitride semiconductor layers. The cladding layers 22, 24, and 26 are, for example, nitride semiconductor layers. The cladding layers 24 and 26 may also be transparent conductive layers. The transparent conductive layer is, for example, ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide).

[0019] The refractive index of the core layer 23 is higher than the refractive indices of the cladding layers 22 and 24. The refractive index of the core layer 25 is higher than the refractive indices of the cladding layers 22 and 26. Thereby, in the Z direction, light is confined in the core layers 23 and 25. The cladding layers 22, 24 and 26 include at least one layer selected from the group consisting of an Al-containing AlGaN layer, an AlInN layer and an AlInGaN layer, for example. The core layers 23 and 25 include at least one layer selected from the group consisting of a GaN layer and an InGaN layer, for example.

[0020] When the optical waveguide 20A is a laser light source or a light receiving element, the cladding layer 22 is, for example, Al x Ga 1-x N (0≦x≦1). The cladding layer 24 is, for example, Al x Ga 1-x N (0≦x≦1) or a transparent conductive material. The cladding layer 22 is n-type doped with Si, Ge or the like, and the cladding layer 24 is p-type doped with Mg or the like. The dopant concentration of the cladding layer 22 is, for example, 1×10 18 cm -3 - 5×10 19 cm -3 The cladding layers 22 and 24 do not need to contain impurities, and n-type or p-type conductivity may be formed by polarization doping by gradiently changing the composition of the semiconductor layer. The dopant concentration of the cladding layer 24 is, for example, 1×10 18 cm -3 - 1×10 20 cm -3 The core layer 23 contains In z Ga 1-z N (0≦z≦1), and includes an active layer having a quantum well structure. When the optical waveguide 20B is an optical modulator, the material of the cladding layer 26 is a nitride semiconductor, and the core layer 25 is a single layer of undoped GaN or Al y Ga 1-y N (0≦y≦1) and In z Ga 1-zThis includes quantum wells of size N (excluding 0≦z≦1 and y=0 and z=0). "Undoped" refers to a state where impurities are not intentionally doped. It also includes states where doping is unavoidable. For example, an undoped quantum well has an impurity concentration of 1 × 10⁻¹⁶. 17 cm -3 The following conditions are also included. Furthermore, undoping may be performed even if the impurity concentration is below the detection limit in SIMS (Secondary Ion Mass Spectrometry).

[0021] Optical waveguides 30 and 30A are, for example, passive optical waveguides. Substrates 31 and 31A are semiconductor substrates or insulating substrates such as silicon, sapphire, or calcium fluoride. Cladding layers 32, 34, 32A, 34A, and core layers 33 and 33A are amorphous or single-crystal oxides, nitrides, or fluorides. It is preferable that the cladding layers 32, 34, 32A, 34A, and core layers 33 and 33A are amorphous. This makes it possible to reduce the losses in optical waveguides 30 and 30A compared to the case of single crystals. The refractive index of core layer 33 is higher than that of cladding layers 32 and 34. The refractive index of core layer 33A is higher than that of cladding layers 32A and 34A. As a result, in the Z direction, light is confined to core layers 33 and 33A. Generally, nitrides have a higher refractive index than oxides and fluorides. Therefore, it is preferable that the core layers 33 and 33A are oxides or nitrides, and the cladding layers 32, 34, 32A, and 34A are oxides or fluorides. By making the core layers 33 and 33A and the cladding layers 32, 34, 32A, and 34A amorphous materials, the refractive index of each layer can be easily adjusted, and the refractive index difference between the core layers 33 and 33A and the cladding layers 32, 34, 32A, and 34A can be increased. This makes it possible to strengthen optical confinement in the core layers 33 and 33A. By strengthening optical confinement, the bending loss of the curved waveguide can be reduced.

[0022] The cladding layers 32, 34, 32A, 34A, and the core layers 33 and 33A can be made of, for example, SiO2, SiN, SiON, Al2O3, AlN, AlON, Ta2O5, Nb2O5, TiO2, HfO2, ZrO2, TaSiO, TaTiO, TaZrO, TaNbO, MgF2, CaF2, and mixtures thereof.

[0023] The optical waveguide 30 has waveguides 35A, 35B, and 35C. Waveguides 35A and 35C are straight waveguides, and their optical axes are in the X direction. Waveguide 35B is a curved waveguide, and its optical axis is curved, for example, along an arc. Waveguide 35A faces optical waveguide 20A in the X direction. Waveguide 35C faces optical waveguide 20B in the X direction. The optical axes of waveguide 35A and optical waveguide 20A are coaxial, and the optical axes of waveguide 35C and optical waveguide 20B are coaxial. This improves the efficiency of optical coupling between waveguide 35A and optical waveguide 20A, and improves the efficiency of optical coupling between waveguide 35C and optical waveguide 20B. The coupling efficiency between optical waveguides 20A and 30, and between optical waveguides 20B and 30, are, for example, 50% or more but less than 100%, 75% or more but less than 100%, or 90% or more but less than 100%. It is preferable that the width of waveguide 35A in the Y direction and the width of optical waveguide 20A in the Y direction are the same. It is also preferable that the width of waveguide 35C in the Y direction and the width of optical waveguide 20B in the Y direction are the same. This makes it easier to align the optical axes in the Y direction. Note that the width of the waveguides may change between waveguide 35A and waveguide 35C.

[0024] For example, optical waveguide 20A is a laser light source, optical waveguide 30 is a passive optical waveguide, and optical waveguide 20B is an optical modulator. In this case, laser light is incident from optical waveguide 20A into waveguide 35A in the +X direction as indicated by arrow 50A. The laser light is bent by waveguide 35B. Laser light is incident from waveguide 35C into optical waveguide 20B in the -X direction as indicated by arrow 50B. Laser light is emitted from optical waveguide 20B in the -X direction as indicated by arrow 50C.

[0025] The optical axis of waveguide 35A and the optical axis of optical waveguide 20A do not need to be strictly coaxial. The optical axis of waveguide 35C and the optical axis of optical waveguide 20B do not need to be strictly coaxial. The optical axes of optically coupled waveguides may have angular misalignment and axial misalignment in the X, Y, or Z directions within the range in which optical coupling is possible. The angular misalignment of the optical axes may be 10° or less, preferably 1° or less, and more preferably 0.5° or less. The axial misalignment of the optical axis in the Y direction may be 50% or less of the width of the smaller of the two coupled optical waveguides in the Y direction, preferably 10% or less, and more preferably 1% or less. The axial misalignment of the optical axis in the Z direction may be 50% or less of the width of the smaller of the two coupled optical waveguides in the Z direction, preferably 10% or less, and more preferably 1% or less.

[0026] (Comparison structure) Optical circuits sometimes use multiple active optical waveguides (e.g., a laser light source, an optical modulator, and a photodetector). By providing multiple active optical waveguides on the same substrate, the heights of their core layers can be aligned. Since the multiple active optical waveguides are provided separately on the substrate, they are coupled via a passive optical waveguide. In this case, it is conceivable to form the passive optical waveguide on the same substrate as the active optical waveguide. However, the materials for the core and cladding layers of the active optical waveguide are determined by the function of the active optical waveguide. If the materials for the core and cladding layers of the active optical waveguide are used for the core and cladding layers of the passive optical waveguide, the losses of the passive optical waveguide will increase. On the other hand, it can be difficult to provide the core and cladding layers of a passive optical waveguide with low losses on the same substrate as the active optical waveguide.

[0027] The effects of the first embodiment will be described below with reference to the comparative structure. The comparative structure is a structure based on Patent Document 1. Figure 4 is a cross-sectional view of the optical circuit according to the comparative structure. As shown in Figure 4, in the optical circuit 110 according to the comparative structure, the optical waveguides 120A, 120B and 130 are arranged on the same substrate 31. The cladding layers 132 of the optical waveguides 120A, 120B and 130 are identical.

[0028] It is conceivable to attach a portion of optical waveguide 120A (the portion above core layer 123), a portion of optical waveguide 120B (the portion above core layer 125), and a portion of optical waveguide 130 (the portion above core layer 133) onto the cladding layer 132. However, if optical waveguides 120A and 120B contain nitride semiconductors, it is difficult to cut out the portions of optical waveguides 120A and 120B above core layers 123 and 125. Therefore, it is difficult to attach a portion of optical waveguides 120A and 120B onto the cladding layer 132.

[0029] When the cladding layer 132 is used as the cladding layer for the optical waveguide 130, the cladding layer 132 is amorphous, and even if an attempt is made to deposit nitride semiconductor core layers 123 and 125 on the cladding layer 132, the films cannot be deposited properly.

[0030] When the cladding layer 132 is used as the cladding layer for optical waveguides 120A and 120B, the cladding layer 32 is a nitride semiconductor. Nitride semiconductors have a high refractive index. Therefore, it becomes difficult to confine light in the core layer 133 in the optical waveguide 130.

[0031] If core layer 133 is made of a nitride semiconductor in order to increase its refractive index, then core layers 123, 133, and 125 will be grown separately. In this case, as a result of regrowing different types of nitride semiconductors, non-flat regions are formed at the regrowth boundaries. This leads to a decrease in the coupling efficiency between optical waveguides.

[0032] As described above, it is difficult to efficiently optically couple multiple optical waveguides 120A and 120B.

[0033] (Description of the first embodiment) According to the first embodiment, the cladding layer 22 of optical waveguide 20A and the cladding layer 22 of optical waveguide 20B are provided on the substrate 21. The cladding layer 32 of optical waveguide 30 is provided on the substrate 31. The substrate 31 is made of a different material from the substrate 21.

[0034] By not providing the optical waveguide 30 on the substrate 21, the material of the substrate 21 can be made a material suitable for forming the optical waveguides 20A and 20B. This allows the functions of the optical waveguides 20A and 20B (for example, a laser light source, an optical modulator, or a light-emitting element) to be exhibited. By forming the optical waveguide 30 on the substrate 31 made of a material different from that of the substrate 21, the substrate 31 can be made a material suitable for forming the optical waveguide 30. This allows the function of the optical waveguide 30 (for example, a low-loss optical waveguide) to be exhibited.

[0035] Here, "different materials" refers to, for example, Al x Ga 1-x N (0≦x≦1) and other nitride semiconductors, versus oxides or fluorides such as SiO2, Al2O3, MgF2, which have different material systems. On the other hand, in a case where only the mixed crystal ratio x is different, such as Al x Ga 1-x N (0<x<1), this shall be treated as "the same material". However, when the mixed crystal ratio x is 0 or 1, that is, GaN and AlN shall be regarded as different materials. The same applies to other material systems.

[0036] In a second direction different from the Y direction in which the optical waveguides 20A and 20B are arranged (that is, the first direction) (for example, the X direction), the optical waveguide 30 is optically coupled to the optical waveguide 20A and is also optically coupled to the optical waveguide 20B. Accordingly, even when the optical waveguides 20A and 20B are provided on the same substrate 21, the optical waveguides 20A and 20B can be coupled using the optical waveguide 30.

[0037] When core layers 23 and 25 contain nitride semiconductors, it becomes difficult to form optical waveguides 20A, 20B, and 30 on the substrate 31, as explained using the comparative structure. Therefore, it is preferable to separate substrate 21 and substrate 31. If substrate 21 is, for example, a GaN substrate, using a GaN substrate for substrate 31 tends to make the optical circuit expensive. On the other hand, by separating the materials of substrate 21 and substrate 31, an inexpensive substrate can be used in parts where a GaN substrate is not needed, and the optical circuit can be manufactured at a low cost. Core layers 23 and 25 may be made of materials other than nitride semiconductors.

[0038] The cladding layer 32A of the optical waveguide 30A is provided on a substrate 31A made of a different material from the substrate 21. Substrate 31A is provided on the opposite side of substrate 21. Optical waveguide 30A is optically coupled to optical waveguide 20B. This allows optical waveguide 20B to be coupled to another optical waveguide 30A.

[0039] The core layers 33 and 33A and the cladding layers 32, 34, 32A, and 34A are made of either oxides, nitrides, or fluorides. This reduces the losses in the optical waveguides 30 and 30A. In addition, the core layers 33 and 33A and the cladding layers 32, 34, 32A, and 34A are amorphous. This makes it easy to create a refractive index difference between the core layers 33 and 33A and the cladding layers 32, 34, 32A, and 34A, thus facilitating the formation of curved waveguides.

[0040] (First embodiment, first modified example) A first modification of the first embodiment is an example in which electrodes are electrically connected to the optical waveguides 20A and 20B. Figures 5A and 5B are cross-sectional views of an optical circuit according to a first modification of the first embodiment. As shown in Figures 5A and 5B, in the optical circuits 101 and 102 according to a first modification of the first embodiment, the common cladding layer 22 includes recesses 12A (i.e., the second recess), 12B (i.e., the first recess), and 12C (i.e., the third recess). Recess 12B is located between the optical waveguides 20A and 20B. Recess 12A is located on the opposite side of recess 12B with the optical waveguide 20A in between. Recess 12C is located on the opposite side of recess 12B with the optical waveguide 20B in between. Recesses 12A to 12C are portions whose bottom surface is lower than the interface between the cladding layer 22 and the core layers 23 and 25. The recesses 12A to 12C do not need to be completely surrounded by walls; it is sufficient if only a portion of their surroundings is surrounded by walls.

[0041] Electrodes 13 (i.e., the first electrode) and 15 (i.e., the third electrode) are provided in any of the recesses 12A to 12C of the cladding layer 22 and are electrically connected to the cladding layer 22. Electrode 13 is the electrode that connects to the cladding layer 22 of the optical waveguide 20A, and electrode 15 is the electrode that connects to the cladding layer 22 of the optical waveguide 20B. Electrode 14 (i.e., the second electrode) is provided on the cladding layer 24 and is electrically connected to the cladding layer 24. Electrode 16 (i.e., the fourth electrode) is provided on the cladding layer 26 and is electrically connected to the cladding layer 26.

[0042] In the optical circuit 101 of Figure 5A, electrodes 13 and 15 are provided in recesses 12A and 12C, respectively. In the optical circuit 102 of Figure 5B, electrodes 13 and 15 are provided in recesses 12B and 12C, respectively.

[0043] According to the first modification of the first embodiment, the cladding layer 22 of optical waveguide 20A and the cladding layer 22 of optical waveguide 20B are a single integrated cladding layer 22. Electrodes 13 and 15 are connected to the cladding layer 22, and electrodes 14 and 16 are connected to cladding layers 24 and 26, respectively. By using an integrated cladding layer 22, the cladding layer 22 can be used as a ground layer, thereby reducing electrical noise.

[0044] Electrode 13 is placed in recess 12A or recess 12B, and electrode 15 is placed in recess 12B or recess 12C. This allows electrode 13 to be placed near optical waveguide 20A and electrode 15 to be placed near optical waveguide 20B. Thus, the parasitic resistance between electrode 13 and optical waveguide 20A, and the parasitic resistance between electrode 15 and optical waveguide 20B can be reduced.

[0045] When used as a single cladding layer 22, the difference between the thickness of the core layer 23 and the thickness of the core layer 25 is preferably 100 nm or less. This brings the centers of the core layer 23 and the core layer 25 in the Y direction closer together. Therefore, the coupling efficiency between optical waveguides 20A and 20B via the optical waveguide 30 can be increased.

[0046] (Second modified example of the first embodiment) A second modification of the first embodiment is an example in which an amorphous optical waveguide is provided between optical waveguides 20A and 20B and optical waveguide 30. Figure 6 is a plan view of the optical circuit according to the second modification of the first embodiment. Figure 7 is a cross-sectional view along the line VII-VII in Figure 6. As shown in Figures 6 and 7, an amorphous optical waveguide 36A (i.e., the first amorphous optical waveguide) is arranged between optical waveguides 20A and 30. An amorphous optical waveguide 36B (i.e., the second amorphous optical waveguide) is arranged between optical waveguides 20B and 30. An amorphous optical waveguide 36C is arranged between optical waveguides 20B and 30A.

[0047] The amorphous optical waveguide 36A has a cladding layer 37A, a core layer 38A, and a cladding layer 39A. The core layer 38A is located between the cladding layers 37A and 39A. The amorphous optical waveguide 36B has a cladding layer 37B, a core layer 38B, and a cladding layer 39B. The core layer 38B is located between the cladding layers 37B and 39B.

[0048] The material of amorphous optical waveguides 36A to 36C is, for example, the same as the material of optical waveguides 30 and 30A. At least a portion of amorphous optical waveguide 36A, at least a portion of amorphous optical waveguide 36B, and at least a portion of amorphous optical waveguide 36C contains amorphous material. The refractive index of core layers 38A to 38C is higher than that of cladding layers 37A to 37C and 39A to 39C. This allows light to be confined in core layers 38A to 38C.

[0049] When optical waveguides 20A and 30 are optically coupled, if the refractive indices of core layers 23 and 33 are different, light is easily reflected between the optical waveguides 20A and 30. For example, if optical waveguide 20A contains a nitride semiconductor, the refractive index of core layer 23 is higher than that of core layer 33. Therefore, the refractive index of core layer 38A is made lower than that of core layer 23 and higher than that of core layer 33. This reduces the reflection of light between optical waveguides 20A and 30. The refractive indices of cladding layers 37A and 39A are made lower than that of cladding layers 22 and 24 and higher than that of cladding layers 32 and 34. This reduces the reflection of light between optical waveguides 20A and 30. Amorphous materials allow for easy control of the refractive index by adjusting the composition. Therefore, the core layers 38A-38C, cladding layers 37A-37C, and 39A-39C can be made of amorphous material.

[0050] Furthermore, in order to reduce light reflection between optical waveguides 20B and 30, the refractive index of core layer 38B is made lower than that of core layer 25 and higher than that of core layer 33. The refractive index of cladding layers 37B and 39B is made lower than that of cladding layers 22 and 26 and higher than that of cladding layers 32 and 34. This reduces light reflection between optical waveguides 20B and 30.

[0051] When the width Y1 of optical waveguide 20A in the Y direction and the width Y2 of optical waveguide 30 in the Y direction are the same, the width Y3 of amorphous optical waveguide 36A in the Y direction is set to be the same as widths Y1 and Y2. This allows for higher coupling efficiency of transverse modes between optical waveguides 20A and 30 compared to the case where width Y3 is different from widths Y1 and Y2. Since optical waveguide 20A has a ridge structure, the ridge width of the cladding layer 24 is set to the width Y1 of optical waveguide 20A. The widths of core layers 33 and 38A are set to the width Y2 of optical waveguide 30 and the width Y3 of amorphous optical waveguide 36A, respectively. Here, width Y3 being the same as width Y1 means that width Y3 is within ±10% of width Y1. Similarly, for optically coupled optical waveguides, if the width of one optical waveguide is the same as the width of the other optical waveguide, it means that the width of one optical waveguide is within ±10% of the width of the other optical waveguide.

[0052] Similarly, when the width Y4 of optical waveguide 20B in the Y direction and the width Y2 of optical waveguide 30 in the Y direction are the same, the width Y5 of amorphous optical waveguide 36B in the Y direction is made the same as widths Y2 and Y4. This allows for a higher coupling efficiency of transverse modes between optical waveguides 20B and 30 compared to the case where width Y5 is different from widths Y4 and Y2.

[0053] Similarly, when the width Y4 of optical waveguide 20B in the Y direction and the width Y6 of optical waveguide 30A in the Y direction are the same, the width Y7 of amorphous optical waveguide 36C in the Y direction is set to be the same as widths Y4 and Y6. This allows for a higher coupling efficiency of transverse modes between optical waveguides 20B and 30A compared to the case where width Y7 is different from widths Y4 and Y6.

[0054] Furthermore, if the difference between the width Y1 of optical waveguide 20A in the Y direction and the width Y2 of optical waveguide 30 in the Y direction is large, transverse mode mismatch is likely to occur between optical waveguides 20A and 30. In this case, the width Y3 of amorphous optical waveguide 36A in the Y direction is set to be between widths Y1 and Y2. This makes it possible to increase the transverse mode coupling efficiency between optical waveguides 20A and 30.

[0055] Similarly, when the width Y4 of optical waveguide 20B and the width Y2 of optical waveguide 30 are different, the width Y7 of amorphous optical waveguide 36B in the Y direction is set to be between the width Y4 of optical waveguide 20B and the width Y6 of optical waveguide 30. This makes it possible to increase the coupling efficiency of transverse modes between optical waveguides 20B and 30.

[0056] Furthermore, the end faces of optical waveguides 20A and 20B may be inclined with respect to the crystal orientation. In this case, due to the inclined surfaces, the end faces of optical waveguides 20A and 20B cannot be brought close enough to the end face of optical waveguide 30, which may reduce the coupling efficiency between optical waveguides 20A and 30, between optical waveguides 20B and 30, and between optical waveguides 20B and 30A. Therefore, by providing amorphous optical waveguides 36A to 36C, the optical coupling efficiency can be improved. This is because amorphous optical waveguides 36A to 36C can be formed to fill the gaps between optical waveguides 20A and 30, and between optical waveguides 20B and 30.

[0057] (Second Embodiment) The second embodiment is an embodiment illustrating a method for manufacturing an optical circuit. Figure 8 is a plan view of the optical circuit according to the second embodiment. As shown in Figure 8, the optical circuit 104 according to the second embodiment is provided with an optical waveguide 20C and an optical circuit section 58 in addition to the optical circuit of the first embodiment.

[0058] The optical waveguide 20C has a core layer 27 and cladding layers 22 and 28. The core layer 27 is located between the cladding layers 22 and 28. The cladding layer 22 is closer to the substrate 21 than the cladding layer 28. The optical circuit section 58 is formed by the optical waveguide 30A. The optical waveguide 20A is, for example, a laser light source, the optical waveguide 20B is, for example, an optical modulator, and the optical waveguide 20C is, for example, a photodetector. The optical circuit section 58 may have desired functions, such as an interferometer, a resonator, a wavelength-selective filter, an optical switch, or an optical isolator.

[0059] Figures 9A to 10C are cross-sectional views showing the manufacturing method of the optical circuit according to the second embodiment, and correspond to the IXA-IXA cross-section in Figure 8.

[0060] As shown in Figure 9A, a substrate 21 is prepared. The substrate 21 is an insulating substrate or a semiconductor substrate, for example, a GaN substrate. A cladding layer 22, a core layer 23, and a cladding layer 24 are deposited sequentially on the substrate 21. For depositing the cladding layer 22, core layer 23, and cladding layer 24, for example, the MOCVD (Metal Organic Chemical Vapor Deposition) method is used. As shown in Figure 9B, a portion of the core layer 23 and cladding layer 24 is removed using an etching method. This forms a laminated structure 40A consisting of the cladding layer 22, core layer 23, and cladding layer 24. As shown in Figure 9C, a patterned mask layer 41 is formed on the cladding layers 22 and 24. The mask layer 41 has an opening 41A. The mask layer 41 is an inorganic material, for example, a silicon oxide layer.

[0061] As shown in Figure 10A, a core layer 25 and a cladding layer 26 are selectively deposited sequentially on the cladding layer 22 within the opening 41A. For example, MOCVD is used to deposit the core layer 25 and the cladding layer 26. This forms a laminated structure 40B consisting of the cladding layer 22, the core layer 25, and the cladding layer 26. As shown in Figure 10B, the mask layer 41 is removed. Next, the mask layer is formed, the core layer 27 and the cladding layer 28 are deposited, and the mask layer is removed to obtain a laminated body 40 as shown in Figure 10C. This forms the core layer 27 and the cladding layer 28 on the cladding layer 22. A laminated structure 40C consisting of the cladding layer 22, the core layer 27, and the cladding layer 28 is formed. A laminated body 40 having laminated structures 40A to 40C is formed. There are no particular restrictions on the height relationship of each core layer 23, 25, and 27 in the laminated structures 40A to 40C, but it is preferable that they be the same height. As a result, if optical waveguides 30 and 30A are formed at the same height, optical coupling with optical waveguides 20A, 20B, and 20C becomes possible, thus simplifying manufacturing. A protective film 48 may be formed on the laminate 40. The protective film 48 is an inorganic insulating film, such as a silicon oxide film.

[0062] Figures 11A and 11B are plan views showing a method for manufacturing an optical circuit according to the second embodiment. As shown in Figure 11A, the stacked structures 40A to 40C are formed on a wafer 43. The stacked structures 40A to 40C are arranged periodically in the Y direction. As shown in Figure 11B, the wafer 43 is divided into individual pieces along lines 44 and 45. The wafer 43 is divided into individual pieces by dicing or cleavage. For example, it is diced along line 44 and cleaved along line 45. This forms a plurality of stacked bodies 40.

[0063] Figures 12A and 12B are cross-sectional views showing a method for manufacturing an optical circuit according to the second embodiment, representing the manufacturing process along the XIIA-XIIA line and the XIIB-XIIB line in Figure 8, respectively. As shown in Figure 12A, a cladding layer 32, a core layer 33, and a protective film 47 are formed on the substrate 31. This forms a laminate 42 having the cladding layer 32, the core layer 33, and the protective film 47. As shown in Figure 12B, a cladding layer 32A, a core layer 33A, and a protective film 47A are formed on the substrate 31A. This forms a laminate 42A having the cladding layer 32A, the core layer 33A, and the protective film 47A.

[0064] For the formation of the cladding layers 32, 32A, core layers 33, 33A, and protective films 47 and 47A, for example, CVD or PVD (Physical Vapor Deposition) methods are used. The protective films 47 and 47A are inorganic insulating films, such as silicon oxide films. The laminates 42 and 42A may be heat-treated. Heat treatment can reduce the loss of core layers 33 and 33A.

[0065] In this way, by forming the laminate 40 and the laminates 42 and 42A separately, thermal damage to each laminate can be reduced compared to when they are formed as a single unit.

[0066] Figures 13A to 16B are cross-sectional views showing a method for manufacturing an optical circuit according to the second embodiment. Figures 13A, 14A, 15A, and 16A are cross-sectional views showing the manufacturing process along the line XIIIA-XIIIA in Figure 8, while Figures 13B, 14B, 15B, and 16B are cross-sectional views showing the manufacturing process along the line XIIIB-XIIIB in Figure 8. Figures 13A to 15B are shown with the top and bottom (Z direction) reversed.

[0067] As shown in Figures 13A and 13B, a temporary substrate 46 is prepared. The temporary substrate 46 is a semiconductor substrate such as a silicon substrate or an insulating substrate. The end face of the laminate 42 in the -X direction is brought into contact with the end face of the laminate 40 in the +X direction. The end face of the core layer 23 in the +X direction faces the end face of the core layer 33 in the -X direction, and the end face of the core layer 25 in the +X direction faces the end face of the core layer 33 in the -X direction. The end face of the laminate 42A in the +X direction is brought into contact with the end face of the laminate 40 in the -X direction. The end face of the core layer 25 in the -X direction faces the end face of the core layer 33A in the +X direction. In this state, the laminates 40, 42 and 42A are bonded to the temporary substrate 46. For bonding the temporary substrate 46 to the laminates 40, 42 and 42A, for example, atomic diffusion bonding, hydroxyl group bonding, or surface activation bonding can be used.

[0068] As shown in Figures 14A and 14B, the heights of the laminates 40, 42, and 42A are made uniform by polishing at least one of the substrates 21, 31, and 31A. The heights of the laminates 40, 42, and 42A may also be made uniform by polishing at least one of the substrates of the laminates 40, 42, and 42A before fixing the laminates 40, 42, and 42A to the temporary substrate 46.

[0069] As shown in Figures 15A and 15B, the substrate 10 is bonded to the side of the laminates 40, 42, and 42A opposite to the temporary substrate 46. For bonding the laminates 40, 42, and 42A to the substrate 10, for example, surface activation bonding, atomic diffusion bonding, or hydroxyl group bonding is used. The bonding of the temporary substrate 46 to the laminates 40, 42, and 42A, and the bonding of the laminates 40, 42, and 42A to the substrate 10, is preferably performed at a relatively low temperature from the viewpoint of reducing thermal stress. From this viewpoint, it is preferable to use surface activation bonding or atomic diffusion bonding for bonding. The temperature during the bonding process may be, for example, 90°C or lower, 70°C or lower, 50°C or lower, or 40°C or lower.

[0070] As shown in Figures 16A and 16B, the temporary substrate 46 is removed. For example, an etching method is used to remove the temporary substrate 46. Preferably, the temporary substrate 46 is made of a material that is easily etched from the laminates 40 and 42.

[0071] Figures 17A and 17B show a method for manufacturing an optical circuit according to the second embodiment, and are cross-sectional views corresponding to the cross-section along the line XVIIA-XVIIA in Figure 8. The protective film 48 on the cladding layers 24 and 26 is removed.

[0072] As shown in Figure 17B, desired regions of cladding layers 24 and 26 are removed using photolithography and etching. This forms a ridge structure on cladding layers 24 and 26. Desired regions of core layers 23 and 25 are removed using photolithography and etching. This separates core layers 23 and 25. As a result, optical waveguides 20A and 20B are separated. At this time, recesses 12A to 12C and electrodes 13 to 16 shown in Figures 5A and 5B may be formed. Subsequently, an inorganic insulating film such as a silicon oxide film may be formed as a protective film to cover cladding layer 22, core layers 23 and 25, and cladding layers 24 and 26. As a result, optical waveguides 20A and 20B are formed. Optical waveguide 20C is formed in the same manner.

[0073] Figures 18A to 19B are cross-sectional views showing a method for manufacturing an optical circuit according to the second embodiment, and correspond to the cross-sections along the XIIA-XIIA line and the XIIB-XIIB line in Figure 8. As shown in Figure 18A, in the state shown in Figures 16A and 16B, protective films 47 and 47A are formed on the core layers 33 and 33A.

[0074] As shown in Figure 18B, the protective films 47, 47A, core layers 33, and 33A in the desired region are removed using photolithography and etching. At this time, recesses may be formed in the cladding layer 32.

[0075] As shown in Figure 19A, protective films 47 and 47A on the core layers 33 and 33A are removed using an etching method. As shown in Figure 19B, cladding layers 34 and 34A are formed on the cladding layer 32 so as to cover the core layers 33 and 33A. The cladding layers 34 and 34A are formed using, for example, a CVD method or a PVD method. At least a portion of the protective films 47 and 47A may be used as at least a portion of the cladding layers 34 and 34A. The optical circuit 104 of the second embodiment is thus manufactured.

[0076] According to the second embodiment, a laminate 40 (i.e., first laminate) having a laminated structure 40A (i.e., first part) and a laminated structure 40B (i.e., second part) is prepared as shown in Figures 9A to 11B. A laminate 42 (i.e., second laminate) is prepared as shown in Figure 12A. Laminates 40 and 42 are arranged so that the core layers 23 and 25 face the core layer 33, and the cladding layers 24 and 26 and the core layer 33 are bonded to a temporary substrate 46 as shown in Figures 13A and 13B. Substrates 21 and 31 are bonded to a substrate 10 (i.e., common substrate) as shown in Figures 15A and 15B. The temporary substrate 46 is removed as shown in Figures 16A and 16B. Laminates 40 are processed to obtain optical waveguides 20A and 20B as shown in Figures 17A and 17B. Laminates 42 are processed to obtain an optical waveguide 30 as shown in Figures 18A to 19B. This manufacturing method makes it possible to produce an optical circuit 104 in which optical waveguides 20A and 20B and optical waveguide 30 are optically coupled.

[0077] As shown in Figure 11B, the laminate 40 is obtained by cleavage along the Y direction. This makes the end faces of the core layers 23, 25, and 27 cleavage surfaces. The flatness of the end faces of the core layers 23, 25, and 27 can be improved. Therefore, the coupling efficiency between the optical waveguides 20A and 20B and the optical waveguide 30 can be improved.

[0078] As shown in Figure 12B, a laminate 42A (i.e., the third laminate) is prepared. As shown in Figure 13B, the laminate 42A is positioned on the opposite side of the laminate 42 from the laminate 40, with the core layer 33 facing the core layer 33A, and the laminate 42A is bonded to the temporary substrate 46. As shown in Figures 18A to 19B, the laminate 42A is processed to obtain an optical waveguide 30A that includes at least a cladding layer 32A and a core layer 33A and optically couples with the optical waveguide 20B. By this manufacturing method, an optical circuit 104 in which the optical waveguide 20B and the optical waveguide 30A are optically coupled can be manufactured.

[0079] (Third embodiment) The third embodiment is an example of an optical gyro sensor using the first embodiment and its modifications. Figure 20 is a plan view of the optical circuit according to the third embodiment. As shown in Figure 20, the optical circuit 105 according to the third embodiment comprises laminates 40, 42, 42A, and 42B. Laminate 40 has a laser light source 64 as an optical waveguide 20A and an optical modulator 65 as an optical waveguide 20B. Laminate 42 has an optical waveguide 30. The optical waveguide 30 forms a waveguide 61A. Laminate 42A has an optical waveguide 30A. The optical waveguide 30A forms optical branch circuits 60A, 60B, waveguides 61B, 61C1, 61C2, 61D1, 61D2, and a ring resonator 62. Laminate 42B comprises optical waveguides 20D1 and 20D2. Optical waveguides 20D1 and 20D2 are photodetectors 66A and 66B, respectively.

[0080] Laser light emitted from the laser light source 64 is incident on the optical modulator 65 via the waveguide 61A. The optical modulator 65 modulates the phase of the incident light. The light emitted from the optical modulator 65 is split into waveguides 61C1 and 61C2 with a 1:1 intensity by the optical branching circuit 60A. Waveguides 61C1 and 61C2 are optically coupled to a ring resonator 62. Light traveling through waveguide 61C1 rotates the ring resonator 62 counterclockwise, and light traveling through waveguide 61C2 rotates the ring resonator 62 clockwise. When the optical circuit 105 rotates, the optical path lengths of the light rotating the ring resonator 62 clockwise and the light rotating counterclockwise differ due to the Sagnac effect. That is, when the optical circuit 105 rotates, the frequencies of the light rotating the ring resonator 62 clockwise and the light rotating counterclockwise differ.

[0081] The laser light from waveguides 61C1 and 61C2 is incident on optical branching circuit 60B. When optical circuit 105 rotates, the phases of the two beams of light incident on optical branching circuit 60B become different. Optical branching circuit 60B is an interferometer and interferes with the laser light from waveguide 61C1 and the light from waveguide 61C2. This creates an intensity difference between the light emitted from optical branching circuit 60B to waveguide 61D1 and the laser light emitted from optical branching circuit 60B to waveguide 61D2. Photodetectors 66A and 66B monitor the light emitted from waveguides 61D1 and 61D2, respectively. Based on the output signals of photodetectors 66A and 66B, the rotation of optical circuit 105 can be detected. The rotation of optical circuit 105 can be detected using either photodetector 66A or 66B alone, but detection accuracy can be improved by using both.

[0082] (First modified example of the third embodiment) The first modification of the third embodiment is an example of an optical intensity control circuit using the first embodiment and its modification. Figure 21 is a plan view of an optical circuit according to the first modification of the third embodiment. As shown in Figure 21, the optical circuit 106 according to the first modification of the third embodiment comprises laminates 40, 42, and 42A. Laminate 40 has a laser light source 64 as an optical waveguide 20A, and optical modulators 65A and 65B as optical waveguides 20B1 and 20B2, respectively. Laminate 42 has an optical waveguide 30. The optical waveguide 30 forms an optical branching circuit 60C, and waveguides 61A, 61E1, and 61E2. Laminate 42A has an optical waveguide 30A. The optical waveguide 30A forms an optical branching circuit 60D, and waveguides 61F1, 61F2, 61G1, and 61G2.

[0083] The laser light emitted from the laser light source 64 enters the optical branching circuit 60C via the waveguide 61A. The light that enters the optical branching circuit 60C is branched into waveguides 61E1 and 61E2. The light from waveguides 61E1 and 61E2 enters optical modulators 65A and 65B, respectively. Optical modulators 65A and 65B independently modulate the phase of the light emitted from waveguides 61E1 and 61E2, respectively. The light output from optical modulators 65A and 65B enters the optical branching circuit 60D via waveguides 61F1 and 61F2, respectively. The optical branching circuit 60D interferes with the light that entered from waveguides 61F1 and 61F2 and outputs it to waveguides 61G1 and 61G2.

[0084] The light intensity output to waveguides 61G1 and 61G2 can be controlled by the phase difference of the light in optical modulators 65A and 65B. The optical branch circuits 60A and 60B of Embodiment 3 and the optical branch circuits 60C and 60D of the first modified example of Embodiment 3 can be appropriately selected, for example, a directional coupler, a Y-shaped waveguide, or a multimode interference type branch circuit.

[0085] (Second modified example of the third embodiment) A second modification of the third embodiment is an example of a beam-steering optical circuit using the first embodiment and its modifications. Figure 22 is a plan view of the optical circuit according to the second modification of the third embodiment. As shown in Figure 22, the optical circuit 107 according to the second modification of the third embodiment comprises laminates 40, 42, and 42A. Laminate 40 has a laser light source 64 as an optical waveguide 20A and optical modulators 65A to 65D as optical waveguides 20B1 to 20B4, respectively. Laminate 42 has an optical waveguide 30. The optical waveguide 30 forms waveguides 61A, 61H1, 61H2, and 61I1 to 61I4. Laminate 42A has an optical waveguide 30A. The optical waveguide 30A forms grating couplers 67A to 67D and waveguides 61J1 to 61J4.

[0086] The laser light emitted from the laser light source 64 is branched through waveguide 61A to waveguides 61H1 and 61H2, and further branched to waveguides 61I1 to 61I4. The light from waveguides 61I1 to 61I4 is incident on optical modulators 65A to 65D, respectively. Optical modulators 65A to 65D independently modulate the phase of the light emitted from waveguides 61I1 to 61I4, respectively. The light output from optical modulators 65A to 65D is incident on grating couplers 67A to 67D via waveguides 61J1 to 61J4, respectively. Grating couplers 67A to 67D emit light into space.

[0087] The optical modulators 65A to 65D modulate the phase of the light, causing the light emitted from grating couplers 67A to 67D to interfere with each other. This enables beam steering of the light emitted from grating couplers 67A to 67D. Although an example with four grating couplers 67A to 67D and four optical modulators 65A to 65D has been described, the number of grating couplers 67A to 67D and optical modulators 65A to 65D can be multiple.

[0088] (Third modified example of the third embodiment) Figure 23 is a plan view of an optical circuit according to a third modification of the third embodiment. As shown in Figure 23, in the optical circuit 108 according to the third modification of the third embodiment, the optical waveguide 30 is equipped with a ring resonator 62A. The ring resonator 62A is optically coupled to the waveguide 61A. The ring resonator 62A is a wavelength filter and wavelength filters the light emitted from the laser light source 64. As a result, it is possible to generate laser light with a narrower spectral width compared to the second modification shown in Figure 22. The other configurations are the same as the third modification of the third embodiment and are therefore omitted from the description.

[0089] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0090] This disclosure includes the following components. (Section 1) A first optical waveguide comprising a first cladding layer, a second cladding layer, and a first core layer disposed between the first cladding layer and the second cladding layer, A second optical waveguide comprising a third cladding layer, a fourth cladding layer, and a second core layer disposed between the third cladding layer and the fourth cladding layer, A third optical waveguide comprising a fifth cladding layer, a sixth cladding layer, and a third core layer disposed between the fifth cladding layer and the sixth cladding layer, Equipped with, The first cladding layer and the third cladding layer are provided on the first substrate. The fifth cladding layer is provided on a second substrate made of a material different from the material of the first substrate. In a second direction different from the first direction in which the first optical waveguide and the second optical waveguide are aligned, the third optical waveguide optically couples with the first optical waveguide and the second optical waveguide. optical circuit. (Section 2) The optical circuit according to item 1, wherein the material of the first core layer includes a nitride semiconductor. (Section 3) The aforementioned first cladding layer and the aforementioned third cladding layer are a single cladding layer. A first electrode connected to the first cladding layer, A second electrode connected to the aforementioned second cladding layer, A third electrode connected to the aforementioned third cladding layer, A fourth electrode connected to the aforementioned fourth cladding layer, The optical circuit according to item 1 or 2, comprising: (Section 4) The optical circuit according to item 3, wherein the integral cladding layer has a first recess between the first optical waveguide and the second optical waveguide aligned in the first direction. (Section 5) The aforementioned integrated cladding layer has a second recess on the opposite side of the first recess with respect to the first optical waveguide, and a third recess on the opposite side of the first recess with respect to the second optical waveguide, The first electrode is located in the first recess or the second recess, and the third electrode is located in the first recess or the third recess. The optical circuit described in item 4. (Section 6) A first amorphous optical waveguide is disposed between the first optical waveguide and the third optical waveguide, A second amorphous optical waveguide is disposed between the second optical waveguide and the third optical waveguide, Furthermore, An optical circuit as described in any one of items 1 to 5. (Section 7) The optical circuit according to any one of claims 1 to 6, wherein the third core layer, the fifth cladding layer, and the sixth cladding layer are one of oxides, nitrides, and fluorides. (Section 8) The first cladding layer is Al x Ga 1-x An optical circuit described in any one of items 1 to 7, including N(0≦x≦1). (Section 9) The material of the fourth cladding layer is a nitride semiconductor. The second core layer is a single layer of i-GaN or Al y Ga 1-yN(0≦y≦1) and In z Ga 1-z Includes a quantum well of size N (excluding 0≦z≦1, y=0 and z=0), An optical circuit as described in any one of items 1 through 8. (Section 10) A fourth optical waveguide comprising a seventh cladding layer, an eighth cladding layer, and a fourth core layer disposed between the seventh cladding layer and the eighth cladding layer, It further possesses, The seventh cladding layer is provided on a third substrate made of a material different from the material of the first substrate. The third substrate is provided on the side opposite to the second substrate relative to the first substrate, The fourth optical waveguide optically couples with the second optical waveguide. An optical circuit as described in any one of items 1 through 9. (Section 11) The fourth optical waveguide is the optical circuit according to item 10, including a grating coupler. (Section 12) The second substrate further comprises a ring resonator that optically couples with the third optical waveguide, The ring resonator is a wavelength filter for the first optical waveguide. An optical circuit as described in any one of items 1 through 11. (Section 13) The fourth optical waveguide includes an optical branching circuit. The optical circuit described in item 10. (Section 14) The fourth optical waveguide further includes a ring resonator and an interferometer. It includes a light-receiving element that monitors the output from the interferometer, The optical circuit described in item 13. (Section 15) To prepare a first laminate having a first portion on a first substrate, having a first cladding layer, a first core layer, and a second cladding layer in that order, and a second portion having a third cladding layer, a second core layer, and a fourth cladding layer in that order. A second laminate is prepared on the second substrate, having a fifth cladding layer and a third core layer in that order. The first and second laminates are arranged so that the first core layer and the second core layer face the third core layer, and the second cladding layer, the fourth cladding layer, and the third core layer are bonded to a temporary substrate. The first substrate and the second substrate are joined to a common substrate. After the first substrate and the second substrate are bonded to the common substrate, the temporary substrate is removed. The first laminate is processed to obtain a first optical waveguide including the first cladding layer, the first core layer, and the second cladding layer, and a second optical waveguide including the third cladding layer, the second core layer, and the fourth cladding layer, and The second laminate is processed to obtain a third optical waveguide which includes at least the fifth cladding layer and the third core layer and optically couples with the first optical waveguide and the second optical waveguide. A method for manufacturing an optical circuit, including the method described above. (Section 16) A method for manufacturing an optical circuit according to claim 15, wherein the first laminate, comprising the first portion and the second portion, is obtained by cleavage along a first direction in which the first portion and the second portion are aligned. (Section 17) A third laminate is prepared having a seventh cladding layer and a fourth core layer on a third substrate in that order. The third laminate is positioned on the side of the first laminate that is opposite to the second laminate, with the second core layer facing the fourth core layer, and the fourth core layer is bonded to the temporary substrate, and After the temporary substrate is removed following bonding to the common substrate, the third laminate is processed to obtain a fourth optical waveguide that includes at least the seventh cladding layer and the fourth core layer and is optically coupled to the second optical waveguide. A method for manufacturing an optical circuit as described in item 15 or 16, including the method described in item 15 or 16. [Explanation of symbols]

[0091] 10, 21, 31, 31A: Circuit board 12A, 12B, 12C: Recessed 13, 14, 15, 16: Electrode 20A, 20B, 20B1, 20B2, 20B3, 20B4, 20C, 20D1, 20D2, 30, 30A: Optical waveguide 22, 24, 26, 32, 32A, 34, 34A, 37A, 37B, 37C, 39A, 39B, 39C: Cladding layer 23, 25, 27, 33, 33A, 38A, 38B, 38C: Core layer 35A, 35B, 35C: Waveguide 40, 42, 42A, 42B: Laminate 40A, 40B, 40C: Laminated structure 60A, 60B, 60C, 60D: Optical branching circuits 62, 62A: Ring resonator 64: Laser light source 65, 65A, 65B, 65C, 65D: Optical modulators 67A, 67B, 67C, 67D: Grating coupler

Claims

1. A first optical waveguide comprising a first cladding layer, a second cladding layer, and a first core layer disposed between the first cladding layer and the second cladding layer, A second optical waveguide comprising a third cladding layer, a fourth cladding layer, and a second core layer disposed between the third cladding layer and the fourth cladding layer, A third optical waveguide comprising a fifth cladding layer, a sixth cladding layer, and a third core layer disposed between the fifth cladding layer and the sixth cladding layer, Equipped with, The first cladding layer and the third cladding layer are provided on the first substrate. The fifth cladding layer is provided on a second substrate made of a material different from the material of the first substrate. In a second direction different from the first direction in which the first optical waveguide and the second optical waveguide are aligned, the third optical waveguide optically couples with the first optical waveguide and the second optical waveguide. optical circuit.

2. The optical circuit according to claim 1, wherein the material of the first core layer includes a nitride semiconductor.

3. The aforementioned first cladding layer and the aforementioned third cladding layer are a single cladding layer. A first electrode connected to the first cladding layer, The second electrode connected to the second cladding layer, A third electrode connected to the aforementioned third cladding layer, The fourth electrode connected to the fourth cladding layer, The optical circuit according to claim 1 or 2, comprising:

4. The optical circuit according to claim 3, wherein the integral cladding layer has a first recess between the first optical waveguide and the second optical waveguide, which are aligned in the first direction.

5. The integral cladding layer has a second recess on the opposite side of the first recess with respect to the first optical waveguide, and a third recess on the opposite side of the first recess with respect to the second optical waveguide, The first electrode is positioned in the first recess or the second recess, and the third electrode is positioned in the first recess or the third recess. The optical circuit according to claim 4.

6. A first amorphous optical waveguide is disposed between the first optical waveguide and the third optical waveguide, A second amorphous optical waveguide is disposed between the second optical waveguide and the third optical waveguide, Furthermore, The optical circuit according to claim 1 or 2.

7. The optical circuit according to claim 1 or 2, wherein the third core layer, the fifth cladding layer, and the sixth cladding layer are any of oxides, nitrides, and fluorides.

8. The first cladding layer is Al ｘ Ga １－ｘ The optical circuit according to claim 1 or 2, including N (0 ≤ x ≤ 1).

9. The material of the fourth cladding layer is a nitride semiconductor. The second core layer is a single layer of i-GaN or Al ｙ Ga １－ｙ N (0 ≤ y ≤ 1) and In ｚ Ga １－ｚ Including quantum wells of size N (excluding 0 ≤ z ≤ 1, y = 0 and z = 0), The optical circuit according to claim 1 or 2.

10. A fourth optical waveguide comprising a seventh cladding layer, an eighth cladding layer, and a fourth core layer disposed between the seventh cladding layer and the eighth cladding layer, It further possesses, The seventh cladding layer is provided on a third substrate made of a material different from the material of the first substrate. The third substrate is provided on the side opposite to the second substrate relative to the first substrate, The fourth optical waveguide optically couples with the second optical waveguide. The optical circuit according to claim 1 or 2.

11. The optical circuit according to claim 10, wherein the fourth optical waveguide includes a grating coupler.

12. The second substrate further comprises a ring resonator that optically couples with the third optical waveguide, The ring resonator is a wavelength filter for the first optical waveguide. The optical circuit according to claim 1 or 2.

13. The fourth optical waveguide includes an optical branching circuit. The optical circuit according to claim 10.

14. The fourth optical waveguide further includes a ring resonator and an interferometer, It includes a light-receiving element that monitors the output from the interferometer, The optical circuit according to claim 13.

15. To prepare a first laminate on a first substrate, having a first portion having a first cladding layer, a first core layer, and a second cladding layer in that order, and a second portion having a third cladding layer, a second core layer, and a fourth cladding layer in that order. A second laminate is prepared on the second substrate, having a fifth cladding layer and a third core layer in that order. The first laminate and the second laminate are arranged so that the first core layer and the second core layer face the third core layer, and the second cladding layer, the fourth cladding layer, and the third core layer are bonded to a temporary substrate. The first substrate and the second substrate are joined to a common substrate. After bonding the first substrate and the second substrate to the common substrate, the temporary substrate is removed. The first laminate is processed to obtain a first optical waveguide including the first cladding layer, the first core layer, and the second cladding layer, and a second optical waveguide including the third cladding layer, the second core layer, and the fourth cladding layer, and The second laminate is processed to obtain a third optical waveguide which includes at least the fifth cladding layer and the third core layer and optically couples with the first optical waveguide and the second optical waveguide. A method for manufacturing an optical circuit, including

16. A method for manufacturing an optical circuit according to claim 15, wherein the first laminate, which includes the first portion and the second portion, is obtained by cleavage along a first direction in which the first portion and the second portion are aligned.

17. A third laminate is prepared having a seventh cladding layer and a fourth core layer on a third substrate in that order. The third laminate is positioned on the side of the first laminate that is opposite to the second laminate, with the second core layer facing the fourth core layer, and the fourth core layer is bonded to the temporary substrate, and After the temporary substrate is removed following bonding to the common substrate, the third laminate is processed to obtain a fourth optical waveguide that includes at least the seventh cladding layer and the fourth core layer and is optically coupled to the second optical waveguide. A method for manufacturing an optical circuit according to claim 15 or 16, including the method described above.

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