Optical circuit, optical sensor using same, and mobile body

Abstract

The present invention provides: an optical circuit that provides stable optical coupling between a resonator and an optical waveguide; and an optical sensor comprising the same. The optical circuit (10) comprises a resonator (11) and an optical waveguide (23) that includes a ridge (231) formed upon substrate or a semiconductor layer (21). The resonator (11) has a light circulation plane (111) and is disposed such that part of the light circulation plane (111) faces the upper surface of the ridge (231), across a first gap (51). The distance (G) between part of the light circulation plane (111) and the upper surface of the ridge (231) facing said part of the light circulation plane (111) is shorter than the distance that an evanescent wave protrudes.

Description

Optical circuit, optical sensor using the same, and mobile object

[0001] The present disclosure relates to an optical circuit, an optical sensor using the same, and a moving object.

[0002] A photonic integrated circuit (PIC) is a circuit incorporating optical elements such as optical switches and wavelength filters on a substrate, and is generally manufactured using a technology known as semiconductor microfabrication. It is desirable for wavelength filters to be composed of optical resonators with high Q values. Whispering-Gallery-Mode (WGM) resonators, which are fabricated by grinding and polishing optical materials, can generally achieve higher Q values ​​than resonators fabricated by semiconductor microfabrication. A LiDAR (Light Detection and Ranging) sensor is known in which a WGM resonator is coupled to an optical waveguide via evanescent waves (see, for example, Patent Document 1).

[0003] US Patent Application Publication No. 2020 / 0400888

[0004] When optically coupling a resonator and an optical waveguide using evanescent waves, it is necessary to precisely control the distance between the resonator and the optical waveguide. In Patent Document 1, the WGM resonator is fixed to a thin cladding layer that covers the optical waveguide via an adhesive. It is difficult to precisely control the thickness of the adhesive, and it is also susceptible to temperature changes.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical circuit that stably optically couples a resonator and an optical waveguide, and an optical sensor and a mobile object that use the same.

[0006] In one embodiment, the optical circuit comprises an optical waveguide including a ridge formed on a substrate or a semiconductor layer, and a resonator, wherein the resonator has an optical circulation surface, and a portion of the optical circulation surface is arranged to face an upper surface of the ridge via a first gap, and the distance between the portion of the optical circulation surface and the upper surface of the ridge facing the portion of the optical circulation surface is shorter than the distance over which an evanescent wave seeps out.

[0007] In one embodiment, the optical circuit comprises an optical waveguide including a ridge formed on a substrate or a semiconductor layer, and a resonator, the resonator being a whispering gallery mode resonator, the resonator having an optical circulation surface, and a portion of the optical circulation surface being positioned so as to face an upper surface of the ridge of the optical waveguide via a first gap.

[0008] It is possible to provide an optical circuit that stably optically couples a resonator and an optical waveguide.

[0009] 7 is a schematic diagram of the waveguiding direction of an optical circuit of an embodiment. FIG. 8 is a top view of an optical circuit of an embodiment. FIG. 9 is a perspective view of a resonator structure including a resonator and a support. FIG. 10 is a diagram illustrating an example of a configuration of an optical waveguide including a ridge. FIG. 11 is a diagram illustrating another example of a configuration of an optical waveguide including a ridge. FIG. 12 is a diagram illustrating coupling of light between an optical waveguide and a resonator. FIG. 13 is a diagram illustrating height control of an optical waveguide. FIG. 14 is a diagram illustrating processing control of a resonator. FIG. 15 is a diagram illustrating installation of a resonator relative to an optical waveguide. FIG. 16 is a schematic plan view illustrating a first example of a configuration of an optical circuit. FIG. 17 is a schematic diagram of an optical sensor using the optical circuit of FIG. 5. FIG. 18 is a top view illustrating fixation of the resonator structure. FIG. 19 is a cross-sectional view taken along the line AA' of FIG. 7. FIG. 19 is a schematic diagram illustrating an example of a method of fixing the resonator structure. FIG. 20 is a schematic diagram of the waveguiding direction of an optical circuit utilizing a higher-order mode. FIG. 21 is a top view of the optical circuit of FIG. 13. FIG. 22 is a top view of a modified example of the optical circuit of FIG. 13. FIG. 23 is a schematic diagram illustrating a second example of a configuration of an optical circuit using a resonator structure. FIG. 24 is a schematic diagram of an optical sensor using the optical circuit of FIG. 12. FIG. 25 is a schematic diagram of a moving body equipped with the optical circuit or optical sensor of an embodiment.

[0010] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. Note that the following description is intended to embody the technical idea of ​​the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following.

[0011] In each drawing, components having the same function may be assigned the same symbol. For convenience, the embodiments may be shown separately to facilitate explanation or understanding of the main points, but partial substitution or combination of the configurations shown in different embodiments or examples is possible. In the embodiments described below, differences from the previous embodiment will be mainly described. Furthermore, explanations of commonalities with the previous embodiment may be omitted. The size and positional relationship of components shown in each drawing may be exaggerated to clarify the explanation.

[0012] Each embodiment will be described below with reference to the drawings.

[0013] First Embodiment In this embodiment, a configuration is provided in which the distance between the upper surface of the ridge of the optical waveguide and the resonator is controlled, and light passing through the optical waveguide is stably coupled to the resonator.

[0014] 1A and 1B show a configuration example of an optical circuit 10 according to an embodiment. Fig. 1A is a schematic diagram of the waveguiding direction of the optical circuit 10, and Fig. 1B is a top view. As a coordinate system, a plane parallel to the substrate or semiconductor layer 21 is defined as the XY plane, and the normal direction of the substrate or semiconductor layer 21 is defined as the Z direction. The optical axis direction of the optical waveguide is defined as the Y direction (which may be either the +Y direction or the -Y direction).

[0015] In the embodiment, the optical circuit 10 includes an optical waveguide 23 including a ridge formed on a substrate or semiconductor layer 21 (hereinafter simply referred to as "substrate or the like 21"), and a resonator 11. The resonator 11 has an optical circulation surface 111, and a portion of the optical circulation surface 111 is disposed so as to face the upper surface of a ridge 231 via a first gap 51. In other words, the optical circuit 10 has the first gap 51 between the resonator 11 and the optical waveguide 23, and the resonator 11 and the optical waveguide 23 are spaced apart. The first gap 51 represents the gap at the location where the resonator 11 and the optical waveguide 23 are closest to each other. Specifically, the first gap 51 represents the gap at the location where the optical circulation surface 111 and the ridge 231 are closest to each other. A distance G between the portion of the optical circulation surface 111 and the upper surface of the ridge 231 facing the optical circulation surface 111 is shorter than the distance over which evanescent waves seep out.

[0016] The degree of optical coupling between the optical waveguide 23 and the resonator 11 is mainly determined by the wavelength of light, the refractive index of the material, and the distance G between the optical waveguide 23 and the resonator 11. In this embodiment, the distance G is precisely controlled by the processing accuracy of the optical waveguide 23 and the resonator 11. This distance G only needs to be approximately the wavelength of light, and more specifically, it only needs to be shorter than the distance at which evanescent waves leak out. This allows the optical waveguide 23 and the resonator 11 to be optically coupled. Note that no material such as an adhesive that connects a portion of the optical circulation surface 111 and the upper surface of the ridge 231 is present in the first gap 51.

[0017] Alternatively, in the embodiment, the optical circuit 10 includes an optical waveguide 23 including a ridge 231 formed on a substrate or the like 21, and a resonator 11. The resonator 11 is a WGM resonator having an optical circulation surface 111, and is disposed so that a portion of the optical circulation surface faces the upper surface of the ridge 231 of the optical waveguide 23 via a first gap 51.

[0018] The resonator 11 is a WGM resonator that can confine light along the light circulation surface 111. The light is confined in the resonator 11 by circulating along the light circulation surface 111 while being totally reflected. The resonator 11 functions as a high-Q filter that resonates with light of a specific wavelength determined by the circumferential length of the light circulation surface 111 and the effective refractive index. By making the light circulation surface 111 a smooth surface, a highly sensitive resonator 11 with low scattering loss can be obtained. The surface roughness (Ra) of the light circulation surface 111 is, for example, 10 nm or less.

[0019] In the optical circuit 10, the resonator 11 is held above the optical waveguide 23 by the support 15A via the first gap 51. Because no material such as adhesive is interposed between the optical circulation surface 111 and the upper surface of the ridge 231, the distance G between the optical circulation surface 111 and the upper surface of the ridge 231 is unlikely to fluctuate due to temperature changes, vibrations, or the like. This allows for stable optical coupling between the optical waveguide 23 and the resonator 11. The support 15A is fixed to the upper surface of the substrate 21 or the like at a position away from the ridge 231. For example, the support 15A is fixed to the substrate 21 at a position in the X-Y plane away from the optical waveguide 23 or the ridge 231 in a direction different from the optical axis of the optical waveguide 23 (in this example, the ±X direction).

[0020] 1C is a perspective view of a resonator structure 150A including a resonator 11 and a support 15A. The support 15A has a first support portion 13a and a second support portion 13b located on either side of the resonator 11. The first support portion 13a supports the first surface 11a of the resonator 11 via a first connecting portion 14a. The second support portion 13b supports the second surface 11b of the resonator 11 opposite the first surface 11a via a second connecting portion 14b. As shown in FIGS. 1A and 1B , the first support portion 13a and the second support portion 13b are fixed onto a substrate or the like 21 on both sides of a ridge 231. This allows the resonator 11 to be stably supported by the support 15A.

[0021] In addition, in the normal direction of the substrate 21 , the maximum length L 1 of the first support portion 13 a and the second support portion 13 b is greater than the maximum length L 2 of the resonator 11 .

[0022] In the example of FIG. 1C , the first support portion 13a and the second support portion 13b have a cylindrical shape and are fixed to the substrate 21 or the like by the side surface 131 of the cylinder, but this example is not limited thereto. The first support portion 13a and the second support portion 13b may be polygonal prisms such as square prisms, hexagonal prisms, or octagonal prisms as long as they can support the resonator 11. In this case, too, the diameter or maximum length L1 of the first support portion 13a and the second support portion 13b is larger than the diameter or maximum length L2 of the resonator 11, and the resonator 11 is held above the optical waveguide 23 at a predetermined distance G. The diameter or maximum length L1 of the first support portion 13a and the second support portion 13b may be, for example, 0.05 mm or more and 50 mm or less, preferably 0.05 mm or more and 10 mm or less. The diameter or maximum length of the resonator 11 may be 0.999 mm or more and 9.999 mm or less. The width of the resonator 11 may be, for example, 1 μm to 100 μm, preferably 10 μm to 50 μm. In this specification, the term "polygonal prism" also includes a shape in which a part of the polygonal prism is chamfered or cornered.

[0023] 2A and 2B show exemplary configurations of the optical waveguide 23 including the ridge 231 as optical waveguide 23A and optical waveguide 23B. In Fig. 2A, the substrate or the like 21A is a substrate 211 having an insulating layer 212. The insulating layer 212 is, for example, a silicon oxide film, and the optical waveguide 23A including the ridge 231 is formed on the insulating layer 212.

[0024] The optical waveguide 23A is formed of a material with a refractive index higher than that of the insulating layer 212. Because the top surface and both side surfaces of the ridge 231 are surrounded by air, light is confined inside the ridge 231 and propagates in the Y direction. When an SOI (Silicon On Insulator) substrate is used as the substrate 21A, the silicon substrate of the SOI substrate may be used as the substrate 211, the silicon oxide film of the SOI substrate may be used as the insulating layer 212, and the optical waveguide 23A may be formed from the silicon layer of the SOI substrate. Alternatively, the ridge 231 may be formed of a silicon oxide film and used as the optical waveguide 23A. A silicon waveguide may be used when the light used is infrared light, and a waveguide such as silicon oxide may be used when the light used is visible light.

[0025] In FIG. 2B , the substrate 21B includes a substrate 211 and an n-side semiconductor layer 213 formed on the substrate 211. The optical waveguide 23B includes a portion of the n-side semiconductor layer 213, a p-side semiconductor layer 215, and an active layer 214 between the n-side semiconductor layer 213 and the p-side semiconductor layer 215. The n-side semiconductor layer 213 includes an n-side cladding layer and an n-side optical guide layer, and includes at least one n-type semiconductor layer. The portion protruding from the n-side semiconductor layer 213 forms a ridge 231. The p-side semiconductor layer 215 includes a p-side optical guide layer and a p-side cladding layer, and includes at least one p-type semiconductor layer. A p-side contact layer may also be included on the p-side cladding layer. The active layer 214 may be a multiple quantum well layer including a plurality of barrier layers and well layers.

[0026] The active layer 214 is sandwiched between an n-side cladding layer and a p-side cladding layer, which have a lower refractive index than the active layer 214, in the stacking direction (Z direction), thereby confining light. In the lateral direction (X direction), the active layer 214 is defined by the width of the ridge 231 of the p-side semiconductor layer 215. Therefore, the region including the active layer 214, determined by the width of the ridge 231, becomes the optical waveguide 23B. That is, the ridge 231 includes a portion of the n-side semiconductor layer 213, the active layer 214, and the p-side semiconductor layer 215. The portion of the n-side semiconductor layer 213 included in the ridge 231 preferably includes an n-side cladding layer and an n-side optical guide layer. This allows light to be efficiently confined within the waveguide and reduces optical loss. The materials for the n-side semiconductor layer 213, the active layer 214, and the p-side semiconductor layer 215 can be compound semiconductors such as GaN-based semiconductors, InP-based semiconductors, or GaAs-based semiconductors. These materials may be binary, ternary, or quaternary. The width of the ridge 231 may be, for example, 0.3 μm or more and 50 μm or less. The material of the substrate 211 may be, for example, sapphire, GaN, GaAs, or the like.

[0027] FIG. 3 is a diagram showing optical coupling between the optical waveguide 23 and the resonator 11. Light L, indicated by a white arrow, propagates through the optical waveguide 23 in the optical axis direction of the optical waveguide 23 (the Y direction in FIG. 3). The light L propagates through the optical waveguide 23 while being totally reflected. During this total reflection process, the light slightly seeps out from the optical waveguide 23 toward the first gap 51. The light that seeps into the gap is called an evanescent wave. The distance that the evanescent wave seeps out is approximately the length of the wavelength. The distance that the evanescent wave seeps out is, for example, 700 nm or less, 500 nm or less, 300 nm or less, or 100 nm or less.

[0028] The resonator 11 is provided above the optical waveguide 23 so as to be located at a height of a distance G from the upper surface of the ridge 231 (see FIG. 1A ) of the optical waveguide 23. The distance G is shorter than the distance over which the evanescent wave seeps out. Therefore, the optical waveguide 23 and the resonator 11 are optically coupled, and a portion of the light L circulates along the optical circulation surface 111 while being totally reflected. The light circulating along the optical circulation surface 111 while being totally reflected slightly seeps out from the optical circulation surface 111 toward the first gap 51. Because the resonator 11 and the optical waveguide 23 are optically coupled, a portion of the light circulating along the optical circulation surface 111 while being totally reflected propagates through the optical waveguide 23 in the optical axis direction (Y direction).

[0029] The light circulates within the resonator 11, causing resonance of light of a specific wavelength determined by the circumferential length of the light circulating surface 111 and the effective refractive index. In an optical sensor described below, the resonant frequency of the resonator 11 can be detected from the output light of the optical circuit 10, allowing it to be used as a gyro sensor.

[0030] Fig. 4A is a diagram showing height control of the optical waveguide 23. Fig. 4B is a diagram showing processing control of the resonator 11. Fig. 4C is a diagram showing installation of the resonator 11 relative to the optical waveguide 23. To precisely control the distance G between the optical waveguide 23 and the optical circulation surface 111 of the resonator 11 and achieve stable optical coupling, it is important to control the height h of the ridge 231 of the optical waveguide 23 and the position of the optical circulation surface 111 of the resonator 11.

[0031] 4A , the precision of the height h of the ridge 231 of the optical waveguide 23 is determined by the precision of the semiconductor microfabrication process. For example, the height h of the ridge 231 can be controlled with high precision by forming a thin film, which will be the material of the optical waveguide 23, on the substrate 21 and controlling the amount of etching of the thin film. Alternatively, the height h of the ridge 231 can be controlled with high precision by stacking the n-side semiconductor layer 213, the active layer 214, and the p-side semiconductor layer 215 on the substrate and controlling the amount of etching of the semiconductor layers. The height h of the ridge 231 is, for example, 300 nm or more and 3000 nm or less, preferably 500 nm or more and 2000 nm or less.

[0032] The optical waveguide 23 may be made of any material that transmits the light to be used and has a refractive index higher than that of the surrounding medium. For example, a III-V group compound semiconductor such as a GaN-based semiconductor, an InP-based semiconductor, or a GaAs-based semiconductor may be used. The optical waveguide 23 may also be made of Si, SiN, SiO ２ , LiNbO ３ It may be formed by the above.

[0033] As shown in FIG. 4B, the resonator 11 can be formed integrally with the support 15A using a material 140 such as a cylinder or polygonal column. In this example, the material 140 is a cylindrical crystal of glass, fluoride, oxide, or the like. As a fluoride crystal, magnesium fluoride (MgF ２ ), calcium fluoride (CaF ２ ), strontium fluoride (SrF ２ ), yttrium lithium fluoride (LiYF ４ ) can be used. These materials have high transmittance over a wide range of wavelengths from visible light to infrared light, and cause almost no light absorption. As the glass, general optical glass such as BK-7 (borosilicate crown glass) can be used. As the oxide, LiNbO ３ , LiTaO ３ , LiCaO ３ , BaTiO ３ , Al ２ O ３ , Ga ２ O ３ , Y ２ O ３ , Y ３ Al ５ O １２ , Lu ３ Al ５ O １２ , ScAlMgO ４ The material 140 can be a crystal such as MgF ２ , CaF ２ , LiNbO ３ These materials have high transmittance and birefringence, and are therefore excellent as resonator materials.

[0034] The processing of the resonator 11 is carried out, for example, by rotating a cylindrical material 140 having a diameter L1 around its central axis while pressing a diamond knife against the side surface 131 of the cylinder. By controlling the rotation speed of the material 140 and the pressure of the diamond knife, and by controlling the amount of engraving d from the side surface 131 of the cylinder, the resonator 11 having the optical circulation surface 111 can be processed with high precision. The amount of engraving d to the optical circulation surface 111 is, for example, 400 nm or more and 3100 nm or less, and preferably 600 nm or more and 2100 nm or less.

[0035] The remaining portions of the material 140 become the first support portion 13a and the second support portion 13b of the support member 15A. This results in a resonator structure 150A in which the resonator 11 and the support member 15A are integrally formed, allowing the resonator 11 to be more stably supported by the substrate or the like 21. The cylindrical side surfaces 131 of the first support portion 13a and the second support portion 13b serve as fixing surfaces to the substrate or the like 21, as described below. Furthermore, the first connection portion 14a formed between the resonator 11 and the first support portion 13a by processing is also integrally formed with the resonator 11 and the first support portion 13a. Similarly, the second connection portion 14b formed between the resonator 11 and the second support portion 13b by processing is also integrally formed with the resonator 11 and the second support portion 13b. The width of the first connection portion 14a, i.e., the distance between the resonator 11 and the first support portion 13a, is longer than the wavelength of light circulating within the resonator 11. The same is true for the width of the second connecting portion 14b, i.e., the distance between the resonator 11 and the second supporting portion 13b. By forming the first connecting portion 14a and the second connecting portion 14b, gaps are formed between the light circulation surface 111 and the side surface of the first supporting portion 13a facing the resonator 11, and between the light circulation surface 111 and the side surface of the second supporting portion 13b facing the resonator 11, making it possible to efficiently confine light within the resonator 11.

[0036] 4C , the resonator structure 150A is fixed to the substrate or the like 21 so that the light circulation surface 111 of the resonator 11 corresponds to the upper surface of the optical waveguide 23. As described with reference to FIGS. 4A and 4B , the height h of the ridge 231 of the optical waveguide 23 and the depth d of the ridge 231 from the side surface 131 of the material 140 are precisely controlled, so that when the resonator structure 150A is placed on the substrate or the like 21, the distance G between the upper surface of the ridge 231 and the light circulation surface 111 is determined in a self-aligned manner during the assembly stage. For example, when the depth d of the ridge 231 is 1100 nm and the height h is 1000 nm, the distance G is approximately 100 nm.

[0037] Since the distance G is precisely controlled, stable optical coupling is achieved between the resonator 11 and the optical waveguide 23. The first gap 51 (see FIG. 1A) is between the resonator 11 and the optical waveguide 23, and since no material such as an adhesive is interposed, the resonator 11 and the optical waveguide 23 are highly stable against temperature changes, vibrations, and the like.

[0038] Fig. 5 is a plan view showing a configuration example of an optical circuit 10A in which a resonator structure 150A is arranged, and Fig. 6 is a schematic diagram of an optical sensor 100A to which the optical circuit 10A is applied. The optical circuit 10A has a light source 31, an optical waveguide 23, a resonator structure 150A including a resonator 11, a first output waveguide 24a, and a second output waveguide 24b. The optical sensor 100A includes the optical circuit 10A, photodetectors PD1 and PD2 that detect light that has circulated within the resonator 11, and a processor that processes the outputs of the photodetectors. The optical sensor 100 is, for example, a gyro sensor.

[0039] The light source 31 is, for example, a ring laser formed with a ring waveguide 311 provided on the substrate 21 or the like. The ring waveguide 311 can be formed with the optical waveguide described with reference to FIG. 2B . The light source 31 outputs light with a peak wavelength of, for example, 200 nm or more and 1600 nm or less. The light source 31 may also output light with a peak wavelength of, for example, 200 nm or more and 550 nm or less. Using light with a relatively short wavelength can increase the phase change associated with the Sagnac effect, improving the sensitivity of the sensor. The light source 31 may also output light with a peak wavelength of, for example, 630 nm or more and 1560 nm or less. Using light with a relatively long wavelength can increase the optical coupling distance between the light source 31 and the optical waveguide 23 and the optical coupling distance between the optical waveguide 23 and the resonator 11. This facilitates fabrication of the optical circuit 10A and the optical sensor 100A. Furthermore, the optical Kerr effect of the resonator 11, described below, can be reduced. The light source 31 preferably outputs light with a single wavelength. This makes it possible to reduce noise in the optical sensor.

[0040] The ring waveguide 311 is preferably a waveguide that satisfies the single-mode condition. The transverse mode being the fundamental mode makes it easy to control the light propagating through the optical waveguide 23. When the ring waveguide 311 satisfies the single-mode condition, the width of the ring waveguide 311 can be, for example, 0.3 μm or more and 2 μm or less. By injecting a current from an electrode provided on the ring waveguide 311, light is generated and amplified in the active layer within the waveguide. The distance between the ring waveguide 311 that constitutes the ring laser and the optical waveguide 23 is shorter than the distance over which evanescent waves leak. Therefore, the ring waveguide 311 and the optical waveguide 23 are optically coupled, and light is output from the light source 31 to the optical waveguide 23.

[0041] The optical waveguide 23 may be a waveguide having the same configuration as the ring waveguide 311, or may be a SiO 2 waveguide as described with reference to FIG. ２Alternatively, a thin-wire waveguide such as a group III-V compound semiconductor may be used. The optical waveguide 23 and the ring waveguide 311 of the light source 31 are preferably formed from the same group III-V compound semiconductor. For example, the optical waveguide 23 and the ring waveguide 311 of the light source 31 can be formed by processing a substrate 21B, which includes a substrate 211, an n-side semiconductor layer 213, an active layer 214, and a p-side semiconductor layer 215 in this order, using photolithography and / or electron beam lithography. The optical waveguide 23 and the ring waveguide 311 of the light source 31 can be formed by removing the substrate 21B from the p-side semiconductor layer 215 to a portion of the n-side semiconductor layer 213 using photolithography and / or electron beam lithography. Since the III-V compound semiconductor emits light upon application of a current, no external light source is required. This allows the optical circuit 10A to be miniaturized. Furthermore, the magnitude of optical coupling between the light source 31 and the optical waveguide 23 can be stabilized.

[0042] The optical waveguide 23 has an optical coupler 32 with a branching ratio of 50:50. The optical coupler 32 is formed by a part of the optical waveguide 23 and another part of the optical waveguide 23. In this specification, the part of the optical waveguide 23 optically coupled by the optical coupler 32, the other part of the optical waveguide 23, and the optical waveguide 23 existing therebetween are collectively referred to as a loop 35. Light output from the light source 31 is branched by the optical coupler 32 at an intensity ratio of 50:50. The optical coupler 32 may be, for example, a directional coupler or a Y-shaped waveguide. One of the branched light beams passes through the loop 35 counterclockwise and circulates around the resonator 11 counterclockwise. The other light beam passes through the loop 35 clockwise and circulates around the resonator 11 clockwise. When the optical sensor 100A is rotated, the optical path length experienced by the light circulating through the resonator 11 changes depending on the rotation angle or angular velocity of the substrate 21. This causes a change in the resonant frequency of the resonator 11 for light circulating clockwise and that for light circulating counterclockwise (Sagnac effect). The angular velocity can be calculated from the difference between the resonant frequency of the resonator 11 for light circulating clockwise and that for light circulating counterclockwise.

[0043] The optical circuit 10A includes optical couplers 33 and 34 in the loop 35. The optical coupler 33 is formed by a portion of the optical waveguide 23 and a portion of the first output waveguide 24a. The optical coupler 34 is formed by a portion of the optical waveguide 23 and a portion of the second output waveguide 24b. As shown in FIG. 5 , in a plan view, the optical couplers 33 and 34 are respectively disposed on one side and the other side of the loop 35 via the resonator structure 150A. The optical couplers 33 and 34 may have a branching ratio of 50:50, for example, and may be directional couplers. A portion of the light that has circulated clockwise through the resonator 11 is guided by the optical coupler 33 to the first output waveguide 24a and detected by a first photodetector (denoted as "PD1" in the figure). A portion of the light that has circulated counterclockwise around the resonator 11 is guided to the second output waveguide 24b by the optical coupler 34 and detected by a second photodetector (denoted as "PD2" in the drawing).

[0044] 6, the intensity of light detected by the first photodetector (PD1) is measured by a lock-in amplifier 41. The measurement result by the lock-in amplifier 41 is fed back to the light source 31 via a control circuit 42 and input to a processor 50A. The wavelength of the light source 31 is controlled based on the feedback from the control circuit 42. The control circuit 42 may be, for example, a PID (Proportional-Integral-Differential) control circuit.

[0045] The intensity of light detected by the second photodetector (PD2) is measured by the lock-in amplifier 43. The measurement result by the lock-in amplifier 43 is input to the processor 50A. The processor 50A processes the input signal. Specifically, the processor 50A calculates and outputs an angular velocity from the difference between the output of the lock-in amplifier 41, i.e., the detection result of the first photodetector (PD1), and the output of the lock-in amplifier 43, i.e., the detection result of the second photodetector (PD2). This means, for example, that the amount of detection by PD1 is used as a reference and the amount of deviation of the amount of detection by PD2 is measured. From this difference, the angular velocity experienced by the optical sensor 100A can be determined and output.

[0046] <Fixing of Resonator Structure> When the optical circuit 10A is applied to the optical sensor 100A that measures angular velocity, it is important that the optical response does not change due to factors other than the angular velocity. In other words, it is important how to stably hold the resonator 11 while maintaining the distance G between it and the upper surface of the optical waveguide 23.

[0047] 7 and 8 are diagrams showing how the resonator structure 150A is fixed to the substrate or the like 21. Fig. 7 is a top view, and Fig. 8 is a cross-sectional view taken along the line A-A' in Fig. 7. Fig. 8 is a vertical cross section of the first support portion 13a as seen in the optical axis direction (X direction) of the optical waveguide 23, and the vertical cross section of the second support portion 13b as seen in the -X direction is the same as the vertical cross section of the first support portion 13a.

[0048] In the examples of Figures 7 and 8, the first support portion 13a and the second support portion 13b are cylindrical. A first groove 25a and a second groove 25b are formed in the substrate 21, extending in a direction (e.g., the ±X direction) different from the optical axis of the ridge 231 (see Figure 1A) of the optical waveguide 23. The width of the first groove 25a and the second groove 25b formed between the first groove 25a and the second groove 25b in the optical axis direction of the optical waveguide 23 is smaller than the maximum length of the first support portion 13a and the second support portion 13b, and may be 0.8 times or less, 0.6 times or less, or 0.4 times or less. As shown in Figure 8, the side surface 131 of the first support portion 13a of the support body 15A contacts the upper edges 252 and 253 of the first groove 25a. A second gap 52 is provided between the bottom surface of the first groove 25a and the first support portion 13a.

[0049] The contact positions of the side surface 131 and the edges 252 and 253 are designated as P1 and P2. The first support portion 13a does not contact the substrate 21 or the first groove 25a at any locations other than P1 and P2. As described above, the second gap 52 is defined between the side surface 131 of the first support portion 13a and the bottom surface 251 of the first groove 25a. The third gap 53 is defined between the first connection portion 14a and the substrate 21. Even when the first groove 25a is provided, the distance G is maintained so that the optical waveguide 23 and the resonator 11 are optically coupled.

[0050] The second support portion 13b of the support body 15A has the same positional relationship with the substrate or the like 21 and the second groove 25b as the first support portion 13a. That is, the side surface 131 of the second support portion 13b contacts the edges 252 and 253 of the second groove 25b at the upper end of the second groove 25b. A second gap 52 is formed between the side surface 131 of the second support portion 13b and the bottom surface 251 of the second groove 25b, and a third gap 53 is formed between the second connection portion 14b and the substrate or the like 21. Hereinafter, the first groove 25a and the second groove 25b may be referred to as the "groove 25" without distinction.

[0051] 8, a first gap 51 is formed between the resonator 11 and the optical waveguide 23, a second gap 52 is formed between the resonator structure 150A and the first groove 25a, and a third gap 53 is formed between the first connection portion 14a and the substrate or the like 21. The resonator structure 150A is supported by edges 252 and 253 at the upper end of the first groove 25a in a state in which the resonator 11 is suspended above the optical waveguide 23. On the side of the second groove 25b, the resonator structure 150A also contacts the substrate or the like 21 only at two points P1 and P2. This makes the entire resonator structure 150A less susceptible to temperature changes and vibrations.

[0052] 7 and 8 , by supporting the first support portion 13 a and the second support portion 13 b of the resonator structure 150A by the upper edges of the first groove 25 a and the second groove 25 b, respectively, it is possible to stabilize the distance G between the upper surface of the ridge 231 and the light circulation surface 111. The distance G is equal to or less than the wavelength in a vacuum of the light propagating through the optical waveguide 23. The distance G may be, for example, 700 nm or less, 500 nm or less, 300 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, or 70 nm or less.

[0053] FIG. 9 shows an example of a method for fixing the resonator structure 150A. The substrate 21 carrying the resonator structure 150A may be sandwiched between plates 61 and 62 from above and below. The plates 61 and 62 may be made of, for example, brass or copper. The plates 61 and 62 may be dielectric substrates having a thermal expansion coefficient that is small compared with that of the substrate 21 and / or the resonator structure 150A. This reduces peeling between the substrate 21 and the plate 61 or between the resonator structure 150A and the plate 62 due to temperature changes, thereby fixing the resonator structure 150A. Fastening the plates 61 and 62 with screws 43 and 44 strengthens contact between the side surface 131 of the support 15A and the edges 252 and 253 of the groove 25 (see FIG. 8 ) at positions P1 and P2. Instead of the screws 43 and 44, the resonator structure 150A may be fixed between the plates 61 and 62 by a clamp or the like.

[0054] Prior to clamping with the screws 43, 44 or a clamp, a part of the resonator structure 150A may be temporarily fixed to the substrate 21 in an area excluding the groove 25 and the optical waveguide 23. When temporarily fixing with an adhesive, it is preferable to temporarily fix the resonator structure 150A to the substrate 21 using an adhesive that is easily removable and at a position that does not affect the optical coupling between the resonator structure 150A and the substrate 21.

[0055] The fixing method shown in FIG. 9 keeps the distance between the resonator 11 and the optical waveguide 23 constant, and stabilizes the optical coupling.

[0056] <Utilization of Higher-Order Modes> When a resonator 11 having an optical circulation surface 111 is used, light circulates multiple times along the optical circulation surface 111, increasing the intensity of the constructively interfering light. When the light intensity is high, the optical Kerr effect occurs, in which the refractive index changes depending on the light intensity. The change in the optical path length of the resonator 11 due to the optical Kerr effect cannot be distinguished from the difference in optical path length of the gyro sensor due to angular velocity, resulting in noise. Therefore, when the optical Kerr effect is taken into consideration, it is difficult to increase the power of light, which can limit the sensitivity.

[0057] To solve this problem, it is conceivable to selectively use a higher-order mode (hereinafter also referred to as a "higher-order mode") among the transverse modes of the resonator. The electric field intensity distribution of a higher-order mode has more antinodes and nodes than the electric field intensity distribution of the fundamental mode, and is also widely distributed. Therefore, by using this higher-order mode, the intensity per unit area of ​​the light coupled to the resonator 11 can be reduced in the resonator 11. This makes it possible to increase the intensity of the light amplified in the resonator 11 while reducing noise due to the optical Kerr effect and improving sensitivity.

[0058] 10 is a schematic diagram of the waveguiding direction of an optical circuit 10C utilizing a higher-order mode. To selectively utilize a higher-order mode, an optical waveguide including two or more ridges is used. Optical waveguides 23a and 23b, each including a ridge 231, are arranged in parallel on a substrate 21. Preferably, the optical waveguides 23a and 23b are arranged so that the top surface of the ridge 231 faces the position on the optical circulation surface 111 of the resonator 11 where the higher-order mode occurs. This allows efficient coupling between the higher-order mode of the resonator 11 and the transverse mode of the optical waveguides 23a and 23b.

[0059] For example, the optical waveguides 23a and 23b each satisfy the single-mode condition. Since the electric field intensity distribution of the fundamental mode is unimodal, it is easy to optically couple with a higher-order mode of the resonator 11, which has multiple loops in the electric field intensity distribution. The widths of the optical waveguides 23a and 23b that satisfy the single-mode condition can be, for example, 0.3 μm or more and 5 μm or less. It is preferable that the ring waveguide 311 of the light source 31 satisfy the single-mode condition. That is, it is preferable that the transverse mode of the light generated by the light source 31 is the fundamental mode. This makes it easy to control the ratio of the optical intensities in the optical waveguides 23a and 23b, and allows efficient optical coupling between the optical waveguides 23a and 23b and the resonator 11.

[0060] The distance G between the upper surface of the ridge 231 of the optical waveguides 23 a and 23 b and the resonator 11 is precisely controlled by the processing accuracy of the optical waveguides 23 a and 23 b and the processing accuracy of the resonator structure 150 A. The structure of the resonator structure 150 A is the same as that in Fig. 1A, and the same components are denoted by the same reference numerals and redundant explanations will be omitted.

[0061] FIG. 11A is a schematic plan view of the optical circuit 10C. The optical waveguide 23 includes a first mode converter 37 that divides the ridge 231 into multiple ridges and a second mode converter 38 that connects the multiple ridges into a single ridge. FIG. 11A illustrates an example in which the ridges are divided into two. A portion of the optical circulation surface 111 of the resonator 11 faces the multiple ridges separated by the first mode converter 37 via a first gap 51. The first mode converter 37 converts the modes, and the second mode converter 38 couples the converted modes. The first mode converter 37 and the second mode converter 38 may be realized by a Y-shaped waveguide that branches one waveguide into two, or may be realized by an optical coupler with a 50:50 branching ratio, a multi-mode interference (MMI) coupler, or the like.

[0062] The two mode-converted lights propagate through the optical waveguides 23a and 23b, respectively, and are optically coupled at a position where a higher-order mode is generated in the resonator 11. The area over which the two transverse-mode lights coupled to the resonator 11 are distributed on the optical circulation surface 111 is wide, and the intensity per unit area can be reduced, so that it is possible to increase the intensity of the light amplified within the resonator 11 while reducing noise due to the optical Kerr effect. Between the first mode converter 37 and the second mode converter 38, the two optical waveguides 23a and 23b preferably have optical path lengths designed to be phase-matched.

[0063] FIG. 11B is a modified plan view schematic diagram of the optical circuit 10C. Only differences from FIG. 11A will be described. The optical waveguide 23a and the optical waveguide 23b form a tapered waveguide. The optical waveguide 23a includes two narrow portions 235a, two tapered portions 236a, and a wide portion 237a. The two tapered portions 236a and the wide portion 237a are provided between the two narrow portions 235a. The wide portion 237a is also provided between the two tapered portions 236a. The waveguide width of the wide portion 237a is larger than the waveguide width of the narrow portion 235a, and may be, for example, 2 to 35 times larger. The waveguide width of the narrow portion 235a may be, for example, 0.3 μm to 5 μm. The waveguide width of the wide portion 237a is larger than the waveguide width of the narrow portion 235a, and may be, for example, 1 μm or more and 10 μm or less. Each of the tapered portions 236a is formed so that the waveguide width increases from the narrow portion 235a to the wide portion 237a. At the wide portion 237a, the optical waveguide 23a and the resonator 11 face each other. By forming such a tapered waveguide, the mode converted by the first mode converter 37 can be increased while maintaining the fundamental mode. The area optically coupled to the resonator 11 can be increased, thereby reducing noise due to the optical Kerr effect. Similarly, the optical waveguide 23b includes two narrow portions 235b, two tapered portions 236b, and a wide portion 237b. Other configurations are similar to those of the optical waveguide 23a forming the tapered waveguide.

[0064] The number of ridges 231 including the optical waveguides 23 may be increased depending on the order of the transverse mode of the resonator 11. As described above, each optical waveguide 23 facing the resonator 11 may be formed to satisfy the single-mode condition. For example, when a third-order transverse mode is used, the optical waveguide 23 may be divided into four using a 1:4 MMI coupler or the like. In this case, it is desirable that at least two of the multiple ridges 231 face positions where higher-order transverse modes of the resonator 11 are generated.

[0065] Second Embodiment Fig. 12 shows a configuration example of an optical circuit 10B using a resonator structure 150B. Fig. 13 is a schematic diagram of an optical sensor using the optical circuit 10B. The optical sensor 100B is, for example, an acceleration sensor.

[0066] The resonator structure 150B used in the optical circuit 10B includes a resonator 11 having an optical circulation surface 111 and a support 15B. The support 15B has a support portion 13c that supports only one of the first surface 11a and the second surface 11b of the resonator 11. In this example, the support portion 13c is connected to the first surface 11a of the resonator 11 by a connection portion 14c.

[0067] The resonator structure 150B can be fabricated by precision machining while controlling the rotation speed of the material 140 and the pressing force of the diamond knife, as described with reference to Fig. 4B. In this embodiment, the resonator 11 is supported by the support 13c via the connection 14c so that the light circulation surface 111 faces the upper surface of the ridge 231 of the optical waveguide 23. The support 13c has, for example, a cylindrical shape.

[0068] As described with reference to FIGS. 7 and 8 , the support portion 13c is supported at two points P1 and P2 by edges 252 and 253 at the upper end of a groove 25 formed in the substrate or the like 21. For example, a cylindrical support portion 13c is supported by the groove 25. The groove 25 extends in a direction different from the optical axis of the optical waveguide 23 or the ridge 231 (e.g., a direction away from the optical axis). The side surfaces of the support portion 13c contact the edges 252 and 253 of the groove at the upper end of the groove 25, and a second gap 52 (see FIG. 8 ) is formed between the support portion 13c and the bottom surface of the groove 25, and a third gap 53 (see FIG. 8 ) is formed between the substrate or the like 21 and the support portion 13c. This makes the optical circuit 10B less susceptible to temperature changes and vibrations, and therefore, changes in the optical response due to factors other than acceleration can be suppressed in the optical circuit 10B. Additionally, the fixation of the resonator structure 150B to the edges 252, 253 of the groove 25 may be strengthened by screws, clamps, or the like.

[0069] In the resonator structure 150B, the resonator 11, which has a smaller mass than the support 13c, is held like a cantilever by the elongated connecting portion 14c. That is, one end of the resonator 11 is fixed to the support 15B, and the other end is free. For example, in the normal direction of the substrate 21, the maximum length of the connecting portion 14c is smaller than the maximum length of the resonator 11. Furthermore, the distance between the support 13c and the resonator 11 is greater than the maximum length of the connecting portion. In the optical circuit 10B, the distance G between the light circulation surface of the resonator 11 and the top surface of the ridge 231 is set to a predetermined design value by controlling the height of the optical waveguide 23 and the depth of the material 140. When the optical circuit 10B is applied to an acceleration sensor, the distance G changes due to inertial force caused by acceleration. The optical sensor 100B can measure acceleration by reading the change in distance G as a change in light intensity.

[0070] 13 , the optical circuit 10B has a resonator structure 150B including a light source 31, an optical waveguide 23, and a resonator 11. The light source 31 is, for example, a single-wavelength laser light source formed by a ring waveguide 311. The ring waveguide 311 and the optical waveguide 23 are optically coupled, and the optical waveguide 23 and the resonator 11 are optically coupled. That is, the distance between the ring waveguide 311 and the optical waveguide 23 is shorter than the distance over which evanescent waves leak, and the distance between the optical waveguide 23 and the resonator 11 is also shorter than the distance over which evanescent waves leak. Light output from the light source 31 propagates through the optical waveguide 23, and the light propagating through the optical waveguide 23 circulates along the optical circulation surface 111 of the resonator 11. The circulating light propagates through the optical waveguide 23 and is detected by a photodetector (PD3).

[0071] The intensity of the light received by the photodetector (PD3) changes depending on the distance G between the optical circulation surface 111 of the resonator 11 and the optical waveguide 23, i.e., the acceleration experienced by the optical sensor 100B. The intensity of the light detected by the photodetector (PD3) is measured by the lock-in amplifier 44 and input to the processor 50B. The processor 50B calculates and outputs the acceleration from the change in the detected light intensity.

[0072] In the optical sensor 100B, the distance G between the upper surface of the optical waveguide 23 and the light circulation surface 111 in a state where no acceleration is applied is precisely set, and the resonator structure 150B is stably fixed to the substrate or the like 21. Furthermore, when acceleration is applied, since only one of the first surface 11a and the second surface 11b of the resonator 11 is supported by the support portion 13c, the resonator 11 moves due to the inertial force caused by the acceleration, and the acceleration can be measured with high precision.

[0073] As in the first embodiment, the ridge of the optical waveguide 23 of the optical circuit 10B may be divided into multiple ridges, and the light circulation surface of the resonator 11 may face the multiple ridges via a first gap 51 (see FIG. 10 ). In this case, as shown in FIGS. 11A and 11B , a first mode converter 37 that divides the optical waveguide 23 into multiple ridges and a second mode converter 38 that connects the multiple ridges into a single ridge may be provided. It is desirable that at least two of the multiple ridges 231 face positions where higher-order transverse modes of the resonator 11 are generated.

[0074] <Application Examples> For example, information terminals such as smartphones, tablet terminals, and watches, as well as mobile objects such as drones, vehicles, ships, and aircraft, can be equipped with the optical circuits 10A, 10B or optical sensors 100A, 100B of the present disclosure. For example, in the case of a drone, the inclination of the aircraft can be controlled by providing a gyro sensor as an optical sensor. The traveling speed can be controlled by providing an acceleration sensor as an optical sensor. Furthermore, in the case of a vehicle, a vehicle equipped with a gyro sensor and / or an acceleration sensor as an optical sensor can form part of a driving assistance system.

[0075] The optical circuits 10A, 10B or the optical sensors 100A, 100B according to the present disclosure can be used, for example, in driving assistance systems for moving objects. The optical sensors 100A, 100B according to the present disclosure have high robustness due to the small number of moving parts, and are therefore suitable for use in moving objects where safety is a requirement.

[0076] Fig. 14 is a schematic diagram of a driving assistance system mounted on a moving body 200 such as a vehicle. The driving assistance system shown in Fig. 14 includes an on-board device 201 that is mounted on the vehicle and performs control related to driving assistance for the vehicle, a LiDAR 202, a gyro sensor 203, a vehicle body acceleration sensor 204, and a LiDAR acceleration sensor 205.

[0077] The on-board device 201 is electrically connected to the LiDAR 202, the gyro sensor 203, the vehicle body acceleration sensor 204, and the LiDAR acceleration sensor 205, and acquires output data from these sensors. The on-board device 201 also stores a map database (DB: DataBase) 210 that stores road data and feature information related to features located near roads. The on-board device 201 estimates the vehicle's position based on the output data and the map DB 210, and performs control related to vehicle driving assistance, such as automatic driving control, based on the estimated vehicle position. The on-board device 201 also estimates the attitude and position of the LiDAR 202 based on the outputs of the LiDAR 202, the gyro sensor 203, the vehicle body acceleration sensor 204, and the LiDAR acceleration sensor 205. Based on this estimation result, the vehicle-mounted device 201 performs processing such as correcting each measurement value of the point cloud data output by the LiDAR 202.

[0078] The LiDAR 202 emits a pulsed laser beam over a predetermined angular range in the horizontal and vertical directions to discretely measure the distance to an object in the external environment and generate three-dimensional point cloud information indicating the position of the object. In this case, the LiDAR 202 includes an irradiation unit that irradiates laser light while changing the irradiation direction, a light receiving unit that receives reflected or scattered light of the irradiated laser light, and an output unit that outputs scan data based on a light receiving signal output by the light receiving unit. The scan data is generated based on the irradiation direction corresponding to the laser light received by the light receiving unit and the distance to the object in that irradiation direction of the laser light, which is determined based on the above-mentioned light receiving signal, and is supplied to the vehicle-mounted device 201. In FIG. 14 , as an example, the LiDAR 202 is provided at both the front and rear of the vehicle.

[0079] The gyro sensor 203 is provided in the vehicle and supplies an output signal corresponding to the yaw rate of the vehicle body to the in-vehicle device 201. The gyro sensor 203 is the optical sensor 100A described in the embodiment according to the present disclosure. A plurality of gyro sensors 203 may be provided. For example, a gyro sensor 203 may be provided on each of the front and rear wheels of the vehicle, and each gyro sensor 203 may be electrically connected to the in-vehicle device 201. This allows for more precise control of the direction of travel of the vehicle.

[0080] The vehicle body acceleration sensor 204 is an acceleration sensor provided on the vehicle, and supplies detection signals corresponding to triaxial acceleration data corresponding to the vehicle body's traveling direction, lateral direction, and vertical direction to the onboard device 201. The LiDAR acceleration sensor 205 is a triaxial acceleration sensor provided on each LiDAR 202, and supplies detection signals corresponding to the triaxial acceleration data of the installed LiDAR 202 to the onboard device 201. The vehicle body acceleration sensor 204 and the LiDAR acceleration sensor 205 are the optical sensor 100B described in the embodiment according to the present disclosure. The triaxial acceleration data can be acquired by providing an optical sensor 100B in each axial direction.

[0081] Although the above description has been based on specific configuration examples, the present invention is not limited to the above configuration examples. Electrodes may be provided near the optical waveguide 23, the optical couplers 32, 33, and 34, or the first and second mode converters 37 and 38 that constitute the optical circuit 10, and voltage may be applied to finely adjust the optical phase, mode branching ratio, and the like. In this case, the electrodes may be formed of a good conductor that has high adhesion to the substrate. Furthermore, in an application example to a gyro sensor or acceleration sensor, the light source 31 outputs light of a single wavelength, and the light of the single wavelength is coupled to the resonator 11, but this example is not limiting. Light containing multiple wavelengths, such as a WDM signal, may be wavelength-separated and optically coupled to the resonator.

[0082] This application claims priority based on Japanese Patent Application No. 2021-194775, filed on November 30, 2021, and includes the entire contents of these Japanese patent applications.

[0083] 10, 10A, 10B, 10C Optical circuit 11 Resonator 11a First surface 11b Second surface 111 Optical circulation surface 13a First support portion 13b Second support portion 14a First connection portion 14b Second connection portion 15A, 15B Support 21 Substrate or semiconductor layer 23, 23a, 23b Optical waveguide 24a First output waveguide 24b Second output waveguide 231 Ridge 25a First groove 25b Second groove 251 Bottom surface 252, 253 Edge 50A, 50B Processor 51 First gap 52 Second gap 53 Third gap 100A, 100B Optical sensor 150A, 150B Resonator structure 200 Moving body 203 Gyro sensor 204 Acceleration sensor for vehicle body 205 Acceleration sensor for LiDAR

Claims

1. an optical waveguide including a ridge formed on a substrate or semiconductor layer; a resonator; Equipped with the resonator has an optical circulating surface, and is disposed so that a portion of the optical circulating surface faces an upper surface of the ridge via a first gap; a distance between a portion of the light circulating surface and an upper surface of the ridge facing the portion of the light circulating surface is shorter than a distance over which an evanescent wave spreads; optical circuit.

2. an optical waveguide including a ridge formed on a substrate or semiconductor layer; a resonator; Equipped with the resonator is a whispering gallery mode resonator; the resonator has an optical circulating surface, and is disposed so that a portion of the optical circulating surface faces an upper surface of the ridge of the optical waveguide via a first gap; optical circuit.

3. a support that supports the resonator and is fixed to an upper surface of the substrate or the semiconductor layer at a position spaced apart from the ridge; 3. The optical circuit according to claim 1, further comprising:

4. a maximum length of the support in a normal direction to an upper surface of the substrate or the semiconductor layer is greater than a maximum length of the resonator; The optical circuit according to claim 3 .

5. the resonator and the support are integrally formed. The optical circuit according to claim 3 .

6. the support member has a first support portion that supports a first surface side of the resonator via a first connection portion, and a second support portion that supports a second surface side of the resonator opposite to the first surface via a second connection portion, the first support portion and the second support portion are fixed onto the substrate or the semiconductor layer on both sides of the ridge; The optical circuit according to claim 3 .

7. the first support portion and the second support portion have a cylindrical shape, a first groove and a second groove extending in a direction different from the optical axis of the ridge are formed in the substrate or the semiconductor layer; a second gap is provided between a bottom surface of the first groove and the first support portion, and between a bottom surface of the second groove and the second support portion; The optical circuit according to claim 6 .

8. the support body further includes a support portion that supports the resonator via a connection portion on only one of the first surface side and the second surface side of the resonator. The optical circuit according to claim 3 .

9. the support portion is cylindrical, a groove formed in the substrate and extending in a direction different from the optical axis of the ridge, wherein a side surface of the support portion contacts an edge of the groove at an upper end of the groove, and a second gap is formed between a bottom surface of the groove and the support portion; a third gap is formed between the connection portion and the substrate or the semiconductor layer; The optical circuit according to claim 8 .

10. the optical waveguide further comprises a first mode converter that divides the ridge into a plurality of ridges, and a second mode converter that connects the plurality of ridges into a single ridge; a part of the optical circulation surface of the resonator faces the plurality of ridges across the first gap; 3. The optical circuit according to claim 1.

11. At least two of the plurality of ridges are opposite to positions where higher-order transverse modes of the resonator occur. The optical circuit according to claim 10.

12. a light source that outputs light of a single wavelength to the optical waveguide; further comprising 3. The optical circuit according to claim 1.

13. the light source is a ring laser provided on the substrate or the semiconductor layer, The optical circuit according to claim 12 , wherein the distance between the light source and the optical waveguide is shorter than the distance over which an evanescent wave spreads.

14. an optical circuit according to claim 1 or 2; a photodetector that detects light that has circulated within the resonator; a processor for processing the output of the photodetector; An optical sensor having

15. A moving object comprising the optical circuit according to claim 1 or 2.