Optical Devices

Abstract

To provide a new optical device capable of realizing optical coupling between waveguides with a relatively simple configuration.SOLUTION: An optical device includes: a first waveguide extending in a first direction; and a second waveguide that extends in the first direction, and has a first mirror having a first reflection surface, a second mirror having a second reflection surface that opposes the first reflection surface, and an optical waveguide layer between the first and second mirrors. The first and / or second waveguide has the first mirror, the second mirror, and at least one grating in one portion of an area with which the first waveguide overlaps when viewed from a direction vertical to the first reflection surface. The at least one grating is separated by distance longer than the thickness of the first and / or second mirror in the first direction from the edge of the first or second mirror in an overlapping area. The optical waveguide layer overlaps with an extension line of the center line of the first waveguide, and the optical waveguide layer includes the at least one grating.SELECTED DRAWING: Figure 8A

Description

[Technical Field]

[0001] The present disclosure relates to optical devices. [Background technology]

[0002] Conventionally, various devices capable of scanning space with light have been proposed.

[0003] Patent Document 1 discloses a configuration in which scanning by light can be performed using a driving device that rotates a mirror.

[0004] Patent Document 2 discloses an optical phased array having multiple nanophotonic antenna elements arranged two-dimensionally. Each antenna element is optically coupled to a variable optical delay line (i.e., a phase shifter). In this optical phased array, a coherent optical beam is guided to each antenna element by a waveguide, and the phase of the optical beam is shifted by the phase shifter. This allows the amplitude distribution of the far-field radiation pattern to be changed.

[0005] Patent Document 3 discloses an optical deflection element comprising a waveguide having an optical waveguide layer through which light is guided and first distributed Bragg reflectors formed on the upper and lower surfaces of the optical waveguide layer, a light inlet for allowing light to enter the waveguide, and a light outlet formed on the surface of the waveguide for allowing light that has entered through the light inlet and is guided within the waveguide to exit.

[0006] Patent Document 4 discloses an optical scanning device including a first waveguide that propagates light by total internal reflection and a second waveguide that propagates light between two multilayer reflective films. The first and second waveguides are connected to each other. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2013 / 168266 [Patent Document 2] Special Publication No. 2016-508235 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-16591 [Patent Document 4] International Publication No. 2018 / 061514 Summary of the Invention [Problem to be solved by the invention]

[0008] One aspect of the present disclosure provides a novel optical device that can achieve optical coupling between waveguides with a relatively simple configuration. [Means for solving the problem]

[0009] An optical device according to one embodiment of the present disclosure comprises a first waveguide extending in a first direction, and a second waveguide connected to the first waveguide, the second waveguide comprising a first mirror having a first reflecting surface, a second mirror having a second reflecting surface opposite the first reflecting surface, and an optical waveguide layer between the first mirror and the second mirror, the optical waveguide layer including a portion including a tip end of the first waveguide. At least one of the first waveguide and the second waveguide has one or more gratings in a part of a connection region where the first mirror, the second mirror, and the first waveguide overlap when viewed from a direction perpendicular to the first reflecting surface. The one or more gratings extend from an end of the first mirror or the second mirror in the connection region in the first direction to a portion of the first mirror. and the second mirror.

[0010] The general or specific aspects of the present disclosure may be realized by a device, a system, a method, or any combination thereof. [Effects of the Invention]

[0011] According to one aspect of the present disclosure, optical coupling between waveguides can be achieved with a relatively simple configuration. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view schematically illustrating an example of an optical scanning device. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of the cross-sectional structure of one waveguide element and propagating light. [Figure 3A] FIG. 3A is a diagram showing a cross section of a waveguide array that emits light in a direction perpendicular to the emission surface of the waveguide array. [Figure 3B] FIG. 3B is a diagram showing a cross section of a waveguide array that emits light in a direction different from the direction perpendicular to the emission surface of the waveguide array. [Figure 4] FIG. 4 is a perspective view schematically illustrating an example of a waveguide array in a three-dimensional space. [Figure 5] FIG. 5 is a schematic diagram of the waveguide array and the phase shifter array as viewed from the normal direction (Z direction) of the light emitting surface. [Figure 6] FIG. 6 is a diagram schematically showing an example of an optical device in which the shape of the end portion of the first mirror is changed by processing. [Figure 7] FIG. 7 is a diagram showing the relationship between the change in thickness of the optical waveguide layer and the divergence angle of the light emitted from the first mirror. [Figure 8A] FIG. 8A is a diagram schematically illustrating an optical device according to an exemplary embodiment of the present disclosure. [Figure 8B] FIG. 8B is a schematic diagram of the connection between the total internal reflection waveguide and the slow light waveguide shown in FIG. 8A, viewed from the Z direction. [Figure 9] FIG. 9 is a diagram schematically illustrating an example of an optical device in which the distance from the interface to the grating is longer. [Figure 10A] FIG. 10A is a diagram schematically illustrating a first modified example of the optical device shown in FIG. 8A. [Figure 10B] FIG. 10B is a diagram schematically illustrating a second modification of the optical device shown in FIG. 8A. [Figure 10C] FIG. 10C is a diagram schematically illustrating a third modification of the optical device shown in FIG. 8A. [Figure 11A] FIG. 11A is a diagram schematically illustrating a fourth modification of the optical device shown in FIG. 8A. [Figure 11B] FIG. 11B is a diagram schematically illustrating a fifth modification of the optical device shown in FIG. 8A. [Figure 12] FIG. 12 is a diagram showing an example of the configuration of an optical scanning device in which elements such as an optical branching unit, a waveguide array, a phase shifter array, and a light source are integrated on a circuit board. [Figure 13] FIG. 13 is a schematic diagram showing a state in which a two-dimensional scan is performed by irradiating a light beam such as a laser from an optical scanning device at a distance. [Figure 14] FIG. 14 is a block diagram showing an example of the configuration of a LiDAR system capable of generating a distance measurement image. DETAILED DESCRIPTION OF THE INVENTION

[0013] In this specification, "at least one of the refractive index, thickness, and wavelength" refers to the refractive index, thickness, and wavelength of the optical waveguide layer. This refers to at least one selected from the group consisting of the refractive index, the thickness of the optical waveguide layer, and the wavelength input to the optical waveguide layer. To change the output direction of light, any one of the refractive index, thickness, and wavelength may be controlled independently. Alternatively, the output direction of light may be changed by controlling any two or all of these three. Instead of or in addition to controlling the refractive index or thickness, the wavelength of light input to the optical waveguide layer may be controlled.

[0014] The above basic principles can be applied not only to applications for emitting light but also to applications for receiving optical signals. By changing at least one of the refractive index, thickness, and wavelength, the direction of the light that can be received can be changed one-dimensionally. Furthermore, by changing the phase difference of the light using multiple phase shifters connected to multiple waveguide elements arranged in one direction, the direction of the light that can be received can be changed two-dimensionally.

[0015] The optical scanning device and optical receiving device disclosed herein may be used, for example, as antennas in optical detection systems such as LiDAR (Light Detection and Ranging) systems. Compared to radar systems that use radio waves such as millimeter waves, LiDAR systems use short-wavelength electromagnetic waves (visible light, infrared light, or ultraviolet light), allowing them to detect the distance distribution of objects with high resolution. Such LiDAR systems may be mounted on mobile objects such as automobiles, UAVs (Unmanned Aerial Vehicles, also known as drones), and AGVs (Automated Guided Vehicles) and used as a collision avoidance technology. In this specification, optical scanning devices and optical receiving devices may be collectively referred to as "optical devices." Furthermore, devices used in optical scanning devices or optical receiving devices may also be referred to as "optical devices."

[0016] <Configuration example of optical scanning device> The following describes, as an example, the configuration of an optical scanning device that performs two-dimensional scanning. However, more detailed descriptions than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the inventors provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims. In the following description, identical or similar components are designated by the same reference numerals.

[0017] In this disclosure, "light" refers to electromagnetic waves including not only visible light (wavelength of about 400 nm to about 700 nm), but also ultraviolet light (wavelength of about 10 nm to about 400 nm) and infrared light (wavelength of about 700 nm to about 1 mm). In this specification, ultraviolet light may be referred to as "ultraviolet light," and infrared light may be referred to as "infrared light."

[0018] In this disclosure, "scanning" with light means changing the direction of light. "One-dimensional scanning" means changing the direction of light linearly along a direction intersecting the direction of light. "Two-dimensional scanning" means changing the direction of light two-dimensionally along a plane intersecting the direction of light.

[0019] FIG. 1 is a perspective view schematically illustrating an example of an optical scanning device 100. The optical scanning device 100 includes a waveguide array including a plurality of waveguide elements 10. Each of the plurality of waveguide elements 10 has a shape extending in a first direction (X direction in FIG. 1). The plurality of waveguide elements 10 are regularly arranged in a second direction (Y direction in FIG. 1) intersecting the first direction. The plurality of waveguide elements 10 propagate light in the first direction, while emitting light in a third direction D3 intersecting an imaginary plane parallel to the first and second directions. In the present disclosure, Although the first direction (X direction) and the second direction (Y direction) are orthogonal to each other, they do not have to be orthogonal to each other. In the present disclosure, the waveguide elements 10 are arranged at equal intervals in the Y direction, but they do not necessarily have to be arranged at equal intervals.

[0020] The orientation of the structures shown in the drawings of this application is set for ease of understanding of the description and does not limit the orientation in practice in any way. Furthermore, the shapes and sizes of the entire or partial structures shown in the drawings do not limit the actual shapes and sizes.

[0021] Each of the multiple waveguide elements 10 has a first mirror 30 and a second mirror 40 (hereinafter, each may be simply referred to as a "mirror") facing each other, and an optical waveguide layer 20 located between the mirrors 30 and 40. Each of the mirrors 30 and 40 has a reflective surface that intersects with the third direction D3 at the interface with the optical waveguide layer 20. The mirrors 30 and 40 and the optical waveguide layer 20 have shapes that extend in the first direction (X direction).

[0022] As will be described later, the multiple first mirrors 30 of the multiple waveguide elements 10 may be multiple portions of a single mirror. The multiple second mirrors 40 of the multiple waveguide elements 10 may be multiple portions of a single mirror. Furthermore, the multiple optical waveguide layers 20 of the multiple waveguide elements 10 may be multiple portions of a single optical waveguide layer. Multiple waveguides can be formed by at least (1) configuring each first mirror 30 separately from the other first mirrors 30, (2) configuring each second mirror 40 separately from the other second mirrors 40, or (3) configuring each optical waveguide layer 20 separately from the other optical waveguide layers 20. "Separately configured" refers not only to providing a physical space but also to separating the layers by sandwiching a material with a different refractive index between them.

[0023] The reflective surface of the first mirror 30 and the reflective surface of the second mirror 40 face each other and are substantially parallel to each other. Of the two mirrors 30 and 40, at least the first mirror 30 has the property of transmitting a portion of the light propagating through the optical waveguide layer 20. In other words, the first mirror 30 has a higher optical transmittance for that light than the second mirror 40. Therefore, a portion of the light propagating through the optical waveguide layer 20 is emitted to the outside from the first mirror 30. Such mirrors 30 and 40 may be multilayer film mirrors formed, for example, by a dielectric multilayer film (sometimes referred to as a "multilayer reflective film").

[0024] Two-dimensional scanning by light can be achieved by controlling the phase of light input to each waveguide element 10 and by simultaneously and synchronously changing the refractive index or thickness of the optical waveguide layer 20 in these waveguide elements 10 or the wavelength of light input to the optical waveguide layer 20.

[0025] In order to realize such two-dimensional scanning, the inventors analyzed the operating principle of the waveguide element 10. Based on the results, they succeeded in realizing two-dimensional scanning by light by synchronously driving multiple waveguide elements 10.

[0026] As shown in FIG. 1, when light is input to each waveguide element 10, the light is emitted from the exit surface of each waveguide element 10. The exit surface is located opposite the reflecting surface of the first mirror 30. The direction D3 of the emitted light depends on the refractive index, thickness, and wavelength of the optical waveguide layer. In the present disclosure, at least one of the refractive index, thickness, and wavelength of each optical waveguide layer is synchronously controlled so that the light emitted from each waveguide element 10 is directed in approximately the same direction. This allows the X-direction component of the wave vector of the light emitted from the multiple waveguide elements 10 to be changed. In other words, the direction D3 of the emitted light can be changed along the direction 101 shown in FIG. 1. do.

[0027] Furthermore, because the light beams emitted from the multiple waveguide elements 10 are directed in the same direction, the emitted light beams interfere with each other. By controlling the phase of the light beams emitted from each waveguide element 10, the direction in which the light beams constructively interfere with each other due to interference can be changed. For example, if multiple waveguide elements 10 of the same size are arranged at equal intervals in the Y direction, light beams with phases that differ by a certain amount are input to the multiple waveguide elements 10. By changing this phase difference, the Y-direction component of the wave vector of the output light beams can be changed. In other words, by changing the phase difference between the light beams introduced into the multiple waveguide elements 10, the direction D3 in which the output light beams constructively interfere with each other due to interference can be changed along the direction 102 shown in FIG. 1. This enables two-dimensional optical scanning.

[0028] The operating principle of the optical scanning device 100 will now be described.

[0029] <Operational principle of waveguide elements> FIG. 2 is a diagram illustrating an example of the cross-sectional structure of a single waveguide element 10 and the light propagating therethrough. In FIG. 2, the direction perpendicular to the X and Y directions shown in FIG. 1 is defined as the Z direction, and a cross section parallel to the XZ plane of the waveguide element 10 is illustrated. In the waveguide element 10, a pair of mirrors 30 and 40 are disposed to sandwich the optical waveguide layer 20. Light 22 introduced into one end of the optical waveguide layer 20 in the X direction propagates through the optical waveguide layer 20 while being repeatedly reflected by the first mirror 30 provided on the upper surface (upper surface in FIG. 2 ) of the optical waveguide layer 20 and the second mirror 40 provided on the lower surface (lower surface in FIG. 2 ). The optical transmittance of the first mirror 30 is higher than that of the second mirror 40. Therefore, a portion of the light can be output mainly from the first mirror 30.

[0030] In a waveguide such as a conventional optical fiber, light propagates along the waveguide while repeatedly undergoing total internal reflection. In contrast, in the waveguide element 10, light propagates while repeatedly reflecting off the mirrors 30 and 40 arranged above and below the optical waveguide layer 20. This allows for unlimited light propagation angles. The "light propagation angle" here refers to the angle of incidence at the interface between the mirror 30 or 40 and the optical waveguide layer 20. Light incident at angles closer to perpendicular to the mirror 30 or 40 can also propagate. In other words, light incident at angles smaller than the critical angle for total internal reflection can also propagate. Therefore, the group velocity of light in the propagation direction is significantly slower than the speed of light in free space. This characteristic of the waveguide element 10 allows for significant changes in light propagation conditions with changes in the wavelength of light, the thickness of the optical waveguide layer 20, and the refractive index of the optical waveguide layer 20. The waveguide element 10 is also known as a "reflective waveguide" or "slow-light waveguide."

[0031] The emission angle θ of light emitted into the air from the waveguide element 10 is expressed by the following equation (1).

number

[0032] As can be seen from equation (1), the wavelength of light in air, λ, and the refractive index of the optical waveguide layer 20, n w and the thickness d of the optical waveguide layer 20, the light emission direction can be changed.

[0033] For example, n w When = 2, d = 387 nm, λ = 1550 nm, and m = 1, the emission angle is 0°. From this state, the refractive index is changed to n w = 2.2, the output angle changes to about 66°. On the other hand, if the thickness is changed to d = 420 nm without changing the refractive index, the output angle changes to about 51°. If the wavelength is changed to λ = 1500 nm without changing either the refractive index or the thickness, the output angle changes to about 30°. In this way, when the wavelength λ of light and the refractive index n of the optical waveguide layer 20 are w By changing either the thickness d of the optical waveguide layer 20 or the thickness d of the optical waveguide layer 20, the light emission direction can be changed significantly.

[0034] Therefore, in the optical scanning device 100 of the present disclosure, the wavelength λ of the light input to the optical waveguide layer 20 and the refractive index n w The direction of light emission is controlled by controlling at least one of the wavelength λ of the light and the thickness d of the optical waveguide layer 20. The wavelength λ of the light may be maintained constant during operation. In this case, optical scanning can be achieved with a simpler configuration. The wavelength λ is not particularly limited. For example, the wavelength λ may be in the wavelength range of 400 nm to 1100 nm (visible light to near-infrared light), which provides high detection sensitivity in a photodetector or image sensor that detects light by absorbing it in common silicon (Si). In another example, the wavelength λ may be in the near-infrared wavelength range of 1260 nm to 1625 nm, which has relatively low transmission loss in optical fibers or Si waveguides. Note that these wavelength ranges are merely examples. The wavelength range of the light used is not limited to the visible light or infrared light wavelength range, and may also be, for example, the ultraviolet light wavelength range.

[0035] To change the direction of the emitted light, the optical scanning device 100 may include a first adjusting element that changes at least one of the refractive index, thickness, and wavelength of the optical waveguiding layer 20 in each waveguide element 10.

[0036] As described above, when the waveguide element 10 is used, the refractive index n w、 By changing at least one of the thickness d and the wavelength λ, the light emission direction can be changed significantly. This allows the emission angle of the light emitted from the mirror 30 to be changed in a direction along the waveguide element 10. By using at least one waveguide element 10, such one-dimensional scanning can be realized.

[0037] The light guide layer 20 may contain a liquid crystal material or an electro-optic material to adjust the refractive index of at least a portion of the light guide layer 20. The light guide layer 20 may be sandwiched between a pair of electrodes. The refractive index of the light guide layer 20 can be changed by applying a voltage to the pair of electrodes.

[0038] To adjust the thickness of the optical waveguide layer 20, for example, at least one actuator may be connected to at least one of the first mirror 30 and the second mirror 40. The thickness of the optical waveguide layer 20 can be changed by changing the distance between the first mirror 30 and the second mirror 40 using the at least one actuator. If the optical waveguide layer 20 is formed from a liquid, the thickness of the optical waveguide layer 20 can be easily changed.

[0039] <Operational principle of 2D scanning> In a waveguide array in which multiple waveguide elements 10 are arranged in one direction, the direction of light emission changes due to interference between the light emitted from each waveguide element 10. The direction of light emission can be changed by adjusting the phase of the light supplied to each waveguide element 10. The principle behind this is explained below.

[0040] 3A is a diagram showing a cross section of a waveguide array that emits light in a direction perpendicular to the exit surface of the waveguide array. Fig. 3A also shows the amount of phase shift of light propagating through each waveguide element 10. Here, the amount of phase shift is a value based on the phase of light propagating through the leftmost waveguide element 10. The waveguide array of the present disclosure includes a plurality of waveguide elements 10 arranged at equal intervals. In FIG. 3A, the dashed arcs indicate the wavefronts of light emitted from each waveguide element 10. The straight lines indicate wavefronts formed by optical interference. The arrows indicate the direction of the light emitted from the waveguide array (i.e., the direction of the wave vector). In the example shown in FIG. 3A, the phases of the light propagating through the optical waveguide layer 20 in each waveguide element 10 are all the same. In this case, the light is emitted in a direction (Z direction) perpendicular to both the arrangement direction of the waveguide elements 10 (Y direction) and the extension direction of the optical waveguide layer 20 (X direction).

[0041] FIG. 3B is a diagram showing a cross section of a waveguide array that emits light in a direction different from the direction perpendicular to the exit surface of the waveguide array. In the example shown in FIG. 3B, the phase of light propagating through the optical waveguide layer 20 of multiple waveguide elements 10 differs by a fixed amount (Δφ) in the arrangement direction. In this case, the light is emitted in a direction different from the Z direction. By changing this Δφ, the Y-direction component of the wave vector of the light can be changed. If the center-to-center distance between two adjacent waveguide elements 10 is p, the light emission angle α0 is expressed by the following equation (2):

number

[0042] In the example shown in FIG. 2, the direction of light emission is parallel to the XZ plane. That is, α0 = 0°. In the example shown in FIGS. 3A and 3B, the direction of light emitted from the optical scanning device 100 is parallel to the YZ plane. That is, θ = 0°. However, in general, the direction of light emitted from the optical scanning device 100 is not parallel to either the XZ plane or the YZ plane. That is, θ ≠ 0° and α0 ≠ 0°.

[0043] FIG. 4 is a perspective view schematically illustrating an example of a waveguide array in three-dimensional space. The thick arrows in FIG. 4 represent the direction of light emitted from the optical scanning device 100. θ is the angle between the light emission direction and the YZ plane. θ satisfies formula (1). α0 is the angle between the light emission direction and the XZ plane. α0 satisfies formula (2).

[0044] <Phase control of light introduced into a waveguide array> To control the phase of light emitted from each waveguide element 10, for example, a phase shifter that changes the phase of light may be provided before the light is introduced into the waveguide element 10. The optical scanning device 100 of the present disclosure includes multiple phase shifters connected to the multiple waveguide elements 10, respectively, and a second adjustment element that adjusts the phase of light propagating through each phase shifter. Each phase shifter includes a waveguide that is connected to the optical waveguide layer 20 of a corresponding one of the multiple waveguide elements 10 directly or via another waveguide. The second adjustment element changes the direction of the light emitted from the multiple waveguide elements 10 (i.e., the third direction D3) by changing the phase difference between the light propagating from the multiple phase shifters to the multiple waveguide elements 10. In the following description, an array of multiple phase shifters may be referred to as a "phase shifter array," similar to a waveguide array.

[0045] FIG. 5 is a schematic diagram of the waveguide array 10A and the phase shifter array 80A as viewed from the normal direction (Z direction) of the light emitting surface. In the example shown in FIG. 5, all the phase shifters 80 have the same propagation characteristics, and all the waveguide elements 10 have the same propagation characteristics. The phase shifters 80 and the waveguide elements 10 may have the same length or different lengths. When the lengths of the phase shifters 80 are equal, the amount of phase shift of each can be adjusted by, for example, the drive voltage. In addition, the length of each phase shifter 80 can be adjusted by, for example, the drive voltage. By using a structure in which the phase shift is changed in equal steps, it is possible to provide equal-step phase shifts with the same driving voltage. Furthermore, this optical scanning device 100 further includes an optical branching unit 90 that branches and supplies light to multiple phase shifters 80, a first driving circuit 110 that drives each waveguide element 10, and a second driving circuit 210 that drives each phase shifter 80. The straight arrows in FIG. 5 represent the optical input. Two-dimensional scanning can be achieved by independently controlling the first driving circuit 110 and the second driving circuit 210, which are provided separately. In this example, the first driving circuit 110 functions as one element of a first adjustment element, and the second driving circuit 210 functions as one element of a second adjustment element.

[0046] The first driving circuit 110 changes the angle of light emitted from the optical waveguide layer 20 by changing at least one of the refractive index and thickness of the optical waveguide layer 20 in each waveguide element 10. The second driving circuit 210 changes the phase of light propagating inside the waveguide 20a by changing the refractive index of the waveguide 20a in each phase shifter 80. The optical branching device 90 may be configured with a waveguide in which light propagates by total reflection, or may be configured with a reflective waveguide similar to the waveguide element 10.

[0047] Note that the phase of each beam split by the optical splitter 90 may be controlled before the beam is introduced into the phase shifter 80. For this phase control, for example, a passive phase control structure may be used, in which the length of the waveguide leading to the phase shifter 80 is adjusted. Alternatively, a phase shifter that has the same function as the phase shifter 80 and can be controlled by an electrical signal may be used. By using this method, for example, the phase may be adjusted before being introduced into the phase shifter 80 so that light of the same phase is supplied to all the phase shifters 80. Such an adjustment can simplify the control of each phase shifter 80 by the second driving circuit 210.

[0048] An optical device having a configuration similar to the optical scanning device 100 described above can also be used as an optical receiving device. Details of the optical device, such as its operating principle and method, are disclosed in U.S. Patent Application Publication No. 2018 / 0224709, the entire disclosure of which is incorporated herein by reference.

[0049] <Connection between total internal reflection waveguide and slow light waveguide> Next, an example will be described in which a total internal reflection waveguide and a slow light waveguide are connected together to input light from the total internal reflection waveguide to the slow light waveguide.

[0050] 6 is a cross-sectional view schematically illustrating an example of an optical device in which a total internal reflection waveguide 1 and a slow-light waveguide 10 are connected. In this specification, the total internal reflection waveguide 1 may be referred to as the "first waveguide 1," and the slow-light waveguide 10 may be referred to as the "second waveguide 10." For the time being, the optical device shown in FIG. 6 will be described without considering the shape of the end 30e of the first mirror 30.

[0051] At least the tip of the total internal reflection waveguide 1 extends in the X direction. The slow-light waveguide 10 is connected to the total internal reflection waveguide 1. The optical waveguide layer 20 in the slow-light waveguide 10 includes a portion including the tip of the total internal reflection waveguide 1. The refractive index of the optical waveguide layer 20 is lower than that of the total internal reflection waveguide 1. In a connection region 111 where the total internal reflection waveguide 1 and the slow-light waveguide 10 overlap as viewed from the Z direction, the total internal reflection waveguide 1 includes a grating 15 whose refractive index varies with a period p along the X direction. The connection region 111 can also be considered as the region where the first mirror 30, the second mirror 40, and the total internal reflection waveguide 1 overlap as viewed from the Z direction. The grating 15 shown in FIG. 6 has four recesses aligned in the X direction. In practice, more recesses may be provided in the grating 15. Instead of recesses, protrusions may be provided. The number of recesses or protrusions arranged in the X direction in the grating 15 is preferably, for example, 4 or more. The number of recesses or protrusions may be greater than or equal to 64 and less than or equal to 64. In one example, the number of recesses or protrusions may be greater than or equal to 8 and less than or equal to 32. In another example, the number of recesses or protrusions may be greater than or equal to 8 and less than or equal to 16. The number of recesses or protrusions may be adjusted depending on the diffraction efficiency of each recess or protrusion. The diffraction efficiency of each recess or protrusion depends on dimensional conditions such as its depth or height and width. Therefore, the number of recesses or protrusions is adjusted depending on the dimensions of each recess or protrusion so that good characteristics can be obtained for the grating 15 as a whole.

[0052] The total internal reflection waveguide 1 has, in the connection region 111, a first surface 1s1 facing the reflecting surface of the first mirror 30 and a second surface 1s2 facing the reflecting surface of the second mirror 40. In the example shown in FIG. 6, the grating 15 is provided on the first surface 1s1 of the total internal reflection waveguide 1. The grating 15 may also be provided on the second surface 1s2. The grating 15 may be provided on at least one of the first surface 1s1 and the second surface 1s2 of the total internal reflection waveguide 1.

[0053] Grating 15 is not limited to being provided at the interface between total internal reflection waveguide 1 and slow light waveguide 10, and may be provided at other positions. Furthermore, multiple gratings may be provided. In connection region 111 where total internal reflection waveguide 1 and slow light waveguide 10 overlap when viewed from a direction perpendicular to the reflecting surface of first mirror 30, at least a portion of total internal reflection waveguide 1 and slow light waveguide 10 may include at least one grating. The refractive index of each grating periodically changes along the X direction in which total internal reflection waveguide 1 and slow light waveguide 10 extend.

[0054] The portion of the total internal reflection waveguide 1 located outside the optical waveguide layer 20 may be supported by another dielectric layer, or may be sandwiched between two dielectric layers.

[0055] The length of the connection region 111 may be, for example, about 3 μm to 50 μm. A grating 15 with about 8 to 32 periods may be formed inside a connection region 111 of such size. The length of the non-connection region 112 may be, for example, about 100 μm to 5 mm. The length of the connection region 111 may be, for example, about one hundredth to one tenth of the length of the non-connection region 112. However, the length is not limited to this, and the dimensions of each component are determined depending on the required characteristics.

[0056] In connection region 111, first mirror 30 does not necessarily have a higher transmittance than second mirror 40. In non-connection region 112 of slow-light waveguide 10 other than connection region 111, first mirror 30 does not necessarily have a higher transmittance than second mirror 40 in a region close to connection region 111. Connection region 111 is provided to increase the light coupling efficiency. For this reason, slow-light waveguide 10 does not necessarily have to emit light in the vicinity of connection region 111.

[0057] The propagation constant of the guided mode in the total reflection waveguide 1 is β1=2πn e1 / λ, and the propagation constant of the guided mode in the slow light waveguide 10 is β2=2πn e2 / λ, where λ is the wavelength of light in air. e1 and n e2 are the effective refractive indices (also called equivalent refractive indices) of the total internal reflection waveguide 1 and the slow-light waveguide 10, respectively. The light propagating in the total internal reflection waveguide 1 is not coupled to the external air. The effective refractive index of such a guided mode is n e1 On the other hand, a part of the light propagating through the optical waveguide layer 20 in the slow-light waveguide 10 is emitted to the outside air. The effective refractive index of such a waveguide mode is 0 <n e2 <1. Therefore, β1 and β2 are significantly different. Therefore, in general, the coupling efficiency of the guided light from the total internal reflection waveguide 1 to the slow light waveguide 10 is low.

[0058] In the connection region 111, when the total internal reflection waveguide 1 is provided with a grating 15, the grating Diffraction occurs due to the lattice pitch 15. In this case, the propagation constant β1 of the guided mode in the total internal reflection waveguide 1 shifts by an integer multiple of the reciprocal lattice 2π / p. For example, if β1 shifts to β1-(2π / p) due to -1st-order diffraction, by appropriately setting p, β1-(2π / p)=β2 can be established. In this case, the two propagation constants in the connection region 111 match, and the guided light is coupled from the total internal reflection waveguide 1 to the slow-light waveguide 10 with high efficiency. From β1-(2π / p)=β2, the period p is expressed by the following equation (3):

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[0059] 0 <n e2 <1, the period p satisfies the following formula (4).

number

[0060] In the slow light waveguide 10, the connection region 111 and the other non-connection region 112 have the same waveguide mode, and therefore the guided light is coupled with high efficiency.

[0061] In the above example, a grating is provided throughout the connection region 111 where the first waveguide 1 and the second waveguide 10 overlap. However, the structure of the optical device of the present disclosure is not limited to such a structure. The grating may be provided only in a portion of the connection region 111, for example, in a portion of the connection region 111 close to the tip of the first waveguide 1. In other words, a grating may not be provided in a portion of the connection region 111 away from the tip of the first waveguide 1. In an embodiment of the present disclosure, one or more gratings are provided in a position in the first direction away from the interface between the optical waveguide layer 20 and a medium (e.g., air) that contacts both the optical waveguide layer 20 and the first waveguide 1, a distance longer than at least one of the thicknesses of the first mirror 30 and the second mirror 40. The inventors' investigations have revealed that such a structure makes it easy to achieve good light output characteristics even when the thickness of the optical waveguide layer 20 is not uniform.

[0062] In the above example, it is assumed that the thickness of the optical waveguide layer 20 is constant along the X direction. However, in reality, the thickness of the optical waveguide layer 20 may vary along the X direction due to various reasons. The following describes in detail the influence of the thickness of the optical waveguide layer 20 varying along the X direction. In the following description, the number of gratings is one, but the number of gratings may be two or more.

[0063] FIG. 7 is a diagram showing an example of calculation results of the relationship between the rate of change in thickness of the optical waveguide layer 20 and the divergence angle of light emitted from the first mirror 30. In the example of FIG. 7, the range of the rate of change in thickness of the optical waveguide layer 20 is 0 nm / mm to 100 nm / mm. Here, the "rate of change in thickness" refers to the amount of change in thickness per 1 mm of displacement along the length direction of the optical waveguide layer 20, i.e., along the first direction. 0 nm / mm indicates that the thickness of the optical waveguide layer 20 does not substantially change along the X direction. 100 nm / mm indicates that the thickness of the optical waveguide layer 20 changes by 100 nm per 1 mm of displacement along the length direction of the optical waveguide layer 20.

[0064] In this calculation, the thickness of the optical waveguide layer 20 was assumed to be 2.15 μm, the refractive index was assumed to be 1.68, and the thickness of the optical waveguide layer 20 varied along the X direction. The complex amplitude of the light emitted from the exit surface of the first mirror 30 was calculated, and then a two-dimensional discrete Fourier transform was performed to calculate the angular spectrum of the emitted light at a distant location. In the following explanation, the divergence angle of the emitted light is expressed as the full width at half maximum of the emitted light in the angular spectrum.

[0065] As shown in FIG. 7, when the thickness change rate of the optical waveguide layer 20 is approximately 10 nm / mm, the divergence angle of the emitted light is approximately the same as when the thickness of the optical waveguide layer 20 is constant. However, when the thickness change rate of the optical waveguide layer 20 is 20 nm / mm or more, the divergence angle of the emitted light increases approximately monotonically with the inclination of the optical waveguide layer 20. This divergence of the emitted light is caused by the uneven thickness of the optical waveguide layer 20, which disrupts the phase distribution of the light emitted from the first mirror 30. If the divergence angle of the emitted light is large, the linearity of the emitted light is lost. In particular, the intensity of the light emitted from the first mirror 30 is higher in the connection region 111 where the total internal reflection waveguide 1 and the slow-light waveguide 10 are connected than in the region where the light travels further from the connection region 111. Therefore, if the thickness of the optical waveguide layer 20 in the connection region 111 is not constant, when light is emitted from the first mirror 30 in the connection region 111, the relatively strong emitted light may spread excessively.

[0066] One possible cause of the change in thickness of the optical waveguide layer 20 is a change in the shape of the end of the first mirror 30 due to processing. As shown in Fig. 6, the end 30e of the first mirror 30 may be tilted by, for example, etching. Another possible cause of the change in thickness of the optical waveguide layer 20 is warping of the first mirror 30 and / or the second mirror 40.

[0067] An example of an optical device that suppresses the influence of changes in the thickness of the optical waveguide layer 20 will be described below.

[0068] FIG. 8A is a schematic diagram illustrating an optical device according to an exemplary embodiment of the present disclosure. The medium surrounding the optical device is, for example, air. An interface 20i between the optical waveguide layer 20 and a medium in contact with both the optical waveguide layer 20 and the total internal reflection waveguide 1 surrounds the total internal reflection waveguide 1. In this embodiment, the ends of the first mirror 30 and the second mirror 40 in the X direction coincide. Therefore, the end face 20i of the connection region 111 in this embodiment is a plane that passes through the ends of the first mirror 30 and the second mirror 40 and is parallel to the Y and Z directions. This end face 20i is the end of the connection region 111 in this embodiment. In this embodiment, the interface 20i between the medium and the optical waveguide layer 20 coincides with the end face 20i of the connection region 111. As shown in FIG. 8A, the grating 15 is located further inside the optical waveguide layer 20 than in the example shown in FIG. 6, away from the end face 30e of the first mirror 30. If the length of the inclined portion of the end 30e of the first mirror 30 projected in the X direction exceeds the thickness of the first mirror 30, such a first mirror 30 is not used in optical devices from the viewpoint of reliability. Therefore, in a first mirror 30 actually used in an optical device, the length of the inclined portion of the end 30e projected in the X direction is equal to or less than the thickness of the first mirror 30. The thickness of the first mirror 30 may be, for example, 3 μm. The same applies to a case where the second mirror 40 has an end face similar to that of the first mirror 30 near the end face 20i. Therefore, to suppress the influence of changes in the thickness of the optical waveguide layer 20, the grating 15 may be positioned in the X direction from the end face 20i by a distance longer than at least one of the thicknesses of the first mirror 30 and the second mirror 40. In other words, the distance L0 from the end face 20i to the grating 15 in the X direction is longer than at least one of the thicknesses of the first mirror 30 and the second mirror 40. Here, the distance L0 from the end face 20i to the grating 15 means the distance between the end face 20i and the end of the two ends of the grating 15 that is closer to the end face 20i.

[0069] 8B is a schematic diagram of the connection between the total internal reflection waveguide 1 and the slow light waveguide 10 shown in FIG. 8A, viewed from the Z direction. In the example shown in FIG. 8B, the total internal reflection waveguide 1 includes a portion outside the optical waveguide layer 20 whose width monotonically increases as it approaches the slow light waveguide 10. That is, a portion of the total internal reflection waveguide 1 has a tapered structure 1t. The width w of the total internal reflection waveguide 1 in the portion far from the optical waveguide layer 20 is w is narrower than the width wc of the total internal reflection waveguide 1 in the connection region 111, which is the coupling portion. w is the width w c The total internal reflection waveguide 1 has a tapered structure 1t between the narrow waveguide portion 1w and the wide waveguide portion 1c. By adopting such a structure, it is possible to suppress reflection of light propagating through the narrow waveguide portion 1w when it enters the wide waveguide portion 1c.

[0070] The warpage of the first mirror 30 and / or the second mirror 40 is smallest near the center of the first mirror 30 and / or the second mirror 40 in the X direction. Therefore, the grating 15 may be located near the center of the first mirror 30 and / or the second mirror 40 in the X direction within the optical waveguide layer 20. On the other hand, the shorter the distance L0 from the end face 20i to the grating 15, the smaller the probability that defects and / or particles will occur in the portion of the total internal reflection waveguide 1 located inside the optical waveguide layer 20. Therefore, the distance L0 from the end face 20i to the grating 15 and the length L of the grating 15 g The sum of L0+L g L0+L may be shorter than half the length of the first mirror 30 or half the length of the second mirror 40, whichever is shorter. g corresponds to the length of the connection region 111 shown in Figure 8A. The overall length of each of the first mirror 30 and the second mirror 40 shown in Figure 8A is not particularly limited, but may be, for example, 300 μm or more and 10 mm or less. In one example, the length may be 1 mm or more and 5 mm or less, for example, about 2 mm.

[0071] The connection region 111 can be divided into a first connection region 111a that does not include a grating and a second connection region 111b that includes a grating 15. The length of the first connection region 111a is L0, and the length of the second connection region 111b is L1. g The length L0 of the first connection region 111a may be, for example, 3 μm or more and 1 mm or less. The length L0 may be 10 μm or more and 1 mm or less. In another example, the length L0 may be set to 150 μm or more and 1 mm or less.

[0072] Next, an example of an optical device in which the distance L0 from the end face 20i to the grating 15 is longer will be described.

[0073] FIG. 9 is a schematic diagram illustrating an example of an optical device in which the distance L0 from the end face 20i to the grating 15 is longer. The distance L0 from the end face 20i to the grating 15 can be set to a value longer than the attenuation distance required for the intensity of light propagating through the slow-light waveguide 10 along the X direction to attenuate by a factor of 1 / e, where e is the base of the natural logarithm. The attenuation distance can be, for example, from about 150 μm to about 200 μm, or longer. The attenuation distance can be several tenths or more of the length of the region where the first mirror 30 and the second mirror 40 overlap when viewed from the Z direction. When Equation (3) is not satisfied, light propagating through the total internal reflection waveguide 1 does not propagate to the non-connection region 112 but is reflected by the end face 1e of the total internal reflection waveguide 1 in the optical waveguide layer 20. A portion of the reflected light leaks into the optical waveguide layer 20 in the connection region 111 and propagates in the −X direction. This allows light propagating in the -X direction within the optical waveguide layer 20 to be emitted backward from the first mirror 30 in the connection region 111. Furthermore, when the optical waveguide layer 20 contains a liquid crystal material or an electro-optical material, the direction of light emission can be switched from backward to forward, and vice versa, by adjusting the refractive index of the optical waveguide layer 20 so as to satisfy formula (3). Note that "forward" refers to the direction of light emitted from the slow-light waveguide 10. 8A in that the output direction of light from the slow-light waveguide 10 has a component in the +X direction from the total internal reflection waveguide 1 to the slow-light waveguide 10. "Backward" means that the output direction of light from the slow-light waveguide 10 has a component in the -X direction from the slow-light waveguide 10 to the total internal reflection waveguide 1. Next, modified examples of the connection between the total internal reflection waveguide 1 and the slow-light waveguide 10 via the grating 15 will be described. The following modified examples, which will be described with reference to FIGS. 10A to 10C and 11A and 11B, have in common with the example shown in FIG. 8A in that the grating 15 is located further inside the optical waveguide layer 20.

[0074] 10A to 10C are cross-sectional views schematically illustrating modifications of the optical device shown in FIG. 8A. In the examples shown in FIGS. 10A to 10C, the total internal reflection waveguide 1 is supported by a dielectric layer 51, which is in turn supported by a second mirror 40. The total internal reflection waveguide 1 and the slow light waveguide 10 share the second mirror 40. The dielectric layer 51 is made of, for example, SiO2. The refractive index n of the dielectric layer 51 is sub is the refractive index n of the total internal reflection waveguide 1 w1 is smaller than . Therefore, light propagating through the total internal reflection waveguide 1 does not leak into the dielectric layer 51. The dielectric layer 51 does not need to be supported by the second mirror 40. In areas other than the connection region 111 and the non-connection region 112, the second mirror 40 may be replaced with a structure made of the same material as the dielectric layer 51. The end face of the connection region 111 in this modification is a plane that passes through the end of the first mirror 30 and is parallel to the Y direction and the Z direction. This end face is the end of the connection region 111 in this embodiment.

[0075] In the example shown in Figure 10A, the total internal reflection waveguide 1 has a grating 15 on the first surface 1s1. In the example shown in Figure 10B, the total internal reflection waveguide 1 has a grating 15 on the second surface 1s2. In the example shown in Figure 10C, the total internal reflection waveguide 1 has gratings 15 on both the first surface 1s1 and the second surface 1s2.

[0076] Thus, the total internal reflection waveguide 1 may include a grating 15 on at least one of the first surface 1s1 and the second surface 1s2.

[0077] 11A and 11B are cross-sectional views schematically illustrating another modified example of the optical device shown in Fig. 8A. In the example shown in Fig. 11A and 11B, the total internal reflection waveguide 1 is supported by a dielectric layer 51, and the dielectric layer 51 is supported by a second mirror 40, similar to the examples shown in Fig. 10A to 10C.

[0078] 11A and 11B, grating 15 is provided on the reflecting surface of first mirror 30 and / or second mirror 40, rather than on total internal reflection waveguide 1. In the example shown in FIG. 11A, slow light waveguide 10 includes grating 15 on the reflecting surface of first mirror 30. In the example shown in FIG. 11B, slow light waveguide 10 includes grating 15 on the reflecting surface of second mirror 40.

[0079] 11A and 11B, the total internal reflection waveguide 1 is relatively close to the first mirror 30 and / or the second mirror 40 in the Z direction. This causes the evanescent light in the total internal reflection waveguide 1 to be diffracted by the grating 15. As a result, as in the previous example, the coupling efficiency of the guided light from the total internal reflection waveguide 1 to the slow light waveguide 10 can be improved. In this way, the slow light waveguide 10 may include a grating 15 on at least one of the reflecting surface of the first mirror 30 and the reflecting surface of the second mirror 40.

[0080] As shown in FIGS. 8A, 10A to 10C, and 11A and 11B, when viewed from the Z direction, at least one of the total internal reflection waveguide 1 and the slow-light waveguide 10 has the following characteristics: A grating 15 is provided in a part of the area where the total internal reflection waveguide 1 and the slow light waveguide 10 overlap.

[0081] The total internal reflection waveguide 1 shown in FIG. 9 may also be supported by a dielectric layer 51 on the second mirror 40, as shown in FIGS. 10A to 10C, 11A and 11B.

[0082] Next, functions that the components in the optical device described above may have will be described.

[0083] At least a part of the optical waveguide layer 20 may have a structure that allows adjustment of the refractive index and / or thickness. By adjusting the refractive index and / or thickness, the X-direction component of the direction of the light emitted from the first mirror 30 changes.

[0084] The light guide layer 20 may contain a liquid crystal material or an electro-optic material to adjust the refractive index of at least a portion of the light guide layer 20. The light guide layer 20 may be sandwiched between a pair of electrodes. The refractive index of the light guide layer 20 can be changed by applying a voltage to the pair of electrodes.

[0085] In the optical waveguide layer 20, the refractive index in the connection region 111 and the refractive index in the non-connection region 112 may be adjusted simultaneously. However, adjusting the refractive index in the connection region 111 may change the condition of formula (3). As a result, the coupling efficiency of the guided light from the total internal reflection waveguide 1 to the slow-light waveguide 10 may decrease. Therefore, the refractive index in the connection region 111 may be kept constant, and only the refractive index in the non-connection region 112 may be adjusted. Even if the refractive indexes in the connection region 111 and the non-connection region 112 are different, the influence of reflection of the guided light that occurs at the interface between the connection region 111 and the non-connection region 112 is small.

[0086] In this case, the pair of electrodes (also referred to as the "first pair of electrodes") sandwich a portion of the optical waveguide layer 20 that is different from the portion that overlaps with the total internal reflection waveguide 1 when viewed from a direction perpendicular to the reflecting surface of the first mirror 30. A control circuit (not shown) applies a voltage to the pair of electrodes, thereby adjusting the refractive index of at least a portion of the non-connected region 112.

[0087] It is sufficient if the condition of formula (3) is satisfied as designed, but in reality, due to manufacturing errors, the condition of formula (3) may not be completely satisfied. To compensate for such cases, the optical device may be provided with a function for adjusting the refractive index of the connection region 111, in addition to adjusting the refractive index of the non-connection region 112.

[0088] In this case, a second pair of electrodes may be provided in addition to the first pair of electrodes. The second pair of electrodes sandwich at least a portion of the optical waveguide layer 20 that overlaps with the total internal reflection waveguide when viewed from the Z direction. The control circuit can independently adjust the refractive index of the portion of the optical waveguide layer located between the first pair of electrodes and the refractive index of the portion of the optical waveguide layer located between the second pair of electrodes by independently applying voltages to the first pair of electrodes and the second pair of electrodes.

[0089] To adjust the thickness of the optical waveguide layer 20, for example, at least one actuator may be connected to at least one of the first mirror 30 and the second mirror 40. The control circuit can change the thickness of the optical waveguide layer 20 by controlling the at least one actuator to change the distance between the first mirror 30 and the second mirror 40. If the optical waveguide layer 20 is formed from a liquid, the thickness of the optical waveguide layer 20 can be easily changed.

[0090] The at least one actuator is connected to the first mirror 30 in the non-connected region 112. and the second mirror 40. The thickness of the optical waveguide layer 20 in the non-connected region 112 can be changed by the actuator. In this case, the condition of equation (3) does not change.

[0091] The at least one actuator may be two actuators. One actuator may be connected to at least one of the first mirror 30 and the second mirror 40 in the connection region 111. The other actuator may be connected to at least one of the first mirror 30 and the second mirror 40 in the non-connection region 112. The two actuators make it possible to separately change the thickness of the optical waveguide layer 20 in the connection region 111 and the thickness of the optical waveguide layer 20 in the non-connection region 112. This makes it possible to compensate for cases where the condition in equation (3) is not satisfied as designed.

[0092] Two-dimensional optical scanning is also possible by configuring an optical device including multiple pairs of total internal reflection waveguides 1 and slow light waveguides 10. Such an optical scanning device includes multiple waveguide units arranged in the Y direction. Each waveguide unit includes the above-mentioned total internal reflection waveguide 1 and slow light waveguide 10. In this optical scanning device, multiple phase shifters are connected to the multiple waveguide units, respectively. Each of the multiple phase shifters includes a waveguide that connects directly to the total internal reflection waveguide 1 in a corresponding one of the multiple waveguide units or via another waveguide. By changing the phase difference between the light passing through the multiple phase shifters, the Y-direction component of the direction of the light emitted from the optical scanning device can be changed. An optical receiving device can also be configured with a similar structure.

[0093] <Application example> FIG. 12 illustrates an example configuration of an optical scanning device 100 in which elements such as an optical splitter 90, a waveguide array 10A, a phase shifter array 80A, and a light source 130 are integrated on a circuit board (e.g., a chip). The light source 130 may be, for example, a light-emitting element such as a semiconductor laser. In this example, the light source 130 emits light of a single wavelength, λ, in free space. The optical splitter 90 splits the light from the light source 130 and introduces it into the waveguides of the multiple phase shifters. In the example illustrated in FIG. 12, an electrode 62A and multiple electrodes 62B are provided on the chip. A control signal is supplied from the electrode 62A to the waveguide array 10A. Control signals are sent from the multiple electrodes 62B to the multiple phase shifters 80 in the phase shifter array 80A, respectively. The electrode 62A and the multiple electrodes 62B may be connected to a control circuit (not shown) that generates the above control signals. The control circuit may be provided on the chip illustrated in FIG. 12 or on another chip in the optical scanning device 100.

[0094] Wide-range optical scanning can be achieved with a small device by integrating all components on a chip as shown in Figure 12. For example, all the components shown in Figure 12 can be integrated on a chip of about 2 mm x 1 mm.

[0095] FIG. 13 is a schematic diagram showing a two-dimensional scan performed by irradiating a light beam, such as a laser, from the optical scanning device 100 to a distant object. The two-dimensional scan is performed by moving the beam spot 310 in the horizontal and vertical directions. For example, by combining this with the well-known TOF (Time of Flight) method, a two-dimensional distance measurement image can be acquired. The TOF method is a method of calculating the time of flight of light by irradiating a laser and observing the light reflected from an object, thereby determining the distance.

[0096] FIG. 14 is a block diagram showing an example of the configuration of a LiDAR system 300, which is an example of a light detection system capable of generating such a distance measurement image. The optical scanning device 100 includes an optical detector 400, a signal processing circuit 600, and a control circuit 500. The optical detector 400 detects light emitted from the optical scanning device 100 and reflected from an object. The optical detector 400 may be, for example, an image sensor sensitive to the wavelength λ of light emitted from the optical scanning device 100, or a photodetector including a light-receiving element such as a photodiode. The optical detector 400 outputs an electrical signal corresponding to the amount of light received. The signal processing circuit 600 calculates the distance to the object based on the electrical signal output from the optical detector 400 and generates distance distribution data. The distance distribution data is data indicating a two-dimensional distribution of distances (i.e., a ranging image). The control circuit 500 is a processor that controls the optical scanning device 100, the optical detector 400, and the signal processing circuit 600. The control circuit 500 controls the timing of irradiation of the light beam from the optical scanning device 100 and the timing of exposure and signal readout of the photodetector 400, and instructs the signal processing circuit 600 to generate a distance measurement image.

[0097] In 2D scanning, the frame rate for acquiring distance measurement images can be selected from among the commonly used frame rates for video, such as 60 fps, 50 fps, 30 fps, 25 fps, and 24 fps. Furthermore, when considering applications to in-vehicle systems, the higher the frame rate, the more frequently distance measurement images are acquired, resulting in more accurate obstacle detection. For example, when traveling at 60 km / h, a frame rate of 60 fps allows an image to be acquired every approximately 28 cm of vehicle movement. A frame rate of 120 fps allows an image to be acquired every approximately 14 cm of vehicle movement. A frame rate of 180 fps allows an image to be acquired every approximately 9.3 cm of vehicle movement.

[0098] The time required to acquire one ranging image depends on the beam scanning speed. For example, to acquire an image with a resolution of 100 x 100 at 60 fps, beam scanning must be completed in 1.67 μs or less per point. In this case, the control circuit 500 controls the emission of the light beam by the optical scanning device 100 and the signal accumulation and readout by the photodetector 400 at an operating speed of 600 kHz.

[0099] <Application example to optical receiving device> The optical scanning device of the present disclosure can also be used as an optical receiving device with a substantially identical configuration. The optical receiving device includes a waveguide array 10A identical to that of the optical scanning device and a first adjustment element that adjusts the direction of receivable light. Each first mirror 30 of the waveguide array 10A transmits light incident on the side opposite the first reflecting surface from a third direction. Each optical waveguide layer 20 of the waveguide array 10A propagates light that has passed through the first mirror 30 in a second direction. The first adjustment element can change the direction of receivable light by changing at least one of the refractive index and thickness of the optical waveguide layer 20 in each waveguide element 10 and the wavelength of light. Furthermore, if the optical receiving device includes multiple phase shifters 80, or 80a and 80b, identical to those of the optical scanning device, and second adjustment elements that change the phase difference between the light output from the multiple waveguide elements 10 after passing through the multiple phase shifters 80, or 80a and 80b, respectively, the direction of receivable light can be changed two-dimensionally.

[0100] For example, an optical receiving device can be constructed by replacing the light source 130 in the optical scanning device 100 shown in Figure 12 with a receiving circuit. When light of wavelength λ enters the waveguide array 10A, the light is sent to the optical branching device 90 through the phase shifter array 80A, and is finally collected at one point and sent to the receiving circuit. The intensity of the light collected at one point can be said to represent the sensitivity of the optical receiving device. The sensitivity of the optical receiving device can be adjusted by adjustment elements separately incorporated into the waveguide array and the phase shifter array 80A. In the optical receiving device, for example, in Figure 4, the directions of the wave vectors (thick arrows in the figure) are reversed. The incident light is divided into an optical component in the direction in which the waveguide element 10 extends (X direction in the figure) and an optical component in the direction in which the waveguide element 10 is arranged. The sensitivity of the optical component in the X direction can be adjusted by an adjustment element incorporated in the waveguide array 10A. On the other hand, the sensitivity of the optical component in the arrangement direction of the waveguide element 10 can be adjusted by an adjustment element incorporated in the phase shifter array 80A. The optical phase difference Δφ when the sensitivity of the optical receiving device is maximized, the refractive index n of the optical waveguide layer 20, w and thickness d, θ and α0 shown in Figure 4 can be determined. This allows the incident direction of light to be identified.

[0101] The above-described embodiments can be combined as appropriate.

[0102] Finally, the optical devices mentioned above are summarized in the following items.

[0103] An optical device according to a first item includes a first waveguide extending in a first direction, and a second waveguide connected to the first waveguide, the second waveguide including a first mirror having a first reflecting surface, a second mirror having a second reflecting surface opposite the first reflecting surface, and an optical waveguide layer between the first mirror and the second mirror, the optical waveguide layer including a portion including a tip end of the first waveguide. At least one of the first waveguide and the second waveguide has one or more gratings in a portion of a connection region where the first mirror, the second mirror, and the first waveguide overlap when viewed from a direction perpendicular to the first reflecting surface. The one or more gratings are spaced apart in the first direction from an end of the first mirror or the second mirror in the connection region by a distance longer than at least one of the thickness of the first mirror and the thickness of the second mirror.

[0104] In this optical device, even if an inclined portion is formed at the end of the first mirror and / or the second mirror closer to the connection region, the light propagating through the first waveguide can be coupled with high efficiency to the second waveguide via the grating without being affected by the inclined portion.

[0105] An optical device according to a second item is the optical device according to the first item, wherein the connection region includes a first region from the end to the one or more gratings and a second region in which the one or more gratings are present, and the sum of the length of the first region in the first direction and the length of the second region in the first direction is shorter than either half the length of the first mirror in the first direction or half the length of the second mirror in the first direction, whichever is shorter.

[0106] In this optical device, the influence of defects and / or particles occurring inside the optical waveguide layer on the optical coupling from the first waveguide to the second waveguide can be suppressed.

[0107] The optical device according to the third item is the optical device according to the first or second item, wherein the distance from the end to the one or more gratings is longer than the distance required for the intensity of light propagating through the second waveguide along the first direction to be attenuated by a factor of 1 / e (e is the base of the natural logarithm).

[0108] In this optical device, when light propagating through the first waveguide is not coupled to the second waveguide via the grating, part of the light propagates through the optical waveguide layer in the connection region in a direction from the second waveguide to the first waveguide, and as a result, part of the light is emitted backward from the first mirror and / or the second mirror.

[0109] An optical device according to a fourth aspect is the optical device according to any one of the first to third aspects, wherein the transmittance of the first mirror is higher than the transmittance of the second mirror, and a portion of light input from the first waveguide to the optical waveguide layer in the second waveguide is output via the first mirror.

[0110] In this optical device, light is emitted through a first mirror.

[0111] An optical device according to a fifth item is the optical device according to any one of the first to fourth items, wherein the effective refractive index of the guided mode of the light propagating through the first waveguide is n e1 , where λ is the wavelength of the light in air, and the period of each of the one or more gratings is λ / n e1 is larger than λ / (n e1 -1).

[0112] In this optical device, by appropriately setting the grating period, light propagating through the first waveguide can be coupled with high efficiency to the second waveguide via the grating. [Industrial Applicability]

[0113] The optical scanning device and optical receiving device disclosed herein can be used in applications such as lidar systems mounted on vehicles such as automobiles, UAVs, and AGVs. [Explanation of symbols]

[0114] 10 Waveguide elements, optical waveguides 11 Optical waveguide 10A Waveguide Array 15, 15a, 15b, 15c, 15m grating 20 Optical waveguide layer 30 First Mirror 40 Second Mirror 51 Dielectric layer 62a, 62b, 62A, 62B electrode 73 Multiple bulkheads 80 Phase Shifter 80A Phase Shifter Array 90 Optical splitter 100 Optical Scanning Device 111 Connection Area 112 Unconnected Area 110 Waveguide array drive circuit 130 light source 210 Phase shifter array driver circuit 310 beam spot 400 photodetectors 500 control circuit 600 Signal Processing Circuit

Claims

1. a first waveguide extending in a first direction; a second waveguide extending in the first direction, a first mirror having a first reflective surface; a second mirror having a second reflecting surface facing the first reflecting surface; a second waveguide comprising an optical waveguide layer between the first mirror and the second mirror; at least one of the first waveguide and the second waveguide has one or more gratings in a part of an area where the first mirror, the second mirror, and the first waveguide overlap when viewed in a direction perpendicular to the first reflecting surface; the one or more gratings are spaced apart in the first direction from an edge of the first mirror or the second mirror in the overlapping region by a distance greater than at least one of a thickness of the first mirror and a thickness of the second mirror; the optical waveguide layer overlaps with an extension of the center line of the first waveguide; the optical waveguide layer contains the one or more gratings; Optical devices.

2. the first waveguide is a total internal reflection waveguide; The optical device of claim 1 .

3. a pair of electrodes sandwiching the optical waveguide layer therebetween; 3. The optical device according to claim 1 or 2.

4. It has a structure that allows adjustment of the refractive index and / or thickness, In the second waveguide, the refractive index of at least a part of the overlapping region and the refractive index of at least a part of the region other than the overlapping region are adjusted separately.

4. The optical device according to claim 1.

5. the overlapping region includes a first region from the end to the one or more gratings and a second region in which the one or more gratings are present; a sum of a length of the first region in the first direction and a length of the second region in the first direction is shorter than either half the length of the first mirror in the first direction or half the length of the second mirror in the first direction, whichever is shorter; 5. The optical device according to claim 1.

6. a distance from the end to the one or more gratings is longer than a distance required for the intensity of light propagating through the second waveguide along the first direction to be attenuated by a factor of 1 / e (e is the base of the natural logarithm); 6. An optical device according to claim 1.

7. the transmittance of the first mirror is higher than the transmittance of the second mirror; a part of the light input from the first waveguide to the optical waveguide layer in the second waveguide is output via the first mirror; 7. An optical device according to claim 1.

8. When the effective refractive index of the guided mode of light propagating through the first waveguide along the first direction is denoted by ne1 and the wavelength in air of the light propagating through the first waveguide along the first direction is denoted by λ, a period of each of the one or more gratings is greater than λ / ne1 and less than λ / (ne1-1); 8. An optical device according to claim 1.

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