Optical device

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 a 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 including 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 admitting light into the waveguide, and a light outlet formed on the surface of the waveguide for exiting the light that is incident from the light inlet and guided within the waveguide.

[0006] Patent Document 4 discloses an optical scanning device including a first waveguide that propagates light by total 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] JP 2013-16591 A [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 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 facing 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 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 a distance greater than at least one of the thickness of the first mirror and the thickness of 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. Effect 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 description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view illustrating a schematic example of an optical scanning device. [Diagram 2] FIG. 2 is a diagram illustrating an example of a 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 a direction perpendicular to the emission surface of the waveguide array. [Figure 4] FIG. 4 is a perspective view that illustrates a schematic example of a waveguide array in a three-dimensional space. [Diagram 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 emission surface. [Figure 6] FIG. 6 is a diagram illustrating 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 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 reflection waveguide and the slow light waveguide shown in FIG. 8A as viewed from the Z direction. [Figure 9] FIG. 9 is a diagram showing a schematic example of an optical device in which the distance from the interface to the grating is longer. [Figure 10A] FIG. 10A is a diagram illustrating a first modified example of the optical device shown in FIG. 8A. [Figure 10B] FIG. 10B is a diagram illustrating a second modified example of the optical device shown in FIG. 8A. [Figure 10C] FIG. 10C is a diagram illustrating a third modified example of the optical device shown in FIG. 8A. [Figure 11A] FIG. 11A is a diagram illustrating a fourth modified example of the optical device shown in FIG. 8A. [Figure 11B] FIG. 11B is a diagram illustrating a fifth modified example of the optical device shown in FIG. 8A. [Figure 12] FIG. 12 is a diagram showing a configuration example 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 PREFERRED EMBODIMENTS

[0013] In this specification, "at least one of the refractive index, thickness, and wavelength" refers to the It means 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. In order to change the output direction of light, any one of the refractive index, the thickness, and the wavelength may be controlled alone. Alternatively, any two or all of these three may be controlled to change the output direction of light. Instead of or in addition to controlling the refractive index or the 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 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 the optical receiving device of the present disclosure may be used as an antenna in an optical detection system such as a LiDAR (Light Detection and Ranging) system. Compared with a radar system using radio waves such as millimeter waves, the LiDAR system uses electromagnetic waves with short wavelengths (visible light, infrared light, or ultraviolet light), and therefore can detect the distance distribution of an object with high resolution. Such a LiDAR system may be mounted on a moving object such as an automobile, a UAV (Unmanned Aerial Vehicle, so-called drone), or an AGV (Automated Guided Vehicle), and may be used as one of collision avoidance technologies. In this specification, the optical scanning device and the optical receiving device may be collectively referred to as an "optical device". In addition, a device used in the optical scanning device or the optical receiving device may also be referred to as an "optical device".

[0016] <Example of optical scanning device configuration> Hereinafter, as an example, the configuration of an optical scanning device that performs two-dimensional scanning will be described. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of already well-known matters and overlapping explanations of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the inventors provide the accompanying drawings and the following explanation so that those skilled in the art can fully understand this disclosure, and do not intend to limit the subject matter described in the claims by them. In the following description, the same or similar components are given the same reference symbols.

[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. "Two-dimensional scanning" means changing the direction of light two-dimensionally along a plane intersecting the direction.

[0019] FIG. 1 is a perspective view showing a schematic 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, The first direction (X direction) and the second direction (Y direction) are perpendicular to each other, but they do not have to be perpendicular to each other. In the present disclosure, the multiple 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 in consideration of the ease of understanding of the description, and does not limit the orientation in practice in any way. Furthermore, the shape and size of the whole or part of the structures shown in the drawings do not limit the actual shape and size.

[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 mirror 30 and the mirror 40. Each of the mirror 30 and the mirror 40 has a reflective surface that intersects with the third direction D3 at the interface with the optical waveguide layer 20. The mirror 30 and the mirror 40, and the optical waveguide layer 20 have a shape that extends in the first direction (X direction).

[0022] As described later, the first mirrors 30 of the waveguide elements 10 may be a plurality of parts of a mirror that is integrally formed. The second mirrors 40 of the waveguide elements 10 may be a plurality of parts of a mirror that is integrally formed. The optical waveguide layers 20 of the waveguide elements 10 may be a plurality of parts of an optical waveguide layer that is integrally formed. At least, (1) each first mirror 30 is formed separately from the other first mirrors 30, (2) each second mirror 40 is formed separately from the other second mirrors 40, or (3) each optical waveguide layer 20 is formed separately from the other optical waveguide layers 20, thereby forming a plurality of waveguides. "Formed separately" includes not only providing a physical space but also sandwiching a material with a different refractive index between them to separate them.

[0023] The reflecting surface of the first mirror 30 and the reflecting surface of the second mirror 40 face each other substantially parallel to each other. Of the two mirrors 30 and 40, at least the first mirror 30 has a property of transmitting a part of the light propagating through the optical waveguide layer 20. In other words, the first mirror 30 has a higher optical transmittance for the light than the second mirror 40. Therefore, a part 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 of, for example, a multilayer film made of a dielectric material (sometimes referred to as a "multilayer reflective film").

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

[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 a plurality of waveguide elements 10.

[0026] As shown in FIG. 1, when light is input to each waveguide element 10, the light is output from the output surface of each waveguide element 10. The output surface is located on the opposite side to the reflecting surface of the first mirror 30. The direction D3 of the output 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 output from each waveguide element 10 is in approximately the same direction. This makes it possible to change the X-direction component of the wave vector of the light output from the multiple waveguide elements 10. In other words, the direction D3 of the output light can be changed along the direction 101 shown in FIG. 1. do.

[0027] Furthermore, since 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 reinforce each other by interference can be changed. For example, when multiple waveguide elements 10 of the same size are arranged at equal intervals in the Y direction, light beams having phases different from each other by a certain amount are input to the multiple waveguide elements 10. By changing the phase difference, the Y-directional component of the wave vector of the emitted light beams can be changed. In other words, by changing the phase difference of the light beams introduced into the multiple waveguide elements 10, the direction D3 in which the emitted light beams reinforce each other by interference can be changed along the direction 102 shown in FIG. 1. This makes it possible to realize two-dimensional scanning by light.

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

[0029] <Operation principle of waveguide elements> FIG. 2 is a diagram showing an example of a cross-sectional structure of one waveguide element 10 and a light propagating therethrough. In FIG. 2, the direction perpendicular to the X and Y directions shown in FIG. 1 is taken as the Z direction, and a cross section parallel to the XZ plane of the waveguide element 10 is shown. In the waveguide element 10, a pair of mirrors 30 and 40 are arranged to sandwich the optical waveguide layer 20. The light 22 introduced from 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 part of the light can be output mainly from the first mirror 30.

[0030] In a waveguide such as a normal optical fiber, light propagates along the waveguide while repeating total reflection. In contrast, in the waveguide element 10, light propagates while repeating reflection by the mirrors 30 and 40 arranged above and below the optical waveguide layer 20. Therefore, there is no restriction on the propagation angle of light. Here, the propagation angle of light means the angle of incidence at the interface between the mirror 30 or 40 and the optical waveguide layer 20. Light that is incident at an angle closer to a right angle to the mirror 30 or 40 can also propagate. In other words, light that is incident at the interface at an angle smaller than the critical angle of total reflection can also propagate. Therefore, the group velocity of light in the propagation direction of light is significantly reduced compared to the speed of light in free space. As a result, the waveguide element 10 has the property that the propagation conditions of light change significantly 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 called a "reflective waveguide" or a "slow light waveguide."

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

number

[0032] As can be seen from formula (1), the wavelength of light in air, λ, the refractive index of the optical waveguide layer 20, n w and the thickness d of the optical waveguide layer 20, the outgoing direction of light 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 n w = 2.2, the output angle changes to approximately 66°. On the other hand, if the thickness is changed to d = 420 nm without changing the refractive index, the output angle changes to approximately 51°. If the wavelength is changed to λ = 1500 nm without changing either the refractive index or the thickness, the output angle changes to approximately 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] 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 , and the thickness d of the optical waveguide layer 20, the light emission direction is controlled. The wavelength λ of the light may be kept constant without being changed during operation. In that case, the light scanning can be realized with a simpler configuration. The wavelength λ is not particularly limited. For example, the wavelength λ may be included in the wavelength range of 400 nm to 1100 nm (visible light to near infrared light) where high detection sensitivity is obtained in a photodetector or image sensor that detects light by absorbing light with general silicon (Si). In another example, the wavelength λ may be included in the wavelength range of near infrared light from 1260 nm to 1625 nm where the transmission loss is relatively small in an optical fiber or a Si waveguide. Note that these wavelength ranges are only examples. The wavelength range of the light used is not limited to the wavelength range of visible light or infrared light, and may be, for example, the wavelength range of ultraviolet light.

[0035] To change the direction of the output 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, by using the waveguide element 10, the refractive index n w、 By changing at least one of the thickness d and the wavelength λ, the emission direction of the light 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 optical waveguide layer 20 may include a liquid crystal material or an electro-optic material to adjust the refractive index of at least a portion of the optical waveguide layer 20. The optical waveguide layer 20 may be sandwiched between a pair of electrodes. The refractive index of the optical waveguide 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 by 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] <Operation principle of 2D scanning> In a waveguide array in which a plurality of waveguide elements 10 are arranged in one direction, the emission direction of the light changes due to interference of the light emitted from each waveguide element 10. The emission direction of the light 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 emission 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 the light emitted from each waveguide element 10. The straight lines indicate the wavefronts formed by the interference of light. 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 emission surface of the waveguide array. In the example shown in FIG. 3B, the phases of light propagating through the optical waveguide layer 20 in the multiple waveguide elements 10 differ by a certain 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 formula (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 FIG. 3A and FIG. 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 showing a schematic example of a waveguide array in a three-dimensional space. The thick arrows shown in Fig. 4 indicate 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> In order to control the phase of the light emitted from each of the waveguide elements 10, for example, a phase shifter that changes the phase of the light may be provided before the light is introduced into the waveguide element 10. The optical scanning device 100 of the present disclosure includes a plurality of phase shifters connected to each of the plurality of waveguide elements 10, and a second adjustment element that adjusts the phase of the light propagating through each phase shifter. Each phase shifter includes a waveguide that is connected directly to the optical waveguide layer 20 in the corresponding one of the plurality of waveguide elements 10 or via another waveguide. The second adjustment element changes the direction of the light emitted from the plurality of waveguide elements 10 (i.e., the third direction D3) by changing the difference in the phase of the light propagating from the plurality of phase shifters to the plurality of waveguide elements 10. In the following description, the plurality of arranged phase shifters may be referred to as a "phase shifter array" in the same manner as the 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 output 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. Each phase shifter 80 and each waveguide element 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, a drive voltage. In addition, the length of each phase shifter 80 can be adjusted by, for example, a drive voltage. By making the structure in which the phase is changed in equal steps, it is also possible to give equal-step phase shifts with the same driving voltage. Furthermore, the optical scanning device 100 further includes an optical splitter 90 that splits and supplies light to a plurality of phase shifters 80, a first driving circuit 110 that drives each of the waveguide elements 10, and a second driving circuit 210 that drives each of the phase shifters 80. The straight arrows in FIG. 5 represent the input of light. Two-dimensional scanning can be realized by independently controlling the first driving circuit 110 and the second driving circuit 210 that are provided separately. In this example, the first driving circuit 110 functions as one element of the first adjustment element, and the second driving circuit 210 functions as one element of the 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 the 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 splitter 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] In addition, each light may be introduced into the phase shifter 80 after controlling the phase of each light branched by the optical branching device 90. For this phase control, for example, a passive phase control structure by adjusting the length of the waveguide leading to the phase shifter 80 may be used. Alternatively, a phase shifter that has a function similar to that of the phase shifter 80 and can be controlled by an electric signal may be used. By such a 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. By such adjustment, the control of each phase shifter 80 by the second driving circuit 210 can be simplified.

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

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

[0050] 6 is a cross-sectional view showing a schematic example of an optical device in which a total reflection waveguide 1 and a slow light waveguide 10 are connected. In this specification, the total reflection waveguide 1 may be referred to as a "first waveguide 1," and the slow light waveguide 10 may be referred to as a "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 reflection waveguide 1 has a structure extending in the X direction. The slow light waveguide 10 is connected to the total reflection waveguide 1. The optical waveguide layer 20 in the slow light waveguide 10 includes a portion including the tip of the total reflection waveguide 1. The refractive index of the optical waveguide layer 20 is lower than that of the total reflection waveguide 1. In the connection region 111 where the total reflection waveguide 1 and the slow light waveguide 10 overlap when viewed from the Z direction, the total reflection waveguide 1 includes a grating 15 whose refractive index changes with a period p along the X direction. It can also be said that the connection region 111 is a region where the first mirror 30, the second mirror 40, and the total reflection waveguide 1 overlap when viewed from the Z direction. The grating 15 shown in FIG. 6 has four recesses aligned in the X direction. In reality, many more recesses can be provided in the grating 15. Instead of the recesses, protrusions may be provided. The number of recesses or protrusions arranged in the X direction in the grating 15 is desirably, for example, 4 or more. The number of recesses or protrusions may be 8 or more and 64 or less. In one example, the number of recesses or protrusions may be 8 or more and 32 or less. In one example, the number of recesses or protrusions may be 8 or more and 16 or less. The number of recesses or protrusions may be adjusted according to 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 according to the dimensions of each recess or protrusion so that good characteristics are obtained for the grating 15 as a whole.

[0052] The total internal reflection waveguide 1 has 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 connection region 111. 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 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] The grating 15 is not limited to being provided at the interface between the total reflection waveguide 1 and the slow light waveguide 10, and may be provided at other positions. Furthermore, multiple gratings may be provided. In a connection region 111 where the total reflection waveguide 1 and the slow light waveguide 10 overlap when viewed from a direction perpendicular to the reflecting surface of the first mirror 30, at least a portion of the total reflection waveguide 1 and the slow light waveguide 10 may include at least one grating. The refractive index of each grating changes periodically along the X direction in which the total reflection waveguide 1 and the slow light waveguide 10 extend.

[0054] The portion of the total internal reflection waveguide 1 that is 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 the 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 tens of a fraction of the length of the non-connection region 112. However, this length is not limited to this length, and the dimensions of each member are determined according to the required characteristics.

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

[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) in 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 outside 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 guiding layer 20 in the slow light waveguide 10 is emitted to the outside air. The effective refractive index of such a guided 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 reflection waveguide 1 to the slow light waveguide 10 is low.

[0058] In the case where the total internal reflection waveguide 1 is provided with a grating 15 in the connection region 111, the grating In this case, the propagation constant β1 of the guided mode in the total reflection waveguide 1 shifts by an integer multiple of the reciprocal lattice 2π / p. For example, when β1 shifts to β1-(2π / p) due to −1st order diffraction, it is possible to make β1-(2π / p)=β2 hold by appropriately setting p. In this case, the two propagation constants in the connection region 111 match, and the guided light is coupled from the total 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 formula (3).

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

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

[0061] In the above example, the grating is provided over the entire 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 part 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, the 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 at 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, at a distance longer than at least one of the thickness of the first mirror 30 and the thickness of the second mirror 40. According to such a structure, the present inventors have found through their studies that even if the thickness of the optical waveguide layer 20 is not uniform, it is easy to achieve good light emission characteristics.

[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. In the following, the influence of the change in the thickness of the optical waveguide layer 20 along the X direction will be described in detail. 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 a calculation result of the relationship between the rate of change in thickness of the optical waveguide layer 20 and the spread angle of the emitted light 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" means 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 for a displacement of 1 mm along the length direction of the optical waveguide layer 20.

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

[0065] As shown in FIG. 7, when the rate of change in thickness of the optical waveguide layer 20 is about 10 nm / mm, the spread angle of the emitted light is almost the same as when the thickness of the optical waveguide layer 20 is constant. However, when the rate of change in thickness of the optical waveguide layer 20 is 20 nm / mm or more, the spread angle of the emitted light increases almost monotonically with respect to the inclination of the optical waveguide layer 20. Such spread of the emitted light is caused by the phase distribution of the light emitted from the first mirror 30 being disturbed due to the non-uniform thickness of the optical waveguide layer 20. If the spread angle of the emitted light is large, the straightness 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 reflection waveguide 1 and the slow light waveguide 10 are connected than in the portion where the light further travels 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] A 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 inclined, for example, by 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 the change in thickness of the optical waveguide layer 20 will be described below.

[0068] FIG. 8A is a diagram showing a schematic diagram of an optical device in an exemplary embodiment of the present disclosure. The medium surrounding the optical device is, for example, air. The interface 20i between the medium in contact with both the optical waveguide layer 20 and the total reflection waveguide 1 and the optical waveguide layer 20 surrounds the total reflection waveguide 1. In this embodiment, the ends of the first mirror 30 and the second mirror 40 in the X direction are coincident. Therefore, the end face 20i of the connection region 111 in this embodiment is a surface that passes through the ends of the first mirror 30 and the second mirror 40 and is parallel to the Y direction and the Z direction. The end face 20i is the end of the connection region 111 in this embodiment. Also, in this embodiment, the interface 20i between the medium and the optical waveguide layer 20 is coincident 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, away from the end 30e of the first mirror 30, compared to the example shown in FIG. 6. 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 an optical device from the viewpoint of reliability. For this reason, in the 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 the case where the second mirror 40 has an end face like the first mirror 30 near the end face 20i. Therefore, in order to suppress the influence of the change in the thickness of the optical waveguide layer 20, the grating 15 may be disposed at a distance from the end face 20i in the X direction that is longer than at least one of the thickness of the first mirror 30 and the thickness of 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 thickness of the first mirror 30 and the thickness of 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 one 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 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 reflection waveguide 1 includes a portion whose width increases monotonically toward the slow light waveguide 10, outside the optical waveguide layer 20. That is, a portion of the total reflection waveguide 1 has a tapered structure 1t. The width w w is narrower than the width wc of the total 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] Incidentally, the warp 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. For this reason, the grating 15 may be located near the center of the first mirror 30 and / or the second mirror 40 in the optical waveguide layer 20 in the X direction. 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 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 g The sum of L0+L g may be shorter than half the length of the first mirror 30 and half the length of the second mirror 40, whichever is shorter. g corresponds to the length of the connection region 111 shown in Fig. 8A. The overall length of each of the first mirror 30 and the second mirror 40 shown in Fig. 8A is not particularly limited, and 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 diagram showing a schematic 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 in the slow-light waveguide 10 along the X direction to be attenuated by 1 / e times. e is the base of natural logarithm. The attenuation distance can be, for example, about 150 μm to about 200 μm, or more. The attenuation distance can be more than one tenth of the length of the region where the first mirror 30 and the second mirror 40 overlap when viewed from the Z direction. When formula (3) is not satisfied, the light propagating in the total reflection waveguide 1 does not propagate to the non-connection region 112, but is reflected by the end face 1e of the total reflection waveguide 1 in the optical waveguide layer 20. A part 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, it is possible to switch the light emission direction 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 in which light is emitted from the slow light waveguide 10. "Backward" means that the output direction of light emitted from the slow light waveguide 10 has a component in the +X direction from the total reflection waveguide 1 to the slow light waveguide 10. "Rear" means that the output direction of light emitted from the slow light waveguide 10 has a component in the -X direction from the slow light waveguide 10 to the total reflection waveguide 1. Next, modified examples of the connection between the total 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 Figures 10A to 10C and Figures 11A and 11B, have in common with the example shown in Figure 8A in that the grating 15 is located further inside the optical waveguide layer 20.

[0074] 10A to 10C are cross-sectional views showing schematic modifications of the optical device shown in FIG. 8A. In the example shown in FIG. 10A to 10C, the total reflection waveguide 1 is supported by a dielectric layer 51, which is supported by a second mirror 40. The second mirror 40 is commonly used in the total reflection waveguide 1 and the slow light waveguide 10. 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. Therefore, the light propagating through the total 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 area 111 and the non-connection area 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 area 111 in this modification is a surface that passes through the end of the first mirror 30 and is parallel to the Y direction and the Z direction. The end face is the end of the connection area 111 in this embodiment.

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

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

[0077] Figures 11A and 11B are cross-sectional views showing another modified example of the optical device shown in Figure 8A. In the example shown in Figures 11A and 11B, the total 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 Figures 10A to 10C.

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

[0079] 11A and 11B, the distance in the Z direction between the total reflection waveguide 1 and the first mirror 30 and / or the second mirror 40 is relatively short. As a result, the evanescent light in the total reflection waveguide 1 is diffracted by the grating 15. As a result, as in the above example, the coupling efficiency of the guided light from the total 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 FIG. 8A , FIG. 10A to FIG. 10C , and FIG. 11A and FIG. 11B , at least one of the total reflection waveguide 1 and the slow light waveguide 10 has the following characteristics when viewed from the Z direction: A grating 15 is provided in a portion where the total reflection waveguide 1 and the slow light waveguide 10 overlap.

[0081] The total 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 optical waveguide layer 20 may include a liquid crystal material or an electro-optic material to adjust the refractive index of at least a portion of the optical waveguide layer 20. The optical waveguide layer 20 may be sandwiched between a pair of electrodes. The refractive index of the optical waveguide 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 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 occurring 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 other than the portion that overlaps with the total 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 making it possible to adjust 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 a case, 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, in addition to the first pair of electrodes, a second pair of electrodes may be provided. The second pair of electrodes sandwich at least a part of the portion of the optical waveguide layer 20 that overlaps with the total 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 formula (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 can 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 separately. This makes it possible to compensate for a case where the condition of formula (3) is not satisfied as designed.

[0092] Two-dimensional optical scanning is also possible by configuring an optical device having a plurality of pairs of the total internal reflection waveguide 1 and the slow light waveguide 10. Such an optical scanning device includes a plurality of waveguide units arranged in the Y direction. Each waveguide unit includes the above-mentioned total internal reflection waveguide 1 and the slow light waveguide 10. In the optical scanning device, a plurality of phase shifters are connected to the plurality of waveguide units, respectively. Each of the plurality of phase shifters includes a waveguide that is connected directly to the total internal reflection waveguide 1 in a corresponding one of the plurality of waveguide units or via another waveguide. By changing the phase difference of the light passing through the plurality of phase shifters, respectively, 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 Examples> FIG. 12 is a diagram showing a configuration example 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 (for example, a chip). The light source 130 may be, for example, a light emitting element such as a semiconductor laser. The light source 130 in this example emits light of a single wavelength, which is a wavelength λ in free space. The optical splitter 90 splits the light from the light source 130 and introduces it into the waveguides in the multiple phase shifters. In the example shown in FIG. 12, an electrode 62A and multiple electrodes 62B are provided on the chip. A control signal is supplied to the waveguide array 10A from the electrode 62A. A control signal is 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 signal. The control circuit may be provided on the chip shown in FIG. 12, or may be provided on another chip in the optical scanning device 100.

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

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

[0096] FIG. 14 is a block diagram showing a configuration example of a LiDAR system 300, which is an example of a light detection system capable of generating such a distance measurement image. The LiDAR system 300 is 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 having sensitivity 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 according 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 distance measurement 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 60 fps, 50 fps, 30 fps, 25 fps, 24 fps, etc., which are commonly used for videos. In addition, when considering application to in-vehicle systems, the higher the frame rate, the more frequently distance measurement images are acquired, and the more accurate obstacle detection is possible. For example, when driving at 60 km / h, at a frame rate of 60 fps, an image can be acquired every time the car moves about 28 cm. At a frame rate of 120 fps, an image can be acquired every time the car moves about 14 cm. At a frame rate of 180 fps, an image can be acquired every time the car moves about 9.3 cm.

[0098] The time required to acquire one distance measurement image depends on the speed of beam scanning. For example, to acquire an image with a resolution of 100 x 100 at 60 fps, beam scanning must be performed 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 to optical receiving device> The optical scanning device of the present disclosure can also be used as an optical receiving device with almost the same configuration. The optical receiving device includes a waveguide array 10A identical to that of the optical scanning device, and a first adjustment element for adjusting the direction of receivable light. Each first mirror 30 of the waveguide array 10A transmits light incident on the opposite side of the first reflecting surface from the third direction. Each optical waveguide layer 20 of the waveguide array 10A propagates light transmitted through the first mirror 30 in the second direction. The first adjustment element changes 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, thereby changing the direction of receivable light. Furthermore, when the optical receiving device includes a plurality of phase shifters 80, or 80a and 80b, identical to that of the optical scanning device, and a second adjustment element for changing the phase difference of light output from the plurality of waveguide elements 10 through the plurality of phase shifters 80, or 80a and 80b, 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 FIG. 12 with a receiving circuit. When light of wavelength λ is incident on the waveguide array 10A, the light is sent to the optical splitter 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 in the waveguide array and the phase shifter array 80A. In the optical receiving device, for example, in FIG. 4, the directions of the wave vectors (thick arrows in the figure) are reversed. The incident light is divided into a light component in the direction in which the waveguide element 10 extends (X direction in the figure) and a light 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. Meanwhile, the sensitivity of the optical component in the arrangement direction of the waveguide elements 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, and the w From the 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 described above are summarized in the following items.

[0103] The optical device according to the 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 facing 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 portion 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 are separated from an end of the first mirror or the second mirror in the connection region in the first direction 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 portion closer to the connection region of the first mirror and / or the second mirror, 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] The optical device according to the 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. 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] An optical device according to a third item is the optical device according to the first or second item, wherein 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).

[0108] In this optical device, when light propagating through the first waveguide is not coupled to the second waveguide via the grating, a portion 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, a portion 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 first mirror has a higher transmittance than the second mirror, and 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.

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

[0111] An optical device according to a fifth aspect of the present invention is an optical device according to any one of the first to fourth aspects, further comprising: a first waveguide having an effective refractive index of a guided mode of the light propagating through the first waveguide, the first waveguide being n e1 , where λ is the wavelength of the light in air, 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 period of the grating, 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 the 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 Driving circuit for waveguide array 130 Light source 210 Driving circuit for phase shifter array 310 Beam Spot 400 Photodetector 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 in the first direction from an edge of the first mirror or the second mirror in the overlap 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 a center line of the first waveguide; the optical waveguide layer includes the one or more gratings; Optical devices.

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

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

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

4. An 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 a length of the first mirror in the first direction or half a length of the second mirror in the first direction, whichever is shorter; 5. An 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 in 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 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. Let ne1 be the effective refractive index of the guided mode of the light propagating through the first waveguide along the first direction, and λ be the wavelength in air of the light propagating through the first waveguide along the first direction, 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.

Images