Optical device and optical detection system

Abstract

The optical device includes: a first mirror having a first reflection surface and extending along a first direction; a second mirror having a second reflection surface opposed to the first reflection surface and extending along the first direction; and an optical waveguide layer located between the first mirror and the second mirror to allow light to propagate along the first direction; the transmittance of the first mirror is higher than that of the second mirror, and the reflection spectrum corresponding to light incident from the normal direction of the reflection surface of at least one of the first mirror and the second mirror is: including a maximum point, a first inflection point, and a second inflection point on the longer wavelength side than the maximum point in a wavelength band where the reflectance is 90% or more.

Description

Technical Field

[0001] The present disclosure relates to an optical device and an optical detection system. Background Art

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

[0003] Patent Document 1 discloses a configuration capable of scanning with light using a driving device that rotates a mirror.

[0004] Patent Document 2 discloses an optical phase array having a plurality of 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 phase array, a coherent light beam is guided to each antenna element through a waveguide, and the light beam is phase-shifted by the phase shifter. Thereby, the amplitude distribution of the far-field radiation pattern can be changed.

[0005] Patent Document 3 discloses an optical deflection element including: a waveguide having an optical waveguide layer that conducts light therein and first distributed Bragg reflectors formed on the upper and lower surfaces of the optical waveguide layer; an optical input port for making light enter the waveguide; and an optical output port formed on the surface of the waveguide for outputting the light that has entered through the optical input port and has been conducted in the waveguide.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: International Publication No. 2013 / 168266

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-508235

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2013-16591 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] One aspect of the present disclosure provides a new optical device capable of realizing scanning with light with a relatively simple configuration.

[0013] Means for Solving the Problems

[0014] An optical device according to an aspect of the present disclosure includes: a first mirror having a first reflection surface and extending along a first direction; a second mirror having a second reflection surface facing the first reflection surface and extending along the first direction; and an optical waveguide layer located between the first mirror and the second mirror and configured to propagate light along the first direction. The transmittance of the first mirror is higher than that of the second mirror, and the reflection spectrum of at least one of the first mirror and the second mirror corresponding to light incident from the normal direction of the reflection surface includes a maximum point, a first inflection point, and a second inflection point on the long-wavelength side of the maximum point in a wavelength band where the reflectance is 90% or more.

[0015] A general or specific aspect of the present disclosure can also be implemented by a device, a system, a method, or any combination thereof.

[0016] Advantageous Effects of the Invention

[0017] According to an aspect of the present disclosure, one-dimensional scanning or two-dimensional scanning can be achieved using light with a relatively simple configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a perspective view schematically showing an example of an optical scanning device.

[0019] Figure 2 is a diagram schematically showing the structure of a cross section of one waveguide element and an example of light propagating therethrough.

[0020] Figure 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.

[0021] Figure 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.

[0022] Figure 4 is a perspective view schematically showing an example of a waveguide array in a three-dimensional space.

[0023] Figure 5 is a schematic view of a waveguide array and a phase shifter array as viewed from the normal direction (Z direction) of the light emission surface.

[0024] Figure 6A is a diagram schematically showing a case where light is emitted from the emission surface when the propagation angle is small.

[0025] Figure 6B is a diagram schematically showing a case where light is emitted from the emission surface when the propagation angle is large.

[0026] Figure 7It is a diagram showing the result obtained by representing the relationship between the calculated propagation length and the beam width of the emitted light.

[0027] Figure 8 It is a diagram showing the reflection spectrum of a conventional DBR corresponding to an incident angle of 0°.

[0028] Figure 9 It is a diagram showing the reflection spectra of a conventional DBR corresponding to incident angles of 0°, 10°, and 15°.

[0029] Figure 10A It is a diagram showing an example of the relationship between the incident angle and the reflectance at a wavelength of 940 nm.

[0030] Figure 10B It is a diagram showing an example of the relationship between the incident angle and the reflectance at a wavelength of 1100 nm.

[0031] Figure 11 It is a diagram showing the reflection spectrum of the chirped DBR of the present embodiment corresponding to an incident angle of 0°.

[0032] Figure 12 It is a diagram showing an example of the relationship between the incident angle and the reflectance at a wavelength of 940 nm.

[0033] Figure 13 It is a diagram showing an example of the relationship between the exit angle and the propagation length.

[0034] Figure 14 It is a diagram showing the reflection spectrum of another chirped DBR of the present embodiment corresponding to an incident angle of 0°.

[0035] Figure 15 It is a diagram showing a configuration example of an optical scanning device in which elements such as a beam splitter, a waveguide array, a phase shifter array, and a light source are integrated on a circuit board.

[0036] Figure 16 It is a schematic diagram showing a situation where a beam such as a laser is irradiated from an optical scanning device to the far field and two-dimensional scanning is performed.

[0037] Figure 17 It is a block diagram showing a configuration example of a LiDAR system capable of generating a ranging image.

[0038] Figure 18 It is a diagram showing an example of the relationship between the incident angle φ and the reflectance at a propagation length of 100 μm. Detailed implementation mode

[0039] Before describing the embodiments of the present disclosure, the insights that form the basis of the present disclosure will be described.

[0040] The present inventor has found that the following problems exist in conventional optical scanning devices: it is difficult to scan a space with light without making the device configuration complex.

[0041] For example, in the technology disclosed in Patent Document 1, a driving device for rotating a mirror is required. Therefore, there are problems that the device configuration becomes complex and it is not stable against vibration.

[0042] In the optical phase array described in Patent Document 2, it is necessary to branch light and introduce it into a plurality of columnar waveguides and a plurality of row waveguides, and guide the light to a plurality of antenna elements arranged two-dimensionally. Therefore, the wiring of the waveguides for guiding light becomes very complex. In addition, the range of two-dimensional scanning cannot be made large. Furthermore, in order to change the amplitude distribution of the emitted light in the far field two-dimensionally, it is necessary to connect phase shifters to each of the plurality of antenna elements arranged two-dimensionally and install wiring for phase control on the phase shifters. As a result, the phases of the light incident on the plurality of antenna elements arranged two-dimensionally change by different amounts. Therefore, the element configuration becomes very complex.

[0043] The present inventor focused on the above problems in the prior art and explored a configuration for solving these problems. The present inventor has found that by using a waveguide element having a pair of opposed mirrors and a light waveguide layer interposed between these mirrors, the above problems can be solved. One of the pair of mirrors in the waveguide element has a higher light transmittance than the other, so that a part of the light propagating in the light waveguide layer is emitted to the outside. As described later, by adjusting the refractive index or thickness of the light waveguide layer, or the wavelength of the light input to the light waveguide layer, the direction (or emission angle) of the emitted light can be changed. More specifically, by changing the refractive index, thickness or wavelength, the component of the wave vector of the emitted light in the direction along the length direction of the light waveguide layer can be changed. Thereby, one-dimensional scanning is achieved.

[0044] Furthermore, in the case of using an array of a plurality of waveguide elements, two-dimensional scanning can also be achieved. More specifically, by giving an appropriate phase difference to the light supplied to the plurality of waveguide elements and adjusting this phase difference, the direction in which the light emitted from the plurality of waveguide elements is strengthened with each other can be changed. Due to the change in the phase difference, the component of the wave vector of the emitted light in the direction crossing the direction along the length direction of the light waveguide layer changes. Thereby, two-dimensional scanning can be achieved. In addition, in the case of performing two-dimensional scanning, it is not necessary to change the refractive index, thickness or wavelength of the plurality of light waveguide layers by different amounts. That is, by giving an appropriate phase difference to the light supplied to the plurality of light waveguide layers and synchronously changing at least one of the refractive index, thickness and wavelength of the plurality of light waveguide layers by the same amount, two-dimensional scanning can be performed.

[0045] In this way, according to the present disclosure, one-dimensional or two-dimensional scanning can be realized using light with a relatively simple configuration.

[0046] In this specification, "at least one of the refractive index, thickness, and wavelength" means at least one selected from the group consisting of the refractive index of the optical waveguide layer, the thickness of the optical waveguide layer, and the wavelength input to the optical waveguide layer. In order to change the emission direction of light, any one of the refractive index, thickness, and wavelength may be controlled alone. Alternatively, any two or all of these three may be controlled to change the emission direction of light. Instead of or in addition to controlling the refractive index or thickness, the wavelength of the light input to the optical waveguide layer may be controlled.

[0047] The above basic principle can be applied not only to the use of emitted light but also to the use of 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, if the phase difference of light is changed using a plurality of phase shifters respectively connected to a plurality of waveguide elements arranged in one direction, the direction of the light that can be received can be changed two-dimensionally.

[0048] The optical scanning device and optical receiving device of the present disclosure can be used, for example, as antennas in optical detection systems such as LiDAR (Light Detection and Ranging) systems. Compared with radar systems using radio waves such as millimeter waves, LiDAR systems use short-wavelength electromagnetic waves (visible light, infrared light, or ultraviolet light), and thus can detect the distance distribution of an object with high resolution. Such LiDAR systems are mounted on mobile bodies such as automobiles, UAVs (Unmanned Aerial Vehicles, so-called drones), and AGVs (Automated Guided Vehicles), and can be used as one of the collision avoidance technologies. In this specification, the optical scanning device and the optical receiving device are sometimes collectively referred to as an "optical device". In addition, a device used in the optical scanning device or the optical receiving device is sometimes also referred to as an "optical device". Sometimes, the term "optical device" is also used for the optical components constituting the optical scanning device or the optical receiving device.

[0049] <Example of the configuration of the optical scanning device>

[0050] Hereinafter, as an example, the configuration of an optical scanning device that performs two-dimensional scanning will be described. In this case, overly detailed descriptions may sometimes be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same configurations may sometimes be omitted. This is to avoid making the following description overly lengthy and to make it easier for those skilled in the art to understand. In addition, the inventors have provided the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and their intention is not to limit the subject matter recited in the claims by these. In the following description, the same reference numerals are given to the same or similar components.

[0051] In the present disclosure, "light" means an electromagnetic wave that includes not only visible light (wavelength of approximately 400 nm to approximately 700 nm) but also ultraviolet light (wavelength of approximately 10 nm to approximately 400 nm) and infrared light (wavelength of approximately 700 nm to approximately 1 mm). In this specification, ultraviolet light may sometimes be referred to as "UV light", and infrared light may sometimes be referred to as "IR light".

[0052] In the present disclosure, performing "scanning" with light means changing the direction of the light. "One-dimensional scanning" means changing the direction of the light linearly along a direction intersecting with that direction. "Two-dimensional scanning" means changing the direction of the light two-dimensionally along a plane intersecting with that direction.

[0053] Figure 1 is a perspective view schematically showing an example of the optical scanning device 100. The optical scanning device 100 includes an array waveguide including a plurality of waveguide elements 10. Each of the plurality of waveguide elements 10 has a shape extending in the first direction ( Figure 1 the X direction in). The plurality of waveguide elements 10 are regularly arranged in a second direction ( Figure 1 the Y direction in) intersecting the first direction. While causing the light to propagate in the first direction, the plurality of waveguide elements 10 cause the light to exit in a third direction D3 intersecting a virtual plane parallel to the first and second directions. In the present disclosure, the first direction (X direction) is orthogonal to the second direction (Y direction), but the two may not be orthogonal. In the present disclosure, the plurality of waveguide elements 10 are arranged at equal intervals in the Y direction, but do not necessarily have to be arranged at equal intervals.

[0054] In addition, the orientation of the structures shown in the drawings of the present application is set in consideration of the understandability of the description, and does not limit the orientation during implementation at all. Also, the shape and size of the whole or a part of the structures shown in the drawings do not limit the actual shape and size.

[0055] The plurality of waveguide elements 10 each have a first mirror 30 and a second mirror 40 facing each other (hereinafter sometimes simply referred to as "mirrors"), and an optical waveguide layer 20 located between the mirror 30 and the mirror 40. The mirrors 30 and 40 each have a reflecting surface intersecting 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 a shape extending in the first direction (X direction).

[0056] The reflecting surface of the first mirror 30 faces the reflecting surface of the second mirror 40 substantially parallel. At least the first mirror 30 among the two mirrors 30 and 40 has the property of transmitting a part of the light propagating in the optical waveguide layer 20. In other words, the first mirror 30 has a higher light transmittance for this light than the second mirror 40. Therefore, a part of the light propagating in the optical waveguide layer 20 exits to the outside from the first mirror 30. Such mirrors 30 and 40 can be, for example, multilayer mirrors formed of a dielectric multilayer film (also referred to as "multilayer reflection film" or "Distributed Bragg Reflector (DBR)").

[0057] 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 simultaneously, two-dimensional scanning can be achieved using light.

[0058] In order to achieve such two-dimensional scanning, the present inventor analyzed the operating principle of the waveguide element 10. Based on the result, by driving the plurality of waveguide elements 10 synchronously, two-dimensional scanning was successfully achieved using light.

[0059] As Figure 1 shown, if light is input to each waveguide element 10, the light exits from the exit surface of each waveguide element 10. The exit surface is located on the opposite side of the reflecting surface of the first mirror 30. The direction D3 of the exit light depends on the refractive index, thickness of the optical waveguide layer, and the wavelength of the light. 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 exiting from each waveguide element 10 becomes substantially the same direction. Thereby, the component in the X direction of the wave vector of the light exiting from the plurality of waveguide elements 10 can be changed. In other words, the direction D3 of the exit light can be changed along the Figure 1 direction 101 shown.

[0060] Furthermore, the light emitted from the plurality of waveguide elements 10 is directed in the same direction, so the emitted light interferes with each other. By controlling the phase of the light emitted from each waveguide element 10, it is possible to change the direction in which the light is enhanced due to interference. For example, in the case where a plurality of waveguide elements 10 of the same size are arranged at equal intervals in the Y direction, light with different phases by a certain amount is input to the plurality of waveguide elements 10 one by one. By changing this phase difference, it is possible to change the component of the wave vector of the emitted light in the Y direction. In other words, by changing the phase differences of the light introduced into the plurality of waveguide elements 10 respectively, it is possible to make the direction D3 in which the emitted light is enhanced due to interference follow Figure 1 the direction 102 shown in the figure. Thus, two-dimensional scanning can be achieved using light.

[0061] Hereinafter, the operation principle of the optical scanning device 100 will be described.

[0062] <Principle of Operation of Waveguide Element>

[0063] Figure 2 FIG. is an example showing the structure of a cross section of one waveguide element 10 and the propagating light schematically. In Figure 2 it, the direction perpendicular to the X direction and the Y direction shown in Figure 1 is taken as the Z direction, and a cross section of the waveguide element 10 parallel to the XZ plane is shown schematically. In the waveguide element 10, a pair of mirrors 30 and a mirror 40 are arranged with the optical waveguide layer 20 therebetween. The light 22 introduced from one end in the X direction of the optical waveguide layer 20 is repeatedly reflected by the first reflection surface 30s of the first mirror 30 provided on the upper surface ( Figure 2 the upper surface in the figure) of the optical waveguide layer 20 and the second reflection surface 40s of the second mirror 40 provided on the lower surface ( Figure 2 the lower surface in the figure) of the optical waveguide layer 20, and propagates in the optical waveguide layer 20. The light 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 exit surface 30es of the first mirror 30. Hereinafter, the first reflection surface 30s may be simply referred to as "reflection surface 30s", and the second reflection surface 40s may be simply referred to as "reflection surface 40s".

[0064] In a normal waveguide such as an optical fiber, light propagates along the waveguide while repeatedly undergoing total internal reflection. In contrast, in the waveguide element 10, light propagates while being repeatedly reflected by the mirrors 30 and 40 disposed 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 incident angle to the interface between the mirror 30 or the mirror 40 and the optical waveguide layer 20. Light incident at an angle closer to perpendicular to the mirror 30 or the mirror 40 can also propagate. That is, light incident on the interface at an angle smaller than the critical angle of total internal reflection can also propagate. Therefore, the group velocity of light in the propagation direction of light is greatly reduced compared to the speed of light in free space. Thus, the waveguide element 10 has the property that the propagation conditions of light vary greatly 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 referred to as a "reflective waveguide" or a "slow light waveguide".

[0065] The exit angle θ of the light exiting from the waveguide element 10 into the air is expressed by the following equation (1).

[0066] [Equation 1]

[0067]

[0068] As can be seen from Equation (1), by changing any one of the wavelength λ of light in the air, the refractive index n w of the optical waveguide layer 20, and the thickness d of the optical waveguide layer 20, the exit direction of light can be changed.

[0069] For example, when n w = 2, d = 387 nm, λ = 1550 nm, and m = 1, the exit angle is 0°. If the refractive index is changed to n w = 2.2 from this state, the exit angle changes to approximately 66°. On the other hand, if the thickness is changed to d = 420 nm without changing the refractive index, the exit angle changes to approximately 51°. If the wavelength is changed to λ = 1500 nm without changing the refractive index or the thickness, the exit angle changes to approximately 30°. Thus, by changing any one of the wavelength λ of light, the refractive index n w of the optical waveguide layer 20, and the thickness d of the optical waveguide layer 20, the exit direction of light can be greatly changed.

[0070] Then, in the light scanning device 100 of the present disclosure, by controlling the wavelength λ of the light input to the optical waveguide layer 20, the refractive index n wAt least one of the refractive index and the thickness d of the optical waveguide layer 20 is used to control the emission direction of light. The wavelength λ of the light may also remain constant without changing during operation. In this case, light scanning can be achieved with a simpler configuration. The wavelength λ is not particularly limited. For example, the wavelength λ may be included in the wavelength band of 400 nm to 1100 nm (visible light to near-infrared light) in which a photodetector or an image sensor that detects light by absorbing light with general silicon (Si) can obtain high detection sensitivity. In other examples, the wavelength λ may be included in the wavelength band of near-infrared light of 1260 nm to 1625 nm in which the transmission loss in an optical fiber or an Si waveguide is relatively small. In addition, these wavelength ranges are just examples. The wavelength band of the light used is not limited to the visible light or infrared light band, and may be, for example, the ultraviolet light band.

[0071] In order to change the direction of the emitted light, the optical scanning device 100 may include a first adjustment element that changes at least one of the refractive index, thickness, and wavelength of the optical waveguide layer 20 in each waveguide element 10.

[0072] As described above, if the waveguide element 10 is used, by changing at least one of the refractive index n w of the optical waveguide layer 20, the thickness d, and the wavelength λ, the emission direction of the light can be greatly changed. Thereby, the emission angle of the light emitted from the mirror 30 can be changed in the direction along the waveguide element 10. By using at least one waveguide element 10, such one-dimensional scanning can be achieved.

[0073] In order to adjust the refractive index of at least a part of the optical waveguide layer 20, the optical waveguide layer 20 may also include a liquid crystal material or an electro-optic material. The optical waveguide layer 20 may be sandwiched between a pair of electrodes. By applying a voltage to the pair of electrodes, the refractive index of the optical waveguide layer 20 can be changed.

[0074] In order 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. By changing the distance between the first mirror 30 and the second mirror 40 by at least one actuator, the thickness of the optical waveguide layer 20 can be changed. If the optical waveguide layer 20 is formed of a liquid, the thickness of the optical waveguide layer 20 can be easily changed.

[0075] <Principle of two-dimensional scanning>

[0076] In a waveguide array in which a plurality of waveguide elements 10 are arranged in one direction, the emission direction of light changes due to the interference of the light emitted from each waveguide element 10. By adjusting the phase of the light supplied to each waveguide element 10, the emission direction of the light can be changed. The principle is described below.

[0077] Figure 3AIt 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. In Figure 3A , the phase shift amount of the light propagating in each waveguide element 10 is also described. Here, the phase shift amount is a value based on the phase of the light propagating in the waveguide element 10 at the left end. The waveguide array of the present disclosure includes a plurality of waveguide elements 10 arranged at equal intervals. In Figure 3A , the dashed circular arcs represent the wavefronts of the light emitted from each waveguide element 10. The straight line represents the wavefront formed by the interference of light. The arrow represents the direction of the light emitted from the waveguide array (i.e., the direction of the wave vector). In Figure 3A In the example shown, the phases of the light propagating in the optical waveguide layer 20 of each waveguide element 10 are all the same. In this case, the light is emitted in a direction perpendicular to both the arrangement direction (Y direction) of the waveguide elements 10 and the extending direction (X direction) of the optical waveguide layer 20 (Z direction).

[0078] Figure 3B It 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 Figure 3B In the example shown, the phases of the light propagating in the optical waveguide layer 20 of the plurality of waveguide elements 10 differ by a certain amount (Δφ) one by one along the arrangement direction. In this case, the light is emitted in a direction different from the Z direction. By changing this Δφ, the component of the wave vector of the light in the Y direction can be changed. If the center-to-center distance between two adjacent waveguide elements 10 is set as p, the emission angle α0 of the light is expressed by the following formula (2).

[0079] [Equation 2]

[0080]

[0081] In Figure 2 In the example shown, the emission direction of the light is parallel to the XZ plane. That is, α0 = 0°. In Figure 3A and Figure 3B In the example shown, the direction of the light emitted from the optical scanning device 100 is parallel to the YZ plane. That is, θ = 0°. However, generally, the direction of the light emitted from the optical scanning device 100 is neither parallel to the XZ plane nor parallel to the YZ plane. That is, θ ≠ 0° and α0 ≠ 0°.

[0082] Figure 4 It is a perspective view schematically showing an example of a waveguide array in a three-dimensional space. Figure 4 The thick arrow shown represents the direction of the light emitted from the optical scanning device 100. θ is the angle formed by the emission direction of the light and the YZ plane. θ satisfies formula (1). α0 is the angle formed by the emission direction of the light and the XZ plane. α0 satisfies formula (2).

[0083] <Phase control of light introduced into the waveguide array>

[0084] In order to control the phase of the light emitted from each waveguide element 10, for example, a phase shifter that changes the phase of the light can be provided at a stage prior to introducing the light into the waveguide element 10. The optical scanning device 100 of the present disclosure includes: a plurality of phase shifters respectively connected to the plurality of waveguide elements 10, and a second adjustment element that adjusts the phase of the light propagating in each phase shifter. Each phase shifter includes a waveguide directly or via another waveguide connected to the optical waveguide layer 20 in one corresponding to the plurality of waveguide elements 10. The second adjustment element changes the phase difference of the light propagating from the plurality of phase shifters to the plurality of waveguide elements 10 respectively, so that the direction of the light emitted from the plurality of waveguide elements 10 (that is, the third direction D3) changes. In the following description, similar to the waveguide array, the arranged plurality of phase shifters are sometimes referred to as a "phase shifter array".

[0085] Figure 5 is a schematic diagram of observing the waveguide array 10A and the phase shifter array 80A from the normal direction (Z direction) of the light exit surface. In Figure 5 In the example shown, 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 respective phase shifters 80 are equal, for example, the phase shift amount of each can be adjusted by a driving voltage. In addition, by adopting a structure in which the lengths of the respective phase shifters 80 change in equal steps, an equal-step phase shift can also be given using the same driving voltage. Further, the optical scanning device 100 further includes: a beam splitter 90 that branches the light and supplies it to the plurality of 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. Figure 5 The straight arrows shown represent the input of light. By independently controlling the individually provided first driving circuit 110 and second driving circuit 210, two-dimensional scanning can be achieved. 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.

[0086] The first driving circuit ********* the refractive index and thickness of the optical waveguide layer 20 in each waveguide element 10, so that the angle of the light emitted from the optical waveguide layer 20 changes. The second driving circuit 210 changes the refractive index of the waveguide 20a in each phase shifter 80, so that the phase of the light propagating inside the waveguide 20a changes. The beam splitter 90 may be composed of a waveguide in which light propagates by total reflection, or may be composed of a reflection type waveguide similar to the waveguide element 10.

[0087] In addition, after the phases of the respective lights branched by the optical splitter 90 are controlled, the respective lights may be introduced into the phase shifter 80. In this phase control, for example, a passive phase control structure achieved by adjusting the length of the waveguide up to the phase shifter 80 can be used. Alternatively, a phase shifter that can be controlled by an electrical signal and has the same function as the phase shifter 80 may be used. By such a method, for example, the phase can also be adjusted before being introduced into the phase shifter 80 so that lights with equal phases are supplied to all the phase shifters 80. By such adjustment, the control of each phase shifter 80 by the second drive circuit 210 can be made simple.

[0088] An optical device having the same configuration as the above-described optical scanning device 100 can also be used as an optical receiving device. Details such as 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 this document is incorporated herein by reference.

[0089] <Emission Angle and Beam Width of Emitted Light>

[0090] The beam width of the light emitted from the slow light waveguide 10 determines the resolution of the scanning. If the beam width becomes narrower, the resolution of the scanning improves, and if the beam width becomes wider, the resolution of the scanning decreases. Hereinafter, the relationship between the beam width of the light emitted from the conventional slow light waveguide 10 and the emission angle will be described.

[0091] The far-field pattern of the light emitted from the slow light waveguide 10 corresponds to Figure 2 the Fourier transform of the electric field distribution at the emission surface 30es shown. That is, the longer the propagation length of the light 22 propagating in the optical waveguide layer 20, the narrower the beam width of the emitted light in the far field. Conversely, if the propagation length of the light propagating in the optical waveguide layer 20 is shorter, the beam width of the emitted light in the far field is wider. Here, the propagation length means the distance at which the intensity of the light 22 propagating while attenuating in the optical waveguide layer 20 decreases to 1 / e times. e is the base of the natural logarithm. The beam width means the angle Δθ that expands to both sides with the emission angle θ as the center. Specifically, the beam width is denoted as the full width at half maximum of the emitted light in the angular spectrum.

[0092] Figure 6A and Figure 6B are diagrams schematically showing the cases where light is emitted from the emission surface 30es in the case where the propagation angle φ is relatively small and relatively large, respectively. For simplicity, the reflectance of the mirror 30 is assumed to be constant regardless of the propagation angle φ. In Figure 6A the example shown, the propagation angle φ is small, so the number of times the reflecting surface 30s reflects the light 22 per unit length is large. Therefore, the propagation length L p is short. In Figure 6BIn the example shown, the propagation angle φ is large, so the number of times the reflecting surface 30s reflects the reflected light 22 per unit length is small. Therefore, the propagation length L p is long. There is a positive correlation between the propagation angle φ and the exit angle θ. Therefore, the larger the exit angle θ, the p longer the propagation length L Figure 6A is. In addition, the propagation length L Figure 6B shown by the double-headed arrow in p is a schematic representation and does not represent the actual length.

[0093] Figure 7 represents the propagation length L p and is a diagram showing an example of the relationship with the beam width Δθ of the exit light. Figure 7 The shown curve graph represents the result of calculating the propagation length by variously changing the line width of the light beam emitted from one slow light waveguide 10 in which the dimensions and dielectric constants of each component are appropriately set. As Figure 7 shown, the longer the propagation length L p is, the narrower the beam width Δθ of the exit light. As described above, if the exit angle θ increases, the propagation length L p increases. Therefore, the larger the exit angle θ, the smaller the beam width Δθ of the exit light. Thus, the beam width Δθ of the exit light depends on the exit angle θ, so if the exit angle θ changes, the resolution of the scan changes.

[0094] The present inventors have found the above problems and explored the configuration of an optical device for solving the problems. As a result, it has been found that by using a mirror having special characteristics not possessed in the past as at least one of the two mirrors in the slow light waveguide, the above problems can be solved. The embodiments of the present disclosure described below are based on this insight. Hereinafter, exemplary embodiments of the present disclosure will be described.

[0095] Here, for comparison, the reflection spectrum of a conventional DBR that can be used for the mirror 30 and / or the mirror 40 in the slow light waveguide 10 will be described.

[0096] As Figure 2 shown, the light 22 propagates in the optical waveguide layer 20 while being reflected by the reflecting surface 30s of the mirror 30 and the reflecting surface 40s of the mirror 40. At this time, the reflectance of the mirror 30 and the mirror 40 is also about 99% on the light exit side. In order to achieve such a high reflectance, the mirror 30 and the mirror 40 can be formed of, for example, a DBR. Hereinafter, an example of the reflection spectrum when light is incident on the reflecting surface of a conventional DBR will be described. The incident angle at which light is incident on this reflecting surface corresponds to the propagation angle φ.

[0097] Figure 8This is a diagram showing the reflection spectrum of a conventional DBR corresponding to light with an incident angle of φ = 0°. The incident angle of φ = 0° corresponds to the angle at which light is incident from the normal direction of the reflection surface of the DBR. In the calculation of the reflection spectrum, DiffractMod of Synopsys was used. The refractive index of the medium on the incident side of the DBR in this example is 1.68. The DBR corresponds to the mirror 30 in the slow light waveguide 10, and the medium on the incident side corresponds to the optical waveguide layer 20 in the slow light waveguide 10. This DBR has a structure in which 9 high-refractive-index layers and 8 low-refractive-index layers are alternately stacked. The refractive index of each high-refractive-index layer is 2.28, and the thickness is 111 nm. The refractive index of each low-refractive-index layer is 1.47, and the thickness is 173 nm. As Figure 8 shown, the reflection spectrum of the conventional DBR shows a reflection rate of approximately 100% in the stop band according to the design, and shows a low reflection rate if it deviates from this stop band. Here, the stop band means the wavelength band in which incident light is strongly reflected due to Bragg reflection caused by the periodic structure.

[0098] Figure 9 This is a diagram showing the reflection spectra of a conventional DBR corresponding to incident angles of φ = 0°, 10°, and 15°. As Figure 9 shown, the reflection spectrum shifts toward the short-wavelength side as the incident angle φ increases. Hereinafter, as an example, it is explained how the reflectance of light with wavelength λ A = 940 nm and wavelength λ B = 1100 nm changes according to the incident angle φ.

[0099] Figure 10A and Figure 10B are diagrams showing the relationship between the incident angle φ and the reflectance of light with wavelength λ A = 940 nm, and the relationship between the incident angle φ and the reflectance of light with wavelength λ B = 1100 nm, respectively. The range of the incident angle φ from 0° to 25° corresponds to the range of the exit angle θ from 0° to approximately 60°. As Figure 10A shown, the wavelength dependence of the reflectance of light with wavelength λ A is small. Therefore, for the above reasons, the beam linewidth Δθ of the emitted light becomes narrower as the exit angle θ increases. On the other hand, as Figure 10B shown, at the wavelength λ B close to the end of the stop band, the reflectance drops sharply near the incident angle φ = 15°. Therefore, the beam linewidth Δθ of the emitted light becomes narrower as the exit angle θ increases in the range of the incident angle φ from 0° to approximately 15°, and increases as the exit angle θ increases in the range of the incident angle φ from approximately 15° to 25°. In Figure 10A and Figure 10BIn the example, the beam line width Δθ of the emitted light varies significantly according to the emission angle θ.

[0100] As described above, the present inventors have found that by using a mirror whose reflectivity decreases gently as the incident angle φ increases, an optical scanning device can be realized in which the beam line width Δθ of the emitted light does not vary significantly according to the emission angle θ. Specifically, by providing an inflection point on the longer wavelength side of the maximum value in the reflection spectrum of the mirror, a mirror whose reflectivity decreases gently as the incident angle φ increases is realized. In the present embodiment, as the mirror having an inflection point in the reflection spectrum, a chirped DBR in which the thicknesses of the high refractive index layer and the low refractive index layer are appropriately adjusted is used. In the present specification, "chirped DBR" means a DBR in which the thicknesses of a plurality of high refractive index layers and / or the thicknesses of a plurality of low refractive index layers are different according to the layer. In the chirped DBR, not only a DBR in which the thicknesses of a plurality of high refractive index layers and / or the thicknesses of a plurality of low refractive index layers gradually increase or decrease along the stacking direction, but also a DBR in which the thicknesses of a plurality of high refractive index layers and / or the thicknesses of a plurality of low refractive index layers irregularly or randomly vary along the stacking direction are included.

[0101] Figure 11 is a diagram showing the reflection spectrum of the chirped DBR of the present embodiment corresponding to an incident angle of φ = 0°. In Figure 11 the example shown, the reflection spectrum includes one maximum point P LM and inflection points P1 to P4 on the longer wavelength side of the maximum point P LM in a wavelength band where the reflectivity is 95% or more. In this reflection spectrum, the reflectivity monotonically decreases on the longer wavelength side of the maximum point P LM . Here, the inflection point means a point where the second derivative of the reflectivity with respect to the wavelength is zero. At this inflection point, the reflectivity changes linearly with respect to the wavelength.

[0102] In the reflection spectrum of the chirped DBR of the present embodiment, the maximum point P LM and the inflection points P1 to P4 exist in a wavelength band showing a reflectivity of 95% or more. According to the design of the chirped DBR, the maximum point P LM and the inflection points P1 to P4 may also exist in a wavelength band where the reflectivity is 90% or more.

[0103] Figure 7 It is shown that in order to make the beam line width Δθ be approximately 0.2° or less, the propagation length needs to be approximately 100 μm or more. Figure 18 is a diagram showing the relationship between the incident angle φ and the reflectivity when the propagation length is 100 μm. As Figure 18 shown, in order to maintain the propagation length up to an incident angle of 25 degrees, the reflectivity needs to be approximately 90% or more.

[0104] Figure 12 represents the calculated wavelength λ A This is a graph showing the relationship between the incident angle φ and the reflectance at 940 nm. As Figure 12 shown, the reflectance decreases gently and monotonically in a very high band where the reflectance is around 95% to 99.9%. More specifically, in this band, the reflectance decreases stepwise as the incident angle φ increases. This band is approximately above 940 nm and approximately below 1090 nm. The reflectance does not decrease sharply as Figure 10B shown. The reflectance is high when the incident angle φ is relatively small and low when the incident angle φ is relatively large. A design method for a chirped DBR for obtaining a desired reflection spectrum as Figure 11 shown is described, for example, in "Thin-Film Optical Filters, 3rd Ed." by H.A. Macleod (P. 193 - P. 204), IoP Publishing (Bristol and Philadelphia).

[0105] As described above, by setting an inflection point on the long - wavelength side of the maximum point P of the reflection spectrum LM , the change in reflectance with respect to the change in the incident angle φ can be made gentle. The maximum point P of the reflection spectrum LM and the inflection point may also exist in the band showing a reflectance of 95% or more. With such a configuration, the reflectance can be kept high and changed gently. The maximum point P of the reflection spectrum LM and the inflection point may also exist in the band showing a reflectance of 90% or more. In the present embodiment, when there is one or more inflection points, the reflectance changes gently at least in the range where the incident angle φ is 0° or more and approximately 10° or less. In particular, when there are two or more inflection points, the reflectance changes gently at least in the range where the incident angle φ is 0° or more and approximately 15° or less. By setting two or more inflection points in this way, the change in reflectance with respect to the change in the incident angle can be made gentle in a wide angle range. In addition, a high reflectance can be maintained and a gentle change in this reflectance can be achieved.

[0106] Next, for comparison, the relationship between the exit angle θ and the propagation length L p is described when using a conventional DBR and the DBR of the present embodiment as the mirror 30.

[0107] Figure 13 represents the exit angle θ and the propagation length L pA diagram of an example of the relationship. The white circle corresponds to the case where the mirror 30 in the slow light waveguide 10 is formed by the conventional DBR in the above example. The black dot corresponds to the case where the mirror 30 in the slow light waveguide 10 is formed by the chirped DBR in the above example. The mirror 40 in the slow light waveguide 10 is formed by a conventional DBR different from the above example. The DBR has a structure in which 11 high refractive index layers and 10 low refractive index layers are alternately stacked. The refractive index of the high refractive index layer is 2.28 and the thickness is 107 nm. The refractive index of the low refractive index layer is 1.47 and the thickness is 172 nm. The refractive index of the optical waveguide layer 20 is 1.68. The refractive index of air as the medium on the light output side is 1.0.

[0108] As shown by the white circle, in the conventional DBR, the propagation length L p increases as the output angle θ increases. In contrast, as shown by the black dot, it can be seen that in the chirped DBR of the present embodiment, even when the output angle θ increases, the propagation length L p hardly changes. In this way, with the chirped DBR of the present embodiment, the dependence of the propagation length L p on the output angle θ can be suppressed. If the propagation length L p is substantially constant regardless of the output angle θ, then Figure 7 the beam width Δθ of the output light shown is also substantially constant with respect to the output angle θ. In the example shown, the propagation length L p is on average approximately 150 μm. As Figure 13 shown, the propagation length Lp≈150 μm corresponds to the beam width Δθ≈0.1° of the output light. Therefore, even when the output angle θ changes, the beam width Δθ of the output light can be maintained at approximately 0.1 degrees. Thereby, the change in the resolution of the scan due to the output angle θ can be suppressed. Furthermore, since the beam width Δθ of the output light is 0.1°, a high resolution can be maintained regardless of the output angle θ.

[0109] In the above example, the reflectivity monotonically decreases on the long wavelength side of the maximum point P LM , but the reflectivity does not necessarily have to monotonically decrease on the long wavelength side of the maximum point P LM . is a diagram showing the reflection spectrum of another chirped DBR of the present embodiment corresponding to the incident angle of φ = 0°. In the Figure 7 example shown, in the wavelength band where the reflectivity is 95% or more, the reflection spectrum includes the maximum point P LM1 and the maximum point P LM2 located on its long wavelength side, and LM1 on the long wavelength side of the maximum point P LM2The inflection points P1 to P3 on the short-wavelength side. In this reflection spectrum, the reflectance is at the maximum point P LM1 On the long-wavelength side of and the maximum point P LM2 On the short-wavelength side, it first decreases and then increases as the wavelength increases. That is, the reflectance is not monotonically decreasing on the long-wavelength side of the maximum point P LM1 On the long-wavelength side of the maximum point P LM2 On the long-wavelength side, it monotonically decreases. In this case, the reflectance also decreases gently and more specifically in a stepwise manner as the incident angle φ increases in a very high wavelength band where the reflectance is around 99.5% to 99.9%. This wavelength band is approximately above 940 nm and below approximately 1000 nm.

[0110] As described above, in the slow light waveguide 10 in the present embodiment, it is possible to suppress the dependence of the beam line width Δθ of the emitted light on the emission angle θ. Furthermore, even when the emission angle θ changes, the beam line width Δθ of the emitted light can be maintained narrow. This effect can be obtained when at least one of the mirrors 30 and 40 in the slow light waveguide 10 has the following reflection spectrum. This reflection spectrum includes one maximum point and a first inflection point and a second inflection point on the long-wavelength side of the maximum point in a wavelength band where the reflectance corresponding to the incident angle φ = 0° is 90% or more. The wavelength of the first inflection point is shorter than the wavelength of the second inflection point. The wavelength λ of the light 22 propagating in the optical waveguide layer 20 is a wavelength that is above the maximum point and below the first inflection point. This wavelength band can also be included, for example, in the wavelength band of 0.8 μm or more and 1.2 μm or less that can be used for the above-mentioned LiDAR system. Either one of the mirrors 30 and 40 can exhibit such a reflection spectrum, or both of the mirrors 30 and 40 can exhibit such a reflection spectrum. In In the example shown, light is emitted from the mirror 30 and reflected by the mirror 40, but it is not limited to this example. Light can also be reflected by the mirror 30, emitted from the mirror 40, or emitted from both the mirror 30 and the mirror 40.

[0111] In the present embodiment, by setting an inflection point on the long-wavelength side of the maximum point P of the reflection spectrum, the change in the reflectance with respect to the change in the incident angle φ becomes gentle, and the region where the reflectance changes gently is used. Therefore, the wavelength λ of the light 22 propagating in the optical waveguide layer 20 is the wavelength expressed by using the maximum point P LM On the long-wavelength side and the first inflection point P1. LM

[0112] [Equation 3]

[0113] (P LM + P1) / 2 < λ < P1 (3)

[0114] <Application Example>

[0115] Figure 14 This is a diagram showing a structural example of an optical scanning device 100 in which components such as a beam splitter 90, a waveguide array 10A, a phase shifter array 80A, and a light source 130 are integrated on a circuit board (such as a chip). The light source 130 can be a light-emitting element such as a semiconductor laser, for example. In this example, the light source 130 emits light of a single wavelength λ in free space. The beam splitter 90 branches the light from the light source 130 and guides it into waveguides among a plurality of phase shifters. In the example shown, an electrode 62A and a plurality of electrodes 62B are provided on the chip. A control signal is supplied from the electrode 62A to the waveguide array 10A. Control signals are respectively sent from the plurality of electrodes 62B to the plurality of phase shifters 80 in the phase shifter array 80A. The electrode 62A and the plurality of electrodes 62B can be connected to a control circuit (not shown) that generates the above control signal. The control circuit can be provided Figure 14 on the chip shown, or can be provided on another chip in the optical scanning device 100.

[0116] As shown, by integrating all components on a chip, a large-range optical scanning can be achieved with a small-sized device. For example, all components shown can be integrated on a chip of about 2 mm × 1 mm. Figure 2 shown.

[0117] This is a schematic diagram showing a situation where a beam such as a laser beam is irradiated from the optical scanning device 100 to the far field and two-dimensional scanning is performed. The two-dimensional scanning is performed by moving the beam spot 310 in the horizontal and vertical directions. For example, by combining with a known TOF (Time Of Flight) method, a two-dimensional ranging image can be obtained. The TOF method is a method of irradiating a laser beam and observing the reflected light from an object to calculate the flight time of the light and obtain the distance.

[0118] Figure 15FIG. 0 is a block diagram showing a configuration example of a LiDAR system 300 as an example of an optical detection system capable of generating such a ranging image. The LiDAR system 300 includes an optical scanning device 100, 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 the 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 received light. 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 representing 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 irradiating a light beam from the optical scanning device 100 and the timing of exposure and signal readout of the optical detector 400, and instructs the signal processing circuit 600 to generate a ranging image.

[0119] In two-dimensional scanning, as the frame rate for obtaining a ranging image, for example, it is possible to select from 60fps, 50fps, 30fps, 25fps, 24fps, etc., which are commonly used in video. In addition, when considering application to a vehicle-mounted system, the higher the frame rate, the higher the frequency of obtaining a ranging image, and obstacles can be detected with high accuracy. For example, when traveling at 60 km / h, at a frame rate of 60fps, an image can be obtained every time the vehicle moves approximately 28 cm. At a frame rate of 120fps, an image can be obtained every time the vehicle moves approximately 14 cm. At a frame rate of 180fps, an image can be obtained every time the vehicle moves approximately 9.3 cm.

[0120] The time required to obtain one ranging image depends on the speed of beam scanning. For example, in order to obtain an image with a resolution of 100×100 at 60fps, the beam needs to be scanned at a point in 1.67 μs or less. In this case, the control circuit 500 controls the emission of the light beam performed by the optical scanning device 100 and the signal accumulation / readout performed by the optical detector 400 at an operating speed of 600 kHz.

[0121] <Application Example to an Optical Receiving Device>

[0122] The optical scanning device of the present disclosure can also be used as an optical receiving device with substantially the same configuration. The optical receiving device includes the same waveguide array 10A as the optical scanning device, and a first adjustment element that adjusts the direction of light that can be received. Each first mirror 30 of the waveguide array 10A transmits light incident from the third direction to the opposite side of the first reflection surface. Each optical waveguide layer 20 of the waveguide array 10A causes the light transmitted through the first mirror 30 to propagate in the second direction. 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 through the first adjustment element, the direction of light that can be received can be changed. Furthermore, in the case where the optical receiving device includes the same plurality of phase shifters 80 or 80a and 80b as the optical scanning device, and a second adjustment element that changes the phase difference of the light output from the plurality of waveguide elements 10 through the plurality of phase shifters 80 or 80a and 80b respectively, the direction of light that can be received can be changed two-dimensionally.

[0123] For example, an optical receiving device can be configured by replacing the light source 130 in the optical scanning device 100 shown in with a receiving circuit. If light with a wavelength λ is incident on the waveguide array 10A, the light is sent to the optical splitter 90 via the phase shifter array 80A, and finally collected at one position and sent to the receiving circuit. The intensity of the light collected at this one position can be said to represent the sensitivity of the optical receiving device. The sensitivity of the optical receiving device can be adjusted by the adjustment elements respectively assembled into the waveguide array and the phase shifter array 80A. In the optical receiving device, for example, in Figure 15 , the direction of the wave vector (the thick arrow in the figure) is opposite. The incident light has a light component in the direction in which the waveguide element 10 extends (the X direction in the figure) and a light component in the arrangement direction of the waveguide elements 10 (the Y direction in the figure). The sensitivity of the light component in the X direction can be adjusted by the adjustment element assembled into the waveguide array 10A. On the other hand, the sensitivity of the light component in the arrangement direction of the waveguide elements 10 can be adjusted by the adjustment element assembled into the phase shifter array 80A. From the phase difference Δφ of the light when the sensitivity of the optical receiving device is maximum, the refractive index n w and thickness d of the optical waveguide layer 20, the θ and α0 shown in Figure 15 Figure 15 Figure 15 Figure 16 Figure 17 Figure 15 Figure 4 Figure 4 can be known. Thus, the incident direction of light can be determined.

[0124] The above-described embodiments can be appropriately combined.

[0125] Finally, the above optical devices are summarized into the following items.

[0126] The optical device related to Item 1 includes: a first mirror having a first reflecting surface and extending along a first direction; a second mirror having a second reflecting surface facing the first reflecting surface and extending along the first direction; and an optical waveguide layer located between the first mirror and the second mirror for propagating light along the first direction. The transmittance of the first mirror is higher than that of the second mirror. The reflection spectrum corresponding to the light incident from the normal direction of the reflecting surface of at least one of the first mirror and the second mirror includes a maximum point, a first inflection point, and a second inflection point on the longer wavelength side than the maximum point in a wavelength band where the reflectance is 90% or more.

[0127] In this optical device, the reflectance of at least one of the first mirror and the second mirror decreases gently as the incident angle of the light increases. Thereby, it is possible to suppress the change in the beam line width of the light emitted from at least one of the first mirror and the second mirror according to the emission angle.

[0128] The optical device related to Item 2 is: in the optical device related to Item 1, the wavelength of the first inflection point is shorter than that of the second inflection point. The wavelength λ of the light propagating in the optical waveguide layer is a wavelength equal to or greater than the maximum point and equal to or less than the first inflection point.

[0129] In this optical device, the reflectance of at least one of the first mirror and the second mirror decreases stepwise as the incident angle of the light increases. Thereby, it is possible to suppress the change in the beam line width of the emitted light according to the emission angle.

[0130] The optical device related to Item 3 is: in the optical device related to Item 1 or 2, the wavelength band is included in the range of 0.8 μm or more and 1.2 μm or less.

[0131] This optical device can be applied to a LiDAR system.

[0132] The optical device related to Item 4 is: in the optical device related to any one of Items 1 to 3, at least one of the first mirror and the second mirror includes a distributed Bragg reflector having a stacked structure.

[0133] In this optical device, the same effects as those of the optical device related to any one of Items 1 to 3 can be obtained.

[0134] The optical device related to Item 5 is: in the optical device related to Item 4, the distributed Bragg reflector is a chirped DBR.

[0135] In this optical device, the same effects as those of the optical device related to Item 4 can be obtained.

[0136] The optical device according to item 6 is the optical device according to item 1, wherein the first reflecting mirror has the reflection spectrum.

[0137] In this optical device, it is possible to suppress the beam width of light emitted from the first reflecting mirror from changing depending on the emission angle.

[0138] Industrial Applicability

[0139] The optical scanning device and the optical receiving device in the present disclosure can be used, for example, in laser radar systems installed in vehicles such as automobiles, UAVs, and AGVs.

[0140] Description of reference numerals:

[0141] 10 Waveguide components, optical waveguides

[0142] 11 Optical waveguide

[0143] 10A waveguide array

[0144] 15, 15a, 15b, 15c, 15m gratings

[0145] 20 Optical waveguide layer

[0146] 22 Dielectric components

[0147] 30 1st reflector

[0148] 40 2nd reflector

[0149] 30es exit surface

[0150] 30s 1st reflective surface

[0151] 40s Second reflective surface

[0152] 51 dielectric layer

[0153] 62a, 62b, 62A, 62B electrodes

[0154] 73 Multiple partitions

[0155] 80 Phase Shifter

[0156] 80A Phase Shifter Array

[0157] 90 Optical Splitter

[0158] 100 optical scanning devices

[0159] 111 connection area

[0160] 112 Non-connected area

[0161] 110 Waveguide Array Driving Circuit

[0162] 130 Light source

[0163] 210 Driving circuit of the phase shifter array

[0164] 310 Beam spot

[0165] 400 Optical detector

[0166] 500 Control circuit

[0167] 600 Signal processing circuit

Claims

1. An optical device, comprising: A first mirror having a first reflecting surface and extending along a first direction; A second mirror having a second reflecting surface opposed to the first reflecting surface and extending along the first direction; and An optical waveguide layer located between the first mirror and the second mirror and allowing light to propagate along the first direction; The transmittance of the first mirror is higher than that of the second mirror, The reflection spectrum corresponding to light incident from the normal direction of the reflecting surface of at least one of the first mirror and the second mirror is: including a maximum point, a first inflection point, and a second inflection point on the longer wavelength side than the maximum point in a wavelength band where the reflectance is 90% or more.

2. The optical device according to claim 1, The wavelength of the first inflection point is shorter than that of the second inflection point, The wavelength λ of the light propagating in the optical waveguide layer is a wavelength equal to or greater than the maximum point and equal to or less than the first inflection point.

3. The optical device according to claim 1 or 2, The wavelength band is included in a range of 0.8 μm or more and 1.2 μm or less.

4. The optical device according to any one of claims 1 to 3, At least one of the first mirror and the second mirror includes a distributed Bragg reflector having a laminated structure.

5. The optical device according to claim 4, The distributed Bragg reflector is a chirped DBR, i.e., a chirped distributed Bragg reflector.

6. The optical device according to claim 1, The first mirror has the reflection spectrum.

7. An optical scanning device, comprising: A first mirror having a first reflecting surface and extending along a first direction; A second mirror having a second reflecting surface opposed to the first reflecting surface and extending along the first direction; and An optical waveguide layer located between the first mirror and the second mirror and allowing light to propagate along the first direction; The transmittance of the first mirror is higher than that of the second mirror, The reflection spectrum corresponding to light incident in the normal direction of the reflection surface of at least one of the first mirror and the second mirror is such that: in a wavelength band where the reflectance is 90% or more, it includes a maximum point P LM , and a first inflection point P1 and a second inflection point P2 on the long wavelength side of the maximum point The light exiting through the first mirror is deflected so as to scan a space.

8. The optical scanning device according to claim 7, The wavelength λ used in the scanning satisfies: (P LM + P1) / 2 < λ < P1.

Images