Light Emitting Device

Abstract

This light emission device comprises: a waveguide element that includes a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer positioned between the first mirror and the second mirror, and causes the light incident onto the optical waveguide layer to propagate in a first direction and to be emitted via the first mirror; a first photodetector that is positioned in the path of the light incident onto the optical waveguide layer or in another path branching from the path and that outputs a first signal according to the amount of received light; and a second photodetector that is positioned in the path of the light which has propagated inside the optical waveguide layer in the first direction and has passed through the optical waveguide layer, and that outputs a second signal according to the amount of received light.

Description

[Technical field]

[0001] The present disclosure relates to a light emitting device. [Background technology]

[0002] Conventionally, various devices capable of changing the emission direction of light have been proposed.

[0003] Patent Document 1 discloses an optical deflection element including a waveguide having an optical waveguide layer and first distributed Bragg reflectors formed on the upper and lower surfaces of the optical waveguide layer, an optical inlet for introducing light into the waveguide, and an optical outlet formed on the surface of the waveguide. Patent Document 1 describes that the light can be deflected over a wide range of deflection angles by changing the wavelength of the incident light.

[0004] Patent Document 2 discloses a waveguide element including two multilayer reflective films and an optical waveguide layer between the two multilayer reflective films. By changing the refractive index or thickness of the optical waveguide layer, the angle of light emitted from the multilayer reflective film can be changed. Such a waveguide is called a "slow light waveguide."

[0005] Patent Document 3 discloses an optical scanning device including a total reflection waveguide and a slow light waveguide connected to the total reflection waveguide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-16591 A [Patent Document 2] US Patent Application Publication No. 2018 / 224709 [Patent Document 3] International Publication No. 2018 / 061514 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure provides a technique for improving the emission characteristics of a light-emitting device capable of changing the emission direction of light. [Means for solving the problem]

[0008] A light emitting device according to one embodiment of the present disclosure includes a waveguide element including a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror, the waveguide element propagating light input to the optical waveguide layer along a first direction and emitting the light via the first mirror; a first photodetector located on a path of the light input to the optical waveguide layer or on another path branching from the first path, the first photodetector outputting a first signal corresponding to an amount of received light; and a second photodetector located on the path of light propagating through the optical waveguide layer in the first direction and passing through the optical waveguide layer, the second photodetector outputting a second signal corresponding to the amount of received light.

[0009] 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

[0010] According to the embodiments of the present disclosure, it is possible to improve the emission characteristics of a light emitting device capable of changing the emission direction of light. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view illustrating a configuration example of a light emitting device. [Diagram 2] FIG. 1 is a diagram illustrating an example of a light emitting device that realizes one-dimensional scanning by a single waveguide element. [Diagram 3] FIG. 2 is a diagram illustrating an example of a cross-sectional structure of one waveguide element and propagating light. [Figure 4A] FIG. 1 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 4B]FIG. 13 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. [Diagram 5] FIG. 1 is a perspective view illustrating a schematic example of a waveguide array. [Figure 6] 1A and 1B are schematic diagrams showing examples of connections between a waveguide array and a phase shifter array. [Figure 7] FIG. 1 is a schematic diagram showing a general configuration of a light emitting device according to an exemplary embodiment. [Figure 8] 1 is a cross-sectional view taken along an XZ plane illustrating an example of the structure of a waveguide element. [Figure 9] 11 is a cross-sectional view taken along the XZ plane showing another example of the structure of a waveguide element. FIG. [Figure 10] FIG. 2 is a block diagram showing a schematic configuration of a drive device. [Figure 11] 1 is a diagram showing an example of the relationship between the angle of light emitted from a waveguide element and the propagation length L of the light in an optical waveguide layer. [Figure 12] 12 is a diagram showing approximate calculation values ​​of the light intensity distribution inside the optical waveguide layer for each output angle shown in FIG. 11. FIG. [Figure 13] This is a diagram in which the ratio I2 / I1 is plotted for each output angle. [Figure 14] This is a diagram in which the difference (I1-I2) between the light intensity I1 at the starting end and the light intensity I2 at the end is plotted for each emission angle. [Figure 15] FIG. 13 is a diagram showing an example of an adjusted light intensity I1. [Figure 16] 10 is a flowchart showing an example of an operation for generating data of a calibration table. [Figure 17] 10 is a flowchart showing an example of an operation of the control circuit when the light emitting device is performing a beam scanning operation. [Figure 18] 11 is a diagram showing an example of change in the relationship between I2 / I1 and the output angle accompanying a change in the extinction coefficient of the liquid crystal layer. FIG. [Figure 19] FIG. 13 is a block diagram showing a configuration of a light emitting device according to another embodiment. [Figure 20] FIG. 11 is a cross-sectional view showing a configuration of a light emitting device according to another embodiment. [Figure 21] 13 is a flowchart illustrating an example of a process for generating calibration data according to another embodiment. [Figure 22] 13 is a flowchart illustrating an example of a calibration data update process according to another embodiment. [Figure 23] 11A and 11B are diagrams illustrating another configuration example of the light emitting device. [Figure 24] 1 is a schematic diagram showing a state in which a light beam is emitted from a light emitting device into a distant location to perform a two-dimensional scan. [Diagram 25] FIG. 1 is a block diagram showing a configuration example of a light detection system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A light-emitting device according to an exemplary embodiment of the present disclosure includes one or more waveguide elements having a slow-light waveguide structure, similar to the devices disclosed in Patent Documents 2 and 3. The waveguide element includes a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror. The waveguide element propagates light input to the optical waveguide layer along a first direction and outputs the light via the first mirror. The direction of the output light can be changed by adjusting the refractive index or thickness of the optical waveguide layer or the wavelength of the light input to the optical waveguide layer, as described later. More specifically, by changing at least one of the refractive index, thickness, and wavelength, the component of the wave vector of the output light in the direction along the longitudinal direction of the optical waveguide layer can be changed. This allows one-dimensional scanning by light to be realized. The light-emitting device may include a driving device that changes the refractive index or thickness of the optical waveguide layer, or the wavelength of the propagating light.

[0013] Furthermore, when an array of multiple waveguide elements is used, two-dimensional scanning can be realized. More specifically, by providing an appropriate phase difference to the light supplied to the multiple waveguide elements and adjusting the phase difference, the direction in which the light emitted from the multiple waveguide elements reinforce each other can be changed. The change in phase difference changes the component of the wave vector of the emitted light in the direction intersecting the longitudinal direction of the optical waveguide layer. This makes it possible to realize two-dimensional scanning.

[0014] In order to change the direction of light emission, any one of the refractive index, thickness, and wavelength may be controlled alone, or any two or all of the three may be controlled to change the direction of light emission.

[0015] 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."

[0016] 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.

[0017] The light emitting device according to the embodiment of the present disclosure may be used, for example, in a LiDAR (Light Detection and Ranging) system. Compared with a radar system that uses radio waves such as millimeter waves, the LiDAR system uses electromagnetic waves with short wavelengths (for example, visible light, infrared light, or ultraviolet light). This allows the distance distribution of an object to be detected with high resolution. The LiDAR system may be mounted on a moving object such as an automobile, a UAV (Unmanned Aerial Vehicle, a so-called drone), or an AGV (Automated Guided Vehicle), and may be used as one of the collision avoidance technologies.

[0018] <Example of light emission device configuration> Hereinafter, as an example, a configuration example of a light emitting device capable of performing two-dimensional scanning and its principle will be described. In the following description, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters and overlapping description of substantially the same configuration may be omitted. This is to avoid the following description becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the inventors provide the attached drawings and the following description 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 these. In the following description, the same or similar components are given the same reference numerals. In the following description, XYZ coordinates indicating mutually orthogonal X, Y, and Z directions are used. 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 when the embodiment of the present disclosure is actually implemented in any way. In addition, the shape and size of the whole or part of the structure shown in the drawings do not limit the actual shape and size.

[0019] FIG. 1 is a perspective view showing a schematic configuration example of a light-emitting device. The light-emitting device 100 shown in FIG. 1 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 and emit light in a direction D3 intersecting a virtual plane parallel to the first and second directions. In this example, the first direction (X direction) and the second direction (Y direction) are orthogonal to each other, but they do not necessarily have to be orthogonal to each other. In the example of FIG. 1, the plurality of 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] Each of the multiple waveguide elements 10 includes a first mirror 30 and a second mirror 40 facing each other, and an optical waveguide layer 20 located between the mirrors 30 and 40. Each of the mirrors 30 and 40 has a reflective surface 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 a first direction (X direction).

[0021] 1, the multiple waveguide elements 10 are separated from one another, but at least some of them may be connected to one another. For example, at least one of the first mirror 30, the second mirror 40, and the optical waveguide layer 20 may be connected to one another between the waveguide elements 10.

[0022] 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 these mirrors, 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 can be formed of, for example, a dielectric multilayer film.

[0023] As shown by the arrows 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 this example, 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.

[0024] 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.

[0025] In addition, in applications that do not require two-dimensional scanning, it is not necessary to provide multiple waveguide elements. If the light emitting device has one waveguide element, one-dimensional scanning along the X direction shown in Figure 1 is possible. Depending on the application, a light emitting device specialized for such one-dimensional scanning may also be used.

[0026] FIG. 2 is a schematic diagram showing an example of a light emitting device 100 that realizes one-dimensional scanning by a single waveguide element 10. In this example, light that spreads in the Y direction is emitted. By changing the refractive index or thickness of the optical waveguide layer 20 or the wavelength of light input to the optical waveguide layer 20, the light emission direction can be moved along the X direction. This realizes one-dimensional scanning. Since the emitted light spreads in the Y direction, even a scan in a uniaxial direction can scan a relatively wide area that spreads two-dimensionally. For applications that do not require two-dimensional scanning, a configuration as shown in FIG. 2 can also be adopted.

[0027] 3 is a diagram showing an example of the cross-sectional structure of one waveguide element 10 and the light propagating therethrough. In FIG. 3, 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. 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 and the second mirror 40. 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.

[0028] In a waveguide such as a general 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. According to this configuration, light that is incident on the interface at an angle smaller than the critical angle of total reflection, that is, at an angle closer to perpendicular, can also propagate. The group velocity of light in the propagation direction of light is lower than 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. Such a waveguide element 10 is also called a "slow light waveguide."

[0029] The wavelength of the propagating light in air is λ, and the refractive index of the optical waveguide layer 20 is n w When the thickness of the optical waveguide layer 20 is d, the emission angle θ of the light emitted from the waveguide element 10 into the air is expressed by the following formula (1).

number

[0030] As can be seen from equation (1), the wavelength λ and the refractive index n w By changing either the thickness d or the thickness d, the light emission direction can be changed.

[0031] 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.

[0032] In the embodiment 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. The wavelength λ may be included in the wavelength range of, for example, 400 nm to 1100 nm (visible light to near infrared light). This wavelength range is a wavelength range in which high detection sensitivity can be obtained in a general photodetector or image sensor that detects light by absorbing light with 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, which has a relatively small transmission loss 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.

[0033] To change the direction of the emitted light, the light emitting device 100 may include a driving device (also referred to as 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.

[0034] The optical waveguide layer 20 may include a material whose refractive index changes with application of a voltage, such as a liquid crystal material or an electro-optic material. The optical waveguide layer 20 may be disposed between a pair of electrodes. The refractive index of at least a portion of the optical waveguide layer 20 may be changed by applying a voltage to the pair of electrodes.

[0035] A driving device for changing the thickness, such as an 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 with such a device, the thickness of the optical waveguide layer 20 can be changed. If the optical waveguide layer 20 is made of gas or liquid, the thickness of the optical waveguide layer 20 can be easily changed.

[0036] Next, the operating principle of two-dimensional scanning by a waveguide array in which multiple waveguide elements are arranged in one direction will be explained.

[0037] In the waveguide array, 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.

[0038] FIG. 4A 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. 4A also shows the phase shift amount of light propagating through each waveguide element 10. Here, the phase shift amount is a value based on the phase of light propagating through the leftmost waveguide element 10. The waveguide array shown in FIG. 4A includes a plurality of waveguide elements 10 arranged at equal intervals. In FIG. 4A, the dashed arc indicates the wavefront of light emitted from each waveguide element 10. The straight line indicates the wavefront formed by the interference of light. The arrow indicates the direction of light emitted from the waveguide array (i.e., the direction of the wave vector). In the example shown in FIG. 4A, the phase of light propagating through the optical waveguide layer 20 in each waveguide element 10 is the same. In this case, the light is emitted in a direction (Z direction) perpendicular to both the arrangement direction (Y direction) of the waveguide elements 10 and the extension direction (X direction) of the optical waveguide layer 20.

[0039] FIG. 4B 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. 4B, the phase of light propagating through the optical waveguide layer 20 in the multiple waveguide elements 10 differs 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

[0040] In the example shown in FIG. 3, the light emission direction is parallel to the XZ plane. That is, α0=0°. In the example shown in FIG. 4A and FIG. 4B, the direction of light emitted from the light emitting device 100 is parallel to the YZ plane. That is, θ=0°. However, in general, the direction of light emitted from the light emitting device 100 is not parallel to either the XZ plane or the YZ plane. That is, θ≠0° and α0≠0°.

[0041] Fig. 5 is a perspective view showing a schematic example of a waveguide array in a three-dimensional space. The thick arrows shown in Fig. 5 indicate the direction of light emitted from the light-emitting 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).

[0042] 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 in front of the waveguide element 10. The light emitting device 100 may include a plurality of phase shifters connected to each of the plurality of waveguide elements 10, and a driving device (hereinafter also referred to as a "second adjustment element") that adjusts the phase of the light propagating through each phase shifter. Each phase shifter may include 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 (direction D3 shown in FIG. 1) 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."

[0043] FIG. 6 is a schematic diagram showing an example of a connection between the waveguide array 10A and the phase shifter array 80A. In the example shown in FIG. 6, all the phase shifters 80 are optical waveguides having 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, for example, the amount of phase shift of each can be adjusted by the driving voltage. Also, by making the length of each phase shifter 80 change in equal steps, it is possible to give equal-step phase shifts with the same driving voltage. Furthermore, this light output device 100 further includes an optical branching unit 90 that branches and supplies light to a plurality of phase shifters 80, a first driving circuit 110 that drives each waveguide element 10, and a second driving circuit 180 that drives each phase shifter 80. The straight arrow shown in FIG. 6 represents the input of light. Two-dimensional scanning can be realized by independently controlling the first driving circuit 110 and the second driving circuit 180. In this example, the first driving circuit 110 functions as a first adjustment element, i.e., one element of a driving device, and the second driving circuit 180 functions as a second adjustment element, i.e., one element of a driving device.

[0044] 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 180 changes the phase of light propagating inside the waveguide by changing the refractive index of the waveguide 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 slow light waveguide similar to the waveguide element 10.

[0045] Note that 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 equal phase is supplied to all the phase shifters 80. By such adjustment, the control of each phase shifter 80 by the second driving circuit 180 can be simplified.

[0046] An optical device having a configuration similar to that of the above-described light emitting device 100 can also be used as an optical receiving device. Details of the structure, operation principle, operation method, etc. of the optical device are disclosed in, for example, Patent Documents 2 and 3. The disclosures of these documents are incorporated herein in their entirety.

[0047] <Controlling the direction and intensity of emitted light> As described above, the light-emitting device having the slow-light waveguide structure can change the direction of the emitted light beam by changing the refractive index or thickness of the light guide layer or the wavelength of the light input to the light guide layer. Also, the intensity of the emitted light beam can be controlled by controlling the intensity of the light input to the light guide layer.

[0048] However, the light emission characteristics of a light-emitting device may change due to various factors such as changes in the environment, such as temperature or humidity, or deterioration of the device over time. For example, if the optical waveguide layer is made of a material whose refractive index changes depending on the applied voltage, such as a liquid crystal material, the response characteristics of the refractive index to the applied voltage may change due to the temperature dependency or aging of the material. As a result, even if the same voltage is applied to the optical waveguide layer, the light emission direction may vary depending on the environment or aging. Similar problems may also occur in a configuration in which the direction of the emitted light is changed by changing the thickness of the optical waveguide layer or the wavelength of the guided light. In addition, since the intensity of the emitted light depends on the emission angle, it is desirable to appropriately adjust the intensity of the emitted light according to the change in the emission angle.

[0049] To solve such problems, a light emitting device according to an embodiment of the present disclosure includes a photodetector in front of and behind the waveguide element. A driving device controls the intensity of light emitted from the light source and / or the direction of light emitted from the waveguide element based on the intensity of light detected by the photodetectors. The configuration and operation of such an embodiment will be described in more detail below.

[0050] FIG. 7 is a schematic diagram showing a schematic configuration of a light emitting device 100A according to an exemplary embodiment. The light emitting device 100A includes a light source 130, an optical waveguide 11, a waveguide element 10, a first optical detector 171, a second optical detector 172, and a driving device 160. The optical waveguide 11 connects the light source 130 and the waveguide element 10. The optical waveguide 11 has a branching portion 11b. Another optical waveguide 13 extends from the branching portion 11b. The first optical detector 171 is disposed at the tip of the optical waveguide 13. The first optical detector 171 detects light propagated through the optical waveguide 13. The second optical detector 172 is disposed at a position where it detects light propagated through the optical waveguide layer of the waveguide element 10. In the example of FIG. 7, the second optical detector 172 is in contact with the waveguide element 10. The second photodetector 172 is not limited to this configuration, and may be configured to detect light propagating through another optical waveguide (not shown) connected to the waveguide element 10.

[0051] The light source 130 is configured to emit light that is input to an optical waveguide layer in the waveguide element 10. The light source 130 may include a light emitting element such as a semiconductor laser element.

[0052] In this example, the waveguide element 10 includes a pair of mirrors, an optical waveguide layer located between the pair of mirrors, and a pair of electrodes for applying a voltage to the optical waveguide layer. The optical waveguide layer may include a material whose refractive index changes when a voltage is applied thereto, such as a liquid crystal material or an electro-optical material.

[0053] The driving device 160 is connected to a pair of electrodes in the waveguide element 10, the light source 130, the first photodetector 171, and the second photodetector 172. During operation, the driving device 160 obtains signals indicating the amount of detected light from the first photodetector 171 and the second photodetector 172, and controls the voltage applied to the pair of electrodes based on these signals. In this way, the driving device 160 controls the direction of the light emitted from the waveguide element 10. The driving device 160 also controls the intensity of the light emitted from the light source 130 based on two signals output from the first photodetector 171 and the second photodetector 172, respectively. A specific example of the control of the light source 130 and the waveguide element 10 by the driving device 160 will be described later.

[0054] FIG. 8 is an XZ cross-sectional view showing an example of the structure of the waveguide element 10. The waveguide element 10 includes a first substrate 70A, a first electrode 60A, a first mirror 30, an optical waveguide layer 20, a second mirror 40, a second electrode 60B, and a second substrate 70B, in this order. The first mirror 30 spreads along a first direction (X direction in this example) and a second direction (Y direction in this example), and has a structure extending in the first direction. The first mirror 30 is optically transparent, and emits a part of the light propagating through the optical waveguide layer 20 along the X direction to the outside. The second mirror 40 spreads along the first direction and the second direction, and has a structure extending in the first direction, similar to the first mirror 30. The second mirror 40 in this example does not have optical transparency.

[0055] The optical waveguide layer 20 is located between the first mirror 30 and the second mirror 40 and extends along a first direction. The optical waveguide layer 20 may be made of, for example, a liquid crystal material or an electro-optical material. The substrates 70A and 70B may be made of, for example, a semiconductor such as Si or a dielectric material such as SiO2.

[0056] The first electrode 60A is between the first mirror 30 and the first substrate 70A and is in contact with both. The second electrode 60B is between the second mirror 40 and the second substrate 70B and is in contact with both. The first electrode 60A may be made of a conductive material having translucency, such as ITO (indium tin oxide). The second electrode 60B may be made of any conductive material other than a conductive material having translucency, such as ITO. As shown in FIG. 7, the electrodes 60A and 60B are connected to a driving device 160. The driving device 160 includes a driving circuit that applies a voltage to the electrodes 60A and 60B. The driving device 160 changes the refractive index of the optical waveguide layer 20 by changing the voltage applied between the first electrode 60A and the second electrode 60B. This makes it possible to change the emission angle of the light beam emitted through the first mirror 30, the first electrode 60A, and the first substrate 70A.

[0057] 8 also shows a first optical waveguide 11 and a second optical waveguide 12 respectively connected to both ends of the optical waveguide layer 20. Each of the first optical waveguide 11 and the second optical waveguide 12 is supported by a dielectric member 50 on the second mirror 40.

[0058] One end of each of the optical waveguides 11 and 12 in this embodiment is inside the optical waveguide layer 20 and includes a grating 15. Each grating 15 includes a plurality of recesses arranged along the X direction. In the example of FIG. 8, each grating 15 includes four recesses, but a larger number of recesses may be provided. Instead of the plurality of recesses, a plurality of protrusions may be provided. The number of recesses or protrusions arranged in the X direction in each grating 15 may be, for example, 4 or more and 64 or less. The number of recesses or protrusions in each grating 15 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 the grating 15 as a whole has good characteristics.

[0059] In the example shown in FIG. 8, the dimension Lg in the X direction of the region where the grating 15 is provided may be, for example, a value within a range of about 4 μm to 50 μm. In a region of such size, the grating 15 with, for example, 8 to 32 periods may be formed. In this embodiment, the dimension L0 in the X direction of the portion of the first optical waveguide 11 located inside the optical waveguide layer 20 is larger than the dimension Lg in the X direction of the region where the grating 15 is provided, but L0 and Lg may be the same. In the example of FIG. 8, the first optical waveguide 11 and the second optical waveguide 12 have a symmetrical structure, but both may have an asymmetrical structure. The dimension L1 in the X direction of the portion of the optical waveguide layer 20 located between the first optical waveguide 11 and the second optical waveguide 12 is larger than Lg, and may be, for example, a value within a range of about 100 μm to 5 mm. However, the dimensions are not limited to these dimensions, and the dimensions of each member are determined according to the required characteristics.

[0060] Each of the first optical waveguide 11 and the second optical waveguide 12 may be made of a dielectric material having a higher refractive index than the dielectric member 50 and the optical waveguide layer 20. Each of these optical waveguides 11 and 12 is a total reflection waveguide, and propagates light along the X direction. Light propagating through the first optical waveguide 11 is converted by the grating 15 into light propagating through the optical waveguide layer 20 with high efficiency. Similarly, light propagating through the optical waveguide layer 20 is converted by the grating 15 in the second optical waveguide 12 into light propagating through the second optical waveguide 12 with high efficiency.

[0061] The connection between each of the first optical waveguide 11 and the second optical waveguide 12 and the optical waveguide layer 20 may be realized by a structure different from that of this embodiment. For example, the tip of each of the optical waveguides 11 and 12 may be in contact with the optical waveguide layer 20 outside the optical waveguide layer 20. As long as optical coupling between the first optical waveguide 11 and the optical waveguide layer 20 and optical coupling between the optical waveguide layer 20 and the second optical waveguide 12 are possible, the structure of each waveguide is arbitrary.

[0062] Although not shown in FIG. 8, as shown in FIG. 7, a first photodetector 171 is disposed to detect light propagating through another optical waveguide 13 branched off from the first optical waveguide 11. The first photodetector 171 includes a photoelectric conversion element such as a photodiode, and outputs a first signal according to the amount of received light. The intensity of the light propagating through the optical waveguide 13 is approximately proportional to the intensity of the light propagating through the first optical waveguide 11 and input to the optical waveguide layer 20. Therefore, the first signal output from the first photodetector 171 reflects the intensity of the light input to the optical waveguide layer 20.

[0063] In the example shown in Fig. 8, the second photodetector 172 detects the light propagated through the second optical waveguide 12. The second optical waveguide 12 guides the light that propagates through the optical waveguide layer 20 in the first direction and passes through the optical waveguide layer 20 to the second photodetector 172. The second photodetector 172 includes a photoelectric conversion element such as a photodiode, and outputs a second signal according to the amount of received light. The second signal reflects the intensity of the light that is input to the optical waveguide layer 20 and is not emitted to the outside via the first mirror 30.

[0064] The arrangement of the second photodetector 172 is not limited to the arrangement shown in Fig. 8, and may be, for example, the arrangement shown in Fig. 9. In the example shown in Fig. 9, the second optical waveguide 12 has a grating 15A not only at the end located inside the optical waveguide layer 20 but also at the opposite end. The second photodetector 172 is arranged so as to detect the light emitted through the grating 15A. Even with such an arrangement, it is possible to obtain a signal according to the amount of light that has passed through the optical waveguide layer 20.

[0065] 7 can be made incident on the first photodetector 171 in the same manner as the method of making light incident on the second photodetector 172 shown in Fig. 8 or 9. In this embodiment, the first photodetector 171 detects light propagating in another waveguide 13 branched off from the first optical waveguide 11, but may be configured to directly detect the propagating light in the first optical waveguide 11.

[0066] Each of the first photodetector 171 and the second photodetector 172 is not limited to a photodetector having a single photoelectric conversion element, but may be a photodetector having a plurality of photoelectric conversion elements, for example, an image sensor. In particular, in a configuration in which a plurality of waveguide elements 10 are arranged along the Y direction, an image sensor in which a plurality of photoelectric conversion elements are arranged in the Y direction may be used as the photodetectors 171 and 172.

[0067] In this embodiment, the first photodetector 171 is disposed at a position away from the light source 130, but the first photodetector 171 may be built into the light source 130. For example, when a laser diode equipped with a feedback function of the optical output is used as the light source 130, an output signal obtained from the feedback mechanism may be used as the detection signal of the first photodetector 171.

[0068] FIG. 10 is a block diagram showing a schematic configuration of the driving device 160 in this embodiment. The driving device 160 includes an interface (IF) 168, a control circuit 162, and a storage device 166. The interface 168 is connected to the light source 130, the first photodetector 171, and the second photodetector 172, and transmits signals between these devices. The control circuit 162 is a circuit that controls the refractive index of the optical waveguide layer 20 and the emission intensity of the light source 130. The control circuit 162 may include one or more processors. The storage device 166 includes memories such as RAM and ROM, and stores computer programs executed by the control circuit 162 and various data. The control circuit 162 controls the emission intensity of the light source 130 and the voltage applied to the optical waveguide layer 20 based on the first signal output from the first photodetector 171 and the second signal output from the second photodetector 172. This controls the intensity and direction of the light emitted through the first mirror 30 of the waveguide element 10.

[0069] In this embodiment, the emission angle of the light emitted through the first mirror 30 depends on the propagation angle of the light propagating inside the optical waveguide layer 20. This propagation angle depends on the refractive index of the optical waveguide layer 20. Therefore, by forming the optical waveguide layer 20 from a material such as liquid crystal whose refractive index can be modulated according to an applied voltage, the emission angle can be controlled by the applied voltage.

[0070] Here, the intensity of the light inside the optical waveguide layer 20 gradually attenuates in the process of propagating along the X direction. This is because part of the propagating light is emitted to the outside through the first mirror 30 during the propagation process. This attenuation rate is determined by the angle dependency of the reflectance of the first mirror 30 and the second mirror 40. Therefore, the attenuation rate depends on the propagation angle of the light propagating through the optical waveguide layer 20. As in this embodiment, by detecting the light intensity at any two points on the path of the light including the optical waveguide layer 20, the attenuation rate and / or the amount of attenuation can be calculated from the detection results. This makes it possible to estimate the propagation angle inside the optical waveguide layer 20 or the angle of the light emitted to the outside, and / or the intensity of the emitted light.

[0071] FIG. 11 is a diagram showing the relationship between the angle of light emitted from the waveguide element 10 in an embodiment and the propagation length L of the light in the optical waveguide layer 20. Here, the propagation length L refers to the distance until the light intensity attenuates to 1 / e times the light intensity at the starting point when the light propagates along the X direction from a certain point in the optical waveguide layer 20. Here, e is the base of the natural logarithm, and e≈2.718. The results shown in FIG. 11 were obtained by performing numerical calculations on the waveguide element 10 having the following configuration. As the first mirror 30, a DBR was used in which 17 layers of high refractive index layers and low refractive index layers were alternately stacked. The refractive index of each high refractive index layer was 2.28, the thickness of each high refractive index layer was 111 nm, the refractive index of each low refractive index layer was 1.47, and the thickness of each low refractive index layer was 173 nm. As the second mirror 40, a DBR was used in which 21 layers of high refractive index layers and low refractive index layers were alternately stacked. The refractive index of each high refractive index layer was 2.36, the thickness of each high refractive index layer was 107 nm, the refractive index of each low refractive index layer was 1.47, and the thickness of each low refractive index layer was 172 nm. For each of the first mirror 30 and the second mirror 40, the first and last layers were both high refractive index layers. The thickness of the optical waveguide layer 20 was 2.02 μm. In order to change the output angle, the refractive index of the optical waveguide layer 20 was changed in the range of 1.68 to 1.55. The output angle refers to the output angle into the atmosphere, where the refractive index is approximately 1, and it was assumed that there was no absorption loss of light during propagation through the waveguide. FemSim by Synopsys was used for the numerical calculation.

[0072] FIG. 12 is a diagram showing approximate calculation values ​​of the light intensity distribution inside the optical waveguide layer 20 for each output angle shown in FIG. 11 in arbitrary units. Here, it is assumed that the light inside the optical waveguide layer 20 attenuates according to exp(-αx). Here, α is the reciprocal of the propagation length L and depends on the output angle θ. x represents the distance from the start end of the optical waveguide layer 20. The start end of the optical waveguide layer 20 refers to the part of the region of length L1 shown in FIG. 8 that contacts the tip of the first optical waveguide 11. Conversely, the part of the region of length L1 shown in FIG. 8 that contacts the tip of the second optical waveguide 12 is called the end end of the optical waveguide layer 20. In this embodiment, the length L1 from the start end to the end end of the optical waveguide layer 20 is set to 1 mm. As shown in FIG. 12, the smaller the output angle θ, the easier the light intensity attenuates with the propagation of light.

[0073] Fig. 13 is a diagram in which the ratio (I2 / I1) of the light intensity I2 at the end of the optical waveguide layer 20 to the light intensity I1 at the start of the optical waveguide layer 20 in this embodiment is plotted for each output angle. The relationship shown in Fig. 13 is a waveguide-specific relationship determined by the propagation angle of the light propagating inside the optical waveguide layer 20 and the angle dependency of the reflectance of the mirrors 30 and 40. By measuring the intensity ratio of I2 to I1, the propagation angle at that point in time can be obtained.

[0074] FIG. 14 is a diagram in which the difference (I1-I2) between the light intensity I1 at the starting end and the light intensity I2 at the end is plotted for each output angle. The intensity difference between I1 and I2 occurs when a part of the light is emitted to the outside during the process of propagating through the optical waveguide layer 20. For example, FIG. 14 In this example, at an output angle of 36°, the light intensity I2 at the end of the optical waveguide layer 20 is about 26% of the light intensity I1 at the beginning. For simplicity, it is assumed that all of the light lost in the optical waveguide layer 20 is output to the outside. In this case, if, for example, 1 W of light is input to the optical waveguide layer 20, about 0.74 W of light is emitted to the outside. In contrast, at an output angle of 25°, the light intensity I2 at the end is about 3% of the light intensity I1 at the beginning, and about 97% of the light is emitted to the outside. In this case, by inputting about 0.76 W of light, an optical output of about 0.74 W can be obtained.

[0075] FIG. 15 is a diagram showing an example of the adjusted light intensity I1 in this example. The input light intensity I1 is controlled to be larger as the output angle becomes larger. By adjusting the intensity of I1 as shown in FIG. 15, it is possible to obtain the same light intensity at any output angle. Note that in an actual device, the absorption loss and scattering loss of the output light change depending on the output angle. For this reason, when calibrating the input light intensity according to the angle as shown in FIG. 15, it is desirable to take into consideration the output angle dependency of the absorption loss and scattering loss.

[0076] In this embodiment, data for calibration is stored in advance in the storage device 166 of the driving device 160 shown in Fig. 10. The control circuit 162 refers to the data, and determines the voltage Vpp to be applied to the optical waveguide layer 20 and a correction value for the intensity of the light emitted from the light source 130 from the data of the intensities I1 and I2.

[0077] The calibration data may be, for example, data in a table format as shown in the following Table 1. Such table data will hereinafter be referred to as a "calibration table" or "calibration data."

[0078] [Table 1]

[0079] Table 1 shows an example of a calibration table used when changing the output angle in 5° increments in the range from 5° to 35°. For each angle, data on the ratio (I2 / I1), applied voltage Vpp, intensity difference (I1-I2), and input correction value I1 / (I1-I2) of the light source 130 are recorded. The relationship between the angle and the ratio (I2 / I1) shown in Table 1 corresponds to the relationship shown in FIG.

[0080] Fig. 16 is a flowchart showing an example of an operation for generating data of a calibration table such as that shown in Table 1. The operation shown in Fig. 16 is performed, for example, during the manufacture of the light emitting device 100A, and the calibration table is stored in advance in the storage device 166. The operation in Fig. 16 can be executed, for example, by the control circuit 162 of the driving device 160.

[0081] First, in step S101, the control circuit 162 acquires data indicating a list of appropriate exit angles according to the application within the angle range required for beam scanning. In the example of Table 1, seven exit angles are set for simplicity, but more exit angles may be set. For example, within a predetermined angle range, many exit angles may be set at relatively small angle intervals, such as 1° or 0.1°.

[0082] The control circuit 162 repeats the operations of steps S102, S103, S104, and S105 until it determines in step S106 that data recording has been completed for all exit angles.

[0083] In step S102, the control circuit 162 selects one angle for which data has not yet been acquired from the list of emission angles as a target emission angle.

[0084] In step S103, the control circuit 162 gradually changes the voltage applied to the optical waveguide layer 20 to determine the peak value of the voltage at which a target output angle is obtained. The control circuit 162 records the value in a calibration table in association with the output angle. The output angle of the light is measured by an output angle measuring device (not shown). In step S104, the control circuit 162 obtains the detection intensity S1 of the first optical detector 171 and the detection intensity S2 of the second optical detector 172 when the target output angle is obtained. Then, the control circuit 162 calculates the estimated optical intensity I1 at the start end of the optical waveguide layer 20 and the estimated optical intensity I2 at the end end by the calculations I1=k1×S1 and I2=k2×S2. Here, k1 and k2 are preset proportionality coefficients. The control circuit 162 records the ratio (I2 / I1), the difference (I1-I2), and the input correction value I1 / (I1-I2) in the calibration table in association with the emission angle. In the calibration table shown in Table 1, the value of the ratio (I2 / I1) is recorded for each angle, but instead, the ratio of S1 to S2 may be recorded for each angle. I1 is proportional to S1, and I2 is proportional to S2. Therefore, in either case, data is stored that specifies the correspondence between the ratio of the first signal output from the first photodetector 171 and the second signal output from the second photodetector 172 and the emission angle.

[0085] In step S105, the control circuit 162 determines whether data has been recorded for all angles included in the list of output angles. If data recording for all angles has not been completed, the process returns to step S102, and the operations of steps S103 and S104 are performed for a different angle. If data recording for all angles has been completed, the process proceeds to step S106.

[0086] In step S106, the control circuit 162 outputs the generated calibration table data and records it in the storage device 166.

[0087] The light emitting device 100A may be used in, for example, a LiDAR system. The control circuit 162 adjusts the voltage applied to the pair of electrodes 60A and 60B so as to scan a predetermined scanning range with light. At this time, the correspondence relationship between the applied voltage and the emission angle may change due to various factors such as the temperature of the environment in which the light emitting device 100A is placed or aging of the light emitting device 100A. In addition, the intensity of the emitted light may differ from the desired intensity.

[0088] To solve this problem, in this embodiment, for example, the following operation is performed when the light emitting device 100A is started or during a scanning operation. First, the control circuit 162 calculates the ratio (I2 / I1) and difference (I1-I2) between the light intensity I1 calculated based on the output signal of the first photodetector 171 and the light intensity I2 calculated based on the output signal of the second photodetector 172 every time the emission angle is changed. Next, the control circuit 162 refers to the calibration data recorded in advance in the storage device 166 to specify the emission angle corresponding to the calculated ratio (I2 / I1). At this time, if there is an error between the original emission angle and the emission angle specified from the calibration data, the control circuit 162 compensates for the error by changing the applied voltage. Furthermore, if there is an error between the emission light intensity estimated from the calculated difference (I1-I2) and the intensity of the light to be emitted at that time, the control circuit 162 compensates for the error by changing the emission light intensity of the light source 130. If an error occurs in the ratio (I2 / I1) or the difference (I1-I2), the control circuit 162 updates the calibration data.

[0089] FIG. 17 is a flowchart showing an example of an operation of updating the calibration data by the light emitting device 100A.

[0090] In this example, in step S201, the control circuit 162 obtains data of a pre-recorded calibration table.

[0091] In the next step S202, the control circuit 162 sets the output angle to an initial value and causes the light beam to be output from the waveguide element. At this time, the control circuit 162 determines the output of the light source 130 based on the input correction value corresponding to the output angle in the calibration table.

[0092] Thereafter, the control circuit 162 repeats the operations of steps S203 to S212 until it determines in step S211 that data acquisition has been completed for all exit angles.

[0093] In step S203, the control circuit 162 calculates a ratio I2 / I1 based on the light intensity I1 based on the output signal of the first photodetector 171 and the light intensity I2 based on the output signal of the second photodetector 172. In the following step S204, the control circuit 162 determines whether there is a difference between the calculated ratio I2 / I1 and a target ratio in the calibration table. The determination of whether there is a difference can be made based on whether the difference between the calculated ratio and the target ratio exceeds a predetermined threshold. If this determination is Yes, proceed to step S205, and if No, proceed to step S207.

[0094] In step S205, the control circuit 162 adjusts the value of the voltage applied to the optical waveguide layer 20 so that the ratio I2 / I1 becomes a target value. In the following step S206, the control circuit 162 records the adjusted voltage value in the calibration table.

[0095] In step S207, the control circuit 162 calculates the intensity difference (I1-I2). In the following step S208, the control circuit 162 determines whether there is a difference between the calculated intensity difference and a target intensity difference in the calibration table. The determination of whether there is a difference can be made based on whether the difference between the calculated intensity difference and the target intensity difference exceeds a predetermined threshold. If this determination is Yes, the process proceeds to step S209, and if this determination is No, the process proceeds to step S211.

[0096] In step S209, the control circuit 162 adjusts the intensity of the light emitted from the light source 130 so that the intensity difference (I1-I2) becomes a target value. At this time, the intensity of the light from the light source 130 is adjusted so that, for example, (I2-I1) / I2 becomes uniform over the entire angle range. In the following step S210, the control circuit 162 records the adjusted input correction value in the calibration table.

[0097] Next, in step S211, the control circuit judges whether or not data acquisition has been completed for all emission angles, and if the judgment is No, the process proceeds to step S212, and if Yes, the process proceeds to step S220.

[0098] In step S211, the control circuit 162 changes the output angle and causes the waveguide element to output the light beam. At this time, the control circuit 162 determines the output of the light source 130 based on the input correction value corresponding to the output angle in the calibration table. Thereafter, the operations of steps S203 to S212 are repeated until data is acquired for all output angles.

[0099] When data is acquired for all output angles, in step S220, the control circuit 162 updates the calibration table and records it in the storage device 166. At this time, among the items shown in Table 1, the items of applied voltage and input correction value are updated, and the items of angle, ratio, and intensity difference are not changed.

[0100] By the above operation, even if the relationship between the voltage applied to the optical waveguide layer 20 and the emission angle, and the relationship between the control command value input to the light source 130 and the intensity of the emitted light change due to the environment or other factors, the direction and intensity of the emitted light can be appropriately controlled. According to this embodiment, the direction and intensity of the emitted light can be estimated without directly detecting a part of the emitted light using an optical element such as a mirror or a beam splitter. Therefore, the emission of light can be optimized with a simpler configuration.

[0101] The light emitting device 100A of the present embodiment includes a single waveguide element 10, but may include an array of a plurality of waveguide elements 10. As described with reference to Fig. 1 to Fig. 6, by imparting an appropriate phase difference to light input to the optical waveguide layer 20 of the plurality of waveguide elements 10, it is possible to two-dimensionally scan a target scene.

[0102] In this embodiment, it is assumed that the relationship between the ratio I2 / I1 and the output angle shown in Fig. 13 does not change. However, this relationship may change due to various factors such as environmental changes or aging. For example, when the optical waveguide layer 20 is made of a liquid crystal material, the optical absorptance of the liquid crystal increases with aging, i.e., the extinction coefficient increases, and the ratio I2 / I1 may decrease.

[0103] Fig. 18 is a diagram showing an example of the change in I2 / I1 when the extinction coefficient k of the liquid crystal is changed. As shown in Fig. 18, when the extinction coefficient k of the liquid crystal is changed, the relationship between the output angle and I2 / I1 changes. As the extinction coefficient k increases, the absorption loss increases and I2 / I1 decreases. If the absorption loss of the optical waveguide layer 20 increases, it may not be possible to obtain the desired beam performance (for example, a divergence angle of 0.17°).

[0104] To solve this problem, a plurality of calibration tables corresponding to the degree of deterioration of the liquid crystal may be prepared in advance, and an optimal calibration table may be selected from the calibration tables during operation. In such an embodiment, the light emitting device includes a measuring device that measures the light transmittance of the optical waveguide layer 20 during operation. An example of such an embodiment will be described below.

[0105] 19 is a block diagram showing a configuration example of a light emitting device including a measuring device 190 that measures the light transmittance of the optical waveguide layer 20. The components of the light emitting device shown in FIG. 19 except for the measuring device 190 are the same as those shown in FIG. 10. The light source 130 is referred to as a "first light source 130" here. The measuring device 190 includes a second light source 132 and a third photodetector 173.

[0106] FIG. 20 is a diagram showing a cross section parallel to the YZ plane of the light-emitting device in this embodiment. In this light-emitting device, a first electrode 60A, a first mirror 30, a plurality of spacers 150, a second mirror 40, and a second electrode 60B are arranged in this order between a first substrate 70A and a second substrate 70B facing each other. The first electrode 60A contacts a part of the first substrate 70A, and the first mirror 30 contacts the first electrode 60A. The second electrode 60B contacts a part of the second substrate 70B, and the second mirror 40 contacts the second electrode 60B. The plurality of spacers 150 contact the second mirror 40, are arranged at intervals in the Y direction, and each extends in the X direction. There is a gap between the first mirror 30 and the spacer 150. The space between the first substrate 70A and the second substrate 70B, including the space between the first mirror 30 and the second mirror 40, is filled with a liquid crystal material. The layer filled with the liquid crystal material is called the liquid crystal layer 140. The optical waveguide layer 20 in this embodiment is a part of the liquid crystal layer 140. The optical waveguide layer 20 is formed in an area partitioned by the first mirror 30, the second mirror 40, and two spacers 150 adjacent to each other in the Y direction. The structure shown in FIG. 20 can be said to be a structure in which a plurality of (two in the example of FIG. 20) waveguide elements 10 are arranged in the Y direction. Each waveguide element 10 has a structure in which the first electrode 30, the first mirror 30, the optical waveguide layer 20, the second mirror 40, and the second electrode 60B are laminated in this order. Each of the first electrode 30, the first mirror 30, the second mirror 40, and the second electrode 40 is shared by these waveguide elements 10. The spacer 150 is a dielectric member that functions as a partition wall that separates the two optical waveguide layers 20 adjacent to each other in the Y direction. The spacer 150 may be in contact with the first mirror 30.

[0107] The light emitting device in this embodiment further includes a second light source 132 and a third photodetector 173. The second light source 132 and the third photodetector 173 are positioned opposite to each other with the first substrate 70A, the liquid crystal layer 140, and the second substrate 70B sandwiched therebetween. The second light source 132 includes a light emitting element that emits light toward the liquid crystal layer 140. The third photodetector 173 includes a light receiving element that detects the light emitted from the second light source 132.

[0108] In this embodiment, in order to compensate for the effect of an increase in the light absorption rate caused by the deterioration of the liquid crystal layer 140, a plurality of types of calibration data corresponding to a plurality of extinction coefficients are pre-recorded in the storage device 166. The calibration data can be obtained, for example, by changing the extinction coefficient on a computer based on the calibration data at the time of shipment. The light transmittance of a portion of the liquid crystal layer 140 that is continuous with the optical waveguide layer 20 is measured using the second light source 132 and the third photodetector 173. Note that, as long as the same deterioration conditions as those of the optical waveguide layer 20 are satisfied, the portion of the liquid crystal layer 140 whose light transmittance is measured may be separated from the optical waveguide layer 20.

[0109] FIG. 21 is a flowchart showing an example of a process for generating calibration data in this embodiment. The flowchart shown in FIG. 21 is basically the same as the flowchart shown in FIG. 16, except that step S111 is added after steps S101 and S102. In step S111, the control circuit 162 measures the transmittance of the liquid crystal layer 140 using the second light source 132 and the third photodetector 173, and records the measured transmittance in the storage device 166. More specifically, the control circuit 162 causes the second light source 132 to emit light with an intensity P1, and causes the third photodetector 173 to detect the light. The transmittance of the liquid crystal layer 140 can be obtained based on the ratio between the intensity P2 of the light detected by the third photodetector and the intensity P1 instructed to the second light source 132. Note that step S111 may be performed before step S101.

[0110] The operations from steps S102 to S105 are the same as the corresponding operations shown in Fig. 16. In this embodiment, in step S106, the transmittance recorded in step S111 is associated with calibration data such as that shown in Table 1 and recorded. Furthermore, by performing calculations on a computer while changing the extinction coefficient in multiple ways based on this calibration data, multiple transmittances or extinction coefficients are associated with calibration data such as that shown in Table 1 and recorded. In this way, the control circuit 162 generates calibration data corresponding to each of the multiple transmittances or extinction coefficients, and records it in the storage device 166.

[0111] FIG. 22 is a flowchart showing an example of the calibration data update operation in this embodiment. The flowchart shown in FIG. 22 is basically the same as the flowchart shown in FIG. 17, except that steps S200 and S230 are added. In this example, first, in step S200, the control circuit 162 measures the light transmittance of the liquid crystal layer 140 and judges whether or not the value is within a preset range. If the judgment is No, the process proceeds to step S230, where an error is output and the process ends. If the judgment in step S200 is Yes, the operations shown in steps S201 to S220 are executed as in the example in FIG. 17. In step S201, the calibration table data corresponding to the transmittance closest to the measured transmittance is acquired from the data of a plurality of calibration tables recorded in advance.

[0112] In the example of FIG. 22, an error output process in step S230 is added in consideration of the influence on the spread angle of the light beam. As an example, in the structure used in the calculation for obtaining the relationship shown in FIG. 13, when the transmittance of the liquid crystal layer 140 decreases by 0.14% (corresponding to an extinction coefficient k=0.00005 for a liquid crystal layer of 2 μm), the scanning range in which the beam spread angle of 0.17° can be maintained decreases to about 10°. When such a significant decrease in transmittance is detected, it is desirable to stop the operation and notify the system or user of the abnormality of the liquid crystal layer 140. Therefore, in the example of FIG. 22, the transmittance of the liquid crystal layer 140 is measured first, and if the transmittance of the liquid crystal is lowered below a preset range, the calibration operation is stopped and an error is output. This realizes a light emitting device with higher reliability.

[0113] In each of the above embodiments, both the direction and intensity of the emitted light are adjusted based on the first signal output from the first photodetector 171 and the second signal output from the second photodetector 172. However, the present disclosure is not limited to such embodiments. Only one of the direction and intensity of the emitted light may be adjusted based on the first signal and the second signal. In addition, the control of the direction of the emitted light may be realized by a method other than the method of controlling the refractive index of the optical waveguide layer 20. For example, the direction of the emitted light may be controlled by changing the thickness of the optical waveguide layer 20. Alternatively, the direction of the emitted light may be controlled by changing the wavelength of the light emitted from the light source 130.

[0114] In each of the above embodiments, the calibration data shown in Table 1 is used, but the calibration data does not necessarily have to be in the same format as that of Table 1. For example, calibration data that specifies only the correspondence between the ratio of the first signal to the second signal and the emission angle may be used. In that case, the intensity of the light output from the light source 130 is not adjusted, and only the voltage applied to the optical waveguide layer 20 is adjusted.

[0115] <Examples of materials> Next, examples of materials that can be used for each component in the embodiment of the present disclosure will be described.

[0116] The material of each of the mirrors 30 and 40 can be, for example, a multilayer film made of a dielectric material. A mirror using a multilayer film can be fabricated, for example, by periodically forming a plurality of films with different refractive indices, each of which has an optical thickness of 1 / 4 wavelength. Such a multilayer film mirror can provide a high reflectance. The film material can be, for example, SiO2, TiO2, Ta2O5, Si, SiN, or the like. Each mirror is not limited to a multilayer film mirror, and may be made of a metal such as Ag or Al.

[0117] Various conductive materials can be used for the electrodes and wiring. For example, metal materials such as Ag, Cu, Au, Al, Pt, Ta, W, Ti, Rh, Ru, Ni, Mo, Cr, Pd, etc., inorganic compounds such as ITO, tin oxide, zinc oxide, indium zinc oxide (IZO: registered trademark), strontium ruthenate (SRO), etc., or conductive polymers such as PEDOT (3,4-ethylenedioxythiophene) and polyaniline, etc., can be used. Transparent conductive materials can be used for electrodes that require light transmission.

[0118] The optical waveguide layer may be made of various light-transmitting materials such as dielectrics, semiconductors, electro-optical materials, and liquid crystal molecules. Examples of dielectrics include SiO2, TiO2, Ta2O5, SiN, and AlN. Examples of semiconductor materials include Si-based, GaAs-based, and GaN-based materials. Examples of electro-optical materials include lithium niobate (LiNbO3), barium titanate (BaTi3), lithium tantalate (LiTaO3), zinc oxide (ZnO), lead lanthanum zirconate titanate (PLZT), and potassium tantalate niobate (KTN).

[0119] There are various methods for modulating the refractive index of the optical waveguide layer, such as those utilizing the carrier injection effect, the electro-optic effect, the birefringence effect, or the thermo-optic effect.

[0120] The method using the carrier injection effect can be realized by a configuration using a pin junction of a semiconductor. In this method, a structure in which a semiconductor with a low doping concentration is sandwiched between a p-type semiconductor and an n-type semiconductor is used, and the refractive index is modulated by injecting carriers into the semiconductor. In this configuration, the optical waveguide layer in each waveguide element 10 includes a semiconductor material. One of the pair of electrodes may include a p-type semiconductor, and the other may include an n-type semiconductor. The driving device applies a voltage to the pair of electrodes to inject carriers into the semiconductor material and change the refractive index of the optical waveguide layer. The optical waveguide layer may be made of a non-doped or low-doped semiconductor, and a p-type semiconductor and an n-type semiconductor may be provided so as to be in contact with the optical waveguide layer. A composite configuration may be used in which the p-type semiconductor and the n-type semiconductor are arranged so as to be in contact with a low-doped semiconductor, and further a conductive material is in contact with the p-type semiconductor and the n-type semiconductor. For example, 10 20 cm -3 When carriers of about 1000 keV are injected, the refractive index of Si changes by about 0.1 (see, for example, “Free charge carrier induced refractive index modulation of crystalline silicon” 7 th (See IEEE International Conference on Group IV Photonics, P102-104, 1-3 Sept. 2010.) When this method is employed, a p-type semiconductor and an n-type semiconductor can be used as the material for the pair of electrodes. Alternatively, the electrodes may be made of metal, and a layer between the electrodes and the optical waveguide layer, or the optical waveguide layer itself, may contain a p-type or n-type semiconductor.

[0121] The method using the electro-optic effect can be realized by applying an electric field to an optical waveguide layer containing an electro-optic material. In particular, if KTN is used as the electro-optic material, a large electro-optic effect can be obtained. Since the relative dielectric constant of KTN increases significantly at a temperature slightly higher than the phase transition temperature from tetragonal to cubic, this effect can be utilized. For example, according to “Low-Driving-Voltage Electro-Optic Modulator With Novel KTa1-xNbxO3 Crystal Waveguides” Jpn. J. Appl. Phys., Vol.43, No. 8B (2004), the electro-optic constant g for light with a wavelength of 1.55 μm is 4.8×10 -15 m 2 / V 2 Therefore, for example, if an electric field of 2 kV / mm is applied, the refractive index becomes 0.1 (=gn 3 E 3 / 2). In this manner, in a configuration utilizing the electro-optic effect, the optical waveguide layer in each waveguide element 10 contains an electro-optic material such as KTN. The driving device can change the refractive index of the electro-optic material by applying a voltage to a pair of electrodes.

[0122] In the method using the birefringence effect of liquid crystal, the refractive index anisotropy of the liquid crystal can be changed by driving an optical waveguide layer containing a liquid crystal material with a pair of electrodes. This makes it possible to modulate the refractive index of light propagating through the optical waveguide layer. Since liquid crystal generally has a birefringence difference of about 0.1 to 0.2, a refractive index change equivalent to the birefringence difference can be obtained by changing the alignment direction of the liquid crystal with an electric field. In this way, in the configuration using the birefringence effect of liquid crystal, the optical waveguide layer in each waveguide element 10 contains a liquid crystal material. The driving device can change the refractive index anisotropy of the liquid crystal material and change the refractive index of the optical waveguide layer by applying a voltage to the pair of electrodes.

[0123] The thermo-optic effect is an effect in which the refractive index of a material changes with a change in temperature. To perform actuation using the thermo-optic effect, the refractive index may be modulated by heating an optical waveguide layer containing a thermo-optic material.

[0124] Instead of changing the refractive index of the optical waveguide layer, the thickness of the optical waveguide layer may be changed. For example, an actuator may be connected to at least one of the pair of mirrors. As the actuator, for example, various actuators using electrostatic force, electromagnetic induction, piezoelectric material, shape memory alloy, or heat may be used. In a configuration using electrostatic force, the actuator moves the mirror using the attractive or repulsive force between electrodes generated by electrostatic force. The mirror may be driven by electromagnetic induction that generates an attractive or repulsive force on a magnetic body in a coil. In an actuator using a piezoelectric material, a shape memory alloy, or deformation due to heat, the phenomenon that a material is deformed by energy applied from the outside is utilized. For example, lead zirconate titanate (PZT), a typical piezoelectric material, expands and contracts by applying an electric field in the polarization direction. The distance between the pair of mirrors can be directly changed by the piezoelectric material. In order to obtain a sufficient movement distance of the mirror, the amount of change may be increased by using a configuration called a unimorph or bimorph.

[0125] <Application Examples> Next, application examples of the above-mentioned light emitting device will be described.

[0126] FIG. 23 is a diagram showing a configuration example of a light emitting device 100B in which elements such as an optical splitter 90, a waveguide array 10A, a phase shifter array 80A, and a light source 130 are integrated on a circuit board (e.g., a chip). The light source 130 may be, for example, a light emitting element such as a semiconductor laser element. 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. 23, one electrode 62A and multiple electrodes 62B are provided on the chip. A control signal is supplied from the electrode 62A to the waveguide array 10A. A control signal is sent from the multiple electrodes 62B to the multiple phase shifters 80 in the phase shifter array 80A. The electrodes 62A and 62B may be connected to a control circuit (not shown) that generates the above control signal. 23 or may be provided on another chip in the light emitting device 100B. The control circuit may also be connected to the light source 130 to control the wavelength or intensity of the light emitted from the light source 130.

[0127] The waveguide array 10A is an assembly of a plurality of waveguide elements 10 arranged in a direction intersecting the direction in which each of the waveguide elements 10 extends. Each of the waveguide elements 10 has a structure similar to that of the waveguide element 10 in the above-described embodiment. That is, each of the waveguide elements 10 includes a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror. Each of the waveguide elements 10 propagates light input to the optical waveguide layer along a first direction and outputs the light via the first mirror. This light output device 100B includes a plurality of first optical waveguides 11 connected to the optical waveguide layers in the plurality of waveguide elements 10, respectively. The plurality of first optical waveguides 11 are connected to the phase shifter array 80A. The light source 130 outputs light input to the plurality of first optical waveguides 11.

[0128] The light emitting device 100B shown in FIG. 23 further includes a first photodetector 171 and a second photodetector 172. The first photodetector 171 is disposed near the light source 130 and outputs a first signal indicating the intensity of the light emitted from the light source 130. The second photodetector 172 is disposed near the end of each optical waveguide layer in the waveguide array 10A. In this example, one first photodetector 171 and one second photodetector 172 are disposed for each of the multiple waveguide elements 10. The second photodetector 172 may have an image sensor configuration so that the light passing through the multiple waveguide elements 10 can be detected collectively. With this configuration, the above control can be performed on each waveguide element 10 without providing a large number of photodetectors. The arrangement of the first photodetector 171 and the second photodetector 172 is not limited to the arrangement in this example. The first photodetector 171 may be positioned at any location as long as it is positioned to detect light at any point on the path from the light source 130 to the multiple waveguide elements 10. Similarly, the second photodetector 172 may be positioned at any location as long as it is positioned to detect light that has passed through an optical waveguiding layer in the multiple waveguide elements 10. Also, multiple first photodetectors may be provided in front of the multiple waveguide elements 10, and multiple second photodetectors may be provided in the rear of the multiple waveguide elements 10.

[0129] By integrating all the components on a chip as shown in Fig. 23, wide-range optical scanning can be realized with a small device. For example, all the components shown in Fig. 23 can be integrated on a chip of about 2 mm × 1 mm.

[0130] 24 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 light emitting 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 light beam and observing the reflected light from an object, thereby determining the distance.

[0131] FIG. 25 is a block diagram showing a configuration example of a light detection system 300. The light detection system 300 can be used as a LiDAR system that generates a distance image, for example. The light detection system 300 includes a light emission device 100, a light detection device 200, a control circuit 500, and a signal processing circuit 600. The light detection device 200 detects light emitted from the light emission device 100 and reflected by an object in a target scene. The light detection device 200 can be realized by, for example, an image sensor having sensitivity to the wavelength λ of light emitted from the light emission device 100. The light detection device 200 includes a plurality of light receiving elements arranged along a light receiving surface. Each light receiving element outputs an electrical signal according to the amount of light received. The signal processing circuit 600 calculates the distance to the target based on the electrical signal output from each light receiving element of the light detection device 200, and generates distance distribution data. The distance distribution data is, for example, data indicating a two-dimensional distribution of distances. The control circuit 500 is a processor that controls the light emitting device 100, the light detecting device 200, and the signal processing circuit 600. The control circuit 500 controls the timing of irradiation of the light beam from the light emitting device 100 and the timing of exposure and signal readout of the light detecting device 200, and instructs the signal processing circuit 600 to generate a distance measurement image.

[0132] 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.

[0133] 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 light emitting device 100 and the signal accumulation and readout by the light detecting device 200 at an operating speed of 600 kHz.

[0134] As described above, the light emitting device according to the embodiment of the present disclosure includes a waveguide element, a first photodetector, and a second photodetector. The waveguide element includes a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror, and propagates light input to the optical waveguide layer along a first direction and outputs the light via the first mirror. The first photodetector is located on a path of light input to the optical waveguide layer or on another path branched from the path, and outputs a first signal according to the amount of received light. The second photodetector is located on a path of light propagating in the optical waveguide layer along the first direction and passing through the optical waveguide layer, and outputs a second signal according to the amount of received light.

[0135] According to the above configuration, the direction and / or intensity of the light emitted from the waveguide element can be estimated based on the first signal and the second signal. Therefore, it is possible to determine whether the direction and / or intensity of the emitted light is appropriate based on the first signal and the second signal, and to perform an operation such as a correction process or an error output as necessary. This makes it possible to realize a more reliable light emitting device.

[0136] The light emitting device may further include a control circuit that controls at least one of an intensity and a direction of the light emitted from the first mirror based on the first signal and the second signal.

[0137] According to the above configuration, when at least one of the intensity and direction of the emitted light is different from a desired intensity or direction, it is possible to correct at least one of the intensity and direction of the emitted light. Note that the control circuit may be an external element independent of the light-emitting device. In this case, the control circuit is connected to the light-emitting device for use.

[0138] The optical waveguide layer may include a material whose refractive index changes in response to an applied voltage. The waveguide element may further include a pair of electrodes on both sides of the optical waveguide layer. The control circuit may control a direction of the emitted light by controlling a voltage applied to the pair of electrodes based on the first signal and the second signal.

[0139] According to the above configuration, when the direction of the emitted light estimated based on the first signal and the second signal differs from the desired direction, the direction of the emitted light can be optimized by controlling the voltage applied to the pair of electrodes.

[0140] The light emitting device may further include a storage device that stores data defining a correspondence relationship between the ratio of the first signal to the second signal and the emission angle of the emitted light. The control circuit may determine the voltage by referring to the data.

[0141] According to the above configuration, the control circuit can estimate the emission angle of light from the ratio between the acquired first signal and second signal by referring to the pre-recorded data. As a result, if the estimated emission angle deviates from the desired emission angle, the deviation of the emission angle can be compensated for by adjusting the voltage.

[0142] The optical waveguide layer may be made of a liquid crystal material. The data may define a correspondence relationship between the ratio and the emission angle for each of a plurality of conditions in which the light transmittance of the liquid crystal material is different. The light emitting device may further include a measuring device for measuring the light transmittance of the liquid crystal material. The control circuit may determine the voltage based on the first signal and the second signal, the measured light transmittance of the liquid crystal material, and the data.

[0143] According to the above configuration, even if the light transmittance of the optical waveguide layer made of a liquid crystal material changes from the initial value due to, for example, aging, the exit direction of the light can be appropriately adjusted.

[0144] The light emitting device may further include a light source that emits the light input to the optical waveguide layer, and the control circuit may control an intensity of the emitted light by controlling an intensity of the light emitted from the light source based on the first signal and the second signal.

[0145] According to the above configuration, when the intensity of the emitted light differs from a desired intensity, the intensity of the emitted light can be adjusted to an appropriate value by adjusting the intensity of the light emitted from the light source.

[0146] The light emitting device may further include a first optical waveguide that connects the optical waveguide layer to a light source that emits the light input to the optical waveguide layer, and the first photodetector may detect light branched from the first optical waveguide and propagating therethrough.

[0147] According to the above configuration, the intensity of the light input to the optical waveguide layer can be detected or estimated with a simple configuration. Note that, in the above configuration, the intensity of the light detected by the first optical detector is different from the intensity of the light input to the optical waveguide layer, but the two are roughly proportional to each other. Therefore, the intensity of the light input to the optical waveguide layer can be estimated from the intensity of the light detected by the first optical detector.

[0148] The light emitting device may further include a second optical waveguide connected to the optical waveguide layer on a side in a direction of propagation of light through the optical waveguide layer, and the second photodetector may detect light propagated through the second optical waveguide.

[0149] According to the above configuration, the intensity of light that has passed through the optical waveguide layer can be detected or estimated with a simple configuration.

[0150] A light emitting device according to another embodiment of the present disclosure includes a plurality of waveguide elements, a plurality of first optical waveguides, a light source, a first optical detector, and a second optical detector. Each waveguide element includes a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror, and propagates light input to the optical waveguide layer along a first direction and outputs the light via the first mirror. The plurality of waveguide elements are arranged in a second direction intersecting the first direction. The plurality of first optical waveguides are respectively connected to the optical waveguide layers in the plurality of waveguide elements. The light source outputs light input to the plurality of first optical waveguides. The first optical detector receives light at any point on a path from the light source to the plurality of waveguide elements, and outputs a first signal according to the amount of received light. The second photodetector receives light that has propagated in the first direction through the optical waveguide layers of the plurality of waveguide elements and passed through the optical waveguide layers, and outputs a second signal according to an amount of received light.

[0151] According to the above configuration, in addition to the above-mentioned effects, two-dimensional optical scanning is possible by providing a plurality of waveguide elements.

[0152] The light emitting device may further include a control circuit that controls at least one of an intensity and a direction of the light emitted from the first mirror based on the first signal and the second signal.

[0153] According to the above configuration, when at least one of the intensity and direction of the emitted light differs from a desired intensity or direction, at least one of the intensity and direction of the emitted light can be corrected.

[0154] The optical waveguide layer in each waveguide element may include a material whose refractive index changes in response to an applied voltage. Each waveguide element may further include a pair of electrodes on both sides of the optical waveguide layer. The control circuit may control a direction of the emitted light by controlling a voltage applied to the pair of electrodes in each waveguide element based on the first signal and the second signal.

[0155] According to the above configuration, when the direction of the emitted light estimated based on the first signal and the second signal differs from the desired direction, the direction of the emitted light can be optimized by controlling the voltage applied to the pair of electrodes.

[0156] The control circuit may control an intensity of the light emitted from the light source based on the first signal and the second signal, thereby controlling an intensity of the emitted light.

[0157] According to the above configuration, when the intensity of the emitted light differs from a desired intensity, the intensity of the emitted light can be adjusted to an appropriate value by adjusting the intensity of the light emitted from the light source. [Industrial Applicability]

[0158] The light emitting device according to the present disclosure can be widely used for applications in which a light beam is emitted, such as a lidar system mounted on a vehicle, such as an automobile, a UAV, or an AGV. [Explanation of symbols]

[0159] 10 Waveguide elements 10A Waveguide Array 11 First optical waveguide 12 Second optical waveguide 15 Grating 20 Optical waveguide layer 22 light 30 Mirror No. 1 40 2nd Mirror 50 Dielectric material 60A, 60B electrode 62A, 62B electrode 70A, 70B board 80 Phase Shifter 80A Phase Shifter Array 90 Optical splitter 100, 100A Light Emitting Device 110 Driving circuit for optical waveguide array 130, 132 light source 140 Liquid crystal layer 150 Spacer 160 Drive Unit 171 First Photodetector 172 Second Photodetector 173 Third Photodetector 180 Driving circuit for phase shifter array 190 Liquid crystal transmittance measuring device 200 Light-detecting devices 300 LiDAR System 310 Beam Spot 500 Control circuit 600 Signal Processing Circuit

Claims

1. a waveguide element comprising: a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror, the optical waveguide layer including a waveguide portion that propagates light input to the optical waveguide layer along a first direction, and emitting a portion of the light that has propagated through the waveguide portion to the outside via the first mirror; a first photodetector that is located on a path of light input to the optical waveguide layer or on another path branched from the path, and that outputs a first signal corresponding to an amount of received light; a second photodetector that is located on a path of light that has propagated through the waveguide portion of the optical waveguide layer in the first direction and passed through the waveguide portion, and that outputs a second signal according to an amount of received light; a control circuit that controls a direction of light emitted from the first mirror based on the first signal and the second signal; A light emitting device comprising:

2. The light emitting device of claim 1, wherein the control circuit further controls the intensity of the emitted light emitted from the first mirror based on the first signal and the second signal.

3. the optical waveguide layer includes a material whose refractive index changes in response to an applied voltage; The waveguide element further includes a pair of electrodes on both sides of the optical waveguide layer, the control circuit controls a voltage applied to the pair of electrodes based on the first signal and the second signal, thereby controlling a direction of the emitted light.

3. A light emitting device according to claim 1 or 2.

4. a storage device that stores data defining a correspondence relationship between the ratio of the first signal to the second signal and an emission angle of the emitted light; The control circuit determines the voltage by referring to the data.

4. A light emitting device according to claim 3.

5. the optical waveguide layer is made of a liquid crystal material; the data defines a correspondence relationship between the ratio and the emission angle for each of a plurality of conditions in which the light transmittance of the liquid crystal material is different; the light-emitting device further comprises a measuring device for measuring the light transmittance of the liquid crystal material; the control circuit determines the voltage based on the first and second signals, the measured light transmittance of the liquid crystal material, and the data.

5. A light emitting device according to claim 4.

6. a light source that emits the light input to the optical waveguide layer, The light emitting device according to claim 1 , wherein the control circuit controls an intensity of the light emitted from the light source based on the first signal and the second signal, thereby controlling an intensity of the emitted light.

7. a first optical waveguide that connects a light source that emits the light input to the optical waveguide layer to the optical waveguide layer; the first photodetector detects light branched and propagating from the first optical waveguide; A light emitting device according to any one of the preceding claims.

8. a second optical waveguide connected to the optical waveguide layer on a side in a direction in which light propagates through the optical waveguide layer; The second photodetector detects light propagated through the second optical waveguide. A light emitting device according to any one of the preceding claims.

9. a plurality of waveguide elements, each of which comprises a first mirror having optical transparency, a second mirror facing the first mirror, and an optical waveguide layer located between the first mirror and the second mirror, the optical waveguide layer being a waveguide portion that propagates light input to the optical waveguide layer along a first direction, and emitting a portion of the light that has propagated through the waveguide portion to the outside via the first mirror, the plurality of waveguide elements being arranged in a second direction intersecting the first direction; a plurality of first optical waveguides respectively connected to the optical waveguide layers in the plurality of waveguide elements; a light source that emits light to be input to the plurality of first optical waveguides; a first photodetector that receives light at any point on a path from the light source to the plurality of waveguide elements and outputs a first signal according to an amount of received light; a second photodetector that is located on a path of light that propagates in the first direction through the waveguide portions of the optical waveguide layers in the plurality of waveguide elements and passes through the waveguide portions, and that outputs a second signal according to an amount of received light; a control circuit that controls a direction of light emitted from the first mirror based on the first signal and the second signal; A light emitting device comprising:

10. The light emitting device of claim 9, wherein the control circuit further controls the intensity of the emitted light emitted from the first mirror based on the first signal and the second signal.

11. the optical waveguide layer in each of the waveguide elements includes a material whose refractive index changes in response to an applied voltage; Each waveguide element further comprises a pair of electrodes on either side of the optical waveguide layer; the control circuit controls a voltage applied to the pair of electrodes in each waveguide element based on the first signal and the second signal, thereby controlling a direction of the emitted light.

11. A light emitting device according to claim 9 or 10.

12. 12. The light emitting device according to claim 9, wherein the control circuit controls an intensity of the light emitted from the light source based on the first signal and the second signal, thereby controlling an intensity of the emitted light.

Images