JP2021135427A - Optical device - Google Patents

Abstract

To provide an optical device capable of acquiring data regarding the distance and/or speed of an object with a simple configuration.SOLUTION: The optical device includes: a light source that includes a light deflector; a beam splitter that is positioned on the light path of the light deflected by the light deflector for splitting the light into a first light and a second light; an optical system that generates a third light by interfering the first light with the second light that is reflected by the object and returned therefrom; a photodetector that detects the third light; and a processing circuit that processes signals output from the photodetector.SELECTED DRAWING: Figure 1A

Description

The present disclosure relates to optical devices.

Conventionally, there is a LiDAR (Light Detection and Ranking) technique for acquiring data on the distance of an object by irradiating the object with light and detecting the reflected light from the object. Typical examples of optical devices using LiDAR technology include light sources, photodetectors, and processing circuits. The light source has a configuration capable of changing the direction of light. The photodetector outputs a signal indicating the intensity of the reflected light by detecting the reflected light from the object. The processing circuit acquires data on the distance of an object based on the signal output from the photodetector, for example, by TOF (Time Of Flight) technology. Patent Documents 1 to 3 disclose examples of configurations capable of changing the direction of light.

International Publication No. 2013/168266 Japanese Unexamined Patent Publication No. 2013-016591 International Publication No. 2014/110017 Christopher V. Poulton, et al., “Frequency-modulated Coutinuous-wave LIDAR Module in Silicon Photonics”, OFC2016, W4E.3, (2016).

The present disclosure provides an optical device capable of acquiring data on the distance and / or velocity of an object in a simple configuration.

The optical device according to one aspect of the present disclosure is located on a light source including a light deflector and an optical path of light deflected by the light deflector, and separates the light into a first light and a second light. An optical system that generates a third light by interfering the beam splitter, the first light, and the second light reflected by an object and returning, and an optical detector that detects the third light. And a processing circuit for processing the signal output from the optical detector.

Comprehensive or specific embodiments of the present disclosure may be implemented in recording media such as systems, devices, methods, integrated circuits, computer programs or computer readable recording disks, systems, devices, methods, integrated circuits, etc. It may be realized by any combination of a computer program and a recording medium. The computer-readable recording medium may include a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). The device may consist of one or more devices. When the device is composed of two or more devices, the two or more devices may be arranged in one device, or may be separately arranged in two or more separated devices. As used herein and in the claims, "device" can mean not only one device, but also a system of multiple devices.

According to the technique of the present disclosure, it is possible to realize an optical device capable of acquiring data on the distance and / or speed of an object with a simple configuration.

FIG. 1A is a cross-sectional view schematically showing a first example of an optical device according to an exemplary embodiment of the present disclosure. FIG. 1B is a cross-sectional view schematically showing a second example of an optical device according to an exemplary embodiment of the present disclosure. FIG. 2 is a flowchart of the operation of the FMCW process executed by the processing circuit. FIG. 3A is a diagram schematically showing a first example of an optical device in a first modification of the present embodiment. FIG. 3B is a diagram schematically showing a second example of the optical device in the first modification of the present embodiment. FIG. 4 is a diagram schematically showing an example of an optical device in the second modification of the present embodiment. FIG. 5 is a diagram schematically showing an example of an optical device in a third modification of the present embodiment. FIG. 6 is a diagram schematically showing an example of an optical device in the fourth modification of the present embodiment. FIG. 7 is a diagram schematically showing an example of an optical device in the fifth modification of the present embodiment. FIG. 8A is a perspective view schematically showing an example of a light source in the present embodiment. FIG. 8B is a diagram schematically showing an example of an optical waveguide element in this embodiment. FIG. 8C is a diagram schematically showing an example of a phase shifter in this embodiment.

Each of the embodiments described below provides a comprehensive or specific example. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps, and the order of the steps shown in the following embodiments are examples, and are not intended to limit the technique of the present disclosure. Among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components. Each figure is a schematic view and is not necessarily exactly illustrated. Further, in each figure, substantially the same or similar components are designated by the same reference numerals. Duplicate descriptions may be omitted or simplified.

Before explaining the specific embodiments of the present disclosure, the findings underlying the present disclosure will be described.

Patent Document 1 discloses a configuration in which the direction of emitted light is changed by rotating a mirror by mechanically driving a MEMS (Microelectric Mechanical System). The mirror is called a MEMS mirror.

Patent Document 2 describes a waveguide provided with an optical waveguide layer in which light is waveguideed inside, a first distributed Bragg reflector formed on the upper surface and the lower surface of the optical waveguide layer, and a waveguide for incident light into the waveguide. A light deflection element including a light incident port and a light emitting port formed on the surface of the waveguide for emitting light incident from the light incident port and waveguide in the waveguide is disclosed.

Patent Document 3 discloses an optical phased array having a plurality of nanophotonic antenna elements arranged two-dimensionally. Each antenna element is optically coupled to a variable light delay line (ie, phase shifter). In this optical phased array, a coherent optical beam is guided to each antenna element by a waveguide, and the phase shifter shifts the phase of the optical beam. This makes it possible to change the amplitude distribution of the far-field radiation pattern.

The light source disclosed in Patent Document 1 can match the optical path of the emitted light with the optical path of the reflected light by rotating the MEMS mirror. On the other hand, the light sources disclosed in Patent Documents 2 and 3 have a structure capable of changing the direction of emitted light without using mechanical drive. The light source can be downsized as compared with a mechanical drive, has excellent vibration resistance, and can change the light emission direction at high speed. However, when the light source disclosed in Patent Documents 2 or 3 is applied to the LiDAR technique, it is not easy to match the optical path of the emitted light with the optical path of the reflected light in the optical device.

Furthermore, in TOF technology, it is important to achieve both a wide dynamic range and high resolution with respect to distance in the acquisition of data regarding the distance of an object. In TOF technology, disturbances such as sunlight or reflected light of low intensity can be a problem from the viewpoint of light sensitivity. In TOF technology, the velocity of an object is calculated from the change in the distance of the object per scan. Therefore, when applying LiDAR technology to autonomous driving, there may be a delay in detecting the speed of a fast moving object.

In recent years, FMCW (Frequency Modified Continues Wave) -LiDAR technology has been developed, which has both a wide dynamic range and high resolution in terms of distance, has high vibration resistance, and can detect the speed of an object moving at high speed. Non-Patent Document 1 discloses an example of FMCW-LiDAR technology. In the FMCW-LiDAR technology, the light source is controlled so that the frequency of the light emitted from the light source changes with time. The light emitted from the light source is separated into object light and reference light. Object light is light that is reflected by an object and enters the photodetector. The reference light is light that enters the photodetector without passing through an object. The object light enters the photodetector later than the reference light. Therefore, when incident on the photodetector, the object light and the reference light have different frequencies. The photodetector detects the interference light in which the object light and the reference light are superimposed and interferes with each other, and outputs a signal indicating the intensity of the interference light. The signal is called a beat signal. The frequency of the beat signal corresponds to the difference between the frequency of the object light and the frequency of the reference light. The difference depends on the distance to the object.

In the FMCW-LiDAR technology, as will be described later, it is possible to achieve both a wide dynamic range and high resolution in terms of distance. The frequency of the beat signal is not easily affected by disturbance. Since the frequency of the beat signal changes with time due to the movement of the object, the velocity of the object can be detected from the time change of the frequency. Object light reflected from a plurality of objects having different distances has a plurality of frequency components. Therefore, even when the beat signal is output from one photodetector, data on the distances of a plurality of objects can be acquired by separating the plurality of frequency components from the beat signal.

When a structure that changes the direction of emitted light by mechanical drive is used as a light source, it is easy to match the optical path of the object light with the optical path of the reference light in the optical device. By matching the optical path of the object light with the optical path of the reference light, the photodetector can detect the interference light between the object light and the reference light. On the other hand, when a structure that changes the direction of emitted light is used as a light source without using mechanical drive, if the optical path of the object light and the optical path of the reference light can be matched in the optical device, the degree of freedom in designing the optical device. Can be improved.

In the optical device of the embodiments of the present disclosure, for example, FMCW-LiDAR technology can be used to obtain data on the distance and / or velocity of an object.

Further, in the optical device according to the embodiment of the present disclosure, the light source and the photodetector are appropriately arranged together with the beam splitter and the optical system so that the optical path of the object light and the optical path of the reference light are matched in the optical device. Can be done. The light source may have a structure that changes the direction of the emitted light without using mechanical drive. According to the optical device according to the embodiment of the present disclosure, it is possible to acquire data on the distance and / or velocity of an object with a simple configuration.

The optical device according to the first item is located on a light source including an optical deflector and an optical path of light deflected by the optical deflector, and separates the light into a first light and a second light. An optical system that generates a third light by interfering the beam splitter, the first light, and the second light reflected by an object and returning, and an optical detector that detects the third light. And a processing circuit for processing the signal output from the optical detector.

In this optical device, a third light in which the first light and the second light interfere with each other can be detected by a photodetector with a simple configuration. Data on the distance and / or velocity of an object can be acquired based on the signal output from the photodetector.

The optical device according to the second item includes a first lens and a mirror in which the optical system is located on the optical path of the first light in the optical device according to the first item. The first lens is located between the beam splitter and the mirror on the optical path of the first light.

In this optical device, the third light can be focused at a specific position in the photodetector's photodetection plane, regardless of the direction of the light deflected by the photodetector in the light source.

The optical device according to the third item further includes a second lens in which the optical system is located on the optical path of the third light in the optical device according to the second item.

In this optical device, the second lens can change the detection position of the third light detected by the photodetector according to the direction of the light deflected by the light deflector in the light source.

The optical device according to the fourth item is the optical device according to the third item, wherein the optical system is located between the second lens and the photodetector on the optical path of the third light. Also includes 3 lenses.

In this optical device, the third lens can change the position in the photodetector's light detection plane where the third light is focused.

The optical device according to the fifth item is the fourth lens in which the optical system is located between the first lens and the mirror on the optical path of the first light in the optical device according to the fourth item. Including further.

In this optical device, the fourth lens can prevent the intensity of the signal output from the photodetector from being extremely reduced even if the mirror is tilted to some extent.

The optical device according to the sixth item includes a concave mirror in which the optical system is located on the optical path of the first light in the optical device according to the first item.

In this optical device, the concave mirror allows the photodetector to detect a third light in which the first light and the second light interfere with each other with only one optical component.

The optical device according to the seventh item includes an optical modulator in which the optical system reflects the first light and controls the reflection direction in the optical device according to the first item.

In this optical device, the light modulator can detect a third light that interferes with the first light and the second light by the photodetector.

The optical device according to the eighth item is the optical device according to the first item, in which the third light is reflected by the first light reflected by the beam splitter and the object, and the beam splitter. It is generated by interfering with the second light that has passed through.

In this optical device, a beam splitter can generate a third light that interferes with the first light and the second light.

The optical device according to the ninth item is the optical device according to any one of the first to eighth items, wherein the light source is a frequency variable light source and the processing circuit is an FMCW processing circuit.

In this optical device, FMCW technology can acquire data on the distance and / or velocity of an object.

In the present disclosure, all or part of a circuit, unit, device, member or part, or all or part of a functional block in a block diagram, is, for example, a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (range scale integration). ) Can be performed by one or more electronic circuits. The LSI or IC may be integrated on one chip, or may be configured by combining a plurality of chips. For example, functional blocks other than the storage element may be integrated on one chip. Here, it is called LSI or IC, but the name changes depending on the degree of integration, and it may be called system LSI, VLSI (very large scale integration), or ULSI (ultra large scale integration). A Field Programmable Gate Array (FPGA), which is programmed after the LSI is manufactured, or a reconfigurable logistic device that can reconfigure the junction relationship inside the LSI or set up the circuit partition inside the LSI can also be used for the same purpose.

Further, all or part of the function or operation of a circuit, unit, device, member or part can be performed by software processing. In this case, the software is recorded on a non-temporary recording medium such as one or more ROMs, optical disks, hard disk drives, etc., and when the software is executed by a processor, the functions identified by the software It is executed by a processor and peripheral devices. The system or device may include one or more non-temporary recording media on which the software is recorded, a processor, and the required hardware devices, such as an interface.

In the present disclosure, "light" refers to electromagnetic waves including not only visible light (wavelength of about 400 nm to about 700 nm) but also ultraviolet rays (wavelength of about 10 nm to about 400 nm) and infrared rays (wavelength of about 700 nm to about 1 mm). means.

Hereinafter, more specific embodiments of the present disclosure will be described.

(Embodiment)
First, an example of an optical device according to an exemplary embodiment of the present disclosure will be described with reference to FIGS. 1A and 1B. 1A and 1B are cross-sectional views schematically showing a first example and a second example of the optical device 100 in the exemplary embodiment of the present disclosure, respectively. In the first example and the second example, the directions of the light emitted to the outside from the optical device 100 in the present embodiment are different. In the following description, the coordinate system including the X-axis, the Y-axis, and the Z-axis, which are orthogonal to each other shown in FIGS. 1A and 1B, is used. The direction of the arrow on the X-axis is referred to as "+ X direction", and the opposite direction is referred to as "-X direction". The same applies to the directions of the arrows on the Y and Z axes and vice versa. These axes and orientations are used for convenience only and are not intended to limit the placement or orientation of the optical device 100 in practice.

The optical device 100 in the present embodiment irradiates an object (not shown) with light, and acquires data on the distance and / or speed of the object from the light reflected by the object by the FMCW-LiDAR technique. The optical device 100 in this embodiment includes a light source 10, a beam splitter 20, an optical system 30, a photodetector 40, and a processing circuit 50. The optical system 30 includes a lens 32 and a mirror 34. In the present specification, the lens 32 _{is also referred to as a "first lens 32 1} ", and the processing circuit is also referred to as a "FMWC processing circuit". In the present specification, the "FMCW processing circuit" means an electronic circuit that performs FMCW processing described later.

In the first example shown in FIG. 1A and the second example shown in FIG. 1B, the light source 10, the beam splitter 20, the lens 32, and the mirror 34 are arranged in this order along the + Y direction. The reflecting surface of the beam splitter 20 is perpendicular to the XY plane and is tilted 45 ° clockwise with respect to the Y axis when viewed from the + Z direction. The optical axis of the lens 32 is parallel to the Y axis. The reflective surface of the mirror 34 is parallel to the XZ plane. The photodetector 40 and the beam splitter 20 are arranged in this order along the + X direction. The photodetector surface of the photodetector 40 is parallel to the YZ plane. The arrangement relationship such as the inclination of the components shown in the first example and the second example can be appropriately adjusted according to the application.

The light source 10 emits 10 L of light. The light source 10 may include, for example, a light emitting element such as a laser diode that emits a single frequency continuous wave laser beam. Instead of the single frequency continuous wave laser light, a pulse wave laser light having an optical frequency comb may be used. An optical frequency comb is a comb-shaped frequency spectrum formed from a plurality of discrete, evenly spaced lines.

The frequency of the light 10L emitted from the light source 10 can be selected according to the application. When the distance to the object is measured by infrared rays, the frequency of the light 10L can be, for example, 120 THz (wavelength 2.5 μm) or more and 428 THz (wavelength 700 nm) or less. The frequency of the light 10L may be a frequency in the visible region, that is, 428 THz (wavelength 700 nm) or more and 749 THz (wavelength 400 nm) or less. The frequency of the light 10L may be 120 THz (wavelength 2.5 μm) or less.

The light source 10 is a variable frequency light source. The frequency of the light 10L may change depending on, for example, the current injected into the light emitting element included in the light source 10 or the temperature of the light emitting element. In this embodiment, since the FMCW-LiDAR technology is used, the light source 10 is controlled by the processing circuit 50 so that the frequency of the light 10L changes with time.

The light source 10 includes a light deflector that deflects the light emitted from the light emitting element. The optical deflector changes a component parallel to the X direction and a component parallel to the Z direction in the direction of the light 10L. The details of the configuration of the light source 10 will be described later. The direction of the light 10L emitted from the light source 10 is different between the first example shown in FIG. 1A and the second example shown in FIG. 1B. In the first example and the second example, the directions of the light 10L are inclined clockwise and counterclockwise with respect to the Y axis in the XY plane when viewed from the + Z direction, respectively. In the following, "clockwise with respect to the Y axis in the XY plane when viewed from the + Z direction" is simply described as "clockwise with respect to the Y axis". The same applies to counterclockwise rotation.

The beam splitter 20 is located on the optical path of 10 L of light. The beam splitter 20 can be, for example, a cube-type beam splitter including two joined right-angle prisms. One right-angled prism has an optical thin film on its slope. An example of a cube-type beam splitter is a polarization-independent beam splitter cube. Alternatively, the beam splitter 20 can be, for example, a plate-type beam splitter having flat glass provided with an optical thin film on the surface.

The beam splitter 20 separates the light 10L emitted from the light source 10 into the first light 10L ₁ and the second light 10L _2. The first light 10L ₁ is a component of the light 10L that has passed through the beam splitter 20. The second light 10L ₂ is a component of the light 10L reflected by the beam splitter 20. The directions of the first light 10L ₁ and the second light 10L ₂ change according to the direction of the light 10L emitted from the light source 10. In the beam splitter 20, _{the intensity ratio of the first light 10L 1} to the second light 10L ₂ can be, for example, 50:50. The ratio of the intensity of the first light 10L ₁ to the second light 10L ₂ may be changed according to the reflectance of the light at the object. The size and position of the beam splitter 20 are designed to cover the entire angular range in which the direction of the light 10L changes.

The optical system 30 includes a lens 32 and a mirror 34 located on the optical path of _{the first light 10L 1.} The lens 32 can be, for example, a biconvex spherical lens capable of focusing _{the first light 10L 1.} In the present embodiment, the focal point of the lens 32 exists in the light emitting surface of the light source 10 and in the light detecting surface of the photodetector 40. The focal point in the light emitting surface of the light source 10 _{is referred to as "first focal point F 1} ", and the focal point in the photodetector surface of the photodetector 40 is referred to as "second focal point F ₂ ". The first focus F ₁ and the second focus F ₂ are mirror-symmetric with respect to the beam splitter 20. The mirror 34 reflects the light propagating along the + Y direction toward the −Y direction. The mirror 34 can be formed, for example, from a metal or dielectric multilayer film.

Light 10L is emitted from the focus _{F 1} at the light emitting plane of the light source 10. _{The first light 10L 1} separated from the light 10L by the beam splitter 20 propagates through the lens 32 in the + Y direction, is reflected by the mirror 34 and propagates in the −Y direction, and propagates through the lens 32 in the −Y direction. It is transmitted again, reflected by the beam splitter 20, and incident _{on the second focal point F 2 in the light detector 40. The second light 10L 2} separated from the light 10L by the beam splitter 20 is reflected by an object and incident _{on the second focal point F 2} in the photodetector 40 via the beam splitter 20. As shown in FIGS. 1A and 1B, the first light 10L ₁ and the second light 10L ₂ are incident _{on the second focal point F 2} in the photodetector 40 regardless of the emission direction of the light 10L.

The photodetector 40 detects _{the third light 10L 3 in which the first light 10L 1} and the second light 10L ₂ are superimposed and interfere with each other, and outputs a signal indicating the intensity of the third light 10L _3. .. The photodetector 40 may include one or more photodetectors. The photodetector 40 may include one photodetector or may include a plurality of photodetectors arranged one-dimensionally or two-dimensionally. The photodetector 40 can be, for example, a Si avalanche photodetector.

The second light 10L ₂ propagates an extra round-trip distance from the optical device 100 to the object as compared to the first light 10L _1. The second light 10L ₂ is incident on the photodetector 40 later than the first light 10L _1. As a result, the _{frequency of the second light 10L 2} is different from the frequency of the first light 10L _1. Due to the different frequencies, beats occur in _{the third light 10L 3.} The above signal output from the photodetector 40 is a beat signal. In the present specification, the first light is referred to as "reference light", the second light is referred to as "object light", and the third light is referred to as "interference light". In the present specification, for the sake of simplicity, not only the second light after being reflected by the object but also the second light before being reflected by the object is referred to as an object light.

The processing circuit 50 controls the light source 10 and the photodetector 40, and processes the signal output from the photodetector 40. The control of the light source 10 can be, for example, control of the frequency, direction, and emission timing of the light emitted from the light source 10, and the position of the light source 10. The control of the photodetector 40 can be, for example, control of the detection timing and the position of the photodetector 40.

The operation of the FMCW processing of the processing circuit 50 will be described below with reference to FIG. FIG. 2 is a flowchart of the operation of the FMCW process executed by the processing circuit 50. The processing circuit 50 executes the operations of steps S101 to S103 below.

In step S101, the processing circuit 50 causes the light source 10 to emit 10 L of light whose frequency f (t) changes with time. Assuming that the optical path length of the reference light 10L ₁ is sufficiently short, the frequency f ₁ of the reference light 10L _{1 at the timing t = t 0} detected by the photodetector 40 is the frequency f (t) of the light 10L at the timing. It can be considered to be equal to _0). Table by _{[df (t) / dt]} t = t0 Δt - If the time until the object light 10L ₂ is returned by being reflected by the object to Delta] t, the frequency _{f 2} of the object light 10L _{2 is,} f (t 0) Will be done. [Df (t) / dt] _{t = t0} represents the rate of change of the frequency f (t) at time t = t _0. The processing circuit 50 may adjust the position of the light source 10 by, for example, an actuator. This adjustment can compensate for the deviation of the light emitting surface of the first focus F ₁ and the light source 10.

In step S102, the processing circuit 50 causes the photodetector 40 to output a beat signal by detecting the _{interference light 10L 3.} The processing circuit 50 may adjust the position of the photodetector 40 by, for example, an actuator. By this adjustment, the _{deviation between the second focal point F 2} and the photodetector surface of the photodetector 40 can be compensated. As a result, the strength of the beat signal can be improved. Table frequency of the beat signal, the frequency _{f 1} of the reference light 10L _1, the object optical frequency difference between the frequency _{f 2} of _{10L 2 Δf = f 1 -f 2} = [df (t) / dt] t = t0 Δt Will be done.

In step S103, the processing circuit 50 processes the beat signal to generate and output data relating to the distance and / or velocity of the object. Assuming that the distance from the optical device 100 to the object is d and the speed of light in the air is c, Δt = 2d / c. Generating a frequency _{f 1} of the reference light 10L _1, the frequency difference Δf = (2d / c) [ df (t) / dt] t = t0 and the frequency _{f 2} of the object light 10L _2, data relating to an object distance d can do. For example, when [df (t) / dt] _{t = t0} = 125 THz / s and the distance d is 5 mm or more and 50 m or less, the frequency difference Δf is 4.17 kHz or more and 4.17 MHz. This frequency difference Δf can be accurately measured by, for example, a spectrum analyzer or an oscilloscope with a resolution on the order of several Hz to several tens of MHz. Therefore, according to the optical device 100 in the present embodiment, it is possible to achieve both a wide dynamic range and a high resolution with respect to the distance in the acquisition of data regarding the distance of the object. When the object is moving, assuming that the velocity of the object, which is the time change rate of the distance d, is v, from the time change rate dΔf / dt = 2v / c [df (t) / dt] _{t = t0 of} the frequency difference Δf, Data on the velocity v of the object can be generated.

According to the optical device 100 in the present embodiment, the processing circuit 50 changes the direction of the light 10L emitted from the light source 10 and processes the beat signal according to the direction of the light 10L, thereby three-dimensionally processing the object. Data on position and / or speed can be obtained.

Further, according to the optical device 100 in the present embodiment, even if the direction of the light 10L emitted from the light source 10 changes due to the presence of the lens 32, the reference light 10L ₁ and the object light 10L ₂ are photodetectors. superposed by the second focal point F ₂ of 40 of the photodetection plane can be interference.

(Modification example)
Next, with reference to FIGS. 3A to 5, the first to third modified examples of the optical device in the present embodiment will be described. The optical devices according to the first to third modifications of the present embodiment further include one or more lenses in addition to the configuration of the optical device 100 according to the present embodiment.

3A and 3B are diagrams schematically showing a first example and a second example of the optical device 110 in the first modification of the present embodiment, respectively. The optical device 110 in the first modified example is different from the optical device 100 in this embodiment, a second lens 32 ₂ between the beam splitter 20 and the photodetector 40. The second lens 32 ₂ is located on the optical path of the interference light 10L _3. The second focal point of the lens 32 ₂ on the side of the beam splitter 20 coincides with the second focal point _{F 2} of the first lens 32 _1. It passes through the second focal point _{F 2,} a third light 10L ₃ that has passed through the second lens 32 _2, along a -X direction and enters the optical detector 40. In the optical device 110 in the first modification, unlike the optical device 100 in the present embodiment, the second focal point F ₂ does not need to be present in the photodetector plane of the photodetector 40. Therefore, it is not necessary to precisely adjust the position of the photodetector 40.

As shown in FIGS. 3A and 3B, _{the position where the third light 10L 3} is incident on the photodetector 40 changes depending on the direction of the light 10L emitted from the light source 10. If the component in the X direction changes in the direction of the light 10L, one-dimensional data regarding the distance of the object can be acquired by the photodetector 40 including a plurality of photodetectors arranged in the Y direction. If the component parallel to the X direction and the component parallel to the Z direction change in the direction of the light 10L, the photodetector 40 including a plurality of photodetectors arranged in the Y direction and the Z direction relates to the distance of the object. Two-dimensional image data can be acquired.

FIG. 4 is a diagram schematically showing an example of the optical device 120 in the second modification of the present embodiment. The optical device 120 in the second modified example is different from the optical device 110 in the first modified, the third lens 32 ₃ located between the second lens 32 ₂ and the photodetector 40 in the optical path of the interference light 10L ₃ Further prepare. The third focal point F ₃ is the focal of the third lens 32 ₃ is located on the light detecting plane of the photodetector 40. In the example shown in FIG. 4, the position of the _third light 10L 3 incident on the photodetector 40 can be changed _{from the second focus F 2} to the third focus F ₃ as compared with the example shown in FIG. 1A. .. Therefore, the degree of freedom in optical design can be improved.

Further, the processing circuit 50 may be adjusted by the first lens 32 ₁ third lens 32 ₃ position, for example, actuators. By this adjustment, the _{deviation between the first focus F 1} and the light emitting surface of the light source 10 can be compensated, the deviation between the third focus F ₃ and the light detection surface of the photodetector 40 can be compensated, and the reference light 10L _{1 can be compensated.} It is possible to compensate for the deviation between the object light and the object light 10L _2. As a result, the strength of the beat signal can be improved. The interference light 10L ₃ Instead of directly incident on the light detector 40, also the interference light 10L ₃ obtained reference light 10L ₁ and the object light 10L ₂ is once introduced into the optical fiber is incident on the photodetector 40 good.

FIG. 5 is a diagram schematically showing an example of the optical device 130 in the third modification of the present embodiment. The optical device 130 in the third modification is different from the optical device 120 in the second modified example, the reference light 10L ₁ and the fourth lens 32 ₄ located between the first lens 32 ₁ and the mirror 34 in the optical path Further prepare. Fourth focal point _{F 4} is the focus of the fourth lens 32 ₄ is located on the reflection plane of the mirror 34. With this arrangement, even if the mirror 34 is tilted to some extent from the XZ plane, it is possible to suppress an extreme decrease in the strength of the beat signal. As a result, the alignment of the mirror 34 becomes easy. In the optical device 130 in the third modification, similarly to the optical device 120 in the second modified example, the processing circuit 50, by adjusting the first lens 32 ₁ by the fourth lens 32 ₄ positions, for example, actuators, beet The signal strength may be improved. In this case, the vector of the reference beam 10L ₁ and the object light 10L ₂ incident on the light detector 40, the beat signal in the third focal point F ₃ in the photodetector plane of the photodetector 40 is determined so as to obtain.

Next, a fourth modification example and a fifth modification example of the optical device according to the present embodiment will be described with reference to FIGS. 6 and 7.

FIG. 6 is a diagram schematically showing an example of the optical device 140 in the fourth modification of the present embodiment. Unlike the optical device 100 in the present embodiment, the optical device 140 in the fourth modification is not an optical system 30 including _{the first lens 32 1} and a mirror 34, but a concave mirror 60 located on the optical path of the _{reference light 10L 1.} The optical system 30 including the optical system 30 is provided. The optical system 30 has a lens effect and a Miller effect with respect to _{the reference light 10L 1.} Similar to the lens 32 shown in FIG. 1A, the concave mirror 60 has a first focal point F _{1 existing in the light emitting surface of the light source 10 and a second focal point F 2} existing in the light detecting surface of the photodetector 40. Have. In the example shown in FIG. 6, the interference light 10L ₃ can be incident on the second focal point F _{2 in the photodetector 40, as in the example shown in FIG. 1A.} The concave mirror 60 shown in FIG. 6 is one optical component unlike the lens 32 and the mirror 34 shown in FIG. 1A. Therefore, the miniaturization and simplification of the optical device 140 in the fourth modification can be realized.

FIG. 7 is a diagram schematically showing an example of the optical device 150 in the fifth modification of the present embodiment. Unlike the optical device 100 in the first embodiment, the optical device 150 in the fifth modification _{reflects the reference light 10L 1} and controls the reflection direction instead of the optical system 30 including _{the first lens 32 1 and the mirror 34.} The optical system 30 including the light modulator 70 is provided. The light modulator 70 may include, for example, a two-dimensional spatial light modulator such as an LCOS (Liquid Crystal on Silicon), an electro-optical modulator, an acousto-optic modulator, a galvano mirror, or a MEMS mirror. Processing circuit 50, the optical modulator 70, the reference light 10L ₁ is modulated and reflected, the reference light 10L _1, focusing on the second focal point _{F 2} via the beam splitter 20. In the example shown in FIG. 7, the second focal point F ₂ exists in the photodetector plane of the photodetector 40.

Due to the distortion of the wave surface of the light due to the fluctuation of the air, the reference light 10L ₁ and the object light 10L ₂ are not superposed at the second focal point F ₂ , and the interference light 10L ₃ may not be effectively obtained. .. As a result, the resolution and contrast of the object can be reduced. By compensating for the distortion of the wave surface of light caused by the fluctuation of air by the light modulator 70, the resolution and contrast of the object can be improved. Even if the optical path length of the reference light 10L ₁ changes due to vibration or deterioration over time, the change in the optical path length can be compensated by the light modulator 70. Compensation by the light modulator 70 does not require the position of the optical component to be physically changed.

In the above example, the first light 10L ₁ is the reference light and the second light 10L ₂ is the object light. Depending on the application, the arrangement of the optical system 30 may be appropriately changed so that the first light 10L ₁ can be used as the object light and the second light 10L ₂ can be used as the reference light. Further, in the above-mentioned example, data on the distance and / or velocity of the object was acquired by the FMCW technique. Depending on the application, other technologies such as TOF technology may be used instead of the FMCW technology.

(Structure example of light source 10)
Next, a configuration example of the light source 10 in the present embodiment that does not use mechanical drive will be described with reference to FIGS. 8A to 8C.

FIG. 8A is a perspective view schematically showing an example of the light source 10 in the present embodiment. The light source 10 includes an optical waveguide array 12A, a phase shifter array 14A, an optical turnout 15, a light emitting element 16, and a substrate 18 on which these components are integrated. The configuration including the optical waveguide array 12A, the phase shifter array 14A, and the optical turnout 15 corresponds to the optical deflector. The optical waveguide array 12A includes a plurality of optical waveguide elements 12 arranged in the Z direction. Each optical waveguide element 12 extends in the X direction. The phase shifter array 14A includes a plurality of phase shifters 14 arranged in the Z direction. Each phase shifter 14 extends in the X direction. The plurality of optical waveguide elements 12 in the optical waveguide array 12A are connected to the plurality of phase shifters 14 in the phase shifter array 14A, respectively. An optical turnout 15 is connected to the phase shifter array 14A.

The light emitted from the light emitting element 16 and input to the optical turnout 15 is input to the plurality of phase shifters 14 in the phase shifter array 14A via the optical turnout 15. The light that has passed through the plurality of phase shifters 14 in the phase shifter array 14A is input to the plurality of optical waveguide elements 12 in the optical waveguide array 12A in a state where the phases are shifted by a constant amount in the Z direction. The light input to each of the plurality of optical waveguide elements 12 in the optical waveguide array 12A is emitted as light 10L from the light emitting surface parallel to the XZ plane in the direction intersecting the light emitting surface.

Next, a configuration example of the optical waveguide element 12 in this embodiment will be described with reference to FIG. 8B. FIG. 8B is a diagram schematically showing an example of the optical waveguide element 12 in this embodiment. The optical waveguide element 12 in the present embodiment _{is located between the first mirror 12m 1} and the second mirror 12m ₂ facing each other and the first mirror 12m ₁ and the second mirror 12m ₂ , and includes a liquid crystal material. It includes a liquid crystal layer 12LC and a pair of first electrodes 12EL for applying a first driving voltage to the liquid crystal layer 12LC. The transmittance of the first mirror 12m ₁ is higher than that of the second mirror 12m _2. At least one of the first mirror 12m ₁ and the second mirror 12m ₂ can be formed, for example, from a multilayer reflective film in which a plurality of high refractive index layers and a plurality of low refractive index layers are alternately laminated. The first mirror 12m ₁ and the second mirror 12m ₂ may be formed from a multilayer reflective film containing the same high refractive index layer and the same low refractive index layer. In this case, if the _{number of layers of the first mirror 12m 1} is smaller than the number of layers of the second mirror 12m _{2 , the transmittance of the first mirror 12m 1} is higher than the transmittance of the second mirror 12m _2.

The light 12L, which is a part of the light emitted from the light emitting element 16, propagates in the liquid crystal layer 12LC along the X direction while being reflected by _{the first mirror 12m 1} and the second mirror 12m _2. At that time, part of the light 12L propagating in the liquid crystal layer 12LC is emitted to the outside from the first mirror 12m _1.

By applying the first driving voltage to the pair of first electrodes 12EL, the refractive index of the liquid crystal material in the liquid crystal layer 12LC changes, and the direction of the light emitted to the outside from the optical waveguide element 12 changes. The rate of change of the refractive index of the liquid crystal material with respect to the change of the first drive voltage can be, for example, 30 Hz or more and 120 Hz or less. According to the change of the first drive voltage, of the direction of the light 10L emitted from the optical waveguide array 12A, the parallel component D ₁ varies in the X direction. Processing circuit 50, by applying a first drive voltage to the pair of first electrodes 12EL, among directions of light 10L emitted from the light source 10, to change the component D ₁ parallel to the X direction.

Next, a configuration example of the phase shifter 14 in the present embodiment will be described with reference to FIG. 8C. FIG. 8C is a diagram schematically showing an example of the phase shifter 14 in the present embodiment. The phase shifter 14 in the present embodiment includes a total reflection waveguide 14w containing a thermooptical material whose refractive index changes with heat, a heater 14h that is in thermal contact with the total reflection waveguide 14w, and a second drive voltage for the heater 14h. Includes a pair of second electrodes 14EL for applying. The refractive index of the total reflection waveguide 14w is higher than the refractive index of the heater 14h, the substrate 18, and air. Due to the difference in refractive index, the light 14L, which is a part of the light emitted from the light emitting element 16, propagates along the X direction while being totally reflected in the total reflection waveguide 14w.

By applying a second drive voltage to the pair of second electrodes 14EL, the total reflection waveguide 14w is heated by the heater 14h. As a result, the refractive index of the total reflection waveguide 14w changes, and the phase of the light 14L output from the end of the total reflection waveguide 14w shifts. The rate of change of the refractive index of the thermooptical material with respect to the change of the second drive voltage can be, for example, 1 kHz or more and 10 kHz or less. In the example shown in FIG. 8A, if the phase of the light 14L output from the plurality of phase shifters 14 in the phase shifter array 14A increases or decreases by a certain amount along the Z direction, the direction of the light 10L emitted from the optical waveguide array 12A Of these, the component D ₂ parallel to the Z direction changes. By applying a second drive voltage to the pair of second electrodes 14EL, the processing circuit 50 changes the _{component D 2 parallel to the Z direction in the direction of the light 10L emitted from the light source 10.}

Instead of the optical waveguide array 12A described above, a _{planar optical waveguide including a first mirror 12m 1} , a second mirror 12m ₂ , and a liquid crystal layer 12LC may be connected to the phase shifter array 14A. _{The first mirror 12m 1} , the second mirror 12m ₂ , and the liquid crystal layer 12LC in the plane optical waveguide extend along the XZ plane. The light propagating through the plurality of phase shifters 14 included in the phase shifter array 14A interferes with each other in the liquid crystal layer 12LC in the planar optical waveguide to form an optical beam. The light beam formed by the liquid crystal layer 12LC is emitted to the outside through the first mirror 12m _1.

Details of the operating principle, operating method, and the like of the light source 10 in the present embodiment are disclosed in US Patent Application Publication No. 2018/0224709. The entire disclosure of this document is incorporated herein by reference.

In addition to the examples shown in FIGS. 8A to 8C, the light source 10 in the present embodiment may include, for example, a light emitting element and an optical modulator that changes the direction of the light emitted from the light emitting element. When changing the direction of light by mechanical drive, the light modulator may include, for example, a galvano mirror, or a MEMS mirror. When changing the direction of light without using mechanical drive, the light modulator may include, for example, a two-dimensional spatial light modulator such as LCOS, an electro-optical modulator, or an acousto-optic modulator.

(Specific example of light source 10)
A specific example of the light source 10 in this embodiment will be described below.

The light emitting element 16 includes a laser diode that emits a continuous wave laser beam having a frequency of 314 THz (wavelength 955 nm) at an injection current of 450 mA and emits a continuous wave laser beam having a frequency of 319 THz (wavelength 940 nm) at an injection current of 550 mA. The laser diode can emit only one wavelength laser beam having a small half width in single mode. An example of such a laser diode is a distributed feedback laser. Alternatively, the laser diode may emit a pulse wave laser beam having the optical frequency comb described above.

In the laser diode that emits the continuous wave laser light, the frequency of the laser light can be changed with time by changing the injection current within the range of 450 mA or more and 550 mA or less. The time change rate of the frequency of the laser beam is 125 THz / s.

One optical waveguide formed on the Si substrate 18 is connected to 128 phase shifters 14 via a multimode interference coupler. The optical waveguide and the multimode interference coupler correspond to the optical turnout 15 shown in FIG. 8A. The optical turnout 15 and the phase shifter 14 are formed of SiN. The phase shifter 14 is designed, for example, to propagate light at a frequency of 319 THz. Heaters 14h are individually arranged on 128 phase shifters 14, and the phase of light propagating through each phase shifter 14 is controlled by applying a voltage to the pair of second electrodes 14EL. Light is input to the optical waveguide element 12 from the end of the phase shifter 14 via the mode converter.

_{Each of the first mirror 12m 1} and the second mirror 12m ₂ in the optical waveguide element 12 is formed of a dielectric multilayer film. The high-refractive-index layer and the low-refractive-index layer contained in the dielectric multilayer film can be formed from TiO and SiO, respectively. The dielectric multilayer film has a frequency range having high reflectance, a so-called stop band. The center frequency of the stopband is 319 THz. The reflectance of the first mirror 12m ₁ can be, for example, 99.6%, and the reflectance of the second mirror 12m ₂ can be, for example, 99.98%. The light 10L is emitted from _{the first mirror 12m 1.} Each of the pair of first electrodes 12EL can be formed, for example, from ITO.

By applying a voltage to the pair of first electrodes 12EL, the processing circuit 50 can change the direction of the light 10L emitted from the light source 10 within a range of 30 ° in the XY plane. Similarly, the processing circuit 50 can change the direction of the light 10L emitted from the light source 10 within a range of 30 ° in the XZ plane by applying a voltage to the pair of second electrodes 14EL.

(Application example)
The optical device 100 in this embodiment can be used, for example, in a distance measuring system that measures a distance to an object. Such a ranging system can be mounted on a moving body such as an automobile, a UAV (Unmanned Aerial Vehicle, so-called drone), or an AGV (Automated Guided Vehicle), and can be used as one of collision avoidance techniques. In the distance measuring system using the optical device 100 in the present embodiment, the distance distribution of an object can be scanned and detected with a wide dynamic range and high resolution with respect to the distance.

The optical device according to the embodiment of the present disclosure can be used for the purpose of a distance measuring system mounted on a vehicle such as an automobile, a UAV, or an AGV.

10 Light source 10L Light 10L ₁ First light 10L ₂ Second light 10L ₃ Third light 12 Optical waveguide element 12A Optical waveguide array 12EL First electrode 12L Light 12LC Liquid crystal layer 12m ₁ First mirror 12m ₂ Second mirror 12s Light emission surface 14 Phase shifter 14A Phase shifter array 14EL 2nd electrode 14L Light 14h Heater 14w Full reflection waveguide 15 Optical branch 16 Light emitting element 18 Substrate 20 Beam splitter 30 Optical system 32 ₁ 1st lens 32 ₂ 2nd lens 32 _3rd 3 Lens 32 ₄ 4th Lens 34 Mirror 40 Optical Detector 50 Processing Circuit 60 Concave Mirror 70 Optical Modulator 100, 110, 120, 130, 140, 150 Optical Device

Claims (9)

A light source with a light deflector and
A beam splitter located on the optical path of the light deflected by the light deflector and splitting the light into a first light and a second light.
An optical system that causes the first light and the second light reflected by an object to interfere with each other to generate a third light.
A photodetector that detects the third light, and
A processing circuit that processes the signal output from the photodetector, and
To prepare
Optical device. The optical system includes a first lens and a mirror located on the optical path of the first light.
The first lens is located between the beam splitter and the mirror on the optical path of the first light.
The optical device according to claim 1. The optical system further includes a second lens located on the optical path of the third light.
The optical device according to claim 2. The optical system further includes a third lens located between the second lens and the photodetector on the optical path of the third light.
The optical device according to claim 3. The optical system further includes a fourth lens located between the first lens and the mirror on the optical path of the first light.
The optical device according to claim 4. The optical system includes a concave mirror located on the optical path of the first light.
The optical device according to claim 1. The optical system includes an optical modulator that reflects the first light and controls the direction of reflection.
The optical device according to claim 1. The third light is generated by interfering the first light reflected by the beam splitter with the second light reflected by the object and transmitted through the beam splitter.
The optical device according to claim 1. The light source is a variable frequency light source.
The processing circuit is an FMCW processing circuit.
The optical device according to any one of claims 1 to 8.

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