Lidar transmitter / receiver

Abstract

To make it possible to acquire IQ signals while suppressing complication of a configuration of an optical system in a technique for separating a light source and a light detector in FMCW-LiDAR.SOLUTION: A LiDAR transmitter / receiver includes a light source 1, a wavelength plate 23, a polarizing beam splitter 22, a first light detector 3a, a second light detector 3b, and a coating 24. The coating 24 is arranged between the polarizing beam splitter 22 and a target TR in a path of emitted light Lp, and has a thickness along a direction of travel of target reflected light Ltr or reference light Lr such that a first phase difference which is a phase difference between the target reflected light Ltr and the reference light Lr in a first beam Lb1, and a second phase difference which is a phase difference between the target reflected light Ltr and the reference light Lr in a second beam Lb2, differ.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This disclosure relates to LiDAR transceivers. [Background technology]

[0002] Conventionally, there is known a technology of FMCW-LiDAR in which a light source emits an emission light whose frequency is continuously modulated, the emission light is reflected by a target, and the target reflected light is caused to interfere with a reference light derived from the emission light, and the target is detected based on the obtained interference light. As a transceiver applicable to this FMCW-LiDAR, a transceiver capable of separating a photodetector from a light source using a polarizing beam splitter and a wave plate is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-505179 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors considered that, in the above technology, if an IQ signal is obtained from the interference light received by a photodetector, it would be possible to obtain instantaneous frequency and instantaneous phase information of the interference light. However, the above document does not disclose a configuration for obtaining an IQ signal, and if one were to simply realize such a configuration, the number of polarizing beam splitters and the number of wave plates would become enormous, making the configuration of the optical system extremely complicated.

[0005] In view of the above, the present disclosure aims to provide a technology for separating a light source and a photodetector in an FMCW-LiDAR that enables acquisition of an IQ signal while preventing the optical system configuration from becoming complicated. [Means for solving the problem]

[0006] The invention described in claim 1 to achieve the above object is: A light source (1) that emits output light (Lp) that is frequency modulated with respect to light of a reference wavelength; a wave plate (23) that changes the polarization direction of the outgoing light by passing the outgoing light through a first side that is a side toward a target (TG) from the light source along a path of the outgoing light, and changes the polarization direction of the interference light (Lb) by passing an interference light (Lb) including a target reflected light (Ltr) after a part of the outgoing light is reflected by the target and a reference light (Lr) after another part of the outgoing light is reflected before hitting the target, through a second side opposite to the first side; a polarizing beam splitter (22) disposed between the light source and the wave plate in a path of the emitted light, for outputting the emitted light to the wave plate according to a polarization state of the emitted light, and outputting the interference light in a direction different from a direction returning to the light source according to a polarization state of the interference light; a first photodetector (3a) that detects a first beam included in the interference light after the first beam exits the polarizing beam splitter; a second photodetector (3b) for detecting a second beam included in the interference light after the second beam exits the polarizing beam splitter; The first beam and the second beam are translated at positions offset from each other, The LiDAR transceiver includes a thickness forming component (23, 24, 25, 30) that is disposed between the polarizing beam splitter and the target in the path of the emitted light, and has a thickness along the traveling direction of the target reflected light or the reference light that makes a first phase difference, which is a phase difference between the target reflected light and the reference light in the first beam, different from a second phase difference, which is a phase difference between the target reflected light and the reference light in the second beam.

[0007] In this way, the difference between the first phase difference and the second phase difference required to acquire an IQ signal is provided by adjusting the thickness of the thickness forming component along the traveling direction of the target reflected light or the reference light in the optical system, thereby reducing the number of components in the optical system and, in turn, the complexity of the optical system.

[0008] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a configuration diagram of a LiDAR transceiver according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing details of an optical system. [Diagram 3] FIG. 2 is a diagram showing the configuration of a wave plate, a coating, and an optical path length compensation element. [Figure 4] FIG. 11 is a diagram showing details of an optical system in a second embodiment. [Diagram 5] 3A and 3B are diagrams illustrating configurations of a wave plate and an optical path length compensation element. [Figure 6] FIG. 13 is a diagram showing details of an optical system in a third embodiment. [Figure 7] FIG. 13 is a diagram illustrating a configuration of a wave plate in a fourth embodiment. [Figure 8] FIG. 13 is a diagram showing details of an optical system in a fifth embodiment. [Figure 9] FIG. 2 is a diagram showing details of a surface reflection optical element. [Figure 10] 13A and 13B are diagrams showing details of a surface reflective optical element in a sixth embodiment. [Figure 11] FIG. 13 is a diagram showing details of an optical system in a seventh embodiment. [Figure 12] FIG. 2 is a diagram showing the configuration of a wave plate and a phase difference generating element. [Figure 13] FIG. 23 is a diagram showing the configurations of a wave plate and a phase difference generating element in the eighth embodiment. [Figure 14]FIG. 13 is a diagram showing the configurations of a wave plate and a phase difference generating element in the ninth embodiment. [Figure 15] FIG. 23 is a diagram showing details of an optical system in a tenth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the present invention will be described below. As shown in Fig. 1, the LiDAR transceiver according to this embodiment identifies the position, shape, speed, etc. of a target TG using the FMCW-LiDAR method. The identified position and speed are the relative position and relative speed of the target TG with respect to the LiDAR transceiver, respectively. FMCW is an abbreviation for Frequency Modulated Continuous Wave.

[0011] This LiDAR transceiver may be used, for example, in a vehicle to determine the position, shape, speed, etc. of objects around the vehicle (e.g., a preceding vehicle, a person, an obstacle), or may be used for other purposes.

[0012] This LiDAR transceiver includes a light source 1, an optical system 2, a first photodetector 3a, a second photodetector 3b, and a processing circuit 4. The light source 1 includes a laser oscillator 11 and a modulator 12. The laser oscillator 11 generates and outputs a laser beam of a predetermined reference frequency (e.g., 1550 nm, 1300 nm). For example, a laser diode is used as the laser oscillator 11, but other devices may also be used.

[0013] The modulator 12 performs frequency modulation with a predetermined modulation amplitude (for example, 0.001 nm width, for example, 0.005 nm width) on the laser light of the reference frequency output by the laser oscillator 11, thereby emitting output light Lp, which is a laser light whose frequency increases and decreases, to the optical system 2. The change in frequency may be, for example, a triangular wave in which the frequency increases at a predetermined chirp rate and then decreases at the same rate, or may be another change mode.

[0014] The optical system 2 is a spatial interference optical system that forms an optical path that guides a portion of the output light Lp emitted from the light source 1 to the target TG. The optical system 2 also combines the target reflected light Ltr generated after the portion of the output light Lp is reflected by the target TG with a reference light Lr generated when another portion of the output light Lp is reflected within the optical system 2 before hitting the target TG, and outputs a first beam Lb1 of the combined interference light Lb to the first photodetector 3a and a second beam Lb2 to the second photodetector 3b.

[0015] The first photodetector 3a is a light receiving element that generates an I signal as an electrical signal corresponding to the received first beam Lb1 and outputs the generated I signal to the processing circuit 4. The second photodetector 3b is a light receiving element that generates a Q signal as an electrical signal corresponding to the received second beam Lb2 and outputs the generated Q signal to the processing circuit 4. The phase difference between the target reflected light Ltr and the reference light Lr contained in the I signal is shifted by 90° with respect to the phase difference between the target reflected light Ltr and the reference light Lr contained in the Q signal. Note that the shift angle is not limited to strictly 90° and may deviate from 90° to an extent that the I signal and the Q signal can be acquired.

[0016] The processing circuit 4 calculates the position, shape, speed, etc. of the target TG based on the I signal output from the first photodetector 3a and the Q signal output from the second photodetector 3b. The processing circuit 4 has, for example, a memory that stores software describing the process of calculating the position, shape, speed, etc. of the target TG from the IQ signal (i.e., the I signal and the Q signal). The processing circuit 4 is also configured as a microcomputer equipped with a CPU or the like that reads and executes the software from the memory. Alternatively, the processing circuit 4 may be a dedicated electronic circuit configured to execute the process of calculating the position, shape, speed, etc. of the target TG from the IQ signal.

[0017] In the above-mentioned processing, the processing circuit uses the IQ signal as a beat signal to calculate the position, shape, speed, etc. of the target TG by the FMCW method. In this case, if both the I signal and the Q signal are obtained, the instantaneous phase of the received interference light Lb can be known, improving the accuracy of distance and speed calculation.

[0018] The following describes the configuration of the optical system 2. As shown in Fig. 2, the optical system 2 has a collimator 21, a polarizing beam splitter 22, a wave plate 23, a coat 24, an optical path length compensation element 25, a beam scanner 26, and a light receiving lens 27. In this embodiment, the coat 24 and the optical path length compensation element 25 constitute thickness forming components.

[0019] The collimator 21 is composed of a single lens or a set of lenses that focuses the output light Lp emitted from the light source 1 into a parallel beam. The polarizing beam splitter 22 is disposed on the target TG side, i.e., the first side, of the collimator 21 along the path of the output light Lp. Hereinafter, the target TG side along the path of the output light Lp will be referred to as the first side, and the opposite side, i.e., the light source 1 side, will be referred to as the second side.

[0020] The polarizing beam splitter 22 is an optical member that passes the output light Lp from the collimator 21 and reflects the interference light Lb from the wave plate 23 in a direction toward the light receiving lens 27 that is different from the direction toward the light source 1. The interference light Lb has a polarization direction different from that of the output light Lp due to the action of the wave plate 23, and the polarizing beam splitter 22 utilizes this difference in polarization direction to realize the traveling direction of the light as described above.

[0021] The wave plate 23 is disposed on the first side with respect to the polarizing beam splitter 22. The wave plate 23 is an optical member that changes the polarization state of light by shifting the phase between two orthogonal polarized components of the light that passes through the wave plate 23. More specifically, the wave plate 23 is composed of a λ / 4 wave plate.

[0022] The coating 24 is an optical film for adjusting the optical path length of light passing through the coating 24. The coating 24 has a refractive index different from that of air, and is disposed on the first side relative to the wave plate 23.

[0023] 2 and 3, the coat 24 is applied to the surface 23a so as to entirely cover the surface 23a on the first side of the wave plate 23, which is located on the path through which the first beam Lb1 passes. The coat 24 is also formed so as not to cover the surface 23b on the first side of the wave plate 23, which is located on the path through which the second beam Lb2 passes.

[0024] Here, the interference light Lb, the first beam Lb1, and the second beam Lb2 will be described. A portion of the output light Lp other than the portion traveling from the optical system 2 toward the target TG is reflected by the wave plate 23 or the coat 24 in the optical system 2, and becomes the reference light Lr traveling toward the polarizing beam splitter 22.

[0025] On the path from the coat 24 and the wave plate 23 through the polarizing beam splitter 22 and the light receiving lens 27 to the first photodetector 3a and the second photodetector 3b, the reference light Lr and the target reflected light Ltr are combined to form a beam of interference light Lb. A part of the interference light Lb is the first beam Lb1, and the other part is the second beam Lb2. In addition, the target reflected light Ltr before being combined with the reference light Lr, which is later combined with the reference light Lr in the first beam Lb1, constitutes the first beam Lb1, and the part later combined with the reference light Lr in the second beam Lb2 constitutes the second beam Lb2.

[0026] In each figure, the emitted light Lp is represented by a solid line, the target reflected light Ltr is represented by a dashed line, and the reference light Lr is represented by a dashed line. The optical axis centers of the emitted light Lp, the target reflected light Ltr, and the reference light Lr are represented by a two-dot chain line. The emitted light Lp, the target reflected light Ltr, and the reference light Lr share a partially common path.

[0027] 2 and 3, the first beam Lb1 and the second beam Lb2 move parallel to each other at positions shifted from each other. The shift in the positions of the first beam Lb1 and the second beam Lb2 is a shift in a direction intersecting the traveling direction of the interference light Lb. More specifically, the shift is a shift in a direction perpendicular to the traveling direction of the interference light Lb.

[0028] Here, the portion of the reference light Lr that constitutes the first beam Lb1 is generated when the output light Lp passes through the inside of the wave plate 23 and the coating 24 and is reflected at the first surface 24a of the coating 24. Meanwhile, the portion of the reference light Lr that constitutes the second beam Lb2 is generated when the output light Lp passes through the inside of the wave plate 23 and is reflected at the surface 23b of the wave plate 23.

[0029] The second side surface of the wave plate 23, the interface between the wave plate 23 and the coating 24, the first side surface of the optical path length compensation element 25, and the second side surface of the optical path length compensation element 25 are treated to suppress light reflection (e.g., AR coating treatment).

[0030] Furthermore, the coat 24 is formed so as to cover a surface 23c, which is adjacent to the surface 23a and corresponds to a path through which neither the first beam Lb1 nor the second beam Lb2 passes, among the surfaces on the first side of the wave plate 23. This is a measure for the case where the position through which the first beam Lb1 passes is slightly shifted.

[0031] In addition, the thickness t1 of the coating 24 along the traveling direction of the first beam Lb1 and the refractive index n1 of the coating 24 satisfy m×λ / 4=2×n1×t1, where m is an odd number, where λ is the reference wavelength corresponding to the above-mentioned reference frequency. The thickness t1 of the coating 24 can be controlled with high precision by deposition techniques such as anti-reflection coating and dielectric multilayer coating. However, this formula is not limited to being strictly satisfied, and may deviate from the strictly satisfied state to the extent that an IQ signal can be acquired. This is the same for the conditions regarding thickness and refractive index shown throughout this specification, including other embodiments.

[0032] The optical path length compensation element 25 is disposed on the first side with respect to the wave plate 23, and is an optical member having a refractive index different from that of air in order to change the optical path length of light passing through the optical path length compensation element 25. The optical path length compensation element 25 may be in contact with the wave plate 23, or there may be an air gap between the optical path length compensation element 25 and the wave plate 23.

[0033] The thickness tc of the optical path length compensation element 25 along the traveling direction of the target reflected light Ltr passing therethrough and the refractive index nc of the optical path length compensation element 25 satisfy (n1-nair)×t1=(nc-nair)×tc. Here, nair is the refractive index of air. This is done in order to make the target reflected light Ltr constituting the first beam Lb1 and the target reflected light Ltr constituting the second beam Lb2 have the same phase. However, this formula is not limited to being strictly satisfied, and may deviate from the strictly satisfied state to the extent that an IQ signal can be acquired. This is the same for the conditions related to thickness and refractive index shown throughout this specification, including other embodiments.

[0034] 2 and 3, the optical path length compensation element 25 is disposed in a path through which the target reflected light Ltr constituting the second beam Lb2 passes. Moreover, the optical path length compensation element 25 is disposed away from the path through which the target reflected light Ltr constituting the first beam Lb1 passes.

[0035] The beam scanner 26 is disposed on the first side with respect to the wave plate 23, the coating 24, and the optical path length compensation element 25. The beam scanner 26 reflects the output light Lp that passes through the wave plate 23, the coating 24, and the optical path length compensation element 25 and enters the beam scanner 26. The beam scanner 26 is a scanning mirror that can manipulate the direction of the output light Lp after reflection to perform beam scanning of a detection range including the target TG according to a predetermined scanning pattern. The beam scanner 26 may be rotatable by one or more galvanometers, may rotate a polygonal mirror, or may be realized by another configuration, for example.

[0036] The beam scanner 26 also reflects target reflected light Ltr, which is generated when the output light Lp is reflected by the target TG, and returns it to the wave plate 23, the coat 24, and the optical path length compensation element 25 as a parallel beam.

[0037] The light receiving lens 27 is composed of a single lens or a set of lenses that collects a part of the light from the polarizing beam splitter 22 and makes it incident on the first photodetector 3a and collects the other part of the light and makes it incident on the second photodetector 3b. The light receiving lens 27 may be composed of two independent lenses, a lens for collecting light on the first photodetector 3a and a lens for collecting light on the second photodetector 3b, or may be composed of a single lens array having two lens shapes to realize the functions of these two lenses.

[0038] The operation of the LiDAR transceiver configured as above will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases relative to a reference frequency. This output light Lp is focused into a parallel beam by the collimator 21 and then enters the polarizing beam splitter 22.

[0039] 3, the output light Lp is adjusted by the light source 1 to be linearly polarized light with a predetermined first direction as the polarization direction Y1, and the polarizing beam splitter 22 transmits the output light Lp in such a polarized state. Therefore, the output light Lp passes through the polarizing beam splitter 22 and enters the wave plate 23. By passing through the wave plate 23, the polarization state of the output light Lp changes from linearly polarized light in the first direction to circularly polarized light.

[0040] The output light Lp that has passed through the region of the first beam Lb1 passes through the wave plate 23 and then enters the coat 24. A part of the output light Lp that has entered the coat 24 passes through the coat 24 and proceeds toward the beam scanner 26. The other part of the output light Lp that has entered the coat 24 becomes the reference light Lr that is reflected by the first surface 24a of the coat 24 and proceeds toward the second side.

[0041] A part of the output light Lp that has passed through the region of the second beam Lb2 passes through the wave plate 23, then passes through the optical path length compensation element 25 and proceeds to the beam scanner 26. Another part of the output light Lp in the region of the second beam Lb2 is reflected by the first surface 23b of the wave plate 23 and becomes the reference light Lr that proceeds to the second side.

[0042] The outgoing light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG, and is further reflected by the target TG to become the target reflected light Ltr traveling in the direction returning to the beam scanner 26. The target reflected light Ltr is circularly polarized light like the outgoing light Lp, but its rotation direction is opposite to that of the outgoing light Lp. Due to the scanning of the beam scanner 26, the outgoing light Lp is sequentially reflected by each part of the target TG in the expanded area.

[0043] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 bypasses the optical path length compensation element 25 and enters the coat 24. The target reflected light Ltr that has entered the coat 24 is combined with the reference light Lr that is generated when the output light Lp is reflected by the surface 24a of the coat 24, to become the first beam Lb1 of the interference light Lb. The first beam Lb1 transmits through the coat 24 and then through the wave plate 23.

[0044] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 passes through the optical path length compensation element 25, bypasses the coat 24, and enters the wave plate 23. The target reflected light Ltr that has entered the wave plate 23 is combined with the reference light Lr generated when the output light Lp is reflected by the surface 24b of the wave plate 23 to become the second beam Lb2 of the interference light Lb, and passes through the wave plate 23.

[0045] The polarization state of the first beam Lb1 and the second beam Lb2 transmitted through the wave plate 23 is changed from circular polarization to linear polarization by the wave plate 23. The polarization direction Y2 of this linear polarization is a second direction that intersects (for example, is perpendicular to) the first direction described above, as shown in FIG. 3. Therefore, the first beam Lb1 and the second beam Lb2 are reflected by the polarizing beam splitter 22 in the direction of the light receiving lens 27, which is different from the direction of the light source 1. Then, the first beam Lb1 and the second beam Lb2 are focused by the light receiving lens 27 onto the first photodetector 3a and the second photodetector 3b, respectively.

[0046] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. The optical path difference between the reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2 until they leave the wave plate 23 toward the polarizing beam splitter 22 is 2×n1×t1=m×λ / 4. This is because, as shown in FIG. 3, the optical path of the reference light Lr of the first beam Lb1 is longer than the optical path of the reference light Lr of the second beam Lb2 by the amount of travel back and forth within the coat 24. The optical path of the reference light Lr also includes the optical path when it was the output light Lp.

[0047] There is no optical path difference between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2 until they exit the wave plate 23 toward the polarizing beam splitter 22. This is because the change in optical path length caused by the target reflected light Ltr in the first beam Lb1 passing through the coat 24 is compensated for by the optical path length compensation element 25 through which the target reflected light Ltr in the second beam Lb2 passes.

[0048] In this way, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 (i.e., the first phase difference) is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2 (i.e., the second phase difference). That is, the target reflected light Ltr and the reference light Lr are split into the first beam Lb1 and the second beam Lb2, and only the reference light Lr has a phase difference of π / 2 between the first beam Lb1 and the second beam Lb2. Then, each reference light Lr interferes with the target reflected light Ltr in the same beam, and the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal are formed.

[0049] Here, the signal intensity of the target reflected light Ltr in the first beam Lb1 and the second beam Lb2 expressed as a function of time t is expressed as E s The signal intensity of the reference light Lr in the first beam Lb1 expressed as a function of time t is denoted as E r_I (t), and the signal intensity of the reference light Lr in the second beam Lb2 expressed as a function of time t is Er_Q (t), the following equation holds:

[0050]

number

[0051]

number

[0052] [1] As described above, in this embodiment, the thickness forming component is disposed between the polarizing beam splitter 22 and the target TG in the path of the output light Lp, and has a thickness along the traveling direction of the target reflected light Ltr and the reference light Lr such that the first phase difference and the second phase difference are different. In this embodiment, the thickness forming component is the coat 24.

[0053] In this way, in the optical system 2, the thickness of the thickness forming component along the traveling direction of the target reflected light Ltr or the reference light Lr is adjusted according to the relationship with the refractive index, thereby providing the difference between the first phase difference and the second phase difference required to acquire the IQ signal. This reduces the number of components in the optical system, and thus reduces the complexity of the optical system.

[0054] [2] Specifically, a difference in optical path length occurs between a portion of the reference light Lr constituting the first beam Lb1 and a portion of the reference light Lr constituting the second beam Lb2 when the reference light Lr passes through the coat 24. In this manner, a difference between the first phase difference and the second phase difference can be created by adjusting the optical path length of the reference light Lr.

[0055] [3] Furthermore, reference light Lr constituting the first beam Lb1 is generated by reflection of another part of the output light Lp on the first side surface 24a of the coating 24. The thickness of the coating 24 at the position through which the reference light Lr constituting the first beam Lb1 passes is different from the thickness of the coating at the position through which the reference light Lr constituting the second beam passes.

[0056] Specifically, in this embodiment, the thickness t1 of the coating 24 at the position through which the reference light Lr constituting the first beam Lb1 passes is greater than 0, and the thickness of the coating 24 at the position through which the reference light Lr constituting the second beam Lb2 passes is 0. In other words, the coating 24 is not present at the position through which the reference light Lr constituting the second beam Lb2 passes.

[0057] Thereby, the coating 24 makes a first phase difference, which is a phase difference between the target reflected light Ltr and the reference light Lr in the first beam Lb1, different from a second phase difference, which is a phase difference between the target reflected light Ltr and the reference light Lr in the second beam Lb2. In this way, an IQ signal can be acquired with a simple configuration of the coating 24 covering the wave plate 23.

[0058] [4] In addition, the optical path length compensation element 25 is disposed at a position through which the target reflected light Ltr passes but the reference light Lr does not pass, so as to reduce and eliminate the phase difference between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2. Specifically, the optical path length compensation element 25 is disposed at a position through which the target reflected light Ltr constituting the second beam Lb2 passes. In this way, the phase difference of the target reflected light Ltr between the first beam Lb1 and the second beam Lb2 can be adjusted independently of the reference light Lr.

[0059]

[20] The optical path length compensation element 25 is disposed on the first side of the wave plate 23 and at a position where the target reflected light Ltr is parallel. In this position, the phase difference of the target reflected light Ltr can be stably adjusted.

[0060] Second embodiment Next, the second embodiment will be described with reference to Fig. 4 and Fig. 5. As shown in Fig. 4, the present embodiment is different from the first embodiment in that the optical path length compensation element 25 is omitted and the configuration of the coating 24 is different. The coating 24 of the present embodiment is different from the first embodiment in either or both of the thickness t1 and the refractive index n1, but the other configurations (e.g., the arrangement with respect to the wave plate 23) are the same as those of the first embodiment.

[0061] The optical path length compensation element 25 is provided in the first embodiment in order to obtain the desired IQ signal according to the phase difference of the target reflected light Ltr that occurs depending on the presence or absence of the coating 24 on the wave plate 23 in the first beam Lb1 and the second beam Lb2.

[0062] A phase difference occurs in the output light Lp as well as in the target reflected light Ltr due to the presence or absence of the coating 24. However, when the output light Lp is reflected and diffused by the target TG and returns to the optical system 2, the target reflected light Ltr is a mixture of two types of light: light that is time-delayed by the thickness of the coating 24 and light that is not delayed. If the thickness of the coating 24 is approximately the reference wavelength λ (for example, 10 times or less the reference wavelength λ), the time delay and the resulting distance difference are very small, and are sufficiently smaller than the measurement resolution of the first photodetector 3a, the second photodetector 3b, and the processing circuit 4 and can be ignored. Therefore, the effect of the phase difference in the output light Lp heading toward the target TG can be ignored.

[0063] In order to generate an appropriate IQ signal, a phase difference of π / 2 is required between the I signal and the Q signal. However, it is not limited to strict π / 2, and it may deviate from π / 2 within a range in which an IQ signal can be obtained. This is not limited to this embodiment, but is similar throughout this specification. In the first embodiment, an example in which two reference lights Lr with different phases are generated to achieve this has been described. However, in order to generate an IQ signal, a phase difference of π / 2 may be provided between the target reflected lights Ltr, and more specifically, a phase difference of π / 2 may be provided in total between the reference lights Lr and the target reflected lights Ltr.

[0064] In other words, if the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 relative to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2, an appropriate IQ signal can be generated.

[0065] Based on this, in this embodiment, the thickness t1 and the refractive index n1 of the coating 24 are set to satisfy m×λ / 4=(n1+nair)×t1. This is because, as shown in Fig. 5, in the first beam Lb1, the reference light Lr passes through the coating 24 twice, and the target reflected light Ltr in the first beam Lb1 passes through the coating 24 only once.

[0066] That is, due to the coating 24, the optical path difference of the reference light Lr in the first beam Lb1 differs from that of the second beam Lb2 by 2×n1×t1, and the optical path difference of the target reflected light Ltr differs by (n1-nair)×t1. Therefore, the presence of the coating 24 alone can cause the phase difference between the reference light Lr and the target reflected light Ltr to differ by (n1+nair)×t1 between the first beam Lb1 and the second beam Lb2. Specifically, in this embodiment, the phase difference between the reference light Lr and the target reflected light Ltr differs by m×λ / 4 between the first beam Lb1 and the second beam Lb2. In this embodiment, the coating 24 constitutes a thickness forming component.

[0067] The operation of the LiDAR transceiver in this embodiment will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as in the first embodiment.

[0068] The output light Lp passes through the polarizing beam splitter 22 and enters the wave plate 23. In the region of the first beam Lb1, the output light Lp passes through the wave plate 23 and then enters the coat 24, a part of which passes through the coat 24 and heads toward the beam scanner 26, and another part is reflected by the surface 24a of the coat 24 to become the reference light Lr. In the region of the second beam Lb2, a part of the output light Lp passes through the wave plate 23 and then heads toward the beam scanner 26, and another part is reflected by the surface 23b of the wave plate 23 to become the reference light Lr.

[0069] The emitted light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the first embodiment, and is reflected by the target TG and is reflected by the beam scanner 26 as target reflected light Ltr.

[0070] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 enters the coat 24 and is combined with the reference light Lr to become the first beam Lb1 of the interference light Lb. Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 bypasses the coat 24 and enters the wave plate 23, where it is combined with the reference light Lr to become the second beam Lb2 of the interference light Lb. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as in the first embodiment.

[0071] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. As described above, the phase difference between the reference light Lr and the target reflected light Ltr differs by m×λ / 4 between the first beam Lb1 and the second beam Lb2. In other words, the first phase difference and the second phase difference differ by m×λ / 4.

[0072] Therefore, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. In this manner, the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal are generated.

[0073] By utilizing such an IQ signal, the processing circuit 4 can determine the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, similarly to the first embodiment, thereby improving the accuracy of distance calculation and relative velocity calculation.

[0074] [1] As described above, the coating 24 is disposed only on the path through which the first beam Lb1 passes out of the path through which the first beam Lb1 passes and the path through which the second beam Lb2 passes. The coating 24 may or may not be disposed on other paths. If the thickness of the coating 24 is t1, the refractive index of the coating 24 is n1, an odd number is m, and the reference wavelength is λ, then the relationship m×λ / 4=n1×t1 is satisfied. In this way, an IQ signal can be obtained without the optical path length compensation element 25 as in the first embodiment. The same effect can be obtained from the same configuration in this embodiment and the first embodiment.

[0075] Third embodiment Next, a third embodiment will be described with reference to Fig. 6. In this embodiment, additional lenses 28 and 29 are provided in addition to the first embodiment. The other configurations are the same as those of the first embodiment. The additional lenses 28 and 29 as a whole constitute a lens combination for expanding or reducing the beam diameters of the output light Lp and the target reflected light Ltr.

[0076] The additional lenses 28 and 29 are disposed on the first side of each of the wave plate 23, the coating 24, and the optical path length compensation element 25, and are disposed between the wave plate 23, the coating 24, the optical path length compensation element 25, and the beam scanner 26. The additional lens 29 is disposed between the additional lens 28 and the beam scanner 26.

[0077] In this way, the output light Lp after passing through the wave plate 23, the coating 24, and the optical path length compensation element 25 is condensed by the additional lens 28, and then collimated again by the additional lens 29, and proceeds to the beam scanner 26. The beam diameter of the output light Lp after passing through the additional lens 29 is larger than the beam diameter of the output light Lp immediately before entering the additional lens 28.

[0078] Furthermore, the target reflected light Ltr after being reflected by the beam scanner 26 is condensed by the additional lens 29, and then collimated again by the additional lens 28, and proceeds to the wave plate 23, the coat 24, and the optical path length compensation element 25. The beam diameter of the target reflected light Ltr after passing through the additional lens 28 is smaller than the beam diameter of the target reflected light Ltr immediately before entering the additional lens 29.

[0079] The addition of the additional lenses 28 and 29 as in this embodiment may be performed on the second embodiment. The same effects can be obtained from the same configuration in this embodiment and in the first and second embodiments.

[0080] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Fig. 7. In this embodiment, the coating 24 is eliminated from the first embodiment, and the configuration of the wave plate 23 is changed. Specifically, the wave plate 23 has a base material 231 and a birefringent portion 232. The base material 231 is a plate-shaped member such as transparent glass arranged to face the output light Lp.

[0081] The birefringent portion 232 is a thin film formed by deposition or the like on the second side surface 23d of the base material 231, and realizes the function of the wave plate 23 as a λ / 4 wave plate by birefringing light passing through the birefringent portion 232. The birefringent portion 232 may be made of an organic material or an inorganic material.

[0082] In this embodiment, a treatment (for example, AR coating) for suppressing reflection of light is also applied to the interface between the substrate 231 and the birefringent portion 232. In this embodiment, a part of the output light Lp is reflected by the first side surface 23a of the substrate 231 to generate a reference light Lr constituting the first beam Lb1, and a part of the output light Lp is reflected by the first side surface 23b of the substrate 231 to generate a reference light Lr constituting the second beam Lb2. Of the surfaces on the first side of the substrate 231, the surface 23a is in an area through which the first beam Lb1 passes, and the surface 23b is in a position through which the second beam Lb2 passes.

[0083] The configuration of the base material 231 will be further described below. The refractive index ns1 of the base material 231 is different from the refractive index of air. In addition, the thickness ts1 of the base material 231 along the traveling direction of the first beam Lb1 at the position where the first beam Lb1 passes through is different from the thickness ts2 along the traveling direction of the second beam Lb2 at the position where the second beam Lb2 passes through. Specifically, the relationship m×λ / 4=2×ns1×|ts1-ts2| is satisfied. In addition, the thickness tc of the optical path length compensation element 25 along the traveling direction of the target reflected light Ltr passing therethrough, and the refractive index nc of the optical path length compensation element 25 satisfy (ns1-nair)×|ts1-ts2|=(nc-nair)×tc. In this embodiment, the thickness ts1 is greater than the thickness ts2.

[0084] The operation of the LiDAR transceiver configured as above will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as those in the first embodiment.

[0085] The output light Lp passes through the polarizing beam splitter 22 and further enters the wave plate 23. A part of the output light Lp that has entered the wave plate 23 passes through the wave plate 23 and proceeds toward the first side. Another part of the output light Lp that has entered the wave plate 23 becomes reference light Lr that is reflected by the surfaces 23a and 23b on the first side of the base material 231 and proceeds toward the second side.

[0086] Specifically, a part of the output light Lp that passes through the region of the first beam Lb1 passes through the wave plate 23 and proceeds toward the beam scanner 26. Another part of the output light Lp that passes through the region of the first beam Lb1 becomes the reference light Lr that is reflected by the first surface 23a of the wave plate 23 and proceeds toward the second side.

[0087] A part of the output light Lp that has passed through the region of the second beam Lb2 passes through the wave plate 23, then passes through the optical path length compensation element 25 and proceeds to the beam scanner 26. Another part of the output light Lp in the region of the second beam Lb2 is reflected by the first surface 23b of the wave plate 23 and becomes the reference light Lr that proceeds to the second side.

[0088] The output light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the first embodiment, and is reflected by the target TG and is reflected as target reflected light Ltr by the beam scanner 26. Furthermore, a portion of the target reflected light Ltr that becomes the first beam Lb1 bypasses the optical path length compensation element 25 and enters the wave plate 23, and a portion that becomes the second beam Lb2 passes through the optical path length compensation element 25 and enters the wave plate 23.

[0089] The target reflected light Ltr that has entered the wave plate 23 interferes with the reference light Lr to form an interference light Lb that includes a first beam Lb1 and a second beam Lb2. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as those in the first embodiment.

[0090] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. The reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2 have an optical path difference of m×λ / 4 until they exit the wave plate 23 toward the polarizing beam splitter 22.

[0091] This is because the optical path of the reference light Lr travels back and forth within the substrate 231 of the wave plate 23, but since the thickness of the substrate 231 differs by ts1-ts2 between the region of the first beam Lb1 and the region of the second beam Lb2, the optical path length also differs by 2×ns1×|ts1-ts2|.

[0092] There is no difference in the optical paths between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2 until they exit the wave plate 23 toward the polarizing beam splitter 22. This is because the optical path length compensation element 25 compensates for the difference in optical path length caused by the difference in thickness of the base material 231.

[0093] In this way, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. That is, the target reflected light Ltr and the reference light Lr are split into the first beam Lb1 and the second beam Lb2, and only the reference light Lr has a phase difference of π / 2 between the first beam Lb1 and the second beam Lb2. Then, each reference light Lr interferes with the target reflected light Ltr in the same beam, and the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal are generated.

[0094] By utilizing such an IQ signal, the processing circuit 4 can identify the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, as in the first embodiment. This improves the accuracy of distance calculation and relative velocity calculation.

[0095] [1] As described above, the reference light Lr is generated by reflection of another part of the output light Lp at the first side surfaces 23a, 23b of the wave plate 23. Then, the first phase difference and the second phase difference are different because the optical path length when the reference light Lr constituting the first beam Lb1 passes through the wave plate 23 is different from the optical path length when the reference light Lr constituting the second beam Lb2 passes through the wave plate 23. In this way, an IQ signal can be obtained by utilizing the difference in the optical path length of the wave plate 23 itself.

[0096] The modification of the first embodiment as in this embodiment can also be applied to the second embodiment. In this case, however, since there is no optical path length compensation element 25, the relationship m×λ / 4=(ns1+nair)×|ts1-ts2| is satisfied instead of the relationship m×λ / 4=2×ns1×|ts1-ts2|.

[0097] Moreover, the modifications made to the first embodiment as in this embodiment can also be applied to the third embodiment. The same effects can be obtained from the same configurations in this embodiment and the first to third embodiments.

[0098] Fifth embodiment Next, a fifth embodiment will be described with reference to Figs. 8 and 9. In this embodiment, a substrate 30 is added and the arrangement of the coating 24 is changed compared to the first embodiment. In this embodiment, the substrate 30 and the coating 24 form a surface reflective optical element. Also, in this embodiment, the surface reflective optical element and the optical path length compensation element 25 form a thickness forming component.

[0099] The substrate 30 is a transparent plate such as glass that is disposed on a first side of the wave plate 23 across a gap, and is disposed on a second side of the optical path length compensation element 25 and the beam scanner 26 .

[0100] 9, the coat 24 is applied to the surface 30a so as to cover the entire surface 30a of the first side of the substrate 30, which corresponds to the path through which the target reflected light Ltr constituting the first beam Lb1 passes. The coat 24 is also formed so as not to cover the surface 30b of the first side of the substrate 30, which corresponds to the path through which the target reflected light Ltr constituting the second beam Lb2 passes.

[0101] Here, the portion of the reference light Lr that constitutes the first beam Lb1 is generated when the output light Lp passes through the wave plate 23, the substrate 30, and the coating 24, and is reflected at the first surface 24a of the coating 24. Also, the portion of the reference light Lr that constitutes the second beam Lb2 is generated when the output light Lp passes through the wave plate 23 and the substrate 30, and is reflected at the first surface 30b of the substrate.

[0102] The first side surface of the wave plate 23, the second side surface of the wave plate 23, the second side surface of the substrate 30, the interface between the substrate 30 and the coating 24, and the first and second side surfaces of the optical path length compensation element 25 are treated to suppress light reflection (e.g., AR coating treatment).

[0103] Furthermore, the thickness t1 of the coating 24 along the traveling direction of the first beam Lb1 and the refractive index n1 of the coating 24 are the same as those in the first embodiment. The thickness t1 of the coating 24 can be controlled with high precision by deposition techniques such as an anti-reflection coating or a dielectric multilayer coating.

[0104] The operation of the LiDAR transceiver in this embodiment will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as in the first embodiment.

[0105] The output light Lp passes through the polarizing beam splitter 22 and the wave plate 23, and then enters the substrate 30. In the region of the first beam Lb1, the output light Lp passes through the substrate 30 and then enters the coating 24, a portion of which passes through the coating 24 and heads toward the beam scanner 26, and another portion is reflected by the surface 24a of the coating 24 to become the reference light Lr. In the region of the second beam Lb2, a portion of the output light Lp passes through the substrate 30 and then transmits through the optical path length compensation element 25 to head toward the beam scanner 26, and another portion is reflected by the surface 30b of the substrate 30 to become the reference light Lr.

[0106] The emitted light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the first embodiment, and is reflected by the target TG and is reflected by the beam scanner 26 as target reflected light Ltr.

[0107] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 bypasses the optical path length compensation element 25 and enters the coat 24. The target reflected light Ltr that entered the coat 24 is combined with the reference light Lr generated when the output light Lp is reflected by the surface 24a of the coat 24, to become the first beam Lb1 of the interference light Lb. After transmitting through the coat 24, the first beam Lb1 transmits through the substrate 30 and the wave plate 23.

[0108] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 passes through the optical path length compensation element 25, bypasses the coat 24, and enters the substrate 30. The target reflected light Ltr that entered the substrate 30 is combined with reference light Lr generated when the output light Lp is reflected by the surface 30b of the substrate 30 to become the second beam Lb2 of the interference light Lb, which passes through the substrate 30 and the wave plate 23. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as those in the first embodiment.

[0109] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. The optical path difference between the reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2 until they leave the wave plate 23 toward the polarizing beam splitter 22 is m×λ / 4. This is because, as shown in FIG. 9, the optical path of the reference light Lr of the first beam Lb1 is longer than the optical path of the reference light Lr of the second beam Lb2 by the amount of travel back and forth within the coat 24.

[0110] There is no optical path difference between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2 until they exit the wave plate 23 toward the polarizing beam splitter 22. This is because the change in optical path length caused by the target reflected light Ltr in the first beam Lb1 passing through the coat 24 is compensated for by the optical path length compensation element 25 through which the target reflected light Ltr in the second beam Lb2 passes.

[0111] In this way, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. That is, the target reflected light Ltr and the reference light Lr are split into the first beam Lb1 and the second beam Lb2, and only the reference light Lr has a phase difference of π / 2 between the first beam Lb1 and the second beam Lb2. Then, each reference light Lr interferes with the target reflected light Ltr in the same beam, and the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal are generated.

[0112] By utilizing such an IQ signal, the processing circuit 4 can determine the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, similarly to the first embodiment, thereby improving the accuracy of distance calculation and relative velocity calculation.

[0113] As another example of this embodiment, the coating 24 may be disposed on the second side of the substrate 30 instead of the first side. In this case, a portion of the emitted light Lp is reflected by the first side surface of the coating 24 to generate the reference light Lr. Alternatively, the coating 24 may be disposed on both the first and second sides of the substrate 30. In this case, a portion of the emitted light Lp is reflected by the first side surface of the coating 24 on the first side of the substrate 30 to generate the reference light Lr.

[0114] [1] As described above, the output light Lp is reflected by the first side surfaces 24a and 30b of the surface reflection optical element provided on the first side of the wave plate 23 with a gap between them, thereby generating the reference light Lr. In addition, the first phase difference and the second phase difference are different because the optical path length when the reference light Lr constituting the first beam Lb1 passes through the surface reflection optical element is different from the optical path length when the reference light Lr constituting the second beam Lb2 passes through the surface reflection optical element. In this way, the IQ signal can be obtained with a simple configuration by disposing the surface reflection optical element that generates the reference light Lr at a position away from the wave plate 23 and providing it with a function of adjusting the phase difference.

[0115] [2] The surface reflective optical element has a substrate 30 and a coating 24 that covers one or both of a first side surface and a second side surface of the substrate 30. A reference light Lr is generated by reflection at a first side surface 24a of the coating 24. The first phase difference and the second phase difference are different because the thickness of the coating 24 at the position where the reference light Lr constituting the first beam Lb1 passes through is different from the thickness of the coating 24 at the position where the reference light Lr constituting the second beam Lb2 passes through.

[0116] Specifically, in this embodiment, the thickness t1 of the coating 24 at the position through which the reference light Lr constituting the first beam Lb1 passes is greater than zero, and the thickness of the coating 24 at the position through which the reference light Lr constituting the second beam Lb2 passes is 0. In other words, the coating 24 is not present at the position through which the reference light Lr constituting the second beam Lb2 passes.

[0117] Thereby, the coating 24 makes a first phase difference, which is a phase difference between the target reflected light Ltr and the reference light Lr in the first beam Lb1, different from a second phase difference, which is a phase difference between the target reflected light Ltr and the reference light Lr in the second beam Lb2. In this way, an IQ signal can be acquired with a simple configuration of the coating 24 covering the wave plate 23.

[0118] [3] The surface reflective optical element is disposed on the first side of the wave plate 23 and at a position where the target reflected light Ltr is parallel light. In this position, the surface reflective optical element can adjust the phases of the target reflected light Ltr and the reference light Lr.

[0119] The changes made to the first embodiment as in this embodiment can also be applied to the second embodiment. In that case, however, since there is no optical path length compensation element 25, the refractive index n1 and thickness t1 of the coat 24 are the same as those in the second embodiment. Also, the same effects can be obtained from the same configuration in this embodiment as in the first and second embodiments.

[0120] Sixth embodiment Next, a sixth embodiment will be described with reference to Fig. 10. In this embodiment, the coat 24 is eliminated from the fifth embodiment, and the configuration of the substrate 30 is changed.

[0121] Specifically, the refractive index ns1 of the substrate 30 is different from the refractive index of air. Also, the thickness ts1 of the substrate 30 along the traveling direction of the first beam Lb1 at the position where the first beam Lb1 passes through is different from the thickness ts2 of the substrate 30 along the traveling direction of the second beam Lb2 at the position where the second beam Lb2 passes through. Specifically, the relationship m×λ / 4=2×ns1×|ts1-ts2| is satisfied. Also, the thickness tc of the optical path length compensation element 25 along the traveling direction of the target reflected light Ltr passing therethrough and the refractive index nc of the optical path length compensation element 25 satisfy (ns1-nair)×|ts1-ts2|=(nc-nair)×tc. In this embodiment, the thickness ts1 is greater than the thickness ts2.

[0122] The operation of the LiDAR transceiver configured as above will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as those in the fifth embodiment.

[0123] The output light Lp passes through the polarizing beam splitter 22 and the wave plate 23, and then enters the substrate 30. In the region of the first beam Lb1, after the output light Lp enters the substrate 30, a part of the output light Lp passes through a surface 30a on the first side of the substrate 30 that is located on the path of the first beam Lb1, and travels toward the beam scanner 26, and another part of the output light Lp is reflected by the surface 30a to become the reference light Lr. In the region of the second beam Lb2, after the output light Lp enters the substrate 30, a part of the output light Lp passes through a surface 30b on the first side of the substrate 30 that is located on the path of the second beam Lb2, and then passes through the optical path length compensation element 25 to become the beam scanner 26. Then, another part of the output light Lp is reflected by the surface 30b to become the reference light Lr.

[0124] The emitted light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the fifth embodiment, and is reflected by the target TG and is reflected by the beam scanner 26 as target reflected light Ltr.

[0125] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 bypasses the optical path length compensation element 25 and enters the substrate 30. The target reflected light Ltr that entered the substrate 30 is combined with the reference light Lr generated when the output light Lp is reflected by the surface 30a of the substrate 30 to become the first beam Lb1 of the interference light Lb. The first beam Lb1 passes through the substrate 30 and the wave plate 23.

[0126] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 passes through the optical path length compensation element 25 and enters the substrate 30. The target reflected light Ltr that entered the substrate 30 is combined with reference light Lr generated when the output light Lp is reflected by the surface 30b of the substrate 30 to become the second beam Lb2 of the interference light Lb, which passes through the substrate 30 and the wave plate 23. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as those in the fifth embodiment.

[0127] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. The reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2 have an optical path difference of m×λ / 4 until they exit the wave plate 23 toward the polarizing beam splitter 22.

[0128] This is because, as shown in Figure 10, the optical path of the reference light Lr travels back and forth within the substrate 30, but the thickness of the substrate 30 differs by ts1-ts2 between the region of the first beam Lb1 and the region of the second beam Lb2, and therefore the optical path length also differs by 2 × ns1 × |ts1-ts2|.

[0129] There is no difference in the optical paths between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2 until they exit the wave plate 23 and head toward the polarizing beam splitter 22. This is because the optical path length compensation element 25 compensates for the difference in optical path length caused by the difference in thickness of the base material 30.

[0130] In this way, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. That is, the target reflected light Ltr and the reference light Lr are split into the first beam Lb1 and the second beam Lb2, and only the reference light Lr has a phase difference of π / 2 between the first beam Lb1 and the second beam Lb2. Then, each reference light Lr interferes with the target reflected light Ltr in the same beam, forming the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal.

[0131] By utilizing such an IQ signal, the processing circuit 4 can identify the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, as in the fifth embodiment, thereby improving the accuracy of distance calculation and relative velocity calculation.

[0132] [1] In addition, in this embodiment, when the reference light Lr passes through the surface reflective optical element, which is a thickness forming component, a difference in optical path length occurs between the part of the reference light Lr that constitutes the first beam Lb1 and the part that constitutes the second beam Lb2.

[0133] [2] Furthermore, the first phase difference and the second phase difference are different because the thickness ts1 of the surface reflective optical element at the position where the reference light Lr constituting the first beam Lb1 passes and the thickness ts2 of the surface reflective optical element at the position where the reference light Lr constituting the second beam Lb2 passes are different.

[0134] Note that this embodiment may be modified to eliminate the optical path length compensation element 25 as in the second embodiment. In that case, however, the base material 30 is configured so that the relationship m×λ / 4=(ns1+nair)×|ts1-ts2| is satisfied instead of the relationship m×λ / 4=2×ns1×|ts1-ts2|.

[0135] Seventh embodiment Next, the seventh embodiment will be described with reference to Figs. 11 and 12. This embodiment differs from the fifth embodiment in the position where the output light Lp is reflected to generate the reference light Lr. Furthermore, the optical path length compensation element 25 is eliminated from the fifth embodiment. In this embodiment, the base material 30 and the coat 24 constitute a phase difference generating element, not a surface reflection optical element. In this embodiment, the phase difference generating element corresponds to a thickness forming component. In addition, the coat 24 of this embodiment differs from the first embodiment in either or both of the thickness t1 and the refractive index n1.

[0136] First, in this embodiment, the output light Lp is reflected by the first side surfaces 23a and 23b of the wave plate 23, thereby generating the reference light Lr. For this reason, in this embodiment, a treatment (for example, an AR coating treatment) for suppressing light reflection is applied to the second side surface of the wave plate 23, the first and second side surfaces of the substrate 30, and the first and second side surfaces of the coating 24.

[0137] In this embodiment, the thickness t1 and the refractive index n1 of the coating 24 are set to satisfy m×λ / 4=(n1-nair)×t1. This is because, as shown in Fig. 12, a portion of the target reflected light Ltr constituting the first beam Lb1 passes through the coating 24 once, and a portion of the target reflected light Ltr constituting the second beam Lb2 does not pass through the coating 24. In this embodiment, since neither the reference light Lr constituting the first beam Lb1 nor the reference light Lr constituting the second beam Lb2 passes through the coating 24, no optical path difference occurs between these two reference lights.

[0138] The operation of the LiDAR transceiver in this embodiment will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as those in the fifth embodiment.

[0139] The output light Lp passes through the polarizing beam splitter 22 and enters the wave plate 23, a part of which passes through the wave plate 23 and proceeds to the side of the surface reflection optical element composed of the substrate 30 and the coating 24, and another part of which is reflected by the first surfaces 23a and 23b of the wave plate 23 to become the reference light Lr. The output light Lp further passes through the phase difference generating element and proceeds to the beam scanner 26.

[0140] The emitted light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the fifth embodiment, and is reflected by the target TG and is reflected by the beam scanner 26 as target reflected light Ltr.

[0141] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 passes through the coating 24 and the substrate 30, and enters the wave plate 23. Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 bypasses the coating 24, passes through the substrate 30, and enters the wave plate 23.

[0142] The target reflected light Ltr that enters the wave plate 23 is combined with the reference light Lr that is generated when the output light Lp is reflected by the surfaces 23a and 23b to become the first beam Lb1 and the second beam Lb2 of the interference light Lb. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as those in the fifth embodiment.

[0143] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. There is no phase difference between the reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2. However, between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2, the optical path difference until leaving the wave plate 23 toward the polarizing beam splitter 22 is (n1-nair)×t1=m×λ / 4. This is because, as shown in FIG. 12, the optical path of the target reflected light Ltr of the first beam Lb1 is different from the optical path of the target reflected light Ltr of the second beam Lb2 by the amount of passing through the coat 24.

[0144] As a result, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. This causes each reference light Lr to interfere with the target reflected light Ltr in the same beam, generating the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal.

[0145] By utilizing such an IQ signal, the processing circuit 4 can identify the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, as in the fifth embodiment, thereby improving the accuracy of distance calculation and relative velocity calculation.

[0146] [1] As described above, the phase difference generating element includes the substrate 30 and the coating 24. Another part of the output light Lp is reflected on the second side of the phase difference generating element to generate the reference light Lr. Specifically, the reference light Lr is generated by reflection on the surfaces 23a and 23b on the first side of the wave plate 23.

[0147] When the target reflected light Ltr passes through the phase difference generating element, a phase difference occurs between a portion of the target reflected light Ltr constituting the first beam Lb1 and a portion of the target reflected light Ltr constituting the second beam Lb2. This causes the first phase difference and the second phase difference to differ. In this way, it is also possible to separate the phase difference generating element, which is a member for making the phase difference between the target reflected light Ltr and the reference light Lr different between the first beam Lb1 and the second beam Lb2, from the wave plate 23, which is a member for generating the reference light Lr.

[0148] [2] In addition, the first phase difference and the second phase difference are different because the thickness of the coating 24 at the position where the target reflected light Ltr constituting the first beam Lb1 passes through is different from the thickness of the coating 24 at the position where the target reflected light Ltr constituting the second beam Lb2 passes through. In this way, by adjusting the thickness of the coating 24, it is possible to easily obtain an IQ signal.

[0149] [3] The phase difference generating element is disposed on the first side of the wave plate 23 and at a position where the target reflected light Ltr is parallel light. In such a position, the phase difference generating element can stably adjust the phase of the target reflected light Ltr.

[0150] It is noted that, in other embodiments of this embodiment, coating 24 may be disposed on the second side of substrate 30 rather than the first side, or coating 24 may be disposed on both the first and second sides of substrate 30.

[0151] As another example of this embodiment, instead of the wavelength plate 23 generating the reference light Lr by reflection, a component that generates the reference light Lr by reflection may be disposed between the wavelength plate 23 and the phase difference generating element.

[0152] As another example of this embodiment, the output light Lp may be reflected between the first surface of the wave plate 23 and the phase difference generating element to generate the reference light Lr, instead of being reflected by the first surface of the wave plate 23. For example, a member that transmits part of the output light Lp and reflects the other part to generate the reference light Lr may be disposed between the wave plate 23 and the phase difference generating element. That is, it is sufficient that the reference light Lr is reflected on the second side of the phase difference generating element to generate the reference light. Note that the same effects can be obtained from the same configuration in this embodiment and the first to fifth embodiments.

[0153] Eighth embodiment Next, an eighth embodiment will be described with reference to Fig. 13. In this embodiment, the coat 24 is eliminated and the configuration of the substrate 30 is changed from that of the seventh embodiment.

[0154] Specifically, the refractive index ns1 of the substrate 30 is different from the refractive index of air. Also, the thickness ts1 of the substrate 30 along the traveling direction of the first beam Lb1 at a position where the substrate 30 passes the first beam Lb1 is different from the thickness ts2 of the substrate 30 along the traveling direction of the second beam Lb2 at a position where the substrate 30 passes the second beam Lb2. Specifically, the relationship m×λ / 4=(ns1−nair)×|ts1−ts2| is satisfied. In this embodiment, the thickness ts1 is greater than the thickness ts2. The operation of the LiDAR transceiver in this embodiment will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as those in the seventh embodiment.

[0155] The output light Lp passes through the polarizing beam splitter 22 and enters the wave plate 23, a part of which passes through the wave plate 23 and proceeds to the side of the phase difference generating element formed by the base material 30, and another part of which is reflected by the first surfaces 23a and 23b of the wave plate 23 to become the reference light Lr. The output light Lp further passes through the phase difference generating element and proceeds to the beam scanner 26.

[0156] The emitted light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the seventh embodiment, and is reflected by the target TG and is reflected by the beam scanner 26 as target reflected light Ltr.

[0157] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 passes through a portion of the base material 30 with a thickness ts1 and enters the wave plate 23. Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 passes through a portion of the base material 30 with a thickness ts2 and enters the wave plate 23.

[0158] The target reflected light Ltr that enters the wave plate 23 is combined with the reference light Lr that is generated when the output light Lp is reflected by the surfaces 23a and 23b to become the first beam Lb1 and the second beam Lb2 of the interference light Lb. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as those in the seventh embodiment.

[0159] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. There is no phase difference between the reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2. However, between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2, there is an optical path difference of m×λ / 4 until the target reflected light Ltr leaves the wave plate 23 toward the polarizing beam splitter 22. This is because, as shown in FIG. 13, the optical path of the target reflected light Ltr of the first beam Lb1 is longer than the optical path of the target reflected light Ltr of the second beam Lb2 by (n1-nair)×(ts1-ts2) through the substrate 30.

[0160] As a result, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. This causes each reference light Lr to interfere with the target reflected light Ltr in the same beam, generating the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal.

[0161] By utilizing such an IQ signal, the processing circuit 4 can identify the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, as in the seventh embodiment, thereby improving the accuracy of distance calculation and relative velocity calculation.

[0162] [1] In addition, the thickness of the substrate 30 at the position where the target reflected light Ltr constituting the first beam Lb1 passes is different from the thickness of the substrate 30 at the position where the target reflected light Ltr constituting the second beam Lb2 passes. In this way, the substrate 30 of the phase difference generating element makes the first phase difference and the second phase difference different from each other, so that an IQ signal can be easily obtained. Note that the same effect can be obtained from the same configuration in this embodiment and the seventh embodiment.

[0163] Ninth embodiment Next, the ninth embodiment will be described with reference to Fig. 14. This embodiment differs from the eighth embodiment in the configuration of the base material 30 constituting the phase difference generating element. Specifically, the base material 30 is disposed at a position through which the target reflected light Ltr constituting the first beam Lb1 passes, and is disposed to avoid a position through which the target reflected light Ltr constituting the second beam Lb2 passes.

[0164] The substrate 30 of this embodiment has a uniform thickness along the traveling direction of the target reflected light Ltr. Specifically, when the thickness of the substrate 30 is ts1, the refractive index of the substrate 30 is ns1, an odd number is m, and the reference wavelength is λ, the relationship m×λ / 4=(ns1−nair)×ts1 is satisfied.

[0165] The operation of the LiDAR transceiver in this embodiment will be described below. As described above, the light source 1 outputs an output light Lp having a frequency that increases or decreases with respect to the reference frequency. This output light is focused into a parallel beam by the collimator 21, and then enters the polarizing beam splitter 22. In this embodiment, the polarization states of the output light Lp, the target reflected light Ltr, and the reference light Lr are the same as those in the eighth embodiment.

[0166] The output light Lp passes through the polarizing beam splitter 22 and enters the wave plate 23, a part of which passes through the wave plate 23 and proceeds to the first side, and another part of which is reflected by the surfaces 23a and 23b on the first side of the wave plate 23 to become the reference light Lr. Furthermore, a part of the output light Lp passes through the substrate 30, and another part of which bypasses the substrate 30 and then travels toward the beam scanner 26.

[0167] The emitted light Lp heading toward the beam scanner 26 is reflected by the beam scanner 26 toward the target TG in the same manner as in the eighth embodiment, and is reflected by the target TG and is reflected by the beam scanner 26 as target reflected light Ltr.

[0168] Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the first beam Lb1 passes through the substrate 30 and enters the wave plate 23. Of the target reflected light Ltr reflected by the beam scanner 26, a portion constituting the second beam Lb2 bypasses the substrate 30 and enters the wave plate 23.

[0169] The target reflected light Ltr entering the wave plate 23 is combined with the reference light Lr generated when the output light Lp is reflected by the surfaces 23a and 23b to become the first beam Lb1 and the second beam Lb2 of the interference light Lb. The subsequent paths of the first beam Lb1 and the second beam Lb2 are the same as those in the eighth embodiment.

[0170] Here, the phases of the target reflected light Ltr and the reference light Lr in the first beam Lb1 and the second beam Lb2 will be described. There is no phase difference between the reference light Lr in the first beam Lb1 and the reference light Lr in the second beam Lb2. However, between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2, there is an optical path difference of (ns1-nair)×ts1=m×λ / 4 until the target reflected light Ltr leaves the wave plate 23 toward the polarizing beam splitter 22. This is because, as shown in FIG. 14, the optical path of the target reflected light Ltr of the first beam Lb1 is longer by (ns1-nair)×ts1 through the substrate 30 than the optical path of the target reflected light Ltr of the second beam Lb2 by the amount of the optical path passing through the substrate 30.

[0171] As a result, the phase difference between the reference light Lr and the target reflected light Ltr constituting the first beam Lb1 is shifted by π / 2 with respect to the phase difference between the reference light Lr and the target reflected light Ltr constituting the second beam Lb2. This causes each reference light Lr to interfere with the target reflected light Ltr in the same beam, generating the first beam Lb1 corresponding to the I signal and the second beam Lb2 corresponding to the Q signal.

[0172] By utilizing such an IQ signal, the processing circuit 4 can specify the instantaneous phase at a certain moment, including the direction of rotation, and can calculate the instantaneous frequency, as in the eighth embodiment. This improves the accuracy of distance and relative velocity calculation.

[0173]

[16] As described above, the phase difference generating element is arranged only on the path through which the first beam Lb1 passes among the paths through which the first beam Lb1 passes and the paths through which the second beam Lb2 passes, so that the first phase difference and the second phase difference are different. In this way, the IQ signal can be easily obtained by adjusting the thickness and arrangement of the phase difference generating element. Note that the same effect can be obtained from the same configuration in this embodiment and the eighth embodiment.

[0174] Tenth embodiment Next, the tenth embodiment will be described with reference to Fig. 15. In this embodiment, additional lenses 28 and 29 are provided in addition to the seventh embodiment. The other configurations are the same as those of the seventh embodiment. The additional lenses 28 and 29 as a whole constitute a combined lens for expanding or reducing the beam diameter of the output light Lp and the target reflected light Ltr.

[0175] The additional lenses 28 and 29 are disposed on the first side of the wave plate 23, and are disposed between the wave plate 23 and the phase difference generating element constituted by the substrate 30 and the coating 24. The additional lens 29 is disposed between the additional lens 28 and the phase difference generating element.

[0176] In this way, the output light Lp after passing through the wave plate 23 is condensed by the additional lens 28, and then collimated again by the additional lens 29 and proceeds to the phase difference generating element. The beam diameter of the output light Lp after passing through the additional lens 29 is larger than the beam diameter of the output light Lp immediately before entering the additional lens 28.

[0177] Furthermore, the target reflected light Ltr after being reflected by the beam scanner 26 passes through the phase difference generating element and is condensed by the additional lens 29, and then becomes parallel light again by the additional lens 28 and proceeds to the wave plate 23. The beam diameter of the target reflected light Ltr after passing through the additional lens 28 is smaller than the beam diameter of the target reflected light Ltr immediately before entering the additional lens 29.

[0178] The addition of the additional lenses 28 and 29 as in this embodiment may be performed in the eighth and ninth embodiments. The same effects can be obtained from the same configuration in this embodiment and the seventh to ninth embodiments.

[0179] (Other embodiments) The present invention is not limited to the above-described embodiment, and can be modified as appropriate. The above-described embodiments are not unrelated to each other, and can be combined as appropriate, except when the combination is clearly impossible. In the above-described embodiments, the elements constituting the embodiment are not necessarily essential, except when it is specifically stated that they are essential or when it is clearly considered essential in principle. In the above-described embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiment are mentioned, they are not limited to the specific numbers, except when it is specifically stated that they are essential or when it is clearly limited to a specific number in principle. In the above-described embodiments, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., except when it is specifically stated that they are essential or when it is clearly limited to a specific shape, positional relationship, etc. in principle. In addition, the present invention also allows the following modifications and modifications within an equivalent range to the above-described embodiments. The following modifications can be independently selected to be applied or not applied to the above-described embodiment. That is, any combination of the following modifications can be applied to the above-described embodiment.

[0180] (Variation 1) In the above embodiment, the optical system 2 has the collimator 21 and the beam scanner 26, but neither of these is essential. When the light source 1 emits the emitted light Lp as parallel light, the collimator 21 is not necessary. Also, when there is no need to scan the detection target, the beam scanner 26 is not necessary.

[0181] (Variation 2) In the above embodiment, the first photodetector 3a and the second photodetector 3b are used to receive the I signal and the Q signal by separate photodetectors. The first photodetector 3a and the second photodetector 3b each have a single structure. That is, each is composed of a single photodetector element. However, the first photodetector 3a and the second photodetector 3b may each have a multiple structure. For example, when a balanced photodetector is used, two photodetector elements are required for each of the I signal and the Q signal, and in that case, both the first photodetector 3a and the second photodetector 3b are composed of two photodetector elements.

[0182] In this case as well, the light-receiving lens 27 has the same number of lenses as the number of light-detecting elements that make up the first light detector 3 a and the second light detector 3 b. Alternatively, the light-receiving lens 27 may be a single lens array having the same number of lens shapes as the number of light-detecting elements that make up the first light detector 3 a and the second light detector 3 b.

[0183] (Variation 3) In the above embodiment, the light source 1 has one laser oscillator, but as another example, the light source 1 may have multiple laser oscillators. When multiple laser oscillators are used, the reference wavelengths of the laser oscillators may be the same or different. The light generated by the multiple laser oscillators may be coupled to a single waveguide using an optical waveguide and then emitted. In this case, the multiple laser oscillators may emit light simultaneously or at different times.

[0184] Furthermore, regardless of whether the wavelengths of the multiple laser oscillators are the same or not, the laser oscillators may be placed at different spatial positions. Alternatively, instead of arranging the multiple laser oscillators side by side, the multiple laser oscillators may be connected to different optical waveguides, and the connected optical waveguides may be placed at different positions. Alternatively, the emitted light from a single laser oscillator, instead of multiple laser oscillators, may be coupled to an optical waveguide, and the light may be branched into multiple waveguides and treated as multiple light sources.

[0185] (Variation 4) In the above embodiment, the optical path length compensation element 25 is used to eliminate the phase difference between the target reflected light Ltr in the first beam Lb1 and the target reflected light Ltr in the second beam Lb2, but instead of eliminating the phase difference, it is also possible to simply reduce the phase difference (for example, to 1 / 2, 1 / 3, or 2 / 3) compared to when there is no optical path length compensation element 25. It is sufficient that the phase difference between the target reflected light Ltr and the reference light Lr is different between the first beam Lb1 and the second beam Lb2 so that an IQ signal can be obtained overall.

[0186] (Variation 5) The thickness and refractive index of the thickness forming member in each of the above embodiments are uniform inside the thickness forming member unless otherwise specified, but in other examples, they do not necessarily have to be uniform. If they are not uniform, they represent the effective thickness and refractive index from the viewpoint of adjusting the optical path length of light passing through the inside in the thickness direction. [Explanation of symbols]

[0187] 1 light source 3a First photodetector 3b Second photodetector 22 Polarizing Beam Splitter 23 Wave plate 24 Court 25 Optical path length compensation element 30 Base material

Claims

1. A light source (1) that emits an emission light (Lp) that is frequency modulated with respect to light of a reference wavelength; a wave plate (23) that changes the polarization direction of the emitted light by passing the emitted light through a first side that is a side toward a target (TG) from the light source along a path of the emitted light, and changes the polarization direction of the interference light (Lb) by passing an interference light (Lb) including a target reflected light (Ltr) after a part of the emitted light is reflected by the target and a reference light (Lr) after another part of the emitted light is reflected before hitting the target, through a second side opposite to the first side; a polarizing beam splitter (22) disposed between the light source and the wave plate in a path of the emitted light, for outputting the emitted light to the wave plate according to a polarization state of the emitted light, and outputting the interference light in a direction different from a direction returning to the light source according to a polarization state of the interference light; a first photodetector (3a) for detecting a first beam included in the interference light after the first beam exits the polarizing beam splitter; a second photodetector (3b) for detecting a second beam included in the interference light after the second beam exits the polarizing beam splitter; The first beam and the second beam are translated at positions offset from each other, The LiDAR transceiver includes a thickness forming component (23, 24, 25, 30) that is arranged between the polarizing beam splitter and the target in the path of the emitted light, and has a thickness along the propagation direction of the target reflected light or the reference light that makes different a first phase difference, which is the phase difference between the target reflected light and the reference light in the first beam, and a second phase difference, which is the phase difference between the target reflected light and the reference light in the second beam.

2. The LiDAR transceiver of claim 1, wherein the thickness of the thickness forming part is configured so as to achieve either or both of the following: a difference in optical path length occurs between a portion of the reference light that constitutes the first beam and a portion of the reference light that constitutes the second beam when the reference light passes through the thickness forming part; and a difference in optical path length occurs between a portion of the target reflected light that constitutes the first beam and a portion of the target reflected light that constitutes the second beam when the target reflected light passes through the thickness forming part.

3. The thickness forming component includes a coating (24) attached to the first side surface of the wave plate; the reference light is generated by reflecting the other part of the emitted light at the first side surface of the coating; The LiDAR transceiver of claim 1, wherein the first phase difference and the second phase difference are different due to a difference between a thickness of the coating at a position where the reference light constituting the first beam passes and a thickness of the coating at a position where the reference light constituting the second beam passes.

4. The thickness forming component includes the wave plate, the reference light is generated by reflecting the other part of the emitted light at the first side surface of the wave plate; The LiDAR transceiver of claim 1, wherein the first phase difference and the second phase difference are different due to a difference between an optical path length when the reference light constituting the first beam passes through the wave plate and an optical path length when the reference light constituting the second beam passes through the wave plate.

5. The wave plate has a plate-shaped base material (231) and a birefringent portion (232) formed on the second side surface of the base material and birefringent the light passing therethrough, the reference light is generated by reflecting the other part of the emitted light on the first side surface of the base material; 5. The LiDAR transceiver of claim 4, wherein the first phase difference and the second phase difference are different due to a difference between an optical path length when the reference light constituting the first beam passes through the substrate and an optical path length when the reference light constituting the second beam passes through the substrate.

6. The thickness forming component includes a surface reflection optical element (30, 24) provided on the first side of the wave plate with a space between the wave plate and the surface reflection optical element (30, 24); the reference light is generated by reflecting the other part of the emitted light on the first side surface of the surface reflection optical element, The LiDAR transceiver of claim 1, wherein the first phase difference and the second phase difference are different due to a difference between an optical path length when the reference light constituting the first beam passes through the surface reflecting optical element and an optical path length when the reference light constituting the second beam passes through the surface reflecting optical element.

7. The surface reflective optical element has a substrate (30) and a coating (24) covering one or both of the first side surface and the second side surface of the substrate; the reference light is generated by reflecting the other part of the emitted light at the first side surface of the coating; The LiDAR transceiver of claim 6, wherein the first phase difference and the second phase difference are different due to a difference between a thickness of the coating at a position where the reference light constituting the first beam passes and a thickness of the coating at a position where the reference light constituting the second beam passes.

8. The LiDAR transceiver of claim 6, wherein the first phase difference and the second phase difference are different due to a difference between a thickness of the surface reflective optical element at a position through which the reference light constituting the first beam passes and a thickness of the surface reflective optical element at a position through which the reference light constituting the second beam passes.

9. the coating is disposed only on the path through which the first beam passes among a path through which the first beam passes and a path through which the second beam passes; A LiDAR transceiver as described in claim 3 or 7, wherein the relationship m×λ / 4=(n1+nair)×t1 is satisfied, where t1 is the thickness of the coating, n1 is the refractive index of the coating, m is an odd number, λ is the reference wavelength, and nair is the refractive index of air.

10. The LiDAR transceiver of claim 5, wherein the thickness of the substrate at the position where the first beam passes is ts1, the thickness of the substrate at the position where the second beam passes is ts2, the refractive index of the substrate is ns1, an odd number is m, the reference wavelength is λ, and the refractive index of air is nair, the relationship of m × λ / 4 = (ns1 + nair) × | ts1 - ts2 | is satisfied.

11. The LiDAR transceiver of claim 8, wherein the thickness of the surface reflective optical element at the position where the first beam passes is ts1, the thickness of the surface reflective optical element at the position where the second beam passes is ts2, the refractive index of the surface reflective optical element is ns1, an odd number is m, the reference wavelength is λ, and the refractive index of air is nair, the relationship m × λ / 4 = (ns1 + nair) × | ts1 - ts2 | is satisfied.

12. 2. The LiDAR transceiver of claim 1, wherein the thickness forming component includes an optical path length compensation element (25) positioned at a position through which the target reflected light passes and which the reference light does not pass, so as to reduce a phase difference between the target reflected light in the first beam and the target reflected light in the second beam.

13. the thickness forming component includes an optical path length compensation element (25) that is arranged at a position through which the target reflected light constituting the second beam passes but through which the reference light constituting the second beam does not pass, so as to cancel a phase difference between the target reflected light in the first beam and the target reflected light in the second beam; the coating is disposed only on a path through which the first beam passes among a path through which the first beam passes and a path through which the second beam passes of the interference light, A LiDAR transceiver as described in claim 3 or 7, wherein the relationship m×λ / 4=2×n1×t1 is satisfied, where t1 is the thickness of the coating, n1 is the refractive index of the coating, m is an odd number, and λ is the reference wavelength.

14. the thickness forming component includes an optical path length compensation element (25) that is arranged at a position through which the target reflected light constituting the second beam passes but through which the reference light constituting the second beam does not pass, so as to cancel a phase difference between the target reflected light in the first beam and the target reflected light in the second beam; The LiDAR transceiver of claim 5, wherein the thickness of the substrate at the position where the first beam passes is ts1, the thickness of the substrate at the position where the second beam passes is ts2, the refractive index of the substrate is ns1, m is an odd number, and the reference wavelength is λ, the relationship m×λ / 4=2×ns1×|ts1−ts2| is satisfied.

15. the thickness forming component includes an optical path length compensation element (25) that is arranged at a position through which the target reflected light constituting the second beam passes but through which the reference light constituting the second beam does not pass, so as to cancel a phase difference between the target reflected light in the first beam and the target reflected light in the second beam; The LiDAR transceiver of claim 8, wherein the thickness of the surface reflective optical element at the position where the first beam passes is ts1, the thickness of the surface reflective optical element at the position where the second beam passes is ts2, the refractive index of the surface reflective optical element is ns1, an odd number is m, and the reference wavelength is λ, and the relationship m×λ / 4=2×ns1×|ts1-ts2| is satisfied.

16. The thickness forming component includes a phase difference generating element (30, 24) provided on a first side of the wave plate, the other part of the emitted light is reflected on a second side of the phase difference generating element to generate the reference light, The LiDAR transceiver of claim 1, wherein when the target reflected light passes through the phase difference generating element, a phase difference occurs between a portion of the target reflected light that constitutes the first beam and a portion of the target reflected light that constitutes the second beam, such that the first phase difference and the second phase difference are different.

17. The phase difference generating element has a substrate (30) and a coating (24) that covers one or both of the first side surface and the second side surface of the substrate, 17. The LiDAR transceiver of claim 16, wherein the first phase difference and the second phase difference are different due to a difference between a thickness of the coating at a position through which the target reflected light constituting the first beam passes and a thickness of the coating at a position through which the target reflected light constituting the second beam passes.

18. The LiDAR transceiver of claim 16, wherein the first phase difference and the second phase difference are different due to a difference between a thickness of the phase difference generating element at a position through which the target reflected light constituting the first beam passes and a thickness of the phase difference generating element at a position through which the target reflected light constituting the second beam passes.

19. The LiDAR transceiver of claim 18, wherein the phase difference generating element is arranged only in the path through which the first beam passes, among the path through which the first beam passes and the path through which the second beam passes, thereby making the first phase difference and the second phase difference different.

20. the coating is disposed only on the path through which the first beam passes among a path through which the first beam passes and a path through which the second beam passes; 18. The LiDAR transceiver of claim 17, wherein the relationship m×λ / 4=(n1−nair)×t1 is satisfied, where t1 is the thickness of the coating, n1 is the refractive index of the coating, m is an odd number, λ is the reference wavelength, and nair is the refractive index of air.

21. The LiDAR transceiver of claim 18 or 19, wherein the thickness of the phase difference generating element at the position where the first beam passes is ts1, the thickness of the phase difference generating element at the position where the second beam passes is ts2, the refractive index of the phase difference generating element is ns1, an odd number is m, the reference wavelength is λ, and the refractive index of air is nair, the relationship of m × λ / 4 = (ns1 - nair) × | ts1 - ts2 | is satisfied.

22. 2. The LiDAR transceiver of claim 1 , wherein the waveplate is a λ / 4 waveplate and is on the first side of the polarizing beam splitter.

23. The LiDAR transceiver of claim 12 , wherein the optical path length compensation element is disposed on a first side of the wave plate and at a position where the target reflected light is parallel light.

24. The LiDAR transceiver of any one of claims 6 to 8, wherein the surface reflection optical element is arranged on a first side of the wave plate and at a position where the target reflected light is parallel light.

25. The LiDAR transceiver of any one of claims 16 to 19, wherein the phase difference generating element is arranged on a first side of the wave plate and at a position where the target reflected light is parallel light.

26. The LiDAR transceiver of claim 1, wherein a collimator (12) consisting of a single lens or a set of lenses is disposed between the light source and the polarizing beam splitter.

27. The LiDAR transceiver of claim 1, wherein a receiving lens (27) consisting of a single lens or a set of lenses is disposed between the polarizing beam splitter and the photodetector.

28. 28. The LiDAR transceiver of claim 27, wherein the receiving lens has a number of lenses equal to the number of photodetecting elements constituting the first photodetector and the second photodetector, or has a single lens array having a number of lens shapes equal to the number of photodetecting elements constituting the first photodetector and the second photodetector.

29. The LiDAR transceiver of claim 1, further comprising a pair of lenses (28, 29) on the first side of the polarizing beam splitter for expanding or reducing the beam diameter of the emitted light and the target reflected light.

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