Measuring device for measuring distance to object and / or speed of object

Abstract

This measurement device comprises: a light source; a first splitter that splits light from the light source into irradiation light and reference light; a second splitter that splits the irradiation light into first irradiation light and second irradiation light; a first waveguide through which pass together the first irradiation light and first reflected which is light reflected from a scene; a second waveguide through which pass together the second irradiation light and second reflected light which is light reflected from the scene; a third waveguide that branches from the first waveguide and through which the first reflected light passes after passing through the first waveguide; a fourth waveguide that branches from the second waveguide and through which the second reflected light passes after passing through the second waveguide; and a photodetector that detects the first reflected light, the second reflected light, and the reference light.

Description

A measuring device for measuring the distance to an object and / or the speed of the object

[0001] The present disclosure relates to a measurement device that measures the distance to an object and / or the velocity of the object.

[0002] Light detection and ranging (LiDAR) technology is being developed, which measures the distance to an object by illuminating the object with light and detecting the light reflected from the object. For example, LiDAR devices have been developed that can measure the distance to an object and the speed of the object using frequency-modulated continuous wave (FMCW) technology. The use of FMCW technology allows for both a wide dynamic range and high resolution for distance, is less susceptible to external disturbances, and can detect not only the distance but also the speed of a moving object.

[0003] A LiDAR device using FMCW technology includes, for example, a light source, a photodetector, and a processing circuit. The light source is controlled to emit light whose frequency changes over time. The photodetector detects interference light between the light reflected from the target and a reference light from the light source, and outputs a beat signal containing a beat having a frequency corresponding to the time delay of the reflected light. The processing circuit calculates the distance to the target and / or the velocity of the target based on the frequency of the beat signal.

[0004] Patent Documents 1 to 3 disclose examples of LiDAR devices using FMCW technology.

[0005] JP 2022-544743 A U.S. Patent No. 11105900 Specification JP 2019-522211 A

[0006] The present disclosure provides a measurement device that can expand the range of measurable distances.

[0007] The measurement device includes a light source, a first splitter that splits light from the light source into illumination light and reference light, a second splitter that splits the illumination light into first illumination light and second illumination light, a first waveguide through which the first illumination light and first reflected light reflected from a scene pass together, a second waveguide through which the second illumination light and second reflected light reflected from the scene pass together, a third waveguide that branches from the first waveguide and through which the first reflected light that has passed through the first waveguide passes, a fourth waveguide that branches from the second waveguide and through which the second reflected light that has passed through the second waveguide passes, and a photodetector that detects the first reflected light, the second reflected light, and the reference light.

[0008] A comprehensive or specific aspect of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable recording disk, or as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium. A computer-readable recording medium includes, for example, a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). An apparatus may consist of one or more devices. When an apparatus consists of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices. In this specification and claims, the term "apparatus" may refer not only to a single device but also to a system consisting of multiple devices. The multiple devices included in a "system" may include devices installed in remote locations away from other devices and connected via a communication network.

[0009] According to the technology of the present disclosure, it is possible to expand the range of measurable distances.

[0010] FIG. 1 is a block diagram schematically illustrating the configuration of an exemplary measurement device of the present disclosure. FIG. 2A is a diagram schematically illustrating an example of changes in the frequency of the reference light and the reflected light over time when the object is stationary. FIG. 2B is a diagram schematically illustrating an example of changes in the frequency of the reference light and the reflected light over time when the object is moving. FIG. 3 is a flowchart outlining an example of a measurement operation performed by a processing circuit. FIG. 4 is a graph showing an example of the power spectrum of a beat signal. FIG. 5 is a diagram for explaining the relationship between the optical path length and the beat frequency, and the influence of various noises. FIG. 6A is a diagram for explaining the relationship between the optical path length and the beat frequency, and the influence of various noises. ５ = d １ +2d ２ +d ４ 6B is a diagram illustrating an example of various noises in the case of d ５ = d １ +d ２ +d ４ 6C is a diagram illustrating an example of various noises in the case of d ５ = d １ +d ４ 7 is a diagram illustrating an example of various noises when the optical path length d ２is a diagram for explaining the influence of optical element noise when adjusting various optical path lengths. FIG. 8A is a first diagram for explaining changes in the frequency of various noises and the target frequency when adjusting various optical path lengths. FIG. 8B is a second diagram for explaining changes in the frequency of various noises and the target frequency when adjusting various optical path lengths. FIG. 8C is a third diagram for explaining changes in the frequency of various noises and the target frequency when adjusting various optical path lengths. FIG. 9 is a block diagram showing the configuration of a measurement device including multiple optical heads. FIG. 10A is a diagram showing an example of the power spectrum of a beat signal obtained when both the first beam and the second beam are irradiated onto the target. FIG. 10B is a diagram showing an example of the power spectrum of a beat signal obtained when both the first beam and the second beam are blocked. FIG. 11 is a block diagram showing the configuration of a measurement device according to an exemplary embodiment of the present disclosure. FIG. 12 is a diagram for explaining the relationship between the optical path length and the beat frequency, and the influence of various noises. FIG. 13A is a diagram showing an example of the power spectrum of a beat signal obtained when both the first beam and the second beam are irradiated onto the target. Fig. 13B is a diagram showing an example of the power spectrum of a beat signal obtained when the first beam is irradiated onto the target and the second beam is blocked. Fig. 13C is a diagram showing an example of the power spectrum of a beat signal obtained when the first beam is blocked and the second beam is irradiated onto the target. Fig. 13D is a diagram showing an example of the power spectrum of a beat signal obtained when both the first beam and the second beam are blocked. Fig. 14 is a block diagram showing the configuration of a measurement device according to a modified example.

[0011] In this disclosure, all or part of a circuit, unit, device, component, or part, or all or part of a functional block in a block diagram, may be implemented by one or more electronic circuits, including, for example, a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (Large Scale Integration). The LSI or IC may be integrated on a single chip or may be configured by combining multiple chips. For example, functional blocks other than memory elements may be integrated on a single chip. While the terms LSI and IC are used here, the term may be changed depending on the degree of integration, and may be called a system LSI, a VLSI (Very Large Scale Integration), or an ULSI (Ultra Large Scale Integration). Field programmable gate arrays (FPGAs), which are programmed after the LSI is manufactured, or reconfigurable logic devices (RLDs), which can reconfigure the connections within the LSI or set up circuit partitions within the LSI, can also be used for the same purpose.

[0012] Furthermore, all or part of the functions or operations of a circuit, unit, device, component, or section can be implemented by software processing. In this case, the software is recorded on one or more non-transitory recording media such as ROMs, optical disks, hard disk drives, etc., and when the software is executed by a processor, the functions specified in the software are performed by the processor and peripheral devices. A system or device may include one or more non-transitory recording media on which the software is recorded, a processor, and necessary hardware devices, such as interfaces.

[0013] In this disclosure, "light" refers to electromagnetic waves including not only visible light (wavelength of about 400 nm to about 700 nm), but also ultraviolet light (wavelength of about 10 nm to about 400 nm) and infrared light (wavelength of about 700 nm to about 1 mm). In this specification, ultraviolet light may be referred to as "ultraviolet light," and infrared light may be referred to as "infrared light."

[0014] Exemplary embodiments of the present disclosure will be described below. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in each figure, substantially identical components are assigned the same reference numerals, and duplicated descriptions may be omitted or simplified.

[0015] (Configuration example of measurement device) First, the principle of distance measurement or velocity measurement by the measurement device used in the embodiment of the present disclosure will be described. For simplicity, an example of the configuration and operation of a measurement device that emits one light beam will be described first. The configuration of a measurement device that emits multiple light beams will be described later.

[0016] FIG. 1 is a block diagram schematically illustrating the configuration of an exemplary measurement device 500A. The measurement device 500A illustrated in FIG. 1A includes a LiDAR unit 100 and an optical head 200. The LiDAR unit 100 includes a light source 20, an interference optical system 30, a photodetector 50, a processing circuit 60, and a memory 62. The interference optical system 30 includes a splitter 32, a branching element 34, and a coupling element 36. The optical head 200 includes an optical element 40, such as a collimator lens. The thick line illustrated in FIG. 1 represents an optical waveguide, such as an optical fiber, that interconnects two components. In this specification, the optical waveguide may be simply referred to as a "waveguide." The solid line with an arrow illustrated in FIG. 1 represents the flow of a signal. The dashed line illustrated in FIG. 1 represents light irradiated onto the target 10.

[0017] The light source 20 may be, for example, a laser light source that emits laser light. Hereinafter, the laser light emitted from the light source 20 may be referred to as "output light." The light source 20 is capable of changing the frequency of the output light. The frequency of the output light may be modulated, for example, in a triangular or sawtooth waveform with a constant time period. The frequency time period does not need to be constant and may change over time. The frequency time period may be, for example, 1 microsecond (μs) or more and 10 milliseconds (ms) or less. The frequency fluctuation range, i.e., the difference between the minimum and maximum frequency values, may be, for example, 100 MHz or more and 1 THz or less. The wavelength of the output light may be within the near-infrared wavelength range, for example, 700 nm or more and 2000 nm or less. Using near-infrared light as the output light can reduce the influence of noise caused by sunlight, even when measurements are taken outdoors during the day. The wavelength of the output light does not necessarily have to be within the near-infrared wavelength range. The wavelength of the output light may be in the visible light wavelength range of 400 nm to 700 nm, or may be in the ultraviolet light wavelength range. Light source 20 may include, for example, a distributed feedback laser diode or an external cavity laser diode. These laser diodes are inexpensive and compact, capable of single-mode oscillation, and can change the frequency of the output light depending on the amount of current applied. The intensity and frequency of the output light output from light source 20 may be controlled by a controller such as processing circuitry 60.

[0018] The splitter 32 is connected to the light source 20 via a waveguide 70, to the branching element 34 via a waveguide 71, and to the coupling element 36 via a waveguide 75. The splitter 32 splits the output light emitted from the light source 20 into a reference light and an irradiation light to be irradiated onto the object 10. The splitter 32 inputs the reference light to the coupling element 36 and the irradiation light to the branching element 34.

[0019] The branching element 34 may be, for example, an optical splitter or a circulator. The branching element 34 is connected to the splitter 32 via a waveguide 71, to the coupling element 36 via a waveguide 74, and to the optical element 40 in the optical head 700 via a waveguide 72. The branching element 34 inputs the illumination light from the splitter 32 to the optical element 40 and inputs the reflected light from the object 10 to the coupling element 36.

[0020] The combining element 36 may be, for example, an optical splitter or an optical coupler. The combining element 36 inputs the interference light between the reference light from the splitter 32 and the reflected light from the branching element 34 to the photodetector 50.

[0021] The optical element 40 emits the illumination light that has passed through the waveguide 72 to the outside and introduces the light reflected from the object 10 into the waveguide 72. The optical element 40 may be, for example, a collimator lens that collimates the illumination light. In this specification, "collimate" refers not only to converting the illumination light into parallel light but also to reducing the spread of the illumination light. The optical element 40 is not limited to a collimator lens, and may also be a diffraction grating that emits the illumination light to the outside as zeroth-order diffracted light and / or ±Nth-order diffracted light (N is an integer greater than or equal to 1). By measuring the distance to the object 10 using multiple diffracted lights emitted in different directions, the angular range of distance measurement for the object 10 can be expanded.

[0022] The optical head 200 may include a beam scanner configured using, for example, a MEMS (Micro Electro Mechanical System), etc. The beam scanner can change the direction of the irradiated light.

[0023] The photodetector 50 detects the interference light output from the coupling element 36. The photodetector 50 includes one or more photodetection elements. The photodetection elements output an electrical signal corresponding to the intensity of the interference light.

[0024] In the measurement device 500A, the optical path of the illumination light from the interference optical system 30 to the object 10 overlaps with the optical path of the reflected light from the object 10 to the interference optical system 30. By employing such a coaxial optical system, the configuration of the measurement device 500A can be simplified and stable measurements can be achieved.

[0025] The processing circuit 60 functions as a controller that controls the operations of the light source 20 and the photodetector 50. The processing circuit 60 performs processing based on FMCW-LiDAR technology. Specifically, the processing circuit 60 causes the light source 20 to emit light whose frequency changes over time, and causes the photodetector 50 to detect interference light between the interference light and light reflected from the object 10. The processing circuit 60 calculates the distance to the object 10 and / or the speed of the object 10 based on the time-series signal output from the photodetector 50, and generates and outputs measurement data related to the distance and / or speed.

[0026] The processing circuit 60 calculates distance and / or speed by executing a computer program stored in a memory 62 such as a ROM or RAM (Random Access Memory). Thus, the measurement device includes a processing device including the processing circuit 60 and the memory 62. The processing circuit 60 and the memory 62 may be integrated on a single circuit board or may be provided on separate circuit boards. The control and signal processing functions of the processing circuit 60 may be distributed across multiple circuits. The processing device may be installed in a location remote from the other components. In this case, the processing device may control the operations of the light source 20 and the photodetector 50 and process signals output from the photodetector 50 via a wired or wireless communication network.

[0027] Next, the principle of distance and velocity measurement based on FMCW-LiDAR technology will be described with reference to FIGS. 2A and 2B.

[0028] FIG. 2A is a schematic diagram illustrating an example of the temporal changes in the frequency of the reference light and the reflected light when the object 10 is stationary. The solid line represents the reference light, and the dashed line represents the reflected light. The frequency of the reference light shown in FIG. 2A repeatedly changes over time in a triangular waveform. That is, the frequency of the reference light alternates between an up-chirp, in which the frequency increases linearly over one period, and a down-chirp, in which the frequency subsequently decreases linearly by the same amount. The frequency increase during the up-chirp period is equal to the frequency decrease during the down-chirp period. When the total optical path length of the irradiated light and the reflected light is longer than that of the reference light, the frequency of the reflected light shifts in the positive direction along the time axis compared to the frequency of the reference light. Conversely, when the total optical path length of the irradiated light and the reflected light is shorter than that of the reference light, the frequency of the reflected light shifts in the negative direction along the time axis compared to the frequency of the reference light. The amount of time shift of the reflected light is proportional to the absolute value of the difference between the total optical path length of the irradiated light and the reflected light and the optical path length of the reference light. Therefore, the interference light between the reference light and the reflected light has a beat frequency corresponding to the absolute value of the difference between the frequency of the reflected light and the frequency of the reference light. The thick double-headed arrow in FIG. 2A represents the difference in frequency between the reference light and the reflected light. The photodetector 50 outputs a time-series signal indicating changes in the intensity of the interference light. This signal is called a beat signal. The frequency of the beat signal, i.e., the beat frequency, is equal to the absolute value of the difference in frequency between the reflected light and the interference light. The processing circuit 60 can calculate the distance to the object 10 based on the beat frequency.

[0029] When the object 10 is stationary, the beat frequency during the up-chirp period is equal to the beat frequency during the down-chirp period. Here, as shown by the thin double-headed arrows in Figure 2A, the fluctuation width of the light frequency during each of the up-chirp period and the down-chirp period is Δf, and the time required for the frequency to change by Δf is Δt. Furthermore, the speed of light is c, and the absolute value of the difference between the total optical path length of the irradiated light and the reflected light and the optical path length of the reference light is Δd. The beat frequency during the up-chirp period or the down-chirp period is f ｂｅａｔ is expressed by the following equation (1).

[0030] Beat frequency f ｂｅａｔis obtained by multiplying the time rate of change of frequency Δf / Δt by the time (Δd / c) required for light to propagate through the optical path length difference Δd. １ , the optical path length of the waveguide 72 is d ２ , the optical path length from the optical element 40 to the object 10 is d ３ , the optical path length of the waveguide 74 is d ４ The optical path difference Δd between the reflected light reflected by the object 10 and returned and the reference light is expressed by the following equation (2).

[0031] Optical path length d １ , d ２ , d ４ , d ５ is a predetermined fixed value. Also, Δf, Δt, and c in equation (1) are known values, and f ｂｅａｔ is obtained by frequency analysis of the beat signal. Therefore, the processing circuit 60 calculates the distance d from the optical element 40 to the object 10 as ３ can be calculated based on equations (1) and (2).

[0032] FIG. 2B is a schematic diagram illustrating an example of the temporal change in the frequency of the reference light and the reflected light when the object 10 is moving. When the object 10 approaches the optical head 200, as shown in FIG. 2B , the frequency of the reflected light shifts in the positive direction along the frequency axis due to Doppler shift compared to when the object 10 is stationary. Conversely, when the object 10 moves away from the optical head 200, the frequency of the reflected light shifts in the negative direction along the frequency axis due to Doppler shift compared to when the object 10 is stationary. The amount of frequency shift of the reflected light depends on the magnitude of the component of the velocity vector of the illuminated portion of the object projected onto the direction of the reflected light. When the object 10 is moving, the beat frequency may differ between the up-chirp period and the down-chirp period. In the example shown in FIG. 2B , the beat frequency fd during the down-chirp period, in which the frequencies of both the reflected light and the reference light linearly decrease, is higher than the beat frequency fu during the up-chirp period, in which the frequencies of both the reflected light and the reference light linearly increase. The processing circuit 60 can calculate the velocity of the object 10 based on this beat frequency difference (fd-fu). The processing circuit 60 calculates the average value of the beat frequency fu in the up-chirp period and the beat frequency fd in the down-chirp period as the beat frequency f in the above equation (1). ｂｅａｔ The distance from the optical head 200 to the object 10 may be calculated as:

[0033] 3 is a flowchart schematically showing an example of a measurement operation performed by the processing circuitry 60. The processing circuitry 60 performs the operations of steps S101 to S103 shown in FIG.

[0034] In step S101, the processing circuitry 60 causes the light source 20 to emit laser light whose frequency changes over time. In the example shown in Figures 2A and 2B, the processing circuitry 60 causes the light source 20 to emit laser light whose frequency changes in a triangular waveform. Note that, in an application in which the speed of the object 10 is not measured but the distance to the object 10 is measured, the frequency of the laser light may be changed in a sawtooth waveform.

[0035] In step S102, the processing circuitry 60 causes the photodetector 50 to detect the interference light between the reflected light and the reference light. The photodetector 50 outputs a signal corresponding to the intensity of the interference light at a predetermined cycle.

[0036] In step S103, the processing circuitry 60 calculates the distance and / or velocity of the object 10 based on the signal output from the photodetector 50. The processing circuitry 60 may perform processing such as a fast Fourier transform (FFT) based on the time-series signal output from the photodetector 50 to determine the intensity of each frequency component and process the frequency at which the intensity exceeds a threshold as the above-mentioned beat frequency. The processing circuitry 60 can generate data regarding the distance and / or velocity of the object 10 by performing the above-mentioned calculation based on the beat frequency.

[0037] In the measurement device 500A shown in FIG. 1 , the LiDAR unit 100 and the optical head 200 are not housed in a single housing but are separated from each other. The waveguide 72 connecting the LiDAR unit 100 and the optical head 200 can be realized, for example, by a relatively long optical fiber cable. This configuration reduces the volume and weight of the optical head 200, increasing the flexibility of installation of the optical head 200. Even if the target object 10 has a complex shape or a large size, the position and orientation of the optical head 200 can be flexibly changed depending on the shape or size of the target object 10.

[0038] Generally, the wavelength stability of the light source 20 is easily affected by temperature, and temperature changes affect the accuracy of distance and velocity measurements. Furthermore, because the processing circuit 60 is a precision device, it is required to be temperature-resistant as well as vibration-resistant. For this reason, the LiDAR unit 100 may include a housing that is temperature-resistant and vibration-resistant. The light source 20, the interference optical system 30, the photodetector 50, the processing circuit 60, and the memory 62 may be housed within the housing. This allows for stable distance and velocity measurement accuracy. The housing may include only some of the light source 20, the interference optical system 30, the photodetector 50, and the processing circuit 60. For example, the housing may include the light source 20, the interference optical system 30, and the photodetector 50, but not the processing circuit 60 or the memory 62. Furthermore, the light source 20, the interference optical system 30, the photodetector 50, the processing circuit 60, the memory 62, and some or all of the optical waveguides or wiring connecting them may be integrated on a single chip. Such a configuration allows for greater freedom in manufacturing and designing the LiDAR unit 100.

[0039] In the configuration shown in FIG. 1 , the beat signal output from the photodetector 50 may contain frequency components due to light reflected from the object 10 as well as frequency components (i.e., noise) due to light other than the light reflected from the object 10. For example, noise may occur when a portion of the illumination light input from the splitter 32 to the branching element 34 is directed toward the coupling element 36 instead of the optical element 40 and then incident on the photodetector 50. Furthermore, noise may occur when a portion of the illumination light passing through the waveguide 72 is reflected by a lens surface without passing through the optical element 40. Furthermore, noise may occur due to light reflection occurring within the waveguide 72 connecting the branching element 34 and the optical element 40. In particular, when the branching element 34 and the optical element 40 are connected by a waveguide 72 such as a relatively long optical fiber cable, as in the example shown in FIG. 1 , the optical path of the illumination light changes depending on the position of the optical head 200, making it more likely that light reflections and crosstalk will occur along the optical path. As a result, noise may occur in the beat signal detected by the photodetector 50, resulting in a range of distances where distance or velocity cannot be measured, leading to a reduction in the measurable distance range.

[0040] According to the study by the present inventors, the optical path length d shown in FIG. １ , d ２ , d ４ , d ５ By appropriately adjusting the optical path length d, it is possible to reduce the influence of noise and expand the range of measurable distances. １ , d ２ , d ４ , d ５ The relationship between the noise effect and the noise level will be explained in more detail.

[0041] Fig. 4 is a graph showing an example of the intensity of each frequency component of the beat signal, i.e., a power spectrum. The processing circuit 60 performs processing such as FFT based on the beat signal output from the photodetector 50, thereby generating power spectrum data as shown in Fig. 4. The horizontal axis of the graph shown in Fig. 4 represents frequency, and the vertical axis represents signal intensity. In the example of Fig. 4, the frequency is represented by a 9-bit number (0 to 511), and the width of one scale represents 250 MHz / 512. The frequency on the horizontal axis is a function of the optical path length from leaving the splitter 32 to reaching the coupling element 36, and the optical path length d of the reference light. ５ The optical path length corresponds to the absolute value of the difference between the optical path length d of the reference light and the ５ When the frequency is equal to , the frequency becomes zero. In Figure 4, the spectrum during the up-chirp period and the spectrum during the down-chirp period are shown superimposed. When the object 10 is stationary, the behavior of both is almost the same.

[0042] In this example, the frequency of the laser light from light source 20 is modulated into a triangular wave as shown in Figure 2A. When object 10 is stationary, a beat signal peak occurs at a frequency corresponding to the optical path length during both the up-chirp and down-chirp periods of the triangular wave. When object 10 is moving, a difference occurs in the frequency of the beat signal between the up-chirp and down-chirp periods, and the velocity can be detected based on the frequency difference.

[0043] 1, when noise light from sources other than the object 10 enters the photodetector 50, noise occurs in the beat signal based on the above-mentioned formula (1). Fig. 4 shows, as examples of noise, optical element noise generated in the optical element 40 and branching element noise generated in the branching element 34.

[0044] The optical element noise may be caused by, for example, reflections at the interface between the optical fiber that constitutes the waveguide 72 and the air, and at the interface between the air and the glass of the optical element 40 (e.g., the collimator lens). The optical element noise is caused by the optical path length d of the light that leaves the splitter 32, is reflected by the optical element 40, and reaches the coupling element 36. １ +2d ２ +d ４ and the optical path length d of the reference light from the splitter 32 to the coupling element 36. ５ Absolute value of the difference |d １ +2d ２ +d ４ -d ５ In the example of FIG. 4, the optical path length d １ +2d ２ +d ４ is the optical path length d of the reference light ５ In this case, the optical path length d of the light from the splitter 32 to the coupling element 36 after being reflected by the object 10 is longer than １ +2d ２ +2d ３ +d ４ and the optical path length of the reference light d ５ Since the difference between the two becomes larger, the corresponding frequency becomes higher. Therefore, the frequency at which optical element noise occurs can be considered to correspond to zero distance, and frequencies higher than this frequency can be processed as frequencies to be measured. Therefore, the effect of optical element noise on distance measurement of the object 10 is small.

[0045] Branching element noise occurs when a portion of the light input from the splitter 32 to the branching element 34 (e.g., a circulator) is directed toward the coupling element 36 instead of the optical element 40 as intended, and enters the photodetector 50. It has been experimentally confirmed that the optical path length within the branching element 34 of the noise light that causes branching element noise is longer than the sum of the optical path lengths within the branching element 34 of the irradiated light traveling from the branching element 34 to the optical element 40 and its reflected light. In the following description, this difference in optical path length is referred to as the optical path length d of the noise light in the branching element 34. ｃ In the example of FIG. 4, the optical path length d １ +d ｃ +d ４ and the optical path length d of the reference light ５ Absolute value of the difference |d １ +d ｃ +d ４ -d ５ | is small, so the effect on the distance measurement of the object is small. ５ When is large, the optical path difference |d １ +d ｃ +d ４ -d ５ | is the optical path difference |d corresponding to the optical element noise １ +2d ２ +d ４ -d ５ |. In this case, the branching element noise may occur near the beat frequency of the object, making it impossible to distinguish between the beat frequency of the object 10 and the noise. As a result, it becomes impossible to measure distance and speed in the frequency band where the branching element noise occurs. As in the example of Figure 4, if the branching element noise is made to occur at a frequency lower than the frequency at which optical element noise occurs, the effect of the branching element noise on measurement can be suppressed.

[0046] In the example of FIG. 4, the noise floor is about 20 dB higher on the low frequency side than on the high frequency side at a frequency of about 280 (×250 MHz / 512) on the horizontal axis. １ , d ２ , d ４ , d ５Depending on the value of , this high noise floor may also occur in the frequency band for measuring the distance or speed of the object 10. If the reflectance of the object is low, a frequency band that cannot be measured may occur due to the influence of the noise floor. Therefore, the frequency band that can be measured even when the reflectance is low (referred to as the "measurable band") may become narrow. In the example of Figure 4, the frequency band that can be detected by the photodetector 50 (referred to as the "PD detectable band") is 250 MHz, of which more than 50% is accounted for by noise. The optical path length d １ , d ２ , d ４ , d ５ Depending on the value of , the measurable band may become even narrower.

[0047] The inventors analyzed the cause of this increase in the noise floor and found that the optical path length d ２ It was found that the cause is the above. The optical fiber that constitutes the waveguide 72 generates Rayleigh scattering due to particles that are sufficiently small compared to the wavelength within the optical fiber, or fluctuations in density, stress, or composition. This can cause backscattering of light throughout the optical fiber. The noise light caused by backscattering within the waveguide 72 travels the same path as the reflected light from the object 10 and enters the photodetector 50. This causes a noise band. Because this noise band originates from the optical fiber, it is called the "fiber noise band." Similar noise can also occur due to the same factors when the waveguide 72 is an optical waveguide other than an optical fiber cable.

[0048] The width of the fiber noise band depends on the optical path length d2 of the waveguide 72. Shortening the optical path length d2 of the waveguide 72 is an effective way to narrow the fiber noise band and expand the measurable band. However, shortening the optical path length d2 makes it difficult to install the optical head 200 and the LiDAR unit 100 at a distance from each other. Figure 5 is a diagram for explaining in more detail the relationship between the optical path length and the beat frequency, and the influence of various noises. Here, the optical path length refers to the optical path length that begins at the splitter 32 and ends at the coupling element 36.

[0049] In the example of FIG. 5, the optical path length d ５ is the optical path length d of the light that causes branching element noise１ +d ｃ +d ４ The optical path length d of the light that causes optical element noise is longer than １ +2d ２ +d ４ The branch element noise is shorter than d １ +d ｃ +d ４ and d ５ The absolute value of the difference Δd １ The frequency f corresponding to ｃ The optical element noise occurs at d １ +2d ２ +d ４ and d ５ The absolute value of the difference Δd ２ The frequency f corresponding to ０ It occurs at frequency f ０ corresponds to the 0 m point of the distance measurement. The maximum frequency that can be detected by the photodetector 50 is f ＰＤ Then, f ０ From f ＰＤ The measurable band is up to f. The beat frequency corresponding to the reflected light from the target object is ｔ Let's say.

[0050] Fiber noise ranges from 0 to f ０ This band is the fiber noise band. １ +d ４ -d ５ The frequency f corresponding to | ｆ Up to 1000 Hz, the noise intensity is approximately doubled due to the double fiber noise.

[0051] In the example of FIG. ５ But, d １ +d ｃ +d ４ and d １ +2d ２ +d ４ Therefore, f ｃ is f ０ In this case, the branch element noise does not affect the distance measurement. ５ d １ +d ｃ +d ４and d １ +2d ２ +d ４ If it is greater than the average value of ｃ ga f ０ This affects distance measurement especially at short distances. １ <Δd ２ That is, |d １ +d ｃ +d ４ -d ５ |<|d １ +2d ２ +d ４ -d ５ so that the optical path length d １ , d ２ , d ４ , d ５ By setting d, the influence of branch element noise on distance measurement can be suppressed. ｃ d １ and d ４ If it is sufficiently small compared to ｃ ≒0, and |d １ +d ４ -d ５ |<|d １ +2d ２ +d ４ -d ５ so that the optical path length d １ , d ２ , d ４ , d ５ may be set.

[0052] The frequency band detectable by the photodetector 50, i.e., the PD detectable band, is from 0 to f ＰＤ The range is up to f ０ From f ＰＤ The range up to frequency f is the measurable band in which the distance or speed of the object can be measured. ０ By reducing the frequency f, the measurable band can be expanded. ０ is the optical path length d １ , d ２ , d ４ , d ５ For example, the optical path length d of the reference beam can be adjusted. ５ d １ +2d ２ +d４ If we approach the frequency f ０ However, simply reducing d ５ d １ +2d ２ +d ４ If the frequency f is simply brought closer to ０ This may result in narrowing the measurable band.

[0053] 6A to 6C show the optical path length d of the reference light. ５ 10 is a diagram showing an example of various frequencies when d is changed. ｃ = 0. In FIG. ５ = d １ +2d ２ +d ４ FIG. 6B shows an example of the case where d ５ = d １ +d ２ +d ４ FIG. 6C shows an example of the case where d ５ = d １ +d ４ This shows an example of the case where

[0054] As shown in FIG. 6A, the optical path length d ５ is the optical path length d of the light reflected by the optical element 40 １ +2d ２ +d ４ , the frequency f0 corresponding to the optical element noise is the minimum of 0 MHz, which corresponds to a distance of 0 m. Therefore, it seems that the range of distances that can be measured (hereinafter also referred to as the "distance measurement range") can be maximized. However, in this case, the fiber noise and branching element noise exceed the optical path length difference 2d. ２ The frequency f corresponding to ｃ occurs from 0 to f ｃ Therefore, the actual distance measurement range is ｃ From f ＰＤ The distance is reduced to a range of distances corresponding to the range of

[0055] When fiber noise is taken into consideration, the maximum distance measurement range is obtained when the optical path length d of the reference light is d , as shown in FIG. ５ d １ +d ２ +d ４ In this case, the optical path difference d ２ The frequencies 0 to f correspond to ｃ In this example, the frequency f ｃ and the frequency f corresponding to the optical element noise ０ In comparison with the example of Fig. 6A, the fiber noise band can be halved, and therefore the measurable band, i.e., the ranging range, can be expanded.

[0056] On the other hand, as shown in FIG. 6C, the optical path length d ５ is the optical path length d corresponding to the branching element noise. １ +d ４ When the optical path length difference is 2d from 0 MHz, ２ The frequencies 0 to f correspond to ０ In this case, the optical element noise does not appear, but the fiber noise appears in the widest band as in FIG. 6A, so the distance measurement range becomes narrow. Note that the optical path length d of the reference light ５ d １ +d ４ When the frequency f ０ becomes even higher, and a band that does not contribute to measurement appears in a band lower than the fiber noise band, so the measurable band becomes even narrower. ５ is d １ +d ４ It can be set to a value equal to or greater than this.

[0057] As shown in FIG. 6C, the optical path length d ５ ga d １ +d ４ and the fiber noise band is equal to the optical path difference 2d ２The measurement device 500A can be designed to enable measurement of the distance and / or velocity of an object even when the noise occurs in the widest band corresponding to the upper frequency limit f of the fiber noise band. ０ is expressed by the following equation (3).

[0058] The measurement device 500A can be designed so that the fiber noise band is within the PD detectable band to enable ranging of the target object 10. That is, the measurement device 500A can be designed so as to satisfy the following equation (4):

[0059] If the maximum frequency that can be detected by the photodetector 50 is lower than the maximum frequency that can be detected by the frequency analysis performed by the processing circuit 60, the latter frequency is set to f ＰＤ , the equation (4) may be satisfied.

[0060] The maximum measurable distance from the optical element 40 to the object 10 is D ｔ When D ｔ The measurement device 500A can be designed so that the target frequency corresponding to d is within the PD detectable band. ２ The frequency f depends on ０ And, D ｔ That is, the measurement device can be designed to satisfy the following equation (5).

[0061] It is desirable that the fiber noise band is less than 50% of the PD detectable band, that is, the ranging range is 50% or more. Therefore, the measurement device 500A can be designed to satisfy the following formula (6).

[0062] As an example, Δf=9.2 GHz, Δt=10 microseconds (μs), f ＰＤ= 250 MHz, and when measuring the distance to an object 20 meters (m) away, the target frequency corresponding to the distance to the object is approximately 170 MHz, which is 68% of the frequency of 250 MHz. If the above formula (6) is satisfied, it is possible to measure the distance to such an object.

[0063] As can be seen from equation (3), the fiber noise bandwidth can be reduced by reducing Δf. On the other hand, the distance measurement resolution depends on Δf. For example, when Δf is 9.2 GHz, the distance to an object 1 meter (m) away can be measured with millimeter (mm) accuracy.

[0064] As described above, the fiber noise bandwidth is ２ Since it depends on ２ The influence of fiber noise can be suppressed by approaching 0. However, ２ If θ approaches 0, the effect of optical element noise may occur.

[0065] FIG. 7 shows the optical path length d ２ 1 is a diagram for explaining the influence of optical element noise when the optical path length d of the noise light inside the branching element 34 is made close to 0. ｃ The optical element noise is considered as １ +d ４ +2d ２ and d ５ It occurs at a frequency that corresponds to the absolute value of the difference between ２ ≒0, the optical element noise is １ +d ４ and d ５ On the other hand, the branching element noise occurs at a frequency corresponding to the absolute value of the difference between the optical path length d １ +d ４ +d ｃ and d ５ In the example shown in FIG. 7, the optical path length d ５ is the optical path length d of the noise light that causes the branching element noise. １ +d ４ +d ｃ In this case, the optical element noise is equal to the optical path difference d ｃ The frequency f corresponding to ｎｏｉｚｅThe point of distance 0 is the optical path length d of the reference light. ５ The optical path length d is shorter than １ +d ４ (+2d ２ ) to correspond to 2d ｃ Within this interval, two different distances correspond to the same target frequency. Therefore, ranging is not possible in this interval. To avoid this problem, the measurement device can be designed to satisfy the following equation (7):

[0066] The branching element 34 may be, for example, a circulator or a splitter. Whether the branching element 34 is a circulator or a splitter, the optical path length d of the noise light that propagates directly from the light source 20 side to the photodetector 50 side is ｃ Taking this into consideration, various optical path lengths can be adjusted to satisfy equation (7).

[0067] Furthermore, the optical path length d of the reference light ５ d １ +d ４ +d ｃ If the wavelengths are different from the wavelengths shown in the figures, splitter noise occurs. By adjusting the lengths of the various optical paths so that the spectroscopic element noise occurs at a lower frequency than the splitter element noise, the distance measurement range can be widened. Therefore, the measurement device 500A can be designed to satisfy the following expressions (8) and (9).

[0068] 8A to 8C are diagrams showing examples of changes in the frequencies of various noises and the target frequency when various optical path lengths are adjusted. In each example, Δf = 9.2 GHz, Δt = 10 microseconds (μs), f ＰＤ = 250 MHz. The optical path length d １ , d ２ , d ３ , d ４ , d ５ , d ｃ is shown on the right side of the graph.

[0069] The optical path length d2 of the waveguide 72 is 22 m in the example of FIG. 8A, 10 m in the example of FIG. 8B, and 1 m in the example of FIG. 8C. The optical path length d5 ​​of the waveguide 75 is d１ +d ４ In the example of FIGS. 8A and 8B, d １ = d ４ = 1 m, and d ５ In the example of FIG. 8C, d １ = d ４ = 10 m, and d ５ = 20 m. Optical path length d ｃ is 0 m in both examples.

[0070] d shown in FIG. ２ In the example where the optical path length d = 22 m, the above formula (4) is not satisfied. Therefore, the fiber noise covers the entire PD detectable band, and distance and velocity cannot be measured. ２ It is necessary to make the time shorter.

[0071] d shown in FIG. ２ In the example where f = 10 m, the formulas (4), (6), (7), (8), and (9) are satisfied. In this case, the measurable band is 50% or more of the PD detectable band, and distance measurement is possible. However, the frequency f shown in formula (3) ０ is high and the measurable band is somewhat narrow, so equation (5) is not satisfied for an object 20 m away, and distance measurement is not possible.

[0072] In contrast, d shown in FIG. ２ = 1 m, d １ = d ４ = 10 m, d ５ In the example where d = 20 m, ２ Since the fiber noise band is short, the fiber noise band can be narrowed and the measurable band can be widened. In this case, all of the formulas (4), (5), (6), (7), (8), and (9) are satisfied, and it is possible to measure an object 20 m away.

[0073] As shown in FIG. 5, the optical path length d ５Depending on the intensity of the fiber noise, the fiber noise band may include a band where the intensity of the fiber noise is twice as high and a band where the intensity is 1. If the intensity of the beat signal caused by the reflected light from the target is higher than 1 time but lower than 2 times the intensity of the fiber noise, it is possible to extend the ranging range by also using the band where the fiber noise is 1 time.

[0074] 1, the LiDAR unit 100 and the optical head 200 are separate, but they do not have to be separate. For example, each component of the LiDAR unit 100 and the optical element 40 may be housed in a single housing. Even in this case, the range of measurable distances can be expanded by setting each optical path length to satisfy some or all of the above formulas (4), (5), (6), (7), (8), and (9).

[0075] When multiple optical heads are provided, an optical router may be installed between the LiDAR unit and each optical head instead of the branching element 34, allowing the optical head that inputs and outputs light to be selected. If the branching element 34 is a splitter, the light intensity is halved when branching and combining light. To prevent this, an optical router may be installed instead of a splitter, allowing the selection of one optical head from multiple optical heads. This makes it possible to suppress light loss during branching and combining.

[0076] (Example of a measurement device equipped with multiple optical heads) In the configuration example of FIG. 1, the number of optical heads 200 is one, but multiple optical heads 200 may be provided. FIG. 9 is a block diagram showing an example of the configuration of a measurement device equipped with multiple optical heads. A measurement device 600A shown in FIG. 9 includes a LiDAR unit 100 and two optical heads 200A and 200B. The components of the LiDAR unit 100 are the same as those in the example of FIG. 1. In the example of FIG. 9, the branching element 34 and the first optical head 200A are connected by a waveguide 72A, and the branching element 34 and the second optical head 200B are connected by a waveguide 72B. The optical path length d of the waveguide 72A ２１ and the optical path length d of the waveguide 72B ２２By making the lengths of the first and second optical elements 40A and 40B different, it is possible to measure the distance or speed of a plurality of objects 10A and 10B, or a plurality of portions of a single object. Here, the distance from the first optical element 40A included in the first optical head 200A to the object 10A is defined as d ３１ , the distance from the second optical element 40B included in the second optical head 200B to the object 10B is d ３２ In this case, the optical path length d ２１ or d ２２ d １ Let d ３１ or d ３２ d ３ The range of measurable distances can be expanded by determining the lengths of the optical paths so as to satisfy some or all of the above-mentioned formulas (4), (5), (6), (7), (8), and (9). The number of optical heads may be three or more.

[0077] According to the configuration shown in FIG. 9 , the positions or angles of the first optical element 40A and the second optical element 40B, which function as beam shapers, can be adjusted according to the respective targets. The target may be one or more. When there is one target, the positions and / or orientations of the optical elements 40A and 40B may be different to illuminate different portions of the target. This allows for more information about the scene being measured. In the following description, the portion of one or more targets onto which light is irradiated and from which distance or velocity is measured may be referred to as a "target." The position of each optical element can be adjusted according to the target by changing the length of the waveguide (e.g., optical fiber cable) from the branching element 34 to each optical element. In particular, to measure the distance or velocity of multiple targets using a single photodetector 50, it is effective to divide the frequency band detectable by the photodetector 50 into a band for the first optical head 200A and a band for the second optical head 200B.

[0078] 10A and 10B are diagrams showing examples of the power spectrum of a beat signal detected in the configuration shown in FIG. 9. The horizontal axis represents frequency, and the vertical axis represents signal intensity. As described above, the frequency of the beat signal is proportional to the absolute value of the difference between the optical path length of the irradiating light and the optical path length of the reference light. When the optical path lengths of the irradiating light and the reference light are the same, the frequency at which the beat signal is generated becomes zero.

[0079] Here, the light beam emitted from the first optical head 200A is referred to as the "first beam," and the light beam emitted from the second optical head 200B is referred to as the "second beam." An object or a portion irradiated by the first beam is referred to as the "first beam target," and an object or a portion irradiated by the second beam is referred to as the "second beam target." Noise caused by reflected light generated on the collimator lens surface of the first optical element 40A is referred to as the "first optical element noise," and noise caused by reflected light generated on the collimator lens surface of the second optical element 40B is referred to as the "second optical element noise."

[0080] 10A shows an example of the power spectrum of the beat signal obtained when both the first beam and the second beam are irradiated onto the target. FIG. 10B shows an example of the power spectrum of the beat signal obtained when both the first beam and the second beam are blocked. In this example, the optical path length d from the splitter element 34 to the optical element 40A is d ２１ is 2.5 m, and the optical path length d from the branching element 34 to the optical element 40B ２２ The optical path length d is set to 5.5 m, and the distance from each optical element to the corresponding irradiation position on the target is 1 m. The optical path length d is set to 5.5 m so that the first beam measurement range, which is the frequency range of the beat signal caused by the reflected light generated by irradiation of the first beam, and the second beam measurement range, which is the frequency band of the beat signal caused by the reflected light generated by irradiation of the second beam, do not overlap. ２１ and d ２２is set. The frequency at which the first optical element noise occurs corresponds to zero distance in distance measurement by the first beam, and the frequency at which the second optical element noise occurs corresponds to zero distance in distance measurement by the second beam. In the example shown in Fig. 10A, a frequency peak corresponding to the first beam target appears within the first beam measurement range, and a frequency peak corresponding to the first beam target appears within the second beam measurement range.

[0081] In this example, the optical path length of the second beam is 6 m longer than that of the first beam (round trip). Due to this optical path length difference, the frequency at which the second optical element noise occurs is higher than the frequency at which the first optical element noise occurs. By appropriately adjusting the optical path length difference, the ranges that can be measured by the first beam and the second beam can be divided as shown in FIG. 10A.

[0082] 10B, the noise level in the first beam measurement range is increased by about 20 dB compared to the second beam measurement range. This increase in noise may make it impossible to measure targets with low reflectivity.

[0083] When the present inventors analyzed the cause of this noise, they found that the optical path length d ２１ and d ２２ As described above, fiber noise occurs when noise light generated by backscattering in the optical fibers in the waveguides 72A and 72B enters the photodetector 50. The fiber noise depends on the lengths of the waveguides 72A and 72B. For example, as shown in FIG. 9, when the waveguide 72B is longer than the waveguide 72A, the influence of fiber noise caused by backscattering in the waveguide 72B may result in a distance range that cannot be measured by the first beam. This problem may also occur when the waveguides 72A and 72B are waveguides other than optical fibers. To narrow the band in which fiber noise occurs and expand the distance measurement range, d ２１ and d ２２ It is effective to design it to be short.

[0084] However, in order to separate the measurement frequency bands for the first beam target and the second beam target, it is necessary to change the optical path length between the first beam target and the second beam target. The difference in optical path length between the first beam target and the second beam target is d ２１ and d ２２ or d ３１ and d ３２ d ３１ and d ３２ is the distance from each optical element to each target, and is difficult to adjust because it depends on the target. ２１ and d ２２ If the optical path length d of the waveguide 72A is different from the optical path length d of the waveguide 72B, the fiber noise due to the longer optical path length will overlap with the beat frequency of the shorter target, and the beam with the shorter optical path length will not be able to measure the distance to an object with low optical reflectivity. ２１ Therefore, distance measurement is not possible in the frequency band from 0 MHz to the frequency at which the first optical element noise occurs. ２１ and d ２２ As the fiber noise band widens due to an increase in , the ranging range decreases.

[0085] FIG. 11 is a block diagram showing the configuration of a measurement device 600B having an optical system for solving the above-mentioned problem. In this measurement device 600B, the interference optical system 30 includes a first splitter 32A, a second splitter 32B, a first coupling element 36A, and a second coupling element 36B. The measurement device 600B also includes a first splitter 39A connected between the second splitter 32B and the first optical element 40A, and a second splitter 39B connected between the second splitter 32B and the second optical element 40B. Each of the first splitter 39A and the second splitter 39B may be, for example, a circulator or a splitter. Using a circulator can reduce propagation loss. Each of the first coupling element 36A and the second coupling element 36B may be, for example, a coupler or a splitter. 11 may be housed in a single housing, or may be housed separately in a housing for the LiDAR unit and housings for multiple optical heads, as in the example of Fig. 9. For example, the first branching element 39A and the first optical element 40A may be housed in one optical head, and the second branching element 39B and the second optical element 40B may be housed in another optical head.

[0086] 11, multiple optical waveguides are indicated by bold lines. These optical waveguides include waveguides 70, 71, 72A, 72B, 73A, 73B, 74A, 74B, 75, and 76. Of these, waveguide 72A may be referred to as the "first waveguide," waveguide 72B as the "second waveguide," waveguide 74A as the "third waveguide," waveguide 74B as the "fourth waveguide," waveguide 73A as the "fifth waveguide," and waveguide 73B as the "sixth waveguide." Each waveguide may be, for example, an optical fiber cable or an optical waveguide on an IC chip.

[0087] The first splitter 32A splits light input from the light source 20 via the waveguide 70 into illumination light for illuminating one or more objects present in the scene and reference light. The illumination light is sent to the second splitter 32B via the waveguide 71. The reference light is sent to the first coupling element 36A via the waveguide 75.

[0088] The second splitter 32B splits the illumination light from the first splitter 32A into a first illumination light and a second illumination light. The first illumination light is sent to the first splitter 39A via the fifth waveguide 73A. The second illumination light is sent to the second splitter 39B via the sixth waveguide 73B.

[0089] The first branching element 39A outputs the first irradiation light input from the fifth waveguide 73A to the first waveguide 72A, and outputs the first reflected light input from the first waveguide 72A to the third waveguide 74A.

[0090] The first optical element 40A shapes the first illumination light transmitted from the first branching element 39A via the first waveguide 72A and emits the light toward the first object 10A. The first optical element 40A also guides the first reflected light from the first object 10A into the first waveguide 72A and transmits the reflected light to the first branching element 39A.

[0091] The second branching element 39B outputs the second irradiation light input from the sixth waveguide 73B to the second waveguide 72B, and outputs the second reflected light input from the second waveguide 72B to the fourth waveguide 74B.

[0092] The second optical element 40B shapes the second irradiation light transmitted from the second branching element 39B via the second waveguide 72B and emits the light toward the second object 10B. The second optical element 40B also guides the second reflected light from the second object 10B into the second waveguide 72B and transmits the reflected light to the second branching element 39B.

[0093] The second coupling element 36B is connected to the first coupling element 36A via the waveguide 76, to the first branching element 39A via the waveguide 74A, and to the second branching element 39B via the waveguide 74B. The second coupling element 36B inputs the first reflected light input from the third waveguide 74A and the second reflected light input from the fourth waveguide 74B to the first coupling element 36A.

[0094] The first coupling element 36A is disposed on the optical path between the first splitter 32A and the photodetector 50. The first coupling element 36A is connected to the first splitter 32A via a waveguide 75, and is connected to the second coupling element 36B via a waveguide 76. The first coupling element 36A sends to the photodetector 50 interference light between the first reflected light and the second reflected light sent from the second coupling element 36B and the reference light sent from the first splitter 32A.

[0095] The photodetector 50 outputs a signal corresponding to the intensity of the interfering light, and the processing circuitry 60 calculates the distance to and / or velocity of one or more objects present in the scene based on the signal.

[0096] As described above, the first waveguide 72A transmits both the first illumination light and the first reflected light reflected from the scene. The second waveguide 72B transmits both the second illumination light and the second reflected light reflected from the scene. The third waveguide 74A branches off from the first waveguide 72A and transmits the first reflected light that has passed through the first waveguide 72A. The fourth waveguide 74B branches off from the second waveguide 72B and transmits the second reflected light that has passed through the second waveguide 72B. The fifth waveguide 73A inputs the first illumination light from the second splitter 32B to the first waveguide 72A. The sixth waveguide 73B inputs the second illumination light from the second splitter 32B to the second waveguide 72B. The photodetector 50 detects the first reflected light, the second reflected light, and the reference light.

[0097] As shown in FIG. 11, the optical path length of the first waveguide 72A is d ２１ , the optical path length of the second waveguide 72B is d ２２ , the optical path length of the third waveguide 74A is d ４１ , the optical path length of the fourth waveguide 74B is d ４１ , the optical path length of the fifth waveguide 73A is d １１ , the optical path length of the sixth waveguide 73B is d １２ The optical path length of the waveguide 71 is d １ , the optical path length of the waveguide 75 is d ５ , the optical path length of the waveguide 76 is d ６ The distance from the first optical element 40A to the object 10A is d ３１ , the distance from the second optical element 40B to the object 10B is d ３２ Let's say.

[0098] The cause of fiber noise is the optical path length d ２１ and the optical path length d of the second waveguide 72B. ２２ In this embodiment, the first splitter 39A is disposed between the second splitter 32B and the first optical element 40A, and the second splitter 39B is disposed between the second splitter 32B and the second optical element 40B. As a result, the optical path length d １１ and d ４１ and the optical path length d １２ and d ４２ By adjusting the distances d and d, the total optical path lengths corresponding to the objects 10A and 10B can be changed. In this embodiment, even if return light occurs in the waveguides 73A and 74A and the waveguides 73B and 74B, the return light does not enter the photodetector 50, and therefore no fiber noise is generated. １１ and d ４１ The sum of and d １２ and d ４２ By making a difference between the sum of the first object 10A and the second object 10B, the frequency band for distance measurement of the first object 10A and the frequency band for distance measurement of the second object 10B can be divided.

[0099] In this manner, in this embodiment, the optical path length d １１ and the optical path length d of the third waveguide 74A from the first branching element 39A to the second coupling element 36B. ４１ The sum of these is the optical path length d of the sixth waveguide 73B from the second splitter 32B to the second branching element 39B. １２ and the optical path length d of the fourth waveguide 74B from the second branching element 39B to the second coupling element 36B. ４２ That is, in this embodiment, the following equation (10) is satisfied: １１ +d ４１ ≠d １２ +d ４２ (10)

[0100] This allows the band of the beat frequency of the reflected light from the first beam to be separated from the band of the beat frequency of the reflected light from the second beam, making it possible to measure the distance or speed of a plurality of targets.

[0101] 12 is a diagram for explaining the relationship between the optical path length and the beat frequency, and the influence of various noises. Here, the optical path length indicates the optical path length starting from the first splitter 32A and ending at the first coupling element 36A. The maximum beat frequency that can be detected by the photodetector 50 and the processing circuit 60 is defined as f ＰＤ The frequency at which the first optical element noise occurs is defined as f ｎ１ , the frequency at which the second optical element noise occurs is f ｎ２ , the frequency at which the first branch element noise occurs is f ｃ１ , the frequency at which the second branch element noise occurs is f ｃ２ , the beat frequency corresponding to the first target is f ｔ１ , the beat frequency corresponding to the second target is f ｔ２ The optical path length is the optical path length d of the reference light. ５ When it coincides with this, the beat frequency becomes 0 MHz.

[0102] Frequency f of the first optical element noise ｎ１ corresponds to the 0 m point of the distance measurement by the first beam. The frequency f of the noise of the second optical element ｎ２ corresponds to the 0 m point of the distance measurement by the second beam. In this example, the optical path length d ４２ is the optical path length d of the waveguide 74A. ４１ By making it longer than ｎ２ at frequency f ｎ１ It is higher than that.

[0103] The first branching element noise is noise caused by a part of the light that should be directed from the waveguide 73A to the waveguide 72A being directed to the waveguide 74A. The optical path length of the noise light that causes the first branching element noise inside the first branching element 39A is defined as d ｃ１ The second branching element noise is noise caused by a part of the light that should be directed from the waveguide 73B to the waveguide 72B being directed to the waveguide 74B. The optical path length of the noise light that causes the second branching element noise inside the second branching element 39B is defined as d ｃ２Let's say.

[0104] Round-trip optical path length 2d of the waveguide 72A ２１ The first fiber noise occurs due to the optical path length 2d of the waveguide 72B. ２２ The second fiber noise occurs due to the above. In the bands where these fiber noises occur, targets with low optical reflectivity cannot be measured. The first beam measurable band and the second beam measurable band that do not overlap with the band where the fiber noises occur are the frequency bands where distance measurement is possible, and distance measurement and velocity measurement are possible within the distance range corresponding to this frequency band. As shown in the configuration shown in FIG. ２１ and d ２２ By shortening the fiber length, the band in which fiber noise occurs can be narrowed, thereby expanding the distance measurement range.

[0105] 13A to 13D are graphs showing examples of power spectra of beat signals in this embodiment. Fig. 13A shows an example of the power spectrum of a beat signal obtained when both the first beam and the second beam are irradiated onto the target. Fig. 13B shows an example of the power spectrum of a beat signal obtained when the first beam is irradiated onto the target and the second beam is blocked. Fig. 13C shows an example of the power spectrum of a beat signal obtained when the first beam is blocked and the second beam is irradiated onto the target. Fig. 13D shows an example of the power spectrum of a beat signal obtained when both the first beam and the second beam are blocked.

[0106] In this example, the targets are sheets of Kent paper placed at positions 1 m away from the first optical element 40A and the second optical element 40B. １１ = d １２ = 2m, d ２１ = 2m, d ２２ = 1 m, and d ４１ = 2m and d ４２By creating a difference of 12 m between the first and second beams, the measurement ranges of the first and second beams were divided. Figures 13B and 13C show the spectra when the light was blocked in front of each target. As shown in Figures 13A to 13C, it was confirmed that the reflected light from the target was detected as a clear frequency peak. Furthermore, as shown in Figure 13D, when both beams were blocked, the measurement ranges of the first and second beams were clearly divided, and fiber noise did not overlap each measurement range, confirming that the noise level could be reduced.

[0107] 11 emits two beams, it may be configured to emit three or more beams. In that case, the second splitter 32B is configured to split the light from the waveguide 71 into three or more beams, and pairs of branching elements and optical elements are added for the number of beams. The second coupling element 36B is configured to couple the return light from the branching elements for the number of beams, and input the combined light to the first coupling element 36A.

[0108] <Modification> Next, a modification of this embodiment will be described.

[0109] FIG. 14 is a block diagram showing the configuration of a measurement device 600C according to a modification of this embodiment. The measurement device 600C in this modification includes a LiDAR unit 100, a first optical head 200A, and a second optical head 200B. The LiDAR unit 100 includes a light source 20, an interference optical system 30, a photodetector 50, a processing circuit 60, and a memory 62. The interference optical system 30 includes a first splitter 32A, a second splitter 32B, a first coupling element 36A, and a second coupling element 36B. The first optical head 200A includes a first branching element 39A and a first optical element 40A. The second optical head 200B includes a second branching element 39B and a second optical element 40B. The components of the LiDAR unit 100 and the optical heads 200A and 200B are the same as the corresponding components shown in FIG. 11 .

[0110] If the target object is large or has a complex structure, it may be necessary to install the optical elements 40A and 40B (e.g., beam shapers) at various positions or angles. As mentioned above, the optical path length d of the waveguide 72A is ２１ and the optical path length d of the waveguide 72B ２２ By shortening the waveguides 72A and 72B, the fiber noise band can be narrowed and the range of distances that can be measured can be expanded. Therefore, in this modification, the first branching element 39A and the first optical element 40A are housed in the housing of the first optical head 200A, and the second branching element 39B and the second optical element 40B are housed in the housing of the second optical head 200B. This allows the waveguides 72A and 72B to be short and the positions and orientations of the optical elements 40A and 40B to be flexibly changed.

[0111] In this modification, the housing of the LiDAR unit 100 houses the light source 20, the interference optical system 30, the photodetector 50, the processing circuit 60, and the memory 62. The LiDAR unit 100 includes a first output unit 91a, a second output unit 91b, a first input unit 92a, and a second input unit 92b. The first output unit 91a is connected to the fifth waveguide 73A. The second output unit 91b is connected to the sixth waveguide 73B. The first input unit 92a is connected to the third waveguide 74A. The second input unit 92b is connected to the fourth waveguide 74B. The first output unit 91a outputs the first irradiation light from the second splitter 32B to the fifth waveguide 73A. The second output unit 91b outputs the second illumination light from the second splitter 32B to the sixth waveguide 73B. The first input unit 92a inputs the first reflected light from the third waveguide 74A to the second coupling element 36B. The second input unit 92b inputs the second reflected light from the fourth waveguide 74B to the second coupling element 36B. The outputs 91a and 91b and the inputs 91a and 91b may be realized, for example, by two optical output ports and two optical input ports provided on the housing of the LiDAR unit 100.

[0112] Note that the LiDAR unit 100 may house portions of the light source 20, the interference optical system 30, the photodetector 50, the processing circuit 60, and the memory 62. For example, the processing circuit 60 and the memory 62 may be provided in a device external to the LiDAR unit 100. Each waveguide (e.g., waveguides 70, 71, 75, and 76) in the LiDAR unit 100 may be an optical fiber waveguide or may be formed on a chip. At least one of the light source 20, the photodetector 50, the processing circuit 60, and the memory 62 may be integrated on such a chip.

[0113] The housing of optical head 200A accommodates first branching element 39A, first optical element 40A, first waveguide 72A, a portion of third waveguide 74A, and a portion of fifth waveguide 73A. The housing of optical head 200B accommodates second branching element 39B, second optical element 40B, second waveguide 72B, a portion of fourth waveguide 74B, and a portion of sixth waveguide 73B. Thus, first head 200A accommodates at least a portion of first waveguide 72A and at least a portion of third waveguide 74A, and second head 200B accommodates at least a portion of second waveguide 72B and at least a portion of fourth waveguide 74B.

[0114] By separating the LiDAR unit 100 from the optical heads 200A and 200B, the optical heads 200A and 200B can be installed away from the LiDAR unit 100. This allows the size and weight of the optical heads 200A and 200B to be reduced, increasing the flexibility of installation of the optical heads 200A and 200B. Furthermore, the temperature-resistant and vibration-resistant housing of the LiDAR unit 100 can house precision equipment such as the light source 20, the photodetector 50, or the processing circuit 60, thereby stabilizing their operation. Furthermore, the freedom of design and manufacturing can be improved, such as by forming the LiDAR unit 100 into a chip.

[0115] In this embodiment, the LiDAR unit 100 and the first optical head 200A are optically coupled by waveguides 73A and 74A. The LiDAR unit 100 and the second optical head 200B are optically coupled by waveguides 73B and 74B. The optical path length d of the waveguide 73A is １１ , the optical path length d of the waveguide 73B １２ , the optical path length d of the waveguide 74A ４１ , and the optical path length d of the waveguide 74B ４２ does not cause fiber noise, and the optical path length d ５ This allows the LiDAR unit 100 to be separated from the optical heads 200A and 200B. ２１ and the optical path length d of the waveguide 72B ２２ This makes it easier to reduce fiber noise and expand the range of distances that can be measured.

[0116] <Calibration Method> Next, an example of a method for calibrating a measurement device will be described.

[0117] First, construct the optical system shown in FIG. 11 or 14 and place the object at a position away from the first optical element 40A and the second optical element 40B. For example, place the object at a distance of 1 m from the first optical element 40A and the second optical element 40B. A silver diffusion plate with a relatively high reflectance can be used as the object. Place the object so that reflected light from the object returns to the optical elements 40A and 40B (e.g., collimator lenses). Irradiate the first and second beams onto the object, and check the spectrum of the beat signal detected by the photodetector 50. Based on the spectrum, check that the respective fiber noise bands do not overlap with the respective distance measurement ranges. If the fiber noise band overlaps with the distance measurement range of either the first or second beam, the optical path length d ２１ , d ２２ , d ５ By adjusting the fiber noise band, it is possible to avoid overlapping with the measurement range of either beam. This allows for a measurement device with a wide measurement range.

[0118] [Note] The present disclosure is not limited to the above-described embodiments. As long as they do not deviate from the spirit of the present disclosure, the scope of the present disclosure also includes various modifications that a person skilled in the art may have made to each embodiment, modifications that a person skilled in the art may have made to each modification, configurations constructed by combining components in different embodiments, configurations constructed by combining components in different modifications, and configurations constructed by combining components in any embodiment and components in any modification.

[0119] The above description of the embodiments discloses the following techniques.

[0120] (Technology 1) A measurement device comprising: a light source; a first splitter that splits light from the light source into illumination light and reference light; a second splitter that splits the illumination light into first illumination light and second illumination light; a first waveguide through which the first illumination light and first reflected light reflected from a scene pass together; a second waveguide through which the second illumination light and second reflected light reflected from the scene pass together; a third waveguide that branches from the first waveguide and through which the first reflected light that has passed through the first waveguide passes; a fourth waveguide that branches from the second waveguide and through which the second reflected light that has passed through the second waveguide passes; and a photodetector that detects the first reflected light, the second reflected light, and the reference light.

[0121] This configuration allows distance and / or velocity measurements to be made for multiple targets, thereby extending the range of distances that can be measured, for example.

[0122] (Technology 2) The measurement device according to Technology 1, further comprising: a fifth waveguide that inputs the first irradiation light from the second splitter into the first waveguide; and a sixth waveguide that inputs the second irradiation light from the second splitter into the second waveguide, wherein a sum of an optical path length of the third waveguide and an optical path length of the fifth waveguide is different from a sum of an optical path length of the fourth waveguide and an optical path length of the sixth waveguide.

[0123] This configuration allows for the separation of the frequency band of measurements by the first beam emitted to the scene via the first waveguide from the frequency band of measurements by the second beam emitted to the scene via the second waveguide, thereby enabling measurements of multiple targets to be performed with higher accuracy.

[0124] (Technology 3) The measurement device according to Technology 1 or 2, further comprising: a first branching element that outputs the first irradiation light input from the fifth waveguide to the first waveguide and outputs the first reflected light input from the first waveguide to the third waveguide; and a second branching element that outputs the second irradiation light input from the sixth waveguide to the second waveguide and outputs the second reflected light input from the second waveguide to the fourth waveguide.

[0125] (Technology 4) The measurement device according to Technology 3, further comprising: a first coupling element disposed on an optical path between the first splitter and the photodetector; and a second coupling element configured to output the first reflected light input from the third waveguide and the second reflected light input from the fourth waveguide to the first coupling element, wherein the light source emits light whose frequency changes over time, and the first coupling element sends interference light between the first reflected light, the second reflected light, and the reference light to the photodetector.

[0126] (Technology 5) The measurement device according to Technology 4, wherein the photodetector outputs a signal according to the intensity of the interference light, and further comprises a processing circuit that calculates a distance to one or more objects present in the scene and / or a speed of the objects based on the signal.

[0127] (Technology 6) The measurement device according to any one of Technologies 1 to 5, comprising: a first head that accommodates at least a portion of the first waveguide and at least a portion of the third waveguide; and a second head that accommodates at least a portion of the second waveguide and at least a portion of the fourth waveguide.

[0128] (Technology 7) The measurement device described in Technology 6, wherein the first head further accommodates a first optical element that collimates the first illumination light that has propagated through the first waveguide and outputs the collimated illumination light toward the scene, and the second head further accommodates a second optical element that collimates the first illumination light that has propagated through the first waveguide and outputs the collimated illumination light toward the scene.

[0129] (Technology 8) The measurement device according to any one of technologies 1 to 7, further comprising a chip that integrates the light source, the first splitter, the second splitter, and the photodetector.

[0130] (Technology 9) The measurement device described in Technology 8, wherein the chip further integrates a processing circuit that calculates the distance to and / or the velocity of at least one object present in the scene based on the signal output from the photodetector.

[0131] (Technology 10) The measurement device according to any one of techniques 1 to 9, further comprising a housing that houses the light source, the first splitter, the second splitter, and the photodetector.

[0132] (Technology 11) The measurement device according to Technology 10, wherein the housing further houses a processing circuit that processes a signal output from the photodetector to calculate a distance to at least one object present in the scene and / or a velocity of the object.

[0133] The measurement device according to the embodiment of the present disclosure can be used, for example, in a ranging system mounted on a vehicle such as an automobile, an unmanned aerial vehicle (UAV), or an automated guided vehicle (AGV), or for vehicle detection purposes.

[0134] 10, 10A, 10B Object 20 Light source 30 Interference optical system 32, 32A, 32B Splitter 34 Branching element 36, 36A, 36B Coupling element 39A, 39B Branching element 40, 40A, 40B Optical element 50 Photodetector 60 Processing circuit 62 Memory 70, 71, 72, 72A, 72B, 73A, 73B, 74, 75, 76 Optical waveguide 100 LiDAR unit 200, 200A, 200B Optical head 500A, 500B, 600A, 600B, 600C Measurement device

Claims

1. A measurement device comprising: a light source; a first splitter that splits light from the light source into an illumination light and a reference light; a second splitter that splits the illumination light into a first illumination light and a second illumination light; a first waveguide through which the first illumination light and a first reflected light reflected from a scene pass together; a second waveguide through which the second illumination light and a second reflected light reflected from the scene pass together; a third waveguide that branches from the first waveguide and through which the first reflected light that has passed through the first waveguide passes; a fourth waveguide that branches from the second waveguide and through which the second reflected light that has passed through the second waveguide passes; and a photodetector that detects the first reflected light, the second reflected light, and the reference light.

2. The measurement device according to claim 1, further comprising: a fifth waveguide that inputs the first irradiation light from the second splitter to the first waveguide; and a sixth waveguide that inputs the second irradiation light from the second splitter to the second waveguide, wherein the sum of the optical path length of the third waveguide and the optical path length of the fifth waveguide is different from the sum of the optical path length of the fourth waveguide and the optical path length of the sixth waveguide.

3. The measurement device according to claim 1 or 2, further comprising: a first branching element that outputs the first irradiation light input from the fifth waveguide to the first waveguide and outputs the first reflected light input from the first waveguide to the third waveguide; and a second branching element that outputs the second irradiation light input from the sixth waveguide to the second waveguide and outputs the second reflected light input from the second waveguide to the fourth waveguide.

4. The measurement device according to claim 3, further comprising: a first coupling element arranged on an optical path between the first splitter and the photodetector; and a second coupling element which outputs the first reflected light input from the third waveguide and the second reflected light input from the fourth waveguide to the first coupling element, wherein the light source emits light having a frequency which changes over time, and the first coupling element sends interference light between the first reflected light and the second reflected light and the reference light to the photodetector.

5. The measurement device according to claim 4, further comprising a processing circuit that outputs a signal corresponding to the intensity of the interference light and calculates the distance to and / or the speed of one or more objects present in the scene based on the signal.

6. The measurement device according to claim 1 or 2, comprising: a first head that accommodates at least a portion of the first waveguide and at least a portion of the third waveguide; and a second head that accommodates at least a portion of the second waveguide and at least a portion of the fourth waveguide.

7. The measurement device of claim 6, wherein the first head further contains a first optical element that collimates the first illumination light that has propagated through the first waveguide and outputs it toward the scene, and the second head further contains a second optical element that collimates the first illumination light that has propagated through the first waveguide and outputs it toward the scene.

8. The measurement device of claim 1 or 2, comprising a chip integrating the light source, the first splitter, the second splitter, and the photodetector.

9. The measurement device of claim 8, wherein the chip further integrates a processing circuit for calculating a distance to and / or a velocity of at least one object present in the scene based on a signal output from the photodetector.

10. The measurement device of claim 1 or 2, further comprising a housing that houses the light source, the first splitter, the second splitter, and the photodetector.

11. The measurement device of claim 10, wherein the housing further houses processing circuitry for processing signals output from the photodetector to calculate a distance to and / or a velocity of at least one object present in the scene.

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