Distance measuring device

Abstract

To provide a distance measuring device capable of reducing speckle without being limited by the multiplexing degree of a single light source.SOLUTION: A distance measuring device 1 includes a light source unit 10, an optical path branching unit 22 that branches reflected light from an object into multiple optical paths, and a lens unit 23 including multiple lenses 231 to 233 that focus the reflected light. The distance measuring device 1 further includes multiple receiving units 31 to 33 that heterodyne-detect the combined light from the reflected light and reference light to output a beat signal, and multiple Fourier transform units 411 to 413 that perform Fourier transforms on the beat signal to obtain power spectra. The distance measuring device 1 also includes a peak extraction unit 415 that extracts the peak frequency from the sum of each power spectrum. The optical path branching unit 22 is configured to branch the reflected light into multiple optical paths using beam splitters BS1 to BS3 that are independent of the polarization of the emitted light. Furthermore, the multiple lenses 231 to 233 are set to different numerical apertures.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a distance measuring device that measures the distance to an object by coherent detection. [Background technology]

[0002] Conventionally, in distance measuring devices, a technology has been known in which the reflected circularly polarized light emitted from a light source is separated into S-polarized and P-polarized light using a polarizing beam splitter, and each of the separated polarized lights is added (hereinafter also referred to as polarization multiplexing) to reduce specifications (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent Publication No. 2021 / 0181320 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the technology for reducing specifications by polarization multiplexing as in Patent Document 1, the reflected circularly polarized light is separated into S-polarized light and P-polarized light by a polarizing beam splitter, so the degree of multiplicity when using a single light source is limited to 2. For this reason, in order to increase the degree of multiplicity, it is necessary to increase the number of light sources.

[0005] An object of the present disclosure is to provide a distance measuring device capable of reducing speckle without being restricted by the multiplicity of a single light source. [Means for solving the problem]

[0006] The invention described in claim 1 is A distance measuring device that measures the distance to an object by coherent detection, a light source unit (10) that emits light; an optical path branching unit (22) that branches reflected light generated when light emitted from the light source unit is reflected by the object into a plurality of optical paths; a lens unit (23) including a plurality of lenses (231 to 234) provided corresponding to each of the plurality of optical paths and configured to condense reflected light branched into the plurality of optical paths; a plurality of receiving units (31 to 34) provided corresponding to the plurality of optical paths, each of which performs heterodyne detection on a combined light of the reflected light and a reference light that is a part of the emitted light, and outputs a beat signal; a plurality of Fourier transform units (411 to 413) provided corresponding to the plurality of receiving units, each of which performs a Fourier transform on a beat signal to obtain a power spectrum; a peak extraction unit (415) that extracts a peak frequency that has a correlation with the distance to the object from the sum of the power spectra obtained by the plurality of Fourier transform units, the optical path branching unit is configured to branch the reflected light into a plurality of optical paths using beam splitters (BS1 to BS3) that are independent of the polarization of the emitted light; The lenses are set to different numerical apertures.

[0007] In this way, in a configuration in which reflected light is split into multiple optical paths using a polarization-independent beam splitter, the number of splits of reflected light can be changed by, for example, increasing or decreasing the number of beam splitters, and therefore there is no restriction on multiplicity as in Patent Document 1. In addition, in this proposal, the combined light of reflected light and reference light is condensed by multiple lenses with different numerical apertures, reducing the correlation of reflected light from each optical path, thereby achieving the effect of reducing speckle by adding power spectra.

[0008] Therefore, according to the present disclosure, it is possible to realize a distance measuring device capable of reducing speckle without being restricted by the multiplicity of a single light source.

[0009] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram of a distance measuring device according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram for explaining emitted light and the like. [Figure 3] FIG. 2 is an explanatory diagram for explaining the numerical aperture of a lens. [Figure 4] FIG. 10 is an explanatory diagram for explaining variations in light intensity due to speckles. [Figure 5] 10A and 10B are explanatory diagrams for explaining probability distributions before and after addition of power spectra. [Figure 6] FIG. 10 is an explanatory diagram for explaining how to obtain a beat frequency. [Figure 7] FIG. 2 is a schematic diagram illustrating the configuration of a distance measuring device according to a modified example of the first embodiment. [Figure 8] FIG. 10 is a schematic configuration diagram of a distance measuring device according to a second embodiment. [Figure 9] FIG. 10 is a schematic configuration diagram of a distance measuring device according to a third embodiment. [Figure 10] FIG. 10 is a schematic configuration diagram of a distance measuring device according to a fourth embodiment. [Figure 11] FIG. 10 is a schematic configuration diagram of a distance measuring device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same as or equivalent to those described in the preceding embodiments will be given the same reference numerals, and their description may be omitted. Furthermore, in the embodiments, when only some of the components are described, the components described in the preceding embodiments can be applied to the remaining components. The following embodiments can be partially combined with each other, even if not specifically stated, as long as there is no particular problem with the combination.

[0012] (First embodiment) This embodiment will be described with reference to Figs. 1 to 6. In this embodiment, an example will be described in which a distance measuring device 1 of the present disclosure is configured as an FMCW LiDAR mounted on a vehicle. FMCW is an abbreviation for Frequency Modulated Continuous Wave. LiDAR is an abbreviation for Light Detection And Ranging.

[0013] The distance measuring device 1 is an optical interference measuring device that measures the distance to a target object by coherent detection. As shown in Fig. 1, the distance measuring device 1 includes a light source unit 10, an optical system 20, an optical receiving unit 30, and a signal processing unit 40.

[0014] The light source unit 10 is a device that emits laser light. Although not shown, the light source unit 10 includes a laser oscillator and a modulator. The laser oscillator generates and outputs laser light of a predetermined frequency. The modulator performs frequency modulation of a predetermined amplitude on the laser light output from the laser oscillator, thereby outputting emitted light whose frequency varies over time to the optical system 20. The emitted light from the light source unit 10 is, for example, a triangular wave having an up-chirp period in which the frequency increases linearly and a down-chirp period in which the frequency decreases linearly, as shown in FIG. 2.

[0015] The optical system 20 is a spatial interference optical system that forms an optical path that guides a portion of the emitted light emitted from the light source unit 10 to a target object. The optical system 20 also combines reflected light generated when the emitted light is reflected by the object with reference light that is a portion of the emitted light, and outputs combined light of the reflected light and the reference light to the receiving unit 30. Specifically, the optical system 20 is configured to include a light guiding unit 21, an optical path branching unit 22, and a lens unit 23.

[0016] The light guiding unit 21 irradiates a part of the light emitted from the light source unit 10 as measurement light toward the target side. The light guiding unit 21 includes a branching filter 211 that branches the light emitted from the light source unit 10, a circulator (not shown), and a beam scanner (not shown).

[0017] The splitter 211 splits the light emitted from the light source unit 10 into measurement light and reference light to be combined with the reflected light. The splitter 211 has a division ratio set so that when the measurement light is 10 to 100 mW, the reference light is several mW.

[0018] The circulator is an optical component having three ports. The circulator outputs emitted light input to a first port via demultiplexer 211 to the beam scanner from a second port, and outputs reflected light input to the second port from the beam scanner to optical path branching unit 22 from a third port.

[0019] The optical path branching unit 22 branches the reflected light, which is generated when the light emitted from the light source unit 10 is reflected by an object, into multiple optical paths. The optical path branching unit 22 of this embodiment is configured to branch the reflected light into three optical paths that guide the reflected light to each of the receiving units 31 to 33.

[0020] Specifically, the optical path branching unit 22 includes a first beam splitter BS1 and a second beam splitter BS2. Each of the beam splitters BS1 and BS2 is configured as a non-polarizing beam splitter that does not depend on the polarization of the emitted light.

[0021] The first beam splitter BS1 combines the reflected light and the reference light output from the circulator, and splits the combined light of the reflected light and the reference light into an optical path toward the first receiving unit 31 (described later) and an optical path toward the second beam splitter BS2. The splitting ratio of the first beam splitter BS1 is set, for example, so that the intensity of the light toward the first receiving unit 31 and the intensity of the light toward the second beam splitter BS2 are the same.

[0022] The second beam splitter BS2 splits the combined light of the reflected light and the reference light output from the first beam splitter BS1 into an optical path toward a second receiving unit 32 (described later) and an optical path toward a third receiving unit 33 (described later). The split ratio of the second beam splitter BS2 is set, for example, so that the intensity of the light toward the second receiving unit 32 and the intensity of the light toward the third receiving unit 33 are the same.

[0023] Here, the optical path branching section 22 in this embodiment is configured to cause the first beam splitter BS1 to function as a multiplexer and a demultiplexer, but is not limited to this and may be configured to have a multiplexer and a demultiplexer separately.

[0024] The lens unit 23 focuses the combined light of the reflected light branched into the multiple optical paths and the reference light that is a part of the emitted light. The lens unit 23 includes lenses 231 to 233, the number of which is the same as the number of optical paths branched by the optical path branching unit 22.

[0025] Specifically, the lens unit 23 includes a first lens 231, a second lens 232, and a third lens 233. Each of the lenses 231 to 233 is set to a different numerical aperture. As shown in FIG. 3, the numerical aperture is defined as the sine value (i.e., sin θ) of the maximum angle θ between the lens and the optical axis Oax multiplied by the refractive index n. Note that the first lens 231, the second lens 232, and the third lens 233 may have the same aperture diameter or different aperture diameters, as long as they have different numerical apertures.

[0026] The optical receiving unit 30 receives the combined light of the reflected wave and the reference light focused by the lens unit 23, and heterodyne-detects the combined light to output a beat signal. The optical receiving unit 30 includes receiving units 31 to 33, the number of which is the same as the number of optical paths branched by the optical path branching unit 22.

[0027] Specifically, the optical receiving unit 30 includes a first receiving unit 31, a second receiving unit 32, and a third receiving unit 33. The first receiving unit 31, the second receiving unit 32, and the third receiving unit 33 each include a photodetector PD and a transimpedance amplifier TIA. The photodetector PD is a photodetector that photoelectrically converts the combined light and is configured to include, for example, a photodiode. The transimpedance amplifier TIA converts the current signal output by the photodetector PD into a voltage signal and outputs the converted voltage signal to the signal processing unit 40 as a beat signal.

[0028] The signal processing unit 40 detects the distance to a target object and the like based on the beat signal received from the optical receiving unit 30. The signal processing unit 40 includes a control unit 41 that executes various types of calculation processing, and a storage unit 42.

[0029] The storage unit 42 includes a non-volatile memory such as a ROM, a volatile memory such as a RAM, and a flash memory. The storage unit 42 stores, for example, programs and various parameters used for arithmetic processing in the control unit 41. The storage unit 42 is configured as a non-transitory tangible storage medium.

[0030] The control unit 41 executes various types of arithmetic processing based on programs stored in the storage unit 42. The control unit 41 serves as a functional unit for realizing various functions of the signal processing unit 40.

[0031] The control unit 41 performs a Fourier transform on the beat signal received from the optical receiving unit 30 to obtain a power spectrum, and detects the distance to the target object based on the peak frequency related to the distance to the object in the obtained power spectrum.

[0032] As shown in the upper left of Figure 4, when laser light hits the unevenness of the surface of an object, random light interference occurs. This causes a random interference pattern in the reflected light observed at the observation point. This phenomenon is called speckle.

[0033] Generally, the statistics of the real and imaginary parts of the complex amplitude of such reflected light can be treated as following a two-dimensional normal distribution, as shown in the upper right of Figure 4. Also, as shown in the lower right of Figure 4, the probability distribution of the light intensity of the reflected light is an exponential distribution. Then, the intensity of the peak frequency in the power spectrum based on the beat signal (hereinafter referred to as peak intensity I peakAs shown in the lower left of Figure 4, the optical signal (also called polarized light) varies exponentially due to the effects of speckle. Note that a technology has been proposed to reduce the speckle by using polarization multiplexing, but this technology splits the circularly polarized reflected wave into S-polarized and P-polarized light using a polarizing beam splitter, so the degree of multiplicity is limited to "2" when using a single light source. For this reason, if the degree of multiplicity is to be increased, it is necessary to increase the number of light sources.

[0034] Taking these factors into consideration, the control unit 41 performs a Fourier transform on each of the beat signals received by the multiple receiving units 31 to 33 to obtain a power spectrum, and then detects the distance to the target object, etc., based on a signal obtained by adding up the obtained power spectra.

[0035] Specifically, the control unit 41 of this embodiment includes a plurality of Fourier transform units 411 to 413, an adder 414, and a peak extractor 415 as functional units for detecting the distance to an object, etc.

[0036] Each of the Fourier transform units 411 to 413 performs a Fourier transform on the beat signal to obtain a power spectrum. The first Fourier transform unit 411 performs a Fourier transform on the beat signal received from the first receiving unit 31 to obtain a power spectrum. The second Fourier transform unit 412 performs a Fourier transform on the beat signal received from the second receiving unit 32 to obtain a power spectrum. The third Fourier transform unit 413 performs a Fourier transform on the beat signal received from the third receiving unit 33 to obtain a power spectrum.

[0037] The adder 414 adds the power spectra calculated by the Fourier transformers 411 to 413, as shown on the left side of Fig. 5. The distance measuring device 1 of the present invention focuses the combined light of the reflected light and the reference light by the lenses 231 to 233 with different numerical apertures. This reduces the correlation between the reflected light from each optical path. Therefore, the power spectrum after addition has a peak intensity I related to the distance to the object in the power spectrum, as shown on the right side of Fig. 5. peak The probability distribution of is a gamma distribution, and the peak intensity I peakAs a result, the speckle reduction effect can be obtained. The addition in the adder 414 may be a simple sum or an averaging.

[0038] The peak extraction unit 415 extracts peak frequencies that have a correlation with the distance to the object from the sum of the power spectra obtained by the Fourier transform units 411 to 413. For example, as shown in FIG. 6, the peak extraction unit 415 extracts peak frequencies that have a correlation with the distance to the object from the power spectrum after the sum. peak The peak frequency having the beat frequency f beat Then, the peak extraction unit 415 extracts the beat frequency f beat The distance to the object is calculated based on the beat frequency f beat As shown in Figure 2, the beat frequency f is the difference between the frequency fr of the reference light, which is part of the emitted light, and the frequency fd of the reflected light. beat is determined by the phase difference between the reference light and the reflected light due to the distance to the target object, and the Doppler shift between the reference light and the reflected light due to the relative velocity of the object. Therefore, the beat frequency f beat By specifying the target object, the position, velocity, etc. can be obtained.

[0039] Next, the operation of the distance measuring device 1 will be described. When the vehicle's start switch is turned on, the operation of the distance measuring device 1 begins. Then, light is emitted from the light source unit 10, and a portion of the emitted light is emitted to a target object via the circulator and scanner of the light guide unit 21 of the optical system 20. In addition, another portion of the emitted light from the light source unit 10 is branched by the branching filter 211 of the optical system 20 as reference light and is led to the first beam splitter BS1 of the optical path branching unit 22.

[0040] The reflected light generated when the emitted light is reflected by a target object passes through a beam scanner and a circulator, and is then combined with the reference light by a first beam splitter BS1.

[0041] The combined light of the reflected light and the reference light is first split by the first beam splitter BS1 into light directed toward the first receiving unit 31 and light directed toward the second beam splitter BS2. The light directed toward the second beam splitter BS2 is then split by the second beam splitter BS2 into light directed toward the second receiving unit 32 and light directed toward the third receiving unit 33.

[0042] Light heading toward the first receiving unit 31 is collected by the first lens 231 and output to the first receiving unit 31. Light heading toward the second receiving unit 32 is collected by the second lens 232 and output to the second receiving unit 32. Light heading toward the third receiving unit 33 is collected by the third lens 233 and output to the third receiving unit 33.

[0043] The receiving units 31 to 33 receive the combined light of the reflected wave and the reference light collected by the lenses 231 to 233, perform heterodyne detection on the combined light, and output a beat signal to the signal processing unit .

[0044] The signal processing unit 40 obtains a power spectrum by Fourier transforming each of the beat signals received from the receiving units 31 to 33, and then adds up the obtained power spectra. Then, the signal processing unit 40 detects the distance to the target object based on the peak frequency related to the distance to the object in the power spectrum after addition.

[0045] In the distance measuring device 1 described above, the optical path branching unit 22 is configured to branch reflected light into a plurality of optical paths using a beam splitter BS that does not depend on the polarization of the emitted light, and the lenses 231 to 233 are set to different numerical apertures.

[0046] In this configuration, in which the reflected light is split into multiple optical paths using a polarization-independent beam splitter BS, the number of splits of the reflected light can be changed by, for example, increasing or decreasing the number of beam splitters BS, and therefore there is no restriction on the degree of multiplicity as in Patent Document 1.

[0047] In addition, in the distance measuring device 1 of the present invention, the combined light of the reflected light and the reference light is focused by multiple lenses 231 to 233 with different numerical apertures, thereby reducing the correlation of the reflected light from each optical path, thereby achieving the effect of reducing speckle by adding power spectra.

[0048] Therefore, according to the distance measuring device 1 of the present invention, speckles can be reduced without being restricted by the multiplicity of a single light source.

[0049] The distance measuring device 1 of this embodiment also has the following features.

[0050] (1) The optical path branching unit 22 of this embodiment is configured to branch the reflected light into three optical paths. In this way, if the optical path branching unit 22 is configured to branch the reflected light into three optical paths, the degree of multiplexing can be increased compared to the technology that reduces speckle by polarization multiplexing, and therefore the speckle reduction effect can be improved without increasing the number of light source units 10.

[0051] (2) In the present embodiment, each of the receiving units 31 to 33 is configured such that the combined light beams collected by each of the lenses 231 to 233 are directly irradiated onto the photodetector PD for photoelectric conversion. This allows each of the receiving units 31 to 33 to appropriately receive combined light beams with low correlation.

[0052] (Modification of the first embodiment) In the first embodiment, an example has been described in which the optical path branching section 22 is configured to branch the reflected light into three optical paths, but the optical path branching section 22 may be configured to branch the reflected light into two optical paths, or may be configured to branch the reflected light into four or more optical paths.

[0053] 7, the distance measuring device 1 may be configured such that the optical path branching unit 22 branches the reflected light into four optical paths. Such a configuration can be realized by adding a third beam splitter BS3, configuring the lens unit 23 with lenses 231-234 in the same number as the optical paths branched by the optical path branching unit 22, and configuring the optical receiving unit 30 with receiving units 31-34 in the same number as the optical paths branched by the optical path branching unit 22.

[0054] (Second embodiment) Next, a second embodiment will be described with reference to Fig. 8. In this embodiment, differences from the first embodiment will be mainly described.

[0055] 8, the distance measuring device 1 of this embodiment is configured such that the optical path branching unit 22 branches the reflected light into two optical paths. Specifically, the optical path branching unit 22 is configured with a first beam splitter BS1. The lens unit 23 is configured with a first lens 231 and a second lens 232 that are disposed on the optical path branched by the optical path branching unit 22. The optical receiving unit 30 is configured with a first receiving unit 31 and a second receiving unit 32 that are connected to the ends of the optical path branched by the optical path branching unit 22. Although not shown, the functional units of the signal processing unit 40 are provided in a number corresponding to the number of optical paths branched by the optical path branching unit 22.

[0056] Here, the splitting ratio of the first beam splitter BS1 is set so that the intensities of the reflected light focused on the first lens 231 and the second lens 232 are the same. In this embodiment, the splitting ratio of the first beam splitter BS1 is set so that the intensities of the reflected light focused on the first lens 231 and the second lens 232 are 1:1.

[0057] Furthermore, in the distance measuring device 1, a part of the optical system 20 is configured by the optical fiber PF. Specifically, in the optical system 20, the optical path from the light source unit 10 to the first port of the circulator CC is configured by the optical fiber PF. The end of the optical fiber PF is connected to the first port of the circulator CC via a collimator CL.

[0058] Here, the circulator CC is configured as a non-polarizing circulator that is not dependent on polarization. The circulator CC is configured as a modularized Faraday rotator FR, a half-wave plate WP, spectrometers SC1 and SC2, and reflecting mirrors MR1 ​​and MR2.

[0059] In the optical system 20 of this embodiment, the optical paths from the lenses 231, 232 to the receiving units 31, 32 and the optical paths connected to these optical paths for guiding the reference light from the demultiplexer 211 to the receiving units 31, 32 are configured by optical fibers PF. As a result, the reflected light after being collected by the lenses 231, 232 is guided to the photodetector PD of each receiving unit 31, 32 via the optical fiber PF and subjected to photoelectric conversion. In this embodiment, the reflected light collected by the lenses 231, 232 and the reference light are combined by the multiplexers 212, 213 provided between the photodetector PD and the lenses 231-233.

[0060] The other points are the same as those in the first embodiment. The distance measuring device 1 of this embodiment can obtain the same effects as those in the first embodiment that are achieved by a configuration common to or equivalent to that of the first embodiment.

[0061] The distance measuring device 1 of this embodiment also has the following features.

[0062] (1) In the optical path branching unit 22 of this embodiment, the splitting ratio of the first beam splitter BS1 is set so that the intensities of the reflected light beams focused on the lenses 231 and 232 are uniform. If there is variation in the intensities of the reflected light beams focused on the lenses 231 and 232, there is a risk that the speckle reduction effect achieved by adding the power spectra may be suppressed. For this reason, it is desirable that the splitting ratio of the first beam splitter BS1 in the optical path branching unit 22 is set so that the intensities of the reflected light beams focused on the lenses 231 and 232 are uniform.

[0063] (2) In each of the receiving units 31 and 32 of this embodiment, the reflected light after being collected by each of the lenses 231 and 232 is introduced to the photodetector PD via the optical fiber PF for photoelectric conversion. This makes it easier to arrange the optical path from each of the lenses 231 and 232 to the photodetector PD. This greatly contributes to making the distance measuring device 1 more compact.

[0064] (Third embodiment) Next, a third embodiment will be described with reference to Fig. 9. In this embodiment, differences from the second embodiment will be mainly described.

[0065] 9, the distance measuring device 1 of this embodiment is configured such that the optical path branching unit 22 branches the reflected light into three optical paths. Specifically, the optical path branching unit 22 is configured with a first beam splitter BS1 and a second beam splitter BS2. The lens unit 23 is configured with a first lens 231, a second lens 232, and a third lens 233 that are arranged on the optical paths branched by the optical path branching unit 22. The optical receiving unit 30 is configured with a first receiving unit 31, a second receiving unit 32, and a third receiving unit 33 that are connected to the ends of the optical paths branched by the optical path branching unit 22. Although not shown, the functional units of the signal processing unit 40 are provided in a number corresponding to the number of optical paths branched by the optical path branching unit 22.

[0066] Here, the splitting ratios of the first beam splitter BS1 and the second beam splitter BS2 are set so that the intensities of the reflected light focused on each of the lenses 231 to 233 are uniform. In this embodiment, the splitting ratio of the first beam splitter BS1 is set so that the ratio between the intensity of the light focused on the first lens 231 and the intensity of the light heading toward the second beam splitter BS2 is 1:2. In addition, the splitting ratio of the second beam splitter BS2 is set so that the intensities of the light focused on the second lens 232 and the third lens 233 are 1:1.

[0067] Furthermore, in the distance measuring device 1, a portion of the optical system 20 is configured using an optical fiber PF. Specifically, in the optical system 20, the optical path from the light source unit 10 to the first port of the circulator CC is configured using the optical fiber PF. In the optical system 20, the optical paths from each of the lenses 231 to 233 to each of the receiving units 31 to 33 and the optical paths connected to the optical paths and guiding the reference light from the demultiplexer 211 to each of the receiving units 31 to 33 are configured using the optical fiber PF. As a result, the reflected light after being collected by each of the lenses 231 to 233 is introduced to the photodetector PD of each of the receiving units 31 to 33 via the optical fiber PF and is photoelectrically converted. In this embodiment, the reflected light collected by each of the lenses 231 to 233 and the reference light are combined in the optical path between the photodetector PD and each of the lenses 231 to 233.

[0068] Furthermore, in the distance measuring device 1 of this embodiment, the collimator CL, the circulator CC, the optical path branching unit 22, and the lens unit 23 are modularized as a single optical path module. Such modularization is realized, for example, by mounting the collimator CL, the circulator CC, the optical path branching unit 22, and the lens unit 23 on a single substrate.

[0069] The other points are the same as those in the second embodiment. The distance measuring device 1 of this embodiment can obtain the same effects as those in the second embodiment, which are achieved by a configuration common to or equivalent to that of the second embodiment.

[0070] The distance measuring device 1 of this embodiment also has the following features.

[0071] (1) In the distance measuring device 1 of this embodiment, the collimator CL, the circulator CC, the optical path branching unit 22, and the lens unit 23 are modularized as an optical path module. This makes it easier to configure the distance measuring device 1 compactly and reduces manufacturing costs.

[0072] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Fig. 10. In this embodiment, differences from the third embodiment will be mainly described.

[0073] 10, in the optical system 20 of this embodiment, the optical path from the light source unit 10 to the first port of the circulator CC is formed by the optical fiber PF. In addition, in the optical system 20, the optical path from the demultiplexer 211 to the first beam splitter BS1 is connected by the optical fiber PF so that the reference light is introduced to the first beam splitter BS1. As a result, the reference light is introduced to the first beam splitter BS1 via the optical fiber PF and is combined with the reflected light at the first beam splitter BS1.

[0074] Furthermore, the combined light of the reflected light and the reference light is split by the first beam splitter BS1 into light directed toward the first receiving unit 31 and light directed toward the second beam splitter BS2. The light directed toward the second beam splitter BS2 is then split by the second beam splitter BS2 into light directed toward the second receiving unit 32 and light directed toward the third receiving unit 33. As a result, in the optical system 20, the reflected light after being collected by each of the lenses 231 to 233 is directly introduced into the photodetector PD of each of the receiving units 31 to 33 and photoelectrically converted.

[0075] Furthermore, in the distance measuring device 1 of this embodiment, the collimator CL, the circulator CC, the optical path branching unit 22, the lens unit 23, and the receiving units 31 to 33 of the optical receiving unit 30 are modularized as a single module. Such modularization is realized, for example, by mounting the collimator CL, the circulator CC, the optical path branching unit 22, the lens unit 23, and the receiving units 31 to 33 on a single substrate.

[0076] The other points are the same as those in the third embodiment. The distance measuring device 1 of this embodiment can obtain the same effects as those in the third embodiment, which are achieved by a configuration common to or equivalent to that of the third embodiment.

[0077] The distance measuring device 1 of this embodiment also has the following features.

[0078] (1) In the distance measuring device 1 of this embodiment, the collimator CL, the circulator CC, the optical path branching unit 22, the lens unit 23, and the receiving units 31 to 33 of the optical receiving unit 30 are modularized into a single module. This configuration makes it easier to configure the distance measuring device 1 compactly and reduces manufacturing costs.

[0079] (Fifth embodiment) Next, a fifth embodiment will be described with reference to Fig. 11. In this embodiment, differences from the first embodiment will be mainly described.

[0080] As shown in FIG. 11 , in the distance measuring device 1 of this embodiment, the light source unit 10 and the optical receiving unit 30 are configured as an optical integrated circuit PIC. The optical integrated circuit PIC is configured of a semiconductor having an optical waveguide LW. The optical integrated circuit PIC is provided with a first optical waveguide LW1 that guides the emitted light to the circulator CC, a second optical waveguide LW2 that guides the reference light to each of the receiving units 31 to 33, and a third optical waveguide LW3 that guides the reflected light after being collected by each of the lenses 231 to 233 to each of the receiving units 31 to 33. As a result, in this embodiment, the reflected light after being collected by each of the lenses 231 to 233 is guided to the photodetector PD of each of the receiving units 31 to 33 via the third optical waveguide LW3 formed inside the optical integrated circuit PIC and subjected to photoelectric conversion. Note that in this embodiment, the reflected light collected by each of the lenses 231 to 233 and the reference light are combined by the photodetector PD.

[0081] In addition, a mirror MR that directs the light emitted from the first optical waveguide LW1 toward the circulator CC is added to the optical system 20 of this embodiment. In addition, a mirror MR that directs the reflected light that has passed through the second beam splitter BS2 toward the third lens 233 is added to the optical path branching unit 22.

[0082] The other points are the same as those in the first embodiment. The distance measuring device 1 of this embodiment can obtain the same effects as those in the first embodiment that are achieved by a configuration common to or equivalent to that of the first embodiment.

[0083] The distance measuring device 1 of this embodiment also has the following features.

[0084] (1) In each of the receiving units 31 to 33, the reflected light after being collected by each of the lenses 231 to 233 is guided to the photodetector PD via the third optical waveguide LW3 provided inside the semiconductor optical integrated circuit PIC for photoelectric conversion. In this way, if the configuration is such that the reflected light is guided to the photodetector PD via the optical waveguide LW inside the semiconductor, further miniaturization can be achieved.

[0085] (Other embodiments) Representative embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as follows.

[0086] In the above embodiment, various configurations of the distance measuring device 1 have been described in detail, but the various configurations of the distance measuring device 1 do not need to be the same as those described above, and some of them may be different from those described above.

[0087] In the above embodiment, an example has been described in which the Fourier transform units 411 to 413, the adder 414, and the peak extractor 415 are configured as functional units of the control unit 41 of the signal processing unit 40. However, the present invention is not limited to this. The Fourier transform units 411 to 413, the adder 414, and the peak extractor 415 may be configured as separate components.

[0088] In the above-described embodiment, an example was described in which the distance measuring device 1 of the present disclosure is configured as an FMCW LiDAR mounted on a vehicle, but the distance measuring device 1 can also be applied to devices other than FMCW LiDAR mounted on a vehicle.

[0089] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle.

[0090] In the above-described embodiments, when numerical values ​​such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless they are specifically stated as essential or are clearly limited to a specific number in principle.

[0091] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., the shapes, positional relationships, etc. are not limited to those unless otherwise specified or when they are fundamentally limited to specific shapes, positional relationships, etc.

[0092] The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor with one or more dedicated hardware logic circuits. The controller and method of the present disclosure may be implemented on one or more special-purpose computers configured with a processor and memory programmed to perform one or more functions in combination with a processor configured with one or more hardware logic circuits. The computer program may also be stored on a computer-readable non-transitory tangible storage medium as instructions executed by a computer. [Explanation of symbols]

[0093] 1 Ranging device 10 light source 22 Optical path branching section 23 Lens section 231~233 Lens 31~33 Receiver 411~413 Fourier transform section 415 Peak Extraction Unit BS1~BS3 beam splitter

Claims

1. A distance measuring device that measures the distance to an object by coherent detection, a light source unit (10) that emits light; an optical path branching unit (22) that branches reflected light generated when light emitted from the light source unit is reflected by the object into a plurality of optical paths; a lens unit (23) including a plurality of lenses (231 to 234) provided corresponding to each of the plurality of optical paths and configured to condense the reflected light branched into the plurality of optical paths; a plurality of receiving units (31 to 34) provided corresponding to the plurality of optical paths, each receiving unit heterodyne-detecting a combined light of the reflected light and a reference light that is a part of the emitted light, and outputting a beat signal; a plurality of Fourier transform units (411 to 413) provided corresponding to the plurality of receiving units, respectively, for Fourier transforming the beat signal to obtain a power spectrum; a peak extraction unit (415) that extracts a peak frequency that has a correlation with the distance to the object from the sum of the power spectra obtained by the plurality of Fourier transform units, the optical path branching unit is configured to branch the reflected light into the plurality of optical paths using beam splitters (BS1 to BS3) that are independent of polarization of the emitted light; A distance measuring device, wherein the plurality of lenses are set to different numerical apertures.

2. The distance measuring device according to claim 1 , wherein the optical path branching section is configured to branch the reflected light into three or more optical paths.

3. 3. The distance measuring device according to claim 2, wherein the optical path branching section has a splitting ratio of the beam splitter set so that the reflected light beams focused on the plurality of lenses have the same intensity.

4. 4. The distance measuring device according to claim 1, wherein the receiving section guides the reflected light collected by the lens to a photodetector via an optical fiber for photoelectric conversion.

5. 4. A distance measuring device according to claim 1, wherein the receiving unit guides the reflected light after being focused by the lens to a photodetector via an optical waveguide provided inside the semiconductor for photoelectric conversion.

6. 4. The distance measuring device according to claim 1, wherein said receiving section directly irradiates said reflected light after being collected by said lens onto a photodetector for photoelectric conversion.

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