Distance measuring device

Abstract

A distance measuring device (1) is provided with: a light source unit (10); an optical path branching unit (22) that branches the reflected light from the object into a plurality of optical paths; and a lens unit (23) including a plurality of lenses (231-233) that condense the reflected light. A distance measuring device (1) is provided with: a plurality of receiving units (31-33) that perform heterodyne detection on combined light of reflected light and reference light and output a beat signal; and a plurality of Fourier transform units (411-413) for performing Fourier transform on the beat signal to obtain a power spectrum. The distance measuring device (1) is provided with a peak value extraction unit (415) that extracts a peak frequency from the result obtained by adding the respective power spectrums. The optical path branching unit (22) is configured so as to branch the reflected light toward a plurality of optical paths using beam splitters (BS1-BS3) that do not depend on polarized light of the emitted light. The plurality of lenses (231-233) are set to have different numerical apertures.

Description

Technical Field

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

[0002] In the past, the following technology was known in ranging devices: the reflected wave of circularly polarized light emitted from a light source is separated into S-polarized light and P-polarized light by a polarization beam splitter, and the separated polarized lights are added together (hereinafter also referred to as polarization multiplexing), thereby reducing speckle (for example, refer to Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent Publication No. 2021 / 0181320 Summary of the Invention

[0006] However, in technologies that use polarization multiplexing to reduce speckle, such as those described in Patent Document 1, since a polarization beam splitter separates the reflected wave of circularly polarized light into S-polarized light and P-polarized light, the multiplexing degree (multiplicity) when using a single light source is limited to 2. Therefore, increasing the multiplexing degree requires increasing the number of light sources.

[0007] An object of the present disclosure is to provide a distance measuring device capable of reducing speckles without being limited by the multiplexing degree of a single light source.

[0008] A distance measuring device according to one embodiment of the present disclosure is a distance measuring device that measures the distance to an object by coherent detection, and includes:

[0009] Light source part, emitting light;

[0010] an optical path branching portion for branching reflected light generated by the outgoing light emitted from the light source portion and reflected on the object into a plurality of optical paths;

[0011] a lens unit including a plurality of lenses provided corresponding to the plurality of optical paths, respectively, for focusing the reflected light branched into the plurality of optical paths;

[0012] A plurality of receiving units are provided corresponding to the plurality of optical paths, respectively, and perform heterodyne detection on a combined light of the reflected light and a reference light which is a part of the outgoing light to output a beat signal;

[0013] a plurality of Fourier transform units provided corresponding to the plurality of receiving units, respectively, for performing Fourier transform on the beat signal to obtain a power spectrum; and

[0014] a peak extraction unit that extracts a peak frequency correlated with the distance to the object from a result obtained by adding the power spectra obtained by the plurality of Fourier transform units;

[0015] The optical path branching unit is configured to branch the reflected light into a plurality of optical paths using a beam splitter that is independent of the polarization of the outgoing light.

[0016] The multiple lenses are set to different numerical apertures.

[0017] In this configuration, where reflected light is branched into multiple optical paths using polarization-independent beam splitters, the number of beam splitters can be increased or decreased to change the number of branches of the reflected light, thereby avoiding the multiplexing restrictions of Patent Document 1. Furthermore, in this scheme, the combined light of reflected light and reference light is focused using multiple lenses with different numerical apertures, reducing the correlation between the reflected light from each optical path. This allows for a speckle reduction effect to be achieved by adding power spectra.

[0018] Therefore, according to the present disclosure, it is possible to realize a distance measuring device capable of reducing speckles without being limited by the degree of multiplexing in the case of a single light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of the distance measuring device of the first embodiment.

[0020] Figure 2 This is an explanatory diagram for explaining emitted light and the like.

[0021] Figure 3 This is an explanatory diagram for explaining the numerical aperture of a lens.

[0022] Figure 4 This is an explanatory diagram for explaining the variation in light intensity caused by speckle.

[0023] Figure 5 This is an explanatory diagram for explaining the probability distribution before and after the power spectrum is added.

[0024] Figure 6 This is an explanatory diagram for explaining how to calculate the beat frequency.

[0025] Figure 7 It is a schematic diagram of the structure of a distance measuring device according to a modified example of the first embodiment.

[0026] Figure 8 It is a schematic structural diagram of a distance measuring device according to a second embodiment.

[0027] Figure 9 It is a schematic structural diagram of a distance measuring device according to a third embodiment.

[0028] Figure 10 It is a schematic structural diagram of a distance measuring device according to a fourth embodiment.

[0029] Figure 11 It is a schematic structural diagram of a distance measuring device according to a fifth embodiment. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present disclosure with reference to the accompanying drawings. In the following embodiments, portions that are identical or equivalent to those described in previous embodiments are denoted by the same reference numerals, and their description may be omitted. Furthermore, in the embodiments, when only a portion of the components is described, the components described in the previous embodiments may be applied to the remaining components.

[0031] In the following embodiments, each embodiment can be partially combined with each other even if not specifically stated otherwise, as long as the combination is not particularly hindered.

[0032] (First embodiment)

[0033] Reference Figures 1 to 6 This embodiment will be described. In this embodiment, an example in which the distance measuring device 1 of the present disclosure is configured as a FMCW LiDAR mounted on a vehicle will be described. FMCW stands for Frequency Modulated Continuous Wave. LiDAR stands for Light Detection And Ranging.

[0034] The distance measuring device 1 is an optical interferometer that measures the distance to a target object by coherent detection. Figure 1 As shown, the distance measuring device 1 is configured to include a light source unit 10 , an optical system 20 , a light receiving unit 30 , and a signal processing unit 40 .

[0035] The light source unit 10 is a device that emits laser light. Although not shown in the figure, the light source unit 10 includes a laser emitter and a modulator. The laser emitter generates and outputs laser light of a predetermined frequency. The modulator modulates the frequency of the laser light output from the laser emitter to a predetermined amplitude, and outputs the output light with a frequency that changes with time to the optical system 20. For example, Figure 2 As shown, the light emitted from the light source unit 10 is 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.

[0036] The optical system 20 is a spatial interference optical system that forms an optical path that guides a portion of the outgoing light emitted from the light source unit 10 toward a target object. Furthermore, the optical system 20 combines reflected light generated by the outgoing light reflecting off the object with reference light, which is a portion of the outgoing light, and outputs the combined light of the reflected light and the reference light to the light receiving unit 30. Specifically, the optical system 20 includes a light output unit 21, an optical path branching unit 22, and a lens unit 23.

[0037] The light guide unit 21 directs a portion of the light emitted from the light source 10 toward the target as measurement light. The light guide unit 21 includes a wavelength splitter 211 for branching the light emitted from the light source 10, a circulator (not shown), and a beam scanner (not shown).

[0038] The splitter 211 splits the emitted light from the light source unit 10 into measurement light and reference light synthesized with the reflected light. The splitter 211 sets a splitting ratio such that, for example, when the measurement light is 10 to 100 mW, the reference light is several mW.

[0039] The circulator is an optical device having three ports. The circulator outputs the outgoing light input to the first port via the demultiplexer 211 to the beam scanner from the second port, and outputs the reflected light input to the second port from the beam scanner to the optical path branching unit 22 from the third port.

[0040] The optical path branching unit 22 branches reflected light generated by light emitted from the light source unit 10 reflecting on an object into a plurality of 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 the respective receiving units 31 to 33 .

[0041] 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-polarization beam splitter that is independent of the polarization of the outgoing light.

[0042] The first beam splitter BS1 combines the reflected light output from the circulator with the reference light, and branches 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 first beam splitter BS1 sets the splitting ratio 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 equal, for example.

[0043] The second beam splitter BS2 branches the combined light of the reflected light and the reference light output from the first beam splitter BS1 into an optical path toward the second receiving unit 32 (described later) and an optical path toward the third receiving unit 33 (described later). The second beam splitter BS2 sets a splitting ratio 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 equal, for example.

[0044] Here, the optical path branching unit 22 of this embodiment is configured so that the first beam splitter BS1 functions as a multiplexer and a demultiplexer, but the present invention is not limited thereto and may be configured to include a multiplexer and a demultiplexer separately.

[0045] The lens unit 23 focuses the combined light of the reflected light branched into the plurality of optical paths and the reference light which is part of the outgoing light. The lens unit 23 includes the same number of lenses 231 to 233 as the number of optical paths branched by the optical path branching unit 22 .

[0046] Specifically, the lens unit 23 includes a first lens 231, a second lens 232, and a third lens 233. Each lens 231 to 233 is set to a different numerical aperture. Figure 3 As shown, the numerical aperture is defined as the value obtained by multiplying the sine value of the maximum angle θ (i.e., sinθ) with the optical axis Oax by the refractive index n. Furthermore, the first lens 231, the second lens 232, and the third lens 233 may have the same or different numerical apertures as long as they have different numerical apertures.

[0047] The light receiving unit 30 receives the combined light of the reflected wave and the reference light focused by the lens unit 23 , performs heterodyne detection on the combined light, and outputs a beat signal.

[0048] Specifically, the light receiving unit 30 includes a first receiving unit 31, a second receiving unit 32, and a third receiving unit 33. Each of the first receiving unit 31, the second receiving unit 32, and the third receiving unit 33 includes a photodetector PD and a transimpedance amplifier TIA. The photodetector PD is a photodetector that performs photoelectric conversion on the combined light, and is configured, for example, to include 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 as a beat signal to the signal processing unit 40.

[0049] The signal processing unit 40 detects the distance to the target object and the like based on the beat signal received from the light receiving unit 30. The signal processing unit 40 includes a control unit 41 and a storage unit 42 that execute various calculation processes.

[0050] The storage unit 42 includes nonvolatile memory such as ROM, volatile memory such as RAM, and flash memory. The storage unit 42 stores, for example, programs and various parameters used for calculation processing in the control unit 41. The storage unit 42 is composed of a non-transitory physical storage medium.

[0051] The control unit 41 executes various calculation processes based on programs stored in the storage unit 42 . The control unit 41 functions as a functional unit for realizing various functions of the signal processing unit 40 .

[0052] The control unit 41 performs Fourier transform on the beat signal received from the light 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.

[0053] Here, if Figure 4 As shown in (a), when laser light strikes the surface of an object, random interference of light occurs. This creates a random interference pattern in the reflected light observed at the observation point. This phenomenon is called speckle.

[0054] Usually, such as Figure 4 As shown in (b) and (c), the statistics of the real and imaginary parts of the complex amplitude of the reflected light can be treated as statistics that follow a two-dimensional normal distribution. Figure 4 As shown in (d), the probability distribution of the light intensity of the reflected light is an exponential distribution. Figure 4 As shown in (e), the intensity of the peak frequency in the power spectrum of the beat signal (hereinafter also referred to as peak intensity I peak ) due to the influence of speckle, resulting in exponentially distributed deviations. Furthermore, a technique for reducing speckle using polarization multiplexing has been proposed. However, this technique uses a polarization beam splitter to separate the reflected wave of circularly polarized light into S-polarized light and P-polarized light. Therefore, the multiplexing degree is limited to 2 when using a single light source. Therefore, increasing the multiplexing degree requires increasing the number of light sources.

[0055] Taking this into consideration, the control unit 41 performs Fourier transform on the beat signals received by the plurality of receiving units 31 to 33 to obtain power spectra, and detects the distance to the target object based on the signal obtained by adding the obtained power spectra.

[0056] Specifically, the control unit 41 of the present 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 and the like.

[0057] 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.

[0058] like Figure 5 As shown in (a), the adding unit 414 adds the power spectra obtained by the Fourier transform units 411 to 413. The distance measuring device 1 of this embodiment uses lenses 231 to 233 with different numerical apertures to focus the combined light of the reflected light and the reference light. Therefore, the correlation between the reflected light from each optical path becomes smaller. Therefore, in terms of the power spectrum after addition, as shown in FIG. Figure 5 As shown in (b), the peak intensity I in the power spectrum is related to the distance to the object. peak The probability distribution becomes a gamma distribution, which suppresses the peak intensity I peak As a result, the speckle reduction effect can be achieved. In addition, the addition in the adding unit 414 can be either a simple sum or an added average.

[0059] The peak extraction unit 415 extracts the peak frequency that is correlated with the distance to the object from the result obtained by adding the power spectra obtained by the Fourier transform units 411 to 413. Figure 6 As shown, the peak extraction unit 415 extracts the peak intensity I exceeding the predetermined detection threshold value from the added power spectrum. peak The peak frequency of the object is the beat frequency f beat Furthermore, the peak extraction unit 415 is based on the beat frequency f beat Calculate the distance to the object, etc. In addition, Figure 2 As shown, the beat frequency f beat The beat frequency f is the difference between the frequency fr of the reference light, which is part of the outgoing light, and the frequency fd of the reflected light. beat The following parameters determine the phase difference between the reference light and the reflected light according to the distance to the target object, and the Doppler shift between the reference light and the reflected light according to the relative speed of the object. beat , it is possible to determine the position, speed, etc. of the target object.

[0060] Next, the operation of the distance measuring device 1 will be described. When the vehicle's start switch is turned on, the distance measuring device 1 begins operation. Light is emitted from the light source unit 10. A portion of this light passes through the circulator and beam scanner of the light output unit 21 of the optical system 20 and is emitted toward the target object. Furthermore, another portion of the light emitted from the light source unit 10 is branched into reference light by the wave splitter 211 of the optical system 20 and directed to the first beam splitter BS1 of the optical path branching unit 22.

[0061] The reflected light generated by the outgoing light reflecting off the target object passes through the beam scanner and the circulator, and then is combined with the reference light by the first beam splitter BS1.

[0062] The combined light of the reflected light and the reference light is first split by the first beam splitter BS1 into light directed to the first receiving unit 31 and light directed to the second beam splitter BS2. The light directed to the second beam splitter BS2 is then split by the second beam splitter BS2 into light directed to the second receiving unit 32 and light directed to the third receiving unit 33.

[0063] The light directed toward the first receiving unit 31 is condensed by the first lens 231 and output to the first receiving unit 31. The light directed toward the second receiving unit 32 is condensed by the second lens 232 and output to the second receiving unit 32. The light directed toward the third receiving unit 33 is condensed by the third lens 233 and output to the third receiving unit 33.

[0064] Each of the receiving units 31 to 33 receives the combined light of the reflected wave focused by the lenses 231 to 233 and the reference light, performs heterodyne detection on the combined light, and outputs a beat signal to the signal processing unit 40 .

[0065] The signal processing unit 40 performs Fourier transform on the beat signals received from each of the receiving units 31 to 33 to obtain power spectra, and then adds the obtained power spectra. Furthermore, the signal processing unit 40 detects the distance to the target object based on the peak frequency associated with the distance to the object in the added power spectra.

[0066] In the distance measuring device 1 described above, the optical path branching unit 22 is configured to branch the reflected light into a plurality of optical paths using the beam splitter BS that does not depend on the polarization of the outgoing light, and the lenses 231 to 233 are set to different numerical apertures.

[0067] In this configuration, in which the reflected light is branched into multiple optical paths using a polarization-independent beam splitter BS, the number of branches of the reflected light can be changed by increasing or decreasing the number of beam splitters BS, and thus is not subject to the multiplexing degree restrictions of Patent Document 1.

[0068] Furthermore, in the distance measuring device 1 of this embodiment, multiple lenses 231 to 233 with different numerical apertures are used to focus the combined light of the reflected light and the reference light, thereby reducing the correlation of the reflected light from each optical path. Therefore, a speckle reduction effect can be achieved by adding power spectra.

[0069] Therefore, according to the distance measuring device 1 of this embodiment, speckle can be reduced without being restricted by the degree of multiplexing in the case of a single light source.

[0070] Furthermore, the distance measuring device 1 of this embodiment has the following features.

[0071] In this embodiment, the optical path branching unit 22 is configured to branch the reflected light into three optical paths. This configuration allows the optical path branching unit 22 to branch the reflected light into three optical paths, thereby increasing the degree of multiplexing compared to techniques that reduce speckle using polarization multiplexing. Therefore, the speckle reduction effect can be enhanced without increasing the number of light source units 10.

[0072] In this embodiment, the receiving units 31 to 33 are configured to directly irradiate the combined light focused by the lenses 231 to 233 onto the photodetector PD for photoelectric conversion.

[0073] (Modification of the first embodiment)

[0074] In the first embodiment, an example is described in which the optical path branching portion 22 is configured to branch the reflected light into three optical paths. However, the optical path branching portion 22 may branch the reflected light into two optical paths, or may branch the reflected light into four or more optical paths.

[0075] For example, Figure 7 As shown, in the distance measuring device 1, the optical path branching unit 22 may be configured to branch the reflected light into four optical paths. Such a configuration can be achieved by adding a third beam splitter BS3, configuring the lens unit 23 with the same number of lenses 231 to 234 as the number of optical paths branched by the optical path branching unit 22, and configuring the light receiving unit 30 with the same number of receiving units 31 to 34 as the number of optical paths branched by the optical path branching unit 22.

[0076] (Second embodiment)

[0077] Next, refer to Figure 8 In this embodiment, the following mainly describes the parts that are different from the first embodiment.

[0078] like Figure 8As shown, in the distance measuring device 1 of this embodiment, the optical path branching unit 22 is configured to branch the reflected light into two optical paths. Specifically, the optical path branching unit 22 is composed of a first beam splitter BS1. In addition, the lens unit 23 is composed of a first lens 231 and a second lens 232 arranged on the optical path branched by the optical path branching unit 22. Furthermore, the light receiving unit 30 is composed of a first receiving unit 31 and a second receiving unit 32 connected to the end of the optical path branched by the optical path branching unit 22. In addition, although not shown in the figure, the various functional units of the signal processing unit 40 are provided corresponding to the number of optical paths branched by the optical path branching unit 22.

[0079] Here, the first beam splitter BS1 sets a splitting ratio so that the intensity of the reflected light focused by the first lens 231 and the second lens 232 is equal. In this embodiment, the splitting ratio of the first beam splitter BS1 is set so that the intensity of the reflected light focused by the first lens 231 and the second lens 232 is 1:1.

[0080] In the distance measuring device 1, a portion of the optical system 20 is formed by an optical fiber PF. Specifically, in the optical system 20, the optical path from the light source 10 to the first port of the circulator CC is formed by the optical fiber PF. Furthermore, the end of the optical fiber PF is connected to the first port of the circulator CC via a collimator CL.

[0081] Here, the circulator CC is configured as a non-polarization circulator that does not depend on polarization of light. The circulator CC is modularized by combining a Faraday rotator FR, a half-wave plate WP, beam splitters SC1 and SC2, and mirrors MR1 and MR2.

[0082] Furthermore, in the optical system 20 of this embodiment, the optical path from each lens 231, 232 to each receiving unit 31, 32, and the optical path connected to this optical path and guiding the reference light from the demultiplexer 211 to each receiving unit 31, 32 are formed by an optical fiber PF. Consequently, the reflected light focused by each lens 231, 232 is guided via the optical fiber PF to the photodetector PD of each receiving unit 31, 32, where it undergoes photoelectric conversion. Furthermore, in this embodiment, the reflected light focused by each lens 231, 232 is combined with the reference light by multiplexers 212, 213 disposed between the photodetector PD and each lens 231-233.

[0083] The other parts are the same as those of the first embodiment. The distance measuring device 1 of this embodiment can obtain the effects achieved by the configuration common to or equivalent to that of the first embodiment, as in the first embodiment.

[0084] Furthermore, the distance measuring device 1 of this embodiment has the following features.

[0085] In this embodiment, the optical path branching unit 22 sets the splitting ratio of the first beam splitter BS1 so that the intensity of the reflected light focused by the lenses 231 and 232 is uniform. If the intensity of the reflected light focused by the lenses 231 and 232 varies, the speckle reduction effect achieved by adding the power spectra may be suppressed. Therefore, the optical path branching unit 22 preferably sets the splitting ratio of the first beam splitter BS1 so that the intensity of the reflected light focused by the lenses 231 and 232 is uniform.

[0086] In each receiving unit 31, 32 of this embodiment, the reflected light focused by each lens 231, 232 is guided via an optical fiber PF to a photodetector PD for photoelectric conversion. This facilitates the processing of the optical path from each lens 231, 232 to the photodetector PD, significantly contributing to the compactness of the distance measuring device 1.

[0087] (Third embodiment)

[0088] Next, refer to Figure 9 In this embodiment, the differences from the second embodiment will be mainly described.

[0089] like Figure 9 As shown, in the distance measuring device 1 of this embodiment, the optical path branching unit 22 is configured to branch the reflected light into three optical paths. Specifically, the optical path branching unit 22 is composed of a first beam splitter BS1 and a second beam splitter BS2. In addition, the lens unit 23 is composed of a first lens 231, a second lens 232, and a third lens 233 arranged on the optical path branched by the optical path branching unit 22. Furthermore, the light receiving unit 30 is composed of a first receiving unit 31, a second receiving unit 32, and a third receiving unit 33 connected to the end of the optical path branched by the optical path branching unit 22. In addition, although not shown in the figure, the various functional units of the signal processing unit 40 are provided corresponding to the number of optical paths branched by the optical path branching unit 22.

[0090] 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 by the lenses 231 to 233 are equal. In this embodiment, the splitting ratio of the first beam splitter BS1 is set so that the intensity of the light focused by the first lens 231 and the intensity of the light traveling toward the second beam splitter BS2 are 1:2. Furthermore, the splitting ratio of the second beam splitter BS2 is set so that the intensity of the light focused by the second lens 232 and the third lens 233 are 1:1.

[0091] Furthermore, in the distance measuring device 1, a portion of the optical system 20 is comprised of 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 comprised of the optical fiber PF. In the optical system 20, the optical path from each lens 231-233 to each receiving unit 31-33, as well as the optical path connected to this optical path and guiding the reference light from the demultiplexer 211 to each receiving unit 31-33, are comprised of the optical fiber PF. Consequently, the reflected light focused by each lens 231-233 is guided via the optical fiber PF to the photodetector PD of each receiving unit 31-33 for photoelectric conversion. Furthermore, in this embodiment, the reflected light focused by each lens 231-233 and the reference light are combined in the optical path between the photodetector PD and each lens 231-233.

[0092] Furthermore, the distance measuring device 1 of this embodiment modularizes the collimator CL, circulator CC, optical path branching unit 22, and lens unit 23 into a single optical path module. Such modularization is achieved, for example, by mounting the collimator CL, circulator CC, optical path branching unit 22, and lens unit 23 on a single substrate.

[0093] The other parts are the same as those of the second embodiment. The distance measuring device 1 of this embodiment can obtain the effects achieved by the configuration common to or equivalent to that of the second embodiment, similarly to the second embodiment.

[0094] Furthermore, the distance measuring device 1 of this embodiment has the following features.

[0095] The distance measuring device 1 of this embodiment modularizes the collimator CL, the circulator CC, the optical path branching unit 22, and the lens unit 23 into an optical path module. This facilitates compact construction of the distance measuring device 1 and reduces manufacturing costs.

[0096] (Fourth embodiment)

[0097] Next, refer to Figure 10 In this embodiment, the differences from the third embodiment will be mainly described.

[0098] like Figure 10 As shown, 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 an optical fiber PF. Furthermore, in order to introduce reference light to the first beam splitter BS1, the optical system 20 also connects the optical path from the demultiplexer 211 to the first beam splitter BS1 via the optical fiber PF. Thus, the reference light is introduced to the first beam splitter BS1 via the optical fiber PF and is combined with the reflected light by the first beam splitter BS1.

[0099] Furthermore, the combined light of the reflected light and the reference light is split by the first beam splitter BS1 into light directed to the first receiving unit 31 and light directed to the second beam splitter BS2. Furthermore, the light directed to the second beam splitter BS2 is split by the second beam splitter BS2 into light directed to the second receiving unit 32 and light directed to the third receiving unit 33. Thus, in the optical system 20, the reflected light focused by each lens 231-233 is directly guided to the photodetector PD of each receiving unit 31-33 for photoelectric conversion.

[0100] Furthermore, the distance measuring device 1 of this embodiment modularizes the collimator CL, circulator CC, optical path branching unit 22, lens unit 23, and each receiving unit 31 to 33 of the light receiving unit 30 into a single module. Such modularization is achieved, for example, by mounting the collimator CL, circulator CC, optical path branching unit 22, lens unit 23, and each receiving unit 31 to 33 on a single substrate.

[0101] The other parts are the same as those of the third embodiment. The distance measuring device 1 of this embodiment can obtain the effects achieved by the configuration common to or equivalent to that of the third embodiment, similarly to the third embodiment.

[0102] Furthermore, the distance measuring device 1 of this embodiment has the following features.

[0103] The distance measuring device 1 of this embodiment modularizes the collimator CL, circulator CC, optical path branching unit 22, lens unit 23, and receiving units 31 to 33 of the light receiving unit 30 into a single module. This structure facilitates compact construction of the distance measuring device 1 and reduces manufacturing costs.

[0104] (Fifth embodiment)

[0105] Next, refer to Figure 11 The fifth embodiment will be described. In this embodiment, the differences from the first embodiment will be mainly described.

[0106] In the distance measuring device 1 of this embodiment, as Figure 11As shown, the light source unit 10 and the light receiving unit 30 are formed by an optical integrated circuit PIC. The optical integrated circuit PIC is constructed from a semiconductor having an optical waveguide LW. The optical integrated circuit PIC includes a first optical waveguide LW1 that guides the outgoing light to the circulator CC, a second optical waveguide LW2 that guides the reference light to the receiving units 31 to 33, and a third optical waveguide LW3 that guides the reflected light focused by the lenses 231 to 233 to the receiving units 31 to 33. Therefore, in this embodiment, the reflected light focused by the lenses 231 to 233 is guided via the third optical waveguide LW3 formed within the optical integrated circuit PIC to the photodetector PD of each receiving unit 31 to 33 for photoelectric conversion. Furthermore, in this embodiment, the reflected light focused by the lenses 231 to 233 and the reference light are combined by the photodetector PD.

[0107] The optical system 20 of this embodiment further includes a mirror MR for directing the light emitted from the first optical waveguide LW1 toward the circulator CC. Furthermore, a mirror MR for directing the reflected light transmitted through the second beam splitter BS2 toward the third lens 233 is added to the optical path branching unit 22 .

[0108] The other parts are the same as those of the first embodiment. The distance measuring device 1 of this embodiment can obtain the effects achieved by the configuration common to or equivalent to that of the first embodiment, as in the first embodiment.

[0109] Furthermore, the distance measuring device 1 of this embodiment has the following features.

[0110] In each receiving unit 31-33, the reflected light focused by each lens 231-233 is guided to the photodetector PD via a third optical waveguide LW3 provided within the optical integrated circuit PIC, which is a semiconductor, for photoelectric conversion. By guiding the reflected light to the photodetector PD via the optical waveguide LW within the semiconductor, further miniaturization can be achieved.

[0111] (Other embodiments)

[0112] While the representative embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible, for example, as described below.

[0113] In the above-mentioned embodiment, various structures of the distance measuring device 1 are described in detail. However, the various structures of the distance measuring device 1 do not need to be the same as the above-mentioned structures, and some of them may be different from the above-mentioned structures.

[0114] In the above embodiment, the control unit 41 of the signal processing unit 40 is described as including the Fourier transform units 411 to 413, the adder 414, and the peak extractor 415 as functional units. 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 devices.

[0115] In the above embodiment, an example in which the distance measuring device 1 of the present disclosure is configured as a FMCW LiDAR mounted on a vehicle has been described. However, the distance measuring device 1 can also be applied to situations other than the FMCW LiDAR mounted on a vehicle.

[0116] In the above-described embodiment, elements constituting the embodiment are, of course, not necessarily essential unless specifically stated as essential or unless clearly considered to be essential in principle.

[0117] In the above-mentioned embodiments, when referring to numerical values such as the number, value, amount, and range of components of the embodiments, they are not limited to specific numbers except for cases where they are specifically stated to be necessary and cases where they are clearly limited to specific numbers in principle.

[0118] In the above-described embodiments, when the shapes, positional relationships, etc. of components are mentioned, they are not limited to the shapes, positional relationships, etc. unless otherwise specified or when they are limited to specific shapes, positional relationships, etc. in principle.

[0119] The control unit and method thereof disclosed herein may also be implemented by a dedicated computer as follows: the dedicated computer is provided by constituting a processor and a memory programmed to execute one or more functions embodied by a computer program. Alternatively, the control unit and method thereof disclosed herein may also be implemented by a dedicated computer as follows: the dedicated computer is provided by constituting a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and method thereof disclosed herein may also be implemented by one or more dedicated computers as follows: the dedicated computer is constituted by a combination of a processor and a memory programmed to execute one or more functions and a processor constituted by one or more hardware logic circuits. In addition, the computer program may also be stored as an instruction executed by a computer in a non-removable tangible recording medium that is readable by a computer.

Claims

1. A distance measuring device for measuring the distance to an object by coherent detection, characterized in that: have: Light source part, emitting light; an optical path branching portion for branching reflected light generated by the outgoing light emitted from the light source portion and reflected on the object into a plurality of optical paths; a lens unit including a plurality of lenses provided corresponding to the plurality of optical paths, respectively, for focusing the reflected light branched into the plurality of optical paths; a plurality of receiving units provided corresponding to the plurality of optical paths, respectively, for performing heterodyne detection on a combined light of the reflected light and a reference light which is a part of the emitted light, and outputting a beat signal; a plurality of Fourier transform units, provided corresponding to the plurality of receiving units, respectively, for performing Fourier transform on the beat signal to obtain a power spectrum; as well as a peak extraction unit that extracts a peak frequency correlated with the distance to the object from a result obtained by adding the power spectra obtained by the plurality of Fourier transform units; The optical path branching portion is configured to branch the reflected light into a plurality of optical paths using a beam splitter that is independent of the polarization of the outgoing light. The plurality of lenses are set to have different numerical apertures.

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

3. The distance measuring device according to claim 2, characterized in that The optical path branching unit sets a division ratio of the beam splitter so that the intensities of the reflected lights focused by the plurality of lenses become uniform.

4. The distance measuring device according to any one of claims 1 to 3, characterized in that In the receiving unit, the reflected light focused by the lens is guided to a photodetector via an optical fiber and subjected to photoelectric conversion.

5. The distance measuring device according to any one of claims 1 to 3, characterized in that: In the receiving unit, the reflected light focused by the lens is introduced into a photodetector via an optical waveguide provided inside a semiconductor, and is photoelectrically converted.

6. The distance measuring device according to any one of claims 1 to 3, characterized in that: In the receiving unit, the reflected light focused by the lens is directly irradiated onto a photodetector to be photoelectrically converted.

Images