Measurement device

Abstract

This measurement device comprises: a light source that emits light having a frequency that temporally changes; an optical splitter that separates the light from the light source into irradiation light for irradiating a scene and reference light; an optical circulator to which the irradiation light from the optical splitter is inputted; an optical switch that switches paths of the irradiation light; a plurality of optical elements for use in emitting the irradiation light and receiving incoming light reflected from the scene; and a photodetector that detects interference light between the reference light and the reflected light. The optical switch switches the paths of the irradiation light from the optical circulator to one of the optical elements. The one of the optical elements emits the irradiation light and receives the reflected light.

Description

Measuring equipment

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

[0002] Conventionally, there exists LiDAR (Light Detection and Ranging) technology, which generates measurement data related to the distance and / or velocity of an object by illuminating the object with light and detecting the light reflected from the object. A typical example of a measurement device using LiDAR technology includes a light source, a photodetector, and a processing circuit. The light source emits light to illuminate the object. The photodetector detects the light reflected from the object and outputs a signal corresponding to the time delay of the reflected light. The processing circuit acquires data related to the distance and velocity of the object based on the signal output from the photodetector, for example, using FMCW (Frequency Modulated Continuous Wave) technology. Patent Documents 1 and 2 disclose examples of measurement devices using FMCW technology.

[0003] International Publication No. 2023 / 145191 Specification Patent Publication No. 2019-522211

[0004] The present disclosure provides a measurement device with a simple configuration that is capable of emitting light of a relatively high intensity from one of a plurality of optical elements when switched over.

[0005] A measurement device according to one aspect of the present disclosure includes a light source that emits light whose frequency changes over time, an optical splitter that separates the light from the light source into illumination light for illuminating a scene and reference light, an optical circulator to which the illumination light from the optical splitter is input, an optical switch that switches the path of the illumination light, a plurality of optical elements used for emitting the illumination light and for receiving reflected light from the scene, and a photodetector that detects interference light between the reference light and the reflected light, wherein the optical switch switches the path of the illumination light from the optical circulator to one of the plurality of optical elements, and the one of the plurality of optical elements emits the illumination light and receives the reflected light.

[0006] 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. The computer-readable recording medium may include, 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.

[0007] According to the technology of the present disclosure, it is possible to realize a measurement device with a simple configuration that is capable of emitting light of a relatively high intensity from one of a plurality of optical elements when switched over.

[0008] FIG. 1 is a block diagram schematically showing the configuration of a measurement apparatus according to an exemplary embodiment of the present disclosure. FIG. 2 is a diagram schematically showing the time changes in the frequencies of reference light and reflected light when an object is stationary. FIG. 3 is a flowchart schematically showing an example of a measurement operation performed by a processing circuit. FIG. 4A is a block diagram schematically showing the configuration of a measurement apparatus of a comparative example. FIG. 4B is a graph showing a signal spectrum when a distance to an object is measured using the measurement apparatus shown in FIG. 4A. FIG. 4C is a graph showing a signal spectrum when an optical element in the measurement apparatus shown in FIG. 4A is shielded from light. FIG. 5A is a block diagram schematically showing the configuration of a measurement apparatus of an example. FIG. 5B is a graph showing a signal spectrum when a distance to a first object is measured using the measurement apparatus shown in FIG. 5A. FIG. 5C is a graph showing a signal spectrum when a first optical element in the measurement apparatus shown in FIG. 5A is shielded from light. FIG. 6A is a block diagram schematically showing the configuration of a measurement apparatus of an example. FIG. 6B is a graph showing a signal spectrum when a distance to a second object is measured using the measurement apparatus shown in FIG. 6A. 6C is a graph showing a signal spectrum when the second optical element in the measurement device shown in FIG. 6A is shielded. FIG. 7A is a block diagram schematically showing example 1 of components arranged outside the housing in the measurement device according to this embodiment. FIG. 7B is a block diagram schematically showing example 2 of components arranged outside the housing in the measurement device according to this embodiment. FIG. 7C is a block diagram schematically showing example 3 of components arranged outside the housing in the measurement device according to this embodiment. FIG. 7D is a block diagram schematically showing example 4 of components arranged outside the housing in the measurement device according to this embodiment. FIG. 8 is a diagram for explaining the relationship between the optical path lengths of the light flows I to V shown in FIG. 1 and the beat frequency.

[0009] In the present 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 referred to as a system LSI, a VLSI (very large scale integration), or an ULSI (ultra large scale integration). A Field Programmable Gate Array (FPGA), which is programmed after the LSI is manufactured, or a reconfigurable logic device, which can reconfigure the connection relationships within the LSI or set up circuit sections within the LSI, can also be used for the same purpose.

[0010] 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 executed 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 required hardware devices, such as interfaces.

[0011] 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."

[0012] 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.

[0013] First, the findings that form the basis of this disclosure will be described.

[0014] In recent years, FMCW-LiDAR technology has been developed that combines a wide dynamic range and high resolution for distance, is less susceptible to disturbances, and can measure distance and / or speed of fast-moving objects. By using light instead of millimeter waves, the diameter of the light spot illuminating the object can be made relatively small, enabling more accurate measurement data of the object.

[0015] Patent Document 1 discloses a measurement device that uses FMCW-LiDAR technology to measure the distance to an object, i.e., distance measurement. In this measurement device, a laser beam whose frequency monotonically increases and decreases over time is emitted from a light source, and this light is separated into a reference beam and an illumination beam for illuminating the object. In this measurement device, an optical detector detects the interference light between the reflected light from the object and the reference beam. A beat signal is generated in the signal spectrum of the interference light, and the distance to the object can be measured based on the peak frequency of the beat signal, i.e., the beat frequency.

[0016] When the sum of the optical path lengths of the irradiated light and the reflected light is the same as the optical path length of the reference light, the beat frequency caused by the object is zero. As the object is farther away from the measurement device, the sum of the optical path lengths of the irradiated light and the reflected light becomes longer than the optical path length of the reference light, so the beat frequency caused by the object shifts to the higher frequency side. This principle makes it possible to measure the distance to an object.

[0017] The device disclosed in Patent Document 1 uses optical fiber to connect components. The device includes a collimator lens that converts illumination light propagating through the optical fiber into a spatial light beam, and an optical circulator that diverges the optical path of the reflected light from that of the illumination light to cause interference between the reflected light from the object and the reference light. Based on the same principle as that in which a beat signal is generated by light reflected from an object, light reflected at the lens interface of the collimator lens and internally scattered light in the optical circulator also generate beat signals as noise light. As a result, in the signal spectrum of the interference light, it becomes difficult to distinguish the beat signal generated by the reflected light from the object from that generated by the noise light. Since the object cannot be measured at or near the beat frequency of the noise light, the ranging range, which is the frequency band in which the object can be measured, becomes narrow. Even when an optical splitter is used instead of an optical circulator, a beat signal is generated due to internally scattered light in the optical splitter. The effect of noise light on ranging can be reduced by appropriately adjusting the distance between the components connected by optical fiber.

[0018] The device disclosed in Patent Document 1 further includes an optical splitter connected to an optical circulator and multiple collimating lenses connected to the splitter. The optical splitter splits illumination light emitted from a light source via the optical circulator into multiple collimating lenses, which then output the light as multiple beams to the outside of the device. The distances from the optical splitter to the multiple collimating lenses are designed to be different. Therefore, although multiple beams are input to the photodetector at the same time, the frequency band in the signal spectrum of the interference light is divided into multiple sub-frequency bands corresponding to the multiple collimating lenses. Focusing on the sub-frequency band corresponding to a certain collimating lens reveals that it is a beat signal generated by the beam emitted from that collimating lens.

[0019] On the other hand, since the frequency band is divided by the number of beam branches, the ranging range becomes narrower. Furthermore, the light intensity of the beam emitted from each collimator lens decreases by the number of branches in the optical splitter. The intensity of the reflected light emitted from each collimator, reflected by an object, and returned to the collimator lens also decreases by the number of branches in the optical splitter. In other words, if the number of branches is N (N is a natural number), the light intensity decreases by the square of N.

[0020] Patent Literature 2 (PTL 2) discloses a measurement device that measures the distance to an object using FMCW technology. In the device disclosed in Patent Literature 2, multiple optical heads are each connected to a housing via multiple waveguides. The housing contains a light source, a light receiver, a controller, and an optical router. In this device, the optical router switches the path of the illumination light emitted from the light source to one of the multiple optical heads. As a result, illumination light is emitted from that one of the multiple optical heads, and reflected light from the object that returns to the same optical head is input to the light receiver. This makes it possible to emit light with a relatively high intensity from the selected one of the multiple optical heads. Unlike the device disclosed in Patent Literature 1, this configuration does not require dividing the frequency band into multiple sub-frequency bands, thereby avoiding narrowing the ranging range.

[0021] On the other hand, if the reflected light from the object is input to a common photodetector from one of the optical heads via an optical router, a complex optical router is required due to the reciprocity of light propagation.If the reflected light from the object is branched from one of the optical heads to the light source and the photodetector, the light intensity of the reflected light is halved.

[0022] In the optical router of Patent Document 2, in which a light source and a light receiver are connected, the point where the irradiated light emitted from the light source is input is different from the point where the reflected light from the object is output to the light receiver. Therefore, the optical router of Patent Document 2 cannot be connected to the optical circulator of Patent Document 1, in which the irradiated light and the reflected light pass through a common point.

[0023] Based on the above considerations, the inventors have conceived of a measurement device using FMCW-LiDAR technology according to an embodiment of the present disclosure. Details of the measurement device according to this embodiment will be described below.

[0024] (Embodiment) [Measurement Apparatus] First, an example configuration of a measurement apparatus according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a block diagram schematically illustrating the configuration of a measurement apparatus according to an exemplary embodiment of the present disclosure. Fig. 1 shows one or more objects 10 to be measured. The measurement apparatus 100 shown in Fig. 1 illuminates a scene with illumination light and measures the distance to one or more objects 10 included in the scene.

[0025] The measurement device 100 shown in FIG. 1 includes a light source 20, an interference optical system 30, an optical switch 40, a plurality of optical elements 50, a photodetector 60, a processing circuit 70, and a memory 72. The measurement device 100 further includes a housing (not shown) that houses at least some of these components. The thick lines shown in FIG. 1 represent optical fibers that connect two components to each other. The solid lines with arrows shown in FIG. 1 represent signal transmission and reception. Note that if the user separately prepares the processing circuit 70 and memory 72, the measurement device 100 may be provided to the user with a configuration that excludes the processing circuit 70 and memory 72.

[0026] In the example shown in Fig. 1 , the one or more objects 10 include a first object 10a and a second object 10b, but the number of objects 10 is not limited to two. The number of objects 10 may be one, or three or more. Similarly, in the example shown in Fig. 1 , the multiple optical elements 50 include a first optical element 50a and a second optical element 50b, but the number of optical elements 50 is not limited to two. The number of optical elements 50 may be three or more. The multiple optical elements 50 include at least a first optical element 50a and a second optical element 50b.

[0027] As will be explained in detail later, in the measurement device 100 according to this embodiment, the optical switch 40 can switch the path of light emitted from the interference optical system 30 to one of the multiple optical elements 50. As a result, the light emitted from the interference optical system 30 can be emitted from the one of the multiple optical elements 50 with almost no reduction in its intensity. Therefore, in the measurement device 100 according to this embodiment, with a simple configuration using the optical switch 40, it is possible to emit light of relatively high intensity from the selected one of the multiple optical elements 50.

[0028] Each component of the measurement device 100 according to this embodiment will be described below.

[0029] <Light Source 20> The light source 20 emits laser light 20L0 whose frequency can be varied. The frequency can be varied over time at a constant time period, for example, in a triangular or sawtooth waveform. The time period of the frequency change may vary. The time period of the frequency can be, for example, 1 μsec or more and 10 ms or less. The frequency width can be, for example, 100 MHz or more and 1 THz or less. The wavelength of the laser light 20L0 can be included in the near-infrared wavelength range, for example, from 700 nm to 2000 nm. Since the amount of near-infrared light in sunlight is less than the amount of visible light, using near-infrared light as the laser light 20L0 can reduce the influence of sunlight as noise. Alternatively, the wavelength of the laser light 20L0 may be included in the visible light wavelength range, from 400 nm to 700 nm or less, or in the ultraviolet light wavelength range.

[0030] The 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 capable of changing the frequency of the laser light depending on the amount of current applied. The relationship between the applied current value and the frequency of the laser light will be described later.

[0031] <Interference Optical System 30> The interference optical system 30 includes a first optical splitter 32a, a first optical splitter 32a, and an optical circulator 34. The first optical splitter 32a splits the laser beam 20L0 emitted from the light source 20 into a reference beam 20L1 and an irradiation beam 20L2 for irradiating a scene. The first optical splitter 32a inputs the reference beam 20L1 to the second optical splitter 32b and inputs the irradiation beam 20L2 to the optical circulator 34. The optical circulator 34 inputs the irradiation beam 20L2 to the optical switch 40. The optical circulator 34 further inputs reflected beam 20L3 from the scene, which is generated by irradiating the scene with the irradiation beam 20L2 via one of the plurality of optical elements 50, to the second optical splitter 32b. In this way, the illumination light 20L2 from the first optical splitter 32a is input to the optical circulator 34. The reflected light 20L3 also returns and is input to the optical circulator 34. The second optical splitter 32b inputs interference light 20L4, which is obtained by superimposing and interfering with the reference light 20L1 and the reflected light 20L3, to the photodetector.

[0032] In this specification, the first optical splitter 32a is also simply referred to as the "optical splitter," and the second optical splitter 32b is also referred to as the "other optical splitter."

[0033] <Optical Switch 40> The optical switch 40 is connected to the interference optical system 30, more specifically, to the optical circulator 34 included in the interference optical system 30. The optical switch 40 switches the path of the irradiation light 20L2. More specifically, the optical switch 40 switches the path of the irradiation light 20L2 from the optical circulator 34 to one of a plurality of optical elements in time series, and inputs the irradiation light 20L2 to that one of the plurality of optical elements. When the number of optical elements 50 is N, the path of the irradiation light 20L2 is sequentially switched from the first optical element 50 to the second optical element 50, ..., the Nth optical element 50. Switching from the first optical element 50 to the Nth optical element 50 constitutes one operation, and this operation is repeated multiple times. The path of the irradiation light 20L2 being switched is also the path of the reflected light 20L3.

[0034] 1 , the optical switch 40 switches the path of the irradiation light 20L2 to one of the first optical element 50a and the second optical element 50b and inputs the irradiation light 20L2 to that one. The optical switch 40 also inputs the reflected light 20L3 that has returned to that one into the optical circulator 34. Thereafter, the optical switch 40 switches the path of the irradiation light 20L2 to the other of the first optical element 50a and the second optical element 50b and performs the same operation.

[0035] The path of the irradiated light 20L2 may be switched using, for example, an electro-optic effect, or may be switched using, for example, a micro electro mechanical systems (MEMS) mirror.

[0036] <Optical Element 50> The optical elements 50 are connected to the optical switch 40. The optical elements 50 are used for emitting the illumination light 20L2 and receiving the reflected light 20L3. The positions of the optical elements 50 are different from one another. The optical elements 50 may be arranged, for example, along an imaginary straight line or curve. The straight line may be parallel to the vertical direction, for example. Alternatively, the straight line or curve may be parallel to a horizontal plane. When the number of optical elements 50 is three or more, the optical elements 50 may be arranged side by side at equal or different intervals.

[0037] As a result of the optical switch 40 switching the path of the irradiated light 20L2, one of the optical elements 50 emits the irradiated light 20L2 to the outside and receives the reflected light 20L3. None of the remaining optical elements 50 emit the irradiated light 20L2 to the outside. From the one of the optical elements 50 that emits the irradiated light 20L2, the direction and / or height at which the object 10 is located can be determined. In this specification, the direction in which the irradiated light 20L2 is emitted from the optical element 50 is also referred to as "forward."

[0038] The optical element 50 may be, for example, a collimator lens that collimates the illumination light 20L2. In this specification, "collimate" refers not only to converting the illumination light 20L2 into parallel light, but also to reducing the spread of the illumination light 20L2. Alternatively, the optical element 50 may be a diffraction grating that outputs the illumination light 20L2 to the outside as zeroth-order diffracted light and / or ±Mth-order diffracted light (M is a natural number). 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. In the following description, the optical element 50 is assumed to be a collimator lens.

[0039] <Photodetector 60> The photodetector 60 detects the interference light 20L4. The photodetector includes one or more photodetection elements. The photodetection elements output signals corresponding to the intensity of the interference light 20L4.

[0040] In the measurement apparatus 100, the optical path of the illumination light 20L2 from the interference optical system 30 to the object 10 overlaps with the optical path of the reflected light 20L3 from the object 10 to the interference optical system 30. By employing such a coaxial optical system, the configuration of the measurement apparatus 100 can be simplified and stable measurements can be achieved.

[0041] <Processing Circuit 70> The processing circuit 70 controls the operations of the light source 20, the optical switch 40, and the photodetector 60. Note that, when the processing circuit 70 samples the signal output from the photodetector 60 at a predetermined timing while the photodetector 60 is constantly detecting the interference light 20L4, the processing circuit 70 does not need to control the operation of the photodetector 60.

[0042] The processing circuit 70 processes the signal output from the photodetector using FMCW-LiDAR technology. Based on the signal, the processing circuit 70 generates and outputs measurement data related to the distance and / or velocity of the object. The operation of the processing circuit will be described in detail below.

[0043] The computer program executed by the processing circuit 70 is stored in memory 72, such as ROM or RAM (Random Access Memory). Thus, the measurement device 100 includes a processing device including the processing circuit 70 and memory 72. The processing circuit 70 and the memory 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 70 may be distributed across multiple circuits. The processing device may be installed in a remote location away from the other components and control the operations of the light source 20, the optical switch 40, and the photodetector 60 via a wired or wireless communication network.

[0044] [FMCW-LiDAR Technology] Next, the FMCW-LiDAR technology will be briefly described with reference to FIG.

[0045] FIG. 2 is a diagram schematically illustrating the temporal changes in the frequency of the reference light 20L1 and the reflected light 20L3 when the object 10 is stationary. The solid line represents the reference light 20L1, and the dashed line represents the reflected light 20L3. The frequency of the reference light 20L1 shown in FIG. 2 repeatedly changes over time in a triangular waveform. That is, the frequency of the reference light 20L1 alternates between up-chirp and down-chirp. The frequency increase during the up-chirp period and the frequency decrease during the down-chirp period are equal to each other. The frequency of the reflected light 20L3 is shifted in the positive direction along the time axis compared to the frequency of the reference light 20L1. The amount of time shift of the reflected light 20L3 is equal to the time it takes for the illumination light 20L2 to be emitted from the measurement device 100 to the outside, reflected by the object 10, and returned as the reflected light 20L3. As a result, the reference light 20L1 and the reflected light 20L3 are superimposed and interfere with each other to produce interference light 20L4, which has a frequency corresponding to the frequency difference between the frequency of the reflected light 20L3 and the frequency of the reference light 20L1. The double-headed arrow in FIG. 2 represents the frequency difference between the two. The photodetector 60 outputs a signal indicating the intensity of the interference light 20L4. A beat signal caused by the object 10 appears in the signal spectrum of the interference light 20L4. The beat frequency is equal to the frequency difference. The processing circuit 70 can generate measurement data regarding the distance to the object 10 from the beat frequency.

[0046] 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. If the increase or decrease in the frequency of light during the up-chirp period or the down-chirp period is Δf, the time required for the change in Δf is Δt, the speed of light is c, and the difference between the optical path length of the reference light 20L1 and the sum of the optical path lengths of the illumination light 20L2 and the reflected light 20L3 is 2d, then the beat frequency during the up-chirp period or the down-chirp period is ｂｅａｔ is expressed by the following equation (1).

[0047] The beat frequency f in equation (1) ｂｅａｔ is obtained by multiplying the time rate of change of frequency Δf / Δt by the time (2d / c) it takes for the irradiated light 20L2 to be emitted from the measuring device 100 to the outside, reflected by the object 10, and returned as reflected light 20L3.

[0048] When the object 10 moves, the frequency of the reflected light 20L3 undergoes a Doppler shift in the positive or negative direction along the frequency axis compared to the frequency of the reference light 20L1. In this case, the beat frequency during the up-chirp period differs from the beat frequency during the down-chirp period. The processing circuitry 70 can generate measurement data regarding the velocity and distance of the object 10 from the frequency difference and average of these beat frequencies, respectively.

[0049] [Operations Executed by Processing Circuitry 70] Next, an example of operations executed by the processing circuitry 70 in embodiment 1 will be described with reference to Fig. 3. Fig. 3 is a flowchart that schematically shows an example of a measurement operation executed by the processing circuitry 70. The processing circuitry 70 executes the operations of steps S101 to S106 shown in Fig. 3.

[0050] <Step S101> The processing circuitry 70 causes the light source 20 to emit laser light 20L0 whose frequency changes over time.

[0051] <Step S102> The processing circuit 70 causes the optical switch 40 to switch the path of the irradiation light 20L2 to one of the plurality of optical elements 50.

[0052] <Step S103> The processing circuitry 70 causes the photodetector 60 to detect the interference light 20L4. The photodetector 60 outputs a signal corresponding to the intensity of the interference light 20L4. Note that the processing circuitry 70 may sample the photodetection signal at a predetermined timing while the photodetector 60 is constantly detecting the interference light 20L4.

[0053] <Step S104 > The processing circuit 70 generates measurement data relating to the distance and / or speed of the object 10 based on the signal output from the photodetector 60 .

[0054] <Step S105> The processing circuit 70 determines whether or not all of the optical elements 50 have been selected. If the determination is Yes, the processing circuit 70 executes the operation of step S106. If the determination is No, the processing circuit 70 executes the operations of steps S102 to S104 again. In this case, in step S102, the processing circuit 70 causes the optical switch 40 to switch the path of the illumination light 20L2 to one of the multiple optical elements 50 that has not been selected so far.

[0055] <Step S106> The processing circuit 70 determines whether or not to end the measurement operation. If the determination is Yes, the processing circuit 70 ends the measurement operation. If the determination is No, the processing circuit 70 executes the operations of steps S102 to S105 again.

[0056] By the above operation, it becomes possible to measure the distance and / or speed of the object 10 by determining the direction and / or height at which the object 10 is located from one of the multiple optical elements 50 that emits the irradiation light 20L2.

[0057] Examples Next, with reference to FIGS. 4A to 6C, examples in which the distance to the object 10 is measured by the measurement device 100 according to this embodiment will be described together with comparative examples.

[0058] <Explanation of Figs. 4A to 6C> Fig. 4A is a block diagram schematically showing the configuration of a measurement device of a comparative example. The triangles in Fig. 4A represent connectors. In the measurement device 90 shown in Fig. 4A, unlike the measurement device 100 shown in Fig. 1, a single optical element 50 is connected to the interference optical system 30 without via the optical switch 40. The housing 80 included in the measurement device 90 shown in Fig. 4A houses the light source 20, the interference optical system 30, the photodetector 60, the processing circuit 70, and the memory 72 shown in Fig. 1. The optical element 50 is disposed outside the housing 80.

[0059] Fig. 4B is a graph showing a signal spectrum when the distance to the object 10 is measured by the measurement device 90 shown in Fig. 4A. Fig. 4C is a graph showing a signal spectrum when the optical element 50 in the measurement device 90 shown in Fig. 4A is shielded from light.

[0060] Fig. 5A is a block diagram schematically illustrating the configuration of a measurement apparatus according to an embodiment. The housing 80 included in the measurement apparatus 100 shown in Fig. 5A houses the light source 20, interference optical system 30, photodetector 60, processing circuit 70, and memory 72 shown in Fig. 1. The optical switch 40, first optical element 50a, and second optical element 50b are disposed outside the housing 80. In the example shown in Fig. 5A, the optical switch 40 switches the path of the illumination light 20L2 to the first optical element 50a, as indicated by the thick line.

[0061] Fig. 5B is a graph showing a signal spectrum when the distance to the first object 10a is measured by the measurement device 100 shown in Fig. 5A. Fig. 5C is a graph showing a signal spectrum when the first optical element 50a in the measurement device 100 shown in Fig. 5A is shielded from light.

[0062] 6A is a block diagram showing a schematic configuration of a measurement device according to an embodiment of the present invention, which is the same as the example shown in FIG. 5A except that the path of the illumination light 20L2 is switched to the second optical element 50b by the optical switch 40.

[0063] Fig. 6B is a graph showing a signal spectrum when the distance to the second object 10b is measured by the measurement device 100 shown in Fig. 6A. Fig. 6C is a graph showing a signal spectrum when the second optical element 50b in the measurement device 100 shown in Fig. 6A is shielded.

[0064] 4A, 5A, and 6A, the optical elements 50, 50a, and 50b are collimator lenses with a focal length f=20 mm. The objects 10, 10a, and 10b are pieces of Kent paper placed 1 m away from the incident surface of the irradiation light 20L2 of the optical elements 50, 50a, and 50b.

[0065] The signal spectra shown in Figures 4B, 4C, 5B, 5C, 6B, and 6C show overlapping beat signals during the up-chirp and down-chirp periods (i.e., T1 and T2). The vertical and horizontal axes in these figures represent signal strength and frequency, respectively. Frequency correlates with distance. The frequency is expressed in arbitrary units. Zero frequency corresponds to the exit surface of the first optical splitter 32a from which the illumination light 20L2 exits, as shown in Figure 1.

[0066] In the comparative example, the irradiation light 20L2 emitted from the interference optical system 30 was directly input to the optical element 50 and emitted from the optical element 50 as a beam of spatial light toward the object 10. In contrast, in the example, the irradiation light 20L2 emitted from the interference optical system 30 was input to the first optical element 50a or the second optical element 50b by the optical switch 40. The irradiation light 20L2 was emitted from the first optical element 50a or the second optical element 50b as a beam of spatial light toward the first object 10a or the second object 10b.

[0067] <Beat Signals Caused by Objects 10, 10a, and 10b> Reflected light 20L3 from the objects 10, 10a, and 10b generates beat signals caused by the objects 10, 10a, and 10b. In the examples shown in Figures 4B, 5B, and 6B, the clearest beat signals caused by the objects 10, 10a, and 10b appeared at the same frequency around 100. The peak intensities of the beat signals caused by the objects 10a and 10b in the example were similar to the peak intensity of the beat signal caused by the object 10 in the comparative example.

[0068] In the example, the irradiation light 20L2 emitted from the interference optical system 30 is input to either the first optical element 50a or the second optical element 50b without being branched to either the first optical element 50a or the second optical element 50b. Therefore, in the example, with the simple configuration of using the optical switch 40, it is possible to emit irradiation light 20L2 of relatively high intensity from the selected one of the first optical element 50a and the second optical element 50b. The intensity of the irradiation light 20L2 in the example is approximately the same as the intensity of the irradiation light 20L2 in the comparative example.

[0069] The reflected light 20L3 from the first object 10a or the second object 10b is input to the photodetector 60 at a relatively high intensity without being branched via the first optical element 50a or the second optical element 50b from which the irradiation light 20L2 is emitted. Therefore, the peak intensity of the beat signal caused by the objects 10a and 10b in the example is approximately the same as the peak intensity of the beat signal caused by the object 10 in the comparative example.

[0070] Since the illumination light 20L2 is not branched into the first optical element 50a and the second optical element 50b, unlike the device disclosed in Patent Document 1, the frequency band is not divided into multiple sub-frequency bands, and the ranging range is not narrowed.

[0071] <Various Beat Signals> The multiple light flows in the measurement apparatus 100 generate various beat signals. Here, referring again to FIG. 1 , the multiple light flows in the measurement apparatus 100 will be described. The dashed lines with arrows in FIG. 1 represent the light flows. Light flow I is the flow of the reference light 20L1 from the first optical splitter 32a to the photodetector 60. Light flow II is the flow of the illumination light 20L2 from the first optical splitter 32a to the object 10, and the reflected light 20L3 from the object 10 to the photodetector 60. Light flow III is the flow of a portion of the illumination light 20L2 from the first optical splitter 32a to be reflected by the optical element 50 and reach the photodetector 60. Light flow IV is the flow of another portion of the illumination light 20L2 from the first optical splitter 32a to the photodetector 60 via the optical circulator 34 without heading to the optical switch 40. It has been experimentally confirmed that the optical path length of light flow IV can be longer than the optical path length of light flow II. Light flow V is the flow of yet another part of the illumination light 20L2 from the first optical splitter 32a to the photodetector 60 after being reflected by the optical switch 40.

[0072] 5B represent beat signals generated by the light flows II to V, respectively. The beat frequencies of the beat signals II to V are proportional to the absolute value of the difference between the optical path length of the light flows II to V and the optical path length of the light flow I.

[0073] Beat signal II is caused by reflected light 20L3 from the first object 10a. Beat signal III is noise caused by a portion of the illumination light 20L2 reflected by the interface between the incident surface of the first optical element 50a and the exit surface of the optical fiber. This portion of the illumination light 20L2 is detected by the photodetector 60, just like the reflected light 20L3. Because the first object 10a is located in front of the incident surface of the first optical element 50a, beat signal III serves as an indicator of zero distance for the first object 10a. Because beat signal III appears at a lower frequency than beat signal II, beat signal III can be distinguished from beat signal II.

[0074] Beat signal IV is noise caused by another portion of irradiated light 20L2 that does not travel toward optical switch 40 but enters photodetector 60 via optical circulator 34. This other portion of irradiated light 20L2 is detected by photodetector 60, similar to reflected light 20L3. Depending on the optical path lengths of light flows III and IV, beat signal IV appears on the lower or higher frequency side than beat signal III. In the example shown in FIG. 5B , beat signal IV appears on the lower frequency side than beat signal III, so beat signal IV can be distinguished from beat signal II. In contrast, if beat signal IV appears on the higher frequency side than beat signal III, it becomes difficult to distinguish beat signal IV from beat signal II.

[0075] Beat signal V is noise resulting from a further portion of the irradiated light 20L2 reflected by the interface between the optical switch 40 and the optical fiber, which has a different refractive index. This further portion of the irradiated light 20L2 is detected by the photodetector 60, similar to the reflected light 20L3. Depending on the optical path lengths of the light flows III and V, beat signal V appears at a lower or higher frequency than beat signal III. In the example shown in FIG. 5 , beat signal V appears at a lower frequency than beat signal III, so beat signal V can be distinguished from beat signal II. However, because the intensity of the reflected light from the optical switch 40 is high, the tail-like phase noise of beat signal V also increases, increasing the noise level in the short-distance range. As a result, it becomes difficult to obtain a low-intensity signal in the short-distance range. If beat signal V appears at a higher frequency than beat signal III, it becomes difficult to distinguish beat signal V from beat signal II.

[0076] From the above, if beat signals IV and V appear on the lower frequency side than beat signal III, the higher frequency side than beat signal III can be used as the distance measurement range. Furthermore, if beat signal V is sufficiently far from beat signal III, the tail-like phase noise of beat signal V has almost no effect on beat signal II.

[0077] In addition to the noise beat signals III to V, fiber noise also appears in the signal spectrum. This fiber noise is noise caused by a further portion of the illumination light 20L2 that is backscattered throughout the entire optical fiber located between the optical circulator 34 and the optical elements 50, 50a, and 50b. This further portion of the illumination light 20L2 is detected by the photodetector 60, similar to the reflected light 20L3. Optical fibers cause Rayleigh scattering due to particles that are sufficiently small compared to the wavelength of the light propagating through them, or fluctuations in density, stress, or composition. Therefore, backscattering occurs throughout the entire optical fiber.

[0078] Fiber noise appears even when the optical elements 50, 50a, and 50b are shielded from light. In the examples shown in Figures 4C, 5C, and 6C, noise resulting from the addition of fiber noise to the shot noise of the photodetector 60 appears in the low-frequency band, while the shot noise of the photodetector 60 appears in other frequency ranges. Because fiber noise appears over a wide band, it narrows the ranging range. The frequency band of the fiber noise can be narrowed by appropriately adjusting the arrangement of the optical circulator 34, the optical switch 40, the first optical element 50a, and the second optical element 50b, as described below.

[0079] As described above, what is actually emitted from the optical element 50 is the remaining portion of the irradiation light 20L2, excluding the portion that causes the noise. However, in this specification, unless there is any misunderstanding, it will be stated that "the optical element 50 emits the irradiation light 20L2."

[0080] [Components Arranged Outside the Housing 80] Next, examples of components arranged outside the housing 80 in the measurement device 100 according to this embodiment will be described with reference to Figures 7A to 7D. Figures 7A to 7D are block diagrams that schematically show examples 1 to 4 of components arranged outside the housing 80 in the measurement device 100 according to this embodiment, respectively. However, in Figures 7A to 7D, the light source 20, the processing circuit 70, and the memory 72 shown in Figure 1 are omitted.

[0081] The example shown in Fig. 7A corresponds to the examples shown in Fig. 5A and Fig. 6A. In the example shown in Fig. 7A, the first optical splitter 32a, the second optical splitter 32b, the optical circulator 34, the photodetector 60, and the light source 20, the processing circuit 70, and the memory 72 shown in Fig. 1 are housed in a housing 80. The optical switch 40, the first optical element 50a, and the second optical element 50b are disposed outside the housing 80. The housing 80 can reduce the influence of the external environment, such as temperature and humidity, on the components inside the housing 80. If a temperature adjustment element is provided in the housing 80, stable measurement is possible even if temperature-sensitive components are present.

[0082] 7B, unlike the example shown in Fig. 7A, the optical switch 40 is disposed inside the housing 80. In this case, the influence of the external environment on the optical switch 40 can be reduced.

[0083] 7A , in the example shown in Fig. 7C , in addition to the optical switch 40, the first optical element 50a, and the second optical element 50b, the optical circulator 34 is also arranged outside the housing 80. Therefore, in the example shown in Fig. 7C , unlike the examples shown in Figs. 7A and 7B in which the optical circulator 34 is housed in the housing 80, it is easy to shorten the fiber noise section between the optical circulator 34 and the first optical element 50a and the fiber noise section between the optical circulator 34 and the second optical element 50b. Because the fiber noise section is shortened, it is possible to narrow the frequency band of the fiber noise and widen the ranging range.

[0084] Furthermore, backscattered light generated in the optical fiber between the first optical splitter 32a and the optical circulator 34 and in the optical fiber between the optical circulator 34 and the second optical splitter 32b does not reach the photodetector 60, and therefore these optical fibers do not generate fiber noise. Since the length of these optical fibers does not affect the distance measurement range, there is no limit to the length of these optical fibers.

[0085] 7D differs from the example shown in Fig. 7C in that the measurement device 100 further includes another housing 82 that houses the optical circulator 34 and the optical switch 40. The other housing 82 may be provided with, for example, a temperature adjustment element, similar to the housing 80. Such another housing 82 can reduce the influence of the external environment on the optical circulator 34 and the optical switch 40.

[0086] In addition to the housing 80, the measurement device 100 may further include at least one optical head that houses the plurality of optical elements 50 shown in FIG. 1 . The optical head helps to protect the optical element 50. The at least one optical head may include, for example, a plurality of optical heads that each house a plurality of optical elements 50.

[0087] 7A to 7D, the optical path length between the components shown in Fig. 7A to 7D is as follows: The optical path length from the first optical splitter 32a to the optical circulator 34 is d １ , the optical path length from the first optical splitter 32a to the second optical splitter 32b is d ２ , the optical path length from the optical circulator 34 to the optical switch 40 is d ３ , the optical path length from the optical circulator 34 to the second optical splitter 32b is d ４ , the optical path length inside the optical circulator 34 from the optical circulator 34 to the second optical splitter 32b is d ｃ , the optical path length from the optical switch 40 to the first optical element 50a is d ５１ , the optical path length from the optical switch 40 to the second optical element 50b is d ５２ , the optical path length from the first optical element 50a to the first object 10a is d ６１ , the optical path length from the second optical element 50b to the second object 10b is d ６２ In the examples shown in FIGS. 7A to 7D, d ５１ <d ５２ is.

[0088] Next, the relationship between the optical path lengths of the light flows I to V shown in FIG. 1 and the beat frequency will be described with reference to FIG. 8 . FIG. 8 is a diagram for explaining the relationship between the optical path lengths of the light flows I to V shown in FIG. 1 and the beat frequency. "(I)," "(IV)," and "(V)" in FIG. 8 represent the optical path lengths of the light flows I, IV, and V, respectively. "(IIa)" and "(IIb)" in FIG. 8 represent the optical path lengths of the light flow II via the first optical element 50a and the second optical element 50b, respectively. "(IIIa)" and "(IIIb)" in FIG. 8 represent the optical path lengths of the light flow III reflected by the incident surfaces of the first optical element 50a and the second optical element 50b, respectively. The "first beam" and "second beam" in FIG. 8 refer to the irradiation light 20L2 emitted as a beam of spatial light from the first optical element 50a and the second optical element 50b, respectively.

[0089] The optical path length of the light flow I is d ２ The optical path length of the light flow IIa is d １ +2d ３ +2d ５１ +2d６１ +d ４ The optical path length of the light flow IIb is d １ +2d ３ +2d ５２ +2d ６２ +d ４ The optical path length of the light flow IIIa is d １ +2d ３ +2d ５１ +d ４ The optical path length of the light flow IIIb is d １ +2d ３ +2d ５２ +d ４ The optical path length of the light flow IV is d １ +d ４ +d ｃ The optical path length of the light flow V is d １ +2d ３ +d ４ The fiber noise is d １ +d ４ The optical path length of the light flows IIIa and IIIb is in the range from the optical path length of the light flows IIIa and IIIb.

[0090] The f shown in FIG. ｃｏｌ , f ｃｉｒ , f ｓｗ , f ＰＤ , and f ｎｏｉｓ The following is true for f ｃｏｌ represents the beat frequency of the beat signals IIIa and IIIb caused by the optical elements 50a and 50b. ｃｏｌ corresponds to the zero distance between the first and second beams. ｃｉｒ represents the beat frequency of the beat signal IV caused by the optical circulator 34. ｓｗ represents the beat frequency of the beat signal V caused by the optical switch 40. ＰＤ represents the cutoff frequency of the photodetector 60. ｎｏｉｓｅ represents the frequency band of fiber noise in the signal spectrum. ｃｏｌ From f ＰＤ The frequency band is up to

[0091] In the example shown in FIG. 8, the optical path length of the light flow V is equal to the optical path length of the light flow I, so the beat frequency f ｓｗIn the example shown in FIG. 8, the optical path length d ２ d １ +d ４ and the optical path length d of the optical flow IIIa １ +2d ３ +2d ５１ +d ４ The average of (d １ +d ４ ) + (d １ +2d ３ +2d ５１ +d ４ ) )] / 2=(d １ +d ３ +d ５１ +d ４ ) and d １ +d ４ and the optical path length d of the optical flow IIIb １ +2d ３ +2d ５２ +d ４ The average of (d １ +d ４ ) + (d １ +2d ３ +2d ５２ +d ４ ) )] / 2=(d １ +d ３ +d ５２ +d ４ ) is shorter than

[0092] Optical path length d of light flow I ２ Even if d is less than the optical path length of the light flows IIIa and IIIb, １ +d ４ and the optical path lengths of the optical flows IIIa and IIIb are longer than the above average, the fiber noise is ｃｏｌ appears in the higher frequency range than

[0093] On the other hand, the optical path length d ２ ga d １ +d ４ longer than the optical path length of d １ +d ４and the optical path lengths of the light flows IIIa and IIIb are less than the above average, the fiber noise is narrow-banded and varies from zero frequency to the beat frequency f of the beat signals IIIa and IIIb. ｃｏｌ It falls within the range of.

[0094] Therefore, the optical path length of the light flow I is d １ +d ４ longer than the optical path length of d １ +d ４ and the average of the optical path lengths of the light flows IIIa and IIIb, and the beat frequency f ｃｉｒ is the beat frequency f of the beat signals IIIa and IIIb ｃｏｌ When the following condition is satisfied, that is, when the following formula (2) is satisfied, the frequency band of the fiber noise can be narrowed and the measurement range can be broadened. However, for simplicity, the beat signal V is not taken into consideration here.

[0095] The intensity of the phase noise of the beat signal V caused by the optical switch 40 is N ｓｗ , the shot noise intensity of the photodetector 60 is N ＰＤ In the distance measurement range, the intensity N of the phase noise of the beat signal V is ｓｗ is the shot noise intensity N of the photodetector 60 ＰＤ , that is, when the following formula (3) is satisfied, the influence of the phase noise of the beat signal V caused by the optical switch 40 on the beat signals IIa and IIb can be reduced. The shot noise of the photodetector 60 has been described with reference to FIGS. 4C, 5C, and 6C.

[0096] 5B , the beat frequency of beat signal V is 60, and the frequency at which the phase noise of beat signal V becomes sufficiently small is 130. That is, the phase noise of beat signal V becomes sufficiently small at a frequency that is 70 or more away from the beat frequency of beat signal V. Since the beat frequency of beat signal III is 80, if the beat frequency of beat signal V is 10 or less, the phase noise of beat signal V has almost no effect on the ranging range. Since 10 / 80 = 0.125, 0.125 can be approximated as 0.15. If the beat frequency of beat signal V is lower than the beat frequency of beat signals IIIa and IIIb × 0.15, that is, if the following formula (4) is satisfied, the effect of the phase noise of beat signal V on beat signal II can be reduced.

[0097] [Calibration Method] Next, a method for calibrating the measurement device 100 according to this embodiment will be described. In calibrating the measurement device 100, the components of the measurement device 100 are arranged as shown in any one of FIGS. 7A to 7D. Furthermore, the objects 10a and 10b are arranged at positions separated from the optical elements 50a and 50b. The objects 10a and 10b are arranged at a predetermined distance, such as 1 m, with the incident surfaces of the optical elements 50a and 50b being set as zero distance. The objects 10a and 10b have a certain degree of reflectivity and may be, for example, Kent paper or a silver diffusion plate.

[0098] 8 is not satisfied for the beat frequencies of beat signals II to V, or if the relationships of formulas (2) to (4) are not satisfied, what is important for calibration is the optical path length d2 of light flow I. For example, the optical path length d2 of light flow I can be appropriately adjusted so that at least one of these relationships is satisfied. Alternatively, the optical path lengths of light flows III to V may be appropriately adjusted based on the optical path length d2 of light flow I.

[0099] As described above, the measurement device 100 according to this embodiment has a simple configuration and can emit irradiation light 20L2 with a relatively high intensity from one of the multiple optical elements 50 that is selected. Reflected light 20L3 from the object 10 enters the photodetector 60 with a relatively high intensity without being branched via the same optical element 50, and therefore the beat signal II resulting from the object 10 clearly appears in the signal spectrum.

[0100] Furthermore, in the measurement device 100 according to this embodiment, by appropriately adjusting the optical path lengths between the components, the beat signal IV caused by the optical circulator 34 and the beat signal V caused by the optical switch 40 appear on the lower frequency side than the beat signal III caused by the optical element 50. In addition, the beat signal V is sufficiently separated from the beat signal III. The beat signal II caused by the object 10 appears on the higher frequency side than the beat signal III. Therefore, not only the beat signals IV and V but also the phase noise of the beat signal V have almost no effect on the beat signal II.

[0101] Furthermore, in the measurement device 100 according to this embodiment, the optical circulator 34, the optical switch 40, and the optical element 50 are disposed outside the housing 80, thereby shortening the fiber noise section between the optical circulator 34 and the optical element 50. As a result, it is possible to narrow the frequency band of the fiber noise and widen the ranging range.

[0102] In the above example, the two components are connected by an optical fiber, but the present invention is not limited to this example. At least some of the components included in the measurement device 100 may be integrated on a chip by a semiconductor process, and the two components may be connected by a waveguide on the chip.

[0103] [Additional Notes] The above description of the embodiments discloses the following techniques.

[0104] [Technology 1] A measurement device comprising: a light source that emits light whose frequency changes over time; an optical splitter that splits the light from the light source into illumination light for illuminating a scene and reference light; an optical circulator to which the illumination light from the optical splitter is input; an optical switch that switches the path of the illumination light; a plurality of optical elements used for emitting the illumination light and for receiving reflected light from the scene; and a photodetector that detects interference light between the reference light and the reflected light, wherein the optical switch switches the path of the illumination light from the optical circulator to one of the plurality of optical elements, and the one of the plurality of optical elements emits the illumination light and receives the reflected light.

[0105] This measurement device has a simple configuration and can emit light of a relatively high intensity from one of the multiple optical elements when switched.

[0106] [Technology 2] The measurement device according to Technology 1, further comprising a housing that houses the light source, the optical splitter, the optical circulator, and the photodetector, and the plurality of optical elements are disposed outside the housing.

[0107] In this measurement device, the housing can reduce the influence of the external environment, such as temperature and humidity, on the light source, optical splitter, optical circulator, and photodetector.

[0108] [Technology 3] The measurement device according to Technology 1, further comprising a housing that houses the light source, the optical splitter, and the photodetector, wherein the optical circulator, the optical switch, and the plurality of optical elements are disposed outside the housing.

[0109] In this measurement device, the fiber noise section between the optical circulator and each optical element can be shortened, so that the frequency band of the fiber noise can be narrowed and the distance measurement range can be widened.

[0110] [Technology 4] The measurement device according to Technology 3, further comprising another housing that houses the optical circulator and the optical switch.

[0111] This measurement device can reduce the influence of the external environment on the optical circulator and the optical switch.

[0112] [Technology 5] The present invention further includes another optical splitter that superimposes the reflected light and the reference light and inputs the superimposed light as the interference light to the photodetector, wherein the plurality of optical elements include at least a first optical element and a second optical element, and the optical path length from the optical splitter to the optical circulator is d １ , the optical path length from the optical splitter to the other optical splitter is d ２ , the optical path length from the optical circulator to the optical switch is d ３ , the optical path length from the optical circulator to the other splitter is d ４ , the optical path length inside the optical circulator from the optical circulator to the other splitter is d ｃ , the optical path length from the optical switch to the first optical element is d ５１ , the optical path length from the optical switch to the second optical element is d ５２ When this is the case, d １ +d ４ ≦d ２ ≦d １ +d ３ +d ５１ +d ４ , d １ +d ４ ≦d ２ ≦d １ +d ３ +d ５２ +d ４ , |d １ +2d ３ +2d ５１ +d ４ -d ２ |≧|d １ +d ４ +d ｃ -d ２ | and |d １ +2d ３ +2d ５２ +d ４ -d ２ |≧|d １ +d ４ +d ｃ -d ２| The measuring device according to any one of techniques 1 to 4.

[0113] This measuring device can narrow the frequency band of fiber noise and widen the measurement range.

[0114] [Technology 6] The measurement device according to any one of Technologies 1 to 5, wherein in a frequency band in which distance measurement is possible in the signal spectrum of the interference light, the intensity of phase noise caused by the optical switch is lower than the intensity of shot noise of the photodetector.

[0115] In this measurement device, the phase noise caused by the optical switch has almost no effect on the beat signal caused by the object.

[0116] [Technology 7] The present invention further includes another optical splitter that superimposes the reflected light and the reference light and inputs the superimposed light as the interference light to the photodetector, wherein the plurality of optical elements include at least a first optical element and a second optical element, and the optical path length from the optical splitter to the optical circulator is d １ , the optical path length from the optical splitter to the other optical splitter is d ２ , the optical path length from the optical circulator to the optical switch is d ３ , the optical path length from the optical circulator to the other optical splitter is d ４ , the optical path length from the optical switch to the first optical element is d ５１ , the optical path length from the optical switch to the second optical element is d ５２ When |d １ +2d ３ +2d ５２ +d ４ -d ２ |×0.15>|d １ +2d ３ +d ４ -d ２ | and |d １ +2d ３ +2d ５１ +d ４ -d ２ |×0.15>|d １ +2d ３ +d ４ -d ２The measuring device according to any one of techniques 1 to 6, wherein |

[0117] In this measurement device, the phase noise caused by the optical switch has almost no effect on the beat signal caused by the object.

[0118] 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.

[0119] REFERENCE SIGNS LIST 10 object 10a first object 10b second object 20 light source 20L0 laser light 20L1 reference light 20L2 irradiation light 20L3 reflected light 20L4 interference light 30 interference optical system 32a first optical splitter 32b second optical splitter 34 optical circulator 40 optical switch 50 optical element 50a first optical element 50b second optical element 60 photodetector 70 processing circuit 72 memory 80 housing 82 other housing 90, 100 measurement device

Claims

1. A measuring device comprising: a light source that emits light whose frequency changes over time; an optical splitter that separates the light from the light source into irradiation light for irradiating a scene and reference light; an optical circulator into which the irradiation light from the optical splitter is input; an optical switch that switches the path of the irradiation light; a plurality of optical elements used for emitting the irradiation light and for the incidence of reflected light from the scene; and a photodetector that detects interference light between the reference light and the reflected light, wherein the optical switch switches the path of the irradiation light from the optical circulator to one of the plurality of optical elements, and the one of the plurality of optical elements emits the irradiation light and receives the reflected light.

2. The measuring device according to claim 1, further comprising a housing that houses the light source, the optical splitter, the optical circulator, and the photodetector, wherein the plurality of optical elements are arranged outside the housing.

3. The measuring device according to claim 1, further comprising a housing that houses the light source, the optical splitter, and the photodetector, wherein the optical circulator, the optical switch, and the plurality of optical elements are arranged outside the housing.

4. The measuring device according to claim 3, further comprising another housing that houses the optical circulator and the optical switch.

5. Further comprising another optical splitter for superimposing the reflected light and the reference light and inputting the interference light to the photodetector, the plurality of optical elements including at least a first optical element and a second optical element, the optical path length from the optical splitter to the optical circulator being d １ , the optical path length from the optical splitter to the other optical splitter being d ２ , the optical path length from the optical circulator to the optical switch being d ３ , the optical path length from the optical circulator to the other splitter being d ４ , the internal optical path length of the optical circulator from the optical circulator to the other splitter being d ｃ , the optical path length from the optical switch to the first optical element being d ５１ , the optical path length from the optical switch to the second optical element being d ５２ When taking, d １ +d ４ ≤d ２ ≤d １ +d ３ +d ５１ +d ４ , d １ +d ４ ≤d ２ ≤d １ +d ３ +d ５２ +d ４ , |d １ +2d ３ +2d ５１ +d ４ -d ２ |≥|d １ +d ４ +d ｃ -d ２ |, and |d １ +2d ３ +2d ５２ +d ４ -d ２ |≥|d １ +d ４ +d ｃ -d ２ |, The measuring device according to any one of claims 1 to 4.

6. The measuring device according to any one of claims 1 to 4, wherein in a measurable frequency band in the signal spectrum of the interference light, the intensity of phase noise caused by the optical switch is lower than the intensity of shot noise of the photodetector.

7. Further comprising another optical splitter for superimposing the reflected light and the reference light and inputting the interference light to the photodetector, the plurality of optical elements includes at least a first optical element and a second optical element, and the optical path length from the optical splitter to the optical circulator is d １ , the optical path length from the optical splitter to the other optical splitter is d ２ , the optical path length from the optical circulator to the optical switch is d ３ , the optical path length from the optical circulator to the other optical splitter is d ４ , the optical path length from the optical switch to the first optical element is d ５１ , the optical path length from the optical switch to the second optical element is d ５２ When it is set as follows, |d １ +2d ３ +2d ５２ +d ４ -d ２ |×0.15>|d １ +2d ３ +d ４ -d ２ |, and |d １ +2d ３ +2d ５１ +d ４ -d ２ |×0.15>|d １ +2d ３ +d ４ -d ２ |, the measuring device according to any one of claims 1 to 4.

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