Measurement device, measurement program, and computer-readable recording medium with computer program recorded thereon

Abstract

The present invention suppresses a condition in which a plurality of reflected laser beams corresponding to a plurality of seed laser beams emitted in mutually different periods cannot be distinguished from each other in a light receiver. This measurement device comprises: a projector having a first seed laser that emits a first seed laser beam having a first wavelength, a second seed laser that emits a second seed laser beam having a second wavelength different from the first wavelength, an optical fiber, and an excitation laser; a light receiver; and a controller. The controller executes first measurement processing for measuring the distance to a measurement object on the basis of a first light reception timing at which the light receiver receives first reflected laser light corresponding to the first seed laser beam, and second measurement processing for measuring the distance to the measurement object on the basis of a second light reception timing at which the light receiver receives second reflected laser light corresponding to the second seed laser beam.

Description

Measurement device, measurement program, and computer-readable recording medium having computer program recorded thereon

[0001] The technology disclosed in this specification relates to a measurement device, a measurement program, and a computer-readable recording medium on which a computer program is recorded.

[0002] With the advancement of AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems), research and development of LiDAR (Light Detection and Ranging) is underway as one of the measurement devices used to grasp the surrounding environment and estimate the vehicle's position while driving. LiDAR includes a projector that projects (irradiates) laser light onto a measurement target, and a photoreceiver that receives the light reflected from the measurement target. LiDAR outputs information about the measurement target by measuring the distance to the measurement target based on the time difference between the time when the projector emits the laser light and the time when the photoreceiver receives the reflected light. The projector includes a fiber laser (see, for example, Patent Document 1). A fiber laser includes a seed laser that emits seed laser light, an optical fiber that is doped with a rare earth element and through which the seed laser light passes, and a pump laser that emits pump light that excites the rare earth element in the optical fiber.

[0003] International Publication No. 2020 / 117912

[0004] In this type of measurement device, it is unclear which laser beams emitted at which light projection timing each reflected light received by the receiver corresponds to, which can result in a decrease in the accuracy of measuring the distance to the measurement target. In particular, if a laser beam emitted at a certain light projection timing is emitted before the laser beam emitted at the next light projection timing is received by the receiver, it is likely to be unclear which laser beams emitted at which light projection timing each reflected light received by the receiver corresponds to. On the other hand, in conventional measurement devices, the light projector is configured to emit laser beams at one light projection timing, and then emit laser beams at the next light projection timing after the laser beam emitted at the previous light projection timing is received by the receiver. However, even with this configuration, it can be unclear which laser beams emitted at which light projection timing each reflected light received by the receiver corresponds to, for example, when multiple light reception timings overlap.

[0005] This specification discloses a technique that can solve the above-mentioned problems.

[0006] The technology disclosed in this specification can be realized, for example, in the following forms.

[0007] (1) The measurement device disclosed in this specification includes a first seed laser that emits first seed laser light having a first wavelength, a second seed laser that emits second seed laser light having a second wavelength different from the first wavelength, an optical fiber doped with a rare earth element and into which the first seed laser light and the second seed laser light are input, and an excitation laser that emits excitation light that excites the rare earth element in the optical fiber, and is equipped with a light projector that emits output laser light output from the optical fiber to the outside, a light receiver that receives reflected laser light that is the output laser light emitted by the light projector and reflected back from an object to be measured, and a controller. The controller executes a seed laser emission process that causes the first seed laser and the second seed laser to emit light at different periods from each other, a first measurement process that measures the distance to the measurement object based on a first light receiving timing at which the photoreceiver receives a first reflected laser light that is the output laser light output from the optical fiber in response to input of the first seed laser light and reflected by the measurement object and returning, and a second measurement process that measures the distance to the measurement object based on a second light receiving timing at which the photoreceiver receives a second reflected laser light that is the output laser light output from the optical fiber in response to input of the second seed laser light and reflected by the measurement object and returning.

[0008] In this measuring device, a first seed laser beam and a second seed laser beam having different wavelengths are input into a common optical fiber with a time difference. Therefore, the optical receiver can distinguish between a first reflected laser beam corresponding to the first seed laser beam and a second reflected laser beam corresponding to the second seed laser beam based on the difference in wavelength. As a result, this measuring device can prevent the optical receiver from being unable to distinguish between multiple reflected laser beams corresponding to multiple seed laser beams emitted in different periods.

[0009] (2) In the above-described measuring device, the light receiver may include a distributor that distributes the first reflected laser light and the second reflected laser light, a first light receiving element that receives the first reflected laser light distributed by the distributor, and a second light receiving element that receives the second reflected laser light distributed by the distributor. This measuring device can prevent the first reflected laser light and the second reflected laser light from being mixed and received by the light receiver, compared to a configuration that does not include a distributor, for example.

[0010] (3) In the above measurement device, the time difference between the emission timing of the first seed laser beam and the emission timing of the second seed laser beam may be shorter than the round-trip time of the output laser beam to travel a measurable distance of the measurement device. According to this measurement device, the sampling rate can be improved by shortening the emission period of the output laser beam, compared to a configuration in which, for example, after emitting the first seed laser beam, the second sheet laser beam is emitted after waiting for reception of the first reflected laser beam.

[0011] (4) In the above measuring apparatus, the optical fiber may include a first optical fiber into which the first seed laser beam and the second seed laser beam are input, and a plurality of second optical fibers, the pumping laser may include a first pumping laser that emits pumping light for exciting the rare earth element in the first optical fiber, and a second pumping laser that emits pumping light for exciting the rare earth element in the plurality of second optical fibers, the projector may further include a demultiplexer that demultiplexes the first output laser beam output from the first optical fiber into a plurality of the first output laser beams, each of the plurality of first output laser beams is input to a respective one of the plurality of second optical fibers, and a plurality of second output laser beams output from each of the plurality of second optical fibers may be emitted to the outside. In this measuring apparatus, the first output laser beam output from the first optical fiber is demultiplexed into a plurality of first output laser beams, and the demultiplexed plurality of first output laser beams are further amplified in the second optical fiber. As a result, with this measuring device, it is possible to suppress the occurrence of insufficient power of the second output laser light output from each second optical fiber, compared to, for example, a configuration in which amplification by the second optical fiber is not performed.

[0012] The measurement device disclosed in this specification does not have the configurations (1) to (3) above, but has a seed laser that emits seed laser light, an optical fiber that is doped with a rare earth element and into which the seed laser light is input, and a pumping laser that emits pumping light that excites the rare earth element in the optical fiber, and is also provided with a light projector that emits output laser light output from the optical fiber to the outside, and a light receiver that receives reflected laser light that is reflected by a measurement object and returned from the output laser light projected by the light projector, and the fibers are a first optical fiber into which the seed laser light is input, and a plurality of second optical fibers. and a laser beam splitter, wherein the pumping laser includes a first pumping laser that emits pumping light to excite the rare earth element in the first optical fiber and a second pumping laser that emits pumping light to excite the rare earth element in the plurality of second optical fibers, the projector further having a demultiplexer that splits a first output laser beam output from the first optical fiber into a plurality of first output laser beams, each of the plurality of first output laser beams being input to a respective one of the plurality of second optical fibers, and a plurality of second output laser beams output from each of the plurality of second optical fibers being emitted to the outside. With this configuration, it is possible to solve the problem of insufficient power output of the second output laser beam output from each second optical fiber.

[0013] (5) In the above measurement device, the projector may further include a second demultiplexer that demultiplexes at least one of the plurality of second output laser beams, and may be configured to emit the plurality of second output laser beams demultiplexed by the second demultiplexer to the outside. In this measurement device, the second output laser beam can be further demultiplexed into a plurality of beams and output while suppressing an insufficient output of the second output laser beams output from each second optical fiber.

[0014] (6) In the above-described measuring device, the first excitation laser and the second excitation laser may be separate and spaced apart from each other. In this measuring device, heat generated by the excitation lasers can be dispersed more effectively than in a case where the first excitation laser and the second excitation laser are a common excitation laser.

[0015] (7) In the above measurement device, the amplification degree of the first optical fiber may be lower than the amplification degree of the second optical fiber. With this measurement device, it is possible to suppress the amplification of noise in the optical fibers, compared to, for example, a configuration in which the amplification degree of the first optical fiber is higher than the amplification degree of the second optical fiber.

[0016] (8) A measurement program disclosed in the present specification is a measurement program for causing a computer included in a measurement device including: a first seed laser that emits a first seed laser beam having a first wavelength; a second seed laser that emits a second seed laser beam having a second wavelength different from the first wavelength; a projector having an optical fiber to which the first seed laser beam and the second seed laser beam are input; and a photoreceiver that receives a reflected laser beam that is an output laser beam emitted by the projector and reflected by a measurement object and returns, to emit the first seed laser and the second seed laser for mutually different periods. a first measurement process for measuring the distance to the measurement object based on a first light-receiving timing at which the photoreceiver receives a first reflected laser beam, which is the output laser beam output from the optical fiber in response to input of the first seed laser beam and reflected by the measurement object and returning, and a second measurement process for measuring the distance to the measurement object based on a second light-receiving timing at which the photoreceiver receives a second reflected laser beam, which is the output laser beam output from the optical fiber in response to input of the second seed laser beam and reflected by the measurement object and returning. This measurement program can prevent the photoreceiver from being unable to distinguish between multiple reflected laser beams corresponding to multiple seed laser beams emitted in different periods from each other.

[0017] The technology disclosed in this specification can be realized in various forms, such as a measurement device, a projector, a measurement method, a measurement program, a computer-readable recording medium on which the measurement program is recorded, etc.

[0018] 1 is a block diagram showing the general configuration of a measurement device according to an embodiment; 2 is an explanatory diagram showing the general configuration of a light-emitting unit; 3 is an explanatory diagram showing the general configuration of a light-receiving unit; 4 is a flowchart showing a measurement process; and 5 is a timing chart showing the timing of light projection and light reception.

[0019] A. Embodiments: A-1. Configuration of Measuring Device 10: Fig. 1 is a block diagram showing a schematic configuration of measuring device 10 in this embodiment. Measuring device 10 measures the difference between the timing at which light projector 20 emits output light Lout and the timing at which light receiver 30 receives reflected light Lin (time of flight of laser light, hereinafter referred to as "TOF" (Time of Flight)) to acquire information about the object to be measured.

[0020] The measuring device 10 is mounted on, for example, a vehicle (not shown) equipped with AD or ADAS. The measuring device 10 assists in detecting objects such as people and other vehicles while the vehicle is traveling, and provides various information to other devices and users that is useful for ensuring the safety of the driver of the vehicle and those around the vehicle, and for reducing damage to surrounding objects while the vehicle is being driven.

[0021] The measurement device 10 is a multi-channel LiDAR that simultaneously emits multiple output light beams Lout. The measurement device 10 is also a scanning-type LiDAR. Specifically, the measurement device 10 scans a measurement target (not shown) so that the irradiation positions of the multiple output light beams Lout move parallel to each other. As shown in FIG. 1 , the measurement device 10 includes a light projector 20 and a light receiver 30.

[0022] The light projector 20 includes a fiber laser 22 that outputs output light Lout and a light projection control device 26. The light projection control device 26 controls the light emission of the fiber laser 22. The light projection control device 26 also inputs a signal indicating the light projection timing of the fiber laser 22 to a controller 40 (described later). The light projection control device 26 periodically and repeatedly turns on and off a current flowing through the fiber laser 22 (seed lasers 112a to 112c (described later)), thereby causing the fiber laser 22 to periodically and repeatedly emit light.

[0023] The light projector 20 is a multi-channel light projector that simultaneously emits a plurality of output lights Lout (Lout1 to Lout6). Specifically, the fiber laser 22 has a light emitting unit 110, a first excitation laser 120a, a second excitation laser 120b, a first optical fiber F1, and a plurality of second optical fibers F2.

[0024] The light emitting unit 110 has seed lasers 112a to 112c, which will be described later, and each of the seed lasers 112a to 112c emits seed light La (La(f1) to La(f3), see FIG. 2) whose peak wavelength falls within the near-infrared range, for example.

[0025] The first optical fiber F1 and the second optical fiber F2 are doped with a rare earth element, and seed light La passes through them. The first optical fiber F1 and the second optical fiber F2 are arranged in series. The optical fibers F1 and F2 are doped with at least one of a rare earth element, such as ytterbium (Yb) or erbium (Er). The length of each of the optical fibers F1 and F2 is, for example, approximately 5 m.

[0026] The first pumping laser 120a emits first pumping light Lb1 (e.g., 940 nm) that excites the rare earth element contained in the first optical fiber F1, and the second pumping laser 120b emits second pumping light Lb2 (e.g., 940 nm) that excites the rare earth element contained in the second optical fiber F2.

[0027] More specifically, the fiber laser 22 includes a first optical isolator (ISO) 130, a first wavelength division multiplexer (WDM) 140, a first seed beam splitter (TAP) 150a, a pump beam splitter 150b, a second optical isolator 160, second multiplexers 170a to 170c, and second seed beam splitters 180a to 180c. The first seed beam splitter 150a is an example of a first splitter, and the second seed beam splitters 180a to 180c are examples of a second splitter.

[0028] The light emitting unit 110 is optically coupled to the first multiplexer 140 via an ordinary optical fiber (not shown) that is not doped with a rare earth element. A first optical isolator 130 is provided between the light emitting unit 110 and the first multiplexer 140. The first multiplexer 140 is coupled to an input portion of a first optical fiber F1. The output portion of the first optical fiber F1 is optically coupled to a first seed beam demultiplexer 150a. A second optical isolator 160 is provided between the first multiplexer 140 and the first seed beam demultiplexer 150a. The first seed beam demultiplexer 150a demultiplexes the seed beam La amplified by the first optical fiber F1 into multiple beams (La1 to La3).

[0029] The first pumping laser 120a is optically coupled to the first multiplexer 140 via an ordinary optical fiber (not shown) that is not doped with a rare earth element. The first multiplexer 140 multiplexes the seed light La emitted by the light emitter 110 and the first pumping light Lb1 emitted by the first pumping laser 120a. The second pumping laser 120b is optically coupled to the pumping light demultiplexer 150b via an ordinary optical fiber (not shown) that is not doped with a rare earth element. The pumping light demultiplexer 150b demultiplexes the second pumping light Lb2 emitted by the second pumping laser 120b into multiple light beams.

[0030] The second multiplexers 170a to 170c are optically coupled to the first seed beam demultiplexer 150a and the pump beam demultiplexer 150b, respectively. Each of the second multiplexers 170a to 170c multiplexes the seed beam La amplified by the first optical fiber F1 with the second pump beam Lb2 emitted by the second pump laser 120b.

[0031] Each of the second multiplexers 170a to 170c is coupled to an input portion of a second optical fiber F2. The output portion of each of the second optical fibers F2 is coupled to a corresponding one of the second seed beam demultiplexers 180a to 180c. Specifically, the second multiplexer 170a is optically coupled to the second seed beam demultiplexer 180a via the second optical fiber F2. The second multiplexer 170b is optically coupled to the second seed beam demultiplexer 180b via the second optical fiber F2. The second multiplexer 170c is optically coupled to the second seed beam demultiplexer 180c via the second optical fiber F2.

[0032] Each of the second seed beam demultiplexers 180a to 180c demultiplexes the seed beams La1 to La3, which have been further amplified by the second optical fiber F2, into a plurality of beams. Each of the second seed beam demultiplexers 180a to 180c is coupled to the input portions of a plurality of third optical fibers F3. The output portions of the third optical fibers F3 are directed toward the outside of the projector 20. The third optical fibers F3 are ordinary optical fibers that are not doped with a rare earth element.

[0033] With this configuration, in the fiber laser 22, the first pumping light Lb1 emitted by the first pumping laser 120a excites the rare earth element contained in the first optical fiber F1, and the second pumping light Lb2 emitted by the second pumping laser 120b excites the rare earth element contained in the second optical fiber F2. By making the seed light La from the light emitting unit 110 incident on the first optical fiber F1 in the excited state, the seed light La is amplified by the first optical fiber F1 and demultiplexed into multiple light beams (La1 to La3) by the first seed light demultiplexer 150a.

[0034] The first seed light La1 separated by the first seed light demultiplexer 150a is amplified by the second optical fiber F2 and further separated into multiple light beams by the second seed light demultiplexer 180a. The multiple first seed light beams La1 separated by the second seed light demultiplexer 180a are respectively emitted to the outside of the light projector 20 as first output light Lout1 and second output light Lout2 via the third optical fiber F3. The second seed light La2 separated by the first seed light demultiplexer 150a is amplified by the second optical fiber F2 and further separated into multiple light beams by the second seed light demultiplexer 180b. The plurality of second seed light beams La2 separated by the second seed light beam splitter 180b are respectively outputted to the outside of the projector 20 as third output light Lout3 and fourth output light Lout4 via the third optical fiber F3. The third seed light beam La3 separated by the first seed light beam splitter 150a is amplified by the second optical fiber F2 and further split into a plurality of light beams by the second seed light beam splitter 180c. The plurality of third seed light beams La3 separated by the second seed light beam splitter 180c are respectively outputted to the outside of the projector 20 as fifth output light Lout5 and sixth output light Lout6 via the third optical fiber F3.

[0035] The light receiver 30 includes six light receiving units 32 (32a to 32c). The light receiving units 32 are light receiving sources having one or more light receiving elements (not shown), or one or more light receiving element arrays (e.g., light receiving elements arranged linearly (one-dimensionally) or planarly (two-dimensionally)). The light receiving elements are, for example, photodiodes, SPADs (Single Photon Avalanche Diodes), balanced photodetectors, etc. The light receiving units 32 photoelectrically convert the incident reflected light Lin to generate a current (hereinafter referred to as a "light receiving current") corresponding to the intensity of the reflected light Lin. The light receiving units 32 input a signal indicating the light receiving timing at which the light receiving elements constituting the light receiving unit 32 received the reflected light Lin and the light receiving current generated by the light receiving elements to a controller 40 (described below).

[0036] The first light-receiving unit 32a is arranged to receive first reflected light Lin1, which is the first output light Lout1 emitted by the light-projector 20 and reflected by the measurement object and returned. The second light-receiving unit 32b is arranged to receive second reflected light Lin2, which is the second output light Lout2 emitted by the light-projector 20 and reflected by the measurement object and returned. The third light-receiving unit 32c is arranged to receive third reflected light Lin3, which is the third output light Lout3 emitted by the light-projector 20 and reflected by the measurement object and returned. The fourth light-receiving unit 32d is arranged to receive fourth reflected light Lin4, which is the fourth output light Lout4 emitted by the light-projector 20 and reflected by the measurement object and returned. The fifth light-receiving unit 32e is arranged to receive fifth reflected light Lin5, which is the fifth output light Lout5 emitted by the light-projector 20 and reflected by the measurement object and returned. The sixth light receiving unit 32f is disposed so as to receive sixth reflected light Lin6 that is returned after being reflected by the measurement object from the sixth output light Lout6 emitted by the projector 20. In this embodiment, the projector 20 and the light receiver 30 are displaced relative to the measurement object, and the irradiation positions of the six output lights Lout1 to Lout3 on the measurement object are moved in parallel in a predetermined direction, thereby making it possible to acquire information about the measurement object (such as the surface shape).

[0037] The measuring device 10 further includes a controller 40 and a communication I / F (Interface) 50 .

[0038] The controller 40 includes, for example, a processor (such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), or DSP (Digital Signal Processor)). The controller 40 calculates the TOF based on a signal indicating the timing of light projection input from the light-projection control device 26 and a signal indicating the timing of light reception input from the light-receiving unit 32. The controller 40 generates information used for various measurements, such as detection of a measurement target and distance measurement, based on the input light-receiving current and the calculated TOF. The information includes, for example, a histogram used in time-correlated single photon counting, distances to each point of the measurement target, a point cloud (point cloud information), etc. The controller 40 also controls the light-projection control device 26 and the light-receiving unit 32. For example, the controller 40 controls the light-projection timing and the light-receiving timing by controlling the light-projection control device 26 and the light-receiving unit 32, thereby controlling the speed or optimization of the process for generating the histogram. The information generated by the controller 40 is provided (transmitted) to devices that use the information (hereinafter referred to as "various use devices 60") via the communication I / F 50.

[0039] The various utilization devices 60 perform, for example, the creation of an environmental map using a point cloud, and self-position estimation (SLAM (Simultaneous Localization and Mapping)) using a scan matching algorithm (NDT (Normal Distributions Transform), ICP (Iterative Closest Point), etc.).

[0040] A-2. Configuration of the light-emitting unit 110 and the light-receiving unit 32: Fig. 2 is an explanatory diagram schematically showing the configuration of the light-emitting unit 110. As shown in Fig. 2, the light-emitting unit 110 has a first seed laser 112a, a second seed laser 112b, a third seed laser 112c, and a third multiplexer 190. The first seed laser 112a, the second seed laser 112b, and the third seed laser 112c emit seed light La having different wavelengths. The first seed laser 112a emits seed light La (f1) with a wavelength of, for example, 1515 nm, the second seed laser 112b emits seed light La (f2) with a wavelength of, for example, 1550 nm, and the third seed laser 112c emits seed light La (f3) with a wavelength of, for example, 1585 nm. The wavelength of each seed light La (f1 to f3) may be in the wavelength range (in this embodiment, 1500 nm or more and 1600 nm or less) that can be amplified by the first optical fiber F1 and the second optical fiber F2.

[0041] The first seed laser 112a, the second seed laser 112b, and the third seed laser 112c are all optically coupled to the third multiplexer 190 via ordinary optical fibers (not shown) that are not doped with rare earth elements. The third multiplexer 190 is optically coupled to the first multiplexer 140. With this configuration, the first seed laser 112a, the second seed laser 112b, and the third seed laser 112c are caused to emit light at different times, so that the light emitting unit 110 can selectively emit seed light La(f1), seed light La(f2), and seed light La(f3).

[0042] Fig. 3 is an explanatory diagram showing a schematic configuration of the light receiving unit 32. As shown in Fig. 3, the light receiving unit 32 has a light receiving optical system 33, a dispersive element 35, three filters 34a to 34c, and three light receiving elements 36a to 36c. The dispersive element 35 is an example of a distributor.

[0043] The light receiving optical system 33 collects reflected light Lin, which is output light Lout from the projector 20 and reflected by a measurement target or the like and returns. The light receiving optical system 33 is configured using optical components such as various lenses such as a collecting lens, various filters such as a wavelength filter, and a reflecting mirror. The dispersive element 35 is an element that disperses the reflected light Lin that has passed through the light receiving optical system 33. The dispersive element 35 can be configured, for example, by a prism, a diffraction grating, a metamaterial, or the like. A metamaterial is an optical element in which minute structures smaller than the wavelength of light are arranged on a substrate (e.g., a glass substrate). The dispersive element 35 may be configured by a metamaterial in which minute structures are arranged three-dimensionally, or by a metamaterial (metasurface) in which minute structures are arranged two-dimensionally.

[0044] The three filters 34a to 34c are each disposed at a position where the reflected light Lin dispersed by the dispersive element 35 is incident. The three filters 34a to 34c are bandpass filters that pass only light of different wavelength bands. The first filter 34a passes the reflected light Lin(f1) corresponding to the seed light La(f1) emitted by the first seed laser 112a, but does not pass the reflected light Lin(f2) and Lin(f3) corresponding to the seed light La(f2) and La(f3) emitted by the other seed lasers 112b and 112c. Specifically, the passband of the first filter 34a is, for example, 1500 nm or more and 1530 nm or less. The second filter 34b passes the reflected light Lin(f2) but does not pass the reflected light Lin(f1) and Lin(f3). Specifically, the pass band of the second filter 34b is, for example, 1535 nm or more and 1565 nm or less. The third filter 34c passes the reflected light Lin(f3) but does not pass the reflected light Lin(f1) and Lin(f2). Specifically, the pass band of the third filter 34c is, for example, 1570 nm or more and 1600 nm or less.

[0045] The first light receiving element 36a receives the reflected light Lin (f1) that has passed through the first filter 34a, the second light receiving element 36b receives the reflected light Lin (f2) that has passed through the second filter 34b, and the third light receiving element 36c receives the reflected light Lin (f3) that has passed through the third filter 34c.

[0046] A-3. Measurement Process: FIG. 4 is a flowchart showing the measurement process, and FIG. 5 is a time chart showing the light projection timing and light reception timing. As shown in FIG. 4, when the measurement process is started, the controller 40 causes the light projector 20 to start a light projection operation (S110). Specifically, the controller 40 executes a seed laser emission process in which the first seed laser 112a, the second seed laser 112b, and the third seed laser 112c emit light for different periods. In this embodiment, as shown in FIG. 5, the light emitter 110 alternately and repeatedly emits seed light La (f1), seed light La (f2), and seed light La (f3) in this order with a predetermined emission time interval ΔT therebetween. As a result, the light projector 20 emits six output beams Lout1 to Lout3 from the third optical fiber F3 in an emission pattern in which three pulse waveforms having different wavelengths (f1 to f3) are sequentially repeated.

[0047] Next, the controller 40 determines whether the first reflected light Lin(f1) has been received by the first light receiving element 36a (S120). If the controller 40 determines that the first reflected light Lin(f1) has been received by the first light receiving element 36a (S120: YES), it executes a first measurement process (S130) and proceeds to S140. In the first measurement process, the distance to the measurement target is measured based on the first light receiving timing T4 at which the first reflected light Lin(f1) is received by the first light receiving element 36a. In other words, the fact that the first reflected light Lin(f1) has been received by the first light receiving element 36a means that the light receiver 30 has received the first reflected light Lin(f1) corresponding to the seed light La(f1). Therefore, the controller 40 measures the distance to the measurement object based on, for example, the time difference ΔT1 between the emission timing T1 and the first light reception timing T4 of the seed light La (f1). Note that, when measuring the distance to the measurement object, the emission timing of the seed light La and the time difference ΔT1 may be corrected taking into account, for example, the lengths of the optical fibers (first optical fiber F1, second optical fiber F2, third optical fiber F3, etc.) included in the fiber laser 22.

[0048] If the controller 40 determines that the first reflected light Lin(f1) has not been received by the first light-receiving element 36a (NO in S120), it determines whether the second reflected light Lin(f2) has been received by the second light-receiving element 36b (S150). If the controller 40 determines that the second reflected light Lin(f2) has been received by the second light-receiving element 36b (YES in S150), it executes a second measurement process (S160) and proceeds to S140. In the second measurement process, the distance to the measurement target is measured based on the second light-receiving timing T5 at which the second reflected light Lin(f2) is received by the second light-receiving element 36b. In other words, the receipt of the second reflected light Lin(f2) by the second light-receiving element 36b means that the photodetector 30 has received the second reflected light Lin(f2) corresponding to the seed light La(f2). Therefore, the controller 40 measures the distance to the measurement object based on the time difference ΔT2 between the emission timing T2 of the seed light La(f2) and the second reception timing T5, for example.

[0049] If the controller 40 determines that the second reflected light Lin(f2) has not been received by the second light receiving element 36b (S150: NO), it determines whether the third reflected light Lin(f3) has been received by the third light receiving element 36c (S170). If the controller 40 determines that the third reflected light Lin(f3) has been received by the third light receiving element 36c (S170: YES), it executes a third measurement process (S180) and proceeds to S140. In the third measurement process, the distance to the measurement target is measured based on the third light receiving timing T6 at which the third reflected light Lin(f3) is received by the third light receiving element 36c. In other words, the receipt of the third reflected light Lin(f3) by the third light receiving element 36c means that the photodetector 30 has received the third reflected light Lin(f3) corresponding to the seed light La(f3). Therefore, the controller 40 measures the distance to the measurement object based on the time difference ΔT3 between the emission timing T3 of the seed light La(f3) and the third reception timing T6, for example.

[0050] If the controller 40 determines that the third reflected light Lin (f3) has not been received by the third light receiving element 36c (S170: NO), the process proceeds to S140. If the controller 40 determines that an instruction to end measurement has not been received (S140: NO), the process returns to S120. If the controller 40 determines that an instruction to end measurement has been received (S140: YES), the process ends this measurement process.

[0051] In this embodiment, as shown in FIG. 5 , the light emission time interval ΔT, which is the time difference between the light emission times T1 to T3, is shorter than the round-trip time (the maximum time difference between the light projection time and the light reception time) for the output light Lout to travel back and forth across the measurable distance of the measurement device 10. For example, after the first light emission time T1 of the seed light La(f1), the seed light La(f2) is emitted at the second light emission time T2 without waiting for the arrival of the first light reception time T4 of the first reflected light Lin(f1). This increases the likelihood that the second reflected light Lin(f2) will be received at 30 before the first reflected light Lin(f1). However, according to this embodiment, the first light reception time T4 and the second light reception time T5 can be distinguished based on the difference in wavelength. For example, when the measurable distance is 250 m, the round trip time is 1.7 μs, when the measurable distance is 500 m, the round trip time is 3.3 μs, and when the measurable distance is 750 m, the round trip time is 5.0 μs.

[0052] A-4. Advantages of this embodiment: In the measurement device 10 according to this embodiment, three seed beams La (f1 to f3) having different wavelengths are input to common optical fibers F1 and F2 at different times (FIGS. 2 and 5). Therefore, the photoreceiver 30 can distinguish between the reflected beams Lin (f1 to f3) corresponding to the three seed beams La (f1 to f3) based on the differences in wavelength. This prevents the photoreceiver 30 from being unable to distinguish between the multiple reflected beams Lin (f1 to f3) corresponding to the multiple seed beams La (f1 to f3) emitted during different periods.

[0053] In this embodiment, the light emission time interval ΔT, which is the time difference between the light emission timings T1 to T3, is shorter than the round-trip time it takes for the output light Lout to travel back and forth over the measurable distance of the measurement device 10 ( FIG. 5 ). Therefore, according to this embodiment, the sampling rate (measurement accuracy) can be improved by shortening the emission period of the output light Lout, compared to a configuration in which, for example, after the first light emission timing T1 of the seed light La(f1), the first reflected light Lin(f1) is received and then the seed light La(f2) is emitted.

[0054] In this embodiment, the seed light La output from the first optical fiber F1 is demultiplexed into multiple seed light beams La (La1 to La3) by the first seed light demultiplexer 150a, and the multiple demultiplexed seed light beams La (La1 to La3) are further amplified by the second optical fiber F2 ( FIG. 1 ). As a result, this embodiment can prevent the occurrence of insufficient output of the output light Lout output from each second optical fiber, compared to a configuration in which amplification by the second optical fiber F2 is not performed. In short, this embodiment can prevent insufficient output of each output light beam Lout while realizing multi-channeling in which multiple output light beams Lout are simultaneously emitted from a common light source (light-emitting unit 110). Furthermore, this embodiment can prevent the structure of the measurement device 10 (projector 20) from becoming more complex, the device from becoming larger, and costs from increasing due to an increase in the number of light-emitting sources.

[0055] In this embodiment, the second seed light La2 demultiplexed by the first seed light demultiplexer 150a is amplified by the second optical fiber F2 and further demultiplexed into a plurality of light beams by the second seed light demultiplexer 180b (FIG. 1). As a result, according to this embodiment, it is possible to further demultiplex the output light Lout output from each second optical fiber F2 and output the output light Lout while suppressing an output shortage of the output light Lout.

[0056] In this embodiment, the first pump laser 120a and the second pump laser 120b are separate and spaced apart ( FIG. 1 ). This allows for more efficient dispersion of heat generated by the pump lasers than, for example, a configuration in which the first pump laser 120a and the second pump laser 120b share a common pump laser. Furthermore, in this embodiment, the amplification factor of the first optical fiber F1 is lower than that of the second optical fiber F2. This allows for more efficient suppression of noise amplification in the optical fibers than, for example, a configuration in which the amplification factor of the first optical fiber F1 is higher than that of the second optical fiber F2.

[0057] B. Modifications: The technology disclosed in this specification is not limited to the above-described embodiment, and can be modified in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0058] The configuration of the measurement device 10 in the above embodiment is merely an example, and various modifications are possible. For example, the projector 20 may be a scanning type equipped with a scanner (optical scanning device). Furthermore, while the above embodiment illustrates a multi-channel measurement device 10 (projector 20), the present invention is not limited to this, and the measurement device 10 may be a single-channel type that emits one output laser beam.

[0059] In the above embodiment, the fiber laser 22 has the first optical fiber F1 and the second optical fiber F2 and is configured to amplify the seed light La in two stages, but this is not limiting, and the fiber laser 22 may be configured to amplify the seed light La in only one stage, or may be configured to amplify the seed light La in three or more stages. Also, in the above embodiment, the amplification degree of the first optical fiber F1 may be the same as or higher than the amplification degree of the second optical fiber F2. Note that the difference in amplification degree between the first optical fiber F1 and the second optical fiber F2 can be achieved by adjusting, for example, the fiber length, the type of rare earth element, the excitation level by the excitation laser, etc.

[0060] In the above embodiment, the projector 20 does not have to include at least one of the second seed light demultiplexers 180a to 180c. The number of demultiplexing steps by the first seed light demultiplexer 150a and the pumping light demultiplexer 150b is not limited to three, and may be two, or four or more. The number of demultiplexing steps by the second seed light demultiplexers 180a to 180c may be three or more. In the above embodiment, the first pumping laser 120a and the second pumping laser 120b may be a common pumping laser. In the above embodiment, the light emitting unit 110 may include two seed lasers having different wavelengths, or may include four or more seed lasers.

[0061] In the measurement process of the above embodiment, the light emission time interval ΔT may be the same as or longer than the round trip time it takes for the output light Lout to travel across the measurable distance of the measurement device 10. In addition, the time difference between each of the light emission timings T1 to T3 does not have to be constant.

[0062] In the above embodiment, the materials used to form the components are merely examples, and the components may be formed from other materials.

[0063] This international application claims priority based on Japanese Patent Application No. 2023-148953, filed on September 14, 2023, the entire contents of which are incorporated herein by reference.

[0064] The above descriptions of specific embodiments of the present invention have been presented for purposes of illustration. They are not intended to be exhaustive or to limit the invention to the precise forms described. Numerous modifications and variations will be apparent to those skilled in the art in light of the above description.

[0065] 10: Measuring device 20: Light projector 22: Fiber laser 26: Light projection control device 30: Light receiver 32: Light receiving section 33: Light receiving optical system 34a to 34c: Filters 35: Dispersion element 36a to 36c: Light receiving elements 40: Controller 110: Light emitting section 112a: First seed laser 112b: Second seed laser 112c: Third seed laser 120a: First excitation laser 120b: Second excitation laser 130: First optical isolator 140: First multiplexer 150a: First seed light demultiplexer 150b: Pumping light demultiplexer 160: Second optical isolator 170a to 170c: Second multiplexer 180a to 180c: Second seed light demultiplexer 190: Third multiplexer F1: First optical fiber F2: Second optical fiber F3: Third optical fiber

Claims

1. A measurement device comprising: a first seed laser that emits a first seed laser light having a first wavelength, a second seed laser that emits a second seed laser light having a second wavelength different from the first wavelength, an optical fiber doped with a rare earth element and into which the first seed laser light and the second seed laser light are input, and a pumping laser that emits pumping light that excites the rare earth element in the optical fiber, a light projector that emits output laser light output from the optical fiber to the outside, a light receiver that receives reflected laser light that is reflected back from a measurement object from the output laser light output by the light projector, and a controller, wherein the controller performs a seed laser emission process that causes the first seed laser and the second seed laser to emit light for mutually different periods, and a first measurement process that measures a distance to the measurement object based on a first light receiving timing at which the light receiver receives first reflected laser light that is reflected back from the measurement object from the output laser light output from the optical fiber in response to input of the first seed laser light, a second measurement process for measuring the distance to the measurement object based on a second reception timing at which the receiver receives a second reflected laser light, which is the output laser light output from the optical fiber in response to the input of the second seed laser light and reflected back from the measurement object.

2. A measuring device as described in claim 1, wherein the optical receiver has: a distributor that distributes the first reflected laser light and the second reflected laser light; a first optical receiving element that receives the first reflected laser light distributed by the distributor; and a second optical receiving element that receives the second reflected laser light distributed by the distributor.

3. A measuring device as described in claim 1 or claim 2, wherein the time difference between the timing of emitting the first seed laser light and the timing of emitting the second seed laser light is shorter than the round-trip time it takes for the output laser light to travel the measurable distance of the measuring device.

4. A measuring device as described in claim 1, wherein the optical fiber includes a first optical fiber into which the first seed laser light and the second seed laser light are input, and a plurality of second optical fibers, the excitation laser includes a first excitation laser that emits excitation light that excites the rare earth element in the first optical fiber, and a second excitation laser that emits excitation light that excites the rare earth element in the plurality of second optical fibers, and the light projector further has a splitter that splits the first output laser light output from the first optical fiber into a plurality of the first output laser lights, each of the plurality of first output laser lights is input to each of the plurality of second optical fibers, and a plurality of second output laser lights output from each of the plurality of second optical fibers is emitted to the outside.

5. A measuring device as described in claim 4, wherein the light projector further has a second splitter that splits at least one of the plurality of second output laser beams, and is configured to emit to the outside the plurality of second output laser beams split by the second splitter.

6. A measuring device according to claim 4 or 5, wherein the first excitation laser and the second excitation laser are separate entities and arranged spaced apart from each other.

7. A measuring device according to claim 4 or 5, wherein the amplification factor of the first optical fiber is lower than the amplification factor of the second optical fiber.

8. A measuring device including a first seed laser that emits a first seed laser light having a first wavelength, a second seed laser that emits a second seed laser light having a second wavelength different from the first wavelength, a projector having an optical fiber to which the first seed laser light and the second seed laser light are input, and a receiver that receives reflected laser light emitted by the projector and reflected off a measurement object, the measuring device having a computer includes: a seed laser emission process that causes the first seed laser and the second seed laser to emit light for mutually different periods; and a first measurement process that measures a distance to the measurement object based on a first light reception timing at which the receiver receives first reflected laser light that is the output laser light output from the optical fiber in response to the input of the first seed laser light and reflected off the measurement object and returned by the measurement object; a second measurement process for measuring the distance to the measurement object based on a second reception timing at which the receiver receives a second reflected laser light, which is the output laser light output from the optical fiber in response to the input of the second seed laser light and reflected back from the measurement object.

9. A computer-readable recording medium having recorded thereon a computer program for controlling a measuring device including a first seed laser that emits a first seed laser light having a first wavelength, a second seed laser that emits a second seed laser light having a second wavelength different from the first wavelength, a projector having an optical fiber to which the first seed laser light and the second seed laser light are input, and a receiver that receives reflected laser light that is an output laser light emitted by the projector and reflected off a measurement object and returned, the computer-readable recording medium comprising: a seed laser emission process that causes the first seed laser and the second seed laser to emit light for mutually different periods; and a first measurement process that measures a distance to the measurement object based on a first light receiving timing at which the receiver receives a first reflected laser light that is the output laser light output from the optical fiber in response to input of the first seed laser light and reflected off the measurement object and returned by the measurement object; a second measurement process for measuring the distance to the measurement object based on a second reception timing at which the receiver receives the second reflected laser light, which is the output laser light output from the optical fiber in response to the input of the second seed laser light, and is reflected back from the measurement object.

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