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

Abstract

To suppress 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.SOLUTION: A measurement device comprises: a projector 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, an optical fiber, and an excitation laser; a light receiver; and a controller. The controller executes: first measurement processing of measuring a distance to a measurement object on the basis of first light reception timing at which the light receiver receives a first reflected laser beam corresponding to the first seed laser beam; and second measurement processing of measuring the distance to the measurement object on the basis of second light reception timing at which the light receiver receives a second reflected laser beam corresponding to the second seed laser beam.SELECTED DRAWING: Figure 2

Description

[Technical field]

[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. [Background technology]

[0002] With the progress of AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems), research and development of LiDAR (Light Detection And Ranging) is being conducted as one of the measurement devices used for grasping the surrounding environment and estimating the vehicle's self-position while driving. LiDAR includes a projector that projects (irradiates) laser light onto a measurement target, and a receiver that receives the reflected light of the laser light reflected off 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 projection timing of the projector emitting the laser light and the reception timing of the receiver receiving the reflected light. The projector includes a fiber laser (see, for example, Patent Document 1). The 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 an excitation laser that emits excitation light that excites the rare earth element of the optical fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 117912 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of measuring device, it becomes unclear which reflected light received by the receiver corresponds to which laser light emitted at which light projection timing, and as a result, there is a risk of a decrease in the measurement accuracy of the distance to the measurement target. In particular, if a laser light emitted at a certain light projection timing is emitted before the laser light emitted at the next light projection timing is received by the receiver, it is easy to become unclear which reflected light received by the receiver corresponds to which laser light emitted at which light projection timing. On the other hand, in a conventional measuring device, after the light projector emits a laser light at a certain light projection timing, the laser light emitted at the certain light projection timing is received by the receiver, and then the laser light emitted at the next light projection timing is emitted. However, even with this configuration, for example, when multiple light reception timings overlap, it may become unclear which reflected light received by the receiver corresponds to which laser light emitted at which light projection timing.

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

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

[0007] (1) The measurement device disclosed in the present specification has 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 an excitation laser that emits excitation light that excites the rare earth element in the optical fiber, and comprises 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 by the output laser light emitted by the light projector, and a controller. The controller executes a seed laser emission process for causing the first seed laser and the second seed laser to emit light for different periods of time, a first measurement process for measuring the distance to the measurement object based on a first light receiving timing at which the receiver receives a first reflected laser light, which is the output laser light output from the optical fiber in response to input of the first seed laser light, reflected off 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 receiver receives a second reflected laser light, which is the output laser light output from the optical fiber in response to input of the second seed laser light, reflected off the measurement object and returning.

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

[0009] (2) In the above measuring device, the light receiver may have 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. According to this measuring device, it is possible to suppress 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 timing of emitting the first seed laser light and the timing of emitting the second seed laser light may be shorter than the round-trip time of the output laser light 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 light, as compared with a configuration in which, for example, after emitting the first seed laser light, the second sheet laser light is emitted after waiting for reception of the first reflected laser light.

[0011] (4) In the above measuring device, the optical fiber may include a first optical fiber to which the first seed laser light and the second seed laser light 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 light projector may further include 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 may be emitted to the outside. In this measuring device, the first output laser light output from the first optical fiber is split into a plurality of first output laser lights, and the split first output laser lights are further amplified in the second optical fiber. As a result, according to this measurement device, it is possible to suppress the occurrence of a power deficiency of the second output laser light output from each second optical fiber, compared to, for example, a configuration in which amplification is not performed by the second optical fiber.

[0012] The measurement device disclosed in the present specification does not have the configurations (1) to (3) above, but has a seed laser that emits seed laser light, an optical fiber 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 equipped 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 target and returned from the output laser light projector, wherein the fibers are a first optical fiber into which the seed laser light is input, and a plurality of second optical fibers. The light projector may further include a splitter that splits a first output laser beam output from the first optical fiber into a plurality of first output laser beams, and a splitter that splits the first output laser beam into a plurality of first output laser beams, each of the plurality of first output laser beams being input to each of the plurality of second optical fibers, and each of the plurality of second output laser beams being 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 of the second output laser beam output from each of the second optical fibers.

[0013] (5) In the above measurement device, the light projector may further include a second splitter that splits at least one of the plurality of second output laser beams, and may be configured to emit the plurality of second output laser beams split by the second splitter to the outside. In this measurement device, the second output laser beam can be further split into a plurality of beams and output while suppressing the occurrence of a power shortage of the second output laser beam output from each second optical fiber.

[0014] (6) In the above-mentioned 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 laser 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 first optical fiber may have a lower amplification factor than the second optical fiber. In this measurement device, the amplification of noise in the optical fibers can be suppressed more effectively than in a configuration in which the first optical fiber has a higher amplification factor than the second optical fiber.

[0016] (8) The 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 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 light projector having an optical fiber to which the first seed laser light and the second seed laser light are input; and a light receiver that receives a reflected laser light that is an output laser light emitted by the light projector and reflected back from a measurement target, to emit the first seed laser and the second seed laser for different periods. a first measurement process for measuring a distance to the measurement object based on a first light receiving timing at which the light receiver receives a first reflected laser light obtained by reflecting back the output laser light output from the optical fiber by input of the first seed laser light from the measurement object, and a second measurement process for measuring a distance to the measurement object based on a second light receiving timing at which the light receiver receives a second reflected laser light obtained by reflecting back the output laser light output from the optical fiber by input of the second seed laser light from the measurement object. This measurement program makes it possible to prevent the light receiver from being unable to distinguish between a plurality of reflected laser light corresponding to each of a plurality of seed laser light emitted in different periods.

[0017] The technology disclosed in this specification can be realized in various forms, for example, a measurement device, a spotlight, a measurement method, a measurement program, a computer-readable recording medium on which the measurement program is recorded, etc. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device according to an embodiment. [Diagram 2] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a light-emitting unit. [Diagram 3] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a light receiving unit; [Figure 4] Flowchart showing measurement process [Diagram 5] Timing chart showing light emission and light reception timing DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A. Embodiment: A-1. Configuration of the measuring device 10: 1 is a block diagram showing a schematic configuration of a measurement device 10 according to the present embodiment. The measurement device 10 measures the difference between the timing at which a projector 20 emits output light Lout and the timing at which a receiver 30 receives reflected light Lin (time of flight of laser light, hereinafter referred to as "TOF" (Time of Flight)), and acquires information about a measurement target.

[0020] The measuring device 10 is mounted on, for example, a vehicle (not shown) equipped with AD or ADAS. For example, while the vehicle is traveling, the measuring device 10 assists in the detection of objects such as people and other vehicles, and provides various types of information to other devices and users that are 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 measuring device 10 is a multi-channel LiDAR that simultaneously emits a plurality of output lights Lout. The measuring device 10 is also a scan-type LiDAR. Specifically, the measuring device 10 scans a measurement target (not shown) such that the irradiation positions of the plurality of output lights Lout move in parallel with each other. As shown in FIG. 1, the measuring device 10 includes a light projector 20 and a light receiver 30.

[0022] The light projector 20 includes a fiber laser 22 that outputs an output light Lout, and a light projection control device 26. The light projection control device 26 controls the emission of the fiber laser 22. The light projection control device 26 also inputs a signal indicating the timing of light projection at which the fiber laser 22 emits light to a controller 40, which will be described later. The light projection control device 26 periodically and repeatedly emits light from the fiber laser 22, for example, by periodically and repeatedly turning on and off a current passed through the fiber laser 22 (seed lasers 112a to 112c, which will be described later).

[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 section 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 the 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 ytterbium (Yb) and erbium (Er) as a rare earth element. The length of each of the optical fibers F1 and F2 is, for example, about 5 m.

[0026] The first pumping laser 120a emits a first pumping light Lb1 (e.g., 940 nm) that excites the rare earth element contained in the first optical fiber F1. The second pumping laser 120b emits a 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 multiplexer (WDM) 140, a first seed light splitter (TAP) 150a, a pump light splitter 150b, a second optical isolator 160, second multiplexers 170a to 170c, and second seed light splitters 180a to 180c. The first seed light splitter 150a is an example of a first splitter, and the second seed light splitters 180a to 180c are an example of a second splitter.

[0028] The light emitting unit 110 is optically coupled to the first multiplexer 140 via a normal 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 light demultiplexer 150a. A second optical isolator 160 is provided between the first multiplexer 140 and the first seed light demultiplexer 150a. The first seed light demultiplexer 150a demultiplexes the seed light La amplified by the first optical fiber F1 into multiple lights (La1 to La3).

[0029] The first pumping laser 120a is optically coupled to the first multiplexer 140 via a normal 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 emitting unit 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 splitter 150b via a normal optical fiber (not shown) that is not doped with a rare earth element. The pumping light splitter 150b splits the second pumping light Lb2 emitted by the second pumping laser 120b into multiple lights.

[0030] The second multiplexers 170a to 170c are optically coupled to the first seed light demultiplexer 150a and the pumping light demultiplexer 150b, respectively. Each of the second multiplexers 170a to 170c multiplexes the seed light La amplified by the first optical fiber F1 and the second pumping light Lb2 emitted by the second pumping 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 each of the second seed light demultiplexers 180a to 180c. Specifically, the second multiplexer 170a is optically coupled to the second seed light demultiplexer 180a via the second optical fiber F2. The second multiplexer 170b is optically coupled to the second seed light demultiplexer 180b via the second optical fiber F2. The second multiplexer 170c is optically coupled to the second seed light demultiplexer 180c via the second optical fiber F2.

[0032] Each of the second seed light demultiplexers 180a-180c demultiplexes the seed light La1-La3 further amplified by the second optical fiber F2 into a plurality of beams. Each of the second seed light demultiplexers 180a-180c is coupled to an input portion of a plurality of third optical fibers F3. An output portion of each of the third optical fibers F3 is directed to the outside of the projector 20. The third optical fibers F3 are normal optical fibers that are not doped with a rare earth element.

[0033] With this configuration, in the fiber laser 22, the rare earth element in the first optical fiber F1 is excited by the first excitation light Lb1 emitted by the first excitation laser 120a, and the rare earth element in the second optical fiber F2 is excited by the second excitation light Lb2 emitted by the second excitation laser 120b. By inputting the seed light La from the light emitting unit 110 to 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 lights (La1 to La3) by the first seed light demultiplexer 150a.

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

[0035] The light receiver 30 includes six light receiving sections 32 (32a to 32c). The light receiving section 32 is a light receiving source having one or a plurality of light receiving elements (not shown), or one or a plurality of light receiving element arrays (for example, 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 section 32 photoelectrically converts the incident reflected light Lin to generate a current (hereinafter, referred to as a "light receiving current") according to the intensity of the reflected light Lin. The light receiving section 32 inputs a signal indicating the light receiving timing at which the light receiving elements constituting the light receiving section 32 received the reflected light Lin and the light receiving current generated by the light receiving elements to a controller 40 described later.

[0036] The first light receiving unit 32a is arranged to receive a first reflected light Lin1 that is the first output light Lout1 emitted by the projector 20 and reflected by the measurement object and returned. The second light receiving unit 32b is arranged to receive a second reflected light Lin2 that is the second output light Lout2 emitted by the projector 20 and reflected by the measurement object and returned. The third light receiving unit 32c is arranged to receive a third reflected light Lin3 that is the third output light Lout3 emitted by the projector 20 and reflected by the measurement object and returned. The fourth light receiving unit 32d is arranged to receive a fourth reflected light Lin4 that is the fourth output light Lout4 emitted by the projector 20 and reflected by the measurement object and returned. The fifth light receiving unit 32e is arranged to receive a fifth reflected light Lin5 that is the fifth output light Lout5 emitted by the projector 20 and reflected by the measurement object and returned. The sixth light receiving unit 32f is disposed so as to receive a sixth reflected light Lin6 that is the sixth output light Lout6 emitted by the projector 20 and reflected by the measurement object and returned. 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, so that information (such as the surface shape) of the measurement object can be acquired.

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

[0038] The controller 40 has, for example, a processor (such as a central processing unit (CPU), a micro processing unit (MPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and a digital signal processor (DSP)). The controller 40 obtains a TOF based on a signal indicating a light projection timing input from the light projection control device 26 and a signal indicating a light reception timing input from the light receiving unit 32. The controller 40 generates information used for various measurements such as detection and distance measurement of a measurement target based on the input light reception current and the obtained TOF. The information is, for example, a histogram used in time correlated single photon counting, a distance to each point of the measurement target, a point cloud (point cloud information), and the like. The controller 40 also controls the light projection control device 26 and the light receiving unit 32. The controller 40 controls the timing of light projection and the timing of light reception so as to speed up or optimize the processing for generating the histogram, for example, by controlling the light projection control device 26 and the light receiving unit 32. The information generated by the controller 40 is provided (transmitted) via the communication I / F 50 to a device that uses the information (hereinafter, referred to as "various utilization devices 60").

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

[0040] A-2. Configuration of the light emitting unit 110 and the light receiving unit 32: FIG. 2 is an explanatory diagram that shows a schematic 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) having a wavelength of, for example, 1515 nm, the second seed laser 112b emits seed light La(f2) having a wavelength of, for example, 1550 nm, and the third seed laser 112c emits seed light La(f3) having a wavelength of, for example, 1585 nm. The wavelength of each seed light La (f1 to f3) may be within a 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 a normal optical fiber (not shown) that is not doped with a rare earth element. 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 emitter 110 can selectively emit the seed light La(f1), the seed light La(f2), and the seed light La(f3).

[0042] Fig. 3 is an explanatory diagram showing a schematic configuration of the light receiving section 32. As shown in Fig. 3, the light receiving section 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 the reflected light Lin that is the output light Lout from the projector 20 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 reflector (mirror). The dispersion element 35 is an element that disperses the reflected light Lin that has passed through the light receiving optical system 33. The dispersion element 35 can be configured by, for example, 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 (for example, a glass substrate). The dispersion element 35 may be configured by a metamaterial in which minute structures are arranged three-dimensionally, or may be configured by a metamaterial (metasurface) in which minute structures are arranged two-dimensionally.

[0044] The three filters 34a to 34c are disposed at positions 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 passband 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) and does not pass the reflected light Lin(f1) and Lin(f2). Specifically, the passband 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 flow chart showing the measurement process, and FIG. 5 is a time chart showing the light projection timing and the 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 the seed light La(f1), the seed light La(f2), and the 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 lights 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 judges whether the first reflected light Lin(f1) is received by the first light receiving element 36a (S120). When the controller 40 judges that the first reflected light Lin(f1) is 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) is 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 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 in consideration of, for example, the lengths of the optical fibers (the first optical fiber F1, the second optical fiber F2, the third optical fiber F3, etc.) included in the fiber laser 22.

[0048] When the controller 40 determines that the first reflected light Lin(f1) is not received by the first light receiving element 36a (S120: NO), it determines whether the second reflected light Lin(f2) is received by the second light receiving element 36b (S150). When the controller 40 determines that the second reflected light Lin(f2) is received by the second light receiving element 36b (S150: YES), 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. That is, the fact that the second reflected light Lin(f2) is received by the second light receiving element 36b means that the light receiver 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 and the second reception timing T5 of the seed beam La(f2), for example.

[0049] When the controller 40 determines that the second reflected light Lin(f2) is not received by the second light receiving element 36b (S150: NO), the controller 40 determines whether the third reflected light Lin(f3) is received by the third light receiving element 36c (S170). When the controller 40 determines that the third reflected light Lin(f3) is received by the third light receiving element 36c (S170: YES), the controller 40 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. That is, the fact that the third reflected light Lin(f3) is received by the third light receiving element 36c means that the light receiver 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 and the third reception timing T6 of the seed beam La(f3), for example.

[0050] If the controller 40 determines that the third reflected light Lin(f3) is not received by the third light receiving element 36c (S170: NO), the process proceeds to S140. If the controller 40 determines that the measurement end instruction has not been received (S140: NO), the process returns to S120, and if the controller 40 determines that the measurement end instruction 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 timings T1 to T3, is shorter than the round trip time (the maximum time difference between the light projection timing and the light reception timing) for the output light Lout to travel the measurable distance of the measurement device 10. For example, after the first light emission timing T1 of the seed light La(f1), the seed light La(f2) is emitted at the second light emission timing T2 without waiting for the arrival of the first light reception timing T4 of the first reflected light Lin(f1). Therefore, the second reflected light Lin(f2) is more likely to be received at 30 before the first reflected light Lin(f1). However, according to this embodiment, the first light reception timing T4 and the second light reception timing 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-f3) having different wavelengths are input to common optical fibers F1, F2 with time differences (FIGS. 2 and 5). Therefore, the photoreceiver 30 can distinguish between the reflected beams Lin (f1-f3) corresponding to the three seed beams La (f1-f3) based on the difference in wavelength. As a result, according to this embodiment, it is possible to prevent the photoreceiver 30 from being unable to distinguish between the multiple reflected beams Lin (f1-f3) corresponding to the multiple seed beams La (f1-f3) emitted in 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 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 seed light La(f2) is emitted after waiting for the reception of the first reflected light Lin(f1).

[0054] In this embodiment, the seed light La output from the first optical fiber F1 is demultiplexed into a plurality of seed lights La (La1 to La3) by the first seed light demultiplexer 150a, and the demultiplexed plurality of seed lights La (La1 to La3) are further amplified by the second optical fiber F2 (FIG. 1). As a result, according to this embodiment, it is possible to suppress the occurrence of an 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, for example. In short, according to this embodiment, it is possible to suppress the insufficient output of each output light Lout while realizing a multi-channel configuration in which a common light source (light emitter 110) simultaneously emits a plurality of output lights Lout. Furthermore, according to this embodiment, it is possible to suppress the complication of the structure of the measuring device 10 (projector 20), the increase in size of the device, and the increase in cost due to an increase in the light source.

[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 lights by the second seed light demultiplexer 180b (FIG. 1). As a result, according to this embodiment, it is possible to further demultiplex and output the output light Lout into a plurality of lights while suppressing the occurrence of an output shortage of the output light Lout output from each second optical fiber F2.

[0056] In this embodiment, the first pump laser 120a and the second pump laser 120b are separate and arranged apart from each other (FIG. 1). As a result, according to this embodiment, heat generated by the pump laser can be dispersed more than in a configuration in which the first pump laser 120a and the second pump laser 120b are a common pump laser. Also, in this embodiment, the amplification degree of the first optical fiber F1 is lower than the amplification degree of the second optical fiber F2. As a result, according to this embodiment, the amplification of noise in the optical fiber can be suppressed more than in a configuration in which the amplification degree of the first optical fiber F1 is higher than the amplification degree of the second optical fiber F2.

[0057] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, 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 measuring device 10 in the above embodiment is merely an example, and various modifications are possible. For example, the projector 20 may be of a scanning type equipped with a scanner (light scanning device). In addition, in the above embodiment, the measuring device 10 (projector 20) is illustrated as a multi-channel measuring device, but the present invention is not limited to this, and may be of 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 the present invention is not limited to this. The seed light La may be amplified in only one stage, or the seed light La may be amplified in three or more stages. In the above embodiment, the amplification degree of the first optical fiber F1 may be the same as that of the second optical fiber F2, or may be higher than that of the second optical fiber F2. The difference in the amplification degree between the first optical fiber F1 and the second optical fiber F2 can be realized by adjusting, for example, the length of the fiber, the type of rare earth element, or the excitation level by the excitation laser.

[0060] In the above embodiment, the projector 20 may not include at least one of the second seed light splitters 180a to 180c. The number of splitting by the first seed light splitter 150a and the pumping light splitter 150b is not limited to three, and may be two, or four or more. The number of splitting by the second seed light splitters 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 equal to or longer than the round trip time of the output light Lout traveling through 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. [Explanation of symbols]

[0063] 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: Filter 35: Dispersion element 36a to 36c: Light receiving element 40: Controller 110: Light emitting section 112a: First seed laser 112b: Second seed laser 112c: Third seed laser 120a: First pumping laser 120b: Second pumping laser 130: First optical isolator 140: First multiplexer 150a: First seed light splitter 150b: Pumping light splitter 160: Second optical isolator 170a to 170c: Second multiplexer 180a to 180c: Second seed light splitter 190: Third multiplexer F1: First optical fiber F2: Second optical fiber F3: Third optical fiber

Claims

1. a first seed laser emitting a first seed laser light having a first wavelength, a second seed laser emitting a second seed laser light having a second wavelength different from the first wavelength, an optical fiber doped with a rare earth element and receiving the first seed laser light and the second seed laser light, and a pumping laser emitting pumping light for exciting the rare earth element in the optical fiber, and a light projector for emitting an output laser light output from the optical fiber to the outside; a light receiver that receives a reflected laser beam that is the output laser beam emitted by the light projector and reflected by a measurement target and returns to the measurement target; A measurement device comprising: The controller: a seed laser light emission process for causing the first seed laser and the second seed laser to emit light for periods different from each other; a first measurement process for measuring a distance to the measurement target based on a first light receiving timing at which the receiver receives a first reflected laser light, the first reflected laser light being reflected back from the measurement target by the optical fiber in response to the 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. 2. The measuring device according to claim 1, The optical receiver includes: 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; a second light receiving element that receives the second reflected laser light distributed by the distributor.

3. The measuring device according to claim 1 or 2, A measurement device, wherein a time difference between an emission timing of the first seed laser light and an emission timing of the second seed laser light is shorter than a round-trip time for the output laser light to travel a measurable distance of the measurement device.

4. 2. The measuring device according to claim 1, 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 pumping laser includes a first pumping laser that emits pumping light for exciting the rare earth elements in the first optical fiber, and a second pumping laser that emits pumping light for exciting the rare earth elements in the plurality of second optical fibers; the light projector further has a splitter that splits a 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 each 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 are emitted to the outside.

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

7. The measuring device according to claim 4 or 5, The first optical fiber has a lower amplification factor than the second optical fiber.

8. a light projector having 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 to which the first seed laser light and the second seed laser light are input, and an optical receiver that receives a reflected laser light that is an output laser light emitted by the light projector and reflected back from a measurement target, the computer having the a seed laser light emission process for causing the first seed laser and the second seed laser to emit light for periods different from each other; a first measurement process for measuring a distance to the measurement target based on a first light receiving timing at which the receiver receives a first reflected laser light, the first reflected laser light being reflected back from the measurement target by the optical fiber in response to the 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.

9. A computer-readable recording medium having recorded thereon a computer program for controlling a measurement 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 light projector having an optical fiber to which the first seed laser light and the second seed laser light are input; and a light receiver that receives a reflected laser light that is an output laser light emitted by the light projector and reflected back from a measurement target, a seed laser light emission process for causing the first seed laser and the second seed laser to emit light for periods different from each other; a first measurement process for measuring a distance to the measurement target based on a first light receiving timing at which the receiver receives a first reflected laser light, the first reflected laser light being reflected back from the measurement target by the optical fiber in response to the 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 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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