Projector, measurement device, projector control method, computer program, and computer-readable recording medium having computer program recorded thereon

Abstract

To obtain a necessary output at an early stage after starting a projector.SOLUTION: The projector includes a seed laser that emits seed laser light, an excitation laser that emits excitation laser light, an optical fiber that is doped with a rare earth element to be excited by the excitation laser light and to which the seed laser light and the excitation laser light are input, and a light projection control device that controls an intensity of the excitation laser light emitted from the excitation laser.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] With the advancement of autonomous driving (AD) systems and advanced driver assistance systems (ADAS), 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 self-position while driving. LiDAR includes a projector that projects laser light onto a measurement target and a photoreceiver that receives the light reflected from the measurement target. LiDAR measures the distance to the measurement target based on the difference between the timing at which the projector emits the laser light and the timing at which the photoreceiver receives 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 doped with a rare earth element and through which the seed laser light passes, and a pump laser that emits pump laser light that excites the rare earth element. [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] The above-mentioned floodlight is required to obtain a required output quickly after activation.

[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. (1) A light projector disclosed in this specification includes a seed laser that emits seed laser light, a pumping laser that emits pumping laser light, an optical fiber doped with a rare earth element that is excited by the pumping laser light and into which the seed laser light and the pumping laser light are input, and a light projecting control device that controls the intensity of the pumping laser light emitted from the pumping laser. After determining that the rare earth element has transitioned to a stable excited state, the light projecting control device reduces the intensity of the pumping laser light output from the pumping laser compared to before determining that the rare earth element has transitioned to a stable excited state.

[0007] According to the above configuration, by relatively increasing the output of the excitation laser beam before it is determined that the rare earth element has transitioned to a stable excited state, the rare earth element can be brought into a stable excited state more quickly than when the output of the excitation laser beam is constant, thereby obtaining the required output soon after the light projector is started.

[0008] (2) The light projector described in (1) above may further include a current source that supplies a drive current to the excitation laser, and the light projecting control device may output the excitation laser light from the excitation laser by outputting a drive current from the current source to the excitation laser, and after determining that the rare earth element has transitioned to a stable excitation state, the drive current output from the current source may be reduced compared to before determining that the rare earth element has transitioned to a stable excitation state.

[0009] With this configuration, the intensity of the excitation laser light can be easily controlled.

[0010] (3) In the light-projecting device described in (1) or (2) above, the light-projecting control device may determine that the rare earth element has transitioned to a stable excited state when a predetermined time has elapsed since the excitation laser started to output the excitation laser light.

[0011] With this configuration, the timing for reducing the intensity of the excitation laser light can be easily set.

[0012] (4) The light projector described in (1) or (2) above may further include a sensor that detects the intensity of the output laser light output from the optical fiber, and the light projecting control device may determine that the rare earth element has transitioned to a stable excited state when the intensity of the output laser light detected by the sensor becomes equal to or greater than a predetermined reference value.

[0013] According to this configuration, it is possible to accurately determine whether the rare earth element has transitioned to a stable excited state.

[0014] (5) The measuring device disclosed in this specification includes the light projector according to any one of (1) to (4) above.

[0015] According to the above configuration, the required output can be obtained quickly after the projector is started up.

[0016] (6) The method for controlling a light projector disclosed in this specification is a method for controlling a light projector including a seed laser that emits seed laser light, an excitation laser that emits excitation laser light, and an optical fiber into which the seed laser light and the excitation laser light are input and which is doped with a rare earth element that is excited by the excitation laser light, and after determining that the rare earth element has transitioned to a stable excitation state, the intensity of the excitation laser light output from the excitation laser is reduced compared to before determining that the rare earth element has transitioned to a stable excitation state.

[0017] According to the above configuration, the required output can be obtained quickly after the projector is started up.

[0018] The technology disclosed in this specification can be realized in various forms, for example, a floodlight, a measuring device, a method for controlling a floodlight, a computer program for controlling a floodlight, and a computer-readable recording medium on which the computer program is recorded. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device according to a first embodiment. [Figure 2] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a floodlight according to a first embodiment; [Figure 3] 1 is a flowchart showing a flow of control of the output of excitation laser light in the first embodiment. [Figure 4] 10 is a time chart showing the transition of the magnitude of the drive current supplied from the second current source and the intensity of the excitation laser light output from the excitation laser in the first embodiment; [Figure 5] FIG. 10 is an explanatory diagram illustrating a schematic configuration of a floodlight according to a second embodiment. [Figure 6] 10 is a flowchart showing the flow of control of the output of excitation laser light in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] (First embodiment) A first embodiment will be described with reference to FIGS. 1 to 4. A measuring device 10 of this embodiment is a LiDAR that uses a fiber laser as a light source. The measuring device 10 is mounted on a vehicle equipped with, for example, an AD (automated drive) or an ADAS (advanced driver assistance system). For example, 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] As shown in FIG. 1, the measurement device 10 includes a light projector 100, a scanning unit 300, a light receiver 400, an information processing device 500, and a communication interface 600.

[0022] As shown in FIGS. 1 and 2, the floodlight 100 includes a light source unit 110 and a control circuit board 210.

[0023] As shown in FIG. 2, the light source unit 110 includes a seed laser 120, an excitation laser 130, a first optical fiber 140 (an example of an optical fiber), a second optical fiber 150 (an example of an optical fiber), a first isolator 161, a first multiplexer 162, a second isolator 163, a second multiplexer 164, a first demultiplexer 165, and a projection optical system 180.

[0024] The seed laser 120 is a laser light source that emits seed laser light La having a peak wavelength within the near-infrared range. In this embodiment, the wavelength of the seed laser light La is 1550 nm.

[0025] The pumping laser 130 is a laser light source and emits pumping laser light Lb. In this embodiment, the wavelength of the pumping laser light Lb is 940 nm.

[0026] The first optical fiber 140 includes a core doped with a rare earth element and a cladding surrounding the core and having a refractive index lower than the maximum refractive index of the core. The rare earth element is an element that is excited by the excitation laser light Lb. Examples of rare earth elements include ytterbium (Yb) and erbium (Er). The second optical fiber 150 is similar. The length of each optical fiber 140, 150 is, for example, approximately 5 m.

[0027] The first isolator 161 and the second isolator 163 are optical components that allow light to pass only in the forward direction from the seed laser 120 toward the light projecting optical system 180 and block light in the opposite direction to the forward direction. The first isolator 161 is optically connected to the seed laser 120. The second isolator 163 is optically connected to the output end of the first optical fiber 140. The isolators 161 and 163 suppress damage to the seed laser 120 due to return light from the optical fibers 140 and 150 flowing back into the seed laser 120.

[0028] The first demultiplexer 165 is an optical component that splits input light into multiple beams. The first demultiplexer 165 is, for example, a tap coupler, and includes an input port optically connected to the pump laser 130 and two output ports optically connected to the first multiplexer 162 and the second multiplexer 164, respectively.

[0029] The first multiplexer 162 and the second multiplexer 164 are optical components that multiplex multiple input beams. The first multiplexer 162 and the second multiplexer 164 are, for example, WDM (wavelength division multiplexing) couplers. The first multiplexer 162 has two input ports optically connected to the first isolator 161 and the first demultiplexer 165, respectively, and an output port optically connected to the input end of the first optical fiber 140. The second multiplexer 164 has two input ports optically connected to the second isolator 163 and the other output port of the first demultiplexer 165, respectively, and an output port optically connected to the input end of the second optical fiber 150.

[0030] The first optical fiber 140 and the second optical fiber 150 are connected in series via a second isolator 163 and a second multiplexer 164 .

[0031] The projection optical system 180 is an optical component arranged on the optical path of the output laser light Lout output from the output end of the second optical fiber 150. The projection optical system 180 may be, for example, a collimator lens that adjusts the output laser light Lout to be parallel light.

[0032] The control circuit board 210 is a circuit board on which electronic components are mounted for controlling the light emission of the seed laser 120 and the excitation laser 130, and as shown in FIG. 2, includes a light projection control device 211, a first current source 221, and a second current source 222 (an example of a current source).

[0033] The light projection control device 211 is, for example, a microcomputer and includes a processor and a storage device. The processor is, for example, a CPU (central processing unit). The storage device includes, for example, a ROM (read only memory) and a RAM (random access memory). The storage device stores various programs and data, and is used as a work area for executing various processes and as a data storage area. For example, the storage device stores a computer program for controlling the intensity of the excitation laser beam Lb. This computer program may be provided in a state where it is stored in a computer-readable recording medium (not shown). The computer-readable recording medium is, for example, a CD-ROM, a DVD-ROM, or a USB memory. Alternatively, the computer program may be provided in a state where it can be obtained from an external device (for example, a server on the cloud) via the communication interface 600.

[0034] The first current source 221 and the second current source 222 are general current circuits including, for example, a capacitor, a resistor, and a switching element. The first current source 221 supplies a drive current to the seed laser 120. The second current source 222 supplies a drive current to the pump laser 130.

[0035] The light-projection control device 211 outputs a drive signal to a first current source 221. The first current source 221 receives the drive signal, generates a drive current corresponding to the drive signal, and supplies the drive current to the seed laser 120. The light-projection control device 211 outputs the drive signal to a second current source 222. The second current source 222 receives the drive signal, generates a drive current corresponding to the drive signal, and supplies the drive current to the pump laser 130. In addition, the light-projection control device 211 outputs a signal indicating the light emission timing at which the seed laser 120 emits the seed laser light La.

[0036] The scanning unit 300 is disposed on the optical path of the output laser light Lout output from the projector 100. The scanning unit 300 is a device for irradiating a measurement area with the output laser light Lout in a predetermined scanning pattern. The scanning unit 300 may include, for example, a micro electro mechanical systems (MEMS) mirror, a digital micromirror device (DMD), a galvanometer mirror, or a polygon mirror.

[0037] As shown in FIG. 1, the light receiver 400 includes a light receiving optical system 410, a light receiving unit 420, and a TOF measurement device 430.

[0038] The light receiving optical system 410 is an optical component for causing the light receiving unit 420 to receive reflected laser light Lre, which is light that is output laser light Lout reflected by the measurement target W and returned. The light receiving optical system 410 may be, for example, any of various lenses such as a condenser lens, any of various filters such as a wavelength filter, or a reflecting mirror.

[0039] The light receiving unit 420 includes a light receiving element, such as a photodiode. The light receiving element receives the reflected laser light Lre incident from the light receiving optical system 410, converts the reflected laser light Lre into a light receiving signal corresponding to the intensity and timing of receiving the reflected laser light Lre, and outputs the signal.

[0040] The TOF measurement device 430 has, for example, a time measurement IC (integrated circuit) equipped with a TDC (time-to-digital converter) circuit. The TOF measurement device 430 is communicably connected to the light-projection control device 211 and the light-receiving unit 420. The TOF measurement device 430 receives a timing signal indicating the light emission timing output from the light-projection control device 211 and a light-receiving signal output from the light-receiving unit 420. Based on these signals, the TOF measurement device 430 calculates the difference between the timing at which the output laser light Lout is emitted and the timing at which the reflected laser light Lre is received, i.e., the time of flight (TOF) of the laser light. The TOF measurement device 430 outputs a signal corresponding to the calculated TOF and the light-receiving signal received from the light-receiving unit 420.

[0041] The information processing device 500 has a processor. The processor may be, for example, a central processing unit (CPU), a microprocessing unit (MPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a digital signal processor (DSP). The information processing device 500 is communicatively connected to the TOF measurement device 430. The information processing device 500 receives a signal corresponding to the TOF output by the TOF measurement device 430 and a light receiving signal, and generates various information based on these signals. The information may be, for example, a histogram used in time-correlated single photon counting, distances to each point on the measurement target W, or point cloud information. The information generated by the information processing device 500 is transmitted via a communication interface 600 to an external device 700 that uses the information.

[0042] The external device 700 may be, for example, a device that creates an environmental map using a point cloud, or may be a device that performs self-location estimation (SLAM: Simultaneous Localization and Mapping) using a scan matching algorithm such as NDT (Normal Distributions Transform) or ICP (Iterative Closest Point).

[0043] Next, the basic operation of the projector 100 will be described. The light-projection control device 211 pulse-controls the seed laser 120. That is, the light-projection control device 211 outputs a drive signal to the first current source 221 so that the seed laser 120 intermittently outputs seed laser light La at predetermined timings. The first current source 221 generates a pulse current having a frequency and magnitude corresponding to the received drive signal and supplies it to the seed laser 120. The seed laser 120 outputs seed laser light La having a frequency and intensity corresponding to the supplied drive current.

[0044] The light-projection control device 211 controls the pump laser 130 with a direct current. That is, the light-projection control device 211 outputs a drive signal to the second current source 222 so that the pump laser 130 continuously outputs the pump laser light Lb. The second current source 222 supplies the pump laser 130 with a drive current having a magnitude corresponding to the received drive signal. The pump laser 130 outputs the pump laser light Lb having an intensity corresponding to the supplied drive current.

[0045] The first demultiplexer 165 demultiplexes the pumping laser light Lb input from the pumping laser 130 into two beams, and outputs them to the first multiplexer 162 and the second multiplexer 164 .

[0046] The seed laser light La output from the seed laser 120 passes through a first isolator 161 and is input to a first multiplexer 162. The first multiplexer 162 multiplexes the seed laser light La input from the seed laser 120 and the excitation laser light Lb input from a first demultiplexer 165, and outputs the multiplexed light to the first optical fiber 140.

[0047] The rare earth element doped in the first optical fiber 140 absorbs and is excited by the pump laser light Lb. A sufficient supply of the pump laser light Lb creates a population inversion. A population inversion is a state in which the number of atoms in an excited state is greater than the number of atoms in a ground state. When seed laser light La is input to the first optical fiber 140 in this state, electrons in the excited atoms move to a lower energy level and emit light having the same wavelength as the seed laser light La. This is called stimulated emission. The seed laser light La is amplified by stimulated emission. The amplified seed laser light La output from the first optical fiber 140 passes through the second isolator 163 and is input to the second multiplexer 164. The second multiplexer 164 multiplexes this seed laser light La with the pump laser light Lb input from the first demultiplexer 165 and outputs the combined light to the second optical fiber 150.

[0048] Inside the second optical fiber 150, the seed laser light La is amplified, similarly to the first optical fiber 140. The amplified seed laser light La is output from the second optical fiber 150 as output laser light Lout, and is output to the outside of the projector 100 via the light projecting optical system 180.

[0049] Next, a process in which the light-projection control device 211 controls the intensity of the excitation laser light Lb in the above-described light projector 100 will be described with reference to FIGS.

[0050] When the measurement device 10 receives an instruction to start measurement, the light-projection control device 211 causes the seed laser 120 to output seed laser light La (S110). More specifically, the light-projection control device 211 outputs a drive signal to the first current source 221. Upon receiving the drive signal, the first current source 221 generates a pulse current corresponding to the drive signal and supplies the pulse current to the seed laser 120. The seed laser 120 receives the current supplied from the first current source 221 and outputs seed laser light La.

[0051] Next, the light-projection control device 211 causes the pumping laser 130 to output the pumping laser light Lb at a first intensity P1 (S120). More specifically, the light-projection control device 211 outputs a drive signal to the second current source 222. Upon receiving the drive signal, the second current source 222 generates a DC current corresponding to the drive signal at a first current value I1 and supplies the DC current to the pumping laser 130. Upon receiving the drive current from the second current source 222, the pumping laser 130 continuously outputs the pumping laser light Lb at a first intensity P1 corresponding to the first current value I1. The start of outputting the drive signal to the second current source 222 may be simultaneous with or different from the start of outputting the drive signal to the first current source 221.

[0052] Next, the light-projection control device 211 executes step S130. In step S130, the light-projection control device 211 uses a built-in timer to measure the time from the start time t0 of outputting the drive signal to the second current source 222 until a certain time t1 has elapsed. The "certain time t1" is, for example, 10 seconds. The light-projection control device 211 determines that the rare earth element doped in the optical fibers 140 and 150 has transitioned to a stable excited state when the certain time t1 has elapsed since the start of outputting the drive signal to the second current source 222. The "stable excited state" is a state in which a population inversion is maintained and amplification of the seed laser light La by stimulated emission continues stably. The certain time t1 can be determined, for example, as follows: A current is supplied to the pump laser 130 at a first current value I1 in advance, and the time required for the intensity of the output laser light Lout output from the light projector 100 to reach the intensity required for measuring the measurement target is measured. The fixed time t1 may be set to a time equal to or slightly longer than the time required for the intensity of the output laser light Lout to reach the required intensity.

[0053] After a certain time t1 has elapsed, the light-projection control device 211 executes step S140. In step S140, the light-projection control device 211 outputs a drive signal so that the pump laser 130 outputs the pump laser light Lb at a second intensity P2. The second intensity P2 is smaller than the first intensity P1, but it need only be equal to or greater than the minimum intensity required for maintaining the population inversion state of the rare earth elements doped in the first optical fiber 140 and the second optical fiber 150 and for maintaining the intensity of the output laser light Lout required for detecting the object W to be measured. Upon receiving the drive signal, the second current source 222 generates a drive current corresponding to the drive signal at a second current value I2 smaller than the first current value I1 and supplies the drive current to the pump laser 130. Upon receiving the current from the second current source 222, the pump laser 130 outputs the pump laser light Lb at a second intensity P2 corresponding to the second current value I2.

[0054] After executing step S140, the light-projection control device 211 determines whether an instruction to end the measurement has been issued (S150). If it is determined that an instruction to end the measurement has not been issued, the light-projection control device 211 returns to step S140 and repeats the process. If it is determined that an instruction to end the measurement has been issued, the light-projection control device 211 stops outputting the drive signals to the first current source 221 and the second current source 222.

[0055] As described above, the measuring device 10 of this embodiment includes the projector 100. The projector 100 includes the seed laser 120, the pumping laser 130, the optical fibers 140 and 150, and the light-projection control device 211. The seed laser 120 emits seed laser light La. The pumping laser 130 emits pumping laser light Lb. The optical fibers 140 and 150 are each doped with a rare earth element that is excited by the pumping laser light Lb. The seed laser light La and the pumping laser light Lb are input to each of the optical fibers 140 and 150. The light-projection control device 211 controls the intensity of the pumping laser light Lb emitted from the pumping laser 130. After determining that the rare earth element has transitioned to a stable excited state, the light-projection control device 211 reduces the intensity of the pumping laser light Lb output from the pumping laser 130 to a level lower than that before determining that the rare earth element has transitioned to a stable excited state.

[0056] According to the above configuration, the output of the excitation laser light Lb before it is determined that the rare earth element has transitioned to a stable excited state is relatively increased, thereby enabling the rare earth element to be brought into a stable excited state early, thereby enabling the required output to be obtained early after activation of the projector 100.

[0057] The floodlight 100 of this embodiment further includes a second current source 222 that supplies a drive current to the excitation laser 130. The light-projection control device 211 causes the second current source 222 to output a drive current to the excitation laser 130, thereby causing the excitation laser light Lb to be output from the excitation laser 130, and after determining that the rare earth element has transitioned to a stable excited state, reduces the drive current output from the second current source 222 compared to before determining that the rare earth element has transitioned to a stable excited state. With this configuration, it is possible to easily control the intensity of the excitation laser light Lb without increasing manufacturing costs.

[0058] The light-projection control device 211 determines that the rare earth element has transitioned to a stable excited state when a predetermined time t1 has elapsed since the excitation laser 130 started to output the excitation laser light Lb. With this configuration, the timing for reducing the intensity of the excitation laser light Lb can be easily set.

[0059] (Second embodiment) The second embodiment will be described with reference to Figures 5 and 6. The light projector 100A of this embodiment is different from the first embodiment in that it includes a sensor 820 that detects the intensity of the output laser light Lout and in part of the procedure for controlling the intensity of the excitation laser light Lb. In this embodiment, the same components as those of the first embodiment are denoted by the same reference numerals and description thereof will be omitted.

[0060] As shown in FIG. 5, a light source unit 110A provided in a floodlight 100A includes a second demultiplexer 810 and a sensor 820. The second demultiplexer 810 and the sensor 820 are arranged in a rectangular parallelepiped pattern.

[0061] The second demultiplexer 810 is disposed between the output end of the second optical fiber 150 and the projection optical system 180. The second demultiplexer 810 is disposed on the optical path of the output laser light Lout output from the output end of the second optical fiber 150. The second demultiplexer 810 splits the output laser light Lout into two beams and guides them to the sensor 820 and the projection optical system 180. The second demultiplexer 810 may be, for example, a plate-type beam splitter that reflects a portion of the output laser light Lout and guides it to the sensor 820, and transmits the remainder and guides it to the projection optical system 180.

[0062] The sensor 820 is a light-receiving sensor that detects a portion of the output laser light Lout branched by the second branching filter 810. The sensor 820 includes a light-receiving element. The light-receiving element is, for example, a photodiode. The sensor 820 converts the received output laser light Lout into a detection signal corresponding to the intensity of the output laser light Lout, and outputs the detection signal to the light-projection control device 211.

[0063] Next, a process in which the light-projection control device 211 controls the intensity of the excitation laser light Lb in the above-described light projector 100A will be described with reference to FIG.

[0064] When the measurement device receives an instruction to start measurement, the light-projection control device 211 causes the seed laser 120 to output the seed laser light La (S210). Subsequently, the light-projection control device 211 causes the excitation laser 130 to output the excitation laser light Lb at a first intensity P1 (S220). The details of the processes in steps S210 and S220 are the same as those in steps S110 and S120 in the first embodiment.

[0065] Next, the light-projection control device 211 receives a detection signal from the sensor 820 (S230). The light-projection control device 211 determines whether the intensity of the output laser light Lout is equal to or greater than a predetermined reference value P0 (S240). This determination is made based on the detection signal received from the sensor 820. The reference value P0 is, for example, the minimum value of the intensity of the output laser light Lout required for the measurement device 10 to detect the object W to be measured. If the light-projection control device 211 determines that the intensity of the output laser light Lout is less than the reference value P0, the light-projection control device 211 returns to step S230 and repeats the process. If the light-projection control device 211 determines that the intensity of the output laser light Lout is equal to or greater than the reference value P0, the light-projection control device 211 determines that the rare earth element doped in the optical fibers 140, 150 has reached a stable excited state, and executes step S250.

[0066] In step S250, the light projection control device 211 causes the excitation laser 130 to output the excitation laser light Lb at the second intensity P2. Details of the process in step S240 are the same as those in step S140 in the first embodiment.

[0067] After executing step S250, the light-projection control device 211 determines whether an instruction to end the measurement has been issued (S260). If it is determined that an instruction to end the measurement has not been issued, the light-projection control device 211 returns to step S250 and repeats the process. If it is determined that an instruction to end the measurement has been issued, the light-projection control device 211 stops outputting the drive signals to the first current source 221 and the second current source 222.

[0068] As described above, the light projector 100A of the present embodiment further includes a sensor 820 that detects the intensity of the output laser light Lout output from the second optical fiber 150. The light projecting control device 211 determines that the rare earth element has transitioned to a stable excited state when the intensity of the output laser light Lout detected by the sensor 820 is equal to or greater than a predetermined reference value P0. With this configuration, it is possible to accurately determine that the rare earth element has transitioned to a stable excited state.

[0069] (Variation) 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 thereof, for example, the following modifications are also possible. (1) In the above embodiment, the projector 100, 100A includes a first optical fiber 140 and a second optical fiber 150, and amplifies the seed laser light La in two stages. However, the projector may amplify the seed laser light in only one stage using one optical fiber, or may amplify the seed laser light in three or more stages using three or more optical fibers. (2) In the above embodiment, the projectors 100 and 100A are of a forward pumping type in which the excitation laser light Lb is input from the input end of the first optical fiber 140. However, the projectors may be of a backward pumping type in which the excitation laser light is input from the output end of the optical fiber. (3) In the above embodiment, after determining that the rare earth element has transitioned to a stable excited state, the light-projection control device 211 reduces the intensity of the excitation laser light Lb output from the excitation laser 130 by reducing the drive current output from the second current source 222. However, the intensity of the excitation laser light Lb may be reduced by a method other than reducing the drive current. For example, the light-projector may include multiple excitation lasers optically connected to an optical fiber, and after determining that the rare earth element has transitioned to a stable excited state, the number of excitation lasers outputting excitation laser light to the optical fiber may be reduced. (4) The determination that the rare earth element has transitioned to a stable excited state may be made by a method other than the method described in the above embodiment. For example, the reach distance of the output laser light Lout may be calculated based on the difference between the timing at which the output laser light Lout is emitted and the timing at which the reflected laser light Lre, which is the light that has been reflected by the measurement target W and returned, is received. When the calculated reach distance value is equal to or greater than a predetermined reference value, it may be determined that the rare earth element has transitioned to a stable excited state. (5) The light projection control device may output different intensities of excitation laser light after determining that the rare earth element has transitioned to a stable excited state, for example, when scanning a relatively distant measurement area and when scanning a relatively close measurement area. In such a case, the intensity of the excitation laser light when scanning a distant measurement area and the intensity of the excitation laser light when scanning a close measurement area may both be smaller than the intensity of the excitation laser light before determining that the rare earth element has transitioned to a stable excited state. [Explanation of symbols]

[0070] 10: Measuring device 100, 100A: Light projector 110, 110A: Light source unit 120: Seed laser 130: Excitation laser 140: First optical fiber (optical fiber) 150: Second optical fiber (optical fiber) 161: First isolator 162: First multiplexer 163: Second isolator 164: Second multiplexer 165: First demultiplexer 180: Light projecting optical system 210: Control circuit board 211: Light projecting control device 221: First current source 222: Second current source (current source) 300: Scanning unit 400: Light receiver 410: Light receiving optical system 420: Light receiving section 430: TOF measuring device 500: Information processing device 600: Communication interface 700: External device 810: Second demultiplexer 820: Sensor I1: First current value I2: Second current value L0: Reference value La: Seed laser light Lb: Excitation laser light Lout: Output laser light Lre: Reflected laser light P0: Reference value P1: First intensity P2: Second intensity W: Measurement object

Claims

1. a seed laser that emits seed laser light; an excitation laser that emits excitation laser light; an optical fiber doped with a rare earth element that is excited by the excitation laser light, and into which the seed laser light and the excitation laser light are input; a light projection control device that controls the intensity of the excitation laser light emitted from the excitation laser; Equipped with The light projection control device After determining that the rare earth element has transitioned to a stable excited state, the intensity of the excitation laser light output from the excitation laser is reduced to a level lower than that before determining that the rare earth element has transitioned to a stable excited state. Floodlight.

2. 2. The floodlight according to claim 1, a current source for supplying a drive current to the pump laser; The light projection control device outputting a drive current from the current source to the pumping laser, thereby causing the pumping laser to output the pumping laser light; After determining that the rare earth element has transitioned to a stable excited state, the driving current output from the current source is reduced compared to that before determining that the rare earth element has transitioned to a stable excited state. Floodlight.

3. 3. The floodlight according to claim 1 or 2, The light projection control device determining that the rare earth element has transitioned to a stable excited state when a predetermined time has elapsed since the excitation laser started to output the excitation laser light; Floodlight.

4. 3. The floodlight according to claim 1 or 2, a sensor for detecting the intensity of the output laser light output from the optical fiber; The light projection control device When the intensity of the output laser light detected by the sensor becomes equal to or greater than a predetermined reference value, it is determined that the rare earth element has transitioned to a stable excited state. Floodlight.

5. A measuring device comprising the light projector according to claim 1 or 2.

6. a seed laser that emits seed laser light; an excitation laser that emits excitation laser light; an optical fiber doped with a rare earth element, into which the seed laser light and the pumping laser light are input and which is excited by the pumping laser light; A method for controlling a floodlight comprising: After determining that the rare earth element has transitioned to a stable excited state, the intensity of the excitation laser light output from the excitation laser is reduced to a level lower than that before determining that the rare earth element has transitioned to a stable excited state. How to control the floodlight.

7. a seed laser that emits seed laser light; an excitation laser that emits excitation laser light; an optical fiber doped with a rare earth element, into which the seed laser light and the pumping laser light are input and which is excited by the pumping laser light; A computer included in a projector comprising: after determining that the rare earth element has transitioned to a stable excited state, a process is performed to reduce the intensity of the excitation laser light output from the excitation laser compared to before determining that the rare earth element has transitioned to a stable excited state. Computer program.

8. a seed laser that emits seed laser light; an excitation laser that emits excitation laser light; an optical fiber doped with a rare earth element, into which the seed laser light and the pumping laser light are input and which is excited by the pumping laser light; A computer-readable recording medium having a computer program recorded thereon for controlling a floodlight comprising: after determining that the rare earth element has transitioned to a stable excited state, a process is performed to reduce the intensity of the excitation laser light output from the excitation laser compared to before determining that the rare earth element has transitioned to a stable excited state. A computer-readable recording medium on which a computer program is recorded.

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