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

Abstract

A projector (100) comprises: a seed laser (120) which emits a seed laser beam; an excitation laser (120) which emits an excitation laser beam; an optical fiber (140) which is doped with a rare earth element that is excited by the excitation laser beam and into which the seed laser beam and the excitation laser beam are input; and a light projection control device (211) which controls the intensity of the excitation laser beam emitted from the excitation laser (120). After the light projection control device (211) has determined that the rare earth element has transitioned to a stable excited state, the intensity of the excitation laser light output from the excitation laser (120) is reduced in comparison with the intensity before it was determined that the rare earth element had transitioned to the stable excited state.

Description

Light projector, measuring device, light projector control method, computer program, and computer-readable recording medium having computer program recorded thereon

[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.

[0002] With the advancement of autonomous driving (AD) systems and advanced driver assistance systems (ADAS), research and development of light detection and ranging (LiDAR) is underway as one of the measurement devices used to grasp the surrounding environment and estimate the vehicle's position while driving. LiDAR includes a light projector that projects laser light onto a measurement target and a light receiver 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 light projector emits the laser light and the timing at which the light receiver receives the reflected light. The light 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.

[0003] International Publication No. 2020 / 117912

[0004] The above-mentioned light projector is required to obtain a required output quickly after activation, and also to reduce adhesion of foreign matter to the output end of the optical fiber.

[0005] Furthermore, it is known that a backward-pumping type light projector, in which a pump laser beam is input from the output end of an optical fiber, can efficiently amplify a seed laser beam. In the backward-pumping type light projector, the pump laser is connected to the output end of the optical fiber via a multiplexer. In such a configuration, the seed laser beam, which is highly amplified and output from the output end of the optical fiber, is input to the multiplexer, which may damage the multiplexer.

[0006] This specification discloses a technique that can solve the above-mentioned problems.

[0007] 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.

[0008] 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.

[0009] (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, may reduce the drive current output from the current source compared to before determining that the rare earth element has transitioned to a stable excitation state.

[0010] With this configuration, the intensity of the excitation laser light can be easily controlled.

[0011] (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.

[0012] With this configuration, the timing for reducing the intensity of the excitation laser light can be easily set.

[0013] (4) The light-projecting device 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.

[0014] According to this configuration, it is possible to accurately determine whether the rare earth element has transitioned to a stable excited state.

[0015] (5) A measuring device disclosed in this specification includes the light projector according to any one of (1) to (4) above.

[0016] According to the above configuration, the required output can be obtained quickly after the projector is started up.

[0017] (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, wherein after it is determined 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 it is determined that the rare earth element has transitioned to a stable excitation state.

[0018] According to the above configuration, the required output can be obtained quickly after the projector is started up.

[0019] The technology disclosed in this specification can be realized, for example, in the following forms. (7) A light projector disclosed in this specification includes a seed laser, a pumping laser, an optical fiber, and a protective member. The seed laser emits seed laser light. The pumping laser emits pumping laser light. The optical fiber is optically connected to the seed laser and the pumping laser. The optical fiber is doped with a rare earth element that is excited by the pumping laser light. The optical fiber has an output end from which output laser light is output, and the protective member covers the output end.

[0020] According to the above configuration, adhesion of foreign matter to the output end of the optical fiber is reduced.

[0021] (8) In the light projector described in (7) above, at least a part of the protective member may be a transmitting portion that transmits the output laser light.

[0022] According to this configuration, it is possible to cover the output end while allowing the output laser light to pass through the transmitting portion and be emitted to the outside of the protective member.

[0023] (9) In the floodlight described in (8) above, the protective member may include a base connected to the optical fiber, and a cover having the transmitting portion and removably connected to the base.

[0024] Such a configuration makes it easy to maintain the transmission section.

[0025] (10) In the light projector described in (8) or (9) above, the transmitting portion may be a beam splitter that reflects a portion of the output laser light and transmits the remainder, and the light projector may further include a sensor disposed inside the protective member that detects the output laser light reflected by the transmitting portion.

[0026] According to this configuration, there is no need to provide a separate, expensive splitter for splitting the output laser light to the sensor, and therefore the manufacturing costs of the projector are reduced.

[0027] (11) The light projector according to (8) or (9) above may further include a sensor disposed on the outer surface of the transmitting portion, which detects the output laser light that has passed through the transmitting portion.

[0028] This configuration eliminates the need for an expensive separate splitter to split the output laser light to the sensor, reducing the manufacturing cost of the projector. In addition, maintenance of the sensor can be performed without removing the protective member from the optical fiber.

[0029] (12) In the light projector described in (7) above, the protective member may have an opening that allows the output laser light to pass through.

[0030] According to this configuration, it is possible to reduce the adhesion of foreign matter to the output end of the optical fiber while allowing the output laser light to be emitted to the outside of the protective member with a simple configuration.

[0031] (13) The measuring device disclosed in this specification includes the light projector according to any one of (7) to (12) above.

[0032] According to the above configuration, adhesion of foreign matter to the output end of the optical fiber is reduced.

[0033] The technology disclosed in this specification can be realized in the following forms, for example. (14) A light projector disclosed in this specification includes a seed laser, an optical fiber, a branching filter, a pumping laser, a specific branching path, and a multiplexer. The seed laser emits seed laser light. The optical fiber has an input end to which the seed laser light is input and an output end to which amplified laser light is output, and is doped with a rare earth element. The branching filter is optically connected to the output end and branches the amplified laser light into a plurality of branched laser light. The pumping laser emits pumping laser light that excites the rare earth element. A specific branched laser light that is one of the plurality of branched laser light is input to the specific branching path. The multiplexer is optically connected to the pumping laser and the specific branching path and is configured to input the pumping laser light to the output end of the optical fiber.

[0034] According to the above configuration, the branched laser light separated by the demultiplexer is input to the multiplexer. As a result, the intensity of the laser light input to the multiplexer is reduced compared to when the amplified laser light is input to the multiplexer without being separated. This reduces the risk of damage to the multiplexer.

[0035] (15) In the light projector described in (14) above, the branching ratio of the specific branched laser light may be higher than the branching ratios of the other branched laser lights.

[0036] With this configuration, the variation in the branched laser light is reduced.

[0037] (16) The measuring device disclosed in this specification includes the light projector described in (14) or (15) above.

[0038] According to the above configuration, damage to the multiplexer is suppressed.

[0039] 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.

[0040] a block diagram schematically showing the configuration of a measuring device of a first embodiment; an explanatory diagram schematically showing the configuration of a light projector of a first embodiment; a flowchart showing the flow of control of the output of excitation laser light in a first embodiment; a time chart showing the transition of the magnitude of the drive current supplied from a second current source and the intensity of excitation laser light output from the excitation laser in a first embodiment; an explanatory diagram schematically showing the configuration of a light projector of a second embodiment; a flowchart showing the flow of control of the output of excitation laser light in a second embodiment; a block diagram schematically showing the configuration of a measuring device of a third embodiment; an explanatory diagram schematically showing the configuration of a light projector of a third embodiment; a partially enlarged cross-sectional view showing an output end of a second optical fiber and a protective member arranged at this output end in a third embodiment; a partially enlarged cross-sectional view showing an output end of a second optical fiber and a protective member arranged at this output end in a fourth embodiment; a partially enlarged cross-sectional view showing an output end of a second optical fiber and a protective member arranged at this output end in a fifth embodiment; a block diagram schematically showing the configuration of a measuring device of a sixth embodiment; and an explanatory diagram schematically showing the configuration of a light projector of a sixth embodiment.

[0041] First Embodiment A first embodiment will be described with reference to FIGS. 1 to 4. A measurement device 10 of this embodiment is a LiDAR that uses a fiber laser as a light source. The measurement device 10 is mounted, for example, on a vehicle equipped with AD or ADAS. The measurement 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 vehicle driver and those around the vehicle and for reducing damage to surrounding objects while the vehicle is being driven.

[0042] As shown in FIG. 1, the measuring 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.

[0043] As shown in FIGS. 1 and 2, the floodlight 100 includes a light source unit 110 and a control circuit board 210.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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. The rare-earth element is, for example, ytterbium (Yb) or erbium (Er). The second optical fiber 150 is similar. The length of each optical fiber 140, 150 is, for example, approximately 5 m.

[0048] 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 projection 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.

[0049] 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.

[0050] 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.

[0051] 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 .

[0052] 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 collimating lens that adjusts the output laser light Lout to be parallel light.

[0053] 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 Figure 2, it is equipped with a light projection control device 211, a first current source 221, and a second current source 222 (an example of a current source).

[0054] 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 central processing unit (CPU). The storage device includes, for example, a read-only memory (ROM) and a random access memory (RAM). 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 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 in which it can be retrieved from an external device (for example, a cloud server) via the communication interface 600.

[0055] 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.

[0056] 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.

[0057] 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 the output laser light Lout onto a measurement area 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.

[0058] 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.

[0059] The light receiving optical system 410 is an optical component that causes 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 reflective mirror.

[0060] The light receiving unit 420 includes a light receiving element, such as a photodiode, that 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.

[0061] The TOF measurement device 430 includes, for example, a time measurement integrated circuit (IC) equipped with a time-to-digital converter (TDC) 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.

[0062] 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 the received signal. 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.

[0063] 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).

[0064] 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.

[0065] The light-projection control device 211 controls the pumping 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 pumping laser 130 continuously outputs the pumping laser light Lb. The second current source 222 supplies a drive current having a magnitude corresponding to the received drive signal to the pumping laser 130. The pumping laser 130 outputs the pumping laser light Lb having an intensity corresponding to the supplied drive current.

[0066] 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 .

[0067] 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 pumping laser light Lb input from a first demultiplexer 165, and outputs the multiplexed light to the first optical fiber 140.

[0068] The rare earth element doped in the first optical fiber 140 absorbs and is excited by the excitation laser light Lb. A sufficient supply of excitation 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 the seed laser light La with the excitation laser light Lb input from the first demultiplexer 165, and outputs the combined light to the second optical fiber 150.

[0069] 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 projection optical system 180.

[0070] 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.

[0071] 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 from the first current source 221 and outputs seed laser light La.

[0072] Next, the light-projection control device 211 causes the excitation laser 130 to output the excitation 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 excitation laser 130. Upon receiving the drive current from the second current source 222, the excitation laser 130 continuously outputs the excitation laser light Lb at the 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.

[0073] 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" refers to 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 excitation 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 a required intensity.

[0074] 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 level at which the population inversion state of the rare earth elements doped in the first optical fiber 140 and the second optical fiber 150 is maintained and the output laser light Lout maintains the intensity required for detecting the measurement target W. 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 the second intensity P2 corresponding to the second current value I2.

[0075] 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 drive signals to the first current source 221 and the second current source 222.

[0076] As described above, the measuring device 10 of this embodiment includes the light projector 100. The light projector 100 includes the seed laser 120, the excitation laser 130, the optical fibers 140 and 150, and the light projecting control device 211. The seed laser 120 emits seed laser light La. The excitation laser 130 emits excitation laser light Lb. The optical fibers 140 and 150 are each doped with a rare earth element that is excited by the excitation laser light Lb. The seed laser light La and the excitation laser light Lb are input to each of the optical fibers 140 and 150. The light projecting control device 211 controls the intensity of the excitation laser light Lb emitted from the excitation laser 130. After determining that the rare earth element has transitioned to a stable excited state, the light projecting control device 211 reduces the intensity of the excitation laser light Lb output from the excitation laser 130 to a level lower than that before determining that the rare earth element has transitioned to a stable excited state.

[0077] 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 floodlight 100.

[0078] 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 to a level lower than that before it was determined that the rare earth element had 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.

[0079] 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.

[0080] Second Embodiment A second embodiment will be described with reference to Figures 5 and 6. A 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 in the first embodiment are denoted by the same reference numerals and descriptions thereof will be omitted.

[0081] As shown in FIG. 5, a light source unit 110A provided in a floodlight 100A includes a second demultiplexer 810 and a sensor 820.

[0082] The second splitter 810 is disposed between the output end of the second optical fiber 150 and the projection optical system 180. The second splitter 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 splitter 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 splitter 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.

[0083] 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.

[0084] Next, a process in which the light-projection control device 211 controls the intensity of the excitation laser light Lb in the light projector 100A will be described with reference to FIG.

[0085] 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 beam La (S210). Subsequently, the light-projection control device 211 causes the excitation laser 130 to output the excitation laser beam Lb at the 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.

[0086] 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 necessary for the measurement device 10 to detect the measurement target W. 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 and 150 has reached a stable excited state, and executes step S250.

[0087] 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 similar to those in step S140 in the first embodiment.

[0088] 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 drive signals to the first current source 221 and the second current source 222.

[0089] As described above, the light projector 100A of this 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-projection 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.

[0090] (Modifications) The technology disclosed in this specification is not limited to the above-described first and second embodiments, and can be modified into various forms without departing from the gist thereof, for example, the following modifications are also possible. (1) In the above-described first and second embodiments, the projector 100, 100A includes the first optical fiber 140 and the 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 a single optical fiber, or may amplify the seed laser light in three or more stages using three or more optical fibers. (2) In the above-described first and second embodiments, the projector 100, 100A is a forward pumping type in which the pumping laser light Lb is input from the input end of the first optical fiber 140. However, the projector may be a backward pumping type in which the pumping laser light is input from the output end of the optical fiber. (3) In the above-described first and second embodiments, 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 after determining that the rare earth element has transitioned to a stable excited state. 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 the number of excitation lasers outputting excitation laser light to the optical fiber may be reduced after determining that the rare earth element has transitioned to a stable excited state. (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-described embodiments. 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 light that the output laser light Lout has reflected off 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 vary the intensity of the excitation laser light output 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 nearby measurement area should both be smaller than the intensity of the excitation laser light before it is determined that the rare earth element has transitioned to a stable excited state.

[0091] Third Embodiment A third embodiment will be described with reference to FIGS. 7 to 9 . A measuring device 1010 of this embodiment is a LiDAR that uses a fiber laser as a light source. The measuring device 1010 is mounted, for example, on a vehicle equipped with AD or ADAS. The measuring device 1010 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 vehicle driver and those around the vehicle and for reducing damage to surrounding objects while the vehicle is being driven.

[0092] As shown in FIG. 7, the measuring device 1010 includes a light projector 1100, a scanning unit 1300, a light receiver 1400, an information processing device 1500, and a communication interface 1600.

[0093] As shown in FIGS. 7 and 8, the floodlight 1100 includes a light source unit 1110 and a control circuit board 1210.

[0094] As shown in Figures 8 and 9, the light source unit 1110 includes a seed laser 1120, an excitation laser 1130, a first optical fiber 1140, a second optical fiber 1150 (an example of an optical fiber), a first isolator 1161, a first multiplexer 1162, a second isolator 1163, a second multiplexer 1164, a first demultiplexer 1165, a protective member 1170, a light projection optical system 1180, and a sensor 1190.

[0095] The seed laser 1120 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.

[0096] The excitation laser 1130 is a laser light source and emits excitation laser light Lb. In this embodiment, the wavelength of the excitation laser light Lb is 940 nm.

[0097] The first optical fiber 1140 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. The rare-earth element is, for example, ytterbium (Yb) or erbium (Er). The second optical fiber 1150 is similar. The length of each optical fiber 1140, 1150 is, for example, approximately 5 m.

[0098] The first isolator 1161 and the second isolator 1163 are optical components that allow light to pass only in the forward direction from the seed laser 1120 toward the light projection optical system 1180 and block light in the opposite direction to the forward direction. The first isolator 1161 is optically connected to the seed laser 1120. The second isolator 1163 is optically connected to the output end of the first optical fiber 1140. The isolators 161 and 163 suppress damage to the seed laser 1120 due to backflow of returning light from the optical fibers 1140 and 1150 back into the seed laser 1120.

[0099] The first demultiplexer 1165 is an optical component that splits input light into multiple beams. The first demultiplexer 1165 is, for example, a tap coupler, and includes an input port optically connected to the pump laser 1130 and two output ports optically connected to the first multiplexer 1162 and the second multiplexer 1164, respectively.

[0100] The first multiplexer 1162 and the second multiplexer 1164 are optical components that multiplex multiple input beams. The first multiplexer 1162 and the second multiplexer 1164 are, for example, WDM couplers. The first multiplexer 1162 has two input ports optically connected to the first isolator 1161 and the first demultiplexer 1165, respectively, and an output port optically connected to the input end of the first optical fiber 1140. The second multiplexer 1164 has two input ports optically connected to the second isolator 1163 and the other output port of the first demultiplexer 1165, respectively, and an output port optically connected to the input end of the second optical fiber 1150.

[0101] The first optical fiber 1140 and the second optical fiber 1150 are connected in series via a second isolator 1163 and a second multiplexer 1164 .

[0102] The protective member 1170 is attached to the second optical fiber 1150 and covers the output end 1151 of the second optical fiber 1150. The protective member 1170 includes a base 1171 and a cover 1172.

[0103] The base 1171 is a member fixed to the second optical fiber 1150. The cover 1172 includes a cover main body 1173 and a transparent member 1175 (an example of a transparent portion). The cover main body 1173 is a member that is removably attached to the base 1171. The cover main body 1173 has a through-hole 1174. The through-hole 1174 is disposed at a position on the optical path of the output laser light Lout output from the output end 1151 of the second optical fiber 1150. The through-hole 1174 is closed by fitting the transparent member 1175. In this embodiment, the transparent member 1175 is a plate-type beam splitter that reflects a portion of the output laser light Lout and transmits the remainder. The transparent member 1175 is disposed on the optical path of the output laser light Lout output from the output end 1151.

[0104] The protective member 1170 is a container sealed by a base 1171 and a cover 1172, and houses the output end 1151 of the second optical fiber 1150 and its vicinity therein. The base 1171 and the cover 1172 may be made of, for example, metal or synthetic resin.

[0105] The sensor 1190 is a light-receiving sensor that is disposed inside the protective member 1170 and detects the output laser light Lout reflected by the transparent member 1175. The sensor 1190 may be bonded to the inner surface of the cover main body 1173. The sensor 1190 includes a light-receiving element. The light-receiving element is, for example, a photodiode. The sensor 1190 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 1211.

[0106] The projection optical system 1180 is an optical component disposed on the optical path of the output laser light Lout that has passed through the transparent member 1175. The projection optical system 1180 may be, for example, a collimator lens that adjusts the output laser light Lout to be parallel light.

[0107] The control circuit board 1210 is a circuit board on which electronic components are mounted for controlling the light emission of the seed laser 1120 and the excitation laser 1130, and as shown in Figure 8, it is equipped with a light projection control device 1211, a first current source 1221, and a second current source 1222.

[0108] The light-projection control device 1211 is, for example, a microcomputer and includes a processor and a storage device. The processor is, for example, a CPU. The storage device includes, for example, a ROM and a RAM. 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 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 in which it can be obtained from an external device (for example, a cloud server) via the communication interface 1600.

[0109] The first current source 1221 and the second current source 1222 are general current circuits including, for example, a capacitor, a resistor, and a switching element. The first current source 1221 supplies a drive current to the seed laser 1120. The second current source 1222 supplies a drive current to the pump laser 1130.

[0110] The light-projection control device 1211 outputs a drive signal to a first current source 1221. The first current source 1221 receives the drive signal, generates a drive current corresponding to the drive signal, and supplies the drive current to the seed laser 1120. The light-projection control device 1211 outputs the drive signal to a second current source 1222. The second current source 1222 receives the drive signal, generates a drive current corresponding to the drive signal, and supplies the drive current to the excitation laser 1130. In addition, the light-projection control device 1211 outputs a signal indicating the light emission timing at which the seed laser 1120 emits the seed laser light La.

[0111] The scanning unit 1300 is disposed on the optical path of the output laser light Lout output from the projector 1100. The scanning unit 1300 is a device for irradiating the output laser light Lout onto a measurement area in a predetermined scanning pattern. The scanning unit 1300 may include, for example, a MEMS mirror, a DMD, a galvanometer mirror, or a polygon mirror.

[0112] As shown in FIG. 7, the light receiver 1400 includes a light receiving optical system 1410, a light receiving unit 1420, and a TOF measurement device 1430.

[0113] The light receiving optical system 1410 is an optical component that causes the light receiving unit 1420 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 1410 may be, for example, any of various lenses such as a condenser lens, any of various filters such as a wavelength filter, or a reflective mirror.

[0114] The light receiving unit 1420 includes a light receiving element, such as a photodiode, that receives the reflected laser light Lre incident from the light receiving optical system 1410, 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.

[0115] The TOF measurement device 1430 includes, for example, a time measurement IC equipped with a TDC circuit. The TOF measurement device 1430 is communicably connected to the light-projection control device 1211 and the light-receiving unit 1420. The TOF measurement device 1430 receives a timing signal indicating the emission timing output from the light-projection control device 1211 and a light-receiving signal output from the light-receiving unit 1420. Based on these signals, the TOF measurement device 1430 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 of the laser light. The TOF measurement device 1430 outputs a signal corresponding to the calculated TOF and the light-receiving signal received from the light-receiving unit 1420.

[0116] The information processing device 1500 has a processor. The processor may be, for example, a CPU, an MPU, an ASIC, an FPGA, or a DSP. The information processing device 1500 is communicatively connected to the TOF measurement device 1430. The information processing device 1500 receives a signal corresponding to the TOF output by the TOF measurement device 1430 and a light receiving signal, and generates various information based on these. The information may be, for example, a histogram used in time-correlated single photon counting, distances to each point (point) of the measurement object W, or point cloud information. The information generated by the information processing device 1500 is transmitted via the communication interface 1600 to an external device 1700 that uses the information.

[0117] The external device 1700 may be, for example, a device that creates an environmental map using a point cloud, or may be a device that estimates its own position using a scan matching algorithm such as NDT or ICP.

[0118] Next, the basic operation of the projector 1100 will be described. The light-projection control device 1211 pulse-controls the seed laser 1120. That is, the light-projection control device 1211 outputs a drive signal to the first current source 1221 so that the seed laser 1120 intermittently outputs seed laser light La at predetermined timings. The first current source 1221 generates a pulse current having a frequency and magnitude corresponding to the received drive signal and supplies it to the seed laser 1120. The seed laser 1120 outputs seed laser light La having a frequency and intensity corresponding to the supplied drive current.

[0119] The light-projection control device 1211 controls the pumping laser 1130 with a direct current. That is, the light-projection control device 1211 outputs a drive signal to the second current source 1222 so that the pumping laser 1130 continuously outputs the pumping laser light Lb. The second current source 1222 supplies a drive current having a magnitude corresponding to the received drive signal to the pumping laser 1130. The pumping laser 1130 outputs the pumping laser light Lb having an intensity corresponding to the supplied drive current.

[0120] The first demultiplexer 1165 demultiplexes the pump laser light Lb input from the pump laser 1130 into two beams and outputs them to the first multiplexer 1162 and the second multiplexer 1164 .

[0121] The seed laser light La output from the seed laser 1120 passes through a first isolator 1161 and is input to a first multiplexer 1162. The first multiplexer 1162 multiplexes the seed laser light La input from the seed laser 1120 with the pumping laser light Lb input from a first demultiplexer 1165, and outputs the multiplexed light to a first optical fiber 1140.

[0122] The rare earth element doped in the first optical fiber 1140 absorbs and is excited by the excitation laser light Lb. A sufficient supply of excitation 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 1140 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 1140 passes through the second isolator 1163 and is input to the second multiplexer 1164. The second multiplexer 1164 multiplexes the seed laser light La with the excitation laser light Lb input from the first demultiplexer 1165, and outputs the combined light to the second optical fiber 1150.

[0123] Inside the second optical fiber 1150, the seed laser light La is amplified, similarly to the first optical fiber 1140. The amplified seed laser light La is output from the second optical fiber 1150 as output laser light Lout. The transparent member 1175 reflects a portion of the output laser light Lout and guides it to the sensor 1190, and transmits the remainder and guides it to the projection optical system 1180. The output laser light Lout that has passed through the transparent member 1175 is output to the outside of the projector 1100 via the projection optical system 1180.

[0124] The output end 1151 of the second optical fiber 1150 has a diameter of about 10 μm and an extremely small area. Output laser light Lout having high optical energy of 1000 W or more is emitted from the output end 1151 having such a small area. For this reason, if foreign matter such as dust, dirt, fiber waste, or deposits from metal gas adheres to the output end 1151, this foreign matter may be burned by the high optical energy of the output laser light Lout, which may reduce the intensity of the output laser light Lout.

[0125] In this embodiment, the output end 1151 is covered with the protective member 1170, so that adhesion of foreign matter to the output end 1151 is reduced, and a decrease in the intensity of the output laser light Lout is suppressed.

[0126] Furthermore, in this embodiment, the protective member 1170 includes a base 1171 connected to the second optical fiber 1150 and a cover 1172 removably connected to the base 1171. The cover 1172 includes a transparent member 1175 that reflects a portion of the output laser light Lout and transmits the remainder. A sensor 1190 that detects the output laser light Lout reflected by the transparent member 1175 is disposed inside the cover 1172. With this configuration, the transparent member 1175 does not prevent the output laser light Lout from being emitted to the outside of the protective member 1170, and the protective member 1170 can be made into a sealed container. This effectively reduces the adhesion of foreign matter to the output end 1151. Furthermore, since there is no need to separately provide an expensive branching filter that branches the output laser light Lout to the sensor 1190, the manufacturing cost of the light projector 1100 is reduced. Additionally, the cover 1172 is removable from the base 1171, which allows for easy maintenance of the transparent member 1175 and the sensor 1190.

[0127] As described above, the measuring apparatus 1010 of this embodiment includes the light projector 1100. The light projector 1100 includes the seed laser 1120, the pumping laser 1130, the second optical fiber 1150, and the protective member 1170. The seed laser 1120 emits seed laser light La. The pumping laser 1130 emits pumping laser light Lb. The second optical fiber 1150 is optically connected to the seed laser 1120 and the pumping laser 1130. The second optical fiber 1150 is doped with a rare earth element that is pumped by the pumping laser light Lb. The second optical fiber 1150 has an output end 1151 from which the output laser light Lout is output. The protective member 1170 covers the output end 1151.

[0128] According to the above configuration, the output end 1151 of the second optical fiber 1150 is covered with the protective member 1170, so that adhesion of foreign matter to the output end 1151 is reduced.

[0129] In this embodiment, a part of the protective member 1170 is a transparent member 1175 that transmits the output laser beam Lout. The presence of this transparent member 1175 makes it possible to form the protective member 1170 into a sealed container shape without preventing the output laser beam Lout from being emitted to the outside of the protective member 1170. This effectively reduces adhesion of foreign matter to the output end 1151.

[0130] In this embodiment, the protective member 1170 includes a base 1171 connected to the second optical fiber 1150 and a cover 1172 detachably connected to the base 1171, and the cover 1172 includes a transparent member 1175. With this configuration, maintenance of the transparent member 1175 becomes easy.

[0131] In this embodiment, the transparent member 1175 is a beam splitter that reflects a portion of the output laser light Lout and transmits the remainder, and the projector 1100 further includes a sensor 1190 that is disposed inside the protective member 1170 and detects the output laser light Lout reflected by the transparent member 1175. With this configuration, there is no need to separately provide an expensive branching filter that branches the output laser light Lout to the sensor 1190, and therefore the manufacturing costs of the projector 1100 are reduced.

[0132] Fourth Embodiment A fourth embodiment will be described with reference to FIG. 10 . Similar to the third embodiment, a floodlight 1100A of this embodiment is provided in a LiDAR system that uses a fiber laser as a light source. The floodlight 1100A of this embodiment differs from the third embodiment in the configuration of a protective member 1170A. In this embodiment, the same components as those in the third embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0133] Similar to the third embodiment, the protective member 1170A is a member that is attached to the second optical fiber 1150 and covers the output end 1151 of the second optical fiber 1150. The protective member 1170A includes a base 1171 and a cover 1172A.

[0134] The cover 1172A includes a cover main body 1173, similar to the third embodiment, and the cover main body 1173 has a through-hole 1174. The through-hole 1174 is blocked by fitting a transparent member 1175A (an example of a transparent portion). The transparent member 1175A is a member that allows the output laser light Lout to pass through. The transparent member 1175A of this embodiment does not need to have the function of reflecting a portion of the output laser light Lout. The transparent member 1175A may be formed of a material commonly used as a cover for an illumination device, such as polycarbonate. The transparent member 1175A is disposed on the optical path of the output laser light Lout output from the output end 1151. The protective member 1170 is a container sealed by the base 1171 and the cover 1172A, and the output end 1151 of the second optical fiber 1150 and its vicinity are housed therein.

[0135] The sensor 1190A is a light-receiving sensor that is disposed outside the protective member 1170A and detects the output laser light Lout that has passed through the transparent member 1175A. The sensor 1190A is bonded to the outer surface of the transparent member 1175A and is disposed on the optical path of the output laser light Lout. The sensor 1190A includes a light-receiving element. The light-receiving element is, for example, a photodiode. The sensor 1190A 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 1211.

[0136] In this embodiment, as in the third embodiment, the output end 1151 of the second optical fiber 1150 is covered with the protective member 1170A, thereby reducing the adhesion of foreign matter to the output end 1151. In addition, the light projector 1100A of this embodiment further includes a sensor 1190A that is disposed on the outer surface of the transparent member 1175A and detects the output laser light Lout that has passed through the transparent member 1175A. This configuration eliminates the need to provide a separate, expensive splitter for splitting the output laser light Lout to the sensor 1190A, thereby reducing the manufacturing cost of the light projector 1100A. In addition, maintenance of the sensor 1190A can be performed without removing the protective member 1170A from the second optical fiber 1150.

[0137] Fifth Embodiment A fifth embodiment will be described with reference to FIG. 11 . Similar to the third embodiment, a floodlight 1100B of this embodiment is provided in a LiDAR system that uses a fiber laser as a light source. The floodlight 1100B of this embodiment differs from the third embodiment in the configuration of a protective member 1170B. In this embodiment, the same components as those in the third embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0138] Similar to the third embodiment, the protective member 1170B is connected to the second optical fiber 1150 and covers the output end 1151 of the second optical fiber 1150. Unlike the above embodiments, the protective member 1170 is integrally formed as a single member. The protective member 1170 may be made of, for example, metal or resin.

[0139] The protective member 1170B has a through-hole 1174B (an example of an opening). The through-hole 1174B is disposed at a position on the optical path of the output laser light Lout output from the output end 1151 of the second optical fiber 1150, and allows the output laser light Lout to pass through. Unlike the above embodiment, the protective member 1170B is a container with an opening that is not sealed by a member that blocks the through-hole 1174B. The output end 1151 of the second optical fiber 1150 and a portion nearby are housed inside the protective member 1170B.

[0140] The projector 1100B further includes a second splitter 1176 and a sensor 1190B. The second splitter 1176 is disposed on the optical path of the output laser light Lout that passes through the through-hole 1174B and is emitted to the outside of the protective member 1170B. The second splitter 1176 is an optical component that splits the output laser light Lout and guides it to the sensor 1190B and the projecting optical system 1180. The second splitter 1176 may be a beam splitter that reflects a portion of the output laser light Lout and guides it to the sensor 1190B, and transmits the remainder and guides it to the projecting optical system 1180.

[0141] The sensor 1190B is a light-receiving sensor disposed outside the protective member 1170B and detects a portion of the output laser light Lout branched by the second branching filter 1176. The sensor 1190 includes a light-receiving element. The light-receiving element is, for example, a photodiode. The sensor 1190 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 1211.

[0142] In this embodiment, as in the third embodiment, the output end 1151 of the second optical fiber 1150 is covered with the protective member 1170B, thereby reducing adhesion of foreign matter to the output end 1151. In addition, in this embodiment, the protective member 1170B has a through hole 1174B that allows the output laser light Lout to pass through. With this configuration, it is possible to reduce adhesion of foreign matter to the output end 1151 of the second optical fiber 1150 with a simple configuration while allowing the output laser light Lout to be emitted to the outside of the protective member 1170B.

[0143] (Modifications) The technology disclosed in this specification is not limited to the above-described third to fifth embodiments and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible. (6) In the above-described third to fifth embodiments, the light projectors 1100, 1100A, and 1100B include the first optical fiber 1140 and the second optical fiber 1150 and amplify the seed laser light La in two stages. However, the light projectors may amplify the seed laser light in only one stage using a single optical fiber, or may amplify the seed laser light in three or more stages using three or more optical fibers. (7) In the above-described third to fifth embodiments, the light projectors 1100, 1100A, and 1100B are of a forward pumping type in which the pumping laser light Lb is input from the input end of the first optical fiber 1140. However, the light projectors may be of a backward pumping type in which the pumping laser light is input from the output end of the optical fiber. (8) In the third embodiment, the protective member 1170 includes a base 1171 and a cover 1172, and a portion of the cover 1172 is the transparent member 1175. However, the protective member may be integrally formed as a single member, and a portion of the protective member may be the transparent portion. The same applies to the fourth embodiment. (9) In the third and fourth embodiments, a portion of the cover 1172, 172A is the transparent member 1175, 1175A. However, the entire cover may be the transparent portion, or both the cover and the base may be the transparent portion. Alternatively, the protective member may be integrally formed as a single member, and the entire protective member may be the transparent portion. (10) In the fifth embodiment, the protective member 1170B is integrally formed as a single member and has a through-hole 1174B. However, for example, the protective member may include a base and a cover, and the cover may have an opening that allows the output laser light to pass through. (11) In the third and fourth embodiments, the protective members 1170 and 170A are hermetically sealed containers. However, the protective members may have openings for, for example, maintenance of the output terminals and sensors disposed therein. (12) In the third embodiment, the sensor 1190 is disposed on the inner surface of the cover 1172. However, the sensor may be positioned anywhere as long as it can receive the output laser light. For example, the sensor may be positioned on the inner surface of the base.(13) In the fourth embodiment, the sensor 1190A is disposed on the outer surface of the transparent member 1175A. However, the sensor may be disposed at any position where it can receive the output laser light. For example, the sensor may be disposed outside the protective member, on the optical path of the output laser light, and away from the transparent member. Alternatively, an optical component may be disposed outside the protective member that splits the output laser light and guides it to the sensor and the projection optical system.

[0144] A sixth embodiment will be described with reference to Figures 12 and 13. A measuring device 2010 of the sixth embodiment is a LiDAR that uses a fiber laser as a light source. The measuring device 2010 is mounted, for example, on a vehicle equipped with AD or ADAS. The measuring device 2010 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 vehicle driver and those around the vehicle and for reducing damage to surrounding objects while the vehicle is being driven.

[0145] As shown in FIG. 12, the measuring device 2010 includes a light projector 2100, a scanning unit 2300, a light receiver 2400, an information processing device 2500, and a communication interface 2600.

[0146] The light projector 2100 is a multi-channel light projector capable of simultaneously emitting a plurality of branched laser beams Lout1, Lout2, Lout3, and Lout4. As shown in FIGS. 12 and 13 , the light projector 2100 includes a light source unit 2110 and a control circuit board 2210.

[0147] As shown in FIG. 13, the light source unit 2110 includes a seed laser 2120, an excitation laser 2130, an optical fiber 2140, an isolator 2161, a multiplexer 2162, a demultiplexer 2170, and a light projection optical system 2180.

[0148] The seed laser 2120 is a laser light source that emits a seed laser beam La having a peak wavelength included in the near-infrared range. In the sixth embodiment, the wavelength of the seed laser beam La is 1550 nm.

[0149] The excitation laser 2130 is a laser light source and emits excitation laser light Lb. In the sixth embodiment, the wavelength of the excitation laser light Lb is 940 nm.

[0150] The optical fiber 2140 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 the rare-earth element include ytterbium (Yb) and erbium (Er). The length of the optical fiber 2140 is, for example, approximately 5 m. One end of the optical fiber 2140 is an input end 2141 to which the seed laser light La is input, and the other end is an output end 2142 from which the amplified laser light Lout is output.

[0151] The isolator 2161 is an optical component that passes light only in the forward direction from the seed laser 2120 toward the light projecting optical system 2180 and blocks light in the opposite direction to the forward direction. The isolator 2161 is optically connected to the seed laser 2120 and the input end 2141 of the optical fiber 2140. The isolator 2161 suppresses damage to the seed laser 2120 caused by return light from the optical fiber 2140 flowing back into the seed laser 2120.

[0152] The demultiplexer 2170 is an optical component that branches input light into multiple beams. The demultiplexer 2170 is, for example, a tap coupler. In the sixth embodiment, the demultiplexer 2170 includes an input port 2171 and four output ports 2172, 2173, 2174, and 2175. The input port 2171 is optically connected to an output end 2142 of an optical fiber 2140. The four output ports 2172, 2173, 2174, and 2175 are optically connected to four branch paths 2191, 2192, 2193, and 2194, respectively. The four branch paths 2191, 2192, 2193, and 2194 are each formed of a general optical fiber that is not doped with a rare earth element. The demultiplexer 2170 branches the amplified laser beam Lout into four branched laser beams Lout1, Lout2, Lout3, and Lout4. The four branched laser beams Lout1, Lout2, Lout3, and Lout4 are output to four branch paths 2191, 2192, 2193, and 2194 via four output ports 2172, 2173, 2174, and 2175, respectively. One of the four branch paths 2191, 2192, 2193, and 2194 is a specific branch path 2191.

[0153] The multiplexer 2162 is an optical component that multiplexes multiple input beams of light. The multiplexer 2162 is optically connected to the pump laser 2130 and the specific branch path 2191. The multiplexer 2162 of the sixth embodiment is an optical filter type multiplexer, and includes an optical filter 2163 that passes the branched laser beam Lout1 and reflects the pump laser beam Lb. In addition to the optical filter 2163, the multiplexer 2162 may include an isolator, a lens, etc.

[0154] The projection optical system 2180 is an optical component arranged on the optical paths of the branched laser beams Lout1, Lout2, Lout3, and Lout4 that have passed through the multiplexer 2162 and the branch paths 2192, 2193, and 2194, respectively. The projection optical system 2180 may be, for example, a collimator lens that adjusts the branched laser beams Lout1, Lout2, Lout3, and Lout4 to become parallel beams.

[0155] The control circuit board 2210 is a circuit board on which electronic components are mounted for controlling the light emission of the seed laser 2120 and the excitation laser 2130, and as shown in Figure 13, it is equipped with a light projection control device 2211, a first current source 2221, and a second current source 2222.

[0156] The light-projection control device 2211 is, for example, a microcomputer and includes a processor and a storage device. The processor is, for example, a CPU. The storage device includes, for example, a ROM and a RAM. 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 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 in which it can be obtained from an external device (for example, a cloud server) via the communication interface 2600.

[0157] The first current source 2221 and the second current source 2222 are general current circuits including, for example, a capacitor, a resistor, and a switching element. The first current source 2221 supplies a drive current to the seed laser 2120. The second current source 2222 supplies a drive current to the pump laser 2130.

[0158] The light-projection control device 2211 outputs a drive signal to a first current source 2221. The first current source 2221 receives the drive signal, generates a drive current corresponding to the drive signal, and supplies the drive current to the seed laser 2120. The light-projection control device 2211 outputs the drive signal to a second current source 2222. The second current source 2222 receives the drive signal, generates a drive current corresponding to the drive signal, and supplies the drive current to the excitation laser 2130. In addition, the light-projection control device 2211 outputs a signal indicating the light emission timing at which the seed laser 2120 emits the seed laser light La.

[0159] The scanning unit 2300 is disposed on the optical paths of the branched laser beams Lout1, Lout2, Lout3, and Lout4 output from the projector 2100. The scanning unit 2300 is a device for irradiating the branched laser beams Lout1, Lout2, Lout3, and Lout4 onto a measurement area in a predetermined scanning pattern. The scanning unit 2300 may include, for example, a MEMS mirror, a DMD, a galvanometer mirror, or a polygon mirror.

[0160] As shown in FIG. 12, the light receiver 2400 includes a light receiving optical system 2410, a light receiving unit 2420, and a TOF measurement device 2430.

[0161] The light receiving optical system 2410 is an optical component for causing the light receiving unit 2420 to receive reflected laser beams Lre1, Lre2, Lre3, and Lre4, which are the branched laser beams Lout1, Lout2, Lout3, and Lout4 that are respectively reflected by the measurement target W and returned. The light receiving optical system 2410 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.

[0162] The light receiving unit 2420 includes a light receiving element, such as a photodiode, that receives the reflected laser beams Lre1, Lre2, Lre3, and Lre4 incident from the light receiving optical system 2410, converts the received laser beams into light receiving signals corresponding to the intensities and light receiving timings of the reflected laser beams Lre1, Lre2, Lre3, and Lre4, and outputs the light receiving signals.

[0163] The TOF measurement device 2430 includes, for example, a time measurement IC equipped with a TDC circuit. The TOF measurement device 2430 is communicably connected to the light-projection control device 2211 and the light-receiving unit 2420. The TOF measurement device 2430 receives a timing signal indicating the light emission timing output from the light-projection control device 2211 and a light-receiving signal output from the light-receiving unit 2420. Based on these signals, the TOF measurement device 2430 calculates the difference between the timing at which the branched laser beams Lout1, Lout2, Lout3, and Lout4 are emitted and the timing at which the reflected laser beams Lre1, Lre2, Lre3, and Lre4 are received, i.e., the time of flight of the laser beam. The TOF measurement device 2430 outputs a signal corresponding to the calculated TOF and the light-receiving signal received from the light-receiving unit 2420.

[0164] The information processing device 2500 has a processor. The processor may be, for example, a CPU, an MPU, an ASIC, an FPGA, or a DSP. The information processing device 2500 is communicatively connected to the TOF measurement device 2430. The information processing device 2500 receives a signal corresponding to the TOF output by the TOF measurement device 2430 and a light receiving signal, and generates various information based on these. The information may be, for example, a histogram used in time-correlated single photon counting, distances to each point (point) of the measurement object W, or point cloud information. The information generated by the information processing device 2500 is transmitted via the communication interface 2600 to an external device 2700 that uses the information.

[0165] The external device 2700 may be, for example, a device that creates an environmental map using a point cloud, or may be a device that estimates its own position using a scan matching algorithm such as NDT or ICP.

[0166] Next, the basic operation of the projector 2100 will be described. The light-projection control device 2211 pulse-controls the seed laser 2120. That is, the light-projection control device 2211 outputs a drive signal to the first current source 2221 so that the seed laser 2120 intermittently outputs seed laser light La at predetermined timings. The first current source 2221 generates a pulse current having a frequency and magnitude corresponding to the received drive signal and supplies it to the seed laser 2120. The seed laser 2120 outputs seed laser light La having a frequency and intensity corresponding to the supplied drive current.

[0167] The light-projection control device 2211 controls the pumping laser 2130 with a direct current. That is, the light-projection control device 2211 outputs a drive signal to the second current source 2222 so that the pumping laser 2130 continuously outputs the pumping laser light Lb. The second current source 2222 supplies a drive current having a magnitude corresponding to the received drive signal to the pumping laser 2130. The pumping laser 2130 outputs the pumping laser light Lb, having an intensity corresponding to the supplied drive current, to the multiplexer 2162.

[0168] The seed laser light La output from the seed laser 2120 passes through the isolator 2161 and is input to the optical fiber 2140 .

[0169] The optical filter 2163 provided in the multiplexer 2162 reflects the excitation laser light Lb input from the excitation laser 2130. The reflected excitation laser light Lb passes through the specific branch path 2191 and the light guide path inside the demultiplexer 2170, and is input from the output end 2142 to the optical fiber 2140.

[0170] The rare earth element doped in the optical fiber 2140 absorbs and is excited by the excitation laser light Lb. A sufficient supply of excitation 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 optical fiber 2140 in this state, electrons held by 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 is output from the output end 2142 to the demultiplexer 2170 as amplified laser light Lout.

[0171] The demultiplexer 2170 branches the input amplified laser light Lout into four branched laser light Lout1, Lout2, Lout3, and Lout4, and outputs the branched laser light to four branch paths 2191, 2192, 2193, and 2194, respectively. The demultiplexer 2170 branches the amplified laser light Lout so that the branching ratio of the specific branched laser light Lout1 output to the specific branch path 2191 is higher than the branching ratios of the other branched laser light Lout2, Lout3, and Lout4. In other words, when the branching ratio of the specific branched laser beam Lout1 output to the specific branch path 2191 is R1, the branching ratio of the branched laser beam Lout2 output to the branch path 2192 is R2, the branching ratio of the branched laser beam Lout3 output to the branch path 2193 is R3, and the branching ratio of the branched laser beam Lout4 output to the branch path 2194 is R4, the branching filter 2170 branches the amplified laser beam Lout so that R1 > R2, R1 > R3, and R1 > R4 all hold. The branching ratios R2, R3, and R4 may be equal to one another. The branching ratio of the branched laser beam output to a certain branch path is the value obtained by dividing the intensity value of the branched laser beam output to that branch path by the total intensity value of the branched laser beams output to all the branch paths. The intensity value of the branched laser beam output to a certain branch path is determined by measuring the intensity of the light output from the output port of the branching filter 2170 connected to that branch path using an integrating sphere or a power meter.

[0172] The specific branched laser beam Lout1 passes through a specific branch path 2191, is input to the multiplexer 2162, and is output after passing through an optical filter 2163. The other branched laser beams Lout2, Lout3, and Lout4 pass through branch paths 2192, 2193, and 2194, respectively, and are output. If the amplified laser beam Lout is input to the multiplexer 2162 without being branched, there is a concern that the high-intensity amplified laser beam Lout may damage the built-in optical filter 2163. If the optical filter 2163 is damaged, the transmittance of the light input to the optical filter 2163 decreases, and the intensity of the laser beam output from the projector 2100 decreases. In the sixth embodiment, the amplified laser beam Lout is branched into a plurality of branched laser beams Lout1, Lout2, Lout3, and Lout4, and one of these beams is input to the multiplexer 2162. This makes it possible to relatively reduce the intensity of the laser beam input to the multiplexer 2162. This prevents the multiplexer 2162 from being damaged.

[0173] Furthermore, when light passes through the optical filter 2163, a relatively large loss occurs compared to when light passes through the other general optical fibers 2192, 2193, and 2194. In the sixth embodiment, the amplified laser light Lout is branched so that the branching ratio R1 of the specific branched laser light Lout1 is higher than the branching ratios R2, R3, and R4 of the other branched laser lights Lout2, Lout3, and Lout4 by the amount of this loss. This reduces variations in the intensities of the output branched laser lights Lout1, Lout2, Lout3, and Lout4.

[0174] The branched laser beams Lout2, Lout3, and Lout4 output from the multiplexer 2162 and the branch paths 2192, 2193, and 2194, respectively, are output to the outside of the projector 2100 via the projection optical system 2180.

[0175] As described above, the measuring apparatus 2010 of the sixth embodiment includes the light projector 2100. The light projector 2100 includes the seed laser 2120, the optical fiber 2140, the pumping laser 2130, the splitter 2170, the specific branch path 2191, and the multiplexer 2162. The seed laser 2120 emits a seed laser beam La. The optical fiber 2140 has an input end 2141 to which the seed laser beam La is input and an output end 2142 from which the amplified laser beam Lout is output, and is doped with a rare earth element. The splitter 2170 is optically connected to the output end 2142 and splits the amplified laser beam Lout into a plurality of split laser beams Lout1, Lout2, Lout3, and Lout4. The pumping laser 2130 emits a pumping laser beam Lb that excites the rare earth element. A specific branch laser beam Lout1, which is one of the plurality of branch laser beams Lout1, Lout2, Lout3, and Lout4, is input to the specific branch path 2191. The multiplexer 2162 is optically connected to the pump laser 2130 and the specific branch path 2191, and is configured to input the pump laser beam Lb to an output end 2142 of the optical fiber 2140.

[0176] According to the above configuration, the specific branch laser beam Lout1 demultiplexed by the demultiplexer 2170 is input to the multiplexer 2162. As a result, the intensity of the laser beam input to the multiplexer 2162 is smaller than when the amplified laser beam Lout is input to the multiplexer 2162 without being demultiplexed. This suppresses damage to the multiplexer 2162.

[0177] In the sixth embodiment, the branching ratio R1 of the specific branched laser beam Lout1 is higher than the branching ratios R2, R3, and R4 of the other branched laser beams Lout2, Lout3, and Lout4. With this configuration, the variations in the branched laser beams Lout1, Lout2, Lout3, and Lout4 are reduced.

[0178] (Modifications) The technology disclosed in this specification is not limited to the sixth embodiment described above and can be modified into various forms without departing from the spirit of the present invention. For example, the following modifications are also possible. (14) In the sixth embodiment, the light projector 2100 amplifies the seed laser light by one stage using a single optical fiber 2140. However, the light projector may amplify the seed laser light by two or more stages using two or more optical fibers. (15) In the sixth embodiment, the multiplexer 2162 is an optical filter type. However, the multiplexer may be a fusion type including multiple optical fibers fused to each other. In the case of a fusion type multiplexer, there is a concern that the optical fibers may be excessively heated and melted by the high-intensity amplified laser light. Even when the multiplexer is a fusion type, as in the case of an optical filter type, the intensity of the laser light input to the multiplexer is reduced by inputting the branched laser light demultiplexed by the demultiplexer to the multiplexer, compared to when the amplified laser light is input to the multiplexer without being demultiplexed. This reduces damage to the multiplexer. (16) In the sixth embodiment, the demultiplexer 2170 demultiplexes the amplified laser beam Lout into four branched laser beams Lout1, Lout2, Lout3, and Lout4, but the demultiplexer may demultiplex the amplified laser beam into two or three branched laser beams, or into five or more branched laser beams. (17) In the sixth embodiment, one specific branched path 2191 is connected to the pump laser 2130 via the demultiplexer 2170, but two or more branched paths may be specific branched paths connected to the pump laser via a demultiplexer.

[0179] This application is based on a Japanese patent application filed on June 21, 2024 (Patent Application No. 2024-100179), a Japanese patent application filed on June 21, 2024 (Patent Application No. 2024-100181), and a Japanese patent application filed on June 21, 2024 (Patent Application No. 2024-100185), the contents of which are incorporated herein by reference.

Claims

1. A light projector comprising: 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, wherein after the light projecting control device determines 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 it determined that the rare earth element has transitioned to a stable excited state.

2. A light projector as claimed in claim 1, further comprising a current source that supplies a drive current to the excitation laser, wherein the light projecting control device causes the excitation laser to output the excitation laser light 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 excited state, reduces the drive current output from the current source compared to before determining that the rare earth element has transitioned to a stable excited state.

3. A light-projecting device as claimed in claim 1 or claim 2, wherein the light-projecting control device determines 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.

4. A light projector as claimed in claim 1 or claim 2, further comprising a sensor that detects the intensity of the output laser light output from the optical fiber, and wherein the light projecting control device determines that the rare earth element has transitioned to a stable excited state when the intensity of the output laser light detected by the sensor reaches or exceeds a predetermined reference value.

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

6. A method for controlling a light projector comprising: a seed laser that emits seed laser light; a pumping laser that emits pumping laser light; and an optical fiber into which the seed laser light and the pumping laser light are input and which is doped with a rare earth element that is excited by the pumping laser light, wherein, after it is determined that the rare earth element has transitioned to a stable excited state, the intensity of the pumping laser light output from the pumping laser is reduced compared to before it was determined that the rare earth element had transitioned to a stable excited state.

7. A computer program for executing, in a computer included in a projector comprising: a seed laser that emits seed laser light; an excitation laser that emits excitation laser light; and an optical fiber that receives the seed laser light and the excitation laser light and is doped with a rare earth element that is excited by the excitation laser light, after determining that the rare earth element has transitioned to a stable excited state, a process of reducing the intensity of the excitation laser light output from the excitation laser compared to before it was determined that the rare earth element has transitioned to a stable excited state.

8. A computer-readable recording medium having recorded thereon a computer program for controlling a light projector comprising: a seed laser that emits seed laser light; a pumping laser that emits pumping laser light; and an optical fiber that receives the seed laser light and the pumping laser light and is doped with a rare earth element that is excited by the pumping laser light, wherein, after it is determined that the rare earth element has transitioned to a stable excited state, a process is executed to reduce the intensity of the pumping laser light output from the pumping laser compared to before it was determined that the rare earth element has transitioned to a stable excited state.

9. A light projector comprising: a seed laser that emits seed laser light; a pumping laser that emits pumping laser light; an optical fiber that is optically connected to the seed laser and the pumping laser, that is doped with a rare earth element that is pumped by the pumping laser light, and that has an output end from which output laser light is output; and a protective member that covers the output end.

10. A light projector according to claim 9, wherein at least a part of the protective member is a transparent portion that transmits the output laser light.

11. A light projector according to claim 10, wherein the protective member comprises: a base connected to the optical fiber; and a cover comprising the transmitting portion and removably connected to the base.

12. A light projector as claimed in claim 10 or claim 11, wherein the transmitting section is a beam splitter that reflects a portion of the output laser light and transmits the remainder, and further comprising a sensor that is disposed inside the protective member and detects the output laser light reflected by the transmitting section.

13. A light projector according to claim 10 or 11, further comprising a sensor disposed on the outer surface of the transmitting portion, for detecting the output laser light that has passed through the transmitting portion.

14. A light projector according to claim 9, wherein the protective member has an opening that allows the output laser light to pass through.

15. A measuring device comprising a light projector according to claim 9 or 10.

16. A light projector comprising: a seed laser that emits seed laser light; an optical fiber doped with a rare earth element, the optical fiber having an input end to which the seed laser light is input and an output end to which amplified laser light is output; a branching filter optically connected to the output end and branching the amplified laser light into a plurality of branched laser lights; a pumping laser that emits pumping laser light that excites the rare earth element; a specific branching path to which a specific branched laser light that is one of the plurality of branched laser lights is input; and a multiplexer optically connected to the pumping laser and the specific branching path and configured to input the pumping laser light to the output end of the optical fiber.

17. A light projector according to claim 16, wherein the branching ratio of the specific branch laser light is higher than the branching ratios of the other branch laser lights.

18. A measuring device comprising a light projector according to claim 16 or 17.

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