Projector and measuring device

Abstract

To suppress the occurrence of damage to a multiplexer.SOLUTION: The light projector includes a seed laser configured to emit seed laser light, an optical fiber having an input end to which the seed laser light is input and an output end from which amplified laser light is output, the optical fiber being doped with a rare earth element, a demultiplexer optically connected to the output end and configured to split the amplified laser light into a plurality of split laser lights, an excitation laser configured to emit excitation laser light for exciting the rare earth element, a specific branched path to which a specific split laser light that is one of the plurality of split laser lights is input, and a multiplexer optically connected to the excitation laser and the specific branched path and configured to input the excitation laser light to the output end of the optical fiber.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a projector and a measurement device. [Background technology]

[0002] With the advancement of autonomous driving (AD) systems and advanced driver assistance systems (ADAS), research and development of LiDAR (light detection and ranging) is underway as one of the measurement devices used to grasp the surrounding environment and estimate the vehicle's self-position while driving. LiDAR includes a projector that projects laser light onto a measurement target and a photoreceiver that receives the light reflected from the measurement target. LiDAR measures the distance to the measurement target based on the difference between the timing at which the projector emits the laser light and the timing at which the photoreceiver receives the reflected light. The projector includes a fiber laser (see, for example, Patent Document 1). The fiber laser includes a seed laser that emits seed laser light, an optical fiber doped with a rare earth element and through which the seed laser light passes, and a pump laser that emits pump laser light that excites the rare earth element. [Prior art documents] [Patent documents]

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

[0004] 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 a 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.

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

[0006] The technology disclosed in this specification can be realized, for example, in the following forms. (1) A light projector disclosed in this specification includes a seed laser, 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 multiple branched laser lights. The pumping laser emits pumping laser light that excites the rare earth element. A specific branched laser light that is one of the multiple branched laser lights 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.

[0007] 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.

[0008] (2) In the light projector described in (1) above, the branching ratio of the specific branched laser light may be higher than the branching ratios of the other branched laser lights.

[0009] With this configuration, the variation in the branched laser light is reduced.

[0010] (3) The measuring device disclosed in this specification includes the light projector described in (1) or (2) above.

[0011] According to the above configuration, damage to the multiplexer is suppressed.

[0012] The technology disclosed in this specification can be realized in various forms, for example, in the form of a projector, a measuring device, etc. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device according to a first embodiment. [Figure 2] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a floodlight according to a first embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment will be described with reference to Fig. 1 and Fig. 2. The measuring device 10 of this embodiment is a LiDAR that uses a fiber laser as a light source. The measuring device 10 is mounted on a vehicle equipped with, for example, an AD (automated drive) or an ADAS (advanced driver assistance system). For example, the measuring device 10 assists in detecting objects such as people and other vehicles while the vehicle is traveling, and provides various information to other devices and users that is useful for ensuring the safety of the vehicle driver and those around the vehicle, and for reducing damage to surrounding objects while the vehicle is being driven.

[0015] As shown in FIG. 1, the measurement device 10 includes a light projector 100, a scanning unit 300, a light receiver 400, an information processing device 500, and a communication interface 600.

[0016] The projector 100 is a multi-channel projector capable of simultaneously emitting a plurality of branched laser beams Lout1, Lout2, Lout3, and Lout4. As shown in FIGS. 1 and 2, the projector 100 includes a light source unit 110 and a control circuit board 210.

[0017] As shown in FIG. 2, the light source unit 110 includes a seed laser 120, an excitation laser 130, an optical fiber 140, an isolator 161, a multiplexer 162, a demultiplexer 170, and a light projection optical system 180.

[0018] 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.

[0019] 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.

[0020] The optical fiber 140 includes a core doped with a rare earth element and a cladding surrounding the core and having a refractive index lower than the maximum refractive index of the core. The rare earth element is an element that is excited by the excitation laser light Lb. Examples of the rare earth element include ytterbium (Yb) and erbium (Er). The length of the optical fiber 140 is, for example, approximately 5 m. One end of the optical fiber 140 is an input end 141 to which the seed laser light La is input, and the other end is an output end 142 from which the amplified laser light Lout is output.

[0021] The isolator 161 is an optical component that passes light only in the forward direction from the seed laser 120 toward the light projecting optical system 180 and blocks light in the opposite direction to the forward direction. The isolator 161 is optically connected to the seed laser 120 and the input end 141 of the optical fiber 140. The isolator 161 suppresses damage to the seed laser 120 caused by return light from the optical fiber 140 flowing back into the seed laser 120.

[0022] The demultiplexer 170 is an optical component that branches input light into multiple beams. The demultiplexer 170 is, for example, a tap coupler. In this embodiment, the demultiplexer 170 has an input port 171 and four output ports 172, 173, 174, and 175. The input port 171 is optically connected to the output end 142 of the optical fiber 140. The four output ports 172, 173, 174, and 175 are optically connected to four branch paths 191, 192, 193, and 194, respectively. The four branch paths 191, 192, 193, and 194 are each formed of a general optical fiber that is not doped with a rare earth element. The demultiplexer 170 branches the amplified laser beam Lout into four branch laser beams Lout1, Lout2, Lout3, and Lout4. The four branched laser beams Lout1, Lout2, Lout3, and Lout4 are output to four branch paths 191, 192, 193, and 194 via four output ports 172, 173, 174, and 175, respectively. One of the four branch paths 191, 192, 193, and 194 is a specific branch path 191.

[0023] The multiplexer 162 is an optical component that multiplexes multiple input beams of light. The multiplexer 162 is optically connected to the pump laser 130 and the specific branch path 191. The multiplexer 162 of this embodiment is an optical filter type multiplexer, and includes an optical filter 163 that passes the branched laser beam Lout1 and reflects the pump laser beam Lb. In addition to the optical filter 163, the multiplexer 162 may include an isolator, a lens, etc.

[0024] The projection optical system 180 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 162 and the branch paths 192, 193, and 194, respectively. The projection optical system 180 may be, for example, a collimator lens that adjusts the branched laser beams Lout1, Lout2, Lout3, and Lout4 to become parallel beams.

[0025] The control circuit board 210 is a circuit board on which electronic components are mounted for controlling the light emission of the seed laser 120 and the excitation laser 130, and as shown in FIG. 2, includes a light projection control device 211, a first current source 221, and a second current source 222.

[0026] The light projection control device 211 is, for example, a microcomputer and includes a processor and a storage device. The processor is, for example, a CPU (central processing unit). The storage device includes, for example, a ROM (read only memory) and a RAM (random access memory). The storage device stores various programs and data, and is used as a work area for executing various processes and as a data storage area. For example, the storage device stores a computer program for controlling the intensity of the excitation laser beam Lb. This computer program may be provided in a state where it is stored in a computer-readable recording medium (not shown). The computer-readable recording medium is, for example, a CD-ROM, a DVD-ROM, or a USB memory. Alternatively, the computer program may be provided in a state where it can be obtained from an external device (for example, a server on the cloud) via the communication interface 600.

[0027] 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.

[0028] 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.

[0029] The scanning unit 300 is disposed on the optical paths of the branched laser beams Lout1, Lout2, Lout3, and Lout4 output from the projector 100. The scanning unit 300 is a device for irradiating a measurement area with the branched laser beams Lout1, Lout2, Lout3, and Lout4 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.

[0030] 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.

[0031] The light receiving optical system 410 is an optical component for causing the light receiving unit 420 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 410 may be, for example, any of various lenses such as a condenser lens, any of various filters such as a wavelength filter, or a reflecting mirror.

[0032] The light receiving unit 420 includes a light receiving element, such as a photodiode. The light receiving element receives the reflected laser beams Lre1, Lre2, Lre3, and Lre4 incident from the light receiving optical system 410, 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 signals.

[0033] The TOF measurement device 430 has, for example, a time measurement integrated circuit (IC) equipped with a TDC (time-to-digital converter) circuit. The TOF measurement device 430 is communicably connected to the light-projection control device 211 and the light-receiving unit 420. The TOF measurement device 430 receives a timing signal indicating the light emission timing output from the light-projection control device 211 and a light-receiving signal output from the light-receiving unit 420. Based on these signals, the TOF measurement device 430 calculates the difference between the timing at which the 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 (TOF) of the laser beam. 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.

[0034] The information processing device 500 has a processor. The processor may be, for example, a central processing unit (CPU), a microprocessing unit (MPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a digital signal processor (DSP). The information processing device 500 is communicatively connected to the TOF measurement device 430. The information processing device 500 receives a signal corresponding to the TOF output by the TOF measurement device 430 and a light receiving signal, and generates various information based on these signals. The information may be, for example, a histogram used in time-correlated single photon counting, distances to each point on the measurement target W, or point cloud information. The information generated by the information processing device 500 is transmitted via a communication interface 600 to an external device 700 that uses the information.

[0035] 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).

[0036] 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.

[0037] 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 the pumping laser 130 with a drive current having a magnitude corresponding to the received drive signal. The pumping laser 130 outputs the pumping laser light Lb, having an intensity corresponding to the supplied drive current, to the multiplexer 162.

[0038] The seed laser light La output from the seed laser 120 passes through the isolator 161 and is input to the optical fiber 140 .

[0039] The optical filter 163 provided in the multiplexer 162 reflects the pumping laser light Lb input from the pumping laser 130. The reflected pumping laser light Lb passes through the specific branch path 191 and the light guide path inside the demultiplexer 170, and is input from the output end 142 to the optical fiber 140.

[0040] The rare earth element doped in the optical fiber 140 absorbs the excitation laser light Lb and becomes excited. 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 the ground state. When seed laser light La is input to the optical fiber 140 in this state, the 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 142 to the demultiplexer 170 as amplified laser light Lout.

[0041] The demultiplexer 170 branches the input amplified laser light Lout into four branched laser light Lout1, Lout2, Lout3, and Lout4, and outputs the four branched laser light Lout to four branch paths 191, 192, 193, and 194, respectively. The demultiplexer 170 branches the amplified laser light Lout so that the branching ratio of the specific branched laser light Lout1 output to the specific branch path 191 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 191 is R1, the branching ratio of the branched laser beam Lout2 output to the branch path 192 is R2, the branching ratio of the branched laser beam Lout3 output to the branch path 193 is R3, and the branching ratio of the branched laser beam Lout4 output to the branch path 194 is R4, the demultiplexer 170 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 demultiplexer 170 connected to that branch path using an integrating sphere or a power meter.

[0042] The specific branched laser beam Lout1 passes through a specific branch path 191, is input to the multiplexer 162, and is output through an optical filter 163. The other branched laser beams Lout2, Lout3, and Lout4 pass through branch paths 192, 193, and 194, respectively, and are output. If the amplified laser beam Lout is input to the multiplexer 162 without being branched, there is a concern that the high-intensity amplified laser beam Lout may damage the built-in optical filter 163. If the optical filter 163 is damaged, the transmittance of light input to the optical filter 163 decreases, and the intensity of the laser beam output from the projector 100 decreases. In this embodiment, the amplified laser beam Lout is branched into multiple branched laser beams Lout1, Lout2, Lout3, and Lout4, and one of these is input to the multiplexer 162. This allows the intensity of the laser beam input to the multiplexer 162 to be relatively small. This prevents the multiplexer 162 from being damaged.

[0043] Furthermore, when light passes through the optical filter 163, a relatively large loss occurs compared to when light passes through the other general optical fibers 192, 193, and 194. In this 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.

[0044] The branched laser beams Lout2, Lout3, and Lout4 output from the multiplexer 162 and the branch paths 192, 193, and 194, respectively, are output to the outside of the projector 100 via the light projection optical system 180.

[0045] As described above, the measuring apparatus 10 of this embodiment includes the projector 100. The projector 100 includes the seed laser 120, the optical fiber 140, the pumping laser 130, the demultiplexer 170, the specific branch path 191, and the multiplexer 162. The seed laser 120 emits seed laser light La. The optical fiber 140 has an input end 141 to which the seed laser light La is input and an output end 142 from which the amplified laser light Lout is output, and is doped with a rare earth element. The demultiplexer 170 is optically connected to the output end 142 and branches the amplified laser light Lout into a plurality of branched laser lights Lout1, Lout2, Lout3, and Lout4. The pumping laser 130 emits pumping laser light Lb that excites the rare earth element. A specific branched laser beam Lout1, which is one of a plurality of branched laser beams Lout1, Lout2, Lout3, and Lout4, is input to the specific branched path 191. The multiplexer 162 is optically connected to the pumping laser 130 and the specific branched path 191, and is configured to input the pumping laser beam Lb to the output end 142 of the optical fiber 140.

[0046] According to the above configuration, the specific branch laser beam Lout1 demultiplexed by the demultiplexer 170 is input to the multiplexer 162. As a result, the intensity of the laser beam input to the multiplexer 162 is reduced compared to when the amplified laser beam Lout is input to the multiplexer 162 without being demultiplexed. This reduces the risk of damage to the multiplexer 162.

[0047] In this 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.

[0048] (Variation) The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible. (1) In the above embodiment, the projector 100 amplifies the seed laser light in only one stage using one optical fiber 140, but the projector may also amplify the seed laser light in two or more stages using two or more optical fibers. (2) In the above embodiment, the multiplexer 162 is an optical filter type, but the multiplexer may be a fusion type having multiple optical fibers fused together. In the case of a fusion type multiplexer, there is a concern that the high-intensity amplified laser light may cause the optical fibers to overheat and melt. Even if 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 the risk of damage to the multiplexer. (3) In the above embodiment, the splitter 170 splits the amplified laser light Lout into four branched laser lights Lout1, Lout2, Lout3, and Lout4, but the splitter may split the amplified laser light into two or three branched laser lights, or may split the amplified laser light into five or more branched laser lights. (4) In the above embodiment, one specific branch path 191 is connected to the excitation laser 130 via the splitter 170, but two or more branch paths may be specific branch paths connected to the excitation laser via a splitter. [Explanation of symbols]

[0049] 10: Measuring device 100: Light projector 110: Light source unit 120: Seed laser 130: Pumping laser 140: Optical fiber 141: Input terminal 142: Output terminal 161: Isolator 162: Multiplexer 163: Optical filter 170: Demultiplexer 171: Input port 172, 173, 174, 175: Output port 180: Light projecting optical system 191: Specific branch path 192, 193, 194: Branch path 210: Control circuit board 211: Light projecting control device 221: First current source 222: Second current source 300: Scanning unit 400: Photoreceiver 410: Light receiving optical system 420: Light receiving section 430: TOF measuring device 500: Information processing device 600: Communication interface 700: External device La: Seed laser light Lb: Excitation laser light Lout: Amplified laser light Lout1: Specific branch laser light Lout2, Lout3, Lout4: Branch laser light Lre1, Lre2, Lre3, Lre4: Reflected laser light R1, R2, R3, R4: Branch ratio W: Measurement object

Claims

1. 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 the amplified laser light is output; a demultiplexer optically connected to the output end for demultiplexing the amplified laser beam into a plurality of branched laser beams; an excitation laser that emits excitation laser light that excites the rare earth element; a specific branch path to which a specific branch laser beam, which is one of the plurality of branch laser beams, is input; a multiplexer optically connected to the pump laser and the specific branch path, configured to input the pump laser light to the output end of the optical fiber; Equipped with Floodlight.

2. 2. The floodlight according to claim 1, a branching ratio of the specific branched laser beam is higher than the branching ratios of the other branched laser beams; Floodlight.

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

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