Light projector and measuring apparatus

Abstract

To suppress emission of excitation light from an excitation laser to the outside of a light projector.SOLUTION: A light projector includes: an excitation laser for emitting excitation light; a solid crystal arranged on an output side of the excitation laser, the solid crystal being doped with a rare-earth element; and a saturable absorber arranged on an output side of the solid crystal. The light projector further includes a band-pass filter. The band-pass filter is arranged on an output side of the saturable absorber, transmitting emitted light output from the saturable absorber and not transmitting the excitation light.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 AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems), research and development of LiDAR (Light Detection and Ranging) is underway as one of the measurement devices used to grasp the surrounding environment and estimate the vehicle's own position while driving. LiDAR includes a projector that projects (irradiates) laser light onto a measurement target, and a photoreceiver that receives the light reflected from the measurement target. LiDAR outputs information about the measurement target by measuring the distance to the measurement target based on the time difference between the time when the projector emits the laser light and the time when the photoreceiver receives the reflected light (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-183141 [Patent Document 2] Japanese Patent Application Publication No. 2019-029477 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors have been considering using a pumped solid-state laser as the light source for the projector of a measuring device. The pumped solid-state laser includes a pumped laser that emits pumped light, a solid crystal doped with a rare earth element and disposed on the output side of the pumped laser, and a saturable absorber disposed on the output side of the solid crystal. However, in this case, there is a risk of the pumped light leaking outside the projector, leaving room for improvement.

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

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

[0007] (1) A light projector disclosed in this specification includes a pump laser that emits pump light, a solid crystal doped with a rare earth element and disposed on the output side of the pump laser, and a saturable absorber disposed on the output side of the solid crystal. The light projector further includes a bandpass filter disposed on the output side of the saturable absorber, which transmits the output light output from the saturable absorber but does not transmit the pump light. This light projector can prevent the pump light from being output to the outside of the light projector.

[0008] (2) The above light projector may further include a housing that houses the excitation laser, the solid-state crystal, and the saturable absorber, the housing having an opening formed on the output side of the saturable absorber, and the band-pass filter being disposed so as to seal the opening of the housing. With this light projector, the presence of the housing can more effectively prevent the excitation light from being output to the outside of the light projector.

[0009] (3) The above-described light projector may further include a reflecting mirror disposed between the saturable absorber and the band-pass filter, for reflecting a portion of the light directed toward the band-pass filter, and a sensor for detecting a portion of the laser light reflected by the reflecting mirror. This light projector can detect the occurrence of an abnormality that may cause the excitation light to be incident on the band-pass filter while suppressing the excitation light from being output to the outside of the light projector.

[0010] (4) The measuring device may be configured to include the light projector of (1) or (2) above, and a light receiver that receives reflected laser light that is output from the light projector and reflected back from the measurement target. This measuring device can prevent the excitation light from being output to the outside of the light projector.

[0011] The techniques disclosed in this specification can be realized in various forms, for example, in the form of a measuring device, a projector, etc. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device 10 according to a first embodiment. [Figure 2] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a projector 20. [Figure 3] Flowchart showing light projection processing DETAILED DESCRIPTION OF THE INVENTION

[0013] A. Implementation: A-1. Configuration of the measuring device 10: Fig. 1 is a block diagram showing a schematic configuration of a measurement device 10 according to the present embodiment. As shown in Fig. 1, the measurement device 10 includes a projector 20 that irradiates a measurement object W with emitted light L1 (e.g., a light beam (laser light)), and a light receiver 30 that receives reflected light L2 (return light) that is generated when the emitted light L1 is reflected back from the measurement object W, and functions as a LiDAR. The measurement device 10 acquires information about the measurement object W by measuring the difference between the timing at which the projector 20 emits the emitted light L1 and the timing at which the light receiver 30 receives the reflected light L2 (time of flight of the laser light, hereinafter referred to as "TOF" (Time of Flight)).

[0014] The measuring device 10 is mounted on, for example, a vehicle (not shown) equipped with AD or ADAS. For example, while the vehicle is traveling, the measuring device 10 assists in detecting objects such as people and other vehicles, 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] The light projector 20 includes a light source 22, a light projecting optical system 24, a light projecting control device 26, and a current source 28.

[0016] The light source 22 includes a light-emitting source having one or more light-emitting elements (not shown), or one or more light-emitting element arrays (for example, light-emitting elements arranged linearly (one-dimensionally) or planarly (two-dimensionally)). The light-emitting element is, for example, a laser diode, a surface-emitting laser light-emitting element (for example, a VCSEL (Vertical Cavity Surface Emitting Laser), hereinafter referred to as a "surface-emitting element"), a surface-emitting element array (for example, a VCSEL array) in which a plurality of surface-emitting elements are arranged one-dimensionally or two-dimensionally on a substrate (semiconductor substrate, ceramic substrate, etc.), etc.

[0017] The current source 28 supplies a current corresponding to a control signal input from the light projection control device 26 to the light emitting element that constitutes the light source 22. The current source 28 supplies, for example, a periodic square wave current to the light emitting element for turning on and off the current flowing through the light emitting element.

[0018] The light-projection control device 26 generates a control signal for the current source 28 and inputs it to the current source 28, thereby controlling the current (drive current) supplied to the light-emitting element from the current source 28. The light-projection control device 26 inputs a signal indicating the timing at which the light-emitting element emits light (the timing at which the light-emitting element emits light; hereinafter referred to as "emission timing") to the TOF measurement device 40. The light-projection control device 26 periodically controls the on / off of the current flowing through the light-emitting element, for example, to cause the light-emitting element to emit light periodically and repeatedly.

[0019] The light projection optical system 24 adjusts the light distribution of the emitted light L1 by, for example, applying optical effects (such as refraction, scattering, or diffraction) to the light emitted by the light source 22. The light projection optical system 24 is configured using optical components such as various lenses, such as collimating lenses, and reflecting mirrors (mirrors).

[0020] The light receiver 30 includes a light receiving section 32 and a light receiving optical system 34 .

[0021] The light receiving optical system 34 collects reflected light L2, which is light L1 emitted from the projector 20 and reflected by the measurement target W or the like, onto the light receiving unit 32. The light receiving optical system 34 is configured using optical components such as various lenses, including a condensing lens, various filters, including a wavelength filter, and a reflecting mirror.

[0022] The light receiving unit 32 has a plurality of light receiving elements. The light receiving elements are, for example, photodiodes, APDs (Avalanche Photodiodes), SPADs (Single Photon Avalanche Diodes), balanced photodetectors, etc. The light receiving unit 32 performs photoelectric conversion on the reflected light L2 incident from the light receiving optical system 34 to generate a light receiving signal with a current level or voltage level corresponding to the intensity of the reflected light L2. The light receiving unit 32 inputs to the TOF measurement device 40 a signal indicating the timing at which the light receiving elements constituting the light receiving unit 32 receive the reflected light L2 (hereinafter referred to as "light receiving timing"), and the light receiving signal generated by the light receiving elements.

[0023] The measurement device 10 further includes a TOF measurement device 40, a control circuit 42, and a communication I / F (Interface) 50. In this embodiment, the TOF measurement device 40 and the control circuit 42 are an example of a controller.

[0024] The TOF measurement device 40 determines the TOF based on a signal indicating the emission timing input from the light projection control device 26 and a signal indicating the light reception timing input from the light receiving unit 32. The TOF measurement device 40 has, for example, a time measurement IC (Integrated Circuit) equipped with a TDC (Time to Digital Converter) circuit. The TOF measurement device 40 inputs the determined TOF and the light reception signal input from the light receiving unit 32 to the control circuit 42.

[0025] The control circuit 42 has a processor (such as a central processing unit (CPU), a micro processing unit (MPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and a digital signal processor (DSP)). Based on the TOF and the light receiving signal input from the TOF measurement device 40, the control circuit 42 generates information used for various measurements such as detection and distance measurement of the measurement target W. This information includes, for example, a histogram used in time correlated signal photon counting, distances to each point on the measurement target W, and a point cloud (point cloud information). The control circuit 42 also controls the light projection control device 26 and the light receiving unit 32. For example, the control circuit 42 controls the light projection control device 26 and the light receiving unit 32 to control the emission timing and light receiving timing described above so as to speed up or optimize the process for generating the histogram. The information generated by the control circuit 42 is provided (transmitted) via the communication I / F 50 to a device that uses the information (hereinafter referred to as "various use devices 60").

[0026] The various utilization devices 60 perform, for example, creation of an environmental map using a point cloud, self-position estimation (SLAM (Simultaneous Localization and Mapping)) using a scan matching algorithm (NDT (Normal Distributions Transform), ICP (Iterative Closest Point), etc.), etc.

[0027] A-2. Configuration of the projector 20: Fig. 2 is an explanatory diagram that schematically shows the configuration of the projector 20. As shown in Fig. 2, the projector 20 includes an LD-pumped solid-state laser (Diode Pumped Solid State) as a light source. The wavelength of light (emitted light L1) emitted from the LD-pumped solid-state laser is, for example, 1550 nm. Specifically, the projector 20 includes a housing 70, a pumping laser 72, a solid crystal 74, and a saturable absorber 75.

[0028] The housing 70 is a rectangular box, and has an opening 70A formed on one surface facing the measurement target W. The housing 70 is made of a material (e.g., metal) that does not transmit the excitation light L3 (having a wavelength of, for example, 940 nm) emitted by the excitation laser 72. The housing 70 accommodates the excitation laser 72, a solid crystal 74, and a saturable absorber 75.

[0029] The excitation laser 72 is a semiconductor laser that emits excitation light L3. The excitation laser 72 emits the excitation light L3 toward the opening 70A. The light projection control device 26, for example, pulse-drives the excitation laser 72 to repeatedly emit the excitation light L3 at a predetermined cycle (for example, 1 ms).

[0030] The solid-state crystal 74 is disposed on the output side of the pump laser 72. That is, the solid-state crystal 74 is disposed between the pump laser 72 and the opening 70A. The solid-state crystal 74 is doped with a rare earth element. Specifically, the solid-state crystal 74 has a laser crystal 82 and a nonlinear crystal 84. The output surface of the laser crystal 82 and the input surface of the nonlinear crystal 84 are in contact with each other. The laser crystal 82 is made of, for example, Nd:YVO4 or Yb:YAG. The nonlinear crystal 84 is made of, for example, KTP or BBP. A first reflective film 80A is formed on the input surface of the solid-state crystal 74 (laser crystal 82), and a second reflective film 80B is formed on the output surface of the solid-state crystal 74 (nonlinear crystal 84).

[0031] The saturable absorber 75 (Q switch) is disposed on the output side of the solid crystal 74. That is, the saturable absorber 75 is disposed between the solid crystal 74 and the opening 70A. The saturable absorber 75 does not transmit light with an intensity below a threshold (for example, the excitation light L3 with a wavelength of 940 nm) but transmits light with an intensity equal to or greater than the threshold (for example, the emitted light L1 with a wavelength of 1550 nm).

[0032] With the above configuration, the LD-pumped solid-state laser operates as follows. When pumping light L3 from the pumping laser 72 is incident on the incident surface of the solid-state crystal 74, it excites the rare-earth element doped in the solid-state crystal 74. Then, stimulated emission is generated, triggered by spontaneous emission. The generated stimulated emission light is amplified by repeatedly reflecting between the first reflecting film 80A and the second reflecting film 80B and traveling back and forth within the solid-state crystal 74. When the intensity of the amplified light reaches or exceeds the threshold, the saturable absorber 75 emits output light L1 toward the opening 70A.

[0033] The projector 20 further includes a first bandpass filter 71. The first bandpass filter 71 is disposed on the output side of the saturable absorber 75. Specifically, the first bandpass filter 71 is disposed so as to seal the opening 70A of the housing 70. The first bandpass filter 71 transmits the output light L1 (for example, light in a first frequency band including 1550 nm) output from the saturable absorber 75, and absorbs and does not transmit the excitation light L3 (for example, light in a second frequency band lower than the first frequency band). The first bandpass filter 71 is an example of a bandpass filter.

[0034] The housing 70 further houses a reflecting mirror 76 , a sensor 78 and a second bandpass filter 73 .

[0035] The reflecting mirror 76 is disposed on the optical path of the output light L1 between the saturable absorber 75 and the first bandpass filter 71. The reflecting mirror 76 reflects a portion of the light (hereinafter referred to as "partial light L1a") heading toward the first bandpass filter 71 and transmits the remaining light. The reflecting mirror 76 is, for example, a one-way mirror (mirror glass, half mirror) or a partial mirror that is made entirely of a light-transmitting material and has a mirror-finished surface or the like on part of the area where light enters.

[0036] The second bandpass filter 73 is disposed on the optical path of the partial light L1a between the reflecting mirror 76 and the sensor 78. The second bandpass filter 73 absorbs and does not transmit the emitted light L1 (e.g., light in a first frequency band including 1550 nm), but transmits the excitation light L3 (e.g., light in a second frequency band lower than the first frequency band). The sensor 78 is a light-receiving sensor that detects the excitation light L3 that has passed through the second bandpass filter 73. The sensor 78 has a light-receiving element such as a photodiode, and outputs a detection signal indicating the timing at which the excitation light L3 is received to the control circuit 42.

[0037] A-3. Light projection processing: Fig. 3 is a flowchart showing the light projection process. When the control circuit 42 receives an instruction to start measurement from, for example, the utilization device 60, it starts the light projection process shown in Fig. 3. The control circuit 42 determines whether the emission timing has arrived (S110). The emission timing is a timing that is repeated at predetermined time intervals. If the control circuit 42 determines that the emission timing has not arrived (S110: NO), it waits as is. If the control circuit 42 determines that the emission timing has arrived (S110: YES), it controls the light projection control device 26 to cause the excitation laser 72 to start emitting the excitation light L3 (S120).

[0038] During the operation of emitting the excitation light L3 by the excitation laser 72, the control circuit 42 determines whether or not the excitation light L3 has been detected based on the presence or absence of a light reception signal from the sensor 78 (S130). When the control circuit 42 determines that the excitation light L3 has not been detected (S130: NO), it continues the operation of emitting the excitation light L3 by the excitation laser 72 and proceeds to S150.

[0039] For example, if the solid crystal 74 or the saturable absorber 75 is displaced or falls off, or a crack occurs in the solid crystal 74 inside the housing 70, the excitation light L3 from the excitation laser 72 will be directed directly toward the opening 70A without passing through the solid crystal 74 or the saturable absorber 75. In such a case, the excitation light L3 from the excitation laser 72 passes through the reflecting mirror 76 and the second band-pass filter 73 and enters the sensor 78. At this time, the control circuit 42 determines that the excitation light L3 has been detected (S130: YES), stops the excitation laser 72 from emitting the excitation light L3, and proceeds to S150. At this time, the control circuit 42 may externally output to the utilization device 60 that the excitation light L3 has been detected. Alternatively, the control circuit 42 may prohibit the excitation laser 72 from emitting the excitation light L3 even when the next emission timing arrives.

[0040] In S150, the control circuit 42 determines whether the time to turn off the light has arrived. If the control circuit 42 determines that the time to turn off the light has not arrived (S150: NO), the process returns to S130. If the control circuit 42 determines that the time to turn off the light has arrived (S150: YES), the control circuit 42 controls the light projection control device 26 to stop the excitation laser 72 from emitting the excitation light L3 (S160), and the process returns to S110.

[0041] A-4. Advantages of this embodiment: As described above, according to the measurement device 10 of this embodiment, in the projector 20, the first bandpass filter 71 is arranged on the output side of the saturable absorber 75. Therefore, even when the excitation light L3 from the excitation laser 72 travels directly toward the opening 70A without passing through the solid crystal 74 or the saturable absorber 75, it is possible to prevent the excitation light L3 from being emitted outside the projector 20.

[0042] In this embodiment, the excitation laser 72, the solid crystal 74, and the saturable absorber 75 are housed in a housing 70, and a first bandpass filter 71 is arranged to seal an opening 70A of the housing 70. Therefore, the presence of the housing 70 can more effectively prevent the excitation light L3 from being emitted outside the projector 20.

[0043] In this embodiment, the projector 20 further includes a reflecting mirror 76, a sensor 78, and a second band-pass filter 73. Therefore, it is possible to detect the occurrence of an abnormality in which the excitation light L3 may be incident on the first band-pass filter 71 while suppressing the emission of the excitation light L3 to the outside of the projector 20.

[0044] B. Variations: 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.

[0045] The configuration of the measuring device 10 in the above embodiment is merely an example and can be modified in various ways. For example, the projector 20 is of a flash type, but is not limited to this, and may be of a scanning type equipped with a scanner.

[0046] In the above embodiment, the first bandpass filter 71 may be disposed inside the housing 70. The projector 20 may not include the second bandpass filter 73, and the reflecting mirror 76 may be a mirror that transmits the emitted light L1 (for example, light in a first frequency band including 1550 nm) and reflects the excitation light L3 (for example, light in a second frequency band lower than the first frequency band). The projector 20 may not include the reflecting mirror 76, the second bandpass filter 73, and the sensor 78.

[0047] In the above embodiment, the materials used to form the components are merely examples, and the components may be formed from other materials. [Explanation of symbols]

[0048] 10: Measuring device 20: Light emitter 22: Light source 24: Light-emitting optical system 26: Light-emitting control device 28: Current source 30: Light receiver 32: Light-receiving section 34: Light-receiving optical system 40: TOF measuring device 42: Control circuit 50: Communication I / F 60: Utilizing device 70: Housing 70A: Opening 71: First band-pass filter 72: Excitation laser 73: Second band-pass filter 74: Solid crystal 75: Saturable absorber 76: Reflecting mirror 78: Sensor 80A: First reflecting film 80B: Second reflecting film 82: Laser crystal 84: Nonlinear crystal L1: Emitted light L1a: Partial light L2: Reflected light L3: Excitation light W: Measurement object

Claims

1. an excitation laser that emits excitation light; a solid crystal doped with a rare earth element, the solid crystal being disposed on the output side of the pump laser; a saturable absorber disposed on the output side of the solid-state crystal, The light projector further comprises a bandpass filter disposed on the output side of the saturable absorber, the bandpass filter transmitting the emitted light output from the saturable absorber but not transmitting the excitation light.

2. 2. The floodlight according to claim 1, The present invention further includes a housing that houses the pump laser, the solid-state crystal, and the saturable absorber, the housing having an opening formed on an output side of the saturable absorber, The bandpass filter is disposed so as to seal the opening of the housing.

3. 3. The floodlight according to claim 1 or 2, a reflecting mirror disposed between the saturable absorber and the bandpass filter, for reflecting a portion of light directed toward the bandpass filter; a sensor that detects a portion of the laser light reflected by the reflecting mirror.

4. The floodlight according to claim 1 or 2; a light receiver that receives reflected laser light that is output from the light projector and reflected back from the object to be measured.

Images