Projector, measuring device, and method for amplifying laser beam

Abstract

To suppress drop of amplification effects of an optical fiber and to suppress drop of an excitation light usage rate.SOLUTION: A projector includes: a seed laser for emitting a seed laser beam; an optical fiber doped with a rare-earth element, the optical fiber receiving input of the seed laser beam emitted from the seed laser; and an excitation laser for emitting excitation light for exciting the rare-earth element of the optical fiber. The projector emits an output laser beam output from the optical fiber, to the outside. The projector is configured to receive input of the excitation light emitted from the excitation laser in a first end part of the optical fiber and output the excitation light from a second end part of the optical fiber, and has a re-input mechanism of inputting the excitation light output from the second end part of the optical fiber, into the optical fiber again.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a light projector, a measurement device, and a method for amplifying laser light. [Background technology]

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

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

[0004] In a conventional floodlight, when attempting to excite a rare earth element over the entire optical fiber from the input to the output, it is necessary to input pumping light with a relatively high optical output that is sufficient for the pumping light to reach the output of the optical fiber to the input of the optical fiber. However, in this case, the pumping light not used to excite the rare earth element leaks out from the output of the optical fiber, and there is a risk of a decrease in the utilization rate of the pumping light for the amplification effect of the optical fiber (hereinafter referred to as the "pumping light utilization rate"). On the other hand, when pumping light with a relatively low optical output that does not reach the output of the optical fiber is input to the input of the optical fiber, it is possible to prevent the pumping light from leaking out from the output of the optical fiber. However, there is a risk of a decrease in the amplification effect of the optical fiber due to insufficient pumping at the output of the optical fiber.

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

[0006] (1) A light projector disclosed in this specification includes a seed laser that emits seed laser light, an optical fiber that is doped with a rare earth element and into which the seed laser light emitted by the seed laser is input, and a pumping laser that emits pumping light that excites the rare earth element in the optical fiber, and emits output laser light output from the optical fiber to the outside. The light projector is configured so that the pumping light emitted by the pumping laser is input to one end of the optical fiber and output from the other end of the optical fiber, and further includes a re-input mechanism that re-inputs the pumping light output from the other end of the optical fiber into the optical fiber.

[0007] In this projector, the pumping light emitted by the pumping laser is input to one end of the optical fiber and output from the other end of the optical fiber, so that the decrease in the amplification effect of the optical fiber is suppressed compared to, for example, a configuration in which the pumping light does not reach the other end of the optical fiber. Also, in this projector, the pumping light output from the other end of the optical fiber is input again to the optical fiber. Therefore, the decrease in the utilization rate of the pumping light for the amplification effect of the optical fiber (hereinafter referred to as the "pumping light utilization rate") is suppressed. In other words, with this projector, it is possible to suppress both the decrease in the amplification effect of the optical fiber and the decrease in the pumping light utilization rate.

[0008] (2) In the above light projector, the re-input mechanism may include a branching element that branches the pumping light from the seed laser light output from the other end of the optical fiber, and a transmission mechanism that guides the pumping light branched by the branching element to the one end side of the optical fiber. According to this light projector, the branching element can be used to suppress both a decrease in the amplification effect of the optical fiber and a decrease in the utilization rate of the pumping light.

[0009] (3) In the above light projector, the re-input mechanism may have a reflecting element that transmits the seed laser light output from the other end of the optical fiber and reflects the pumping light to re-input it to the other end of the optical fiber. According to this light projector, by using a reflecting element, it is possible to simultaneously suppress a decrease in the amplification effect of the optical fiber and a decrease in the utilization rate of the pumping light.

[0010] (4) A measuring device may include the above-mentioned light projector and a light receiver that receives a reflected laser light that is the output laser light emitted by the light projector and reflected back from a measurement target. According to this measuring device, the light projector may be configured to be capable of suppressing both a decrease in the amplification effect of the optical fiber and a decrease in the utilization rate of the pumping light.

[0011] (5) A method for amplifying laser light disclosed in the present specification includes an input step of inputting seed laser light and pumping light into one end of an optical fiber doped with a rare earth element, a branching step of branching the seed laser light and the pumping light output from the other end of the optical fiber, and a re-inputting step of re-inputting the branched pumping light into the optical fiber. This method for amplifying laser light can suppress both a decrease in the amplification effect of the optical fiber and a decrease in the utilization rate of the pumping light.

[0012] The technology disclosed in this specification can be realized in various forms, for example, in the form of a light projector, a measuring device, a method for amplifying laser light, and the like. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device according to an embodiment. [Diagram 2] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a projector. [Diagram 3] FIG. 1 is an explanatory diagram showing a schematic relationship between the optical output of pump light and the state of light entering an optical fiber; [Figure 4] FIG. 13 is an explanatory diagram illustrating a schematic configuration of a floodlight according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A. Embodiment: A-1. Configuration of the measuring device 10: 1 is a block diagram showing a schematic configuration of a measuring device 10 according to the present embodiment. The measuring device 10 is a scan-type LiDAR. The measuring device 10 measures the difference between the timing at which the light projector 20 emits the output laser light Lout and the timing at which the light receiver 30 receives the input laser light Lin (time of flight of the laser light, hereinafter referred to as "TOF" (Time of Flight)), and acquires information about the measuring object W.

[0015] The measuring device 10 is mounted on, for example, a vehicle (not shown) equipped with AD or ADAS. For example, while the vehicle is traveling, the measuring device 10 assists in the detection of objects such as people and other vehicles, and provides various types of information to other devices and users that are useful for ensuring the safety of the driver of the vehicle and those around the vehicle, and for reducing damage to surrounding objects while the vehicle is being driven.

[0016] The measuring device 10 includes a light projector 20, a light receiver 30, a scanner (beam deflector) 40, and a mirror 50.

[0017] The projector 20 includes a fiber laser 22 that outputs an output laser light Lout, and a light-projection control device 26 (see FIG. 2 described later). The light-projection control device 26 controls the emission of the fiber laser 22. The light-projection control device 26 also inputs a signal indicating the timing of light projection at which the fiber laser 22 emits light to a TOF measurement device 36 described later. The light-projection control device 26 periodically and repeatedly emits light from the fiber laser 22, for example, by periodically repeating the on-off control of a current flowing through the fiber laser 22 (a seed laser 110 described later). A detailed configuration of the projector 20 will be described later.

[0018] The scanner 40 has an optical scanning optical system that deflects the optical path (direction) of the output laser light Lout output by the projector 20, and scans the output laser light Lout in a predetermined direction. The scanner 40 has a polygon mirror 42 and a scanning mirror 46 as an optical scanning optical system. The polygon mirror 42 has a plurality of reflecting surfaces 44 (four in FIG. 1), and is a rotating body that is provided so as to be rotatable about a first rotation axis G1. The scanning mirror 46 is provided so as to be rotatable about a second axis G2. The output laser light Lout output by the projector 20 is reflected by a reflecting surface 48 of the scanning mirror 46, reflected by one reflecting surface 44 of the rotating polygon mirror 42, and emitted toward the measurement object W. The input laser light Lin reflected by the measurement object W is again reflected by one reflecting surface 44 of the rotating polygon mirror 42, and reflected by the reflecting surface 48 of the scanning mirror 46.

[0019] The mirror 50 reflects the input laser light Lin reflected by the reflecting surface 48 of the scanning mirror 46 and guides it to the photoreceiver 30. Specifically, the input laser light Lin reflected by the reflecting surface 48 of the scanning mirror 46 is reflected by the reflecting surface 52 of the mirror 50 and heads toward the photoreceiver 30.

[0020] The light receiver 30 includes a light receiving optical system 34, a light receiving section 32, and a TOF measurement device 36.

[0021] The light receiving optical system 34 collects the input laser light Lin to form a spot on the light receiving unit 32. The light receiving optical system 34 is configured using optical components such as various lenses such as a collecting lens, various filters such as a wavelength filter, and a reflecting mirror.

[0022] The light receiving unit 32 is a receiving light source having one or more light receiving elements (not shown), or one or more light receiving element arrays (for example, light receiving elements arranged linearly (one-dimensionally) or planarly (two-dimensionally)). The light receiving elements are, for example, photodiodes, SPADs (Single Photon Avalanche Diodes), balanced photodetectors, etc. The light receiving unit 32 photoelectrically converts the input laser light Lin incident from the light receiving optical system 34 to generate a current corresponding to the intensity of the input laser light Lin (hereinafter referred to as a "light receiving current"). The light receiving unit 32 inputs to the TOF measurement device 36 a signal indicating the light receiving timing at which the light receiving elements constituting the light receiving unit 32 received the input laser light Lin, and the light receiving current generated by the light receiving elements.

[0023] The TOF measurement device 36 obtains the TOF based on a signal indicating the light projection 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 36 has, for example, a time measurement IC (Integrated Circuit) equipped with a TDC (Time to Digital Converter) circuit. The TOF measurement device 36 inputs the obtained TOF and the light reception current input from the light receiving unit 32 to the information processing unit 54.

[0024] With the above configuration, the irradiation position of the output laser light Lout on the measurement object W can be moved in a first scanning direction (e.g., vertical direction on the paper in FIG. 1) according to a change in the rotation angle (θx) accompanying the rotation of the polygon mirror 42, thereby obtaining image information of the measurement object W in the first scanning direction. Also, the irradiation position of the output laser light Lout on the measurement object W can be moved in a second scanning direction (e.g., a direction perpendicular to the first scanning direction, the depth direction on the paper in FIG. 1) according to a change in the rotation angle (θy) accompanying the rotation of the scanning mirror 46, thereby obtaining information of the measurement object W in the second scanning direction.

[0025] The measuring device 10 further includes an information processing unit 54 and a communication I / F (Interface) 56.

[0026] The information processing unit 54 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)). The information processing unit 54 generates information used for various measurements such as detection and distance measurement of the measurement target W based on the light receiving current and TOF input from the TOF measurement device 36. The information is, for example, a histogram used in time correlated single photon counting, a distance to each point of the measurement target W, a point cloud (point cloud information), and the like. The information processing unit 54 also controls the light projection control device 26 and the light receiving unit 32. The information processing unit 54 controls, for example, the light projection control device 26 and the light receiving unit 32 to control the light projection timing and the light receiving timing described above so that the processing for generating the histogram is accelerated or optimized. The information generated by the information processing unit 54 is provided (transmitted) via the communication I / F 56 to a device that uses the information (hereinafter, referred to as "various use devices 60").

[0027] The various utilization devices 60 perform, for example, creating an environmental map using a point cloud, self-position estimation (SLAM (Simultaneous Localization and Mapping)) using a scan matching algorithm (NDT (Normal Distributions Transform), ICP (Iterative Closest Point), etc.), and the like.

[0028] A-2. Configuration of projector 20: Fig. 2 is an explanatory diagram that shows a schematic configuration of the projector 20. As shown in Fig. 2, the projector 20 includes a fiber laser 22, a light projection optical system 24, and the light projection control device 26.

[0029] The projection optical system 24 adjusts the light distribution of the output laser light Lout by, for example, applying an optical effect (such as refraction, scattering, or diffraction) to the light emitted by the fiber laser. The projection optical system 24 is configured using optical components such as various lenses, such as a collimator lens, and a reflector (mirror).

[0030] The fiber laser 22 includes a seed laser 110, a pump laser 120, and an optical fiber F.

[0031] The seed laser 110 emits seed light La having a peak wavelength included in the near-infrared range, for example. In this embodiment, the wavelength of the seed light La is 1550 nm, but is not limited to this and may be, for example, 900 nm.

[0032] The optical fiber F is doped with a rare earth element and passes the seed light La. The optical fiber F is doped with at least one of ytterbium (Yb) and erbium (Er) as the rare earth element. The length of the optical fiber F is, for example, about 5 m.

[0033] The pumping laser 120 emits pumping light Lb (for example, 940 nm) that excites the rare earth element contained in the optical fiber F.

[0034] More specifically, the fiber laser 22 includes a first optical isolator (ISO) 130 , a first wavelength division multiplexer (WDM) 140 , and a second optical isolator 160 .

[0035] The seed laser 110 is optically coupled to the first multiplexer 140 via a normal optical fiber (not shown) that is not doped with a rare earth element. A first optical isolator 130 is provided between the seed laser 110 and the first multiplexer 140. The first multiplexer 140 is coupled to an input portion of an optical fiber F. The output portion of the optical fiber F is optically coupled to a second multiplexer 170, which will be described later. A second optical isolator 160 is provided between the first multiplexer 140 and the second multiplexer. The second multiplexer 170 is coupled to an input portion of an output optical fiber F1 that is not doped with a rare earth element. The output portion of the output optical fiber F1 is directed toward the light projection optical system 24.

[0036] The pump laser 120 is optically coupled to the first multiplexer 140 via a normal optical fiber (not shown) that is not doped with a rare earth element. The first multiplexer 140 multiplexes the seed light La emitted by the seed laser 110 and the pump light Lb from the pump laser 120.

[0037] With this configuration, in the fiber laser 22, the rare earth element in the optical fiber F is excited by the excitation light Lb emitted by the excitation laser 120. The seed light La of the seed laser 110 is incident on the optical fiber F in the excited state, whereby the seed light La is amplified. As a result, a high-power output laser light Lout is output via the projection optical system 24.

[0038] A-3. Re-input mechanism 180 for excitation light Lb: The floodlight 20 of the present embodiment is configured such that the excitation light Lb emitted by the excitation laser 120 is input to an input portion of the optical fiber F and output from an output portion of the optical fiber F. In other words, the optical output of the excitation light Lb emitted by the excitation laser 120 is such that the excitation light Lb input to the input portion of the optical fiber F reaches the output portion of the optical fiber F and is further output from the output portion to the outside. The floodlight 20 includes a re-input mechanism 180 that re-inputs the excitation light Lb output from the output portion of the optical fiber F into the optical fiber F.

[0039] The re-input mechanism 180 has a second multiplexer 170 and a return optical fiber F2. The second multiplexer 170 is an example of a branching element, and the return optical fiber F2 and the first multiplexer 140 are an example of a transmission mechanism.

[0040] The second multiplexer (WDM coupler) 170 separates and outputs multiple light beams (seed light La, pumping light Lb) having different wavelengths output from the optical fiber F. Specifically, the seed light La and the pumping light Lb are multiplexed by the first multiplexer 140, input to the input part of the optical fiber F, and output from the output part of the optical fiber F. The output seed light La and pumping light Lb are demultiplexed by the second multiplexer 170. The demultiplexed seed light La is output to the outside via the projection optical system 24 as output laser light Lout.

[0041] The return optical fiber F2 guides the pumping light Lb demultiplexed by the second multiplexer 170 to the input part of the optical fiber F. Specifically, the input part of the return optical fiber F2 is coupled to the second multiplexer 170, and the output part of the return optical fiber F2 is coupled to the first multiplexer 140. The pumping light Lb demultiplexed by the second multiplexer 170 is guided to the first multiplexer 140 via the return optical fiber F2, and is re-input to the input part of the optical fiber F via the first multiplexer 140. That is, the first multiplexer 140 multiplexes the pumping light Lb regressed via the return optical fiber F2 in addition to the seed light La from the seed laser 110 and the pumping light Lb from the pumping laser 120, and inputs the multiplexed light to the input part of the optical fiber F.

[0042] A-4. Advantages of this embodiment: FIG. 3 is an explanatory diagram that shows a schematic relationship between the optical output of the pumping light Lb and the state of the pumping light Lb entering the optical fiber F. FIG. 3(A) shows an ideal state of the pumping light Lb entering the optical fiber F. The ideal state of the pumping light Lb is a state in which the pumping light Lb reaches the output part of the optical fiber F, the rare earth element is sufficiently excited over the entire length H1 of the optical fiber F, and the pumping light Lb does not leak out from the output part of the optical fiber F. In an ideal state of the light entering, it is possible to suppress both the reduction in the amplification effect of the seed light La (hereinafter simply referred to as the "amplification effect of the seed light La") caused by insufficient pumping and the reduction in the utilization rate of the pumping light Lb with respect to the amplification effect of the optical fiber F (hereinafter simply referred to as the "utilization rate of the pumping light Lb"). However, in reality, it is extremely difficult to adjust the optical output of the pumping light Lb of the pumping laser 120 and the length of the optical fiber F to achieve the ideal state of the light entering.

[0043] 3(B) shows a light-entry state where the optical output of the pump light Lb is insufficient. The light-entry state where the optical output is insufficient is a state where the pump light Lb does not reach the output part of the optical fiber F, and rare earth elements present up to the intermediate length H2 of the optical fiber F are excited. In the light-entry state where the optical output is insufficient, the pump light Lb does not leak out from the output part of the optical fiber F, so that a decrease in the utilization rate of the pump light Lb can be suppressed. However, because the rare earth elements present near the output part of the optical fiber F are not excited, the amplification effect of the seed light La decreases.

[0044] 3(C) shows an excessive optical output entrance state of the pump light Lb. The excessive optical output entrance state is a state in which the pump light Lb reaches the output part of the optical fiber F and further leaks out from the output part of the optical fiber F. In the excessive optical output entrance state, the pump light Lb reaches the output part of the optical fiber F and the rare earth element is sufficiently excited over the entire length H1 of the optical fiber F, so that a decrease in the amplification effect of the seed light La can be suppressed. However, since the pump light Lb leaks out from the output part of the optical fiber F, the utilization rate of the pump light Lb decreases.

[0045] In contrast, in the projector 20 according to the present embodiment, the pumping light Lb emitted by the pumping laser 120 is input to the input section of the optical fiber F and is output from the output section of the optical fiber F. Therefore, according to the present embodiment, the decrease in the amplification effect of the seed light La is suppressed, as compared to, for example, a light-entering state in which the optical output of the pumping light Lb is insufficient (FIG. 3(B)). Also, in the present embodiment, the pumping light Lb output from the output section of the optical fiber F is input again to the optical fiber F (see FIG. 2). Therefore, as compared to, for example, a light-entering state in which the optical output of the pumping light Lb is excessive (FIG. 3(C)), the decrease in the utilization rate of the pumping light Lb is suppressed. That is, according to the present embodiment, it is possible to achieve both the suppression of the decrease in the amplification effect of the seed light La and the suppression of the decrease in the utilization rate of the pumping light Lb without the need for adjustment to achieve an ideal light-entering state of the pumping light Lb (FIG. 3(A)).

[0046] A-5. Modifications of this embodiment: 4 is an explanatory diagram that shows a schematic configuration of a projector 20A in a modified example. The projector 20A according to the modified example has a different configuration of a re-input mechanism from the projector 20 in the above embodiment. The re-input mechanism 180A of the projector 20A has a reflecting element 170A. The reflecting element 170A is disposed opposite to an output portion of an optical fiber F, and transmits the seed light La output from the output portion of the optical fiber F, and reflects the excitation light Lb to re-input it to the output portion of the optical fiber F. The reflecting element 170A is, for example, a reflecting mirror that reflects light in the wavelength band of the excitation light Lb and transmits light in the wavelength band of La.

[0047] Specifically, the seed light La and the excitation light Lb are multiplexed by the first multiplexer 140, input to the input section of the optical fiber F, and output from the output section of the optical fiber F. The output seed light La passes through the reflecting element 170A and is output to the outside as the output laser light Lout via the light projection optical system 24. The output excitation light Lb is reflected by the reflecting element 170A and returned to the optical fiber F. The excitation light Lb returned to the optical fiber F is reused for exciting the rare earth element contained in the optical fiber F.

[0048] According to this embodiment, by using a reflecting element, it is possible to simultaneously suppress a decrease in the amplification effect of the seed light La and a decrease in the utilization rate of the pump light Lb.

[0049] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0050] The configuration of the measuring device 10 in the above embodiment is merely an example, and various modifications are possible. For example, the projector 20 is of a scanning type equipped with the scanner 40, but is not limited to this, and may be of a flash type or the like.

[0051] In the above embodiment, the fiber laser 22 has an optical fiber F and is configured to amplify the seed light La in one stage, but is not limited to this, and may be configured to amplify the seed light La in multiple stages. In the above embodiment, the return optical fiber F2 and the first multiplexer 140 are exemplified as the transmission mechanism, but are not limited to this, and may be configured to guide the pumping light branched by the branching element to the input part or an intermediate part of the optical fiber. For example, an optical system such as multiple reflecting mirrors may be used to guide the pumping light branched by the branching element to the input part or an intermediate part of the optical fiber. In the above embodiment, the second multiplexer 170 (WDM coupler) is exemplified as the branching element, but is not limited to this, and may be, for example, a reflecting mirror that reflects light in the wavelength band of the pumping light Lb and transmits light in the wavelength band of the seed light La.

[0052] 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]

[0053] 10: Measuring device 20, 20A: Light projector 22: Fiber laser 24: Light projecting optical system 26: Light projecting control device 30: Light receiver 32: Light receiving section 34: Light receiving optical system 36: TOF measuring device 40: Scanner 42: Polygon mirror 46: Scanning mirror 50: Mirror 54: Information processing section 56: Communication I / F 60: Utilization device 110: Seed laser 120: Excitation laser 130: First optical isolator 140: First multiplexer 160: Second optical isolator 170: Second multiplexer 170A: Reflection element 180, 180A: Re-input mechanism F1: Output optical fiber F2: Return optical fiber F: Optical fiber La: Seed light Lb: Excitation light W: Measurement object

Claims

1. A light projector comprising: a seed laser that emits seed laser light; an optical fiber that is doped with a rare earth element and into which the seed laser light emitted by the seed laser is input; and an excitation laser that emits excitation light that excites the rare earth element in the optical fiber, the light projector emitting an output laser light output from the optical fiber to the outside, The excitation light emitted by the excitation laser is input to one end of the optical fiber and output from the other end of the optical fiber, The light projector further comprises a re-input mechanism that re-inputs the excitation light output from the other end of the optical fiber into the optical fiber.

2. 2. The floodlight according to claim 1, The re-entry mechanism includes: a branching element that branches the pumping light from the seed laser light output from the other end of the optical fiber; a transmission mechanism that guides the excitation light branched by the branching element to the one end side of the optical fiber.

3. 2. The floodlight according to claim 1, The re-entry mechanism includes: a light projector having a reflecting element that transmits the seed laser light output from the other end of the optical fiber and reflects the pumping light to re-input it into the other end of the optical fiber.

4. A floodlight according to any one of claims 1 to 3; a light receiver that receives a reflected laser light that is the output laser light emitted by the light projector and reflected back from an object to be measured.

5. an input step of inputting the seed laser light and the pumping light into one end of an optical fiber doped with a rare earth element; a branching step of branching the seed laser light and the pumping light outputted from the other end of the optical fiber; and re-inputting the branched pumping light into the optical fiber.

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