Optical scanner module and wind speed detection device

Abstract

An optical scanner module 7 comprises: a lens optical system 22 that controls the condensed state of a light beam which is input light; and a reflection type optical scanner 23 that has a rotating stage 31 in which a rotation axis K1 is inclined at an angle β with respect to the optical axis of the light beam from the lens optical system 22, and a mirror unit 32 in which a mirror 34 is held with respect to the rotating stage 31 so as to be inclined at an angle α with respect to a rotating surface 31a of the rotating stage 31, the optical scanner causing the optical axis, of a light beam reflected by the mirror 34, to rotate at a beam deflection angle θ as a result of rotation of the rotating stage 31.

Description

Optical scanner module and wind velocity detection device

[0001] The present disclosure relates to an optical scanner module and a wind velocity detection device.

[0002] As one of sensing technologies using light, LIDAR (Light Detection and Ranging) is known. In recent years, LIDAR has been increasingly applied in the field of autonomous driving, but it is originally a technology widely used in fields such as meteorology. As LIDAR used in the field of meteorology, so-called WindLIDAR that detects wind velocity is known. WindLIDAR is used, for example, for wind condition surveys to select installation sites for wind power generators. In recent years, application to safe operation management of unmanned aerial vehicles such as drones, and manned aircraft such as AAM (Advanced Air Mobility) or UAM (Urban Air Mobility) is expected.

[0003] Coherent detection is used for wind velocity detection by LIDAR. In this method, laser light output from a light source is split into measurement light and reference light, the measurement light is modulated and amplified, and then emitted into the atmosphere. The signal source in WindLIDAR is scattered light generated by scattering of measurement light by countless aerosols in the atmosphere. When wind blows, aerosols move with the wind, and the frequency of the scattered light changes (Doppler shift). Therefore, by taking scattered light from the atmosphere as signal light and causing it to interfere with reference light, and obtaining the shift amount of the peak frequency in the beat spectrum of the interference light, the wind velocity in the atmosphere can be detected (see, for example, Non-Patent Documents 1 and 2).

[0004] In wind velocity detection by LIDAR, a method of emitting measurement light in different directions toward the atmosphere by using an optical scanner module is employed. In wind velocity detection by LIDAR, the wind velocity and wind direction in the optical axis direction of the measurement light can be measured. By scanning the azimuth angle of the measurement light using an optical scanner module, the wind velocity and wind direction in a plane orthogonal to the optical axis direction of the measurement light can be calculated from the measurement results, and a three-dimensional wind velocity vector at a predetermined measurement point can be acquired.

[0005] S. Kameyama et al., “Compact all-fiber pulsed coherent Doppler lidar system for wind sensing” Applied Optics, Vol. 46, NO.11, 10 April 2007, p.1953-1962Andreu Salcedo-Bosch et al., “Enhanced Dual Filter for Floating Wind Lidar Motion Correction: The Impact of Wind and Initial Scan Phase Models” Remote Sens.2022, 14, 4704

[0006] In LiDAR-based wind speed detection, a so-called transmissive optical scanner module is sometimes used, which transmits the measurement light through a polarizing beam splitter. When such a transmissive optical scanner module is used for LiDAR-based wind speed detection, it is not a problem for general long-distance measurements, but for short-distance measurements of 100m or less, for example, astigmatism caused by the prism becomes large enough to be considered significant.

[0007] If significant astigmatism occurs in the measurement light, the energy density of the measurement light at the measurement point decreases, which can lead to a decrease in the intensity of the signal light from the atmosphere. A decrease in the intensity of the signal light reduces the signal-to-noise ratio, making high-speed measurements difficult. For example, in the context of safe operation management of manned aircraft as described above, it is necessary to accurately measure the turbulent components of rapidly changing winds in short-range measurements in urban areas, and therefore, optical scanner modules and wind speed measuring devices that enable such measurements are desired.

[0008] This disclosure was made to solve the above-mentioned problems and aims to provide an optical scanner module and a wind speed detection device that enable high-speed measurement of wind speed at short distances.

[0009] The gist of this disclosure is as follows:

[0010] [1] A reflective optical scanner module comprising: a lens optical system for controlling the focusing state of an input light beam; a rotating stage whose rotation axis is inclined at an angle β with respect to the optical axis of the light beam from the lens optical system; and a mirror unit that holds a mirror relative to the rotating stage so as to be inclined at an angle α with respect to the rotation plane of the rotating stage, wherein the rotation of the rotating stage rotates the optical axis of the light beam reflected by the mirror by a beam deflection angle θ.

[0011] This optical scanner module is a so-called reflective type optical scanner module that reflects the light beam from the lens optical system using a mirror on a rotating stage. In a reflective optical scanner module, the light beam does not pass through a prism, thus avoiding the effects of astigmatism caused by the prism. By using this optical scanner module for wind speed detection using LIDAR, it is possible to acquire signal light from the atmosphere with sufficient intensity even at short distances of, for example, less than 100m. Therefore, a sufficient signal-to-noise ratio can be ensured, enabling high-speed wind speed measurement. In addition, in this optical scanner module, if the angle of the mirror with respect to the rotation surface of the rotating stage is α, the beam deflection angle θ of the light beam reflected by the mirror is θ = 2 × α. Therefore, the desired beam deflection angle θ can be obtained by adjusting the angle of the mirror.

[0012] [2] The optical scanner module according to [1], wherein the mirror unit has a cutout portion that is eccentric with respect to the rotation axis of the rotating stage, such that the center of gravity of the mirror unit coincides with the rotation axis of the rotating stage. This configuration makes it possible to improve the stability of the mirror when the rotating stage is rotated.

[0013] [3] The optical scanner module according to [1] or [2], wherein the mirror unit comprises a first holding portion having a first fixed surface fixed to the rotating surface of the rotating stage and a first inclined surface inclined at a first angle ω1 with respect to the first fixed surface, and a second holding portion having a second fixed surface detachably fixed to the first fixed surface and a second inclined surface inclined at a second angle ω2 different from the first angle ω1 with respect to the second fixed surface. In this case, a desired beam deflection angle θ can be obtained by adjusting the rotation angle around the rotation axis when fixing the second holding portion to the first holding portion, without having to prepare a mirror unit for each angle α.

[0014] [4] An optical scanner module according to any one of [1] to [3], further comprising a circulator that guides the light beam, which is the input light, to the lens optical system, while outputting the reflected light generated by the light beam reflected by the mirror to a path different from that of the input light. This makes it possible to easily separate the measurement light and the signal light when this optical scanner module is used for wind speed detection using LIDAR.

[0015] [5] A wind speed detection device comprising: an output unit that outputs a light beam as measurement light; an optical scanner module according to any one of [1] to [4] that uses the measurement light as the input light, outputs the light beam of the measurement light into the atmosphere while rotating it with a beam deflection angle θ, and receives the reflected light from the atmosphere generated by the output of the measurement light as signal light; a detection unit that detects the signal light and outputs a detection signal based on the detection result; and an analysis unit that calculates the amount of Doppler shift of the signal source in the atmosphere based on the detection signal and analyzes the wind speed in the atmosphere based on the amount of Doppler shift.

[0016] This wind speed detection device, by using the aforementioned optical scanner module, enables the measurement of high wind speeds at short distances.

[0017] According to this disclosure, it will be possible to measure wind speed at high speeds over short distances.

[0018] (a) and (b) are schematic diagrams showing an example of an aircraft control device incorporating a wind speed detection device according to one embodiment of the present disclosure. This is a schematic diagram of a wind speed detection device according to one embodiment of the present disclosure. This is a schematic diagram showing an example of the configuration of an optical scanner module. This is a perspective view showing an example of the configuration of a reflective optical scanner. This is a cross-sectional view of the reflective optical scanner shown in Figure 4. (a) and (b) are schematic diagrams showing an example of the configuration of an optical scanner module according to a modified example. This is a perspective view showing an example of the configuration of a reflective optical scanner according to a modified example. This is a cross-sectional view of the reflective optical scanner shown in Figure 7. This is a perspective view showing an example of beam deflection angle adjustment in a reflective optical scanner according to a modified example.

[0019] Hereinafter, with reference to the drawings, preferred embodiments of an optical scanner module and an air velocity detection device relating to one aspect of this disclosure will be described in detail.

[0020] Figures 1(a) and 1(b) are schematic diagrams showing an example of an aircraft control device incorporating a wind speed detection device according to one embodiment of the present disclosure. As shown in Figures 1(a) and 1(b), the aircraft control device 101 comprises a wind speed detection device 1 and a control device 102 that controls the operation of the aircraft H based on a detection signal D (see Figure 2) output from the wind speed detection device 1. Examples of aircraft H include unmanned aircraft such as drones, and manned aircraft such as AAMs (Advanced Air Mobility) or UAMs (Urban Air Mobility).

[0021] The aircraft control device 101 is installed, for example, near the ground surface. The installation height of the aircraft control device 101 is assumed to be, for example, the atmospheric layer called the ground layer. The ground layer refers to the atmospheric layer at a height of 100m or less from the ground surface, where the vertical gradient of wind speed and temperature is particularly large. The aircraft control device 101 may be installed on the ground surface, for example, as shown in Figure 1(a). The aircraft control device 101 may be installed on the roof or roof of a building, such as a building, as shown in Figure 1(b). The aircraft control device 101 may be incorporated as a device in the control tower that operates the aircraft H.

[0022] The wind speed detection device 1 is a device that detects the wind speed in the atmosphere. In the aircraft control device 101, the wind speed detection device 1 detects complex turbulence caused in particular by many structures near the ground and outputs a detection signal D to the control device 102. The control device 102 is a device that generates control signals Q related to the takeoff and landing of the aircraft H. Physically, the control device 102 is a computer system equipped with memory such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, a storage unit such as a hard disk, and a display unit such as a display. Based on the detection signal D from the wind speed detection device 1, the control device 102 outputs control signals Q to the aircraft H, for example, regarding the speed during takeoff and landing of the aircraft H, the travel path, or permission / prohibition of takeoff and landing.

[0023] The wind speed detection device 1 may transmit the detection signal D to a server owned by the weather information provider. In this case, for example, the weather information provider may make a weather forecast based on the detection signal D and weather data transmitted to the server, and transmit the generated weather forecast information from a terminal device or the like to the aircraft control device 101 in the control tower. The aircraft control device 101 in the control tower may generate a control signal Q based on the weather forecast information. The wind speed detection device 1 may also transmit the detection signal D directly to the aircraft control device 101 in the control tower.

[0024] Next, the wind speed detection device 1 described above will be explained in detail. The wind speed detection device 1 is a device that detects wind speed in the atmosphere M using LIDAR (Light Detection and Ranging). The wind speed detection device 1 uses pulsed laser light Lm as measurement light and detects wind speed in the atmosphere M by performing coherent detection using signal light Ls and reference light Lr. In this embodiment, for example, in the short-range detection area where the detection distance is 100 m or less, the wind speed detection device 1 performs wind speed detection using a pulse focusing method, and in the long-range detection area where the detection distance exceeds 100 m, it performs wind speed detection using a pulse collimation method.

[0025] Figure 2 is a schematic diagram of a wind speed detection device according to one embodiment of the present disclosure. As shown in Figure 2, the wind speed detection device 1 includes an output unit 2, a branching unit 3, a frequency shifter 4, a first amplification unit 5, a second amplification unit 6, an optical scanner module 7, a multiplexing unit 8, a detection unit 9, a digitizer 10, an analysis unit 11, and a control unit 15. In this embodiment, the output unit 2 and the branching unit 3, the branching unit 3 and the frequency shifter 4, the frequency shifter 4 and the first amplification unit 5, the first amplification unit 5 and the second amplification unit 6, the second amplification unit 6 and the optical scanner module 7, the optical scanner module 7 and the multiplexing unit 8, the branching unit 3 and the multiplexing unit 8, and the multiplexing unit 8 and the detection unit 9 are all optically connected by an optical fiber F.

[0026] In the wind speed detection device 1, at least the output unit 2, branching unit 3, and detection unit 9 are composed of a photonic integrated circuit (PIC) 12. In this embodiment, the output unit 2, branching unit 3, frequency shifter 4, first amplification unit 5, second amplification unit 6, multiplexing unit 8, detection unit 9, and the optical fiber F connecting them are all composed of a photonic integrated circuit 12.

[0027] The output unit 2 is the part that outputs laser light L. Examples of laser devices that constitute the output unit 2 include distributed feedback (DFB) laser devices, dispersed Bragg reflection (DBR) laser devices, and external resonant laser devices. Here, the laser light L output from the output unit 2 is continuous wave (CW) light. The laser light L is not diffuse light, but a beam of light (optical beam) with a certain directivity.

[0028] The output unit 2 is connected to a current control unit and a temperature control unit (not shown). The current control unit is a controller that supplies drive current to the laser device that constitutes the output unit 2. The current control unit modulates the frequency of the laser light L output from the output unit 2 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the laser device that constitutes the output unit 2. The temperature control unit is composed of, for example, a thermistor and a Peltier element, and drives the Peltier element to maintain a constant temperature of the laser device based on the temperature measurement value of the thermistor attached to the laser device.

[0029] The signal generation unit 13 is connected to the output unit 2. The signal generation unit 13 is the part that generates a modulation signal G for the laser light L. The signal generation unit 13 is composed of, for example, a waveform generator, a function generator, etc. The signal generation unit 13 generates a voltage signal for modulating the current waveform output from the current control unit connected to the output unit 2 into an arbitrary shape. The modulation signal G generated by the signal generation unit 13 is also output to the digitizer 10 in order to synchronize the operation of the output unit 2 and the operation of the analysis unit 11.

[0030] The branching section 3 is the part that splits the laser light L from the output section 2 into a measurement light Lm and a reference light Lr. The branching section 3 is composed of, for example, an optical fiber coupler. The measurement light Lm is output to the frequency shifter 4 from one output port of the branching section 3, and the reference light Lr is output to the multiplexing section 8 from another output port of the branching section 3. The reference light Lr is input to the multiplexing section 8 as CW light.

[0031] In this embodiment, a delay fiber 16 is connected between the branching section 3 and the multiplexing section 8. The delay fiber 16 is composed of, for example, a polarization-maintaining fiber or a fiber coil. The delay fiber 16 can adjust the optical path length difference between the signal light Ls and the reference light Lr input to the multiplexing section 8. By reducing the optical path length difference between the signal light Ls and the reference light Lr, the Phase Induced Intensity Noise (PIIN) is reduced.

[0032] The frequency shifter 4 is the part that shifts the frequency of the measurement light Lm. The frequency shifter 4 is composed of, for example, an acousto-optic element, an electro-optic element, an IQ modulator, a phase modulator, an intensity modulator, etc. The frequency shifter 4 may have a signal generation unit (not shown) that generates a voltage signal for driving the frequency shifter 4. The signal generation unit may be composed of, for example, a waveform generator, a function generator, etc.

[0033] By shifting the frequency of the measurement light Lm using the frequency shifter 4, it becomes possible to determine the wind direction in the optical axis direction of the measurement light Lm. If the frequency of the measurement light Lm is not shifted, the beat spectrum of the interference light Ld (described later) shifts to a higher frequency relative to the reference beat spectrum (beat spectrum when there is no wind) according to the wind speed, regardless of the wind direction. On the other hand, if the frequency of the measurement light Lm is shifted, the beat spectrum of the interference light Ld (described later) shifts to a lower frequency relative to the reference beat spectrum if the wind is blowing in the positive direction relative to the optical axis of the measurement light Lm (tailwind), and shifts to a higher frequency relative to the reference beat spectrum if the wind is blowing in the negative direction relative to the optical axis of the measurement light Lm (headwind). Therefore, by shifting the frequency of the measurement light Lm using the frequency shifter 4, both the wind speed and wind direction in the optical axis direction of the measurement light Lm can be suitably detected.

[0034] The first amplification unit 5 is the part that converts the measurement light Lm from the branching unit 3 into pulsed light. The first amplification unit 5 is composed of, for example, a semiconductor optical amplifier, an optical fiber amplifier, etc. The first amplification unit 5 converts the measurement light Lm, which is CW light, into pulsed light by amplifying a specific component of the measurement light Lm. A current control unit and a temperature control unit (not shown) are connected to the first amplification unit 5. The current control unit is a controller that supplies drive current to the amplification device that constitutes the first amplification unit 5. The current control unit controls the amplification rate of the measurement light Lm in the first amplification unit 5 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the amplification device that constitutes the first amplification unit 5. The temperature control unit is composed of, for example, a thermistor and a Peltier element, and drives the Peltier element to maintain a constant temperature of the amplification device based on the temperature measurement value of the thermistor attached to the amplification device. It is also possible to convert the measurement light Lm, which is CW light, into pulsed light by frequency shifting a specific component of the measurement light Lm using the frequency shifter 4 described above.

[0035] The measurement light Lm is generated by converting the CW laser light L output from the output unit 2 into pulsed light using the frequency shifter 4, the first amplification unit 5, or both. The measurement light Lm is light whose intensity rises intermittently on the time axis with a pulse width Δt. When the output unit 2 outputs frequency-modulated light as the laser light L, light with linearly and periodically modulated frequency can be used as the measurement light Lm. The measurement light Lm may be modulated in a way that creates a ramp waveform, with an UP ramp where the frequency gradually increases linearly and a DOWN ramp where the frequency gradually decreases linearly alternating with each pulse.

[0036] The second amplification unit 6 is the part that amplifies the intensity of the pulsed measurement light Lm. The second amplification unit 6 is composed of, for example, a semiconductor optical amplifier, an optical fiber amplifier, etc. A current control unit and a temperature control unit (not shown) are connected to the second amplification unit 6. The current control unit is a controller that supplies drive current to the amplification device that constitutes the second amplification unit 6. The current control unit controls the amplification rate of the measurement light Lm in the second amplification unit 6 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the amplification device that constitutes the second amplification unit 6. The temperature control unit is composed of, for example, a thermistor and a Peltier element, and drives the Peltier element to maintain a constant temperature of the amplification device based on the temperature measurement value of the thermistor attached to the amplification device.

[0037] The optical scanner module 7 outputs measurement light Lm into the atmosphere M and receives the scattered light Lf of the measurement light Lm in the atmosphere M as signal light Ls. The configuration of the optical scanner module 7 will be described later. In the optical scanner module 7, the measurement light Lm emitted from the optical fiber F on the output side of the second amplification unit 6 is emitted into the atmosphere M in the form of an optical beam with a certain directionality. The signal source in the wind speed detection device 1 is the scattered light Lf generated when the measurement light Lm is scattered by countless aerosols P in the atmosphere M. A portion of the scattered light Lf returns to the optical scanner module 7, is separated from the measurement light Lm, and is output to the wave multiplexing unit 8.

[0038] The multiplexing section 8 is the part that combines the reference light Lr from the branching section 3 with the signal light Ls that has returned from the atmosphere M. The multiplexing section 8 is composed of, for example, an optical fiber coupler. The multiplexing section 8 generates interference light Ld from the reference light Lr and the signal light Ls. The interference light Ld is output from the output port of the multiplexing section 8 to the detection section 9.

[0039] The detection unit 9 is the part that outputs a detection signal D based on the interference result between the reference light Lr and the signal light Ls. In this embodiment, since the measurement light Lm is pulsed light, the scattered light Lf (signal light Ls) generated by the scattering of the measurement light Lm at a specific distance is also pulsed light. On the other hand, the reference light Lr is a part of the laser light L from the output unit 2 that is branched at the branching unit 3, and is CW light. Therefore, in the pulse focusing method, the detection unit 9 outputs a detection signal D based on the interference result between the reference light Lr, which is CW light, and the signal light Ls, which is pulsed light. In the pulse collimation method, the detection unit 9 outputs a detection signal D based on the interference result between the reference light Lr, which is CW light, and the signal light Ls, which is a temporal superposition of multiple pulsed lights.

[0040] The detection unit 9 is composed of, for example, a photodetector, an avalanche photodiode, a balance detector, etc. The detection unit 9 outputs an analog electrical signal based on the intensity of the interference light Ld input from the multiplexing unit 8 as a detection signal D to the digitizer 10. The digitizer 10 is a device that converts analog electrical signals into digital signals. The digitizer 10 is composed of, for example, an A / D converter, etc. The digitizer 10 converts the detection signal D, which is an analog electrical signal, into a digital signal and outputs the converted digital signal to the analysis unit 11.

[0041] The analysis unit 11 is the part that analyzes the wind speed in the atmosphere M based on the detected signal D. Physically, the analysis unit 11 is a computer system equipped with memory such as RAM and ROM, a processor such as a CPU and GPU, a communication interface, and a storage unit such as a hard disk. Examples of such a computer system include personal computers, cloud servers, smart devices (smartphones, tablet terminals, etc.), microcomputers, and FPGAs (field-programmable gate arrays). This computer system functions as the analysis unit 11 by executing a program stored in memory using the CPU or GPU.

[0042] As described above, the signal source in the wind speed detection device 1 is scattered light Lf, which is generated when the measurement light Lm is scattered by countless aerosols P in the atmosphere M. When wind blows in the atmosphere M, the aerosols P move with the wind, and the frequency of the scattered light Lf changes (Doppler shift). When the analysis unit 11 receives the detection signal D output from the digitizer 10, it refers to the peak frequency of the beat spectrum of the interference light Ld based on the detection signal D. The analysis unit 11 detects the wind speed in the atmosphere M by determining the amount of Doppler shift of the peak frequency of the beat spectrum of the interference light Ld.

[0043] The control unit 15 controls the state of the measurement light Lm output from the optical scanner module 7 based on the detection distance by the measurement light Lm. Similar to the analysis unit 11, the control unit 15 is physically a computer system equipped with memory such as RAM and ROM, a processor such as a CPU and GPU, a communication interface, and storage such as a hard disk. Examples of such computer systems include personal computers, cloud servers, smart devices (smartphones, tablet terminals, etc.), microcomputers, and FPGAs (field-programmable gate arrays). This computer system functions as the control unit 15 by executing a program stored in memory using the CPU or GPU. The analysis unit 11 and the control unit 15 may be configured using the same computer system.

[0044] The control unit 15 receives an input of a detection distance setting for the measurement light Lm. The control unit 15 controls the state of the measurement light Lm output from the optical scanner module 7 based on the input detection distance setting. In the present embodiment, a threshold for the detection distance is set. The control unit 15 controls the optical scanner module 7 such that the measurement light Lm output into the atmosphere M is condensed when the detection distance belongs to a short-distance range equal to or less than the threshold. The control unit 15 controls the optical scanner module 7 such that the measurement light Lm output into the atmosphere M is collimated when the detection distance belongs to a long-distance range exceeding the threshold.

[0045] Next, the above-described optical scanner module 7 will be described in further detail.

[0046] FIG. 3 is a schematic diagram showing the configuration of the optical scanner module. As shown in FIG. 3, the optical scanner module 7 includes a spatial optical system type circulator 21, a lens optical system 22, and a reflective optical scanner 23. The circulator 21 guides an input light beam, which is input light, to the lens optical system 22, and outputs return light generated by the light beam reflected by the reflective optical scanner 23 to a path different from that of the input light. Here, the input light is the measurement light Lm emitted from the optical fiber F on the output side of the second amplification unit 6. Further, the return light is scattered light Lf generated when the measurement light Lm is scattered by countless aerosols P in the atmosphere M (see FIG. 2).

[0047] The circulator 21 is configured by a polarizing beam splitter 24 and a λ / 4 wavelength plate 25. An input lens 26 is arranged on the input side of the polarizing beam splitter 24 (between the optical fiber F on the output side of the second amplification unit 6 and the polarizing beam splitter 24). The λ / 4 wavelength plate 25 is arranged on one output side of the polarizing beam splitter 24. An output lens 27 is arranged on the other output side of the polarizing beam splitter 24 (between the optical fiber F on the input side of the detection unit 9 and the polarizing beam splitter 24).

[0048] In order to stabilize the performance of the circulator 21, control may be performed by a temperature control unit (not shown) such that the overall temperature of the circulator 21 is kept constant. The temperature control unit is configured to include, for example, a thermistor and a Peltier element, and drives the Peltier element based on the temperature measurement value of the thermistor attached to the circulator 21 so that the overall temperature of the circulator 21 is maintained constant.

[0049] The lens optical system 22 is an optical system that controls the condensing state of an input light beam. The lens optical system 22 is configured to include a condensing state adjustment unit 28. The condensing state adjustment unit 28 includes a pair of lenses 29A, 29B and a movable stage 30. Among the pair of lenses 29A, 29B, the lens 29A arranged on the preceding stage (the circulator 21 side) is mounted on the movable stage 30. The movable stage 30 is a stage having a movable shaft at least in the optical axis direction of the measurement light Lm. For driving the movable stage 30, for example, a driving element such as a stepping motor or a piezo element is used. A stage controller (not shown) is connected to the movable stage 30. The stage controller outputs a control signal for controlling the position of the movable stage 30 to the driving element.

[0050] Among the pair of lenses 29A, 29B, the lens 29B arranged on the subsequent stage (the reflective optical scanner 23 side) is a lens that outputs the measurement light Lm into the atmosphere M. As the lenses 29A, 29B, for example, a convex lens, an achromatic lens, an aspherical lens, a combined lens formed by combining a plurality of lenses, or the like is used. The lenses 29A, 29B function as a lens pair constituting a telescope. When the movable stage 30 is displaced in the optical axis direction of the measurement light Lm, the distance between the lenses 29A and 29B is adjusted, and the focal position of the measurement light Lm emitted into the atmosphere M can be displaced in the optical axis direction of the measurement light Lm.

[0051] The reflective optical scanner 23 is the part that rotates the light beam (in this case, the measurement light Lm) from the lens optical system 22 with a predetermined beam deflection angle θ. As shown in Figures 3 to 5, the reflective optical scanner 23 is composed of a rotating stage 31 and a mirror unit 32. The rotating stage 31 is disc-shaped and can rotate freely about a rotation axis K1. The rotating stage 31 is positioned so as to be inclined at an angle β with respect to the optical axis x1 of the measurement light Lm from the lens optical system 22. In this case, the angle of the scan center axis K2 of the measurement light Lm by the reflective optical scanner 23 (hereinafter referred to as "scan center axis angle γ") is expressed as γ = 2 × β, using the angle β of the rotation axis K1 with respect to the optical axis x1 of the measurement light Lm from the lens optical system 22.

[0052] The rotating stage 31 is driven by a drive element such as a stepping motor or a piezoelectric element. The rotation of the rotating stage 31 is controlled, for example, based on a control signal from the control unit 15. The rotating stage 31 is equipped with a sensor 33 (see Figure 5) that detects the rotational position, such as a photointerrupter. The sensor 33 generates a detection signal J indicating the detection result. The detection signal J is output to the signal generation unit 13 for the synchronization of the operation of the output unit 2 and the analysis unit 11 (see Figure 2).

[0053] The mirror unit 32 is the part that holds the mirror 34 relative to the rotating stage 31. The mirror unit 32 has a holding portion 35 that holds the mirror 34 so as to be inclined at an angle α with respect to the rotation surface 31a of the rotating stage 31. Specifically, the holding portion 35 has a fixed surface 36 that is fixed concentrically to the rotation surface 31a of the rotating stage 31, and an inclined surface 37 that is inclined at an angle α with respect to the fixed surface 36. In this embodiment, the holding portion 35 has a flattened truncated cylindrical shape, with its bottom surface being the fixed surface 36 and its top surface being the inclined surface 37, which is inclined at an angle α with respect to the bottom surface.

[0054] In this embodiment, as shown in Figure 5, the mirror unit 32 has a weight-reducing portion 38 that is eccentric to the rotation axis K1 such that the center of gravity Z of the mirror unit 32 coincides with the rotation axis K1 of the rotating stage 31. In the example in Figure 5, the weight-reducing portion 38 is formed in a part where the holding portion 35 is relatively thicker, so as to include the rotation axis K1. In the example in Figure 5, the weight-reducing portion 38 penetrates from the fixed surface 36 to the inclined surface 37, but it may be formed to be exposed on only one of the surfaces, or it may be formed only inside the holding portion 35. The planar shape of the weight-reducing portion 38 when viewed from the thickness direction of the holding portion 35 can be various shapes such as circular, semicircular, elliptical, sector, or polygonal.

[0055] The mirror 34 is an optical element that reflects the measurement light Lm toward the atmosphere M and reflects the scattered light Lf from the atmosphere M toward the circulator 21. Considering that the disturbance in the polarization state of the measurement light Lm when reflected by the mirror 34 is a factor in the decrease in the intensity of the signal light Ls, the mirror 34 may be constructed using a zero-shift mirror that can suppress the disturbance in the polarization state. In the example in Figure 5, the mirror 34 has an elliptical shape that is slightly smaller than the inclined surface 37 of the holding part 35 and is fixed to the inclined surface 37 so as to cover the cutout 38. Note that the mirror 34 does not necessarily have to be smaller in dimensions than the inclined surface 37 of the holding part 35, and may have the same dimensions as the inclined surface 37 or be slightly larger than the inclined surface 37. Also, the mirror 34 does not necessarily have to cover the cutout 38, and the cutout may be exposed to the mirror 34 side in a range in which the measurement light Lm can be sufficiently reflected.

[0056] The angle θ between the scan central axis K2 and the optical axis x2 of the measurement light Lm emitted toward the atmosphere M is the angle (hereinafter referred to as "beam deflection angle θ") when the optical axis x2 of the measurement light Lm reflected by the mirror 34 rotates around the scan central axis K2 due to the rotation of the rotating stage 31, as shown in Figure 3. The beam deflection angle θ is expressed as θ = 2 × α, where α is the angle of the mirror 34 with respect to the rotation plane 31a of the rotating stage 31.

[0057] As explained above, the optical scanner module 7 used in the wind speed detection device 1 is a so-called reflective type optical scanner module 7 that reflects the measurement light Lm from the lens optical system 22 with a mirror 34 on the rotating stage 31. In a reflective type optical scanner module 7, the light beam is not transmitted through a prism, so the effects of astigmatism caused by the prism can be avoided. By using this optical scanner module 7 for wind speed detection using LIDAR, for example, signal light Ls from the atmosphere can be obtained with sufficient intensity even for short-distance measurements of 100m or less. Therefore, the signal-to-noise ratio of the signal can be sufficiently ensured, and high-speed wind speed measurement becomes possible. In addition, in the optical scanner module 7, when the angle of the mirror 34 with respect to the rotation surface 31a of the rotating stage 31 is α, the beam deflection angle θ of the measurement light Lm reflected by the mirror 34 is θ = 2 × α. Therefore, the desired beam deflection angle θ can be obtained by adjusting the angle of the mirror 34.

[0058] In this embodiment, the mirror unit 32 has a weight-reducing portion 38 that is eccentric to the rotation axis K1 such that the center of gravity Z of the mirror unit 32 coincides with the rotation axis K1 of the rotating stage 31. This configuration makes it possible to improve the stability of the mirror 34 when the rotating stage 31 is rotated.

[0059] In this embodiment, the optical scanner module 7 guides the input light, measurement light Lm, to the lens optical system 22, while a circulator 21 outputs the scattered light Lf (signal light Ls) generated by the measurement light Lm reflected by the mirror 34 to a different path from the measurement light Lm. This makes it easy to separate the measurement light Lm and the signal light Ls when the optical scanner module 7 is used for wind speed detection using LIDAR.

[0060] Figures 6(a) and 6(b) are schematic diagrams showing an example configuration of an optical scanner module according to a modified example. Figure 7 is a perspective view showing an example configuration of a reflective optical scanner applied to the optical scanner module in Figure 6, and Figure 8 is a cross-sectional view thereof. As shown in Figures 6(a) and 6(b), Figure 7, and Figure 8, the optical scanner module 7A according to the modified example differs from the optical scanner module 7 described above in the configuration of the mirror unit 32 in the reflective optical scanner 23A.

[0061] More specifically, the mirror unit 32 of the reflective optical scanner 23A has a first holding portion 35A and a second holding portion 35B. Both the first holding portion 35A and the second holding portion 35B have a flattened truncated cylindrical shape. The first holding portion 35A has a first fixed surface 36A that is fixed concentrically to the rotation surface 31a of the rotating stage 31 and a first inclined surface 37A that is inclined with respect to the first fixed surface 36A at a first angle ω1 (see Figure 8). The second holding portion 35B has a second fixed surface 36B that is detachably fixed to the first fixed surface 36A and a second inclined surface 37B that is inclined with respect to the second fixed surface 36B at a second angle ω2 (see Figure 8) that is different from the first angle ω1.

[0062] With such an optical scanner module 7A, different beam deflection angles θ can be obtained by adjusting the rotation angle around the rotation axis K1 when fixing the second holding part 35B to the first holding part 35A, without having to prepare a mirror unit 32 for each angle α (see Figures 6(a) and 6(b)). Figure 9 shows the holding state of the mirror 34 when the rotation angle of the second holding part 35B around the rotation axis K1 relative to the first holding part 35A is 0°, 60°, 120°, 180°, 240°, and 300°. By changing the rotation angle of the second holding part 35B around the rotation axis K1 relative to the first holding part 35A according to the angle α obtained from the desired beam deflection angle θ and fixing the second holding part 35B to the first holding part 35A, the desired beam deflection angle θ can be easily formed.

[0063] 1... Wind speed detection device, 2... Output unit, 7, 7A... Optical scanner module, 9... Detection unit, 11... Analysis unit, 21... Circulator, 22... Lens optical system, 23, 23A... Reflective optical scanner, 31... Rotating stage, 31a... Rotating surface, 32... Mirror unit, 34... Mirror, 35A... First holding part, 35B... Second holding part, 36A... First fixed surface, 36B... Second fixed surface, 37A... First inclined surface, 37B... Second inclined surface, 38... Lightweight cutout, K1... Rotation axis, Z... Center of gravity, M... Atmosphere, Lm... Measurement light, Ls... Signal light.

Claims

1. An optical scanner module comprising: a lens optical system for controlling the focusing state of an input light beam; a rotating stage whose rotation axis is inclined at an angle β with respect to the optical axis of the light beam from the lens optical system; and a mirror unit that holds a mirror relative to the rotating stage so as to be inclined at an angle α with respect to the rotation plane of the rotating stage, wherein the rotation of the rotating stage rotates the optical axis of the light beam reflected by the mirror by a beam deflection angle θ.

2. The optical scanner module according to claim 1, wherein the mirror unit has a weight-reducing portion that is eccentric with respect to the rotation axis of the rotating stage, such that the center of gravity of the mirror unit coincides with the rotation axis of the rotating stage.

3. The optical scanner module according to claim 1 or 2, wherein the mirror unit comprises: a first holding portion having a first fixed surface fixed to the rotating surface of the rotating stage and a first inclined surface inclined at a first angle ω1 with respect to the first fixed surface; and a second holding portion having a second fixed surface detachably fixed to the first fixed surface and a second inclined surface inclined at a second angle ω2 different from the first angle ω1 with respect to the second fixed surface.

4. The optical scanner module according to any one of claims 1 to 3, further comprising a circulator that guides the light beam, which is the input light, to the lens optical system, while outputting the reflected light generated by the light beam reflected by the mirror to a path different from that of the input light.

5. A wind speed detection device comprising: an output unit that outputs a light beam as measurement light; an optical scanner module according to any one of claims 1 to 4, which uses the measurement light as the input light, outputs the light beam of the measurement light into the atmosphere while rotating it with a beam deflection angle θ, and receives the reflected light from the atmosphere generated by the output of the measurement light as signal light; a detection unit that detects the signal light and outputs a detection signal based on the detection result; and an analysis unit that calculates the amount of Doppler shift of the signal source in the atmosphere based on the detection signal and analyzes the wind speed in the atmosphere based on the amount of Doppler shift.

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