Wind speed detection device, wind speed detection method, and flying body control device

Abstract

A wind speed detection device 1 includes: an output unit 2 that outputs laser light L of which the frequency is nonlinearly and periodically modulated; a branching part 3 that branches the laser light L into measurement light Lm and reference light Lr; a first amplification unit (conversion unit) 5 that converts the measurement light Lm into pulsed light; a measurement optical system 7 that outputs the measurement light Lm into an atmosphere M and receives, as signal light Ls, scattered light Lf of the measurement light Lm in the atmosphere M; and a detection unit 9 that outputs a detection signal D based on an interference result between the reference light Lr and the signal light Ls.

Description

Wind speed detection device, wind speed detection method, and aircraft control device

[0001] The present disclosure relates to a wind speed detection device, a wind speed detection method, and an aircraft control device.

[0002] Light detection and ranging (LIDAR) is known as one of the sensing technologies using light. While LIDAR has recently been increasingly applied in the field of autonomous driving, it is originally a technology widely used in fields such as meteorology. As a LIDAR used in the field of meteorology, so-called wind LIDAR, which detects wind speed, is known. Wind LIDAR is used, for example, for wind condition surveys to select installation locations for wind power generators. In addition, in recent years, wind LIDAR is expected to be applied to the safe operation management of unmanned aerial vehicles such as drones, and manned aerial vehicles such as advanced air mobility (AAM) and urban air mobility (UAM).

[0003] Coherent detection is used to detect wind speed in LIDAR. In this method, laser light output from a light source is split into measurement light and reference light, and the measurement light is modulated and amplified before being emitted into the atmosphere. The signal source in WindLIDAR is scattered light generated when the measurement light is scattered by countless aerosols in the atmosphere. When the wind blows, the aerosols move with the wind, causing a change in the frequency of the scattered light (Doppler shift). Therefore, wind speed in the atmosphere can be detected by interfering the scattered light from the atmosphere as signal light with the reference light and determining the amount of peak frequency shift in the beat spectrum of the interference light (see, for example, Patent Document 1).

[0004] US Patent Application Publication No. 2021 / 0109218

[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.1953-1962

[0006] One LIDAR method uses pulsed light as the measurement light (see, for example, Non-Patent Document 1). However, in existing methods using pulsed light, the distance resolution does not depend on the detection distance, but depends on the pulse width, which is a technical issue.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a wind speed detection device, a wind speed detection method, and an aircraft control device that can perform wind speed detection with high distance resolution independent of pulse width.

[0008] The gist of the present disclosure is as follows.

[0009] [1] A wind speed detection device comprising: an output unit that outputs laser light whose frequency is nonlinearly and periodically modulated; a branching unit that branches the laser light into measurement light and reference light; a conversion unit that converts the measurement light into pulsed light; a measurement optical system that outputs the measurement light into the atmosphere and receives scattered light of the measurement light in the atmosphere as signal light; and a detection unit that outputs a detection signal based on the interference result between the reference light and the signal light.

[0010] In this wind speed detection device, laser light with a nonlinear and periodically modulated frequency is converted into pulsed light and used as the measurement light. When coherent detection based on optical correlation-domain reflectometry (OCDR) is performed using this measurement light, the distance resolution depends on the frequency modulation width, eliminating dependency on the pulse width. Therefore, this wind speed detection device can detect wind speed with high distance resolution, regardless of the pulse width.

[0011] [2] The wind speed detection device according to [1], wherein the output unit outputs light whose frequency is modulated in a sinusoidal waveform as the laser light. In this case, coherent detection according to the OCDR method can be suitably performed.

[0012] [3] The wind speed detection device according to [1] or [2], wherein the output unit outputs CW light as the laser light, and the detection unit outputs a detection signal based on the interference result between the reference light, which is CW light, and the signal light, which is a temporal superposition of multiple pulsed light. In this wind speed detection device, the frequency of the measurement light is nonlinearly and periodically modulated, thereby forming multiple measurement points determined by integer multiples of the modulation frequency. Therefore, by using CW light as the reference light, interference signals between the signal light and the reference light at multiple measurement points can be obtained, allowing wind speed to be detected simultaneously at multiple measurement points.

[0013] [4] The wind speed detection device according to any one of [1] to [3], wherein the measurement optical system includes an optical element that collimates the measurement light and outputs it into the atmosphere. In this wind speed detection device, the frequency of the measurement light is nonlinearly and periodically modulated, thereby forming multiple measurement points determined by integer multiples of the modulation frequency. Therefore, by collimating the measurement light, interference signals between the signal light and the reference light at multiple measurement points can be obtained, allowing wind speed to be detected simultaneously at multiple measurement points.

[0014] [5] The wind speed detection device according to any one of [1] to [4], wherein the measurement optical system has a deflection unit that deflects the output direction of the measurement light toward the atmosphere. In this case, the output direction of the measurement light is variable, making it possible to measure a three-dimensional wind speed vector including information on wind direction and wind speed.

[0015] [6] The wind speed detection device according to any one of [1] to [5], wherein at least the output section, the branching section, and the detection section are configured by optical integrated circuits. By configuring at least the output section, the branching section, and the detection section by optical integrated circuits, it is possible to achieve miniaturization of the device.

[0016] [7] The wind speed detection device according to any one of [1] to [6], further comprising a signal generation unit that generates a modulation signal for the laser light output from the output unit. In this case, modulation of the laser light can be easily performed.

[0017] [8] The wind speed detection device according to any one of [1] to [7], further comprising an analysis unit that analyzes the wind speed in the atmosphere based on the detection signal. In this case, a series of processes from outputting the laser light to analyzing the wind speed can be performed within a single device.

[0018] [9] A wind speed detection method comprising: an output step of outputting laser light whose frequency is nonlinearly and periodically modulated; a branching step of branching the laser light into measurement light and reference light; a conversion step of converting the measurement light into pulsed light; a measurement step of outputting the measurement light into the atmosphere and receiving scattered light of the measurement light in the atmosphere as signal light; and a detection step of outputting a detection signal based on the interference result between the reference light and the signal light.

[0019] In this wind speed detection method, laser light with a nonlinear and periodically modulated frequency is converted into pulsed light and used as the measurement light. When coherent detection based on optical correlation-domain reflectometry (OCDR) is performed using this measurement light, the distance resolution depends on the frequency modulation width, eliminating dependency on the pulse width. Therefore, this wind speed detection method can detect wind speed with high distance resolution, regardless of the pulse width.

[0020]

[10] The wind speed detection method according to [9], wherein the output step outputs light whose frequency is modulated in a sinusoidal waveform as the laser light. In this case, coherent detection based on the OCDR method can be suitably performed.

[0021]

[11] The wind speed detection method according to [9] or

[10] , wherein the output step outputs CW light as the laser light, and the detection step outputs a detection signal based on the interference result between the reference light, which is CW light, and the signal light, which is a temporal superposition of multiple pulsed light. In this wind speed measurement method, the frequency of the measurement light is nonlinearly and periodically modulated, thereby forming multiple measurement points determined by integer multiples of the modulation frequency. Therefore, by using CW light as the reference light, interference signals between the signal light and the reference light at multiple measurement points can be obtained, and wind speed can be detected simultaneously at multiple measurement points.

[0022]

[12] The wind speed detection method according to any one of [9] to

[11] , wherein the measurement step collimates the measurement light and outputs it into the atmosphere. In this wind speed detection device, the frequency of the measurement light is nonlinearly and periodically modulated, thereby forming multiple measurement points determined by integer multiples of the modulation frequency. Therefore, by collimating the measurement light, interference signals between the signal light and the reference light at multiple measurement points can be obtained, and wind speed can be detected simultaneously at multiple measurement points. In this wind speed measurement method, the frequency of the measurement light is nonlinearly and periodically modulated, thereby forming multiple measurement points determined by integer multiples of the modulation frequency. Therefore, by collimating the measurement light, interference signals between the signal light and the reference light at multiple measurement points can be obtained, and wind speed can be detected simultaneously at multiple measurement points.

[0023]

[13] The wind speed detection method according to any one of [9] to

[12] , wherein the measurement step includes deflecting the output direction of the measurement light toward the atmosphere. In this case, the output direction of the measurement light is variable, and it is possible to measure a three-dimensional wind speed vector including information on wind direction and wind speed.

[0024]

[14] The wind speed detection method according to any one of [9] to

[13] , further comprising an analysis step of analyzing the wind speed in the atmosphere based on the detection signal. In this case, a series of processes from outputting the measurement light to analyzing the wind speed can be performed.

[0025]

[15] An aircraft control device comprising a wind speed detection device according to any one of [1] to [8] and a control device that generates control signals related to takeoff and landing of the aircraft based on the detection signal output from the wind speed detection device.

[0026] This aircraft control device enables safe operation management of aircraft such as drones, AAMs, and UAMs by detecting complex turbulence with high distance resolution using a wind speed detection device.

[0027] According to the present disclosure, wind speed detection can be performed with high distance resolution without relying on the pulse width.

[0028] 1A and 1B are schematic diagrams of an aircraft control device according to an embodiment of the present disclosure; FIG. 1C is a schematic diagram of a wind speed detection device according to an embodiment of the present disclosure; FIG. 1A is a schematic diagram of a beat spectrum between a signal light and a reference light when a frequency shifter is not used, and FIG. 1B is a schematic diagram of a beat spectrum between a signal light and a reference light when a frequency shifter is used; FIG. 1A is a schematic diagram of a time waveform of the intensity of a measurement light, and FIG. 1B is a schematic diagram of a time waveform of the frequency of the measurement light; FIG. 1C is a diagram of an example of a relationship between a modulation frequency and a measurement point; FIG. 1D is a schematic diagram of a relationship between a measurement light and a measurement point; FIG. 1E is a flowchart showing an example of a wind speed detection method according to an embodiment of the present disclosure; FIG. 1A is a schematic diagram of a modulation of a measurement light, and FIG. 1B is a schematic diagram of a detection signal; FIG. 1A to FIG. 1C are schematic diagrams of beat spectra of interference light at each detection distance; FIG. 1D is a diagram of wind speed detection results; FIG. 1E is a diagram of simulation conditions for wind speed detection; and FIG. 1F is a diagram of simulation results for wind speed detection. Fig. 13 is a diagram showing a beat spectrum of interference light obtained in the process of wind speed detection shown in Fig. 12. Fig. 14 is a schematic diagram of a wind speed detection device according to a modified example. Fig. 15 is a schematic diagram showing another example of frequency modulation of measurement light.

[0029] Hereinafter, preferred embodiments of a wind speed detection device, a wind speed detection method, and an aircraft control device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0030] 1(a) and 1(b) are diagrams schematically illustrating an aircraft control device according to an embodiment of the present disclosure. As shown in Fig. 1(a) and 1(b), the aircraft control device 101 is configured to include 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 Fig. 2) output from the wind speed detection device 1. Examples of the aircraft H include unmanned aircraft such as drones, and manned aircraft such as advanced air mobility (AAM) or urban air mobility (UAM).

[0031] 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, an atmospheric layer called the ground layer. The ground layer refers to an atmospheric layer at a height of 100 m 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 FIG. 1( a). The aircraft control device 101 may be installed on the rooftop or roof of a building or other structure, as shown in FIG. 1( b). The aircraft control device 101 may be incorporated as a device in a control tower that operates the aircraft H.

[0032] The wind speed detection device 1 is a device that detects wind speed in the atmosphere. In the aircraft control device 101, the wind speed detection device 1 detects complex turbulence caused by many structures, particularly near the ground, and outputs a detection signal D to the control device 102. The control device 102 is a device that generates a control signal Q related to takeoff and landing of the aircraft H. The control device 102 is physically a computer system that includes memories 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 a control signal Q to the aircraft H, for example, related to the speed, route, or permission / prohibition of takeoff and landing of the aircraft H during takeoff and landing.

[0033] The wind speed detection device 1 may transmit the detection signal D to a server owned by a 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 transmit the detection signal D directly to the aircraft control device 101 in the control tower.

[0034] Fig. 2 is a schematic diagram of a wind speed detection device according to an embodiment of the present disclosure. The wind speed detection device 1 shown in Fig. 2 is a device that detects wind speed in the atmosphere M using LIDAR (Light Detection and Ranging). The wind speed detection device 1 employs a frequency modulation method using pulsed light. The wind speed detection device 1 detects wind speed in the atmosphere M by nonlinearly and periodically modulating the frequency of measurement light Lm, which is laser light, and performing coherent detection based on optical correlation-domain reflectometry (OCDR) between signal light Ls and reference light Lr.

[0035] 2, the wind speed detection device 1 includes an output unit 2, a branching unit 3, a frequency shifter 4, a first amplifier (conversion unit) 5, a second amplifier 6, a measurement optical system 7, a multiplexing unit 8, a detection unit 9, a digitizer 10, and an analysis unit 11. 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 amplifier 5, the first amplifier 5 and the second amplifier 6, the second amplifier 6 and the measurement optical system 7, the measurement optical system 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 optical fibers F.

[0036] In the wind speed detection device 1, at least the output unit 2, branch unit 3, and detection unit 9 are configured using a photonic integrated circuit (PIC) 12. In this embodiment, the output unit 2, branch unit 3, frequency shifter 4, first amplification unit 5, second amplification unit, multiplexer 8, detection unit 9, and the optical fiber F connecting these are configured using the photonic integrated circuit 12.

[0037] The output unit 2 is a part that outputs laser light L whose frequency is nonlinearly and periodically modulated. Examples of laser devices that make up the output unit 2 include a distributed feedback (DFB) laser device, a distributed Bragg reflector (DBR) laser device, and an external cavity laser device. In this example, the laser light L output from the output unit 2 is CW light. The laser light L is not light such as diffused light, but is beam-like light with a certain directivity.

[0038] A current control unit and a temperature control unit (not shown) are connected to the output unit 2. The current control unit is a controller that supplies a drive current to the laser device that constitutes the output unit 2. The current control unit modulates the drive current to modulate the frequency of the laser light L output from the output unit 2. 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 configured to include, 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.

[0039] A signal generating unit 13 is connected to the output unit 2. The signal generating unit 13 generates a modulation signal G for the laser light L. The signal generating unit 13 is configured by, for example, a waveform generator, a function generator, etc. The signal generating 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 generating unit 13 is also output to the digitizer 10 in order to synchronize the operation of the output unit 2 with the operation of the analysis unit 11.

[0040] The branching unit 3 is a unit that branches the laser light L from the output unit 2 into measurement light Lm and reference light Lr. The branching unit 3 is configured, for example, by an optical fiber coupler. The measurement light Lm is output from one output port of the branching unit 3 to the frequency shifter 4, and the reference light Lr is output from another output port of the branching unit 3 to the multiplexing unit 8. The reference light Lr has a frequency that is nonlinearly and periodically modulated, but is input to the multiplexing unit 8 as CW light.

[0041] The frequency shifter 4 is a part that shifts the frequency of the measurement light Lm. The frequency shifter 4 is configured, for example, by an acousto-optic element, an electro-optic element, an IQ modulator, a phase modulator, an intensity modulator, or the like. The frequency shifter 4 may have a signal generating unit (not shown) that generates a voltage signal for driving the frequency shifter 4. The signal generating unit may be configured, for example, by a waveform generator, a function generator, or the like.

[0042] Shifting the frequency of the measurement light Lm using the frequency shifter 4 makes it possible to determine the wind direction in the optical axis direction of the measurement light Lm. When 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 a reference beat spectrum (a beat spectrum without wind speed) depending on the wind speed, regardless of the wind direction, as shown in FIG. 3A, for example. When 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 a positive direction (tailwind) relative to the optical axis of the measurement light Lm, and shifts to a higher frequency relative to the reference beat spectrum if the wind is blowing in a negative direction (headwind) relative to the optical axis of the measurement light Lm, for example. 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.

[0043] The first amplifier 5 converts the measurement light Lm from the branching unit 3 into pulsed light. The first amplifier 5 is composed of, for example, a semiconductor optical amplifier or an optical fiber amplifier. The first amplifier 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 amplifier 5. The current control unit is a controller that supplies a drive current to the amplifier device that constitutes the first amplifier 5. The current control unit controls the amplification factor of the measurement light Lm in the first amplifier 5 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the amplifier device that constitutes the first amplifier 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 amplifier device based on the temperature measurement value of the thermistor attached to the amplifier device. The measurement light Lm, which is CW light, can also be converted into pulsed light by frequency-shifting a specific component of the measurement light Lm using the frequency shifter 4 described above.

[0044] The second amplifier 6 amplifies the intensity of the measurement light Lm converted into pulsed light. The second amplifier 6 is composed of, for example, a semiconductor optical amplifier or an optical fiber amplifier. A current control unit and a temperature control unit (not shown) are connected to the second amplifier 6. The current control unit is a controller that supplies a drive current to the amplifier device that constitutes the second amplifier 6. The current control unit controls the amplification factor of the measurement light Lm in the second amplifier 6 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the amplifier device that constitutes the second amplifier 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 amplifier device based on the temperature measurement value of the thermistor attached to the amplifier device.

[0045] FIG. 4( a) is a schematic diagram showing the time waveform of the intensity of the measurement light Lm. FIG. 4( b) is a schematic diagram showing the time waveform of the frequency of the measurement light Lm. As described above, the measurement light Lm is generated by converting the CW laser light L, whose frequency is nonlinearly and periodically modulated, into pulsed light. Therefore, as shown in FIG. 4( a), the measurement light Lm is light whose intensity rises intermittently on the time axis, and as shown in FIG. 4( b), the measurement light Lm is light whose frequency changes nonlinearly and periodically within the period during which the intensity rises intermittently. In the example of FIG. 4( b), the frequency of the measurement light Lm is modulated sinusoidally. The frequency of the measurement light Lm may also be modulated cosine-wavewise, with a phase lead of 90° relative to the sine wave.

[0046] The measurement optical system 7 outputs the measurement light Lm into the atmosphere M and receives scattered light Lf of the measurement light Lm in the atmosphere M as signal light Ls. As shown in FIG. 2 , the measurement optical system 7 includes a spatial optical system circulator 21, a movable stage 22, a lens (optical element) 23, and a rotating stage (deflection unit) 25 on which a beam deflector 24 is mounted. The circulator 21 includes a polarizing beam splitter 26 and a λ / 4 wave plate 27. A lens 28 is disposed upstream of the polarizing beam splitter 26, and a lens 29 mounted on the movable stage 22 is disposed downstream of the λ / 4 wave plate 27. Furthermore, a lens 30 is disposed upstream of the optical fiber F connected to the detection unit 9, and is used to optically couple the signal light Ls to the optical fiber F.

[0047] To stabilize the performance of the circulator 21, a temperature control unit (not shown) may be used to control the temperature of the entire circulator 21 to be constant. The temperature control unit includes, 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 temperature of the entire circulator 21 is maintained constant.

[0048] The movable stage 22 is a stage having a movable axis at least in the optical axis direction of the measurement light Lm. A driving element such as a stepping motor or a piezoelectric element is used to drive the movable stage 22. A stage controller (not shown) is connected to the movable stage 22. The stage controller outputs a control signal to the driving element to control the position of the movable stage 22.

[0049] The lens 23 is an optical element that collimates the measurement light Lm and outputs it into the atmosphere M. Examples of the lens 23 that can be used include a convex lens, an achromatic lens, an aspherical lens, and a combination lens formed by combining multiple lenses. The lenses 23 and 29 form a pair of lenses that constitute a telescope. The distance between the lenses 23 and 29 is adjusted by displacing the movable stage 22 in the optical axis direction of the measurement light Lm. This allows the focal position of the measurement light Lm emitted into the atmosphere M via the lens 23 to be displaced in the optical axis direction of the measurement light Lm. In this embodiment, the distance between the lenses 23 and 29 is adjusted so that the measurement light Lm is output into the atmosphere M in a collimated state.

[0050] The beam deflector 24 is a component that deflects the output direction of the measurement light Lm toward the atmosphere M in any direction. For example, a wedge substrate or the like can be used as the beam deflector 24. The rotation stage 25 is a stage that rotates the beam deflector 24 around the optical axis of the measurement light Lm. Driving elements such as a stepping motor and a piezoelectric element are used to drive the rotation stage 25. A stage controller (not shown) is connected to the movable stage 22. The stage controller outputs a control signal J to the driving element to control the position of the rotation stage. The control signal J is output to the signal generating unit 13 to synchronize the operations of the output unit 2 and the analyzing unit 11.

[0051] In the measurement optical system 7, the measurement light Lm emitted from the optical fiber F on the output side of the second amplifier 6 passes through a lens 23 and is emitted into the atmosphere M as a beam of light with a certain directivity. The output direction of the measurement light Lm changes based on the rotation angle of the beam deflector 24 caused by the rotary stage 25. The signal source in the wind speed detection device 1 is 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 measurement optical system 7 as signal light Ls via the lens 23. The signal light Ls is separated from the measurement light Lm by the circulator 21 and output to the multiplexer 8.

[0052] The multiplexing unit 8 multiplexes the reference light Lr from the branching unit 3 with the signal light Ls that has returned from the atmosphere M. The multiplexing unit 8 is configured, for example, by an optical fiber coupler. The multiplexing unit 8 generates interference light Ld between the reference light Lr and the signal light Ls. The interference light Ld is output from an output port of the multiplexing unit 8 to the detection unit 9.

[0053] The detector 9 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 scattering of the measurement light Lm at a specific distance is also pulsed light. On the other hand, the reference light Lr is a CW light that is obtained by branching a portion of the laser light L from the output unit 2 at the branch unit 3. Therefore, the detector 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.

[0054] The detection unit 9 is composed of, for example, a photodetector, an avalanche photodiode, a balanced detector, etc. The detection unit 9 outputs an analog electrical signal based on the intensity of the interference light Ld input from the multiplexer 8 as a detection signal D to the digitizer 10. The digitizer 10 is a device that converts an analog electrical signal into a digital signal. 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.

[0055] The analysis unit 11 is a part that analyzes the wind speed in the atmosphere M based on the detection signal D. Physically, the analysis unit 11 is a computer system that includes memories such as RAM and ROM, processors such as CPU and GPU, a communication interface, and a storage unit 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). The computer system functions as the analysis unit 11 by executing a program stored in the memory with the CPU or GPU.

[0056] As described above, the signal source in the wind speed detection device 1 is scattered light Lf 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, causing a change in frequency (Doppler shift) of the scattered light Lf. 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 calculating the amount of shift in the peak frequency of the beat spectrum of the interference light Ld.

[0057] As shown in Figures 4(a) and 4(b), when coherent detection is performed using pulsed light whose frequency is nonlinearly and periodically modulated as the measurement light Lm, the distance resolution and detection distance for wind speed detection can be calculated in accordance with the distance resolution and detection distance in optical correlation-domain reflectometry (OCDR), which is used in optical fiber sensing.

[0058] When the frequency modulation width of the measurement light Lm is B (see FIG. 4(b)) and the speed of light is c, the distance resolution ΔZr is independent of the pulse width Δt of the measurement light Lm (see FIG. 4(a)) and is expressed as ΔZr = 0.48 × (c / B). When the modulation frequency of the measurement light Lm is fm (see FIG. 4(b)) and the speed of light is c, the detection distance ZN is expressed as ZN = c / (2 × fm). For example, when the frequency modulation width B is 100 MHz and the modulation frequency fm is 214 kHz, the distance resolution ΔZr is estimated to be 1.4 m and the detection distance ZN is estimated to be 700 m.

[0059] In optical fiber sensing using the ODCR method, where N is an integer number of measurement points, ZN = (c / (2 × fm)) × N holds. That is, in coherent detection in the wind speed detection device 1, multiple measurement points exist for one modulation frequency fm, as shown in FIG. 5, for example. At each distance corresponding to these measurement points, a first-order correlation peak, a second-order correlation peak, a third-order correlation peak, ... and an N-order correlation peak appear, as shown in FIG.

[0060] 7 is a flowchart showing an example of a wind speed detection method according to an embodiment of the present disclosure. The wind speed detection method according to this embodiment is implemented using the above-described wind speed detection device 1. As shown in FIG. 7 , this wind speed detection method includes a setting step S01, an output step S02, a branching step S03, a conversion step S04, a measurement step S05, a detection step S06, and an analysis step S07.

[0061] The setting step S01 is a step for setting various measurement conditions used for wind speed detection. In the setting step S01, parameters that are independent of the detection distance are first set. Examples of parameters that are independent of the detection distance include the diameter of the lens 23, the pulse waveform of the measurement light Lm, the frequency shift by the frequency shifter 4, and the pulse repetition frequency of the measurement light Lm. Next, in the setting step S01, the detection distance is set, and the modulation frequency fm of the measurement light Lm is determined according to the set detection distance. Other settings in the setting step S01 include the intensity of the laser light L output from the output unit 2, the light amplification factors in the first amplifier 5 and the second amplifier, and the output direction of the measurement light Lm by the beam deflector 24.

[0062] The output step S02 is a step of outputting laser light L whose frequency is nonlinearly and periodically modulated. In the output step S02, the modulation signal G generated by the signal generating unit 13 is input to the output unit 2. As a result, laser light L whose frequency is nonlinearly and periodically modulated is generated and output from the output unit 2.

[0063] The branching step S03 is a step of branching the laser light L into measurement light Lm and reference light Lr. In the branching step S03, the laser light L output from the output unit 2 is branched by the branching unit 3, one of which is the measurement light Lm and the other is the reference light Lr. The measurement light Lm is input to the first amplifier 5 via the frequency shifter 4, and the reference light Lr is input to the multiplexer 8.

[0064] The conversion step S04 is a step of converting the measurement light Lm into pulsed light. In the conversion step S04, the first amplifier 5 amplifies a specific component of the measurement light Lm, thereby converting the measurement light Lm, which is CW light, into pulsed light. In the conversion step S04, the frequency shifter 4 may shift a specific frequency component of the measurement light Lm to convert the measurement light Lm, which is CW light, into pulsed light. In the conversion step S04, both the first amplifier 5 and the frequency shifter 4 may shift and amplify a specific frequency component of the measurement light Lm to convert the measurement light Lm, which is CW light, into pulsed light. Converting the measurement light Lm into pulsed light by both the first amplifier 5 and the frequency shifter 4 can generate pulsed light with a high extinction ratio. The measurement light Lm converted into pulsed light is input to the measurement optical system 7 after its intensity is amplified by the second amplifier 6.

[0065] The measurement step S05 is a step of outputting the measurement light Lm into the atmosphere M and receiving scattered light Lf of the measurement light Lm in the atmosphere M as signal light Ls. In the measurement step S05, the measurement light Lm is output into the atmosphere M in a collimated state via the measurement optical system 7. The measurement light Lm is scattered by countless aerosols P in the atmosphere M and becomes scattered light Lf. A portion of the scattered light Lf returns to the measurement optical system 7 and is input to the multiplexing unit 8 as signal light Ls. In the multiplexing unit 8, the reference light Lr, which is CW light, and the signal light Ls, which is a temporal superposition of multiple pulsed light beams, are multiplexed to generate interference light Ld.

[0066] The detection step S06 is a step of outputting a detection signal based on the interference result between the reference light Lr and the signal light Ls. In the detection step S06, the interference light Ld generated by the multiplexer 8 is detected by the detector 9, and an analog electrical signal based on the interference light Ld is generated as the detection signal D. The generated detection signal D is analog-to-digital converted by the digitizer 10 and output to the analyzer 11.

[0067] The analysis step S07 is a step of analyzing the wind speed in the atmosphere M based on the detection signal D. In the analysis step S07, the peak frequency of the beat spectrum of the interference light Ld is referenced based on the detection signal D. Then, the wind speed in the atmosphere M is detected by determining the amount of shift in the peak frequency in the beat spectrum of the interference light Ld. If detection is to be performed at a different distance, the detection distance, etc. is reset in step S01, and steps S02 to S07 are executed again. After wind speed detection has been performed within the desired distance range, the process ends.

[0068] As described above, in the wind speed detection device 1, the laser light L, whose frequency is nonlinear and periodically modulated, is converted into pulsed light and used as the measurement light Lm. When coherent detection based on optical correlation-domain reflectometry (OCDR) is performed using such measurement light Lm, the distance resolution depends on the frequency modulation width, and dependency on the pulse width can be eliminated. Therefore, the wind speed detection device 1 can detect wind speed with high distance resolution, regardless of dependency on the pulse width.

[0069] In this embodiment, the output unit 2 outputs light whose frequency is modulated in a sinusoidal waveform as the laser light L. By performing such modulation, coherent detection according to the OCDR method can be suitably performed.

[0070] In this embodiment, the output unit 2 outputs CW light as the laser light L, and the detection unit 9 outputs a detection signal D based on the interference between the reference light Lr, which is CW light, and the signal light Ls, which is a temporal superposition of multiple pulsed lights. The measurement optical system 7 also includes a lens 23 that collimates the measurement light Lm and outputs it into the atmosphere. In the wind speed detection device 1, the frequency of the measurement light Lm is nonlinearly and periodically modulated, thereby forming multiple measurement points determined by integer multiples of the modulation frequency (see FIG. 5 ). Therefore, by collimating the measurement light Lm and using the reference light Lr as CW light, interference signals between the signal light Ls and the reference light at multiple measurement points can be obtained, enabling wind speed to be detected simultaneously at multiple measurement points.

[0071] In this embodiment, the measurement optical system 7 has a rotation stage 25 on which a beam deflector 24 is mounted as a deflection unit that deflects the output direction of the measurement light Lm toward the atmosphere M. By using such a deflection unit, the output direction of the measurement light Lm can be changed, and it becomes possible to measure a three-dimensional wind speed vector including information on the wind direction and wind speed.

[0072] In this embodiment, among the components of the wind speed detection device 1, at least the output unit 2, the branching unit 3, and the detection unit 9 are configured using optical integrated circuits 12. By configuring at least the output unit 2, the branching unit 3, and the detection unit 9 using optical integrated circuits 12, it is possible to reduce the size of the device.

[0073] In this embodiment, a signal generating section 13 is provided that generates a modulation signal G for the laser light L output from the output section 2. By providing such a signal generating section 13, modulation of the laser light L can be easily performed.

[0074] This embodiment further includes an analysis unit 11 that analyzes the wind speed in the atmosphere M based on the detection signal D. This allows a series of processes from outputting the laser light L to analyzing the wind speed to be performed within a single device.

[0075] Hereinafter, examples of the present disclosure will be described.

[0076] In this example, we first introduce an example of wind speed analysis over a detection distance range of 60 m to 240 m. In this example, the detection distances were set to 60 m, 120 m, and 180 m. The modulation frequency fm of the measurement light Lm was set to 2498270 Hz, and the pulse width Δt was set to 400.277 ns. The diameter of the lens 23 was set to 50 mm, a parameter independent of the detection distance. As shown in Figure 8(a), the pulse waveform of the measurement light Lm was set to rectangular, the frequency shift by the frequency shifter 4 was set to 80 MHz, and the pulse repetition frequency of the measurement light Lm was set to 100 kHz (= pulse interval Δr = 10 μs).

[0077] The measurement light Lm was emitted into the atmosphere M, and the signal light Ls from the atmosphere M was detected by coherent detection. As shown in Fig. 8(b), the detection signal D output from the digitizer 10 is a signal with a time interval corresponding to the pulse repetition frequency of the measurement light Lm. Each pulse component of the signal includes information Da on the peak frequency of the beat spectrum of the interference light Ld at a detection distance of 60 m, information Db on the peak frequency of the beat spectrum of the interference light Ld at a detection distance of 120 m, and information Dc on the peak frequency of the beat spectrum of the interference light Ld at a detection distance of 180 m.

[0078] For wind speed analysis, first, the detection signal D is divided into time slots with a pulse interval (= 10 μs). Each time slot is then divided into sub-slots with a pulse width Δt. Here, sub-slot #1 is set for a detection distance of 60 m, sub-slot #2 for a detection distance of 120 m, and sub-slot #3 for a detection distance of 180 m. Each data point in sub-slots #1 to #3 is multiplied by a window function based on the pulse width Δt, and then a Fourier transform is performed to calculate the respective intensity spectra.

[0079] For each of sub-slots #1 to #3, the intensity spectra for 1000 time slots are averaged to obtain an average intensity spectrum S60 at a detection distance of 60 m (see FIG. 9(a)), an average intensity spectrum S120 at a detection distance of 120 m (see FIG. 9(b)), and an average intensity spectrum S180 at a detection distance of 180 m (see FIG. 9(c)). From the obtained average intensity spectra S60, S120, and S180, the peak frequencies f60m, f120m, and f180m of each average intensity spectrum are obtained.

[0080] Peak frequency f of the average intensity spectrum ｐｅａｋ The line-of-sight wind speed V based on ＬＯＳ The calculation formula for is as follows: ＬＯＳ is the wind speed in the output direction of the measurement light Lm emitted into the atmosphere M. In the following equations (1) and (2), λ is the wavelength of the measurement light Lm, f ｓｈｉｆｔ is the frequency shift by the frequency shifter 4, f ｄоｐｐｌｅｒ is the Doppler shift. V ＬＯＳ= λ × (f ｄоｐｐｌｅｒ / 2) ... (1) f ｄоｐｐｌｅｒ = f ｐｅａｋ -f ｓｈｉｆｔ …(2)

[0081] Figure 10(a) plots the results of line-of-sight wind speed detection at each detection distance. After detecting line-of-sight wind speed at detection distances of 60 m, 120 m, and 180 m, the combination of detection distances was changed and line-of-sight wind speed was detected at each detection distance using the procedure described above. Here, line-of-sight wind speed was detected at detection distances of 62 m, 124 m, and 186 m, and at detection distances of 115 m and 230 m, and the detection results at each detection distance were further plotted. As a result, wind speed analysis results were obtained for detection distances ranging from 60 m to 240 m, as shown in Figure 10(b).

[0082] Furthermore, in this embodiment, a simulation was carried out to verify the distance resolution of wind speed detection. In this simulation, the pulse waveform of the measurement light Lm was set to a rectangular waveform, and the frequency shift f ｓｈｉｆｔ The frequency modulation width B of the measurement light Lm was 80 MHz, and the number of times the intensity spectrum was averaged was 1000. As shown in Figure 11, the measurement targets were set at constant wind speeds within distance ranges of 60 m ± 2 m, 120 m ± 2 m, and 180 m ± 2 m. In Figure 11, the horizontal axis represents distance and the vertical axis represents frequency. The line at a frequency of 80 MHz on the vertical axis represents f ｓｈｉｆｔ is equivalent to

[0083] 12 is a diagram showing the simulation results. From the results shown in FIG. 12, it is clear that f ｐｅａｋ are respectively f ｓｈｉｆｔ It can be seen that the wind speed is shifted from 60m±2m, 120m±2m, and 180m±2m, and a constant wind speed can be detected within the respective distance ranges. This result confirms that the distance resolution of this example is 4m or less.

[0084] 13(a) to 13(d) are diagrams showing beat spectra of the interference light Ld obtained in the process of wind speed detection shown in FIG. 12. FIG. 13(a) is the beat spectrum of the interference light Ld at a distance of 62 m, and FIG. 13(b) is the beat spectrum of the interference light Ld at a distance of 90 m. FIG. 13(c) is the beat spectrum of the interference light Ld at a distance of 122 m. FIG. 13(d) is the beat spectrum of the interference light Ld at a distance of 230 m. As shown in FIGS. 13(a) to 13(d), in the beat spectra at distances of 62 m and 122 m where a constant wind speed is set, the peak frequency f ｐｅａｋ ga f ｓｈｉｆｔ In addition, in the beat spectra at distances of 90 m and 230 m where a constant wind speed is not set, the peak frequency f ｐｅａｋ ga f ｓｈｉｆｔ From the above results, it can be seen that in the present disclosure, wind speed detection can be performed with high distance resolution, regardless of the pulse width Δt of the measurement light Lm.

[0085] The present disclosure is not limited to the above-described embodiments. For example, in the above-described embodiments, a configuration in which the spatial optical system circulator 21 is used in the measurement optical system 7 is illustrated. However, as shown in FIG. 14 , the measurement optical system 7 may also use an optical fiber device circulator 31. In the example of FIG. 14 , an end Fa of an optical fiber F connected to an output port of the optical fiber device circulator 31 is mounted on a movable stage 32. By using the movable stage 32 to change the distance from the end Fa of the optical fiber F to the lens 23, the focal position of the measurement light Lm emitted into the atmosphere M via the lens 23 can be displaced in the optical axis direction of the measurement light Lm.

[0086] 2, the output direction of the measurement light Lm toward the atmosphere M is deflected in an arbitrary direction using the beam deflector 24, but deflection of the output direction of the measurement light Lm may be achieved using other configurations. For example, a mirror may be disposed outside the lens 23, and the output direction of the measurement light Lm toward the atmosphere M may be deflected in an arbitrary direction by adjusting the angle of the mirror. In the example of FIG. 14, the output direction of the measurement light Lm toward the atmosphere M may be deflected in an arbitrary direction by moving the orientation of the end Fa of the optical fiber F up, down, left, or right.

[0087] In the above embodiment, sine wave (or cosine wave) modulation is exemplified as an example of nonlinear and periodic modulation of the frequency, but as another example of nonlinear and periodic modulation, for example, rectangular and discrete modulation as shown in Fig. 15 may be used. In the example of Fig. 15, the frequency is modulated rectangular and discrete, and the frequency modulation width B gradually increases over time. Even when using measurement light Lm having such modulation, the same effects as those of the above embodiment can be achieved.

[0088] 1...wind speed detection device, 2...output section, 3...branching section, 5...first amplifier section (conversion section), 7...measurement optical system, 9...detection section, 11...analysis section, 12...optical integrated circuit, 13...signal generation section, 23...lens (optical element), 24...beam deflection plate (deflection section), 25...rotation stage (deflection section), M...atmosphere, L...laser light, Lm...measurement light, Lf...scattered light, Ls...signal light, Lr...reference light, D...detection signal, G...modulation signal, 101...aircraft control device, 102...control device, H...aircraft, Q...control signal.

Claims

1. A wind speed detection device comprising: an output unit that outputs laser light whose frequency is nonlinearly and periodically modulated; a branch unit that branches the laser light into measurement light and reference light; a conversion unit that converts the measurement light into pulsed light; a measurement optical system that outputs the measurement light into the atmosphere and receives light scattered by the measurement light in the atmosphere as signal light; and a detection unit that outputs a detection signal based on the interference result between the reference light and the signal light.

2. A wind speed detection device according to claim 1, wherein said output section outputs light whose frequency is modulated in a sinusoidal waveform as said laser light.

3. A wind speed detection device as claimed in claim 1 or 2, wherein the output unit outputs CW light as the laser light, and the detection unit outputs a detection signal based on the result of interference between the reference light, which is CW light, and the signal light, which is a temporal superposition of multiple pulsed lights.

4. A wind speed detection device according to any one of claims 1 to 3, wherein the measurement optical system has an optical element that collimates the measurement light and outputs it into the atmosphere.

5. A wind speed detection device according to any one of claims 1 to 4, wherein the measurement optical system has a deflection unit that deflects the output direction of the measurement light toward the atmosphere.

6. A wind speed detection device according to any one of claims 1 to 5, wherein at least the output section, the branching section, and the detection section are configured by optical integrated circuits.

7. A wind speed detection device according to any one of claims 1 to 6, further comprising a signal generation section for generating a modulation signal for the laser light output from the output section.

8. A wind speed detection device according to any one of claims 1 to 7, further comprising an analysis unit that analyzes the wind speed in the atmosphere based on the detection signal.

9. A wind speed detection method comprising: an output step of outputting laser light whose frequency is nonlinearly and periodically modulated; a branching step of branching the laser light into measurement light and reference light; a conversion step of converting the measurement light into pulsed light; a measurement step of outputting the measurement light into the atmosphere and receiving scattered light of the measurement light in the atmosphere as signal light; and a detection step of outputting a detection signal based on the interference result between the reference light and the signal light.

10. A wind speed detection method according to claim 9, wherein in said outputting step, light whose frequency is modulated in a sinusoidal waveform is output as said laser light.

11. A wind speed detection method according to claim 9 or 10, wherein in the output step, CW light is output as the laser light, and in the detection step, a detection signal is output based on the result of interference between the reference light, which is CW light, and the signal light, which is a temporal superposition of multiple pulsed lights.

12. A wind speed detection method according to any one of claims 9 to 11, wherein in the measuring step, the measurement light is collimated and output into the atmosphere.

13. A wind speed detection method according to any one of claims 9 to 12, wherein in the measuring step, the output direction of the measurement light directed into the atmosphere is deflected.

14. A wind speed detection method according to any one of claims 9 to 13, further comprising an analysis step of analyzing the wind speed in the atmosphere based on the detection signal.

15. An aircraft control device comprising: a wind speed detection device according to any one of claims 1 to 8; and a control device that generates control signals related to takeoff and landing of the aircraft based on the detection signal output from the wind speed detection device.

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