Wind speed detection device and wind speed detection method

Abstract

A wind speed detection device 1 comprises an output unit 2 that outputs CW laser light L for which the frequency is nonlinear and periodically modulated, a branch unit 3 that branches the CW laser light L into measurement light Lm and reference light Lr, a measurement optical system 6 that outputs the measurement light Lm to the atmosphere and receives scattered light Lf of the measurement light Lm in the atmosphere as signal light Ls, and a detection unit 8 that outputs a detection signal D based on the result of interference between the reference light Lr and the signal light Ls.

Description

Wind speed detection device and wind speed detection method

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

[0002] Light detection and ranging (LIDAR) is known as one of the sensing technologies using light. While LIDAR has recently been applied to 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 WindLIDAR, which detects wind speed, is known. WindLIDAR is used, for example, for wind condition surveys to select installation locations for wind power generators, and in recent years, it is expected to be applied to the safe operation management of aircraft such as drones.

[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] LIDAR methods include those using pulsed light and those using continuous wave (CW) light. Pulsed light methods have a problem in that the distance resolution depends on the pulse width and not on the detection distance, but the cost required for optical amplification of the measurement light is high. In contrast, CW light methods have a problem in that the cost required for optical amplification of the measurement light is low, but because measurements are performed while changing the focal position of the measurement light, the distance resolution depends on the focal depth of the measurement light and is therefore dependent on the detection distance.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a wind speed detection device and a wind speed detection method that can perform wind speed detection at low cost and with high distance resolution independent of the detection distance.

[0007] The gist of the present disclosure is as follows.

[0008] [1] A wind speed detection device comprising: an output unit that outputs CW laser light whose frequency is nonlinearly and periodically modulated; a branching unit that branches the CW laser light into measurement light and reference 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.

[0009] In this wind speed detection device, the CW laser light used as the measurement light and reference light is modulated to have a nonlinear and periodic frequency. Using CW laser light reduces the cost required for optical amplification of the measurement light compared to using pulsed light. Furthermore, modulating the CW laser light to have a nonlinear and periodic frequency enables coherent detection based on optical correlation-domain reflectometry (OCDR). In this coherent detection, distance resolution depends on the frequency modulation width, eliminating dependency on the detection distance. Therefore, this wind speed detection device can detect wind speed at low cost and with high distance resolution independent of the detection distance.

[0010] [2] The wind speed detection device according to [1], wherein the frequency of the CW laser light is modulated into a sinusoidal wave. In this case, coherent detection according to the OCDR method can be suitably performed.

[0011] [3] The wind speed detection device according to [2], wherein the measurement optical system has an optical element that focuses the measurement light into the atmosphere. In the OCDR method, multiple measurement points exist for a certain modulation frequency, but by focusing the measurement light into the atmosphere and adjusting a range weighting function (RWF) for the detection distance to the focal position of the measurement light, a single measurement point can be extracted from the multiple measurement points.

[0012] [4] The wind speed detection device according to [3], wherein the measurement optical system has a scanning unit that scans the focusing position of the measurement light in the atmosphere in the optical axis direction of the measurement light. In this case, wind speed detection can be performed over a wide range by scanning a single measurement point extracted by the weighting function RWF in the optical axis direction of the measurement light.

[0013] [5] The wind speed detection device according to [1] or [2], wherein the measurement optical system has an optical element that collimates the measurement light and outputs it into the atmosphere. Even when the measurement light is collimated, a single measurement point can be extracted by a weighting function RWF under collimated conditions.

[0014] [6] The wind speed detection device according to [1] or [2], wherein the frequency of the CW laser light is modulated so that a linear change is superimposed on a nonlinear and periodic modulation, and the measurement optical system has an optical element that collimates the measurement light and outputs it into the atmosphere. In this case, even when the measurement light is collimated, by separating multiple measurement points for a certain modulation frequency on the frequency axis, it is possible to extract a single measurement point from the multiple measurement points.

[0015] [7] The wind speed detection device according to any one of [1] to [6], 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, so that wind speed detection can be performed over a wide range.

[0016] [8] The wind speed detection device according to any one of [1] to [7], wherein at least the output section, the branching section, and the detection section are configured by an optical integrated circuit, thereby enabling miniaturization of the device.

[0017] [9] The wind speed detection device according to any one of [1] to [8], further comprising a signal generation unit that generates a modulation signal for the CW laser light, thereby enabling modulation of the CW laser light to be easily performed.

[0018]

[10] The wind speed detection device according to any one of [1] to [9], 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 measurement light to analyzing the wind speed can be performed within a single device.

[0019]

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

[0020] In this wind speed detection method, the CW laser light used as the measurement light and reference light is modulated so that its frequency is nonlinear and periodic. Using CW laser light reduces the cost required for optical amplification of the measurement light compared to using pulsed light. Furthermore, modulating the CW laser light so that its frequency is nonlinear and periodic enables coherent detection based on optical correlation-domain reflectometry (OCDR). In this coherent detection, the distance resolution depends on the frequency modulation width, eliminating dependency on the detection distance. Therefore, this wind speed detection method enables wind speed detection to be performed at low cost and with high distance resolution independent of the detection distance.

[0021]

[12] The wind speed detection method according to

[11] , wherein the output step modulates the frequency of the CW laser light into a sinusoidal wave. In this case, coherent detection based on the OCDR method can be suitably performed.

[0022]

[13] The wind speed detection method according to

[12] , wherein the measurement step focuses the measurement light in the atmosphere. In the OCDR method, multiple measurement points exist for a certain modulation frequency, but by focusing the measurement light in the atmosphere and aligning a weighting function RWF for the detection distance with the focal position of the measurement light, a single measurement point can be extracted from the multiple measurement points.

[0023]

[14] The wind speed detection method according to

[13] , wherein the measurement step scans the focusing position of the measurement light in the atmosphere in the optical axis direction of the measurement light. In this case, wind speed detection can be performed over a wide range by scanning a single measurement point extracted by the weighting function RWF in the optical axis direction of the measurement light.

[0024]

[15] The wind speed detection method according to

[11] or

[12] , wherein the measurement step collimates the measurement light and outputs it to the atmosphere. Even when the measurement light is collimated, a single measurement point can be extracted by a weighting function RWF under collimated conditions.

[0025]

[16] The wind speed detection method according to

[11] or

[12] , wherein in the output step, the frequency of the CW laser light is modulated so that a linear change is superimposed on a nonlinear and periodic modulation, and in the measurement step, the measurement light is collimated and output into the atmosphere. In this case, even in a state where the measurement light is collimated, a single measurement point can be extracted from the multiple measurement points by separating multiple measurement points for a certain modulation frequency on the frequency axis.

[0026]

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

[11] to

[16] , wherein the measurement step deflects the output direction of the measurement light toward the atmosphere. In this case, the output direction of the measurement light is variable, so that wind speed detection can be performed over a wide range.

[0027]

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

[11] to

[17] , 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.

[0028] According to the present disclosure, wind speed detection can be performed at low cost and with high distance resolution independent of the detection distance.

[0029] 1A and 1B are schematic diagrams showing a configuration of a wind speed detection device according to an embodiment of the present disclosure. (a) and (b) are diagrams showing an example of frequency-modulated CW laser light. (b) is a diagram showing an example of the relationship between modulation rate and measurement points. (c) is a schematic diagram showing a first measurement method. (d) is a diagram showing simulation conditions for wind speed detection using a measurement method according to a comparative example, and (b) is a diagram showing the results. (a) to (d) are diagrams showing fluctuations in peak frequency of the beat spectrum of interference light in the comparative example. (a) is a diagram showing simulation conditions for wind speed detection using a measurement method according to Example 1 (first measurement method), and (b) is a diagram showing the results. (c) is a diagram showing the waveform of the beat spectrum of interference light in Example 1. (a) is a diagram showing simulation conditions for wind speed detection using a measurement method according to Example 2 (second measurement method), and (b) is a diagram showing the results. 1A to 1D are diagrams showing fluctuations in the peak frequency of the beat spectrum of interference light in Example 2. FIG. 1A is a diagram showing simulation conditions for wind speed detection using a measurement method according to Example 3 (third measurement method), and FIG. 1B is a diagram showing the results. FIG. 1A to 1D are diagrams showing fluctuations in the peak frequency of the beat spectrum of interference light in Example 3. FIG. 1B is a diagram showing the beat spectrum of interference light over a wide area in Example 3. FIG. 1A is a diagram showing simulation conditions for wind speed detection using a measurement method according to Example 4 (combination of the second measurement method and the third measurement method), and FIG. 1B is a diagram showing the results. FIG. 1A to 1D are diagrams showing fluctuations in the peak frequency of the beat spectrum of interference light in Example 4. FIG. 1C is a schematic diagram showing the configuration of a wind speed detection device according to a modified example.

[0030] Hereinafter, a preferred embodiment of a wind speed detection device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0031] Fig. 1 is a schematic diagram showing the configuration of a wind speed detection device according to an embodiment of the present disclosure. The wind speed detection device 1 shown in Fig. 1 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 a CW laser light L. The wind speed detection device 1 detects wind speed in the atmosphere M by modulating the CW laser light L so that its frequency is nonlinear and periodic, and performing coherent detection based on optical correlation-domain reflectometry (OCDR) between signal light Ls and reference light Lr.

[0032] 1, the wind speed detection device 1 includes an output unit 2, a branching unit 3, a frequency shifter 4, an amplifier unit 5, a measurement optical system 6, a multiplexing unit 7, a detection unit 8, a digitizer 9, and an analysis unit 10. In this embodiment, the output unit 2 and the frequency shifter 4, the frequency shifter 4 and the amplifier unit 5, the amplifier unit 5 and the measurement optical system 6, the output unit 2 and the detection unit 8, and the measurement optical system 6 and the detection unit 8 are all optically connected by optical fibers F.

[0033] In this embodiment, at least the output unit 2, the branching unit 3, and the detection unit 8 are configured by a photonic integrated circuit (PIC) 11. In this embodiment, the output unit 2, the branching unit 3, the frequency shifter 4, the amplification unit 5, the multiplexing unit 7, the detection unit 8, and the optical fiber F connecting these are configured by the photonic integrated circuit 11.

[0034] The output unit 2 is a part that outputs CW 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. Here, the CW laser light L is not light such as diffused light, but is beam-like light with a certain directivity.

[0035] 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 CW 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.

[0036] A signal generating unit 12 is connected to the output unit 2. The signal generating unit 12 generates a modulation signal G for the CW laser light L. The signal generating unit 12 is configured by, for example, a waveform generator, a function generator, etc. The signal generating unit 12 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 12 is also output to the digitizer 9 in order to synchronize the operation of the output unit 2 with the operation of the analysis unit 10.

[0037] 2(a) and 2(b) are diagrams illustrating an example of frequency-modulated CW laser light L. In this embodiment, the frequency of the CW laser light L output from the output unit 2 is modulated nonlinearly and periodically based on the modulation signal G from the signal generating unit 12. In FIG. 2(a), as an example of nonlinear and periodic modulation, the frequency of the CW laser light L is modulated sinusoidally. The frequency of the CW laser light L may also be modulated into a cosine wave whose phase is advanced by 90° relative to the sine wave. In FIG. 2(b), a linear change is superimposed on the modulation of FIG. 2(a). In the example of FIG. 2(b), the frequency of the CW laser light L is modulated sinusoidally, and further, its amplitude is modulated so as to linearly decrease over time. The superimposition of a linear change as in FIG. 2(b) is performed, for example, by modulating the drive current as described above.

[0038] The branching unit 3 is a part that branches the CW laser light L, whose frequency is nonlinearly and periodically modulated, 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 multiplexer 7.

[0039] 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.

[0040] The amplifier 5 amplifies the intensity of the measurement light Lm. The amplifier 5 is composed of, for example, a semiconductor optical amplifier, an optical fiber amplifier, or the like. A current control unit and a temperature control unit (not shown) are connected to the amplifier. The current control unit is a controller that supplies a drive current to the amplifier device that constitutes the amplifier 5. The current control unit controls the multiplication factor of the measurement light Lm in the amplifier 5 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the multiplication device that constitutes the 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 multiplication device based on the temperature measurement value of the thermistor attached to the multiplication device.

[0041] The measurement optical system 6 outputs 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. The measurement optical system 6 includes a movable stage (scanning unit) 21, a lens (optical element) 22, and a rotating stage (deflection unit) 23 on which a beam deflector 24 is mounted. The movable stage 21 has a movable axis in the optical axis direction of the measurement light Lm output from at least the end Fa of the optical fiber F connected to the output port of the amplifier unit 5. A driving element such as a stepping motor or a piezoelectric element is used to drive the movable stage 21. A stage controller (not shown) is connected to the movable stage 21. The stage controller outputs a control signal to the driving element to control the position of the movable stage.

[0042] The movable stage 21 is displaced in the optical axis direction of the measurement light Lm output from the end Fa of the optical fiber F, thereby changing the distance from the end Fa of the optical fiber F to the lens 22. This makes it possible to displace the focal position of the measurement light Lm emitted into the atmosphere M via the lens 22 in the optical axis direction of the measurement light Lm, or to collimate the measurement light Lm emitted into the atmosphere M via the lens 22.

[0043] The beam deflector 24 is a part 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 rotating stage 23 is a stage that rotates the beam deflector 24 around the optical axis of the measurement light Lm. The rotating stage 23 is driven by a driving element such as a stepping motor or a piezoelectric element, similar to the driving element for the movable stage 21. A stage controller (not shown) is connected to the movable stage 21. The stage controller outputs a control signal to the driving element to control the position of the rotating stage.

[0044] The lens 22 is an optical element that focuses or collimates the measurement light Lm. Examples of the lens 22 include a convex lens, an achromatic lens, an aspherical lens, and a combination lens formed by combining multiple lenses. In the measurement optical system 6, the measurement light Lm output from the end Fa of the optical fiber F passes through the lens 22 in a direction based on the rotation angle of the beam deflector 24 and is emitted into the atmosphere M as a beam of light with a certain directivity. The signal source in this 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 end Fa of the optical fiber F via the lens 22 as signal light Ls. The signal light Ls is separated from the measurement light Lm by the circulator 25 and output to the multiplexer 7.

[0045] The multiplexing unit 7 multiplexes the reference light Lr from the output unit 2 with the signal light Ls that has returned from the atmosphere M. The multiplexing unit 7 is configured, for example, by an optical fiber coupler. The multiplexing unit 7 generates interference light Ld between the reference light Lr and the signal light Ls. The interference light Ld is output from the output port of the multiplexing unit 7 to the detection unit 8.

[0046] The detection unit 8 is a part that outputs a detection signal D based on the result of interference between the reference light Lr and the signal light Ls. The detection unit 8 is configured by, for example, a photodetector, an avalanche photodiode, a balanced detector, etc. The detection unit 8 outputs an analog electrical signal based on the interference light Ld input from the multiplexer 7 to the digitizer 9 as the detection signal D.

[0047] The digitizer 9 is a device that converts an analog electrical signal into a digital signal. The digitizer 9 is configured, for example, with an A / D converter. The digitizer 9 converts the analog electrical signal, which is the detection signal D, into a digital signal and outputs the converted digital signal to the analysis unit 10.

[0048] The analysis unit 10 is a part that analyzes the wind speed in the atmosphere M based on the detection signal D. Physically, the analysis unit 10 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 analysis unit functions as the analysis unit 10 by executing a program stored in the memory using the CPU or GPU.

[0049] 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 10 receives the detection signal D output from the digitizer 9, it refers to the peak frequency of the beat spectrum of the interference light Ld based on the detection signal D. The analysis unit 10 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.

[0050] As shown in Figure 2(a) or 2(b), when coherent detection is performed using CW laser light L whose frequency is nonlinear and periodically modulated, 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) used in optical fiber sensing.

[0051] 2(a) or 2(b), where B is the modulation width of the CW laser light L and c is the speed of light, the distance resolution ΔZr is expressed as ΔZr = 0.48 × (c / B). Furthermore, where fm is the modulation rate of the CW laser light L modulated as shown in FIG. 2(a) or 2(b), and c is the speed of light, the detection distance ZR is expressed as ZR = c / (2 × fm). For example, if the modulation width B is 100 MHz and the modulation rate fm is 214 kHz, the distance resolution ΔZr is estimated to be 1.4 m and the detection distance ZR is estimated to be 700 m.

[0052] In optical fiber sensing using the ODCR method, where N is the number of measurement points, ZN = (c / (2 × fm)) × N holds. Therefore, as shown in FIG. 3, for example, multiple measurement points exist for one modulation rate fm. In an example of optical fiber sensing, the length of the delay fiber that guides the reference light and the length of the fiber under test (FUT) are adjusted so that a single measurement point exists on the FUT. For example, in FIG. 3, if the modulation rate fm is 457.4 kHz to 458.4 kHz, the length of the delay fiber is 2 km, and the length of the FUT is 100 m, a single measurement point can be extracted around 2350 m, where the seventh-order peak of the beat spectrum of the interference light is located.

[0053] On the other hand, in the wind speed detection device 1, the object to be measured is the atmosphere M, and the measurement light is emitted into free space (i.e., there is no FUT), so it is impossible to unify the measurement point by adjusting the length of the FUT. Also, from the perspective of miniaturizing the device, it is difficult to place a long delay fiber in the optical path of the reference light Lr. Therefore, in the wind speed detection device 1, unification of the measurement point for one modulation rate fm is achieved by applying one of the following three measurement methods.

[0054] The first measurement method is a method in which the measurement optical system 6 is set to a collimated condition under which the detection distance is the widest, and a weighting function (RWF: Range Weighting Function) under the collimated condition is used to reduce the influence of the second and subsequent peaks in the beat spectrum of the interference light Ld and to unify the measurement points.

[0055] In the first measurement method, for example, as shown in FIG. 2A, CW laser light L whose frequency is sinusoidally modulated is used as the measurement light Lm. Also, as shown in FIG. 4, the distance from the end Fa of the optical fiber F to the lens 22 is adjusted by a movable stage 21, and the measurement light Lm emitted into the atmosphere M via the lens 22 is made into a parallel beam. The RWF under collimated conditions is not constant, but is a function that decreases as the distance from the lens 22 increases. This behavior of the RWF is due to the fact that the laser beam diameter expands as the beam propagates due to the diffraction phenomenon in free space, and the amount of scattered light Lf captured (i.e., the amount of scattered light Lf that returns to the lens 22) decreases as the beam propagates.

[0056] 4, the RWF under the collimated condition takes a substantially constant first value within a certain range from 0 to the distance from the lens 22, and then gradually decreases as the distance increases, converging to a second value smaller than the first value. Therefore, for example, by adjusting the modulation rate fm or the RWF so that the first peak of the beat spectrum of the interference light Ld is located in the range where the RWF takes the first value and the second peak of the beat spectrum of the interference light Ld is located in the range where the RWF takes the second value, it is possible to unify the measurement points for wind speed detection.

[0057] FIG. 5 is a diagram showing an example of calculating the RWF under collimated conditions. FIG. 5 shows simulation results of the RWF versus distance when the lens diameter is 50 mm, the lens focal length is 237 mm, the distance between the end of the optical fiber and the lens is 237 mm, and the wavelength of the measurement light is 1550 nm. According to these results, for example, a first-order peak appears in the beat spectrum of the interference light at a position of 1000 m, and second-order and third-order peaks appear at positions that are integer multiples of that, 2000 m and 3000 m, respectively. Because the RWF at a distance of 1000 m exceeds 0.4 and the RWF at distances of 2000 m and beyond is less than 0.2, the influence of second-order and subsequent peaks can be reduced when detecting wind speed based on the first-order peak.

[0058] In the first measurement method, if the influence of the zeroth-order peak is to be reduced when detecting wind speed based on the first-order peak, a delay fiber may be introduced into the optical path of the reference light Lr. In this case, by adjusting the length of the delay fiber and setting the zeroth-order peak outside the detection range, the influence of the zeroth-order peak can be reduced when detecting wind speed based on the first-order peak.

[0059] In the second measurement method, as shown in FIG. 2A, for example, CW laser light L whose frequency is sinusoidally modulated is used as the measurement light Lm. Also, as shown in FIG. 6, the distance from the end Fa of the optical fiber F to the lens 22 is adjusted by a movable stage 21, and the measurement light Lm emitted through the lens 22 is focused into the atmosphere M. The RWF under the focusing condition is a Lorentzian function whose peak is at the focusing position C of the measurement light Lm, as shown in FIG. 6, for example. Therefore, by adjusting the modulation rate fm or the full width at half maximum of the RWF so that the first-order peak of the beat spectrum of the interference light Ld is located at the focusing position C of the measurement light Lm (the peak position of the RWF), and the zeroth-order and subsequent peaks of the beat spectrum of the interference light Ld are located at positions other than the focusing position C of the measurement light Lm (the peak position of the RWF), it is possible to unify the measurement points for wind speed detection.

[0060] In the third measurement method, as shown in FIG. 2(b), for example, a CW laser beam L whose frequency is modulated sinusoidally and whose amplitude is further modulated so as to decrease linearly with time is used as the measurement beam Lm. Also, as shown in FIG. 7, a movable stage 21 adjusts the distance from the end Fa of the optical fiber F to a lens 22, and the measurement beam Lm emitted into the atmosphere M through the lens 22 is converted into a parallel beam. In the third measurement method, because the frequency of the measurement beam Lm decreases linearly with time, each order peak of the beat spectrum of the interference beam Ld can be separated on the frequency axis according to the distance. Therefore, a single measurement point for wind speed detection is possible without setting a RWF.

[0061] 8 is a flowchart showing an example of a wind speed detection method according to an embodiment of the present disclosure. In this embodiment, the wind speed detection method is performed using the above-described wind speed detection device 1. This wind speed detection method includes a setting step (step S01), an output step (step S02), a branching step (step S03), a measurement step (step S04), a detection step (step S05), and an analysis step (step S06).

[0062] The setting step S01 is a step for setting various measurement conditions for wind speed detection. In the setting step S01, for example, a detection distance is set, and a modulation rate fm of the frequency of the measurement light Lm is set according to the set detection distance. When using the first or third measurement method, the distance between the end Fa of the optical fiber F and the lens 22 is set so that the measurement light Lm emitted into the atmosphere M via the lens 22 becomes a parallel beam. When using the second measurement method, the focusing position C of the measurement light Lm is set according to the set detection distance, and the distance between the end Fa of the optical fiber F and the lens 22 is set according to the set focusing position C. Other settings in the setting step S01 include the intensity of the CW laser light L output from the output unit 2, the multiplication factor of the signal light Ls in the amplifier unit 5, and the output direction of the measurement light Lm by the beam deflector 24.

[0063] The output step S02 is a step of outputting CW laser light L whose frequency is modulated nonlinearly and periodically. In the output step S02, the modulation signal G generated by the signal generating unit 12 is input to the output unit 2, and the frequency of the CW laser light L is modulated. When the first or second measurement method is used, the CW laser light L whose frequency is modulated sinusoidally is output from the output unit 2, as shown in FIG. 2( a). When the third measurement method is used, the CW laser light L whose frequency is modulated sinusoidally and whose amplitude is further modulated so as to linearly decrease with time is output from the output unit 2, as shown in FIG. 2( b).

[0064] The branching step S03 is a step of branching the CW laser light L into measurement light Lm and reference light Lr. In the branching step S03, the CW laser light L output from the output unit 2 is branched, one as measurement light Lm and the other as reference light Lr. The measurement light Lm is guided to the measurement optical system 6 via the frequency shifter 4 and the amplifier unit 5. The reference light Lr is guided directly to the combiner unit 7 without passing through these components.

[0065] The measurement step S04 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 S04, the measurement light Lm output from the end Fa of the optical fiber F is emitted into the atmosphere M via the lens 22. 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 end Fa of the optical fiber F via the lens 22 as signal light Ls and is multiplexed with the reference light Lr by the multiplexer 7 to generate interference light Ld.

[0066] The detection step S05 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 S05, the interference light Ld generated by the multiplexer 7 is detected by the detector 8, 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 9 and output to the analyzer 10.

[0067] Analysis step S06 is a step of analyzing the wind speed in the atmosphere M based on the detection signal D. In analysis step S06, 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. Thereafter, if detection is to be performed at a different distance, the detection distance, etc. is reset in step S01, and steps S02 to S08 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 CW laser light L used as the measurement light Lm and the reference light Lr is modulated to have a nonlinear and periodic frequency. Using the CW laser light L reduces the cost required for optical amplification of the measurement light Lm compared to using pulsed light. Furthermore, modulating the CW laser light L to have a nonlinear and periodic frequency enables coherent detection based on optical correlation-domain reflectometry (OCDR). In this coherent detection, distance resolution depends on the frequency modulation width, eliminating dependency on the detection distance. Therefore, the wind speed detection device 1 can detect wind speed at low cost and with high distance resolution independent of the detection distance.

[0069] In this embodiment, the frequency of the CW laser light L is modulated into a sinusoidal wave. Such modulation makes it possible to suitably perform coherent detection in accordance with the OCDR method.

[0070] In this embodiment, the measurement optical system 6 has a lens 22 that focuses the measurement light Lm in the atmosphere M. In the OCDR method, multiple measurement points exist for a certain modulation frequency, but by focusing the measurement light Lm in the atmosphere M and adjusting the weighting function RWF for the detection distance to the focusing position C of the measurement light Lm, a single measurement point can be extracted from the multiple measurement points (second measurement method).

[0071] In this embodiment, the measurement optical system 6 has a movable stage 21 to which the end Fa of the optical fiber F is fixed, as a scanning unit that scans the focusing position C of the measurement light Lm in the atmosphere M in the optical axis direction of the measurement light Lm. By using this movable stage 21 to scan a single measurement point extracted by the weighting function RWF in the optical axis direction of the measurement light Lm, wind speed detection can be performed over a wide range.

[0072] In this embodiment, the measurement optical system 6 has a lens 22 that collimates the measurement light Lm and outputs it into the atmosphere M. Even when the measurement light Lm is collimated, a single measurement point can be extracted by the weighting function RWF under the collimated condition (first measurement method).

[0073] In this embodiment, the frequency of the CW laser light L is modulated so that a linear change is superimposed on the nonlinear and periodic modulation, and the measurement optical system 6 collimates the measurement light Lm and outputs it into the atmosphere M (third measurement method). In this case, even when the measurement light Lm is collimated, a single measurement point can be extracted from the multiple measurement points by separating multiple measurement points for a certain modulation frequency on the frequency axis.

[0074] In this embodiment, the measurement optical system 6 has a rotation stage 23 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. This makes it possible to vary the output direction of the measurement light Lm, allowing wind speed detection to be performed over a wide range.

[0075] In this embodiment, at least the output unit 2, the branching unit 3, and the detection unit 8 are configured using an optical integrated circuit 11. This allows the device to be made smaller. In addition, this embodiment further includes a signal generating unit 12 that generates a modulation signal G for the CW laser light L. This allows the CW laser light L to be modulated easily.

[0076] Hereinafter, examples of the present disclosure will be described.

[0077] FIG. 9( a) shows the simulation conditions for wind speed detection using a measurement method according to a comparative example. FIG. 9( b) shows the results. In the comparative example, the simulation conditions were a lens diameter of 50 mm, a detection distance of 100 m, a Lorentzian RWF, and a full width at half maximum of the RWF of 34 m. In the comparative example, the measurement target (constant wind speed) was set within a distance range of 100 m ± 2 m, as shown in FIG. 9( a). The peak position of the RWF generated by the focusing of the measurement light was varied in 1 m increments, and the shift amount of the peak frequency in the beat spectrum of the interference light was obtained.

[0078] In the comparative example, as shown in Figure 9(b), no peak frequency shift was observed even within a distance range of 100 m ± 2 m, and the constant wind speed that was the measurement target was not detected. This is thought to be because the measurement target range was 4 m, while the full width at half maximum of the RWF was 34 m, which increased the influence of the detection signal in the range outside the measurement target, preventing a peak frequency shift. This can also be confirmed by the fact that, as shown in Figures 10(a) to 10(d), in the beat spectra at distances of 90 m, 95 m, 100 m, and 105 m, a peak appears at a frequency of 90 MHz, but the peak at a frequency of 80 MHz is dominant.

[0079] 11(a) shows the simulation conditions for wind speed detection using the measurement method according to Example 1 (first measurement method), and FIG. 11(b) shows the results. In Example 1, as shown in FIG. 11(a), the measurement target (constant wind speed) was set within a distance range of 995 m ± 5 m. Then, the modulation rate fm was changed between 148.4 kHz and 152.8 kHz in 0.4 kHz increments to obtain the beat spectrum of the interference light, and its peak frequency was extracted.

[0080] In Example 1, when the modulation rate fm was 148.4 kHz, the detection distance ZR was 1010 m, and when the modulation rate fm was 152.8 kHz, the detection distance ZR was 981 m. The modulation width B was 100 MHz. The distance resolution ΔZr in this case was 1.4 m. The RWF under the collimated condition was the same as that shown in FIG. 5.

[0081] In Example 1, as shown in Figure 11(b), the peak frequency shifts by approximately 10 MHz within a distance range of 995 ± 5 m, indicating that a constant wind speed, the target of measurement, was detected. Figure 12 is a diagram showing the waveform of the beat spectrum of the interference light at a distance of 995.3 m in Example 1. As shown in Figure 12, the beat spectrum at a distance of 995.3 m shows a weak secondary peak at a frequency of 80 MHz, but the peak at a frequency of 90 MHz is dominant. This shows that in Example 1, wind speed detection can be performed by extracting one measurement point from multiple measurement points for a certain modulation frequency.

[0082] Fig. 13(a) shows the simulation conditions for wind speed detection using the measurement method according to Example 2 (second measurement method), and Fig. 13(b) shows the results. In Example 2, the simulation conditions were a lens diameter of 50 mm, a detection distance of 100 m, a Lorentzian RWF, and a full width at half maximum of 34 m. The modulation width B of the measurement light was 100 MHz. The distance resolution ΔZr in this case was 1.4 m.

[0083] 13A, the measurement target (constant wind speed) was set within a distance range of 100 m±2 m. The peak position of the RWF generated by the focusing of the measurement light was fixed at 100 m, and the beat spectrum of the interference light was acquired while changing the modulation rate fm between 1.37 MHz and 1.66 MHz in 10 kHz increments, and the peak frequency was extracted.

[0084] In Example 2, as shown in Figure 13(b), the peak frequency shifts by approximately 10 MHz within a distance range of 100 ± 2 m, indicating that a constant wind speed, the target of measurement, was detected. Furthermore, in Example 2, as shown in Figures 14(a) to 14(d), the beat spectra at distances of 90.3 m and 97.3 m show peaks at a frequency of 80 MHz, the beat spectrum at a distance of 98.0 m shows peaks at frequencies of 79 MHz and 90 MHz, and the beat spectrum at a distance of 99.9 m shows a peak at a frequency of 90 MHz. These results demonstrate that, similar to Example 1, Example 2 also allows wind speed detection by extracting one measurement point from multiple measurement points for a given modulation frequency.

[0085] 15(a) shows the simulation conditions for wind speed detection using the measurement method according to Example 3 (third measurement method), and (b) shows the results. In Example 3, the simulation conditions were a lens diameter of 50 mm and a detection distance of 100 m. The modulation width B of the measurement light was set to 100 MHz. In this case, the distance resolution ΔZr was 1.4 m. The chirp rate of the measurement light (the slope of the linear change superimposed on the sinusoidal modulation) was set to 160 THz / sec.

[0086] 15A, the measurement target (constant wind speed) was set within a distance range of 100 m±2 m. The RWF generated by the focusing of the measurement light was kept constant regardless of the distance, and the beat spectrum of the interference light was acquired while changing the modulation rate fm between 1.37 MHz and 1.66 MHz in 10 kHz increments, and its peak frequency was extracted.

[0087] In Example 3, as shown in Fig. 15(b), the peak frequency shifts by about 10 MHz within a distance range of 100 ± 2 m, indicating that a constant wind speed, which is the measurement target, is detected. In Fig. 15(b), the peak frequency increases linearly with respect to distance with a slope based on the chirp rate of the measurement light. However, by correcting the linear increase in peak frequency based on the chirp rate of the measurement light, wind speed detection can be performed in the same way as in Example 2.

[0088] 16(a) to 16(d), in Example 3, the beat spectrum at a distance of 90.3 m shows a peak at a frequency of 176 MHz, the beat spectrum at a distance of 97.3 m shows a peak at a frequency of 184 MHz, the beat spectrum at a distance of 98.0 m shows peaks at frequencies of 184 MHz and 195 MHz, and the beat spectrum at a distance of 99.9 m shows a peak at a frequency of 196 MHz.

[0089] Fig. 17 shows the beat spectrum of the interference light in Example 3 in the range of 0 MHz to 500 MHz. In the example shown in Fig. 17, it can be seen that the zeroth to third peak frequencies of the beat spectrum are separated on the frequency axis at intervals of about 100 MHz. From these results, it can be seen that in Example 3 as well, as in Examples 1 and 2, it is possible to detect wind speed by extracting one measurement point from multiple measurement points for a certain modulation frequency.

[0090] 18(a) shows the simulation conditions for wind speed detection using the measurement method according to Example 4 (a combination of the second and third measurement methods), and (b) shows the results. In Example 4, the simulation conditions were a lens diameter of 50 mm, a detection distance of 100 m, a Lorentzian RWF, and a full width at half maximum of 34 m. The modulation width B of the measurement light was 100 MHz. The distance resolution ΔZr in this case was 1.4 m. The chirp rate (the slope of the linear change superimposed on the sinusoidal modulation) of the measurement light was 160 THz / sec.

[0091] 18A, the measurement target (constant wind speed) was set within a range of 100 m±2 m. The peak position of the RWF generated by the focusing of the measurement light was fixed at 100 m, and the beat spectrum of the interference light was acquired while changing the modulation rate fm between 1.37 MHz and 1.66 MHz in 10 kHz increments, and the peak frequency was extracted.

[0092] In Example 4, as shown in Fig. 18(b), the peak frequency shifts by about 10 MHz within a distance range of 100 ± 2 m, indicating that a constant wind speed, which is the measurement target, is detected. In Fig. 18(b), the peak frequency increases linearly with respect to distance with a slope based on the chirp rate of the measurement light. However, by correcting the linear increase in the peak frequency based on the chirp rate of the measurement light, wind speed detection can be performed in the same way as in Example 2.

[0093] 19(a) to 16(d), in Example 4, the beat spectrum at a distance of 90.3 m shows a peak at a frequency of 176 MHz, and the beat spectrum at a distance of 97.3 m shows a peak at a frequency of 184 MHz. Furthermore, the beat spectrum at a distance of 98.0 m shows peaks at frequencies of 184 MHz and 195 MHz, and the beat spectrum at a distance of 99.9 m shows a peak at a frequency of 196 MHz. These results demonstrate that, similar to Examples 1 to 3, Example 4 also allows wind speed detection by extracting one measurement point from multiple measurement points for a certain modulation frequency.

[0094] The present disclosure is not limited to the above-described embodiment. For example, in the above-described embodiment, the output direction of the measurement light Lm toward the atmosphere M is deflected in an arbitrary direction using the beam deflector 24. However, the 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 22, 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. Furthermore, 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.

[0095] Furthermore, although the above embodiment has exemplified the optical fiber device type circulator 25, a spatial optical system type circulator 31 as shown in Fig. 20 may also be used. In the example of Fig. 20, the spatial optical system type circulator 31 is composed of a polarizing beam splitter 32 and a λ / 4 wave plate 33. A lens 34 is disposed in front of the polarizing beam splitter 32, and a lens 35 mounted on the movable stage 21 is disposed in the rear of the λ / 4 wave plate 33. The lenses 34 and 35 may be either convex lenses or concave lenses.

[0096] With this configuration, the distance between the lens 35 and the lens 22 can be adjusted by displacing the movable stage 21 in the optical axis direction of the measurement light Lm. This makes it possible to displace the focal position of the measurement light Lm emitted into the atmosphere M via the lens 22 in the optical axis direction of the measurement light Lm, or to collimate the measurement light Lm emitted into the atmosphere M via the lens 22.

[0097] 1...wind speed detection device, 2...output section, 3...branching section, 6...measurement optical system, 8...detection section, 10...analysis section, 11...optical integrated circuit, 12...signal generation section, 21...movable stage (scanning section), 22...lens (optical element), 23...rotating stage (deflection section), 24...beam deflection plate (deflection section), L...CW laser light, Lm...measurement light, Lr...reference light, Lf...scattered light, Ls...signal light, C...focusing position, D...detection signal, G...modulation signal, M...atmosphere.

Claims

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

2. A wind speed detection device as claimed in claim 1, wherein the frequency of said CW laser light is modulated into a sinusoidal wave.

3. The wind speed detection device according to claim 2, wherein said measurement optical system has an optical element for focusing said measurement light into said atmosphere.

4. A wind speed detection device according to claim 3, wherein said measurement optical system has a scanning section which scans the focusing position of said measurement light in the atmosphere in the direction of the optical axis of said measurement light.

5. A wind speed detection device according to claim 1 or 2, wherein said measurement optical system has an optical element which collimates said measurement light and outputs it into said atmosphere.

6. A wind speed detection device as claimed in claim 1 or 2, wherein the frequency of the CW laser light is modulated so that a linear change is superimposed on a non-linear and periodic modulation, and the measurement optical system has an optical element that collimates the measurement light and outputs it into the atmosphere.

7. A wind speed detection device according to any one of claims 1 to 6, wherein the measurement optical system has a deflection section that deflects the output direction of the measurement light toward the atmosphere.

8. A wind speed detection device according to any one of claims 1 to 7, wherein at least the output section, the branching section, and the detection section are constituted by an optical integrated circuit.

9. A wind speed detection device according to any one of claims 1 to 8, further comprising a signal generating section for generating a modulation signal for said CW laser light.

10. A wind speed detection device according to any one of claims 1 to 9, further comprising an analysis unit that analyzes the wind speed in the atmosphere based on the detection signal.

11. A wind speed detection method comprising: an output step of outputting a CW laser light whose frequency is non-linearly and periodically modulated; a branching step of branching the CW laser light into a measurement light and a reference light; a measurement step of outputting the measurement light into the atmosphere and receiving scattered light of the measurement light in the atmosphere as a signal light; and a detection step of outputting a detection signal based on the result of interference between the reference light and the signal light.

12. The wind speed detection method according to claim 11, wherein in said outputting step, the frequency of said CW laser light is modulated into a sine wave.

13. The wind speed detection method according to claim 12, wherein in said measuring step, said measuring light is focused in said atmosphere.

14. The wind speed detection method according to claim 13, wherein in said measuring step, the focusing position of said measurement light in the atmosphere is scanned in the direction of the optical axis of said measurement light.

15. The wind speed detection method according to claim 11 or 12, wherein in said measuring step, said measuring light is collimated and outputted into said atmosphere.

16. A wind speed detection method as claimed in claim 11 or 12, wherein in the output step, the frequency of the CW laser light is modulated so that a linear change is superimposed on a non-linear and periodic modulation, and in the measurement step, the measurement light is collimated and output into the atmosphere.

17. The wind speed detection method according to any one of claims 11 to 16, wherein in the measuring step, an output direction of the measurement light directed into the atmosphere is deflected.

18. The wind speed detection method according to any one of claims 11 to 17, further comprising an analysis step of analyzing wind speed in the atmosphere based on the detection signal.

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