Wind speed detection device and wind speed detection method

Abstract

To provide a wind speed detection device and a wind speed detection method with which wind speed detection can be executed with high distance resolution at low cost without depending on a detected distance.SOLUTION: A wind speed detection device 1 comprises: an output unit 2 that outputs CW laser light L the frequency of which is nonlinearly and periodically modulated; a branching 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 a result of the interference between the reference light Lr and the signal light Ls.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As one of the sensing technologies using light, LIDAR (Light Detection and Ranging) is known. Although the application of LIDAR has been developing in the field of autonomous driving in recent years, it is a technology originally widely used in fields such as meteorology. As LIDAR used in the field of meteorology, so-called WindLIDAR for detecting wind speed is known. WindLIDAR is used, for example, in wind condition surveys for selecting the installation location of wind turbines, and in recent years, its application to the safe operation management of flying objects such as drones is expected.

[0003] Coherent detection is used for wind speed detection with LIDAR. In this method, the laser light output from the light source is branched into measurement light and reference light, modulated and amplified on the measurement light, and then emitted into the atmosphere. The signal source in WindLIDAR is the scattered light generated by the scattering of the measurement light by innumerable aerosols in the atmosphere. When the wind blows, the aerosols move along with the wind, and the frequency of the scattered light changes (Doppler shift). Therefore, by using the scattered light from the atmosphere as the signal light and interfering it with the reference light, and obtaining the shift amount of the peak frequency in the beat spectrum of the interference light, the wind speed in the atmosphere can be detected (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] There are two types of LIDAR methods: a method using pulsed light and a method using CW (Continuous Wave) light. In the method using pulsed light, the range resolution depends on the pulse width and does not depend on the detection range, but there is a problem that the cost required for optical amplification of the measurement light is high. On the other hand, in the method using CW light, while the cost required for optical amplification of the measurement light is low, since measurement is performed while changing the focal position of the measurement light, the range resolution depends on the depth of focus of the measurement light and has a dependency on the detection range.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide a wind speed detection device and a wind speed detection method capable of performing wind speed detection with high range resolution at low cost and without depending on the detection range.

Means for Solving the Problems

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

[0008] [1] An output unit that outputs CW laser light whose frequency is non-linearly 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 an interference result between the reference light and the signal light. A wind speed detection device comprising:

[0009] In this wind speed detection device, the CW laser light used as the measurement light and the reference light is modulated so that the frequency is non-linear and periodic. By using CW laser light, the cost required for optical amplification of the measurement light can be reduced compared to the case of using pulsed light. Further, by modulating the CW laser light so that the frequency is non-linear and periodic, coherent detection according to the optical correlation domain reflectometry (OCDR method) can be performed. In this coherent detection, the range resolution depends on the frequency modulation width, and the dependence on the detection distance can be eliminated. Therefore, in this wind speed detection device, wind speed detection can be performed with low cost and high range resolution without depending on the detection distance.

[0010] [2] The wind speed detection device according to [1], wherein the frequency of the CW laser light is sinusoidally modulated. 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 includes an optical element that condenses the measurement light in the atmosphere. In the OCDR method, there are a plurality of measurement points for a certain modulation frequency. However, by condensing the measurement light in the atmosphere and adjusting the range weighting function (RWF) with respect to the detection distance to the focal position of the measurement light, a single measurement point can be extracted from among the plurality of measurement points.

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

[0013] [5] The wind speed detection device according to [1] or [2], wherein the measurement optical system includes 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 the range weighting function RWF under collimation conditions.

[0014] [6] The frequency of the CW laser light is modulated such 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. The wind speed detection device according to [1] or [2]. In this case, even in a state where the measurement light is collimated, a single measurement point can be extracted from a plurality of measurement points by separating the plurality of measurement points for a certain modulation frequency on the frequency axis.

[0015] [7] The measurement optical system has a deflection unit that deflects the output direction of the measurement light toward the atmosphere. The wind speed detection device according to any one of [1] to [6]. In this case, since the output direction of the measurement light is variable, wind speed detection can be performed over a wide range.

[0016] [8] At least the output unit, the branching unit, and the detection unit are configured by an optical integrated circuit. The wind speed detection device according to any one of [1] to [7]. Thereby, miniaturization of the device can be achieved.

[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, modulation of the CW laser light can 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 the output of the measurement light to the analysis of the wind speed can be performed within one device.

[0019]

[11] 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 measurement light and 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 signal light, and a detection step of outputting a detection signal based on an interference result between the reference light and the signal light. A wind speed detection method.

[0020] In this wind speed detection method, the CW laser light used as the measurement light and the reference light is modulated so that the frequency is non-linear and periodic. By using CW laser light, the cost required for optical amplification of the measurement light can be reduced compared to the case of using pulsed light. Further, by modulating the CW laser light so that the frequency is non-linear and periodic, coherent detection according to the optical correlation domain reflectometry (OCDR method) can be performed. In this coherent detection, the range resolution depends on the frequency modulation width, and the dependence on the detection distance can be eliminated. Therefore, in this wind speed detection method, wind speed detection can be performed with high range resolution at low cost and without depending on the detection distance.

[0021]

[12] In the output step, the wind speed detection method according to

[11] , wherein the frequency of the CW laser light is modulated in a sine wave shape. In this case, coherent detection according to the OCDR method can be preferably performed.

[0022]

[13] In the measurement step, the wind speed detection method according to claim 12, wherein the measurement light is focused in the atmosphere. In the OCDR method, there are a plurality of measurement points for a certain modulation frequency. However, by focusing the measurement light in the atmosphere and adjusting the weighting function RWF with respect to the detection distance to the focal position of the measurement light, a single measurement point can be extracted from among the plurality of measurement points.

[0023]

[14] In the measurement step, the wind speed detection method according to

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

[0024]

[15] In the measurement step, the wind speed detection method according to

[11] or

[12] , wherein the measurement light is collimated and output into the atmosphere. Even when the measurement light is collimated, a single measurement point can be extracted by the weighting function RWF under collimation conditions.

[0025]

[16] In the output step, the frequency of the CW laser light is modulated such 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, the wind speed detection method according to

[11] or

[12] . In this case, even when the measurement light is collimated, a single measurement point can be extracted from a plurality of measurement points by separating the plurality of measurement points for a certain modulation frequency on the frequency axis.

[0026]

[17] In the measurement step, the output direction of the measurement light directed into the atmosphere is deflected, the wind speed detection method according to any one of

[11] to

[16] . In this case, since the output direction of the measurement light is variable, wind speed detection can be carried out 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 the output of the measurement light to the analysis of the wind speed can be carried out.

Advantages of the Invention

[0028] According to the present disclosure, wind speed detection can be carried out at low cost and with high range resolution without depending on the detection distance.

Brief Description of the Drawings

[0029]

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Embodiments for Carrying Out the Invention

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

[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 the wind speed in the atmosphere M by LIDAR (Light Detection and Ranging). In the wind speed detection device 1, a frequency modulation method using CW laser light L is adopted. In the wind speed detection device 1, the CW laser light L is modulated so that the frequency is non-linear and periodic, and coherent detection according to the optical correlation-domain reflectometry (OCDR method) is performed between the signal light Ls and the reference light Lr, thereby detecting the wind speed in the atmosphere M.

[0032] As shown in FIG. 1, the wind speed detection device 1 includes an output unit 2, a branching unit 3, a frequency shifter 4, an amplification unit 5, a measurement optical system 6, a multiplexing unit 7, a detection unit 8, a digitizer 9, and an analysis unit 10. In the present embodiment, the output unit 2 and the frequency shifter 4, the frequency shifter 4 and the amplification unit 5, the amplification 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 an optical fiber F.

[0033] Further, in the present embodiment, at least the output unit 2, the branching unit 3, and the detection unit 8 are constituted by a photonic integrated circuit (PIC) 11. In the present 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 constituted by the photonic integrated circuit 11.

[0034] The output unit 2 is a part that outputs a CW laser beam L whose frequency is non-linearly and periodically modulated. Examples of the laser device constituting the output unit 2 include a distributed feedback (DFB) laser device, a distributed Bragg reflector (DBR) laser device, an external cavity laser device, and the like. Here, the CW laser beam L is not light such as diffused light, but is beam-shaped light having 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 constituting the output unit 2. The current control unit modulates the drive current to modulate the frequency of the CW laser beam L output from the output unit 2. The temperature control unit is a controller that maintains the temperature of the laser device constituting the output unit 2 at a constant level. The temperature control unit includes, for example, a thermistor and a Peltier element, and drives the Peltier element so that the temperature of the laser device is maintained constant based on the temperature measurement value of the thermistor attached to the laser device.

[0036] A signal generation unit 12 is connected to the output unit 2. The signal generation unit 12 is a part that generates a modulation signal G for the CW laser beam L. The signal generation unit 12 is constituted by, for example, a waveform generator, a function generator, and the like. The signal generation 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 generation unit 12 is also output to the digitizer 9 for synchronization between the operation of the output unit 2 and the operation of the analysis unit 10.

[0037] Figs. 2(a) and 2(b) are diagrams showing an example of frequency-modulated CW laser beam L. In the present embodiment, based on the modulation signal G from the signal generation unit 12, the frequency of the CW laser beam L output from the output unit 2 is modulated non-linearly and periodically. In Fig. 2(a), as an example of non-linear and periodic modulation, the frequency of the CW laser beam L is modulated in a sine wave shape. The frequency of the CW laser beam L may be modulated in a cosine wave shape with a phase advanced by 90° with respect to the sine wave. In Fig. 2(b), in addition to the modulation in Fig. 2(a), a linear change is superimposed. In the example of Fig. 2(b), the frequency of the CW laser beam L is modulated in a sine wave shape, and further, its amplitude is modulated so as to decrease linearly with time. The superimposition of the linear change as in Fig. 2(b) is performed, for example, by modulating the drive current described above.

[0038] The branching unit 3 is a part that branches the CW laser beam L whose frequency is modulated non-linearly and periodically into the measurement light Lm and the reference light Lr. The branching unit 3 is constituted by, for example, 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 7.

[0039] The frequency shifter 4 is a part that shifts the frequency of the measurement light Lm. The frequency shifter 4 is constituted by, for example, 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 generation unit (not shown) that generates a voltage signal for driving the frequency shifter 4. The signal generation unit may be constituted by, for example, a waveform generator, a function generator, or the like.

[0040] The amplifying unit 5 is a part that amplifies the intensity of the measurement light Lm. The amplifying unit 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 amplifying unit. The current control unit is a controller that supplies a drive current to the amplifying device constituting the amplifying unit 5. The current control unit controls the amplification factor of the measurement light Lm in the amplifying unit 5 by modulating the drive current. The temperature control unit is a controller that keeps the temperature of the multiplying device constituting the amplifying unit 5 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 multiplying device so that the temperature of the multiplying device is kept constant.

[0041] The measurement optical system 6 is a part that outputs the measurement light Lm into the atmosphere M and receives the scattered light Lf of the measurement light Lm in the atmosphere M as the signal light Ls. The measurement optical system 6 includes a movable stage (scanning unit) 21, a lens (optical element) 22, and a rotating stage (deflecting unit) 23 on which a beam deflector plate 24 is mounted. The movable stage 21 is a stage having a movable axis in the optical axis direction of the measurement light Lm output from the end Fa of the optical fiber F connected to at least the output port of the amplifying unit 5. For driving the movable stage 21, drive elements such as a stepping motor and a piezo element are used. A stage controller (not shown) is connected to the movable stage 21. The stage controller outputs a control signal for controlling the position of the movable stage to the drive element.

[0042] By displacing the movable stage 21 in the optical axis direction of the measurement light Lm output from the end Fa of the optical fiber F, the distance from the end Fa of the optical fiber F to the lens 22 can be changed. Thereby, it becomes 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 an arbitrary direction. As the beam deflector 24, for example, a wedge substrate or the like can be used. The rotary stage 23 is a stage that rotates the beam deflector 24 around the optical axis of the measurement light Lm. For driving the rotary stage 23, similar to the driving of the movable stage 21, driving elements such as a stepping motor and a piezo element are used. A stage controller (not shown) is connected to the movable stage 21. The stage controller outputs a control signal for controlling the position of the rotary stage to the driving element.

[0044] The lens 22 is an optical element that condenses or collimates the measurement light Lm. As the lens 22, for example, a convex lens, an achromatic lens, an aspherical lens, a combination lens formed by combining a plurality of lenses, or the like is used. In the measurement optical system 6, the measurement light Lm output from the end portion Fa of the optical fiber F is emitted into the atmosphere M as a beam-shaped light having a certain directivity through the lens 22 in a direction based on the rotation angle of the beam deflector 24. The signal source in this wind speed detection device 1 is the scattered light Lf generated by the measurement light Lm being scattered by innumerable aerosols P in the atmosphere M. A part of the scattered light Lf returns to the end portion Fa of the optical fiber F again as the signal light Ls through the lens 22. The signal light Ls is separated from the measurement light Lm by the circulator 25 and output to the multiplexing unit 7.

[0045] The multiplexing unit 7 is a part that multiplexes the reference light Lr from the output unit 2 and the signal light Ls returned from the atmosphere M. The multiplexing unit 7 is constituted by, for example, an optical fiber coupler. By the multiplexing unit 7, the interference light Ld of the reference light Lr and the signal light Ls is generated. 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 interference result of the reference light Lr and the signal light Ls. The detection unit 8 is constituted by, for example, a photodetector, an avalanche photodiode, a balanced detector, or the like. The detection unit 8 outputs an analog electrical signal based on the interference light Ld input from the multiplexing unit 7 as the detection signal D to the digitizer 9.

[0047] The digitizer 9 is a device that converts an analog electrical signal into a digital signal. The digitizer 9 is constituted by, for example, an A / D converter or the like. 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 including memories such as a RAM and a ROM, processors such as a CPU and a GPU, a communication interface, and a storage unit such as a hard disk. Examples of such a computer system include a personal computer, a cloud server, a smart device (such as a smartphone and a tablet terminal), a microcomputer, and an FPGA (field-programmable gate array). The analysis unit functions as the analysis unit 10 by executing a program stored in the memory with the CPU or the GPU.

[0049] As described above, the signal source in the wind speed detection device 1 is the scattered light Lf generated by the measurement light Lm being scattered by innumerable aerosols P in the atmosphere M. When the wind blows in the atmosphere M, the aerosol P moves along with the wind, and the frequency of the scattered light Lf changes (Doppler shift). 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 obtaining the shift amount of the peak frequency of the beat spectrum of the interference light Ld.

[0050] As shown in Fig. 2(a) or Fig. 2(b), when coherent detection is performed using a CW laser beam L whose frequency is non-linearly and periodically modulated, the distance resolution and the detection distance of the wind speed detection can be calculated according to the distance resolution and the detection distance in the optical correlation-domain reflectometry (OCDR method) used in the optical fiber sensing.

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

[0052] In the optical fiber sensing by the ODCR method, when the measurement point is N, ZN = (c / (2×fm))×N holds. Therefore, as shown in Fig. 3 for example, there are a plurality of measurement points for a single 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 FUT are adjusted so that a single measurement point exists on the fiber under test (FUT). For example, in Fig. 3, when 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 vicinity of 2350 m where the seventh peak of the beat spectrum of the interference light is located can be extracted as a single measurement point.

[0053] On the other hand, in the wind speed detection device 1, since the measurement target is the atmosphere M and the measurement light is emitted into free space (i.e., there is no FUT), it is impossible to make the measurement points single by adjusting the length of the FUT. Also, from the viewpoint of downsizing the device, it is difficult to arrange a long delay fiber in the optical path of the reference light Lr. Therefore, in the wind speed detection device 1, the singulation of the measurement points for a single modulation rate fm is realized by applying any one of the following three measurement methods.

[0054] The first measurement method is a method of making the measurement optical system 6 set to the collimation condition where the detection distance is the widest, and using the weighting function (RWF: Range Weighting Function) under the collimation condition to reduce the influence of peaks of the second order and higher of the beat spectrum of the interference light Ld to achieve the unification of the measurement points.

[0055] In the first measurement method, for example, as shown in Fig. 2(a), the 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 the movable stage 21, and the measurement light Lm emitted into the atmosphere M through the lens 22 is made parallel light. The RWF under the collimation condition is not constant, but is a function that decreases as the distance from the lens 22 increases. Such behavior of the RWF is due to the fact that the laser beam diameter expands with propagation 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 with propagation.

[0056] The RWF under the collimation condition, for example, as shown in Fig. 4, 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 and converges 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-order 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-order peak of the beat spectrum of the interference light Ld is located in the range where the RWF takes the second value, it becomes possible to unify the measurement points for wind speed detection.

[0057] FIG. 5 is a diagram showing an example of calculating the RWF under collimation conditions. In FIG. 5, the simulation results of the RWF with respect to distance are shown 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 this result, for example, the first peak of the beat spectrum of the interference light appears at the position of 1000 m, and the second and third peaks of the beat spectrum of the interference light appear at the positions of 2000 m and 3000 m, which are integer multiples thereof, respectively. Since the RWF at a distance of 1000 m exceeds 0.4 and the RWF after a distance of 2000 m is less than 0.2, the influence of the peaks after the second order can be reduced in detecting the wind speed based on the first peak.

[0058] In the first measurement method, when reducing the influence of the zero-order peak in detecting the wind speed based on the first 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 zero-order peak outside the detection range, the influence of the zero-order peak can be reduced in detecting the wind speed based on the first peak.

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

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

[0061] FIG. 8 is a flowchart showing an example of a wind speed detection method according to an embodiment of the present disclosure. In the present embodiment, the wind speed detection method is implemented 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 of setting various measurement conditions for wind speed detection. In the setting step S01, for example, the detection distance is set, and the modulation rate fm of the frequency of the measurement beam Lm is set according to the set detection distance. When the first measurement method or the third measurement method is used, the distance between the end Fa of the optical fiber F and the lens 22 is set so that the measurement beam Lm emitted into the atmosphere M through the lens 22 becomes a parallel beam. When the second measurement method is used, the condensing position C of the measurement beam 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 condensing position C. Further, in the setting step S01, the intensity of the CW laser beam L output from the output unit 2, the amplification factor of the signal beam Ls in the amplification unit 5, the output direction of the measurement beam Lm by the beam deflector 24, etc. are set.

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

[0064] The branching step S03 is a step of branching the CW laser beam L into a measurement light Lm and a reference light Lr. In the branching step S03, the CW laser beam L output from the output unit 2 is branched, with one being the measurement light Lm and the other being the reference light Lr. The measurement light Lm is guided to the measurement optical system 6 through the frequency shifter 4 and the amplifier 5. The reference light Lr is directly guided to the multiplexer 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 the scattered light Lf of the measurement light Lm in the atmosphere M as the 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 through the lens 22. The measurement light Lm is scattered by innumerable aerosols P in the atmosphere M to become the scattered light Lf. A part of the scattered light Lf returns to the end Fa of the optical fiber F as the signal light Ls through the lens 22 and is multiplexed with the reference light Lr by the multiplexer 7 to generate the 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 subjected to analog / digital conversion by the digitizer 9 and output to the analysis unit 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 referred to based on the detection signal D. Then, the wind speed in the atmosphere M is detected by obtaining the shift amount of the peak frequency in the beat spectrum of the interference light Ld. After that, when detection is performed at different distances, the detection distance etc. are reset in step S01, and steps S02 to S08 are executed again. After performing wind speed detection within a desired distance range, the process is terminated.

[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 so that the frequency is non-linear and periodic. By using the CW laser light L, the cost required for optical amplification of the measurement light Lm can be reduced compared to the case of using pulsed light. Also, by modulating the CW laser light L so that the frequency is non-linear and periodic, coherent detection according to the optical correlation-domain reflectometry (OCDR method) can be performed. In this coherent detection, the distance resolution depends on the frequency modulation width, and the dependence on the detection distance can be eliminated. Therefore, in this wind speed detection device 1, wind speed detection can be performed with low cost and high distance resolution without depending on the detection distance.

[0069] In the present embodiment, the frequency of the CW laser light L is modulated in a sine wave shape. By such modulation, coherent detection according to the OCDR method can be suitably performed.

[0070] In the present embodiment, the measurement optical system 6 has a lens 22 that condenses the measurement light Lm into the atmosphere M. In the OCDR method, there are a plurality of measurement points for a certain modulation frequency. However, by condensing the measurement light Lm into the atmosphere M and adjusting the weighting function RWF with respect to the detection distance to the condensing position C of the measurement light Lm, a single measurement point can be extracted from among the plurality of measurement points (second measurement method).

[0071] In this embodiment, the measurement optical system 6 has a movable stage 21 to which the end portion Fa of the optical fiber F is fixed, as a scanning unit that scans the condensing position C of the measurement light Lm in the atmosphere M in the optical axis direction of the measurement light Lm. By this movable stage 21, by scanning 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 carried out 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 collimation conditions (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 a non-linear and periodic modulation, and the measurement optical system 6 includes a mode in which the measurement light Lm is collimated and output into the atmosphere M (third measurement method). In this case, even when the measurement light Lm is collimated, by separating a plurality of measurement points for a certain modulation frequency on the frequency axis, a single measurement point can be extracted from the plurality of measurement points.

[0074] In this embodiment, the measurement optical system 6 has a rotary stage 23 equipped with a beam deflector plate 24 as a deflecting unit that deflects the output direction of the measurement light Lm toward the atmosphere M. Thereby, since the output direction of the measurement light Lm becomes variable, wind speed detection can be carried out over a wide range.

[0075] In this embodiment, at least the output unit 2, the branching unit 3, and the detection unit 8 are constituted by an optical integrated circuit 11. Thereby, miniaturization of the apparatus is achieved. Further, in this embodiment, a signal generation unit 12 that generates a modulation signal G for the CW laser light L is further provided. Thereby, modulation of the CW laser light L can be easily carried out.

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

[0077] Fig. 9(a) is a diagram showing the simulation conditions for wind speed detection by the measurement method according to the comparative example. Fig. 9(b) is a diagram showing the results. In the comparative example, as the simulation conditions, the lens diameter was 50 mm, the detection distance was 100 m, the RWF was of the Lorentz type, and the full width at half maximum of the RWF was 34 m. Also, in the comparative example, as shown in Fig. 9(a), a measurement target (constant wind speed) was set in the range of 100 m ± 2 m. Then, while varying the peak position of the RWF generated by the condensing of the measurement light in 1 m increments, 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 Fig. 9(b), no shift in the peak frequency was observed even in the range of 100 m ± 2 m, and a constant wind speed that was the measurement target was not detected. This is presumably because the full width at half maximum of the RWF is 34 m while the measurement target is in the range of 4 m, so the influence of the detection signal in the range outside the measurement target becomes large and no shift in the peak frequency occurs. This can also be confirmed from the fact that, as shown in Figs. 10(a) to 10(d), although peaks appear at the position of a frequency of 90 MHz in the respective beat spectra at distances of 90 m, 95 m, 100 m, and 105 m, the peak at the position of a frequency of 80 MHz is dominant.

[0079] Fig. 11(a) is a diagram showing the simulation conditions for wind speed detection by the measurement method according to Example 1 (the first measurement method), and Fig. 11(b) is a diagram showing the results. In Example 1, as shown in Fig. 11(a), a measurement target (constant wind speed) was set in the range of 995 m ± 5 m. Then, while changing the modulation rate fm in 0.4 kHz increments between 148.4 kHz and 152.8 kHz, the beat spectrum of the interference light was obtained, and the peak frequency thereof was extracted.

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

[0081] In Example 1, as shown in FIG. 11(b), it can be seen that in the range of a distance of 995 ± 5 m, the peak frequency has shifted by about 10 MHz, and a certain wind speed that is the measurement target has been detected. FIG. 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 FIG. 12, although a secondary peak appears weakly at the position of a frequency of 80 MHz in the beat spectrum at a distance of 995.3 m, it can be confirmed that the peak at the position of a frequency of 90 MHz is dominant. From this, it can be seen that in Example 1, it is possible to extract one measurement point from among a plurality of measurement points for a certain modulation frequency and perform wind speed detection.

[0082] FIG. 13(a) is a diagram showing the simulation conditions for wind speed detection by the measurement method according to Example 2 (the second measurement method), and FIG. 13(b) is a diagram showing the results. In Example 2, as simulation conditions, the lens diameter was 50 mm, the detection distance was 100 m, the RWF was of the Lorentz type, and the full width at half maximum of the RWF was 34 m. The modulation width B of the measurement light was 100 MHz. In this case, the distance resolution ΔZr was 1.4 m.

[0083] Also, in Example 2, as shown in FIG. 13(a), a measurement target (a certain wind speed) was set in the range of a distance of 100 m ± 2 m. Then, the peak position of the RWF generated by the condensing of the measurement light was fixed at the position of 100 m, and the beat spectrum of the interference light was acquired while changing the modulation rate fm in steps of 10 kHz between 1.37 MHz and 1.66 MHz, and the peak frequency was extracted.

[0084] In Example 2, as shown in FIG. 13(b), in the range of a distance of 100 ± 2 m, it can be seen that the peak frequency has shifted by about 10 MHz and a certain wind speed to be measured has been detected. Also, in Example 2, as shown in FIGS. 14(a) to 14(d), in the beat spectra at distances of 90.3 m and 97.3 m, peaks appear at the position of a frequency of 80 MHz, in the beat spectrum at a distance of 98.0 m, peaks appear at the positions of frequencies of 79 MHz and 90 MHz, and in the beat spectrum at a distance of 99.9 m, a peak appears at the position of a frequency of 90 MHz. From these results, it can be seen that also in Example 2, as in Example 1, it is possible to extract one measurement point from among a plurality of measurement points for a certain modulation frequency and perform wind speed detection.

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

[0086] Also, in Example 3, as shown in FIG. 15(a), a measurement object (a certain wind speed) was set in the range of a distance of 100 m ± 2 m. Then, the RWF generated by the condensing of the measurement light was always made constant regardless of the distance, and while changing the modulation rate fm in steps of 10 kHz between 1.37 MHz and 1.66 MHz, the beat spectrum of the interference light was acquired and its peak frequency was extracted.

[0087] In Example 3, as shown in Fig. 15(b), in the range of a distance of 100 ± 2 m, the peak frequency has shifted by about 10 MHz, and it can be seen that a certain wind speed being measured has been detected. In Fig. 15(b), the peak frequency with respect to the distance increases linearly with the slope based on the chirp rate of the measurement light. However, by correcting the linear increase of the peak frequency based on the chirp rate of the measurement light, the wind speed can be detected in the same manner as in Example 2.

[0088] In Example 3, as shown in Figs. 16(a) to 16(d), in the beat spectrum at a distance of 90.3 m, a peak appears at a frequency of 176 MHz, and in the beat spectrum at a distance of 97.3 m, a peak appears at a frequency of 184 MHz. Also, in the beat spectrum at a distance of 98.0 m, peaks appear at the positions of frequencies 184 MHz and 195 MHz, and in the beat spectrum at a distance of 99.9 m, a peak appears 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 0th to 3rd peak frequencies of the beat spectrum are separated from each other with an interval of about 100 MHz on the frequency axis. From these results, it can be understood that also in Example 3, as in Examples 1 and 2, one measurement point can be extracted from among a plurality of measurement points for a certain modulation frequency to perform wind speed detection.

[0090] Fig. 18(a) is a diagram showing the simulation conditions for wind speed detection by the measurement method according to Example 4 (a combination of the second measurement method and the third measurement method), and (b) is a diagram showing the results. In Example 4, as simulation conditions, the lens diameter was 50 mm, the detection distance was 100 m, the RWF was of the Lorentz type, and the full width at half maximum of the RWF was 34 m. The modulation width B of the measurement light was 100 MHz. In this case, the distance resolution ΔZr 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 / second.

[0091] In Example 4, as shown in Fig. 18(a), a measurement target (constant wind speed) was set within a range of 100 m ± 2 m. Then, while fixing the peak position of the RWF generated by the condensing of the measurement light at the 100 m position, the beat spectrum of the interference light was acquired while changing the modulation rate fm in steps of 10 kHz between 1.37 MHz and 1.66 MHz, and the peak frequency was extracted.

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

[0093] In Example 4, as shown in Figs. 19(a) to 16(d), in the beat spectrum at a distance of 90.3 m, a peak appears at a frequency of 176 MHz, and in the beat spectrum at a distance of 97.3 m, a peak appears at a frequency of 184 MHz. Also, in the beat spectrum at a distance of 98.0 m, peaks appear at the positions of frequencies 184 MHz and 195 MHz, and in the beat spectrum at a distance of 99.9 m, a peak appears at a frequency of 196 MHz. From these results, it can be seen that in Example 4 as well, similar to Examples 1 to 3, one measurement point can be extracted from among a plurality of measurement points for a certain modulation frequency to perform wind speed detection.

[0094] The present disclosure is not limited to the above embodiments. For example, in the above embodiments, the output direction of the measurement light Lm directed into 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 realized using other configurations. For example, a mirror may be disposed outside the lens 22, and the output direction of the measurement light Lm directed into the atmosphere M may be deflected in an arbitrary direction by adjusting the angle of the mirror. Also, by moving the direction of the end portion Fa of the optical fiber F up, down, left, or right, the output direction of the measurement light Lm directed into the atmosphere M may be deflected in an arbitrary direction.

[0095] Further, in the above embodiments, an optical fiber device type circulator 25 is exemplified. However, a free space optical system type circulator 31 as shown in FIG. 20 may be used. In the example of FIG. 20, the free space optical system type circulator 31 is composed of a polarization beam splitter 32 and a λ / 4 wave plate 33. A lens 34 is disposed in front of the polarization beam splitter 32, and a lens 35 mounted on the movable stage 21 is disposed behind the λ / 4 wave plate 33. The lenses 34 and 35 may be either convex lenses or concave lenses.

[0096] According to such a configuration, by displacing the movable stage 21 in the optical axis direction of the measurement light Lm, the distance between the lens 35 and the lens 22 can be adjusted. Thereby, it becomes 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.

Explanation of Reference Numerals

[0097] 1... Wind speed detection device, 2... Output unit, 3... Branch unit, 6... Measurement optical system, 8... Detection unit, 10... Analysis unit, 11... Optical integrated circuit, 12... Signal generation unit, 21... Movable stage (scanning unit), 22... Lens (optical element), 23... Rotating stage (deflection unit), 24... Beam deflector (deflection unit), L... CW laser light, Lm... Measurement light, Lr... Reference light, Lf... Scattered light, Ls... Signal light, C... Condensing position, D... Detection signal, G... Modulation signal, M... Atmosphere.

Claims

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

2. The wind speed detection device according to claim 1, wherein the frequency of the CW laser beam is modulated in a sine wave shape.

3. The wind speed detection device according to claim 2, wherein the measurement optical system has an optical element that condenses the measurement light beam into the atmosphere.

4. The wind speed detection device according to claim 3, wherein the measurement optical system has a scanning unit that scans a condensing position of the measurement light beam in the atmosphere in a direction of an optical axis of the measurement light beam.

5. The wind speed detection device according to claim 1, wherein the measurement optical system has an optical element that collimates the measurement light beam and outputs it into the atmosphere.

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

7. The wind speed detection device according to claim 1, wherein the measurement optical system has a deflection unit that deflects an output direction of the measurement light beam toward the atmosphere.

8. The wind speed detection device according to claim 1, wherein at least the output unit, the branching unit, and the detection unit are configured by an optical integrated circuit.

9. The wind speed detection device according to claim 1, further comprising a signal generation unit that generates a modulation signal for the CW laser beam.

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

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

12. In the output step, the frequency of the CW laser beam is modulated in a sine wave shape, the wind speed detection method according to claim 11.

13. The wind speed detection method according to claim 12, wherein in the measurement step, the measurement light is condensed in the atmosphere.

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

15. The wind speed detection method according to claim 11, wherein in the measurement step, the measurement light is collimated and output into the atmosphere.

16. In the output step, the frequency of the CW laser light is modulated such that a linear change is superimposed on a non-linear and periodic modulation, The wind speed detection method according to claim 11, wherein in the measurement step, the measurement light is collimated and output into the atmosphere.

17. The wind speed detection method according to claim 11, wherein in the measurement step, the 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 the wind speed in the atmosphere based on the detection signal.

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