A coherent wind measurement laser radar and a wind measurement method thereof

Abstract

This invention discloses a coherent wind-measuring lidar and its wind measurement method, relating to the field of lidar. The lidar includes a light source, a beam splitter, a modulator, an optical amplifier, a circulator, an optical transceiver module, and a signal detection and processing module. The light source is coupled to the beam splitter; the optical amplifier and modulator are both coupled to the beam splitter; the modulator is coupled to the signal detection and processing module; the optical amplifier is coupled to the circulator; and both the optical transceiver module and the signal detection and processing module are coupled to the circulator. The output beam of the light source is split into a probe beam and a local oscillator beam by the beam splitter. The probe beam is amplified by the optical amplifier and output to the target. The echo beam returned from the target is incident on the signal detection and processing module, and the local oscillator beam is modulated into pulsed light and then incident on the signal detection and processing module. The signal detection and processing module performs mixing, conversion, and signal processing on the received signals to obtain the target information. This invention can reduce the manufacturing cost of lidar and improve the accuracy of wind measurement.

Description

Technical Field

[0001] This invention relates to the field of lidar technology, and more particularly to a coherent wind-measuring lidar and its wind-measuring method. Background Technology

[0002] Coherent laser wind measurement is a high-precision wind speed remote sensing technology based on the Doppler effect, widely used in wind power generation, aviation, meteorology, and other fields. A coherent wind lidar, as the device for implementing this technology, mainly consists of three parts: a laser, an optical transceiver system, and a signal processing system.

[0003] In commonly used coherent wind lidar, the continuous light output from the laser is split into two paths by a beam splitter. One path serves as the local oscillator, while the other enters an external modulator for pulse modulation and frequency shifting, and then enters an optical amplifier for power amplification. The amplified pulsed light is then emitted into the atmosphere via a circulator and an optical transceiver system. The returning aerosol backscattered light is coherently mixed with the local oscillator light by a coupler, and the beat frequency signal is obtained by photoelectric detection. Wind speed information can then be obtained by performing digital signal analysis on the beat frequency signal.

[0004] To improve detection range and carrier-to-noise ratio, pulsed light is typically amplified. However, higher pulse energy and peak power can cause a series of problems, including the following:

[0005] 1. When the pulsed light power is too high, nonlinear effects such as stimulated Brillouin scattering (SBS) are prone to occur in the optical fiber. SBS can cause pulse waveform distortion and generate new frequency components, thereby interfering with the coherent mixing process of backscattered light and local oscillator light, resulting in a decrease in the carrier-to-noise ratio of the coherent wind lidar and affecting the stability and accuracy of the wind measurement results.

[0006] 2. Since the peak power of pulsed light typically exceeds 500W, it places extremely high demands on the power tolerance of optical components. Optical devices operating under high-power conditions for extended periods are prone to failure, which significantly increases the maintenance and replacement costs of coherent wind-measuring lidar.

[0007] 3. Due to the high peak power characteristics of pulses with pulse widths in the hundreds of nanosecond range, semiconductor optical amplifiers cannot achieve effective amplification while maintaining the waveform and spectral quality of the pulsed light. Therefore, larger and more power-consuming amplification solutions such as fiber optic amplifiers or solid-state amplifiers must be used. Although these amplifiers can provide sufficient gain, their large size and high power consumption are not conducive to the miniaturization, modularization, and high reliability design of coherent wind lidar. Summary of the Invention

[0008] This invention provides a coherent wind-measuring lidar and its wind measurement method. By separating pulse modulation and optical amplification, the pulse modulation is set in the optical path of the local oscillator light; the optical amplification is used to amplify continuous light instead of pulsed light, thereby reducing nonlinear effects in the optical fiber, avoiding the use of high-power-tolerant and high-cost optical devices, reducing the manufacturing cost of the coherent wind-measuring lidar, and improving the accuracy of wind measurement.

[0009] The first aspect of this invention provides a coherent wind-measuring lidar, which includes a light source, a beam splitter, a modulator, an optical amplifier, a circulator, an optical transceiver module, and a signal detection and processing module. The output terminal of the light source is coupled to the input terminal of the beam splitter, the first output terminal of the beam splitter is coupled to the input terminal of the optical amplifier, the second output terminal of the beam splitter is coupled to the input terminal of the modulator, the output terminal of the modulator is coupled to the signal detection and processing module, the output terminal of the optical amplifier is coupled to the first terminal of the circulator, the second terminal of the circulator is coupled to the optical transceiver module, and the third terminal of the circulator is coupled to the signal detection and processing module.

[0010] The output beam of the light source is split into a probe beam and a local oscillator beam by the beam splitter. The probe beam is amplified by the optical amplifier and then output to the target under test through the first and second ends of the circulator and the optical transceiver module. The echo beam returned by the target under test passes through the optical transceiver module, the second and third ends of the circulator, and then enters the signal detection and processing module. The local oscillator beam is modulated into pulse light by the modulator and then enters the signal detection and processing module.

[0011] The signal detection and processing module is used to perform coherent mixing, photoelectric conversion, and signal processing on the received echo beam and pulse light to obtain information about the target under test.

[0012] Optionally, the signal detection and processing module includes a coupler, a photodetector, and a processor. The first input terminal of the coupler is used to receive the pulsed light, the second input terminal of the coupler is used to receive the echo beam, the output terminal of the coupler is connected to the photodetector, and the photodetector is connected to the processor.

[0013] Optionally, the coherent wind-measuring lidar further includes a signal generation module, wherein both the modulator and the processor are connected to the signal generation module. The signal generation module is used to provide a pulse modulation signal to the modulator, and the processor is also used to acquire the signal of the photodetector based on the pulse modulation signal.

[0014] Optionally, the repetition frequency of the pulsed light satisfies:

[0015] ;

[0016] Among them, f rep The repetition frequency of the pulsed light is represented by c, the speed of light is represented by L0, and the minimum measurement distance is represented by L0.

[0017] Optionally, the beam splitter's splitting ratio is less than or equal to a preset value, and the power ratio of the probe beam and the local oscillator beam is less than or equal to a preset value.

[0018] Optionally, the optical amplifier includes a semiconductor optical amplifier.

[0019] Optionally, the modulator includes an acousto-optic modulator, an electro-optic modulator, a semiconductor optical amplifier, or an on-chip integrated pulse modulator.

[0020] Optionally, the light source includes a continuous wave laser.

[0021] Optionally, the target to be measured is the atmosphere, and the information of the target to be measured is wind speed.

[0022] A second aspect of the present invention provides a wind measurement method for a coherent wind-measuring lidar, applicable to the coherent wind-measuring lidar described above, the wind measurement method comprising:

[0023] The light source is controlled to generate an output beam, which is then split into a probe beam and a local oscillator beam by the beam splitter.

[0024] The optical amplifier amplifies the detection beam, and the modulator modulates the local oscillator beam into pulsed light. The amplified detection beam is output to the target after passing through the first and second ends of the circulator and the optical transceiver module. The echo beam returned by the target passes through the optical transceiver module, the second and third ends of the circulator, and then enters the signal detection and processing module. The pulsed light is also entered into the signal detection and processing module.

[0025] The signal detection and processing module performs coherent mixing, photoelectric conversion, and signal processing on the received echo beam and pulse light to obtain the wind speed information of the target.

[0026] The technical solution of this invention, by setting up a light source, beam splitter, modulator, optical amplifier, circulator, optical transceiver module, and signal detection and processing module in a coherent wind-measuring lidar, and by coupling the output end of the light source with the input end of the beam splitter, allows the output beam of the light source to be split into a probe beam and a local oscillator beam by the beam splitter. By coupling the first output end of the beam splitter with the input end of the optical amplifier, the beam splitter can output the probe beam formed by the split beam to the optical amplifier through the first output end. Since the probe beam is continuous light, its power after amplification by the optical amplifier is significantly lower than the peak power after pulsed light amplification, thereby reducing the power tolerance requirements of the optical amplifier, circulator, and optical transceiver module. Moreover, for continuous light, a semiconductor amplifier can be used as the optical amplifier, which helps to realize the chip integration of the optical amplifier, reduce the power consumption and manufacturing cost of the coherent wind-measuring lidar, and the stimulated Brillouin scattering threshold of continuous light is high, thereby reducing nonlinear effects and improving the accuracy of wind measurement. By coupling the output of the optical amplifier to the first end of the circulator, and the second end of the circulator to the optical transceiver module, the probe beam, after being amplified by the optical amplifier, can pass through the first and second ends of the circulator and the optical transceiver module before being output to the target. Furthermore, by coupling the third end of the circulator to the signal detection and processing module, the echo beam carrying wind speed information returned by the target can pass through the optical transceiver module, the second and third ends of the circulator, and then be incident on the signal detection and processing module. Simultaneously, by coupling the second output of the beam splitter to the input of the modulator, the beam splitter can output the local oscillator beam formed by the split beam to the modulator. By coupling the output of the modulator to the signal detection and processing module, the local oscillator beam, after being modulated into pulsed light by the modulator, can be incident on the signal detection and processing module. This allows the signal detection and processing module to coherently mix the received echo beam and pulsed light to generate a beat frequency signal and obtain information about the target. The pulsed light after modulation by the modulator has a low power and is not amplified, thus avoiding waveform distortion caused by amplification. This ensures the quality of the beat frequency signal generated by the signal detection and processing module and improves the accuracy of wind measurement.

[0027] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of a coherent wind-measuring lidar in the existing technology.

[0030] Figure 2 This is a schematic diagram of the structure of a coherent wind-measuring lidar provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of waveform distortion generated during pulsed light amplification according to an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of another coherent wind-measuring lidar provided in an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram comparing the differences between the two optical waveforms of a beam splitter according to an embodiment of the present invention;

[0034] Figure 6 This is a flowchart illustrating a wind measurement method using a coherent wind-measuring lidar provided in an embodiment of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0037] Figure 1 This is a schematic diagram of the structure of a coherent wind-measuring lidar in the existing technology. For example... Figure 1 As shown, the coherent wind-measuring lidar includes a light source 01, a beam splitter 02, a modulator 03, an optical amplifier 04, a circulator 05, an optical transceiver module 06, and a signal detection and processing module 07. Specifically, the continuous light output from the light source 01 is split into two by the beam splitter 02. One path serves as the local oscillator light and enters the signal detection and processing module 07, while the other path serves as the probe light and enters the modulator 03 for pulse modulation and frequency shifting to form pulsed light, which is then amplified by the optical amplifier 04. The amplified pulsed light then enters the atmosphere through the circulator 05 and the optical transceiver module 06 to obtain wind speed information. The returned echo beam enters the signal detection and processing module 07, where the returned echo beam and the local oscillator light are coherently mixed by a coupler. Finally, the beat frequency signal is obtained through photoelectric detection. The wind speed information is obtained by performing digital signal analysis on the beat frequency signal. Based on this coherent wind-measuring lidar and wind-measuring method, in order to ensure the radar's detection range and carrier-to-noise ratio, it is necessary to amplify the pulse light after pulse modulation and frequency shifting by modulator 03. The high-energy pulse light and high pulse peak power will induce nonlinear effects and damage the optical devices.

[0038] Understandably, due to the high peak power of pulsed light, such as above 500W, it is prone to SBS (Short-Side Backscattering) during amplification, leading to unstable pulse waveforms. Furthermore, the detector end is susceptible to backscattering interference from SBS, resulting in abnormal spectra and reduced carrier-to-noise ratio. Simultaneously, high peak power places stringent demands on the tolerance of optical components, and prolonged operation can easily lead to component failure, thus increasing the manufacturing and maintenance costs of coherent wind lidar. In addition, pulsed light with pulse widths in the hundreds of nanoseconds cannot be amplified to micro-joule level single-pulse energy using semiconductor optical amplifiers (SOAs) due to its excessively high peak power and strong nonlinear effects. Therefore, large-size, high-power fiber amplifiers or solid-state amplifiers are required, which is detrimental to the miniaturization, modularization, high reliability, and ease of maintenance of coherent wind lidar. Therefore, this invention proposes a coherent wind lidar that separates pulse modulation and optical amplification to reduce nonlinear effects, avoids the use of high-power-tolerant, high-cost optical components, reduces the manufacturing cost of coherent wind lidar, and improves the accuracy of wind measurement.

[0039] Figure 2 This is a schematic diagram of the structure of a coherent wind-measuring lidar provided in an embodiment of the present invention. Figure 2As shown, the coherent wind-measuring lidar includes a light source 1, a beam splitter 2, a modulator 3, an optical amplifier 4, a circulator 5, an optical transceiver module 6, and a signal detection and processing module 7. The output terminal 11 of the light source 1 is coupled to the input terminal 21 of the beam splitter 2. The first output terminal 22 of the beam splitter 2 is coupled to the input terminal 41 of the optical amplifier 4. The second output terminal 23 of the beam splitter 2 is coupled to the input terminal 31 of the modulator 3. The output terminal 32 of the modulator 3 is coupled to the signal detection and processing module 7. The output terminal 42 of the optical amplifier 4 is coupled to the first terminal 51 of the circulator 5. The second terminal 52 of the circulator 5 is coupled to the optical transceiver module 6. The third terminal 53 of the circulator 5 is coupled to the signal detection module 7. The processing module 7 is coupled; the output beam of the light source 1 is split into a probe beam and a local oscillator beam by the beam splitter 2. The probe beam is amplified by the optical amplifier 4 and then output to the target under test through the first end 51, the second end 52 of the circulator 5 and the optical transceiver module 6. The echo beam returned by the target under test passes through the optical transceiver module 6, the second end 52 and the third end 53 of the circulator 5 and is then incident on the signal detection and processing module 7. The local oscillator beam is modulated into pulse light by the modulator 3 and then incident on the signal detection and processing module 7. The signal detection and processing module 7 is used to perform coherent mixing, photoelectric conversion and signal processing on the received echo beam and pulse light to obtain the information of the target under test.

[0040] Specifically, light source 1 provides initial continuous light, laying the foundation for subsequent continuous light beam splitting, optical mixing, and signal processing. Optionally, light source 1 includes a continuous-wave laser. The narrow-linewidth continuous light output of a continuous-wave laser has a uniform power distribution in the time domain, exhibiting high stability and low noise characteristics. Beam splitter 2 can be understood as an optical beam splitting element, used to split the input beam into two paths at a specific ratio. Specifically, the output end 11 of light source 1 is coupled to the input end 21 of beam splitter 2, so that the output beam of light source 1 can be split into a probe beam and a local oscillator beam by beam splitter 2, thus laying the foundation for subsequent wind measurement using the probe beam and for mixing the echo beam and pulse light. Beam splitter 2 can adjust the splitting ratio of the probe beam and the local oscillator beam according to the insertion loss of modulator 3 itself and the duty cycle of pulse modulation, thereby optimizing the energy distribution of the probe beam and the local oscillator beam.

[0041] The first output terminal 22 of the beam splitter 2 is coupled to the input terminal 41 of the optical amplifier 4, so that the beam splitter 2 can output the probe beam formed by the split beam to the optical amplifier 4 through the first output terminal 22. The optical amplifier 4 can be specifically understood as a device for enhancing the intensity of the probe beam, which can amplify the power of the probe beam several times to ensure that the probe beam interacts with the aerosol after being emitted into the atmosphere to generate an echo beam with sufficient intensity. For example, the optical amplifier 4 may include an optical fiber amplifier or a waveguide amplifier. Optical fiber amplifiers are often used in lidar to amplify pulsed light because of their convenient coupling with optical fibers and low loss, but they require optical pumping, resulting in larger device size and higher power consumption. Optionally, the optical amplifier 4 may include a semiconductor optical amplifier. Semiconductor optical amplifiers have the characteristics of easy chip integration, small size, and low power consumption. It is understood that since the probe beam is continuous light, its power after amplification by the optical amplifier is significantly lower than the peak power after pulsed light amplification, thereby reducing the power tolerance requirements of the optical amplifier 4, circulator 5, and optical transceiver module 6. Furthermore, for continuous light, a semiconductor amplifier can be used as optical amplifier 4 to amplify the detection beam, which belongs to continuous light. This facilitates the chip-based integration of optical amplifier 4, thereby optimizing the structure of the coherent wind lidar and reducing its power consumption. It is also understandable that the generation threshold of SBS is low, typically in the range of tens to hundreds of milliwatts, and is closely related to the temporal density of photons. The SBS threshold for narrow pulses is much lower than that for continuous light. In cases such as... Figure 1 In existing coherent wind lidar systems, the pulsed light modulation and amplification in the probe beam branch easily induces the SBS effect, leading to unstable pulse waveforms and backscattering interference, thus affecting the system performance. This invention significantly reduces nonlinear effects and improves the accuracy of wind measurement using a coherent wind lidar by employing an optical amplifier 4 to amplify continuous light in the probe beam branch.

[0042] The circulator 5 can be specifically understood as a three-port optical device. The circulator 5 may include polarization-maintaining fiber and magneto-optical elements to achieve unidirectional ring optical path transmission based on the magneto-optical effect. Light can be transmitted between the three ports of the circulator 5 according to the port order; for example, light can be transmitted from the first port 51 to the second port 52, and from the second port 52 to the third port 53. The output port 42 of the optical amplifier 4 is coupled to the first port 51 of the circulator 5, and the second port 52 of the circulator 5 is coupled to the optical transceiver module 6, so that the probe beam, after being amplified by the optical amplifier 4, can be output to the target under test through the first port 51, the second port 52, and the optical transceiver module 6. The optical transceiver module 6 may include a transceiver lens group for transmitting and receiving light. The optical transceiver module 6 can transmit the amplified probe beam output from the second port 52 of the circulator 5 to the target under test in the atmosphere. Optionally, the target under test can be the atmosphere, and the information of the target under test can be wind speed. Understandably, the detection beam can be scattered by aerosols in the atmosphere, such as dust, smoke, or water vapor condensate. When aerosols move within the atmospheric molecular environment (i.e., when there is wind), the frequency of the scattered echo beam changes due to the Doppler effect. The third end 53 of the circulator 5 is coupled to the signal detection and processing module 7 so that the echo beam returned by the target can pass through the optical transceiver module 6, the second end 52 of the circulator 5, and the third end 53 before entering the signal detection and processing module 7. The echo beam carries wind speed information, and its frequency difference with the local oscillator beam is the Doppler frequency shift, reflecting the wind speed. Therefore, the echo beam and the local oscillator beam undergo coherent mixing in the signal detection and processing module 7, followed by photoelectric conversion and signal processing, enabling the radar to determine the information of the target.

[0043] The second output terminal 23 of beam splitter 2 is coupled to the input terminal 31 of modulator 3, so that beam splitter 2 can output the local oscillator beam formed by beam splitting to modulator 3 through the second output terminal 23. Modulator 3 can be specifically understood as a pulse signal generation device, used to modulate the local oscillator beam into pulse light. The pulse light can have a specific repetition frequency and pulse width, thus laying the foundation for subsequent coherent mixing of the echo beam and the local oscillator beam by signal detection and processing module 7 to determine the information of the target under test. It can be understood that each pulse in the pulse light corresponds to a specific emission time, and the echo beam can only generate an interference signal when it overlaps with the pulse light, so that the minimum distance for radar wind measurement can be determined by the repetition frequency and pulse width of the pulse light. Optionally, modulator 3 may include an acousto-optic modulator (AOM), an electro-optic modulator (EOM), a semiconductor optical amplifier, or an on-chip integrated pulse modulator. Among them, the acousto-optic modulator can modulate the beam by the refractive index change caused by the sound wave in the medium; the electro-optic modulator can achieve modulation by changing the refractive index of the crystal by applying an electric field; the semiconductor optical amplifier can combine amplification and time-domain switching functions and control the gain by current injection; the on-chip integrated pulse modulator can achieve modulation based on on-chip optical structures such as Mach-Zehnder interferometers and micro-rings. It is understandable that when both the modulator 3 of the local oscillator beam branch and the optical amplifier 4 of the probe beam branch adopt SOA, the local oscillator beam branch and the probe beam branch can be hybridized in packaging or hybrid on-chip integrated, so as to further reduce the size of the coherent wind lidar, optimize space utilization, and reduce the power consumption of the coherent wind lidar.

[0044] The output terminal 32 of modulator 3 is coupled to signal detection and processing module 7, so that the local oscillator beam, after being modulated into pulsed light by modulator 3, can be incident on signal detection and processing module 7. This allows signal detection and processing module 7 to perform coherent mixing, photoelectric conversion, and signal processing on the received echo beam and pulsed light to obtain information about the target. For example, signal detection and processing module 7 may include a coupler and a photodetector, allowing the echo beam and pulsed light to be coherently mixed within the coupler, and a beat frequency signal generated by the photodetector. This allows signal detection and processing module 7 to calculate wind speed information based on the spectrum of the beat frequency signal to determine the information of the target. It can also be understood that, in cases such as... Figure 1 In the existing coherent wind lidar shown, the probe light branch first undergoes pulse modulation and frequency shifting before amplification, and the amplified pulse light is prone to waveform distortion. Figure 3 This is a schematic diagram of waveform distortion generated during pulsed light amplification according to an embodiment of the present invention, as shown below. Figure 3As shown, the three waveforms represent the waveform before pulse amplification, the ideal amplified waveform, and the actual amplified waveform, respectively. The horizontal axis t represents time, and the vertical axis amp represents amplitude. During pulse amplification, the upper-level particles in the gain medium are gradually consumed and reduced within the pulse's duration. This causes the instantaneous gain at the pulse's leading and trailing edges to decrease, resulting in waveform distortion. Specifically, the actual amplified waveform exhibits a higher amplitude at the beginning and a lower amplitude at the end, leading to a local peak power in the time domain at the leading edge. This local peak power not only exacerbates the SBS effect but may also cause saturation distortion in the Balanced Photodetector (BPD) in the signal detection and processing module 7, generating abnormal beat frequency signals. These beat frequency signals may manifest as time-domain signal asymmetry, waveform broadening, or tailing, leading to abnormal spectra, such as excessive low-frequency noise in the spectrum. This embodiment of the invention moves the modulator 3 to the local oscillator beam branch, ensuring that the pulsed light modulated by the modulator 3 has lower power and is not amplified. This effectively avoids waveform distortion, ensures beat frequency signal quality, and improves the accuracy of wind measurement using coherent wind lidar.

[0045] In this embodiment, a coherent wind-measuring lidar includes a light source, beam splitter, modulator, optical amplifier, circulator, optical transceiver module, and signal detection and processing module. The output of the light source is coupled to the input of the beam splitter, allowing the output beam to be split into a probe beam and a local oscillator beam. The first output of the beam splitter is coupled to the input of the optical amplifier, enabling the beam splitter to output the probe beam to the optical amplifier via its first output. Since the probe beam is continuous light, its power after amplification by the optical amplifier is significantly lower than the peak power of pulsed light, thus reducing the power tolerance requirements of the optical amplifier, circulator, and optical transceiver module. Furthermore, for continuous light, a semiconductor amplifier can be used as the optical amplifier, facilitating chip-based integration of the optical amplifier, reducing the power consumption and manufacturing cost of the coherent wind-measuring lidar. The higher threshold of stimulated Brillouin scattering for continuous light also reduces nonlinear effects and improves wind measurement accuracy. By coupling the output of the optical amplifier to the first end of the circulator, and the second end of the circulator to the optical transceiver module, the probe beam, after being amplified by the optical amplifier, can pass through the first and second ends of the circulator and the optical transceiver module before being output to the target. Furthermore, by coupling the third end of the circulator to the signal detection and processing module, the echo beam carrying wind speed information returned by the target can pass through the optical transceiver module, the second and third ends of the circulator, and then be incident on the signal detection and processing module. Simultaneously, by coupling the second output of the beam splitter to the input of the modulator, the beam splitter can output the local oscillator beam formed by the split beam to the modulator. By coupling the output of the modulator to the signal detection and processing module, the local oscillator beam, after being modulated into pulsed light by the modulator, can be incident on the signal detection and processing module. This allows the signal detection and processing module to coherently mix the received echo beam and pulsed light to generate a beat frequency signal and obtain information about the target. The pulsed light modulated by the modulator has a low power and is not amplified, thus ensuring the quality of the beat frequency signal generated by the signal detection and processing module and improving the accuracy of wind measurement.

[0046] Optional, Figure 4 This is a schematic diagram of another coherent wind-measuring lidar provided in an embodiment of the present invention. Figure 4 As shown, the signal detection and processing module 7 includes a coupler 71, a photodetector 72, and a processor 73. The first input terminal 711 of the coupler 71 is used to receive pulsed light, the second input terminal 712 of the coupler 71 is used to receive echo beams, the output terminal 713 of the coupler 71 is connected to the photodetector 72, and the photodetector 72 is connected to the processor 73.

[0047] Specifically, coupler 71 can be understood as an optical coupling device, which may include a fiber optic coupler or a waveguide structure, used to efficiently combine two beams of light to achieve coherent mixing. Specifically, the first input terminal 711 of coupler 71 is used to receive pulsed light, enabling the pulsed light modulated by modulator 3 to serve as the reference light for mixing, providing a stable frequency and phase reference. The second input terminal 712 of coupler 71 is used to receive the echo beam transmitted via optical transceiver module 6 and circulator 5, the echo beam carrying wind speed information. The output terminal 713 of coupler 71 is connected to photodetector 72, allowing coupler 71 to superimpose the pulsed light and echo beam and output them to photodetector 72 through output terminal 713 to generate a coherently mixed optical signal, thus laying the foundation for subsequent photoelectric conversion and beat frequency signal generation.

[0048] The photodetector 72 is specifically used to convert the coherently mixed optical signal output from the coupler 71 into an electrical signal, namely a beat frequency signal. The difference between the carrier frequency of the beat frequency signal and the frequency shift frequency of the modulator is the Doppler frequency shift caused by the wind speed component along the direction of the radar beam. For example, the photodetector 72 may include a balanced photodetector to enhance the signal and suppress noise through differential detection technology, thereby improving the carrier-to-noise ratio. The photodetector 72 is connected to the processor 73 so that it can output the beat frequency signal to the processor 73, providing the processor 73 with high-quality input data.

[0049] The processor 73 is specifically used to perform digital signal processing on the beat frequency signal to calculate the wind speed information of the target. For example, the processor 73 can integrate an analog-to-digital converter, a digital signal processor, or a field-programmable gate array (FPGA) to execute complex algorithms and perform real-time calculations. Specifically, the digital signal processing process performed by the processor 73 can be described as follows: after receiving the acquisition start signal, the processor 73 enters a digital sampling waiting state, preparing to acquire the beat frequency signal output by the photodetector 72. After receiving the synchronization clock signal, the processor 73 can start data sampling according to the trigger timing of the pulse modulation signal to ensure time alignment. Simultaneously, the processor 73 can also divide the sampled data into multiple distance gates based on the distance gate start point parameters determined by the repetition frequency of the pulse light. Each distance gate corresponds to a different time delay, reflecting wind speed information at different distances, thereby achieving spatial resolution wind measurement. Subsequently, processor 73 can use Fast Fourier Transform (FFT) to perform spectrum estimation on the time-domain signal. FFT is an optimized algorithm of Discrete Fourier Transform (DFT), and the specific calculation formula is as follows: Where ω is the frequency and x[n] is the discrete time-domain signal obtained by sampling the time-domain signal. FFT reduces computation by using odd-even grouping and the periodicity and symmetry of the rotation factor, enabling efficient conversion of the time-domain signal into a power spectrum. After converting the time-domain signal into a power spectrum, the processor 73 can also accumulate the power spectra calculated multiple times within the same distance gate to superimpose the Doppler frequency shift characteristics of the echo signal from the same target area, enhancing the target signal strength. This effectively improves the carrier-to-noise ratio, suppresses random noise, and facilitates subsequent peak detection. After accumulating the power spectrum, the processor 73 will perform peak point detection on the power spectrum to determine the frequency of the peak (i.e., the Doppler frequency shift), thereby enabling the calculation of wind speed information using the Doppler frequency shift formula. The Doppler frequency shift formula can be: , where f 峰 f0 is the peak detection frequency, f0 is the modulator frequency shift frequency, and λ is the wavelength of the continuous wave laser. This represents the wind speed component corresponding to the distance from the door.

[0050] The signal detection and processing module 7 achieves coherent mixing of the local oscillator beam and the echo beam through coupler 71, converts the coherently mixed optical signal into an electrical signal through photodetector 72, and completes sampling, distance gating, and wind speed information calculation through processor 73 in conjunction with a synchronous clock and FFT algorithm. The wind speed information calculation process makes full use of the timing of pulse modulation and the stability of continuous light, improving the accuracy of wind measurement by coherent wind-measuring lidar.

[0051] Optional, continue to refer to Figure 4 The coherent wind-measuring lidar also includes a signal generation module 8. The modulator 3 and the processor 73 are both connected to the signal generation module 8. The signal generation module 8 is used to provide pulse modulation signals to the modulator 3, and the processor 73 is also used to acquire signals from the photodetector 72 based on the pulse modulation signals.

[0052] Specifically, the signal generation module 8 is used to output a pulse modulation signal with a specific carrier frequency, repetition frequency, and pulse width to ensure effective interference between the pulsed light and the echo beam, thereby achieving high-resolution wind speed measurement. Specifically, the signal generation module 8 is connected to the modulator 3 so that it can transmit the generated pulse modulation signal, for example, a pulse modulation (and frequency shift) signal with a repetition frequency of 5MHz, a pulse width of 200ns, and a carrier frequency of 150MHz, to the modulator 3 as a modulation command. This allows the modulator 3 to perform pulse modulation and frequency shifting on the local oscillator beam according to the pulse modulation signal to generate a pulse corresponding to the range gate, and to output the pulse to the first input terminal 711 of the coupler 71. It is understood that the period and trigger time of the pulse modulation signal directly affect the transmission timing of the local oscillator beam and determine the window for coherent mixing of subsequent pulses and the echo beam.

[0053] Simultaneously, the signal generation module 8 is also connected to the processor 73, enabling the signal generation module 8 to synchronously transmit the pulse modulation signal and the synchronization clock signal to the processor 73, serving as the trigger and time reference for the processor 73 to acquire the signal from the photodetector 72. The processor 73 can initiate digital sampling of the beat frequency signal output by the photodetector 72 based on the trigger time of the pulse modulation signal, ensuring that the sampling of the beat frequency signal is aligned with the pulse. The processor 73 can also combine the synchronization clock signal with the time delay information of the pulse modulation signal to divide a distance threshold, for example, 30m, to calculate the wind speed information corresponding to that threshold.

[0054] Understandably, when the probe beam is continuous, the distance gate corresponding to the acquired wind speed information needs to be determined by the time delay after the local oscillator beam is triggered. For example, the signal generation module 8 can first calculate the round-trip time t0 as 2L / c based on the target distance L for measuring the wind speed information, where c is the speed of light, so that the pulse period of the pulse modulation signal can be set to t0. For example, when L is 30m, t0 is approximately 0.2μs, and the corresponding repetition frequency of the pulse modulation signal is approximately 5MHz. This allows the modulator 3 to modulate and frequency-shift the local oscillator beam into pulsed light according to the pulse modulation signal, coherently mixing it with the echo light only within the t0 time window to generate a beat frequency signal. Simultaneously, the processor 73 can receive the synchronization clock signal output by the signal generation module 8 to identify each pulse trigger moment, correspondingly acquire the beat frequency time-domain signal, and ensure that the echo beam only overlaps with the pulsed local oscillator beam within distances of L and its multiples, such as 2L, thus generating an effective beat frequency signal. By using a synchronous clock count, the processor 73 can distinguish signals from gates at different distances; for example, the first pulse corresponds to L, and the second pulse corresponds to 2L.

[0055] Furthermore, to eliminate internal optical path delay in the coherent wind-measuring lidar equipment and ensure the accuracy of distance measurement, a hard target can be placed at the transmitting end face L of the distance optical transceiver module 6. Then, the signal generation module 8 triggers the modulator 3 to modulate the local oscillator beam into a pulsed beam. This pulsed beam is coherently mixed with the return beam from the hard target within the coupler 71, and a beat frequency signal is generated by the photodetector 72. This allows the processor 73 to determine the time corresponding to the 0-distance transmitting end face based on the beat frequency signal, and to correct the start time of the pulse modulation based on this time, thereby aligning the start time of the pulse modulation signal with the transmitting end face, i.e., the 0-distance gate. For example, if the start time of the pulse modulation signal is delayed by t1 relative to the start time of the synchronization clock signal, and the start time of the hard target beat frequency signal is delayed by t1+Δt relative to the start time of the synchronization clock signal, then the zero-distance gate can be aligned by correcting the start time delay of the pulse modulation signal relative to the start time delay of the synchronization clock signal to t1+Δt. This ensures the accuracy of distance measurement, enables the continuous probe light and pulse to be effectively coherently mixed, and achieves high-resolution wind speed measurement.

[0056] Optionally, the repetition frequency of the pulsed light satisfies:

[0057] ;

[0058] Among them, f rep The repetition frequency of the pulse light is represented by , c represents the speed of light, and L0 represents the minimum measurement distance.

[0059] Specifically, the repetition frequency of a pulsed light can be understood as the number of times the pulse signal repeats per second. The repetition frequency of the pulsed light can be determined based on the speed of light c and the minimum measurement distance L0. The repetition frequency of the pulse determines the transmission interval of the pulse signal, thus affecting the spatial resolution and measurement range of the coherent wind lidar, and defining the ability of the coherent wind lidar to resolve wind speeds at different distances.

[0060] It is also understandable that, in cases such as Figure 1 In the existing coherent wind lidar shown, pulse modulation and frequency shifting are performed on the probe light branch, and the repetition frequency f of the pulse light... rep The maximum detection distance D is determined by the following formula: In other words, the lower the repetition frequency of the pulsed light and the longer the pulse interval, the greater the maximum detection distance. For example, when the maximum detection distance is 300m, the repetition frequency of the pulsed light is approximately 500kHz. If the maximum detection distance increases to 1000m, the repetition frequency of the pulsed light needs to be less than 150kHz to avoid pulse overlap. Therefore, in existing coherent wind lidar, the repetition frequency of the pulsed light limits the maximum detection distance, making it suitable for large-area wind measurement, but with low wind measurement resolution. In this embodiment of the invention, pulse modulation and frequency shifting are moved to the local oscillator beam branch, and the repetition frequency f of the pulsed light... rep The minimum measurement distance L0 is determined by the formula. It is known that the higher the repetition frequency of the pulsed light and the shorter the pulse interval, the smaller the minimum measurement distance. For example, when the repetition frequency of the pulsed light is 150kHz, the minimum measurement distance is approximately 1000m, which results in excessively low wind measurement resolution. If the minimum measurement distance is 30m, the repetition frequency of the pulsed light is approximately 5MHz, suitable for high-resolution wind measurement applications. Therefore, the repetition frequency of the pulsed light in this embodiment of the invention can optimize the minimum distance gate size and enhance the resolution of near-range wind measurement. By increasing the repetition frequency of the pulsed light to 5MHz, this embodiment of the invention can achieve a minimum distance gate of 30m, significantly improving the spatial resolution of near-range wind speed measurement. Compared to the 1000m distance gate of the traditional solution, it can meet the requirements of fine wind measurement and improve wind measurement accuracy.

[0061] Optionally, the splitting ratio of beam splitter 2 is less than or equal to a preset value, and the power ratio of the probe beam and the local oscillator beam is less than or equal to a preset value.

[0062] Specifically, in this embodiment of the invention, the pulse modulation and frequency shift are moved to the local oscillator beam branch. Due to the insertion loss of the modulator 3 itself and the duty cycle of the pulse modulation, the beam splitting ratio of the beam splitter 2 to the local oscillator beam can be improved compared to the beam splitting ratio of the local oscillator beam in existing coherent wind lidar. In one embodiment, the preset value can be 9.7:1. In other embodiments, the size of the preset value can be designed according to the actual situation, and this embodiment of the invention does not limit it.

[0063] It is understood that, in order to ensure that the wind measurement effect of the embodiments of the present invention achieves the same wind measurement effect as existing coherent wind measurement lidar, the scheme of the embodiments of the present invention can be compared with that of existing coherent wind measurement lidar. Figure 1 The existing coherent wind-measuring lidar scheme shown is used to calculate light intensity alignment in order to determine the splitting ratio of beam splitter 2 in this embodiment of the invention. For example, Figure 5 This is a schematic diagram comparing the differences between the two optical waveforms of a beam splitter according to an embodiment of the present invention, as shown below. Figure 5 As shown, the optical waveforms of the detection light and local oscillator light of existing coherent wind lidar correspond to... Figure 5 The light waveform in group a, and the E marked on the right.s and E LO These correspond to the peak electric field intensity of the probe light and the electric field intensity of the local oscillator light in existing coherent wind-measuring lidar, respectively; the optical waveforms of the probe light and the local oscillator light in this embodiment of the invention correspond to... Figure 5 The light waveform in group b, and E' marked on the right. s and E' LO These correspond to the electric field intensity of the probe light and the peak electric field intensity of the local oscillator light in the embodiments of the present invention, respectively. The pulse width of coherent wind-measuring lidar is typically in the nanosecond range. For short-range wind measurement, the single-pulse energy of the probe light in existing coherent wind-measuring lidars is approximately 10 μJ, and the peak power of the local oscillator light is several hundred microwatts. Taking a 10 μJ lidar polarization-maintaining pulse light source module as an example, it can detect wind speed information at 400m. Its single-pulse output energy is 10 μJ, the pulse width is 200 ns, and the repetition frequency is 10 kHz. The peak power P of the light pulse can be calculated. s It is 50W. It's also understandable that, as an electromagnetic wave, light has a square relationship between its electric field strength E and peak power P, that is: Therefore, to ensure that the light intensity of the solution in this embodiment of the invention is aligned with that of existing coherent wind-measuring lidar solutions, i.e. In existing coherent wind lidar schemes, the peak power of the probe light and the power P of the local oscillator light are... s and P LO And the power of the probe light and the peak power P of the local oscillator light in the embodiments of the present invention. ' s and P ’ LO The required relationship is: Assuming the beam splitter 2 in this embodiment has a splitting ratio of k:1 and the local oscillator pulse repetition frequency is f... rep The pulse width is τ ’ LO In this embodiment of the invention, the radar's detection beam power P ’ s and the peak power P of the local oscillator beam ’ LO The ratio is (k×f) rep ×τ ’ LO ): 1. Based on technical experience in the field, it is assumed that the repetition frequency f of the local oscillator optical pulse in the embodiments of the present invention is... rep 5MHz, pulse width τ ’ LO If the value is 200 ns, then P is obtained. ’ s :P ’ LO =k: 1. Furthermore, assume that in the existing coherent wind-measuring lidar scheme, P... LOFor 500μW and P s The value is 50W. Substituting this into the previously mentioned approximate equation regarding power, we can obtain... W. Existing semiconductor optical amplifiers can typically withstand continuous light of less than or equal to 500mW, i.e., P ’ s Since the power is ≤0.5W, considering the upper limit of the value, we can conclude that k≤9.7, that is, the splitting ratio of beam splitter 2 is less than or equal to 9.7:1. In actual use, the splitting ratio of beam splitter 2 can be selected as, for example, 7:1 or 5:1, or it can be specifically calculated and determined according to the radar transmission power of the actual application. Through light intensity alignment calculation, it is ensured that the wind measurement effect of the embodiment of the present invention can achieve the same wind measurement effect as the existing coherent wind measurement lidar, thereby improving the stability and reliability of the coherent wind measurement lidar while reducing the generation of nonlinear effects.

[0064] Based on the same inventive concept, this embodiment of the invention also provides a wind measurement method for coherent wind-measuring lidar, applicable to the coherent wind-measuring lidar of the above embodiments. Figure 6 This is a flowchart illustrating a wind measurement method using a coherent wind-measuring lidar according to an embodiment of the present invention, as shown below. Figure 6 As shown, wind measurement methods include:

[0065] S110: Control the light source to generate an output beam. The output beam is split into a probe beam and a local oscillator beam by a beam splitter.

[0066] S120 controls the optical amplifier to amplify the probe beam, controls the modulator to modulate the local oscillator beam into pulsed light, and the amplified probe beam is output to the target after passing through the first and second ends of the circulator and the optical transceiver module. The echo beam returned by the target passes through the optical transceiver module, the second and third ends of the circulator, and is then incident on the signal detection and processing module. The pulse is incident on the signal detection and processing module.

[0067] S130, the signal detection and processing module performs coherent mixing, photoelectric conversion and signal processing on the received echo beam and pulse light to obtain the wind speed information of the target.

[0068] Specifically, an output beam is generated by controlling the light source, which is then split into a probe beam and a local oscillator beam by a beam splitter. This lays the foundation for subsequent wind measurement using the probe beam and reference mixing using the local oscillator beam. The probe beam is amplified by controlling an optical amplifier, allowing it to pass through the first and second ends of the circulator and the optical transceiver module before being output to the target. The echo beam carrying wind speed information returned by the target passes through the optical transceiver module, the second and third ends of the circulator, and is then incident on the signal detection and processing module. Because the probe beam is continuous light, its power is much lower than the peak power of pulsed light at the same average power. Therefore, compared to traditional solutions, this solution reduces the power tolerance requirements for the optical amplifier, circulator, and optical transceiver module (optical components). Furthermore, for continuous light, semiconductor amplifiers can be used as optical amplifiers, facilitating chip-based integration of optical amplifiers. This optimizes the structure of the coherent wind-measuring lidar, reduces its power consumption, and the higher threshold of stimulated Brillouin scattering of continuous light significantly reduces nonlinear effects, improving the accuracy of wind measurement using coherent wind-measuring lidar. Simultaneously, by controlling the modulator to modulate the local oscillator beam into pulsed light, the pulses can be incident on the signal detection and processing module. This allows the module to coherently mix the received echo beam and pulses, generating a beat frequency signal to obtain the wind speed information of the target. When both the modulator and the optical amplifier are semiconductor optical amplifiers, the local oscillator beam branch and the detection beam branch can be integrated on-chip, further reducing the size of the coherent wind-measuring lidar, optimizing space utilization, and lowering its power consumption. Furthermore, by moving the modulator to the local oscillator beam branch, the power of the pulsed light modulated by the modulator is lower and not amplified, thereby effectively avoiding waveform distortion problems, ensuring beat frequency signal quality, and improving the accuracy of wind measurement using coherent wind lidar.

[0069] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0070] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A coherent wind-measuring lidar, characterized in that, The system includes a light source, a beam splitter, a modulator, an optical amplifier, a circulator, an optical transceiver module, and a signal detection and processing module. The output of the light source is coupled to the input of the beam splitter. The first output of the beam splitter is coupled to the input of the optical amplifier. The second output of the beam splitter is coupled to the input of the modulator. The output of the modulator is coupled to the signal detection and processing module. The output of the optical amplifier is coupled to the first end of the circulator. The second end of the circulator is coupled to the optical transceiver module. The third end of the circulator is coupled to the signal detection and processing module. The output beam of the light source is split into a probe beam and a local oscillator beam by the beam splitter. The probe beam is amplified by the optical amplifier and then output to the target under test through the first and second ends of the circulator and the optical transceiver module. The echo beam returned by the target under test passes through the optical transceiver module, the second and third ends of the circulator, and then enters the signal detection and processing module. The local oscillator beam is modulated into pulse light by the modulator and then enters the signal detection and processing module. The signal detection and processing module is used to perform coherent mixing, photoelectric conversion, and signal processing on the received echo beam and pulse light to obtain information about the target under test.

2. The coherent wind-measuring lidar according to claim 1, characterized in that, The signal detection and processing module includes a coupler, a photodetector, and a processor. The first input terminal of the coupler is used to receive the pulsed light, the second input terminal of the coupler is used to receive the echo beam, the output terminal of the coupler is connected to the photodetector, and the photodetector is connected to the processor.

3. The coherent wind-measuring lidar according to claim 2, characterized in that, It also includes a signal generation module, to which both the modulator and the processor are connected. The signal generation module is used to provide a pulse modulation signal to the modulator, and the processor is also used to acquire the signal of the photodetector based on the pulse modulation signal.

4. The coherent wind-measuring lidar according to claim 1, characterized in that, The repetition frequency of the pulsed light satisfies: ； Among them, f rep The repetition frequency of the pulsed light is represented by c, the speed of light is represented by L0, and the minimum measurement distance is represented by L0.

5. The coherent wind-measuring lidar according to claim 1, characterized in that, The beam splitter's splitting ratio is less than or equal to a preset value, and the power ratio of the probe beam and the local oscillator beam is less than or equal to a preset value.

6. The coherent wind-measuring lidar according to claim 1, characterized in that, The optical amplifier includes a semiconductor optical amplifier.

7. The coherent wind-measuring lidar according to claim 1, characterized in that, The modulator includes an acousto-optic modulator, an electro-optic modulator, a semiconductor optical amplifier, or an on-chip integrated pulse modulator.

8. The coherent wind-measuring lidar according to claim 1, characterized in that, The light source includes a continuous wave laser.

9. The coherent wind-measuring lidar according to claim 1, characterized in that, The target to be measured is the atmosphere, and the information of the target to be measured is wind speed.

10. A wind measurement method using a coherent wind-measuring lidar, characterized in that, The coherent wind-measuring lidar applicable to any one of claims 1 to 9, wherein the wind measurement method comprises: The light source is controlled to generate an output beam, which is then split into a probe beam and a local oscillator beam by the beam splitter. The optical amplifier amplifies the detection beam, and the modulator modulates the local oscillator beam into pulsed light. The amplified detection beam is output to the target after passing through the first and second ends of the circulator and the optical transceiver module. The echo beam returned by the target passes through the optical transceiver module, the second and third ends of the circulator, and then enters the signal detection and processing module. The pulsed light is also entered into the signal detection and processing module. The signal detection and processing module performs coherent mixing, photoelectric conversion, and signal processing on the received echo beam and pulse light to obtain the wind speed information of the target.

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