Wind measurement laser radar

Abstract

The utility model relates to a wind lidar. The laser radar comprises a first light source, a beam splitter, a mixed light annular module, an adjusting module, a rotary scanning module and a detection module, and by adopting the laser radar, through cooperative use of the mixed light annular module and the adjusting module, two times of frequency modulation, two times of pulse modulation and two times of power amplification can be performed on signal light of a to-be-detected target; the design of the hybrid optical annular module is adopted, the number of passive optical devices is reduced, the additional insertion loss is small, wind speed scanning of a target wind field area is achieved by matching the rotary scanning module with the single-stage double-pass amplification laser, the length of a transmission optical fiber can be reduced, the SBS threshold value is increased, and therefore the pulse peak power is increased, and the measurement distance of the system is increased.

Description

Technical Field

[0001] This application relates to the field of lidar technology, and in particular to a wind-measuring lidar. Background Technology

[0002] With the development of lidar technology, lidar wind measurement technology has emerged. Wind measurement lidar obtains wind speed by measuring the Doppler frequency shift of the backscattered signal of aerosol particles.

[0003] Currently, the mainstream forms of near-range wind measurement lidar systems are nacelle-type and ground-based type. Nacelle-type wind measurement lidar is used for wind turbine yaw calibration, wind power prediction, etc., while ground-based wind measurement lidar is used for wind power prediction in the early stage of wind turbine site selection.

[0004] With the development of the wind power industry, higher requirements are being placed on the cost, size, and power consumption of near-range wind measurement lidar. Utility Model Content

[0005] Therefore, it is necessary to provide a wind measurement lidar that can meet the wind power industry's requirements for low cost, low power consumption, and high reliability, addressing the aforementioned technical issues.

[0006] This application provides a wind-measuring lidar, comprising: a first light source emitting a first laser beam with a first wavelength; a beam splitter receiving the first laser beam and splitting it into a local oscillator beam and a first signal beam; a hybrid optical ring module including a first port and a second port; the hybrid optical ring module receiving the first signal beam through the first port and outputting the first signal beam from the second port; an adjustment module receiving the first signal beam from the second port and performing two frequency modulations, two pulse modulations, and two power amplifications on the first signal beam to obtain a second signal beam; the hybrid optical ring module further includes a third port for the hybrid optical ring. The second port of the shaping module also receives the second signal light and outputs the second signal light from the third port; the rotating scanning module receives the second signal light from the third port, deflects the second signal light, and emits it to the target under test, and performs spatial scanning on the target test area of ​​the target under test; the rotating scanning module also receives the echo signal reflected by the target under test in the target test area; the hybrid optical ring module also includes a detection port, the third port of the hybrid optical ring module also receives the echo signal, and transmits the echo signal to the detection port; the detection module receives the echo signal and local oscillator light output from the detection port, thereby generating the wind speed signal of the target under test.

[0007] In one embodiment, the rotating scanning module includes: a telescope that receives and transmits a second signal light from a third port; an encoder that receives and transmits position and rotation speed information of the target under test; a motor module including a motor connected to the encoder that receives the position and rotation speed information and rotates based on the position and rotation speed information; a first gear connected to the motor module and driving the motor to rotate; a second gear meshing with the first gear and rotating under the drive of the first gear; and a wedge prism disposed in the inner ring of the second gear that receives the second signal light transmitted by the telescope and deflects the second signal light beam to perform spatial scanning of the target test area of ​​the target under test; the wedge prism also receives the echo signal reflected by the target under test in the target test area and transmits the echo signal to the telescope; the telescope receives the echo signal and transmits the echo signal to the detection port.

[0008] In one embodiment, the adjustment module includes: an acousto-optic module that receives a first signal light and performs frequency modulation and pulse modulation on the first signal light to obtain a third signal light; a second light source that emits a second laser with a second wavelength; an erbium-doped fiber that receives and transmits the third signal light and the second laser, and the third signal light is amplified and transmitted along a first direction in the erbium-doped fiber under the action of the second laser to obtain a fourth signal light; a reflection module that receives the fourth signal light and the second laser and reflects the fourth signal light and the second laser back to the erbium-doped fiber; the fourth signal light is amplified and transmitted again along a second direction in the erbium-doped fiber under the action of the second laser, and is incident again on the acousto-optic module, where it undergoes frequency modulation and pulse modulation to obtain the second signal light; the second direction is opposite to the first direction.

[0009] In one embodiment, the lidar further includes: an FPGA module for sending pulse signals to an acousto-optic module; within each pulse period of the pulse signal, the voltage value changes from a first voltage to a second voltage; the first voltage is greater than the second voltage; the acousto-optic module modulates the first signal light pulse, including: the acousto-optic module receiving the pulse signal sent by the FPGA module and performing pulse modulation on the first signal light based on the pulse signal.

[0010] In one embodiment, the second laser is transmitted along a second direction.

[0011] In one embodiment, the reflection module includes: a lens for receiving a fourth signal light and a second laser, and for adjusting the fourth signal light and the second laser; a color filter for receiving the fourth signal light and the second laser regulated by the lens, reflecting the second laser and transmitting the fourth signal light; the second laser being reflected to the lens, and after being reregulated by the lens, being incident into the erbium-doped fiber; and a polarization rotation unit for receiving the fourth signal light, rotating the polarization direction of the fourth signal light by 90 degrees, and reflecting it to the color filter; the fourth signal light after being rotated 90 degrees in polarization direction is again incident into the erbium-doped fiber after passing through the color filter and the lens.

[0012] In one embodiment, the hybrid optical ring module further includes a polarization beam splitter and an optical circulator; a first signal light is received through a first port, deflected to a second port via the polarization beam splitter, and the first signal light is output from the second port; the second port of the hybrid optical ring module also receives a second signal light, which is deflected to the optical circulator via the polarization beam splitter, and the optical circulator outputs the second signal light from a third port.

[0013] In one embodiment, the repetition frequency of the first laser is between 1 kHz and 15 kHz.

[0014] In one embodiment, the repetition frequency of the first laser is 10 kHz.

[0015] In one embodiment, the polarization rotation unit includes: a Faraday rotation unit for receiving the fourth signal light and rotating the polarization direction of the fourth signal light by 45 degrees under the action of a magnetic field; a reflector for receiving the fourth signal light with the polarization direction rotated by 45 degrees and reflecting the fourth signal light with the polarization direction rotated by 45 degrees back to the Faraday rotation unit; the fourth signal light with the polarization direction rotated by 45 degrees passes through the Faraday rotation unit again, and the polarization direction is rotated by 45 degrees again before being incident on the color filter.

[0016] In one embodiment, the reflection module further includes a dual-core ferrule, which includes: a first ferrule port for receiving a second laser and transmitting the second laser to the reflection module; and a second ferrule port connected to an erbium-doped fiber for receiving a fourth signal light and transmitting the fourth signal light to the reflection module; and also for receiving the second laser and the fourth signal light reflected by the reflection module and transmitting the second laser and the fourth signal light to the erbium-doped fiber.

[0017] In one embodiment, the first port, second port, third port and probe port of the hybrid optical ring module all use polarization-maintaining fiber. The slow axis of the polarization-maintaining fiber of the second port is aligned with the slow axis of the polarization-maintaining fiber of the first port, the fast axis of the polarization-maintaining fiber of the third port is aligned with the slow axis of the polarization-maintaining fiber of the second port, and the slow axis of the polarization-maintaining fiber of the probe port is aligned with the slow axis of the polarization-maintaining fiber of the third port.

[0018] In one embodiment, the detection module includes: a coupler for coupling the echo signal and the local oscillator light to obtain a coupled optical signal; and a balanced detector for receiving the coupled optical signal, performing frequency beating on the coupled optical signal, and converting the frequency-beating coupled optical signal into an electrical signal.

[0019] The aforementioned wind-measuring lidar includes a first light source, a beam splitter, a hybrid optical ring module, an adjustment module, a rotating scanning module, and a detection module. The lidar emits a first laser beam with a first wavelength from the first light source; the beam splitter splits the first laser beam into a local oscillator beam and a first signal beam; the hybrid optical ring module transmits the first signal beam to the adjustment module, which performs two frequency modulations, two pulse modulations, and two power amplifications on the first signal beam to obtain a second signal beam; and the hybrid optical ring module transmits the second signal beam to the rotating scanning module, thereby emitting the second signal beam to the target and receiving it through the rotating scanning module. The system measures the echo signal reflected from the target; and then transmits the echo signal back to the detection module via a hybrid optical ring module to generate the wind speed signal of the target. Through the combined use of the hybrid optical ring module and the adjustment module, the signal light of the target can be frequency modulated twice, pulse modulated twice, and power amplified twice. The hybrid optical ring module design reduces the number of passive optical devices and has low additional insertion loss. Furthermore, the rotation scanning module matches a single-stage double-pass amplified laser to achieve wind speed scanning of the target wind field area, which can reduce the length of the transmission fiber, increase the SBS threshold, thereby increasing the pulse peak power and increasing the measurement distance of the system. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a wind-measuring lidar in one embodiment;

[0022] Figure 2 This is a schematic diagram of the rotating scanning module in one embodiment;

[0023] Figure 3 This is a schematic diagram of a wind-measuring lidar in another embodiment;

[0024] Figure 4 This is a digitally modulated square wave waveform output by the FPGA module in one embodiment;

[0025] Figure 5 for Figure 4 The output result of the digitally modulated square wave waveform of the FPGA module in the digital modulation mode of the acousto-optic driver;

[0026] Figure 6 This is a schematic diagram of a wind-measuring lidar in yet another embodiment;

[0027] Figure 7 This is a digitally modulated square wave waveform output by the FPGA module in one embodiment;

[0028] Figure 8 for Figure 7 The output result of the digitally modulated square wave waveform of the FPGA module in the digital modulation mode of the acousto-optic driver;

[0029] Figure 9 This is a schematic diagram of a reflection module in one embodiment;

[0030] Figure 10 This is a schematic diagram of a hybrid optical ring module in one embodiment;

[0031] Figure 11 This is a schematic diagram of a wind-measuring lidar in another embodiment;

[0032] Figure 12 This is a schematic diagram of a wind-measuring lidar in another embodiment. Detailed Implementation

[0033] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a full understanding of this utility model. However, this utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed below.

[0034] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0036] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0037] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0038] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0039] Due to atmospheric loss and a small aerosol backscattering coefficient, the laser pulse emitted by a lidar results in a weak reflected signal at the pW level. Therefore, to ensure the short-range detection range of the wind-measuring lidar while maintaining its accuracy, this invention provides a short-range wind-measuring lidar in one embodiment.

[0040] Please see Figure 1Figure 1 shows a schematic diagram of a wind-measuring lidar according to an embodiment of the present invention. The lidar provided in this embodiment includes: a first light source 10, which emits a first laser beam with a first wavelength; a beam splitter 20, which receives the first laser beam and splits it into a local oscillator beam and a first signal beam; a hybrid optical ring module 30, including a first port 31 and a second port 32; the hybrid optical ring module 30 receives the first signal beam through the first port 31 and outputs the first signal beam from the second port 32; and an adjustment module 40, which receives the first signal beam from the second port 32 and performs two frequency modulations, two pulse modulations, and two power amplifications on the first signal beam to obtain a second signal beam. It also includes a third port 33, where the second port 32 of the hybrid optical ring module 30 also receives the second signal light and outputs the second signal light from the third port 33; a rotating scanning module receives the second signal light from the third port 33, deflects the second signal light, and emits it to the target under test, and performs spatial scanning on the target test area of ​​the target under test; the rotating scanning module also receives the echo signal reflected by the target under test in the target test area; the hybrid optical ring module 30 also includes a detection port 34, where the third port 33 of the hybrid optical ring module 30 also receives the echo signal and transmits the echo signal to the detection port 34; and a detection module 60 receives the echo signal and local oscillator light output from the detection port 34, thereby generating the wind speed signal of the target under test.

[0041] The beam splitter can be a polarization-maintaining fiber beam splitter. The beam splitting ratio of the beam splitter for the first laser beam can be 5 / 95, 10 / 90, or 15 / 85. It can be understood that the beam splitting ratio is affected by the power of the first light source, the small-signal input requirements of the amplifier, and the optimal local oscillator power for balanced detection. The beam splitting ratio can be determined based on the power of the first light source, the small-signal input requirements of the amplifier, and the optimal local oscillator power for balanced detection. For example, the beam splitting ratio is 5 / 95.

[0042] In one embodiment, the first laser emitted by the first light source 10, such as a seed laser, is split into two beams by a beam splitter 20. One beam serves as the local oscillator and is connected to the detection module 60. The other beam serves as the first signal light and is transmitted to the first port 31 of the hybrid optical ring module 30, such as a four-port optical circulator. The signal light is then output from the second port 32 and transmitted to the adjustment module 40. The adjustment module 40 performs two frequency shifts, chopping, and amplifications on the incident first laser to convert it into a pulse of the second signal light, which is then reflected back to the second port 32.

[0043] The second signal light is then emitted into the atmosphere through the rotating scanning module 50 via the third port 33. The rotating scanning module receives the second signal light from the third port 33, deflects the second signal light, and then emits it to the target under test. It also performs a spatial scan of the target test area of ​​the target under test. After being reflected by aerosol particles, the emitted light is transmitted again through the rotating scanning module 50 to the detection module 60 via the hybrid light ring module 30. The detection module 60 receives the echo signal and local oscillator light output from the detection port 34, thereby generating the wind speed signal of the target under test.

[0044] In this embodiment, by using the hybrid optical ring module and the adjustment module together, the signal light of the target to be detected can be frequency modulated twice, pulse modulated twice, and power amplified twice. Furthermore, the design of the hybrid optical ring module 30 reduces the number of passive optical devices and has low additional insertion loss. The use of a rotating prism scanning structure to match a single-stage double-pass amplified laser can shorten the physical fiber length and increase the upper limit of the system's single-pulse energy.

[0045] Please refer to Figure 2 , Figure 2 The diagram below illustrates the structure of a rotating scanning module in one embodiment. The rotating scanning module includes: a telescope 501, which receives and transmits a second signal light from a third port 33; an encoder 502, which receives and transmits the position and rotation speed information of the target under test; a motor module 503, including a motor 5031, connected to the encoder 502, which receives the position and rotation speed information and rotates based on the position and rotation speed information; a first gear, connected to the motor module 503, which drives the rotation of the motor 5031; a second gear 505, meshing with the first gear and rotating under the drive of the first gear; a wedge prism 506, disposed in the inner ring of the second gear 505, which receives the second signal light transmitted by the telescope 501 and deflects the second signal light beam to perform spatial scanning of the target test area of ​​the target under test; the wedge prism 506 also receives the echo signal reflected by the target under test in the target test area and transmits the echo signal to the telescope 501; the telescope 501 receives the echo signal and transmits the echo signal to the detection port 34.

[0046] Furthermore, the motor module 503 includes a reducer 5032 and a coupling 5033, wherein the reducer 5032 is connected to the motor 5031 and is used to reduce the speed of the motor 5031; the coupling 5033 is connected to the output shaft of the reducer 5032.

[0047] For example, in an acousto-optic dual-pass and two-way fiber optic amplification system architecture, if a fiber-optic time-division switching module is used, the pulse after exiting the two-way amplifier will pass through a wavelength division multiplexer, an acousto-optic modulator, a polarization beam splitter, an optical circulator, and an optical switching module. The typical length of the transmission fiber is 2 meters. The stimulated Brillouin scattering threshold is inversely proportional to the length of the transmission fiber. Such a long transmission fiber length will limit the peak power of the pulse, thus limiting the detection range of the wind lidar system in this architecture. Therefore, by adopting a spatial rotating scanning prism scheme, such as... Figure 2 As shown, the emitted light from the hybrid optical ring module 30 is connected to the flange of the telescope 501 via a jumper, and the emitted light is deflected by a wedge prism 506. The radar system sends position and rotation speed information to the encoder 502 in the form of commands. After receiving the commands from the radar system, the encoder 502 drives the first gear to rotate via the motor 5031, reducer 5032, and coupling 5033. The first gear drives the second gear 505, which has a wedge prism 506, to achieve wind speed scanning of the target wind field area. The first gear is, for example, a small gear, and the second gear 505 is, for example, a large gear. The large gear has a position sensor, forming a closed-loop control to improve pointing accuracy.

[0048] In this embodiment, by using a rotating wedge prism scanning scheme instead of the traditional optical switch scheme and matching it with a single-stage double-pass amplification laser, approximately 50cm to 70cm of physical fiber length is saved, the SBS threshold is increased, the system can withstand higher single-pulse energy, and the measurement distance of the system is increased.

[0049] In one embodiment, the adjustment module 40 includes: an acousto-optic module 41, which receives a first signal light and performs frequency modulation and pulse modulation on the first signal light to obtain a third signal light; a second light source 43, which emits a second laser with a second wavelength; an erbium-doped fiber 42, which receives and transmits the third signal light and the second laser, and the third signal light is amplified and transmitted along a first direction in the erbium-doped fiber 42 under the action of the second laser to obtain a fourth signal light; a reflection module 44, which receives the fourth signal light and the second laser and reflects the fourth signal light and the second laser back to the erbium-doped fiber 42; the fourth signal light is amplified and transmitted again along a second direction in the erbium-doped fiber 42 under the action of the second laser, and is incident again on the acousto-optic module 41, where it is frequency-modulated and pulse-modulated to obtain the second signal light; the second direction is opposite to the first direction.

[0050] Please see Figure 3 Figure 3 shows a schematic diagram of a wind-measuring lidar in another embodiment of the present invention.

[0051] For example, a first laser emitted by a first light source 10, such as a 1550 nm single-frequency laser, is split into two beams by a beam splitter, such as a 5 / 95 optical beam splitter. 5% of the beam's intensity is used as the local oscillator and connected to the detection module 60. The remaining 95% of the beam's intensity is used as the signal light and transmitted to the first port 31 of the hybrid optical ring module 30, then output from the second port 32 and transmitted to the acousto-optic module 41. The acousto-optic module 41 frequency-shifts and chops the incident continuous light into a third signal light, i.e., a pulsed light, which is then incident on the erbium-doped fiber 42. A second light source 43, such as a 974 nm single-mode pump laser, transmits a second laser with a second wavelength, i.e., the pump light, into the erbium-doped fiber 42. Under the influence of the second laser, the third signal light is amplified along a first direction in the erbium-doped fiber 42, resulting in a fourth signal light. The fourth signal light and the second laser are reflected by the reflection module 44 and then amplified again by the erbium-doped fiber 42. Then, the signal light is transmitted again through the acousto-optic module 41. Utilizing the shutdown function of the acousto-optic module 41, the ASE in the adjacent pulse interval is turned off, resulting in a second signal light. This second signal light is then transmitted through the second port 32 of the hybrid optical ring module 30 to the third port 33. The second signal light is then emitted into the atmosphere through the rotating scanning module 50. The rotating scanning module 50 receives the second signal light from the third port 33, deflects the beam, and then emits it to the target under test. It performs a spatial scan of the target test area. After being reflected by aerosol particles, the emitted light is again transmitted through the rotating scanning module 50 to the detection module 60 via the hybrid optical ring module 30. The detection module 60 receives the echo signal and local oscillator light output from the detection port 34, thereby generating the wind speed signal of the target under test.

[0052] It is understood that the first light source mentioned in this application as a 1550 nm single-frequency laser and the second light source as a 974 nm single-mode pump laser are exemplary and not limiting. For example, the second light source may also include a 976 nm pump laser. The frequency shifting frequency of the acousto-optic module, such as the acousto-optic modulator, is determined by the wind speed measurement range of the wind lidar system, with typical values ​​being 40 MHz, 60 MHz, 80 MHz, etc.

[0053] Among them, inter-pulse ASE (Amplified Spontaneous Emission) refers to the amplified spontaneous emission generated between laser pulses.

[0054] In pulsed laser systems, especially in high-power laser amplifiers, there is a time interval between pulses. During this time, the gain medium in the laser amplifier still retains gain, resulting in spontaneous emission that is amplified, forming inter-pulse ASE (associated emission). Inter-pulse ASE can interfere with the normal operation of the system, reduce the signal-to-noise ratio, and affect measurement accuracy.

[0055] In this embodiment, a hybrid dual-pass optical path combining acousto-optic and fiber optic amplification is employed. The fiber-optic amplification double-pass amplifier, passing through gain fiber twice, improves the amplifier's small-signal gain and slope efficiency, resulting in greater small-signal gain. Simplifying the optical components in the hybrid dual-pass link reduces optical losses and improves the laser's slope efficiency. Furthermore, the amplified pulse undergoes secondary chopping via the acousto-optic module, ensuring the system's 100 dB extinction ratio requirement (the typical dynamic extinction ratio for a single acousto-optic pulse is 50 dB) and acting as an optical switch to filter inter-pulse ASE, thus improving the laser's output side-mode suppression ratio (SMSR) and signal-to-noise ratio. Moreover, the double-pass amplification achieved through erbium-doped fiber enables a wind measurement range of hundreds of meters for the lidar while maintaining high integration in a single-stage amplification system.

[0056] In one embodiment, the repetition frequency of the first laser is between 1 kHz and 15 kHz.

[0057] Optionally, the repetition frequency of the first laser is 1 kHz, 2 kHz, 3 kHz, 4 kHz, 5 kHz, 6 kHz, 7 kHz, 8 kHz, 9 kHz, 10 kHz, 11 kHz, 12 kHz, 13 kHz, 14 kHz, or 15 kHz.

[0058] In one embodiment, the repetition frequency of the first laser is 10 kHz.

[0059] The optical system for wind-measuring lidar needs to meet the signal-to-noise ratio and accuracy requirements of the radar system. Considering that the system noise is shot noise, the lidar equation is shown in formula (1):

[0060] (1)

[0061] Where CNR is the carrier-to-noise ratio, η is the optical system efficiency factor, and E p λ is the laser single pulse energy, β is the atmospheric backscattering coefficient, λ is the center wavelength of the emitted laser, T is the atmospheric one-way loss coefficient, D is the telescope aperture, h is Planck's constant, B is the circuit detection bandwidth, and R is the detection distance.

[0062] Under low carrier-to-noise ratio conditions, the formula for the velocity measurement accuracy of wind-measuring lidar is shown in formula (2):

[0063] (2)

[0064] Where σ υ Let δ be the standard deviation of velocity. υ N represents the signal spectral bandwidth. p N represents the number of pulses accumulated.g is the number of sampling points within the distance gate, and CNR is the carrier-to-noise ratio.

[0065] According to formulas (1) and (2), the factors affecting the accuracy of wind measurement within a single distance gate include signal spectral bandwidth, pulse accumulation count, number of sampling points, and signal-to-noise ratio. Considering only the influence of the laser, the factor affecting wind measurement accuracy is the pulse accumulation count N. p and laser single pulse energy E p .

[0066] Since the wind direction of the wind-measuring lidar is synthesized from the radial wind speed vector, and the number of pulse accumulations N p Limited by integration time. The radial wind speed integration time is defined as T. 积分 Pulse accumulation count N p Radial wind speed integration time and pulse repetition frequency f p The relationship is shown in formula (3):

[0067] N p = T 积分 ×f p (3)

[0068] The F-factor can be defined using the above formula. The F-factor is used to evaluate the correlation between laser parameters and wind measurement accuracy, as shown in formula (4):

[0069] (4)

[0070] As shown in formula (4), the larger the F factor, the smaller the velocity measurement accuracy of the wind-measuring lidar, meaning the higher the velocity measurement accuracy of the lidar. The laser single-pulse energy E... p and pulse output average power P avg The relationship between the pulse repetition frequency and the pulse repetition frequency is shown in formula (5):

[0071] (5)

[0072] From formulas (4) and (5), we can obtain formula (6):

[0073] (6)

[0074] As defined by the F-factor, when a low pulse repetition frequency f is used... p and large laser single pulse energy E p The solution can also meet the needs of close-range wind measurement.

[0075] To achieve the same amplification effect as traditional two-stage amplification with a single-stage two-way amplification, the laser repetition frequency operates at a low repetition frequency, typically below 15 kHz. The specific frequency must consider the pulse duty cycle and the number of pulse accumulations in the radar system. In this embodiment, the repetition frequency of the first laser is designed to be 10 kHz. Typical pulse widths are 200, 300, or 400 ns, taking into account the blind zone and measurement distance of the wind-measuring lidar system. In one embodiment, the pulse width is 300 ns. Due to the high small-signal gain and high slope efficiency characteristics of two-way amplification, and its operation at a low repetition frequency, the single-pulse energy output by this light source is large, and the peak power of the laser output pulse is also large. This easily reaches the stimulated Brillouin scattering (SBS) threshold, causing pulse trailing edge jitter and affecting wind measurement accuracy.

[0076] In this embodiment, by designing the repetition frequency of the first laser to be 10 kHz, the single-pulse energy is increased under the condition of a certain average power, so that the single-pulse energy of the single-stage amplification reaches the level of the traditional two-stage amplification, eliminating the need for the second-stage amplifier and reducing the cost and power consumption of the radar system. In addition, in this embodiment, based on the lidar equation and wind measurement accuracy, the design of the single-stage fiber amplifier is optimized by optimizing the relationship between the number of pulse accumulations and the single-pulse energy, so that the amplifier operates in a low repetition rate and high pulse energy mode, reducing one stage of amplifier, that is, reducing the number of optical amplification stages, thereby reducing cost, power consumption and size.

[0077] To achieve the same amplification effect as traditional two-stage amplification in a single-stage two-way amplification, the repetition frequency of the first light source 10 operates at a low repetition frequency, typically below 15 kHz. The specific frequency depends on the pulse duty cycle and the number of pulse accumulations in the radar system; optionally, the repetition frequency of the first light source 10 is 10 kHz. Typical pulse widths are 200 ns, 300 ns, and 400 ns, etc., taking into account the blind zone and measurement distance of the wind-measuring lidar system; optionally, the pulse width of the first light source 10 is 300 ns. Due to the high small-signal gain and high slope efficiency characteristics of two-way amplification, and its operation at a low repetition frequency, the single-pulse energy output by this light source is large, and the peak power of the laser output pulse is also large. This easily reaches the stimulated Brillouin scattering (SBS) threshold, causing pulse trailing edge jitter and affecting wind measurement accuracy.

[0078] For traditional small-signal input single-stage amplifiers, due to the small input pulse power and small single-stage gain coefficient, the entire pulse can be uniformly amplified with little change in pulse waveform before and after input. In this embodiment, on the one hand, a two-way amplification scheme is adopted, which has high slope efficiency and small-signal gain. On the other hand, the first light source 10 operates at a low repetition frequency, resulting in high single-pulse energy. When the leading edge of the pulse enters the amplifier first, it depletes the inverted particle count, and the trailing edge enters later, resulting in a gain much smaller than that of the leading edge.

[0079] Figure 4 A digitally modulated square wave waveform is output to the FPGA module 80 (e.g., an FPGA signal board). After being loaded onto the acousto-optic driver 70, it generates a square wave modulation for the acousto-optic module 41. After double-pass amplification, the waveform is output from the hybrid optical ring module 30 as shown below. Figure 5 The image shows the output result in the digital modulation mode of the acousto-optic driver. Due to the high gain at the pulse leading edge and the low gain at the trailing edge, the laser output pulse waveform is characterized by a high leading edge and a low trailing edge. This results in a high pulse peak power, easily reaching the SBS threshold, which is detrimental to increasing the single-pulse energy of the laser source and limits the measurement range of the wind-measuring radar.

[0080] To address this issue, in one embodiment, a simulated acousto-optic pre-shaping method is used to solve the single-pulse energy limitation problem caused by SBS in low-repetition-rate single-stage two-way amplified lasers. Please refer to... Figure 6 The lidar also includes: an FPGA module 80, used to send pulse signals to the acousto-optic module 41; within each pulse period of the pulse signal, the voltage value changes from a first voltage to a second voltage; the first voltage is greater than the second voltage; the acousto-optic module 41 modulates the first signal light pulse, including: the acousto-optic module 41 receives the pulse signal sent by the FPGA module 80, and modulates the first signal light pulse based on the pulse signal.

[0081] In this embodiment, a pulse waveform premodulation method is used, employing a pulse waveform with a low initial amplitude followed by a high amplitude to balance the high initial amplitude followed by a low amplitude phenomenon caused by the amplification gain. For example... Figure 6 As shown, FPGA module 80 outputs a pulse signal, and the voltage value at different times follows a low-then-high pattern, as follows: Figure 7 As shown. The signal is then loaded into the acousto-optic driver 70. The acousto-optic driver 70 converts the signal into an acoustic wave signal through the transducer inside the acousto-optic modulator to modulate the waveform of the incident light. Because the pre-modulated waveform has a low leading edge and a high trailing edge, the pulse leading edge, after amplification, still retains a residual number of inverted particles that amplify the pulse trailing edge. Therefore, the overall output waveform of the laser is Gaussian-like, as shown. Figure 8 As shown, this uniform distribution of single-pulse energy across the entire waveform reduces peak pulse power, allowing the system to withstand greater pulse energy with the same pulse width and thus increasing the system's measurement distance.

[0082] In this embodiment, a simulated acousto-optic scheme is used to pre-modulate the waveform. By reducing the pulse front-high and back-low effect caused by uneven gain during pulse amplification, the pulse front-end is lowered, reducing the pulse peak power. Under the condition of a certain SBS threshold, the upper limit of the laser single pulse energy is increased.

[0083] In one embodiment, the reflection module 44 includes: a lens 441 for receiving a fourth signal light and a second laser, and for adjusting the fourth signal light and the second laser; a color filter 442 for receiving the fourth signal light and the second laser adjusted by the lens 441, reflecting the second laser and transmitting the fourth signal light; the second laser is reflected to the lens 441, and after being adjusted again by the lens 441, it is incident into the erbium-doped fiber 42; a polarization rotation unit 443 for receiving the fourth signal light, rotating the polarization direction of the fourth signal light by 90 degrees, and reflecting it to the color filter 442; the fourth signal light after being rotated 90 degrees in polarization direction is again incident into the erbium-doped fiber 42 after passing through the color filter 442 and the lens 441.

[0084] When the first signal light is incident on the acousto-optic module, since the acousto-optic module includes a first surface and a second surface, both the first surface and the second surface will reflect the first signal light. The reflected light will beat with the echo signal, which will make the detection result inaccurate.

[0085] To address the aforementioned issues, in one embodiment, the hybrid optical ring module 30 further includes a polarization beam splitter and an optical circulator; a first signal light is received through the first port 31, deflected by the polarization beam splitter to the second port 32, and the first signal light is output from the second port 32; the second port 32 of the hybrid optical ring module also receives a second signal light, which is deflected by the polarization beam splitter to the optical circulator, and the optical circulator outputs the second signal light from the third port 33.

[0086] For example, when the first signal light received by the hybrid optical ring module through the first port 31 is in a first polarization state, such as P-light, the polarization beam splitter can reflect the first signal light in the first polarization state to the second port 32 and exit from the second port 32. After being processed by the adjustment module, the polarization state of the first signal light changes by 90 degrees, becoming a second signal light in a second polarization state, such as S-light. The second signal light is again incident on the hybrid optical ring module 30 through the second port 32, transmitted through the polarization beam splitter to the optical circulator, and then transmitted through the optical circulator to the third port 33, and exiting from the third port 33. The adjustment module includes an acousto-optic module. It can be understood that the polarization state of the first signal light can also be a second polarization state, such as S-light, and thus the polarization state of the second signal light can also be a first polarization state, such as P-light. It can also be understood that the polarization beam splitter can transmit light in the first polarization state and reflect light in the second polarization state, which is not limited in this application.

[0087] When the first signal light passes through the acousto-optic module for the first time, most of the light, after diffraction by the acousto-optic module, enters the subsequent amplification through the output fiber collimator. However, a small portion of the light returns to the input fiber collimator of the acousto-optic module after a single frequency shift, and then is transmitted to the first port of the hybrid optical ring module. Without special processing, the signal light amplified by the second frequency shift and the stray light after the single frequency shift will interfere with each other, causing envelope modulation of the output pulse and affecting the wind measurement accuracy. In this embodiment, by setting a polarization beam splitter in the hybrid optical ring module, the polarization state of the light reflected by the first or second surface of the acousto-optic module is different from that of the echo signal when the first signal light passes through the acousto-optic module. Therefore, the light reflected by the first or second surface of the acousto-optic module will not beat with the echo signal on the detector surface, thereby reducing noise interference and improving the accuracy of lidar detection.

[0088] In one embodiment, the second laser is transmitted along a second direction.

[0089] For example, please refer to Figure 9 , Figure 9This is a schematic diagram of the reflection module 44 in one embodiment. The first laser beam splitter 20 emitted by the first light source 10 splits the light into two beams. For example, 5% of the beam's intensity is used as the local oscillator and connected to the detection module 60. The remaining 95% of the beam's intensity is used as the signal light, transmitted to the first port 31 of the hybrid optical ring module 30, and output from the second port 32, transmitted to the acousto-optic module 41. The acousto-optic module 41 frequency-shifts and chops the incident continuous light into a third signal light, i.e., a pulsed light, which is then incident on the erbium-doped fiber 42. The second light source 43, for example a 974 nm single-mode pump laser, transmits a second laser beam, i.e., the pump light, with a second wavelength to the reflection module 44. The lens 441 of the reflection module 44 receives the fourth signal light and the second laser beam, adjusts the fourth signal light and the second laser beam, and then projects them onto the color filter 442. The color filter 442 receives the fourth signal light and the second laser light adjusted by the lens 441, reflects the second laser light and transmits the fourth signal light; the second laser light is reflected back to the lens 441, adjusted again by the lens 441, and then incident into the erbium-doped fiber 42. The fourth signal light passing through the color filter 442 is incident into the polarization rotation unit 443, which receives the fourth signal light, rotates the polarization direction of the fourth signal light by 90 degrees, reflects it back to the color filter 442, and then passes through the color filter 442 and the lens 441 again before being incident into the erbium-doped fiber 42. Thus, the fourth signal light obtained after the amplification of the third signal light is reflected by the reflection module 44, its polarization state is rotated by 90 degrees, and then it is amplified again by the erbium-doped fiber 42. Afterwards, it passes through the acousto-optic module 41 again, and using the shutdown function of the acousto-optic module 41, the ASE in the adjacent pulse interval is turned off to obtain the second signal light, which is then transmitted to the third port 33 through the second port 32 of the hybrid optical ring module 30. The second signal light is then emitted into the atmosphere through the rotating scanning module 50 via the third port 33. The rotating scanning module receives the second signal light from the third port 33, deflects the second signal light, and then emits it to the target under test. It also performs a spatial scan of the target test area of ​​the target under test. After being reflected by aerosol particles, the emitted light is transmitted again through the rotating scanning module 50 to the detection module 60 via the hybrid light ring module 30. The detection module 60 receives the echo signal and local oscillator light output from the detection port 34, thereby generating the wind speed signal of the target under test.

[0090] In this implementation, by transmitting the pump light in reverse, it is convenient to integrate optical devices such as wavelength division multiplexers and reflection modules, shorten the length of the transmission fiber, and reduce the nonlinear effects caused by SBS (Stimulated Brillouin scattering).

[0091] In one embodiment, the polarization rotation unit 443 includes: a Faraday rotation unit 4431 for receiving the fourth signal light and rotating the polarization direction of the fourth signal light by 45 degrees under the action of a magnetic field; a reflector 4432 for receiving the fourth signal light with the polarization direction rotated by 45 degrees and reflecting the fourth signal light with the polarization direction rotated by 45 degrees back to the Faraday rotation unit 4431; the fourth signal light with the polarization direction rotated by 45 degrees passes through the Faraday rotation unit again, and the polarization direction is rotated by 45 degrees again before being incident on the color filter 442.

[0092] For example, please refer to again Figure 9 , Figure 9This is a schematic diagram of the reflection module 44 in one embodiment. The first laser beam splitter 20 emitted by the first light source 10 splits the light into two beams. For example, 5% of the beam's intensity is used as the local oscillator and connected to the detection module 60. The remaining 95% of the beam's intensity is used as the signal light, transmitted to the first port 31 of the hybrid optical ring module 30, and output from the second port 32, transmitted to the acousto-optic module 41. The acousto-optic module 41 frequency-shifts and chops the incident continuous light into a third signal light, i.e., a pulsed light, which is then incident on the erbium-doped fiber 42. The second light source 43, for example a 974 nm single-mode pump laser, transmits a second laser beam, i.e., the pump light, with a second wavelength to the reflection module 44. The lens 441 of the reflection module 44 receives the fourth signal light and the second laser beam, adjusts the fourth signal light and the second laser beam, and then projects them onto the color filter 442. The color filter 442 receives the fourth signal light and the second laser light, which are adjusted by the lens 441. It reflects the second laser light and transmits the fourth signal light. The second laser light is reflected back to the lens 441, and after being adjusted again by the lens 441, it enters the erbium-doped fiber 42. The fourth signal light that has passed through the color filter 442 enters the polarization rotation unit 443. The Faraday rotation unit 4431 of the polarization rotation unit 443 receives the fourth signal light and rotates the polarization direction of the fourth signal light by 45 degrees under the action of a magnetic field. The reflector 4432 receives the fourth signal light with the polarization direction rotated by 45 degrees and reflects the fourth signal light with the polarization direction rotated by 45 degrees back to the Faraday rotation unit 4431. The fourth signal light with the polarization direction rotated by 45 degrees passes through the Faraday rotation unit again, and after being rotated by 45 degrees again, it enters the color filter 442 and then enters the erbium-doped fiber 42 after passing through the color filter 442 and the lens 441 again. Thus, the fourth signal light, obtained after amplification of the third signal light, is reflected by the reflection module 44, its polarization state rotated by 90°, and then amplified again by the erbium-doped fiber 42. It then passes through the acousto-optic module 41 again, and using the shutdown function of the acousto-optic module 41, the ASE in the adjacent pulse interval is turned off, resulting in the second signal light. The second signal light is then transmitted to the third port 33 via the second port 32 of the hybrid optical ring module 30. The second signal light is then emitted into the atmosphere through the rotating scanning module 50 via the third port 33. The rotating scanning module receives the second signal light from the third port 33, deflects the beam, and emits it to the target under test, performing a spatial scan of the target test area of ​​the target under test. After reflection by aerosol particles, the emitted light is again transmitted through the rotating scanning module 50 to the detection module 60 via the hybrid optical ring module 30. The detection module 60 receives the echo signal and local oscillator light output from the detection port 34, thereby generating the wind speed signal of the target under test.

[0093] The increased single-pulse energy leads to a higher peak pulse power and intensifies the stimulated Brillouin scattering (SBS) effect, resulting in increased pulse trailing edge jitter and affecting wind measurement accuracy. The stimulated Brillouin scattering threshold (SBS threshold, SBST) is shown in formula (7):

[0094] (7)

[0095] Where P SBST Let be the stimulated Brillouin scattering threshold, and be the peak pulse power. A eff g is the fiber mode field area. B (Ω B ) represents the Brillouin gain. L eff This represents the effective fiber length. For gain fiber, this value is the path integral; for ordinary transmission fiber, it is equivalent to the physical length L of the transmission fiber. Optimizing the length of the gain fiber to reduce SBS also affects amplifier gain. Therefore, from an engineering perspective, the most effective way to suppress SBS is to reduce the length L of the transmission fiber.

[0096] For example, the reflection module 44 further includes a dual-core pin, which includes: a first pin port for receiving the second laser and transmitting the second laser to the reflection module 44; and a second pin port connected to the erbium-doped fiber 42 for receiving the fourth signal light and transmitting the fourth signal light to the reflection module 44; and also for receiving the second laser and the fourth signal light reflected by the reflection module 44 and transmitting the second laser and the fourth signal light to the erbium-doped fiber 42.

[0097] The backward-pumped two-way amplified optical path of this application facilitates the integration of wavelength division multiplexers and Faraday rotator optical devices. Considering device loss rate and fusion splicer operability, we assume that the length of each fiber pigtail of the optical device is 10 cm. Considering the two-way optical path, the optical path length saved after device integration is 40 cm. The 980 pump light, i.e., the second laser, passes through the first port of the ferrule and is focused onto the color filter 442 by a self-focusing collimator. The color filter 442 reflects the second laser, i.e., the pump light, to the common terminal (COM), i.e., the second port of the ferrule. The signal light is input through the COM port, and after being reflected by the Faraday rotator and the reflector, it returns to the common terminal for output.

[0098] In this embodiment, the second port 32 of the hybrid optical ring module 30 and the Faraday rotation unit 4431 form a polarization switch, which can effectively isolate the single-path stray light inside the acousto-optic modulator. By adopting a dual-pass structure of polarization beam splitter and Faraday rotation mirror, the polarization state of the signal light with secondary frequency shift changes by 90° after passing through the Faraday rotation mirror, while the stray light with single frequency shift caused by reflection from the internal surface of the acousto-optic modulator does not pass through the Faraday rotation mirror, and its polarization state differs from that of the signal light by 90°. Thus, by utilizing the polarization separation principle, the signal light and stray light are separated, avoiding the pulse envelope modulation problem caused by their interference. Furthermore, by making the pump light, i.e., the second laser, transmit in the opposite direction to the first laser, it is convenient to integrate the wavelength division multiplexer and the Faraday rotation mirror, shorten the transmission fiber length, and reduce the nonlinear effect caused by SBS.

[0099] In one embodiment, the first port 31, the second port 32, the third port 33, and the probe port 34 of the hybrid optical ring module 30 all use polarization-maintaining fibers. The slow axis of the polarization-maintaining fiber of the second port 32 is aligned with the slow axis of the polarization-maintaining fiber of the first port 31, the fast axis of the polarization-maintaining fiber of the third port 33 is aligned with the slow axis of the polarization-maintaining fiber of the second port 32, and the slow axis of the polarization-maintaining fiber of the probe port 34 is aligned with the slow axis of the polarization-maintaining fiber of the third port 33.

[0100] For example, please refer to Figure 10 , Figure 10 A schematic diagram of a hybrid optical ring module in one embodiment. In this module, the first port 31, second port 32, third port 33, and probe port 34 all use polarization-maintaining fibers. The slow axis of the polarization-maintaining fiber at the second port 32 is aligned with the slow axis of the polarization-maintaining fiber at the first port 31, the fast axis of the polarization-maintaining fiber at the third port 33 is aligned with the slow axis of the polarization-maintaining fiber at the second port 32, and the slow axis of the polarization-maintaining fiber at the probe port 34 is aligned with the slow axis of the polarization-maintaining fiber at the third port 33.

[0101] In one embodiment, the polarization state of the first signal light output by the beam splitter 20 is input along the slow axis direction of the first port 31 of the hybrid optical ring module 30, and then output along the slow axis direction of the second port 32 to the acousto-optic module 41. After being chopped and frequency-shifted by the acousto-optic module 41, it is amplified by the erbium-doped fiber 42, passes through the lens 441 and the color filter 442 to reach the polarization rotation unit 443 and is reflected back to the erbium-doped fiber 42. At this time, the polarization state changes by 90° and is transmitted along the fast axis of the polarization-maintaining fiber. After being amplified a second time and passing through the acousto-optic module 41 for the second time, it is transmitted along the fast axis direction of the second port 32 to the hybrid optical ring module 30. Then it is output from the third port 33. After passing through the rotating shaft, it is output along the slow axis of the third port 33 and then emitted into the atmosphere through the rotating scanning module 50. Ignoring atmospheric depolarization effects, the polarization state of the scattered return light received by the rotating scanning module 50 still propagates along the slow axis of the polarization-maintaining fiber. After passing through the optical switch, it reaches the third port 33 of the hybrid optical ring module 30, and then propagates along the slow axis direction of the third port 33 to the hybrid optical ring module 30. After that, it is output to the detection module 60 along the slow axis direction of the detection port 34.

[0102] When the laser passes through the gain fiber a second time, the single-pulse energy is further amplified, and the SBS effect intensifies. At this point, the length of the transmission fiber after the gain fiber output has a greater impact. In this embodiment, by coordinating the four ports of the polarization beam splitter, such as the PBS, and the hybrid optical ring module 30, and designing the transmission characteristics of each port, the polarization separation effect of the PBS + Faraday rotator mirror is ensured, thereby saving 20 cm of fiber length and reducing the SBS effect.

[0103] In one embodiment, the detection module 60 includes: a coupler 61 for coupling the echo signal and the local oscillator light to obtain a coupled optical signal; and a balanced detector 62 for receiving the coupled optical signal, performing frequency beating on the coupled optical signal, and converting the frequency-beating coupled optical signal into an electrical signal.

[0104] For example, the coupler 61 can be a 50 / 50 optical coupler. When coherent detection is possible, the coherent laser signal and the local oscillator signal are incident together on the photosensitive surface of the balanced detector 62 under the condition of wavefront matching, generating beat frequency or coherent superposition, so that the magnitude of the output electrical signal of the balanced detector 62 is proportional to the square of the sum of the echo signal (backscattered signal light) and the local oscillator light.

[0105] Furthermore, the slow axis of the detection port 34 of the hybrid optical ring module 30 and the slow axis of the local oscillator light of the beam splitter 20 are both connected to the slow axis of the input end of the coupler 61, such as a 50 / 50 optical coupler. The signal light and the local oscillator light are transmitted along the slow axis of the input end of the 50 / 50 optical coupler, and their vibration directions are consistent, which can ensure the coherence efficiency of the beat frequency of the subsequent local oscillator light and the echo signal scattered by the aerosol surface.

[0106] For example, please refer to Figure 11The first laser emitted by the 1550 nm single-frequency seed laser (i.e., the first light source 10) is split into two beams by the beam splitter 20. One beam serves as the local oscillator beam, and the other as the first signal beam. The beam splitting ratio of the beam splitter needs to comprehensively consider three factors: the seed laser power, the small signal power incident on the amplifier, and the optimal local oscillator beam power for balanced detection. Common values ​​are 5 / 95, 10 / 90, and 15 / 85, etc. The first signal beam is then incident on the first port 31 of the polarization beam splitter and transmitted to the second port 32. The slow axis of the polarization-maintaining fiber at the first port 31 and the second port 32 is aligned. The signal beam output from the second port 32 is incident on the acousto-optic module 41, which frequency-shifts and chops the input continuous light, such as the first signal beam, into pulsed light. The acousto-optic frequency shift is determined by the wind speed measurement range of the wind lidar system, with typical values ​​being 40 MHz, 60 MHz, and 80 MHz, etc. The third signal beam obtained after chopping is transmitted to the backward-pumped erbium-doped fiber amplifier. The second laser from the second light source 43, after being combined with the third signal light by the wavelength division multiplexer 440, is incident into the erbium-doped fiber 42. The third signal light and the second laser propagate in opposite directions. The amplified third signal light, resulting in a fourth signal light, is transmitted to the Faraday rotation unit 4431. The Faraday rotation unit 4431 incorporates a 45° optical rotator crystal and a reflector. During a single incident event, the polarization state rotates by 45°. After reflection by the reflector, the returning light passes through the optical rotator crystal again, resulting in another 45° rotation of the polarization state. The returning fourth signal light then undergoes a second amplification via the erbium-doped fiber amplifier, i.e., the erbium-doped fiber 42. At this point, the fourth signal light and the second laser propagate in the same direction. The amplified pulse light undergoes a second frequency shift and chopping by the acousto-optic module 41 to obtain the second signal light. The second chopping filters out acousto-optic leakage pulses, increasing the system extinction ratio to 100 dB (the typical acousto-optic dynamic extinction ratio is 50 dB). It also filters out spontaneous emission (ASE) generated during fiber amplification, improving the side-mode suppression ratio (SMSR) of the laser output. The returned light is incident on the polarization beamsplitter through the second port 32. When the incident continuous light, such as the first signal light, passes through the acousto-optic module 41 for the first time, most of the light, after diffraction by the acousto-optic module 41, will enter the subsequent amplification through the output fiber collimator. However, a small portion of the light will return to the input fiber collimator of the acousto-optic module 41 after a single frequency shift, and then be transmitted to the second port 32 and incident on the polarization beamsplitter. Without special processing, the secondary frequency-shifted amplified signal light and the stray light after the single frequency shift will interfere with each other, causing envelope modulation of the output pulse and affecting the accuracy of wind measurement. By using a polarization beamsplitter and a Faraday rotation unit 4431, a 90° difference in polarization state can be generated between the single frequency-shifted stray light and the secondary frequency-shifted amplified signal light. The fast axis of the collimator of the output fiber of the polarization beam splitter connected to the circulator is aligned with the slow axis of the second port 32. In this way, the single-frequency shift stray light is transmitted out through the first port 31 of the polarization beam splitter, and the second-frequency shift amplified signal light is transmitted to the optical circulator after passing through the polarization beam splitter.After the amplified signal light is output from the circulator and passes through the telescope 501, the incident light is spatially deflected by the wedge prism 506. Then, the wedge prism 506 is rotated by a motor, thereby realizing spatial scanning of the target test area. After being reflected by aerosol particles, the outgoing light is received again by the telescope 501 and transmitted from the circulator to the 50:50 coupler 61. After coupling with the local oscillator light, the light is mixed at the balanced detector 62 to obtain the difference frequency analog signal.

[0107] For alternatives, please refer to [link / reference]. Figure 12 For two-way amplification, the following structural scheme can also be adopted: In the first amplification, the signal light and pump light propagate in the same direction; in the second amplification, the signal light and pump light propagate in opposite directions. Figure 11 The difference between the back-pass amplification results and those of the two-way amplification lies in the different transmission directions of the signal light and pump light during single amplification.

[0108] For example, please refer to Figure 11The first laser emitted by the 1550 nm single-frequency seed laser (i.e., the first light source 10) is split into two beams by the beam splitter 20. One beam serves as the local oscillator beam, and the other as the first signal beam. The beam splitting ratio of the beam splitter needs to comprehensively consider three factors: the seed laser power, the small signal power incident on the amplifier, and the optimal local oscillator beam power for balanced detection. Common values ​​are 5 / 95, 10 / 90, and 15 / 85, etc. Afterward, the first signal beam is incident on the first port 31 of the polarization beam splitter and then transmitted to the second port 32. The slow axis of the polarization-maintaining fiber at the first port 31 and the second port 32 is aligned. The signal beam output from the second port 32 is incident on the acousto-optic module 41. The acousto-optic module 41 frequency-shifts and chops the input continuous light, such as the first signal beam, into pulsed light. The acousto-optic frequency shift is determined by the wind speed measurement range of the wind lidar system, with typical values ​​being 40 MHz, 60 MHz, 80 MHz, etc. The second laser from the second light source 43 is combined with the third signal light obtained after wavelength division multiplexing (WDM) and chopping by the second laser light source 440 and then transmitted to the erbium-doped fiber 42. The third signal light and the second laser light are transmitted in the same direction. The third signal light is amplified to obtain a fourth signal light, which is then transmitted to the Faraday rotation unit 4431. The Faraday rotation unit 4431 contains a 45° optical rotation crystal and a reflector. During a single incident event, the polarization state is rotated by 45°. After being reflected by the reflector, the returning light passes through the optical rotation crystal again, and the polarization state is rotated by another 45°. Then, the returning fourth signal light is amplified a second time by the erbium-doped fiber amplifier, i.e., the erbium-doped fiber 42. At this time, the fourth signal light and the second laser light are transmitted in opposite directions. The amplified pulse light is then frequency-shifted and chopped twice by the acousto-optic module 41 to obtain the second signal light. The secondary chopping process filters out acousto-optic leakage pulses, increasing the system extinction ratio to 100 dB (the typical acousto-optic dynamic extinction ratio is 50 dB). It also filters out spontaneous emission (ASE) generated during fiber amplification, improving the laser's side-mode suppression ratio (SMSR). The returned light is incident on the polarization beam splitter through the second port 32. When the incident continuous light, such as the first signal light, first passes through the acousto-optic module 41, most of it is diffracted by the module and enters subsequent amplification through the output fiber collimator. However, a small portion returns to the acousto-optic module 41's incident fiber collimator after a single frequency shift, and then is transmitted to the second port 32 and incident on the polarization beam splitter. Without special processing, the secondary frequency-shifted amplified signal light and the stray light after the single frequency shift will interfere with each other, causing envelope modulation of the output pulse and affecting wind measurement accuracy. By employing a polarization beam splitter and Faraday rotation unit 4431, a 90° difference in polarization state can be created between the single-frequency-shifted stray light and the secondary frequency-shifted amplified signal light. The fast axis of the collimator of the output fiber of the polarization beam splitter connected to the circulator is aligned with the slow axis of the second port 32. In this way, the single-frequency shift stray light is transmitted out through the first port 31 of the polarization beam splitter, and the second-frequency shift amplified signal light is transmitted to the optical circulator after passing through the polarization beam splitter.After the amplified signal light is output from the circulator and passes through the telescope 501, the incident light is spatially deflected by the wedge prism 506. Then, the wedge prism 506 is rotated by a motor, thereby realizing spatial scanning of the target test area. After being reflected by aerosol particles, the outgoing light is received again by the telescope 501 and transmitted from the circulator to the 50:50 coupler 61. After coupling with the local oscillator light, the light is mixed at the balanced detector 62 to obtain the difference frequency analog signal.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A wind measuring lidar, characterized by The laser radar comprises: a first light source emitting first laser light with a first wavelength; a beam splitter receiving the first laser light and splitting the first laser light into local light and first signal light; a hybrid optical ring module comprising a first port and a second port; the hybrid optical ring module receives the first signal light through the first port and outputs the first signal light from the second port; an adjustment module receiving the first signal light from the second port, for twice frequency modulation, twice pulse modulation and twice power amplification of the first signal light to obtain second signal light; the hybrid optical ring module further comprises a third port, and the second port of the hybrid optical ring module further receives the second signal light and outputs the second signal light from the third port; a rotating scanning module receiving the second signal light from the third port and emitting the second signal light to a target to be measured after beam deflection, and performing spatial scanning on a target test area of the target to be measured; the rotating scanning module further receives echo signals reflected by the target to be measured in the target test area; the hybrid optical ring module further comprises a detection port, and the third port of the hybrid optical ring module further receives the echo signals and transmits the echo signals to the detection port; a detection module receiving the echo signals output by the detection port and the local light to generate a wind speed signal of the target to be measured.

2. The lidar of claim 1, wherein, The rotating scanning module comprises: a telescope receiving and transmitting the second signal light from the third port; an encoder receiving and emitting position information and rotation speed information of the target to be measured; a motor module comprising a motor, connected with the encoder, receiving the position information and the rotation speed information, and rotating based on the position information and the rotation speed information; a first gear connected with the motor module and transmitting power of rotation of the motor; a second gear meshing with the first gear and rotating under the driving of the first gear; a wedge-shaped prism arranged in an inner ring of the second gear, receiving the second signal light transmitted by the telescope, and performing beam deflection on the second signal light to perform spatial scanning on the target test area of the target to be measured; the wedge-shaped prism further receives echo signals reflected by the target to be measured in the target test area and transmits the echo signals to the telescope; the telescope receives the echo signals and transmits the echo signals to the detection port.

3. The lidar of claim 1, wherein, The adjustment module comprises: an acousto-optic module receiving the first signal light and performing frequency modulation and pulse modulation on the first signal light to obtain third signal light; a second light source emitting second laser light with a second wavelength; an erbium-doped optical fiber receiving and transmitting the third signal light and the second laser light, and amplifying the third signal light in the first direction in the erbium-doped optical fiber under the action of the second laser light to obtain fourth signal light; The reflection module receives the fourth signal light and the second laser light, and reflects the fourth signal light and the second laser light back to the erbium-doped fiber; the fourth signal light is amplified again in the erbium-doped fiber under the action of the second laser light and is incident into the acousto-optic module again, and the acousto-optic module performs frequency modulation and pulse modulation on the fourth signal light to obtain the second signal light; the second direction is opposite to the first direction.

4. The lidar of claim 3, wherein, Further comprising: The FPGA module is configured to send a pulse signal to the acousto-optic module; in each pulse period of the pulse signal, the voltage value changes from a first voltage to a second voltage; The first voltage is greater than the second voltage; The acousto-optic module pulse-modulates the first signal light, including: The acousto-optic module receives the pulse signal sent by the FPGA module and pulse-modulates the first signal light based on the pulse signal.

5. The lidar of claim 3, wherein, The reflection module includes: A lens configured to receive the fourth signal light and the second laser light and adjust the fourth signal light and the second laser light; A color filter configured to receive the fourth signal light and the second laser light adjusted by the lens, reflect the second laser light and transmit the fourth signal light; the second laser light is reflected to the lens, and after being adjusted by the lens again, the second laser light is incident into the erbium-doped fiber; A polarization rotation unit configured to receive the fourth signal light, rotate the polarization direction of the fourth signal light by 90 degrees, and reflect the fourth signal light with the rotated polarization direction to the color filter; the fourth signal light with the rotated polarization direction is incident into the erbium-doped fiber again after passing through the color filter and the lens.

6. The lidar of claim 5, wherein, The hybrid optical circulator further includes a polarization beam splitter and an optical circulator; the first signal light received by the first port is deflected to the second port by the polarization beam splitter, and the first signal light is output from the second port; the second signal light is also received by the second port of the hybrid optical circulator, the second signal light is deflected to the optical circulator by the polarization beam splitter, and the optical circulator outputs the second signal light from the third port.

7. The lidar of claim 3, wherein, The repetition frequency of the first laser is between 1 kHz and 15 kHz.

8. The lidar of claim 3, wherein, The repetition frequency of the first laser is 10 kHz.

9. The lidar of claim 5, wherein, The polarization rotation unit includes: A Faraday rotation unit configured to receive the fourth signal light and rotate the polarization direction of the fourth signal light by 45 degrees under the action of a magnetic field; A mirror configured to receive the fourth signal light with the rotated polarization direction by 45 degrees, and reflect the fourth signal light with the rotated polarization direction by 45 degrees back to the Faraday rotation unit; the fourth signal light with the rotated polarization direction by 45 degrees is incident into the color filter again after the polarization direction is rotated by 45 degrees again by the Faraday rotation unit.

10. The lidar of claim 9, wherein, The second laser light is transmitted along the second direction.

11. The lidar of claim 1, wherein, The first port, the second port, the third port and the probe port of the hybrid optical ring module all use polarization maintaining optical fibers, the slow axis of the polarization maintaining optical fiber of the second port is aligned with the slow axis of the polarization maintaining optical fiber of the first port, the fast axis of the polarization maintaining optical fiber of the third port is aligned with the slow axis of the polarization maintaining optical fiber of the second port, and the slow axis of the polarization maintaining optical fiber of the probe port is aligned with the slow axis of the polarization maintaining optical fiber of the third port.

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