Wind measuring lidar system

Abstract

The application relates to a wind measurement laser radar system, comprising a temperature control-free light source for emitting second laser light, wherein the second laser light is multimode pumped laser light; a first optical fiber for twice amplifying signal light emitted by a seed light source; a third optical fiber for again amplifying the signal light after twice amplification; and a time division switching device comprising a deflection module and a beam splitting module, wherein the signal light after three times of amplification is deflected by controlling the deflection module, so that the signal light is split by the beam splitting module at different times to obtain eighth signal light, and the eighth signal light is emitted through different ports. The application uses a pump beam splitting double-clad double-pass amplification scheme of the temperature control-free light source for a preamplifier, so that preamplification is realized in a low-power-consumption, small-size and low-cost mode, the power consumption of the wind measurement laser radar is reduced, and the demand for improving the detection distance of the future wind radar is met.

Description

Technical Field

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

[0002] With the future development of the wind power industry, there is a demand for wind measurement lidar with small size and low power consumption.

[0003] With the widespread application of wind-measuring lidar in the wind power industry, insufficient power supply is a problem under extreme outdoor conditions, necessitating the use of unconventional methods such as solar panels. When the overall power consumption of the wind-measuring lidar is too high, its effective working time is limited due to power supply constraints, resulting in insufficient data utilization and impacting customer usability.

[0004] Therefore, there is an urgent need for a wind measurement lidar with low power consumption. Utility Model Content

[0005] Therefore, it is necessary to provide a wind-measuring lidar system that can reduce the power consumption of wind-measuring lidar in response to the above-mentioned technical problems.

[0006] This application provides a wind-measuring lidar system, comprising: a seed light source assembly emitting a first signal light having a first polarization state; an acousto-optic device receiving the first signal light and performing pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; a temperature-controlled light source emitting a second laser with power consumption between 4.8W and 5.2W; the second laser being a multimode pumped laser; a first optical fiber receiving the second signal light and the second laser, and amplifying the second signal light to obtain a third signal light; the third signal light also containing amplified spontaneous emission light; wherein the first optical fiber is a double-clad erbium-ytterbium co-doped fiber; and a polarization reflection device receiving the third signal light and filtering out the amplified spontaneous emission light from the third signal light. The polarization state of the third signal light is rotated to obtain a fourth signal light with a second polarization state; the second polarization state is perpendicular to the first polarization state; the first optical fiber also receives the fourth signal light and amplifies it again to obtain a fifth signal light; the acousto-optic device also receives the fifth signal light and performs pulse modulation and frequency shift modulation on it again to obtain a sixth signal light; the third optical fiber receives the second laser and the sixth signal light and amplifies the sixth signal light to obtain a seventh signal light; the time-division switching device includes a deflection module and a beam splitting module, which controls the deflection of the seventh signal light by the deflection module so that the seventh signal light is split into eight beams by the beam splitting module at different times to obtain an eighth signal light, which is emitted through different ports.

[0007] In one embodiment, the power consumption of the temperature-controlled light source is between 4.8W and 5.2W.

[0008] In one embodiment, the first optical fiber includes: a core in which the second signal light is transmitted; and an inner cladding in which the second laser light is transmitted through multiple reflections.

[0009] In one embodiment, light between the seed light source assembly, the acousto-optic device, the second light source, the polarization reflection device, and the time-division switching device is transmitted via a second optical fiber.

[0010] In one embodiment, the wind-measuring lidar system further includes a first beam combiner, through which a second signal light and a second laser are incident into a first optical fiber.

[0011] In one embodiment, the wind-measuring lidar system further includes a second beam combiner through which a second laser beam is incident into a third optical fiber.

[0012] In one embodiment, in the third optical fiber, the transmission direction of the second laser is opposite to the transmission direction of the sixth signal light.

[0013] In one embodiment, the wind-measuring lidar system further includes: a second beam splitter, which receives the second laser and splits the second laser beam through the second beam splitter, and then directs it into the first beam combiner and the second beam combiner respectively.

[0014] In one embodiment, the mode field diameter of the second fiber at the input end of the second combiner signal arm is matched with the mode field diameter of the third fiber; and / or the mode field diameter of the polarization-maintaining fiber collimator fiber at different ports of the time-division switching device is matched with the mode field diameter of the fiber at the output end of the second combiner signal arm.

[0015] In one embodiment, the third optical fiber is the same as the first optical fiber, both being erbium-ytterbium co-doped optical fibers.

[0016] In one embodiment, the polarization reflection device includes: a polarization rotator that receives a third signal light and rotates the polarization state of the third signal light along a first polarization rotation direction to obtain a third deflected signal light; and a passband mirror that receives the third deflected signal light, transmits and amplifies spontaneous emission light, and reflects the third deflected signal light back to the polarization rotator; the polarization state of the third deflected signal light is rotated again along the first polarization rotation direction after passing through the polarization rotator to obtain a fourth signal light with a second polarization state.

[0017] In one embodiment, the polarization reflection device includes: a polarization rotator, which receives a third signal light and rotates the polarization state of the third signal light along a first polarization rotation direction to obtain a third deflected signal light; a filter, which is tilted relative to the third deflected signal light, receives the third deflected signal light, transmits the third deflected signal light, and filters out amplified spontaneous emission light; a reflector, which receives and reflects the third deflected signal light; the third deflected signal light passes through the filter again and then through the polarization rotator, and after passing through the polarization rotator, the polarization state is rotated again along the first polarization rotation direction to obtain a fourth signal light with a second polarization state.

[0018] In one embodiment, the time-division switching device further includes a processing module and a detection port; the different ports include a first port, a second port, a third port, and a fourth port, and a preprocessing module, a deflection module, and a beam splitting module are arranged sequentially; the seventh signal light of the second polarization state from the third optical fiber is preprocessed by the preprocessing module to obtain a seventh signal light rotated by a first angle along the first polarization rotation direction, and then deflected by the deflection module to obtain an eighth signal light with different deflection states and different exit positions. The eighth signal light with different deflection states and different exit positions is output to the target under test from the first port, the second port, the third port, and the fourth port respectively through the beam splitting module; the first port, the second port, the third port, and the fourth port respectively receive the echo signal reflected back from the target under test, and the echo signal is again incident on the deflection module through the beam splitting module for deflection processing and then incident on the preprocessing module to obtain the second polarization state echo signal, and is transmitted to the detection port through the preprocessing module; the light between the preprocessing module, the first port, the second port, the third port, the fourth port, and the detection port is transmitted through the second optical fiber.

[0019] In one embodiment, the preprocessing module includes: a second polarization beamsplitter that receives and transmits a seventh signal light of a second polarization state emitted from a third optical fiber; a second half-wave plate that receives and rotates the polarization state of the seventh signal light of the second polarization state transmitted by the second polarization beamsplitter along a first polarization rotation direction by a first angle; a Faraday rotor that receives and rotates the polarization state of the seventh signal light emitted from the second half-wave plate along the second polarization rotation direction by a first angle to obtain a seventh signal light of a first polarization state; the second polarization rotation direction is opposite to the first polarization rotation direction; and a third half-wave plate that receives and rotates the polarization state of the seventh signal light of the first polarization state emitted from the Faraday rotor along the first polarization rotation direction. The first half-wave plate rotates at a first angle; it also receives the first echo signal emitted by the first electronically controlled rotating unit, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle to obtain the echo signal of the first polarization state; the second half-wave plate also receives the first echo signal emitted by the Faraday rotor, and rotates the polarization state of the first echo signal along the second polarization rotation direction by a first angle to obtain the echo signal of the second polarization state; the second polarization beam splitter also receives the echo signal of the second polarization state emitted by the second half-wave plate, and reflects the echo signal to the detection port.

[0020] In one embodiment, the deflection module includes: a first electrically controlled rotation unit, including a first DC coil, which controls the rotation direction of the polarization state of the seventh signal light passing through the first electrically controlled rotation unit by controlling the current direction of the first DC coil; a birefringent crystal, which receives the seventh signal light passing through the first electrically controlled rotation unit and deflects the seventh signal light based on its polarization state; a fourth half-wave plate, which receives the seventh signal light emitted from the birefringent crystal and rotates the polarization state of the seventh signal light along the first polarization rotation direction by a first angle; and a second electrically controlled rotation unit, including a second DC coil, which controls the rotation direction of the polarization state of the seventh signal light passing through the first electrically controlled rotation unit by controlling the current direction of the second DC coil. The polarization state rotation direction is used to obtain the eighth signal light; it also receives the echo signal transmitted by the beam splitter module, and controls the rotation direction of the polarization state of the echo signal passing through the second electrically controlled rotation unit by controlling the current direction of the second DC coil; the fourth half-wave plate also receives the echo signal emitted by the second electrically controlled rotation unit, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle; the birefringent crystal also receives the echo signal, and deflects the echo signal based on the polarization state of the echo signal; the first electrically controlled rotation unit also receives the echo signal emitted by the birefringent crystal, and controls the rotation direction of the polarization state of the echo signal passing through the first electrically controlled rotation unit by controlling the current direction of the first DC coil.

[0021] In one embodiment, when the current direction of the first DC coil and the current direction of the second DC coil are both set to the first direction, the birefringent crystal does not deflect the passing seventh signal light but deflects the passing echo signal; when the current direction of the first DC coil and the current direction of the second DC coil are both set to the second direction, the birefringent crystal deflects the passing seventh signal light but does not deflect the passing echo signal; when the current direction of the first DC coil is set to the second direction and the current direction of the second DC coil is set to the first direction, the birefringent crystal deflects the passing seventh signal light but does not deflect the passing echo signal; when the current direction of the first DC coil is set to the first direction and the current direction of the second DC coil is set to the second direction, the birefringent crystal does not deflect the passing seventh signal light but deflects the passing echo signal.

[0022] In one embodiment, the beam splitting module includes: a third polarization beam splitter for receiving an eighth signal light; when the eighth signal light is not deflected by the deflection module and has a first polarization state, it is transmitted from a first position of the third polarization beam splitter and incident on a first port; when the eighth signal light is deflected by the deflection module and has a first polarization state, it is transmitted from a second position of the third polarization beam splitter; when the eighth signal light is deflected by the deflection module and has a second polarization state, it is reflected from the second position of the third polarization beam splitter and incident on a third port; when the eighth signal light is not deflected by the deflection module and has a second polarization state, it is reflected from the first position of the third polarization beam splitter; and a first folding prism for receiving light from... The eighth signal light transmitted from the second position is deflected and incident on the second port; the second folding prism receives the eighth signal light reflected from the first position, deflects it and incident on the fourth port; and receives the echo signal passing through the fourth port, deflects the echo signal and incident on the third polarization beam splitter; the first folding prism also receives the echo signal passing through the second port, deflects the echo signal and incident on the third polarization beam splitter; the third polarization beam splitter also receives the echo signals from the first port and the first folding prism respectively, transmits the echo signals to the deflection module; and also receives the echo signals from the third port and the second folding lens respectively, reflects the echo signals to the deflection module.

[0023] In one embodiment, the wavelength of the second laser is between 920nm and 940nm.

[0024] The aforementioned wind-measuring lidar, wherein the temperature-controlled light source emits a second laser, which is a multimode pumped laser. This second laser signal is received via a first optical fiber, and the second signal is amplified to obtain a third signal. Subsequently, a fourth signal is received and amplified again to obtain a fifth signal. This fifth signal is then pulse-modulated and frequency-shifted by an acousto-optic device to generate a sixth signal. A third optical fiber receives the second laser and the sixth signal, amplifying the sixth signal to obtain a seventh signal. A time-division switching device, including a deflection module and a beam-splitting module, controls the deflection of the seventh signal, causing it to be split into eighth signal beams at different times. These eighth signal beams are emitted through different ports. This application utilizes a temperature-controlled light source-free pumped beam splitting double-clad double-pass amplification scheme for the preamplifier, achieving pre-amplification in a low-power, small-size, and low-cost manner, reducing the power consumption of the wind-measuring lidar and meeting the future requirements for increased wind-measuring lidar detection range. Attached Figure Description

[0025] 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.

[0026] Figure 1 This is a structural block diagram of a wind-measuring lidar system in one embodiment;

[0027] Figure 2 This is a schematic diagram of the wind-measuring lidar in yet another embodiment;

[0028] Figure 3 This is a comparison curve of single-pass and double-pass amplification efficiency based on 940nm pump in one embodiment;

[0029] Figure 4 This is a schematic diagram of the polarization reflection device in one embodiment;

[0030] Figure 5 This is a schematic diagram of the polarization reflection device in yet another embodiment;

[0031] Figure 6 The SMSR curve of the pre-amplification stage before filtering;

[0032] Figure 7 The pre-amplification stage SMSR curve after filtering;

[0033] Figure 8 This is the slope efficiency curve of the main amplification stage output in one embodiment;

[0034] Figure 9 This refers to the side-mode suppression ratio of the main amplification stage in one embodiment;

[0035] Figure 10 This is a schematic diagram of the time-division switching device in one embodiment;

[0036] Figure 11 The curve showing the relationship between the SBS threshold and the length of the transmission fiber;

[0037] Figure 12 The curve showing the relationship between the SBS threshold and the fiber mode field diameter;

[0038] Figure 13 This is a diagram showing the polarization state transformation and path propagation of light as it propagates forward and backward through the first port in one embodiment.

[0039] Figure 14 This is a diagram showing the polarization state transformation and path propagation of light as it propagates forward and backward through the second port in one embodiment.

[0040] Figure 15 This is a diagram showing the polarization state transformation and path propagation of light as it propagates forward and backward through the third port in one embodiment.

[0041] Figure 16 This is a diagram showing the polarization state transformation and path propagation of light as it travels forward and backward through the fourth port in one embodiment.

[0042] 110. Seed light source assembly; 111. Seed light source; 112. First beam splitter; 230. First polarization beam splitter; 231. First polarization port; 232. Second polarization port; 233. Third polarization port; 130. Acousto-optic device; 150. First beam combiner; 160. First optical fiber; 170. Polarization reflection device; 220. Second beam splitter; 140. Temperature-controlled light source; 250. Second beam combiner; 240. Isolator; 260. Third optical fiber; 120. Time-division switching device; 121. First port; 122. Second port; 123. Third port; 124. Fourth port; 125. Detection port; 126. Fifth port; 180. Telescope; 19 0. Coupler; 200. Balanced detector; 210. Signal processing device; 127. Preprocessing module; 128. Deflection module; 129. Beam splitting module; 1271. Second polarization beam splitter; 1272. Second half-wave plate; 1273. Faraday rotor; 1274. Third half-wave plate; 1281. First electrically controlled rotation unit; 1282. Birefringent crystal; 1283. Fourth half-wave plate; 1284. Second electrically controlled rotation unit; 1291. Third polarization beam splitter; 1292. First folding prism; 1293. Second folding prism; 171. Polarization-maintaining fiber collimator; 172. Polarization rotator; 173. Passband mirror; 174. Filter; 175. Mirror. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Depending on the application environment, wind-measuring lidar includes nacelle-type wind-measuring lidar for wind turbine feedforward control and ground-based wind-measuring lidar for wind resource surveying. However, traditional wind-measuring lidar has the following main shortcomings:

[0050] Firstly, for nacelle-type mid-range wind-measuring lidar, the main pain points are its large usage and high cost. This mainly focuses on the use of two acousto-optic devices and the high-cost single-mode pumped laser and multi-mode pumped laser.

[0051] Secondly, ground-based medium-range wind-measuring lidar is a mobile wind measurement device with a wider range of applications, including plains, mountains, and oceans. However, its large size makes it inconvenient to move. Size is another major drawback. For example, the laser circuit driver board needs to perform constant current and temperature control on single-mode and multi-mode lasers, requiring numerous functions and resulting in a large board size. The combined effect of these two factors increases the laser's size, leading to an excessively large radar system. When deployed in remote areas, this large size increases transportation costs and deployment time, resulting in higher overall costs.

[0052] Thirdly, when ground-based wind-measuring lidar is deployed in remote areas such as oceans and mountains, power shortages necessitate the use of unconventional power supply methods such as solar panels, making power consumption a significant challenge. In wind-measuring lidar systems, the laser is the primary source of overall power consumption. If the pre-amplification stage fiber amplifier uses a single-mode erbium-doped fiber amplifier design, amplifying small signals by pumping the erbium-doped fiber with a single-mode pumped laser; and if the main amplification stage fiber amplifier is a multimode-pumped double-clad erbium-ytterbium co-doped fiber amplifier, then to ensure high-efficiency and high-reliability operation of the laser, a thermoelectric cooler (TEC) is needed to control the temperature of both the single-mode and multimode pumped lasers, with a typical constant temperature of 25°C. Under high and low temperature conditions, the large temperature difference between the control temperature and the ambient temperature leads to high power consumption of the thermoelectric cooler and a significant increase in laser power consumption. When the wind measurement lidar system is in extreme high and low temperature conditions outdoors (low temperature is -40℃, high temperature is 60℃), the power consumption is high, which will limit the effective working time of the wind measurement lidar, resulting in insufficient data efficiency and affecting customer use.

[0053] Fourth, with the increasing size of wind turbine blades in the future, there is a further need to improve the detection range of wind-measuring radar. When the laser pulse passes through the main amplifier, if it goes through the circulator and optical switch based on discrete structures in the traditional solution, the transmission fiber is too long, the peak power of the output pulse is limited, and the detection range of the wind-measuring radar is affected.

[0054] Therefore, this application proposes a wind-measuring lidar that can improve upon the above-mentioned shortcomings.

[0055] Please see Figure 1 and Figure 2 , Figure 1 This invention illustrates a schematic diagram of a wind-measuring lidar according to one embodiment of the present application, and alternatively, Figure 2A schematic diagram of a wind-measuring lidar system according to another embodiment of this application is shown. One embodiment of this application provides a wind-measuring lidar system comprising: a seed light source assembly 110 that emits a first signal light; the first signal light having a first polarization state; an acousto-optic device 130 that receives the first signal light and performs pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; a temperature-controlled light source 140 that emits a second laser, the second laser being a multimode pumped laser; a first optical fiber 160 that receives the second signal light and the second laser, and amplifies the second signal light to obtain a third signal light; the third signal light also contains amplified spontaneous emission light; wherein the first optical fiber 160 is a double-clad erbium-ytterbium co-doped fiber; and a polarization reflection device 170 that receives the third signal light, filters out the amplified spontaneous emission light in the third signal light, and rotates the polarization of the third signal light. The first optical fiber 160 receives the fourth signal light and amplifies it again to obtain the fifth signal light. The acousto-optic device 130 receives the fifth signal light and performs pulse modulation and frequency shift modulation on it again to obtain the sixth signal light. The third optical fiber 260 receives the second laser and the sixth signal light and amplifies the sixth signal light to obtain the seventh signal light. The time-division switching device 120 includes a deflection module 128 and a beam splitting module 129. By controlling the deflection module 128 to deflect the seventh signal light, the seventh signal light is split by the beam splitting module 129 at different times to obtain the eighth signal light. The eighth signal light is emitted through different ports.

[0056] For example, the seed light source assembly 110 includes a seed light source 111 that emits a first laser beam with a first wavelength; the first laser beam is a continuous laser beam; the seed light source assembly 110 also includes a first beam splitter 112 that receives the first laser beam and splits it into a local oscillator beam and a first signal beam, the first signal beam having a first polarization state. The seed light source assembly 110 can be, for example, a seed module, the seed light source 111 can be a 1550nm single-frequency seed laser, and the first beam splitter 112 can be a polarization-maintaining beam splitter.

[0057] The wind-measuring lidar system also includes a telescope 180, which is a multi-channel telescope 180, optionally a four-channel telescope 180. The telescope 180 receives an eighth signal light, transmits the eighth signal light to the target, receives the echo signal reflected back from the target, and returns the echo signal to the different ports. The time-division switching device 120 also includes a detection port 125, which transmits the echo signals received from different ports to the detection port 125. The wind-measuring lidar system also includes a detection module, which receives the echo signal and local oscillator light output from the detection port 125, thereby generating a wind speed signal for the target via the signal processing device 210. Optionally, the detection module includes a coupler 190 and a balanced detector 200. The coupler 190 can be a 50:50 optical coupler 190.

[0058] As further exemplarily, the detection module includes a coupler 190 and a balanced detector 200, wherein the coupler 190 can be a 50:50 fiber coupler. The time-division switching device 120 can be a hybrid integrated circulator magneto-optical switch. The first optical fiber 160 can be a double-clad erbium-ytterbium co-doped fiber. The polarization reflection device 170 can be a Faraday rotation filter reflector.

[0059] In one embodiment, such as Figure 1 and Figure 2The diagram shows the structural block diagram of a wind-measuring lidar system. The seed light source 111 of the seed light source assembly 110, for example, a 1550nm single-frequency seed laser, is split into two beams by a first beam splitter 112, for example, a polarization-maintaining beam splitter: one beam serves as the local oscillator and is transmitted to a coupler 190, for example, a 50:50 fiber coupler 190; the other beam serves as the signal light, for example, a first signal light, and is transmitted to the first polarization port 231 of the first polarization beam splitter 230, where the first signal light has a first polarization state. The first polarization port 231 of the first polarization beam splitter 230 transmits the input light to the second polarization port 232 of the first polarization beam splitter 230, and then to the acousto-optic device 130. The acousto-optic device 130 consists of an acousto-optic driver and an acousto-optic modulator, which frequency-shifts and chops the input continuous light, i.e., the first signal light, into pulsed light to obtain the second signal light, which also has the first polarization state. The second laser emitted by the temperature-controlled light source 140, i.e., the multimode pump laser, is split into two beams; one beam is used for pre-amplification and input into the first optical fiber 160. The first optical fiber 160 receives the second signal light and the second laser, amplifying the second signal light to obtain the third signal light; the third signal light also contains amplified spontaneous emission light; wherein the first optical fiber 160 is a double-clad erbium-ytterbium co-doped fiber. The pulsed signal light, after one amplification, is transmitted to the polarization reflection device 170, such as a Faraday rotation filter reflector. The polarization reflection device 170 receives the third signal light, filters out the amplified spontaneous emission light in the third signal light, and rotates the polarization state of the third signal light to obtain a fourth signal light with a second polarization state; the second polarization state is perpendicular to the first polarization state; the fourth signal light is transmitted along the fast axis direction of the polarization-maintaining fiber to the first optical fiber 160, such as a double-clad gain fiber, and after a second amplification, obtains the fifth signal light. The signal light output from the seed light source assembly 110, after a second amplification, has its power level amplified to the tens of milliwatts level. Then, the fifth signal light is transmitted to the acousto-optic module, where it undergoes a second frequency shift and chopping to obtain the sixth signal light. The second chopping process filters out acousto-optic leakage pulses, improving the system's dynamic extinction ratio. Furthermore, the time-gating method filters out amplified spontaneous emission (ASE) generated during fiber amplification, improving the preamplifier's side-mode suppression ratio (SMSR) and facilitating low-noise amplification in the second-stage amplifier. The returned light contains amplified signal light (e.g., the sixth signal light) and stray light. The stray light is formed by the reflection of the incident light from the acousto-optic modulator surface and propagates along the slow axis of the fiber. The sixth signal light, having been reflected twice by the Faraday rotator, has a 90° polarization rotation and propagates along the fast axis of the fiber, thus possessing a second polarization state.When the two signals pass through the birefringent crystal 1282 within the first polarization beamsplitter 230, the stray light propagates along the direction of the first polarization port 231, while the sixth signal light propagates from the third polarization port 233. They are spatially separated, preventing beat frequency interference between the signal light and stray light to form an envelope modulation pulse. The slow axis of the polarization-maintaining fiber collimator at the third polarization port 233 of the first polarization beamsplitter 230 is aligned with the polarization state direction of the incident light, ensuring that the incident light propagates along the slow axis of the fiber. The pre-amplified signal light, such as the sixth signal light, then enters the second-stage amplifier after passing through the optical isolator 240. The second-stage amplifier includes, for example, a third fiber 260. The seventh signal light is obtained by amplifying the sixth signal light. After the second-stage amplification, the signal light power level is increased from the tens of milliwatts to the hundreds of milliwatts. Subsequently, the amplified signal light, such as the seventh signal light, is incident on the fifth port 126 of the time-division switching device 120, such as the integrated circulator magneto-optical switch. Through circuit control, the seventh signal light is split into an eighth signal light at different times via the beam-splitting module 129. The eighth signal light is output from different ports, thus achieving the time-division multiplexing effect. The eighth signal light passes through the four-way telescope 180 and is incident into the atmosphere. After being reflected by the aerosol in the target detection area, it passes through the telescope 180 and the time-division switching device 120 again. Each return signal light is transmitted from the detection port 125 to the coupler 190, such as a 50:50 optical coupler 190, and coupled with the local oscillator light. After being mixed at the balanced detector 200, an analog signal is obtained. The analog signal is converted from analog to digital by the sampling module in the signal processing device 210, and then subjected to a Fast Fourier Transform (FFT) in the signal processor chip. After accumulation and noise reduction, the spectral information of the radial wind speed is obtained.

[0060] In this embodiment, the second laser emitted by the temperature-controlled light source 140 of the wind-measuring lidar is a multimode pumped laser. The second signal light and the second laser are received via the first optical fiber 160. The second signal light is amplified to obtain a third signal light. Subsequently, a fourth signal light is received and amplified again to obtain a fifth signal light. A sixth signal light, modulated again by the acousto-optic device 130, is then amplified again via the third optical fiber 260 to obtain a seventh signal light. Through multimode pumping and a three-pass amplification structure, the power of the two-pass amplifier is increased with low-cost pumping (around 100 yuan), meeting the future requirements for increased wind-measuring lidar detection range and reducing power consumption. Furthermore, by using the acousto-optic device 130 to perform secondary chopping on the first signal light, the acousto-optic leakage pulse is filtered out, improving the system's dynamic extinction ratio. On the other hand, the amplified spontaneous emission (ASE) generated during fiber amplification is further filtered out, improving the side-mode suppression ratio (SMSR) of the laser output.

[0061] In one embodiment, there is no temperature-controlled light source 140, which emits a second laser with a power consumption between 4.8W and 5.2W, for example, a power consumption of 4.8W, 4.85W, 4.9W, 4.95W, 5.0W, 5.05W, 5.1W, 5.15W or 5.2W; the second laser is a multimode pumped laser.

[0062] In this embodiment, the power consumption of the temperature-controlled light source 140 of the wind-measuring lidar is between 4.8W and 5.2W, thus eliminating the need for temperature control and reducing power consumption. The second laser emitted by the temperature-controlled light source 140 is a multimode pumped laser. The second signal light and the second laser are received via the first optical fiber 160. The second signal light is amplified to obtain a third signal light. Subsequently, a fourth signal light is received and amplified again to obtain a fifth signal light. A sixth signal light, modulated again by the acousto-optic device 130, is amplified again via the third optical fiber 260 to obtain a seventh signal light. Through multimode pumping and a three-pass amplification structure, the power of the two-pass amplifier is increased with low-cost pumping (around 100 yuan), meeting the future requirements for increased wind-measuring lidar detection range and reducing power consumption. Furthermore, by employing an acousto-optic device 130 to perform secondary chopping on the first signal light, the acousto-optic leakage pulse is filtered out, thereby improving the dynamic extinction ratio of the system. On the other hand, the amplified spontaneous emission (ASE) generated during fiber amplification is further filtered out, thereby improving the side-mode suppression ratio (SMSR) of the laser output.

[0063] In one embodiment, the wavelength of the second laser is between 920nm and 940nm. For example, the wavelength of the second laser can be 900nm, 910nm, 920nm, 930nm, or 940nm.

[0064] In this embodiment, a single acousto-optic dual-pass scheme is adopted, realizing the function of a dual acousto-optic device 130 with a single acousto-optic device 130, thus saving costs. The input 10μW-level pulse signal light is amplified to the 10mW level via the first optical fiber 160. Traditional solutions involve erbium-doped fiber amplifiers for single-mode pumped lasers, with a typical small-signal amplification gain of 30dB and a typical output side-mode rejection ratio (SMSR) of 50dB. However, multimode-pumped double-clad erbium-ytterbium co-doped fiber amplifiers are generally used for amplifying large pulse signals with an input of 10mW, increasing the power level from the 10mW level to the 100mW level. The typical gain is 10dB, and the typical output SMSSR is 50dB. To reduce laser costs, this embodiment uses a temperature-controlled 940nm multimode pumping scheme for the pre-amplification stage. When a 10μW-level small-signal pulse is input to an erbium-ytterbium co-doped double-clad fiber amplifier, the large pump power of the multimode pump results in a significant amount of ASE light generated. This competition between the small signal and ASE light leads to amplification, impacting signal amplification efficiency and output SMSR. Therefore, for a 940nm multimode pumping scheme, achieving 30dB small-signal gain amplification while ensuring an SMSR output of over 50dB with a 10μW-level small-signal input is a technical challenge. To address this issue, this embodiment optimizes the preamplifier in the following ways: First, it employs a two-pass amplification structure to improve laser slope efficiency and output SMSR. Figure 3 The figure shows the difference in amplification efficiency between single-pass and double-pass amplification using 940nm pump. As can be seen from the figure, the double-pass amplification structure achieves a higher conversion efficiency of 7.6%. This decomposes the 30dB small-signal gain into a secondary amplification process, which is beneficial for the competition between the signal light and the ASE light, thus improving the output SMSR. When the slope efficiencies of both are similar, this embodiment uses a multimode beam splitter to transmit the pump light to the pre-amplification stage, saving the need for a traditional single-mode pump laser and laser driver, thereby reducing power consumption and size.

[0065] Furthermore, traditional two-stage amplification structures require two acousto-optic devices (130), one single-mode pump, and one multi-mode pump, resulting in large active optics components. They also require a single-mode circuit driver with constant current and temperature control, and a multi-mode circuit driver with constant current and temperature control, leading to numerous circuit functions and a large circuit board size. By adopting, for example, a 940nm multi-mode pump-based dual-pass amplification and single acousto-optic dual-pass scheme in the pre-amplification stage, a single 940nm multi-mode pump beam splitting scheme can be used, saving one single-mode pump source and circuit driver board. Moreover, the 940nm multi-mode pump operates over a wide temperature range, requiring no separate temperature control; therefore, the 940nm multi-mode pump circuit driver does not require temperature control design, simplifying the circuit board. It can be understood that for traditional light sources, the typical temperature control value is 25℃, and at a high temperature of 60℃, the typical overall power consumption is 11W. However, for the 940nm light source, due to the elimination of temperature control power consumption, the typical power consumption is 5W.

[0066] In summary, the new structural design eliminates the need for an acousto-optic module and a single-mode pump in terms of optical components; it also eliminates the need for a single-mode pump driver in terms of circuitry, removes the temperature control component of the multi-mode pump driver, and reduces the size of the laser driver board. The reduction in active optical components and the decrease in the size of the laser driver board result in an overall laser size reduction to 50% of its original size.

[0067] Furthermore, the pump efficiency is low when the main amplification stage is designed with a 940nm wavelength. This leads to two problems: first, to achieve the same output power, a higher pump power is required, thus increasing the laser's power consumption; second, due to the low pump efficiency, the gain fiber length needs to be longer to achieve the same gain, resulting in a lower SBS threshold and affecting the laser's peak output power. To address this issue, the preamplifier in this solution is optimized. The preamplifier employs a two-way amplification technique based on 940nm multimode pumping. Compared to traditional solutions, this approach achieves a higher average power pulse output at a lower cost, typically reaching 60mW, while the traditional solution typically reaches 20mW. The increased output power of the preamplifier stage reduces the pump current of the main amplifier and shortens the gain fiber length, which is beneficial for efficient amplification and high peak power pulse output in the main amplification stage.

[0068] In one embodiment, the wind-measuring lidar system further includes a first beam combiner 150, through which a second signal light and a second laser are incident into a first optical fiber 160.

[0069] In one embodiment, the first optical fiber 160 includes: a core in which the second signal light is transmitted; and an inner cladding in which the second laser light is transmitted through multiple reflections.

[0070] The first optical fiber 160 can be a double-clad erbium-ytterbium co-doped optical fiber.

[0071] The second laser emitted by the temperature-controlled light source 140, i.e., the multimode pump laser, is split into two beams by the second beam splitter 220, such as a multimode beam splitter. One beam is used for pre-amplification, and the pump light is input into the first optical fiber 160 through the first beam combiner 150, such as an optical fiber combiner. The pulsed signal light is transmitted in the core of the double-clad optical fiber, and the second laser is transmitted through multiple reflections in the inner cladding. When it repeatedly passes through the erbium-ytterbium ion-doped core, population inversion is achieved, and the signal light is amplified as it passes through.

[0072] In one embodiment, the wind-measuring lidar system further includes a second beam combiner 250 through which a second laser beam is incident into a third optical fiber 260.

[0073] In one embodiment, in the third optical fiber 260, the transmission direction of the second laser is opposite to the transmission direction of the sixth signal light.

[0074] Please see Figure 1The seed light source 111 of the seed light source assembly 110, for example a 1550nm single-frequency seed laser, is split into two beams by a first beam splitter 112, for example a polarization-maintaining beam splitter: one beam serves as the local oscillator light and is transmitted to a coupler 190, for example a 50:50 fiber coupler 190; the other beam serves as the signal light, for example a first signal light, and is transmitted to the first polarization port 231 of the first polarization beam splitter 230, wherein the first signal light has a first polarization state. The first polarization port 231 of the first polarization beam splitter 230 transmits the input light to the second polarization port 232 of the first polarization beam splitter 230, and then to the acousto-optic module. The acousto-optic module consists of an acousto-optic driver and an acousto-optic modulator, which frequency-shifts and chops the input continuous light, i.e., the first signal light, into pulsed light to obtain the second signal light, which at this time has the first polarization state. The second laser emitted by the temperature-controlled light source 140, i.e., the multimode pump laser, is split into two beams, one of which is used for pre-amplification and input into the first optical fiber 160. The first optical fiber 160 receives the second signal light and the second laser, amplifying the second signal light to obtain the third signal light; the third signal light also contains amplified spontaneous emission light; wherein the first optical fiber 160 is a double-clad erbium-ytterbium co-doped fiber. The pulsed signal light, after one amplification, is transmitted to the polarization reflection device 170, such as a Faraday rotation filter reflector. The polarization reflection device 170 receives the third signal light, filters out the amplified spontaneous emission light in the third signal light, and rotates the polarization state of the third signal light to obtain a fourth signal light with a second polarization state; the second polarization state is perpendicular to the first polarization state; the fourth signal light is transmitted along the fast axis direction of the polarization-maintaining fiber to the first optical fiber 160, such as a double-clad gain fiber, and after a second amplification, obtains the fifth signal light. The signal light output from the seed light source assembly 110, after a second amplification, has its power level amplified to the tens of milliwatts level. Then, the fifth signal light is transmitted to the acousto-optic module, where it undergoes a second frequency shift and chopping to obtain the sixth signal light. The second chopping process filters out acousto-optic leakage pulses, improving the system's dynamic extinction ratio. Furthermore, the time-gating method filters out amplified spontaneous emission (ASE) generated during fiber amplification, improving the preamplifier's side-mode suppression ratio (SMSR) and facilitating low-noise amplification in the second-stage amplifier. The returned light contains amplified signal light (e.g., the sixth signal light) and stray light. The stray light is formed by the reflection of the incident light on the acousto-optic modulator surface and propagates along the slow axis of the fiber. The sixth signal light, having been reflected twice by the Faraday rotator, has a 90° polarization rotation and propagates along the fast axis of the fiber, possessing a second polarization state. When both pass through the birefringent crystal 1282 within the first polarization beam splitter 230, the stray light propagates along the first polarization port 231, while the sixth signal light propagates from the third polarization port 233. This spatial separation prevents beat frequency interference between the signal light and stray light, thus avoiding the formation of envelope modulation pulses.The third polarization port 233 of the first polarization beam splitter 230 aligns the slow axis of the polarization-maintaining fiber collimator with the polarization state direction of the incident light, ensuring that the incident light propagates along the slow axis of the fiber. The pre-amplified signal light, such as the sixth signal light, then passes through the optical isolator 240 and enters the second-stage amplifier. The second-stage amplifier includes, for example, a third fiber 260. The second laser transmitted from the temperature-controlled light source 140 of the second-stage fiber amplifier has the opposite propagation direction to the sixth signal light, forming a back-pumped structure. This amplifies the sixth signal light to obtain the seventh signal light. After the second-stage amplification, the signal light power level increases from the tens of milliwatts to the hundreds of milliwatts. The amplified signal light, such as the seventh signal light, is then incident on the time-division switching device 120, for example, the fifth port 126 of the circulator magneto-optical switch. Through circuit control, the seventh signal light is split at different times by the beam-splitting module 129 to obtain the eighth signal light. The eighth signal light is output from different ports, thus achieving a time-division multiplexing effect. The eighth signal light passes through the four-way telescope 180 and enters the atmosphere. After being reflected by the aerosol in the target detection area, it passes through the telescope 180 and the time-division switching device 120 again. Each returning signal light is transmitted from the detection port 125 to the coupler 190, for example, a 50:50 optical coupler 190, and coupled with the local oscillator light. The signal is then mixed at the balanced detector 200 to obtain an analog signal. The analog signal is converted from analog to digital by the sampling module in the signal processing device 210, and then subjected to a Fast Fourier Transform (FFT) in the signal processor chip. After accumulation and noise reduction, the radial wind speed spectral information is obtained.

[0075] Furthermore, when the main amplification stage is designed with a 940nm wavelength, the pump efficiency is low. This leads to two problems: first, to achieve the same output power, a higher pump power is required, thus increasing the laser's power consumption; second, due to the low pump efficiency, to achieve the same gain, the gain fiber length needs to be longer, resulting in a lower SBS threshold and affecting the laser's peak output power. To address this issue, the preamplifier in this solution is optimized. The preamplifier employs a two-way amplification technique based on 940nm multimode pumping. Compared to traditional solutions, this approach can achieve a higher average power pulse output at a lower cost, typically reaching 60mW, while the traditional solution typically reaches 20mW. The increased output power of the preamplifier stage reduces the pump current of the main amplifier and shortens the gain fiber length, which is beneficial for the efficient amplification and high peak power pulse output of the main amplification stage. Simultaneously, this embodiment employs a backward-pumped structure for the main amplification stage, which also improves the laser's output efficiency.

[0076] In this embodiment, the pump light and the signal light are amplified in opposite directions, thereby reducing the nonlinear effects caused by the amplification of the sixth signal light in the third optical fiber 260.

[0077] In one embodiment, the wind-measuring lidar system further includes: a second beam splitter 220, which receives the second laser and splits the second laser beam through the second beam splitter 220 and then incident it into the first beam combiner 150 and the second beam combiner 250 respectively.

[0078] The second laser emitted by the temperature-controlled light source 140, namely the multimode pump laser, is split into two beams by the second beam splitter 220, for example, a multimode beam splitter. One beam is used for pre-amplification and then passes through the first beam combiner 150, for example, an optical fiber beam combiner, to input the pump light into the first optical fiber 160. The other beam is used for a third amplification and passes through the second beam combiner 250 to be incident into the third optical fiber 260.

[0079] In one embodiment, the third optical fiber 260 is the same as the first optical fiber 160, both being erbium-ytterbium co-doped optical fibers.

[0080] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the polarization reflection device 170 in one embodiment. In another embodiment, the polarization reflection device 170 includes: a polarization rotator 172, which receives a third signal light and rotates the polarization state of the third signal light along a first polarization rotation direction to obtain a third deflected signal light; and a passband reflector 173, which receives the third deflected signal light, transmits and amplifies spontaneously emitted light, and reflects the third deflected signal light back to the polarization rotator 172; the polarization state of the third deflected signal light is rotated again along the first polarization rotation direction after passing through the polarization rotator 172 to obtain a fourth signal light with a second polarization state.

[0081] Please refer to Figure 5 , Figure 5 The following is a schematic diagram of the structure of a polarization reflection device 170 in another embodiment. The polarization reflection device 170 includes: a polarization rotator 172, which receives a third signal light and rotates the polarization state of the third signal light along a first polarization rotation direction to obtain a third deflected signal light; a filter 174, which is tilted relative to the third deflected signal light, receives the third deflected signal light, transmits the third deflected signal light, and filters out amplified spontaneous emission light; a reflector 175, which receives and reflects the third deflected signal light; the third deflected signal light passes through the filter again and then through the polarization rotator, and after passing through the polarization rotator, the polarization state is rotated again along the first polarization rotation direction to obtain a fourth signal light with a second polarization state.

[0082] For example, the pre-amplification stage of a wind-measuring lidar system includes a temperature-controlled light source 140, a second beam splitter 220, a first beam combiner 150, a first optical fiber 160, and a polarization reflection device 170. After the signal light is amplified once, the pulsed signal light contains ASE light. To prevent ASE light from being reflected back and amplified again, thus affecting the amplification efficiency, the pulsed signal light is filtered, such as... Figure 5As shown, the polarization-maintaining fiber collimator 171 directs the incident light to a polarization rotator 172, such as a Faraday rotator, which consists of an optically rotating crystal and coils, rotating the polarization state of the incident light by 45°. The light then travels to a filter 174, which is tilted to allow transmission of the incident pulse signal light within its operating bandwidth and reflection of other wavelengths. The filtered signal light is reflected back by a reflector 175, such as a fiber optic reflector, and then passes through the filter 174 again before being transmitted to the polarization rotator, where its polarization state is rotated by 45°. Finally, the light is output from the polarization-maintaining fiber collimator.

[0083] In this embodiment, the polarization reflection device 170 can change the polarization state of the incident light from the slow axis direction of the polarization-maintaining fiber to the fast axis direction for transmission, while simultaneously filtering out ASE light in the signal light using spectral filtering. By employing spectral filtering and acousto-optic time-domain switching methods, ASE light in the pre-amplification stage double-clad amplification process is filtered out from both spectral and temporal perspectives, resulting in a 27dB improvement in SMSR, which is beneficial for high-efficiency and low-noise amplification in subsequent amplifier stages.

[0084] In this embodiment, further technical improvements were made to the two-way amplification structure of the multimode pump. Firstly, the Faraday rotator mirror integrates a filtering function, employing spectral filtering technology to filter out ASE light outside the bandpass range. In this embodiment, a design was made to the conventional Faraday rotator filter, adding a bandpass filter between the Faraday rotor 1273 and the reflector. This filter transmits the working wavelength and reflects other wavelengths. Simultaneously, the filter is tilted at a certain angle to spatially separate the reflected ASE light and signal light, improving the SMSR through spectral filtering. Secondly, a single-pass acoustic-optical dual-pass scheme was adopted, using time-domain switching filtering technology to filter out inter-pulse ASE light, thus improving the SMSR within the filter's bandpass range. Figure 6 and Figure 7 The curves show the comparison of the pre-amplification stage SMSR before and after filtering. Figure 6 The SMSR curve of the pre-amplification stage before filtering. Figure 7 The figure shows the SMSR curve of the pre-amplified stage after filtering. As can be seen from the figure, the SMSR output reaches 62dB after adopting spectral filtering and time-domain switching filtering techniques, which is an improvement of 31dB.

[0085] In this embodiment, the above-mentioned technical optimizations ensure both a small-signal gain of 30dB and an SMSR of over 55dB, making it possible to replace the traditional single-mode erbium-doped fiber amplification with, for example, a 940nm multimode double-clad pumping scheme in the pre-amplification stage. Furthermore, both the pre-amplification and main amplification stages can use a unified 940nm pumping scheme. Therefore, a single 940nm pump source multimode beam splitting technique can replace the traditional two pump sources and two laser drive circuits, saving one pump source and one laser drive circuit, thus reducing laser cost.

[0086] In one exemplary embodiment, the mode field diameter of the second fiber at the input end of the signal arm of the second combiner 250 is matched with the mode field diameter of the third fiber 260; and / or the mode field diameter of the incident fiber of the polarization-maintaining fiber collimator at different ports of the time-division switching device 120 is matched with the mode field diameter of the fiber at the output end of the signal arm of the second combiner 250.

[0087] To avoid ASE self-excitation during amplification and reduce accessory insertion loss, the mode field diameter of the fiber at the input end of the signal arm of the second combiner 250 is matched with that of the double-clad erbium-ytterbium co-doped fiber. The mode field diameter of the polarization-maintaining collimator fiber at different ports of the time-division switching device 120, such as the integrated circulator magneto-optical switch, is matched with that of the fiber at the output end of the signal arm of the second combiner 250. In this embodiment, on the one hand, the mode field diameter of the integrated circulator magneto-optical incident light is increased, reducing the peak power density. On the other hand, increasing the mode field area also helps to reduce the SBS (Stimulated Brillouin Scattering) threshold, enabling the system to withstand higher peak power pulses.

[0088] In one exemplary embodiment, the third optical fiber 260 is the same as the first optical fiber 160, both being erbium-ytterbium co-doped optical fibers.

[0089] Please refer to this again. Figure 1In one embodiment, the seed light source 111 of the seed light source assembly 110, for example a 1550nm single-frequency seed laser, is split into two beams by a first beam splitter 112, for example a polarization-maintaining beam splitter: one beam serves as the local oscillator light and is transmitted to a coupler 190, for example a 50:50 fiber coupler 190; the other beam serves as the signal light, for example a first signal light, and is transmitted to the first polarization port 231 of the first polarization beam splitter 230, wherein the first signal light has a first polarization state. The first polarization port 231 of the first polarization beam splitter 230 transmits the input light to the second polarization port 232 of the first polarization beam splitter 230, and then to the acousto-optic device 130. The acousto-optic device 130 consists of an acousto-optic driver and an acousto-optic modulator, which frequency-shifts and chops the input continuous light, i.e., the first signal light, into pulsed light to obtain the second signal light, at which time the second signal light has the first polarization state. The second laser emitted by the temperature-controlled light source 140, namely the multimode pump laser (940nm multimode pump laser), is split into two beams by the second beam splitter 220 (multimode beam splitter). One beam is used for pre-amplification, and the pump light is input into the first fiber 160 (e.g., double-clad erbium-ytterbium co-doped fiber) via the first beam combiner 150. When the second signal light of the pulsed signal light propagates in the core of the double-clad fiber, the 940nm multimode pump light is reflected multiple times in the inner cladding of the first fiber 160. When it repeatedly passes through the erbium-ytterbium doped fiber core, population inversion is achieved, and the second signal light is amplified to obtain the third signal light, which also contains amplified spontaneous emission light. The pulsed signal light obtained after one amplification, namely the third signal light, is transmitted to the polarization reflection device 170 (e.g., Faraday rotation filter mirror). The polarization reflection device 170 may have a built-in polarization rotator and a passband mirror. The polarization rotator can be a 45° polarization rotator. A passband mirror filters out the ASE light generated during the first amplification process. The polarization reflection device 170 receives the third signal light, filters out the amplified spontaneous emission light from it, and the filtered signal light passes through a polarization rotator again, where its polarization state is deflected by 45° to obtain a fourth signal light with a second polarization state; this second polarization state is perpendicular to the first polarization state. The fourth signal light is transmitted along the fast axis of the polarization-maintaining fiber to the first fiber 160, and after secondary amplification, it becomes the fifth signal light. The signal light output from the seed light source assembly 110 is amplified twice, increasing its power level to the 10mW level. Then, the fifth signal light is transmitted again to the acousto-optic module, where it undergoes secondary frequency shifting and chopping to obtain the sixth signal light. This secondary chopping filters out acousto-optic leakage pulses, improving the system's dynamic extinction ratio, and also filters out the amplified spontaneous emission (ASE) light generated during fiber amplification using a time-gating method, improving the preamplifier's side-mode rejection ratio (SMSR) and facilitating low-noise amplification in the second-stage amplifier. The returned light at this point contains the amplified signal light, the sixth signal light, and stray light.Stray light is formed by the reflection of incident light on the surface of the acousto-optic modulator and propagates along the slow axis of the fiber. The sixth signal light, being a beam reflected twice from the Faraday rotator, has its polarization state rotated by 90° and propagates along the fast axis of the fiber, thus possessing a second polarization state. When both pass through the birefringent crystal 1282 within the first polarization beam splitter 230, the stray light propagates along the direction of the first polarization port 231, while the sixth signal light propagates from the third polarizer port, spatially separating them to prevent beat frequency interference and the formation of an envelope modulation pulse. The slow axis of the polarization-maintaining fiber collimator at the third polarization port 233 of the first polarization beam splitter 230 is aligned with the polarization state direction of the incident light, ensuring that the incident light propagates along the slow axis of the fiber. The pre-amplified signal light, such as the sixth signal light, then enters the second-stage amplifier after passing through the optical isolator 240. The second-stage amplifier includes, for example, a third fiber 260. In the second-stage fiber amplifier, the 940nm pump light propagates in the opposite direction to the signal light, forming a back-pumping structure. The sixth signal light is amplified in the second stage to obtain the seventh signal light, increasing the pulse signal light power level from the tens of milliwatts to the hundreds of milliwatts. Then, the amplified signal light, i.e., the seventh signal light, is incident on the fifth port 126 of the time-division switching device 120, such as an integrated circulator magneto-optical switch. Through circuit control, the seventh signal light is split at different times by the beam splitting module 129 to obtain the eighth signal light, which is output from different ports, thus achieving a time-division multiplexing effect. To avoid ASE self-excitation during amplification and reduce accessory insertion loss, the second fiber at the input end of the signal arm of the second combiner 250 is matched with the mode field diameter of the double-clad erbium-ytterbium co-doped fiber. The mode field diameter of the polarization-maintaining collimator fiber at different ports of the time-division switching device 120, such as an integrated circulator magneto-optical switch, is matched with the mode field diameter of the fiber at the output end of the signal arm of the second combiner 250. This design, on the one hand, increases the mode field diameter of the incident magneto-optical light from the integrated circulator, reducing the peak power density. On the other hand, increasing the mode field area also helps to reduce the SBS threshold, enabling the system to withstand higher peak power pulses. The emitted signal light passes through the four-way telescope 180 and enters the atmosphere. After being reflected by the aerosol in the target detection area, it passes again through the telescope 180 and the time-division switching device 120. Each returning signal light is transmitted from the detection port 125 to the coupler 190, for example, a 50:50 optical coupler 190, and coupled with the local oscillator light. The signal is then mixed at the balanced detector 200 to obtain an analog signal. The analog signal is converted from analog to digital by the sampling module in the signal processing device 210, and then subjected to a Fast Fourier Transform (FFT) in the signal processor chip. After accumulation and noise reduction, the spectral information of the radial wind speed is obtained.

[0090] For example, the pre-amplification stage of the wind-measuring lidar system consists of a temperature-controlled light source 140, a second beam splitter 220, a first beam combiner 150, a first optical fiber 160, and a polarization reflection device 170. After the signal light is amplified once, the pulsed signal light contains ASE light. To prevent ASE light from being reflected back and amplified again, thus affecting the amplification efficiency, the pulsed signal light is filtered, such as... Figure 5 As shown, the polarization-maintaining fiber collimator directs incident light onto a polarization rotator, such as a Faraday rotator. The Faraday rotator, composed of an optically active crystal and coils, rotates the polarization state of the incident light by 45°. The light is then transmitted to a filter, which is tilted to allow transmission within the operating bandwidth of the incident pulse signal light while reflecting other wavelengths. The filtered signal light is reflected back by a mirror, such as a fiber optic mirror, passes through the filter again, and is then transmitted to the polarization rotator, where its polarization state is rotated by 45°. Finally, it is output from the polarization-maintaining fiber collimator. The overall function of the Faraday rotator is to change the polarization state of the incident light from the slow axis direction of the polarization-maintaining fiber to the fast axis direction, while simultaneously filtering out ASE light from the signal light using spectral filtering.

[0091] In this embodiment, the pump efficiency is low when the main amplification stage is designed with a 940nm wavelength. This leads to two problems: first, to achieve the same output power, a higher pump power is required, which increases the laser's power consumption; second, due to the low pump efficiency, the gain fiber length needs to be longer to achieve the same gain, resulting in a lower SBS threshold and affecting the laser's peak output power. To address this issue, the preamplifier in this solution is optimized. The preamplifier employs a two-way amplification technique based on 940nm multimode pumping. Compared to traditional solutions, this approach achieves a higher average power pulse output at a lower cost, typically reaching 60mW, while the traditional solution typically reaches 20mW. The increased output power of the preamplifier stage reduces the pump current of the main amplifier and shortens the gain fiber length, which is beneficial for the efficient amplification and high peak power pulse output of the main amplification stage. Simultaneously, this solution uses a backward-pumped structure for the main amplification stage, which also improves the laser's output efficiency.

[0092] The aforementioned technical improvements make it possible to base the main amplification stage on a 940nm pump scheme. Figure 8 and Figure 9 The figures show the efficiency curve and side-mode suppression ratio curve of the laser output based on the above structure. Figure 8 and Figure 9 It can be seen that the slope efficiency reaches 12% and the output SMSR reaches 60dB. These indicators are no less than those of the 976nm multimode pumping scheme.

[0093] Because the 940nm multimode pump has a low temperature drift coefficient, this solution does not require temperature control of the 940nm multimode pump. When the laser is under extreme conditions (low temperature -40℃, high temperature 60℃), the uncontrolled 940nm pumping solution can reduce the peak power consumption of the laser by 30%.

[0094] In one embodiment, the time-division switching device 120 further includes a processing module and a detection port 125; the different ports include a first port 121, a second port 122, a third port 123, and a fourth port 124, and a preprocessing module 127, a deflection module 128, and a beam splitting module 129 are arranged sequentially; the seventh signal light of the second polarization state from the third optical fiber 260 is preprocessed by the preprocessing module 127 to obtain a seventh signal light rotated by a first angle along the first polarization rotation direction, and then deflected by the deflection module 128 to obtain an eighth signal light with different deflection states and different exit positions. The eighth signal lights with different deflection states and different exit positions are respectively separated from the beam splitting module 129 by the beam splitting module 129. The first port 121, the second port 122, the third port 123, and the fourth port 124 output to the target under test; the first port 121, the second port 122, the third port 123, and the fourth port 124 respectively receive the echo signals reflected from the target under test, and the echo signals are again incident on the deflection module 128 through the beam splitting module 129 for deflection processing, and then incident on the preprocessing module 127 to obtain the echo signal of the second polarization state, and are transmitted to the detection port 125 through the preprocessing module 127; the light between the preprocessing module 127, the first port 121, the second port 122, the third port 123, the fourth port 124 and the detection port 125 is transmitted through the second optical fiber.

[0095] Please refer to Figure 10 , Figure 10This is a schematic diagram of the structure of a time-division switching device 120 according to an embodiment of this application. In this embodiment, the time-division switching device 120 integrates a preprocessing module 127, a deflection module 128, and a beam splitting module 129. The seventh signal light of the second polarization state from the third optical fiber 260 is transmitted to the fifth port 126 of the time-division switching device 120 and is incident on the preprocessing module 127 via a polarization-maintaining fiber collimator. The polarization direction of the incident light at the fifth port 126 is along the slow axis direction of the polarization-maintaining fiber, and the polarization direction is horizontal, defined as P-light; the vertical polarization direction is defined as S-light. After the incident light in the P-direction is preprocessed by the preprocessing module 127, a seventh signal light is obtained that has been rotated by a first angle along the first polarization rotation direction, exemplarily 45°. Subsequently, the seventh signal light is deflected by the deflection module 128 to obtain an eighth signal light with different deflection states and different exit positions. Afterward, the eighth signal light passes through the beam splitting module 129, the P-light is transmitted, and it is emitted from the first port 121 to the second port 122, respectively. The S-beams are reflected and emitted from either the third port 123 or the fourth port 124, i.e., the seventh signal light with different deflection states and different emission positions is output to the target under test from the first port 121, the second port 122, the third port 123, and the fourth port 124 respectively through the beam splitting module 129. The first port 121, the second port 122, the third port 123, and the fourth port 124 respectively receive the echo signals reflected from the target under test. The echo signals are then incident on the deflection module 128 through the beam splitting module 129 for deflection processing and then incident on the preprocessing module 127 to obtain the echo signal with the second polarization state. The echo signal is then transmitted to the detection port 125 through the second preprocessing module 127. The light between the first preprocessing module 127, the second preprocessing module 127, the first port 121, the second port 122, the third port 123, the fourth port 124, and the detection port 125 is transmitted through the second optical fiber.

[0096] For example, the light between the seed light source assembly 110, the acousto-optic device 130, the second light source, the polarization reflection device 170, and the time-division switching device 120 is transmitted through the second optical fiber.

[0097] In this embodiment, the main amplification stage uses 940nm pumped backward amplification technology to improve amplification efficiency and reduce laser power consumption. However, this presents a technical challenge: with the backward pumping amplification scheme, the second beam combiner 250 is located at the rear end. Therefore, in the structures of the second beam combiner 250, the traditional circulator, and the optical switch, the passive fiber length of these three devices is relatively long, reducing the SBS threshold and thus limiting the peak power of the laser output pulse. The theoretical calculation formula (1) for the SBS threshold in the optical fiber is as follows:

[0098]

[0099] Where PSBST A is the SBS threshold in the optical fiber. eff For the effective modulus area, L eff For short passive optical fibers, the effective length can be approximated as the physical fiber length, g. B (Ω B ) represents the Brillouin gain coefficient of silica optical fiber, with a typical value of 5 × 10⁻⁶. -11 m / W. From this formula, the relationship curve between the SBS threshold and the transmission fiber length in quartz optical fiber can be obtained, such as... Figure 11 As shown.

[0100] When using a discrete approach, the signal light output from the main amplification stage passes sequentially through a combiner, circulator, and optical switch. Taking a 20cm segment length as an example, the total length of the transmission fiber is 1.2m, and the theoretical SBS threshold is 27W according to the SBS threshold formula. Taking a pulse width of 200ns as an example, the maximum single-pulse energy it can withstand is 5.4μJ, limiting the detection range of the wind-measuring radar. In this embodiment, by integrating the preprocessing module 127, deflection module 128, and beam splitter module 129, a hybrid integration of the traditional circulator and magneto-optical switch is achieved, shortening the transmission fiber length to 0.8m and achieving a theoretical SBS threshold of 41.2W. Taking a pulse width of 200ns as an example, the maximum single-pulse energy it can withstand is increased to 8.2μJ, and the peak power reaches 41W.

[0101] Traditional magneto-optical switches, commonly used in the optical communication industry, often employ a dual-core collimator design. However, this approach has limitations when applied to wind-measuring lidar systems. Wind-measuring lidar systems output high-peak-power pulsed light from single-frequency lasers, resulting in very high energy density per unit area. Dual-core collimators, due to their small mode area, are at risk of damage during prolonged operation. Furthermore, high-peak-power pulses are highly sensitive to SBS (Special Shorting Beam), requiring a large mode area in the transmission fiber. Dual-core collimators, however, are difficult to expand or utilize large-mode-area fiber structures due to manufacturing limitations. Therefore, this embodiment employs a large-angle spatial separation method, extending the splitting distance of the birefringent crystal 1282. This makes it possible to expand the single-core collimator or use a large-mode-area fiber design. After expansion, the mode area of ​​the incident light spot is increased, the peak power density per unit area is reduced, and device reliability is improved. Additionally, using a single-core collimator allows for the use of large-mode-area fiber for the pigtail. Figure 12 The graph shows the relationship between the SBS threshold and the fiber mode field diameter. As the fiber mode field diameter increases, the SBS threshold also increases. Commercially available large-mode-field fibers have mode field diameters of 12μm, 15μm, and 25μm. Figure 11Based on length optimization, the SBS thresholds for fibers with mode field diameters of 12μm, 15μm, and 25μm are 59W, 92.7W, and 257.6W, respectively. Taking a pulse width of 200ns as an example, the corresponding tolerable single-pulse energy is 11.8μJ, 18.5μJ, and 51.5μJ, thus improving the radar's detectable range.

[0102] In this embodiment, through the design of the time-division switching device 120, namely by integrating the preprocessing module 127, the deflection module 128 and the beam splitting module 129, the length of the passive optical fiber is shortened, the mode field area is increased, SBS is suppressed, the output single pulse energy is increased, and the radar detection range is increased.

[0103] In one embodiment, the preprocessing module 127 includes: a second polarization beamsplitter 1271, which receives and transmits a seventh signal light of a second polarization state emitted from a third optical fiber 260; a second half-wave plate 1272, which receives and rotates the polarization state of the seventh signal light of the second polarization state transmitted by the second polarization beamsplitter 1271 along a first polarization rotation direction by a first angle; a Faraday rotor 1273, which receives and rotates the polarization state of the seventh signal light emitted from the second half-wave plate 1272 along the second polarization rotation direction by a first angle to obtain a seventh signal light of a first polarization state; the second polarization rotation direction is opposite to the first polarization rotation direction; and a third half-wave plate 1274, which receives and rotates the polarization state of the seventh signal light of the first polarization state emitted from the Faraday rotor 1273 along the first polarization rotation direction by a first angle. The first half-wave plate 1273 receives the echo signal emitted by the first electronically controlled rotating unit 1281 and rotates the polarization state of the echo signal along the second polarization rotation direction by the first angle to obtain the echo signal of the first polarization state; the second half-wave plate 1272 receives the echo signal emitted by the Faraday rotor 1273 and rotates the polarization state of the echo signal along the second polarization rotation direction by the first angle to obtain the echo signal of the second polarization state; the second polarization beam splitter 1271 receives the echo signal of the second polarization state emitted by the second half-wave plate 1272 and reflects the echo signal to the detection port 125.

[0104] Please refer to this again. Figure 10The seventh signal light, amplified by the third optical fiber 260, passes through the second polarization beam splitter 1271 and is transmitted to the second half-wave plate 1272. The second half-wave plate rotates the polarization state of the incident light by 45° before it enters the Faraday rotor 1273. The Faraday rotor 1273 also rotates the polarization state of the incident light by 45°, in the opposite direction to that of the second half-wave plate 1272. Thus, during a single pass, the polarization direction of the incident light remains unchanged and is still P-light. The third half-wave plate 1274 receives and rotates the polarization state of the seventh signal light with the second polarization state emitted from the Faraday rotor 1273 by a first angle along the first polarization rotation direction, exemplarily, the first angle is 45°. Furthermore, the third half-wave plate 1274 also receives the echo signal emitted by the first electronically controlled rotating unit 1281, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle to obtain the echo signal of the first polarization state; the Faraday rotor 1273 also receives the echo signal emitted by the third half-wave plate 1274, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle; the second half-wave plate 1272 also receives the echo signal emitted by the Faraday rotor 1272, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle to obtain the echo signal of the second polarization state; the second polarization beam splitter 1271 also receives the echo signal of the second polarization state emitted by the second half-wave plate 1272, and reflects the echo signal to the detection port 125.

[0105] In one embodiment, the deflection module 128 includes: a first electrically controlled rotation unit 1281, including a first DC coil, which controls the rotation direction of the polarization state of the seventh signal light passing through the first electrically controlled rotation unit 1281 by controlling the current direction of the first DC coil; a birefringent crystal 1282, which receives the seventh signal light passing through the first electrically controlled rotation unit 1281 and deflects the seventh signal light based on its polarization state; a fourth half-wave plate 1283, which receives the seventh signal light emitted from the birefringent crystal 1282 and rotates the polarization state of the seventh signal light along the first polarization rotation direction by a first angle; and a second electrically controlled rotation unit 1284, including a second DC coil, which controls the rotation direction of the seventh signal light passing through the first electrically controlled rotation unit 1281 by controlling the current direction of the second DC coil. The polarization state of the light is rotated to obtain the eighth signal light; the echo signal transmitted by the beam splitter 129 is also received, and the rotation direction of the polarization state of the echo signal passing through the second electrically controlled rotation unit 1284 is controlled by controlling the current direction of the second DC coil; the fourth half-wave plate 1283 also receives the echo signal emitted by the second electrically controlled rotation unit 1284, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle; the birefringent crystal 1282 also receives the echo signal and deflects the echo signal based on the polarization state of the echo signal; the first electrically controlled rotation unit 1281 also receives the echo signal emitted by the birefringent crystal 1282, and controls the rotation direction of the polarization state of the echo signal passing through the first electrically controlled rotation unit 1281 by controlling the current direction of the first DC coil.

[0106] Please continue to refer to Figure 10The first electrically controlled rotation unit 1281, composed of a Faraday rotator, a magnet, and a first DC coil, rotates the polarization of the incident light by controlling the direction of the current. When the current is positive, the rotation is 45°, opposite to the rotation direction of the third half-wave plate 1274. In this case, the polarization state of the incident light remains unchanged after passing through the third half-wave plate 1274 and the first electrically controlled rotation unit 1281, resulting in P-light. When the current in the first electrically controlled rotation unit 1281 is negative, the rotation direction is the same as that of the third half-wave plate 1274, and the polarization state rotates by 90°, resulting in S-light. After passing through the third half-wave plate 1274 and the first electrically controlled rotation unit 1281, the signal light is transmitted to the birefringent crystal 1282. The optical axis of the birefringent crystal 1282 is designed so that P-light in the horizontal direction is transmitted, while S-light in the vertical direction is deflected downwards. The seventh signal light then passes through the fourth half-wave plate 1283 and the second electrically controlled rotation unit 1284. Similar to the third half-wave plate 1274 and the first electrically controlled rotation unit 1281, the polarization state of the seventh signal light is rotated by controlling the positive and negative directions of the current in the second electrically controlled rotation unit 1284, thus obtaining the eighth signal light. The second electrically controlled rotation unit 1284 also receives the echo signal transmitted by the beam splitter module 129, and controls the rotation direction of the polarization state of the echo signal passing through the second electrically controlled rotation unit 1284 by controlling the current direction of the second DC coil; the fourth half-wave plate 1283 also receives the echo signal emitted by the second electrically controlled rotation unit 1284, and rotates the polarization state of the echo signal along the second polarization rotation direction by a first angle; the birefringent crystal 1282 also receives the echo signal, and deflects the echo signal based on the polarization state of the echo signal; the first electrically controlled rotation unit 1281 also receives the echo signal emitted by the birefringent crystal 1282, and controls the rotation direction of the polarization state of the echo signal passing through the first electrically controlled rotation unit 1281 by controlling the current direction of the first DC coil.

[0107] In one embodiment, the beam splitting module 129 includes: a third polarization beam splitter 1291, which receives an eighth signal light; when the eighth signal light is not deflected by the deflection module 128 and has a first polarization state, it is transmitted from a first position of the third polarization beam splitter 1291 and incident on a first port 121; when the eighth signal light is deflected by the deflection module 128 and has a first polarization state, it is transmitted from a second position of the third polarization beam splitter 1291; when the eighth signal light is deflected by the deflection module 128 and has a second polarization state, it is reflected from the second position of the third polarization beam splitter 1291 and incident on a third port 123; when the eighth signal light is not deflected by the deflection module 128 and has a second polarization state, it is reflected from the first position of the third polarization beam splitter 1291; and a first reflecting prism 1292, which receives light from... The eighth signal light transmitted from the second position is deflected and incident on the second port 122; the second folding prism 1293 receives the eighth signal light reflected from the first position, deflects it and incident on the fourth port 124; and receives the echo signal passing through the fourth port 124, deflects the echo signal and incident on the third polarization beam splitter 1291; the first folding prism 1292 also receives the echo signal passing through the second port 122, deflects the echo signal and incident on the third polarization beam splitter 1291; the third polarization beam splitter 1291 also receives the echo signals from the first port 121 and the first folding prism 1292 respectively, transmits the echo signals to the deflection module 128, and also receives the echo signals from the third port 123 and the second folding lens respectively, reflects the echo signals to the deflection module 128.

[0108] In one embodiment, when the current direction of the first DC coil and the current direction of the second DC coil are both set to the first direction, the birefringent crystal 1282 does not deflect the passing seventh signal light but deflects the passing echo signal; when the current direction of the first DC coil and the current direction of the second DC coil are both set to the second direction, the birefringent crystal 1282 deflects the passing seventh signal light but does not deflect the passing echo signal; when the current direction of the first DC coil is set to the second direction and the current direction of the second DC coil is set to the first direction, the birefringent crystal 1282 deflects the passing seventh signal light but does not deflect the passing echo signal; when the current direction of the first DC coil is set to the first direction and the current direction of the second DC coil is set to the second direction, the birefringent crystal 1282 does not deflect the passing seventh signal light but deflects the passing echo signal.

[0109] For example, please refer to Figure 13This diagram illustrates the polarization state transformation and path propagation of light emitted through the first port 121 in one embodiment, during forward and reverse transmission. When the current directions of the first electrically controlled rotating unit 1281 and the second electrically controlled rotating unit 1284 are both positive, the input signal of the time-division switching device 120 is output from the first port 121, and its polarization state transformation and path propagation during forward and reverse transmission are as follows: Figure 13As shown. The seventh signal light of the second polarization state emitted from the third optical fiber 260 is transmitted to the fifth port 126, passes through the second polarization beam splitter 1271, and is transmitted onto the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light clockwise by 45° before it enters the Faraday rotor 1273. The Faraday rotor 1273 rotates the polarization state of the incident light counterclockwise by 45°. During a single forward pass, the polarization direction of the incident light remains unchanged and is still P-light. The third half-wave plate 1274 receives and rotates the polarization state of the seventh signal light of the second polarization state emitted from the Faraday rotor 1273 by a first angle along the first polarization rotation direction. The exemplary third half-wave plate 1274 rotates the polarization state of the incident light clockwise by 45°. The first electrically controlled rotation unit 1281 includes a Faraday rotator, a magnet, and a DC coil, and achieves the rotation of the polarization of the incident light by the positive and negative directions of the current. When the current is in the positive direction, the rotation is 45° counterclockwise. At this point, the incident light remains polarized (P-polarized) after passing through the third half-wave plate 1274 and the first electrically controlled rotation unit 1281. After passing through the third half-wave plate 1274 and the first electrically controlled rotation unit 1281, the seventh signal light is transmitted to the birefringent crystal 1282. The optical axis of the birefringent crystal 1282 is designed so that the horizontal P-polarized light is transmitted, while the vertical S-polarized light is deflected downwards. The P-polarized light, without deflection, passes through the birefringent crystal 1282 and is transmitted to the fourth half-wave plate 1283, where its polarization state rotates 45° clockwise. Then, it passes through the second electrically controlled rotation unit 1284 with a positive current direction, where its polarization state rotates 45° counterclockwise, resulting in the eighth signal light, which is also P-polarized. The eighth signal light then passes through the third polarization beam splitter 1291 and is transmitted through the collimator at the first port 121, thus exiting through the first port 121. The pigtail of the collimator at the first port 121 is connected to a polarization-maintaining fiber jumper and then to the farad plate of the telescope 180. Telescope 180 incident the eighth signal light onto the target detection area. After reflection by aerosol particles in the target detection area, the returned signal light, i.e., the echo signal, is received by telescope 180. The echo signal is transmitted to the third polarization beam splitter 1291 and then transmitted through the second electrically controlled rotation unit 1284 and the fourth half-wave plate 1283. Due to the difference in the dissimilar properties of the half-wave plate and the Faraday rotation plate, when it passes through the second electrically controlled rotation unit 1284, the polarization state rotates counterclockwise by 45°. After passing through the fourth half-wave plate 1283, the polarization state rotates counterclockwise by 45°, and the polarization direction changes from P-light to S-light. Then, the echo signal is transmitted to the birefringent crystal 1282, with the polarization state being S-light. When passing through the birefringent crystal 1282, it is deflected downwards, as shown by the dotted line in the figure. The polarization state is transmitted to the first electrically controlled rotating unit 1281, where it rotates 45° counterclockwise. It is then transmitted to the third half-wave plate 1274, where it rotates 45° counterclockwise again, changing its polarization direction from S-wave to P-wave. The polarization state is then transmitted to the Faraday rotor 1273, where it rotates 45° counterclockwise. After passing through the second half-wave plate 1272, it rotates 45° counterclockwise again, changing its polarization state back to S-wave.The light is transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125. At this time, the polarization state is S-light in the vertical direction. The slow axis direction of the fiber collimator at the detection port 125 is aligned with the polarization state direction of the incident light to ensure that the signal is transmitted along the slow axis of the fiber in the polarization-maintaining fiber.

[0110] For example, please refer to Figure 14 This diagram illustrates the polarization state preference and path propagation of light emitted through the second port 122 in one embodiment, during forward and reverse propagation. When the current directions of the first electrically controlled rotating unit 1281 and the second electrically controlled rotating unit 1284 are both negative, the input signal of the time-division switching device 120 is output from the second port 122, and its polarization state transformation and path propagation during forward and reverse propagation are as follows: Figure 14 As shown. The seventh signal light of the second polarization state emitted from the third optical fiber 260 is transmitted to the fifth port 126. The polarization direction of the incident light at the fifth port 126 is along the slow axis of the polarization-maintaining fiber, and the polarization direction is horizontal, which is P light. After passing through the second polarization beam splitter 1271, it is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light 45° clockwise before it is incident into the Faraday rotor 1273. The Faraday rotor 1273 rotates the polarization state of the incident light 45° counterclockwise. During a single pass, the polarization direction of the incident light remains unchanged, still P light. The third half-wave plate 1274 receives and rotates the polarization state of the light emitted from the Faraday rotor 1273 clockwise by 45°. When the current direction of the first electrically controlled rotation unit 1281 is negative, the polarization state rotates 45° clockwise. After passing through the first electrically controlled rotation unit 1281, the polarization state is in the S direction. The light is then transmitted to the birefringent crystal 1282, where its polarization direction is S-polarization, resulting in a downward deflection. The deflected seventh signal light is transmitted to the fourth half-wave plate 1283, where its polarization state rotates 45° clockwise. It then passes through the second electrically controlled rotating unit 1284 with a negative current direction, resulting in another 45° clockwise rotation and the formation of the eighth signal light, which is P-polarized. This eighth signal light is transmitted to the third polarization beam splitter 1291, then transmitted through the first reflecting prism 1292, where it is deflected and transmitted to the second port 122. The collimator pigtail of the second port 122 is connected to a polarization-maintaining jumper, which is then connected to the farad plate of the telescope 180. The telescope 180 directs the eighth signal light to the target detection area. After reflection by aerosol particles in the target detection area, the returned signal light, i.e., the echo signal, is received by the telescope 180. The echo light is transmitted to the second port 122, passes through the first reflecting prism 1292, and then again through the third polarization beam splitter 1291 before being transmitted. Upon passing through the second electrically controlled rotating unit 1284, the polarization state rotates 45° clockwise. After passing through the fourth half-wave plate 1283, the polarization state rotates 45° counterclockwise, while the polarization direction remains unchanged. Subsequently, the echo signal is transmitted to the birefringent crystal 1282, where the polarization state is P-light. It passes through the birefringent crystal 1282 without deflection, following the path shown below. Figure 14The internal structure of the birefringent crystal 1282 is shown by dashed lines. The signal is transmitted to the first electrically controlled rotating unit 1281, where the polarization state rotates 45° clockwise. It is then transmitted to the third half-wave plate 1274, where the polarization state rotates 45° counterclockwise, while the polarization direction remains unchanged. It is then transmitted to the Faraday rotor 1273, where the polarization state rotates 45° counterclockwise. After passing through the second half-wave plate 1272, the polarization state rotates 45° counterclockwise, converting to S-polarization. The signal is then transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125. At this point, the polarization state is vertical S-polarization. The slow axis of the fiber collimator at the detection port 125 is aligned with the polarization direction of the incident light to ensure that the signal is transmitted along the slow axis of the polarization-maintaining fiber.

[0111] For example, please refer to Figure 15 This diagram illustrates the polarization state preference and path propagation of light emitted through the third port 123 in one embodiment, during forward and reverse transmission. When the current direction of the first electrically controlled rotating unit 1281 is negative and the current direction of the second electrically controlled rotating unit 1284 is positive, the input signal of the time-division switching device 120 is output from the third port 123, and its polarization state transformation and path propagation during forward and reverse transmission are as follows: Figure 15As shown. The seventh signal light in the second polarization state emitted from the third optical fiber 260 is transmitted to the fifth port 126. The polarization direction of the incident light at the fifth port 126 is along the slow axis of the polarization-maintaining fiber, and the polarization direction is horizontal, which is P-light. After passing through the second polarization beam splitter 1271, it is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light 45° clockwise before it enters the Faraday rotor 1273. The Faraday rotor 1273 rotates the polarization state of the incident light 45° counterclockwise. During a single pass, the polarization direction of the incident light remains unchanged, still P-light. The third half-wave plate 1274 receives and rotates the polarization state of the seventh signal light in the second polarization state emitted from the Faraday rotor 1273 clockwise by 45°. When the current direction of the first electrically controlled rotation unit 1281 is negative, the polarization state of the seventh signal light rotates 45° clockwise. After passing through the first electrically controlled rotation unit 1281, the polarization state of the seventh signal light is in the S direction. The seventh signal light is then transmitted to the birefringent crystal 1282, where its polarization direction is S-polarization, resulting in a downward path deflection. Subsequently, the seventh signal light is transmitted to the fourth half-wave plate 1283, where its polarization state rotates 45° clockwise. After passing through the second electrically controlled rotation unit 1284 with a positive current direction, its polarization state rotates 45° counterclockwise, resulting in the eighth signal light, which is S-polarized. The eighth signal light is transmitted to the third polarization beam splitter 1291 and reflected to the third port 123. The collimator pigtail of the third port 123 is connected to a polarization-maintaining jumper and then to the farad plate of the telescope 180. The telescope 180 incident the eighth signal light onto the target detection area. After reflection by aerosol particles in the target detection area, the returning signal light, i.e., the echo signal, is received by the telescope 180. The echo signal is transmitted to the third polarization beam splitter 1291 and then reflected back to the second electrically controlled rotation unit 1284. Upon passing through the second electrically controlled rotating unit 1284, the polarization state rotates counterclockwise by 45°. After passing through the fourth half-wave plate 1283, the polarization state rotates counterclockwise by 45° again, and the polarization direction changes by 90°, converting to P-polarized light. Then, the echo signal is transmitted to the birefringent crystal 1282, where the polarization state is P-light. It passes through the birefringent crystal 1282 without deflection, following the path shown below. Figure 15 The internal structure of the birefringent crystal 1282 is shown by dashed lines. The signal is transmitted to the first electrically controlled rotating unit 1281, where the polarization state of the echo signal rotates 45° clockwise. It is then transmitted to the third half-wave plate 1274, where the polarization state rotates 45° counterclockwise, while the polarization direction remains unchanged. The echo signal is transmitted to the Faraday rotor 1273, where the polarization state rotates 45° counterclockwise. After passing through the second half-wave plate 1272, the polarization state rotates 45° counterclockwise, converting to S-polarization. This signal is then transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125. At this point, the polarization state is vertical S-polarization. The slow axis of the fiber collimator at the detection port 125 is aligned with the polarization state direction of the incident light to ensure that the signal propagates along the slow axis of the polarization-maintaining fiber.

[0112] For example, please refer to Figure 16This diagram illustrates the polarization state transformation and path propagation of light emitted through the fourth port 124 in one embodiment, during forward and reverse transmission. When the current direction of the first electrically controlled rotating unit 1281 is positive and the current direction of the second electrically controlled rotating unit 1284 is negative, the input signal of the time-division switching device 120 is output from the fourth port 124, and its polarization state transformation and path propagation during forward and reverse transmission are as follows: Figure 16 As shown. The seventh signal light in the second polarization state emitted from the third optical fiber 260 is transmitted to the fifth port 126. The polarization direction of the incident light at the fifth port 126 is along the slow axis of the polarization-maintaining fiber, and is horizontal, i.e., P-light. After passing through the second polarization beam splitter 1271, it is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the seventh signal light 45° clockwise before it is incident into the Faraday rotor 1273. The Faraday rotor 1273 rotates the polarization state of the incident light 45° counterclockwise. During a single pass, the polarization direction of the incident light remains unchanged, still P-light. The third half-wave plate 1274 receives and rotates the polarization state of the seventh signal light in the second polarization state emitted from the Faraday rotor 1273 clockwise by 45°. When the current direction of the first electrically controlled rotation unit 1281 is positive, the polarization state rotates 45° counterclockwise. After passing through the first electrically controlled rotation unit 1281, the polarization state remains unchanged, still P-polarized. The light is then transmitted to the birefringent crystal 1282 without deflection. It is then transmitted to the fourth half-wave plate 1283, where its polarization state is rotated 45° clockwise. After passing through the second electrically controlled rotation unit 1284 (with a negative current direction), the polarization state is rotated 45° clockwise again, resulting in the eighth signal light, which is S-polarized. This light is transmitted to the third polarization beam splitter 1291, reflected, and transmitted to the second folding prism 1293, where it is refracted to the fourth port 124. The collimator pigtail of the fourth port 124 is connected to a polarization-maintaining jumper, which is connected to the farad plate of the telescope 180. The telescope 180 incident the laser onto the target detection area. After reflection by aerosol particles in the target detection area, the returned signal light, i.e., the echo signal, is received by the telescope 180. The echo signal is transmitted to the second folding prism 1293, passes through the third polarization beam splitter 1291, and is reflected back to the second electrically controlled rotation unit 1284. Upon passing through the second electrically controlled rotating unit 1284, the polarization state of the echo signal rotates 45° clockwise. After passing through the fourth half-wave plate 1283, the polarization state rotates 45° counterclockwise, while the polarization direction remains unchanged. Subsequently, the echo signal is transmitted to the birefringent crystal 1282, where it is polarized as S-beams and deflects downwards through the birefringent crystal 1282, following the path shown below. Figure 16The birefringent crystal 1282 is shown by dashed lines inside. The signal is transmitted to the first electrically controlled rotating unit 1281, where the current direction is positive. After the echo signal's polarization state rotates counterclockwise by 45°, it is transmitted to the third half-wave plate 1274. The polarization state of the echo signal rotates counterclockwise by 45°, and the polarization direction changes by 90°, converting from S-polarization to P-polarization. It is then transmitted to the Faraday rotor 12734, where the polarization state rotates counterclockwise by 45°. After passing through the second half-wave plate 1272, the polarization state rotates counterclockwise by 45°, converting to S-polarization. It is then transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125. At this point, the polarization state is vertical S-polarization. The slow axis of the fiber collimator at the detection port 125 is aligned with the polarization state direction of the incident light to ensure that the signal is transmitted along the slow axis of the polarization-maintaining fiber.

[0113] In this embodiment, a hybrid filtering technique combining spectral filtering and time-domain switching filtering is employed. By integrating a Faraday rotating mirror filtering scheme and a single acousto-optic dual-pass scheme, the problem of excessively low SMSR for microwatt-level signals in traditional multimode-pumped double-clad amplification schemes is solved. Furthermore, the pre-amplification stage in this embodiment utilizes a 940nm pumped double-clad double-pass amplification scheme, combined with hybrid filtering techniques, to achieve high output power (pulse average power up to 60mW) and high SMSR (62dB) pulse signal output. Additionally, the main amplifier in this embodiment employs back-pumped 940nm multimode pump amplification technology, combined with the aforementioned high output power and high SMSR signal of the pre-amplifier. A high-efficiency (12%) and high SMSR (60dB) main amplifier signal output is obtained; furthermore, by employing multimode pump beam splitting technology, amplification of the pre-amplification stage and the main amplification stage is achieved using a single 940nm pump source and a single circuit, saving costs, reducing size, and lowering power consumption; and, by integrating a circulator and a magneto-optical switch, the time-division switching device 120 shortens the transmission fiber length, increases the pulsed light SBS threshold, and weakens the SBS effect; finally, the time-division switching device 120 of this embodiment adopts a large spatial separation optical path, making it suitable for large mode field fiber collimator design, increasing the mode field area of ​​the transmission fiber, increasing the pulsed light SBS threshold, and weakening the SBS effect.

[0114] It is understood that although the above embodiments of this application use a wavelength of 940nm as an example, this application is not limited to this. Second lasers with wavelengths between 920nm and 940nm can be applied to the embodiments of this application. For example, the wavelength of the second laser can be 900nm, 910nm, 920nm, 930nm, or 940nm.

[0115] 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.

[0116] 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 system, characterized in that, include: A seed light source assembly emits a first signal light; the first signal light has a first polarization state. An acoustic-optical device receives the first signal light and performs pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; Without a temperature-controlled light source, a second laser is emitted; the second laser is a multimode pumped laser. A first optical fiber receives the second signal light and the second laser, and amplifies the second signal light to obtain a third signal light; the third signal light also contains amplified spontaneous emission light; wherein the first optical fiber is a double-clad erbium-ytterbium co-doped optical fiber; A polarization reflection device receives the third signal light, filters out the amplified spontaneous emission light in the third signal light, and rotates the polarization state of the third signal light to obtain a fourth signal light with a second polarization state; the second polarization state is perpendicular to the first polarization state. The first optical fiber also receives the fourth signal light and amplifies the fourth signal light again to obtain the fifth signal light; the acousto-optic device also receives the fifth signal light and performs pulse modulation and frequency shift modulation on the fifth signal light again to obtain the sixth signal light; The third optical fiber receives the second laser and the sixth signal light, and amplifies the sixth signal light to obtain the seventh signal light; The time-division switching device includes a deflection module and a beam splitting module. By controlling the deflection module to deflect the seventh signal light, the seventh signal light is split into an eighth signal light by the beam splitting module at different times, and the eighth signal light is emitted through different ports.

2. The wind-measuring lidar system according to claim 1, characterized in that, The power consumption of the temperature-controlled light source is between 4.8W and 5.2W.

3. The wind-measuring lidar system according to claim 1, characterized in that, The first optical fiber includes: Fiber core, in which the second signal light is transmitted; and The inner cladding layer contains the second laser beam, which is transmitted through multiple reflections within the inner cladding layer.

4. The wind-measuring lidar system according to claim 1, characterized in that, The light between the seed light source assembly, the acousto-optic device, the temperature-controlled light source, the polarization reflection device, and the time-division switching device is transmitted through a second optical fiber.

5. The wind-measuring lidar system according to claim 4, characterized in that, Also includes: The second beam splitter receives the second laser beam and splits it into beams that are then incident into the first beam combiner and the second beam combiner, respectively.

6. The wind-measuring lidar system according to claim 5, characterized in that, Also includes: The first beam combiner is used to input the second signal light and the second laser light into the first optical fiber.

7. The wind-measuring lidar system according to claim 5, characterized in that, Also includes: The second beam combiner is used to direct the second laser beam into the third optical fiber.

8. The wind-measuring lidar system according to claim 6, characterized in that, In the third optical fiber, the transmission direction of the second laser is opposite to the transmission direction of the sixth signal light.

9. The wind-measuring lidar system according to claim 6, characterized in that: The mode field diameter of the second fiber at the input end of the second combiner signal arm is matched with the mode field diameter of the third fiber; and / or the mode field diameter of the incident fiber of the polarization-maintaining fiber collimator at different ports of the time-division switching device is matched with the mode field diameter of the fiber at the output end of the second combiner signal arm.

10. The wind-measuring lidar system according to claim 3, characterized in that, The third light The fiber is the same as the first optical fiber, both being erbium-ytterbium co-doped optical fibers.

11. The wind-measuring lidar system according to claim 1, characterized in that, The polarization reflection device includes: A polarization rotator receives the third signal light and rotates the polarization state of the third signal light along a first polarization rotation direction to obtain a third deflected signal light; and A passband mirror receives the third deflected signal light, transmits the amplified spontaneous emission light, and reflects the third deflected signal light back to the polarization rotator; the third deflected signal light passes through the polarization... After the rotator rotates, the polarization state is rotated again along the first polarization rotation direction to obtain a fourth signal light with a second polarization state.

12. The wind-measuring lidar system according to claim 1, characterized in that, The polarization reflection device includes: A polarization rotator receives the third signal light and rotates the polarization state of the third signal light along a first polarization rotation direction to obtain a third deflected signal light; The filter is tilted relative to the third deflection signal light, receives the third deflection signal light, transmits the third deflection signal light, and filters out the amplified spontaneous emission light. The reflector receives and reflects the third deflection signal light; the third deflection signal light then passes through again. After passing through the filter, the polarization state is rotated again along the first polarization rotation direction by the polarization rotator to obtain a fourth signal light with a second polarization state.

13. The wind-measuring lidar system according to claim 1, characterized in that, The time-division switching device further includes a preprocessing module and a detection port; the different ports include a first port, a second port, a third port and a fourth port, and the preprocessing module, the deflection module and the beam splitting module are arranged sequentially; The seventh signal light of the second polarization state from the third optical fiber is preprocessed by the preprocessing module to obtain a seventh signal light rotated by a first angle along the first polarization rotation direction. Then, it is deflected by the deflection module to obtain an eighth signal light with different deflection states and different exit positions. The eighth signal light with different deflection states and different exit positions is output to the target under test from the first port, the second port, the third port and the fourth port respectively through the beam splitting module. The first port, the second port, the third port and the fourth port respectively receive the echo signal reflected back from the target under test. The echo signal is again incident on the deflection module through the beam splitting module and then incident on the preprocessing module to obtain the echo signal of the second polarization state, and is transmitted to the detection port through the preprocessing module. The light between the preprocessing module, the first port, the second port, the third port, the fourth port and the detection port is transmitted through a second optical fiber.

14. The wind-measuring lidar system according to claim 13, characterized in that, The deflection module includes: The first electronically controlled rotating unit includes a first DC coil, which controls the rotation direction of the polarization state of the seventh signal light passing through the first electronically controlled rotating unit by controlling the direction of the current in the first DC coil. A birefringent crystal receives the seventh signal light passing through the first electrically controlled rotation unit and deflects the seventh signal light based on its polarization state. The fourth half-wave plate receives the seventh signal light emitted from the birefringent crystal and rotates the polarization state of the seventh signal light by a first angle along the first polarization rotation direction. The second electrically controlled rotating unit includes a second DC coil, which controls the rotation direction of the polarization state of the seventh signal light passing through the first electrically controlled rotating unit by controlling the current direction of the second DC coil, thereby obtaining an eighth signal light; it also receives the echo signal transmitted by the beam splitter module, and controls the rotation direction of the polarization state of the echo signal passing through the second electrically controlled rotating unit by controlling the current direction of the second DC coil. The fourth half-wave plate also receives the echo signal emitted by the second electronically controlled rotating unit, and rotates the polarization state of the echo signal by a first angle along the second polarization rotation direction; The birefringent crystal also receives the echo signal and deflects the echo signal based on the polarization state of the echo signal; the first electrically controlled rotation unit also receives the echo signal emitted by the birefringent crystal and controls the rotation direction of the polarization state of the echo signal passing through the first electrically controlled rotation unit by controlling the current direction of the first DC coil.

15. The wind-measuring lidar system according to claim 14, characterized in that, The preprocessing module includes: The second polarization beam splitter receives and transmits the seventh signal light of the second polarization state emitted from the third optical fiber; The second half-wave plate receives and rotates the polarization state of the seventh signal light in the second polarization state transmitted by the second polarization beam splitter by a first angle along the first polarization rotation direction; The Faraday rotor receives and rotates the polarization state of the seventh signal light emitted from the second half-wave plate by a first angle along the second polarization rotation direction to obtain the seventh signal light with a first polarization state; the second polarization rotation direction is opposite to the first polarization rotation direction. The third half-wave plate receives and rotates the polarization state of the seventh signal light of the first polarization state emitted by the Faraday rotor by a first angle along the first polarization rotation direction; it also receives the first echo signal emitted by the first electronically controlled rotating unit, and rotates the polarization state of the echo signal by a first angle along the second polarization rotation direction to obtain the echo signal of the first polarization state. The Faraday rotor also receives the first echo signal emitted from the third half-wave plate and rotates the polarization state of the first echo signal by a first angle along the second polarization rotation direction. The second half-wave plate also receives the first echo signal emitted by the Faraday rotor, and rotates the polarization state of the first echo signal by a first angle along the second polarization rotation direction to obtain the echo signal of the second polarization state. The second polarization beam splitter also receives the echo signal of the second polarization state emitted from the second half-wave plate and reflects the echo signal to the detection port.

16. The wind-measuring lidar system according to claim 15, characterized in that, When the current direction of the first DC coil and the current direction of the second DC coil are both set to the first direction, the birefringent crystal does not deflect the passing seventh signal light, but deflects the passing echo signal. When the current direction of the first DC coil and the current direction of the second DC coil are both set to the second direction, the birefringent crystal deflects the passing seventh signal light but does not deflect the passing echo signal. When the current direction of the first DC coil is set to the second direction and the current direction of the second DC coil is set to the first direction, the birefringent crystal deflects the passing seventh signal light but does not deflect the passing echo signal. When the current direction of the first DC coil is set to the first direction and the current direction of the second DC coil is set to the second direction, the birefringent crystal does not deflect the passing seventh signal light, but deflects the passing echo signal.

17. The wind-measuring lidar system according to claim 13, characterized in that, The beam splitting module includes: The third polarization beam splitter receives the eighth signal light; when the eighth signal light is not deflected by the deflection module and has a first polarization state, it is transmitted from the first position of the third polarization beam splitter and incident on the first port; when the eighth signal light is deflected by the deflection module and has a first polarization state, it is transmitted from the second position of the third polarization beam splitter; when the eighth signal light is deflected by the deflection module and has a second polarization state, it is reflected from the second position of the third polarization beam splitter and incident on the third port; when the eighth signal light is not deflected by the deflection module and has a second polarization state, it is reflected from the first position of the third polarization beam splitter. The first folding prism receives the eighth signal light transmitted from the second position, deflects the eighth signal light, and then directs it to the second port; The second folding prism receives the eighth signal light reflected from the first position, deflects the eighth signal light, and then incident it onto the fourth port; and receives the echo signal passing through the fourth port, deflects the echo signal, and then incident it onto the third polarization beam splitter. The first folding prism also receives the echo signal passing through the second port, deflects the echo signal, and then directs it to the third polarization beam splitter. The third polarization beam splitter also receives the echo signals from the first port and the first folding prism respectively, and transmits the echo signals to the deflection module; and also receives the echo signals from the third port and the second folding prism respectively, and reflects the echo signals to the deflection module.

18. The wind-measuring lidar system according to claim 1, characterized in that, The wavelength of the second laser is between 920nm and 940nm.

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