Wind measurement laser radar system and wind measurement method of wind measurement laser radar

Abstract

The invention relates to a wind measurement laser radar system, which comprises a first light source assembly for emitting first signal light and a second light source for emitting multimode pump laser, the acousto-optic device is used for performing pulse and frequency shift modulation on the first signal light to obtain second signal light; the first optical fiber is a double-cladding erbium-ytterbium co-doped optical fiber and is used for amplifying the second signal light to obtain third signal light; the polarization reflection device filters amplified spontaneous emission light in the third signal light to obtain fourth signal light; the first optical fiber further amplifies the fourth signal light again to obtain fifth signal light; the acousto-optic device performs pulse and frequency shift modulation on the fifth signal light again to obtain sixth signal light; the time division switching device controls the deflection module to deflect the sixth signal light, so that the sixth signal light is split by the beam splitting module at different time to obtain seventh signal light, the seventh signal light is emitted through different ports, the power of the two-way amplifier can be further improved, and the detection distance of the wind measurement radar is increased.

Description

Technical Field

[0001] The present application relates to the field of laser radar technology, and in particular to a wind measurement laser radar system and a wind measurement method of a wind measurement laser radar. Background Art

[0002] As the wind power industry develops, wind turbine manufacturers will develop turbines with larger rotor diameters to improve power generation efficiency. This will require both ground-based wind lidars used for early wind resource surveys and nacelle-mounted wind lidars used for wind turbine feedforward control to have longer detection ranges.

[0003] When other parameters remain constant, the energy of a single laser pulse determines the measurement distance of the wind lidar.

[0004] Therefore, there is an urgent need for a wind measurement lidar that can improve the single pulse energy of the laser. Summary of the Invention

[0005] Based on this, it is necessary to provide a wind measurement lidar system and a wind measurement lidar wind measurement method that can improve the single pulse energy of the laser to address the above technical problems.

[0006] In the first aspect, the present application provides a wind measurement lidar system, comprising: a first light source component, emitting a first signal light; the first signal light has a first polarization state; an acousto-optic device, receiving the first signal light, performing pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; a second light source, emitting a second laser; the second laser is a multi-mode pump laser; a first optical fiber, receiving the second signal light and the second laser, amplifying the second signal light to obtain a third signal light; the third signal light also has amplified spontaneous radiation light; wherein the first optical fiber is a double-clad erbium-ytterbium co-doped optical fiber; a polarization reflection device, receiving the third signal light, filtering out the third signal light The amplified spontaneous emission light in the signal light is amplified and 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 the fourth signal light again to obtain a fifth signal light; the acousto-optic device also receives the fifth signal light and pulse-modulates and frequency-shifts the fifth signal light again to obtain a sixth signal light; the time-division switching device includes a deflection module and a beam splitting module, and by controlling the deflection of the sixth signal light by the deflection module, the sixth signal light is split by the beam splitting module at different times to obtain a seventh signal light, and the seventh signal light is emitted through different ports respectively.

[0007] 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 after multiple reflections.

[0008] In one embodiment, the wind measurement lidar system further includes: a beam combiner, through which the second signal light and the second laser are incident into the first optical fiber.

[0009] In one embodiment, the polarization reflection device includes: a polarization rotator, which receives the third signal light and rotates the polarization state of the third signal light along the first polarization rotation direction to obtain a third deflected signal light; and a reflector, which receives the third deflected signal light, transmits and amplifies the spontaneous radiation light, and reflects the third deflected signal light back to the polarization rotator; after the third deflected signal light passes 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.

[0010] In one embodiment, the time-division switching device further includes a first preprocessing module, a second 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 first preprocessing module, the second preprocessing module, the deflection module and the beam splitting module are arranged in sequence; the sixth signal light of the second polarization state from the acousto-optic device is preprocessed by the first preprocessing module to obtain the sixth signal light of the first polarization state, and is preprocessed again by the second preprocessing module to obtain the sixth signal light rotated by the first angle along the first polarization rotation direction, and then deflected by the deflection module to obtain the seventh signal light with different deflection states and different exit positions. light, and seventh signal lights with different deflection states and different exit positions are output from the first port, the second port, the third port and the fourth port to the target to be measured respectively through the beam splitting module; the first port, the second port, the third port and the fourth port respectively receive echo signals reflected from the target to be measured, and the echo signals are again incident on the deflection module through the beam splitting module for deflection processing, and then incident on the second preprocessing module to obtain echo signals of the second polarization state, and are transmitted to the detection port through the second preprocessing module; light between the first preprocessing module, the second 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.

[0011] In one embodiment, the first preprocessing module includes: a first polarization beam splitter, which receives and reflects the sixth signal light of the second polarization state from the acousto-optic device; and a first half-wave plate, which receives the sixth signal light of the second polarization state emitted by the first polarization beam splitter and modulates the polarization state of the sixth signal light into the first polarization state before emitting it.

[0012] In one embodiment, the second pre-processing module includes: a second polarization beam splitter, receiving and transmitting the sixth signal light of the first polarization state emitted by the first pre-processing module; a second half-wave plate, receiving and rotating the polarization state of the sixth signal light of the first polarization state transmitted by the second polarization beam splitter by a first angle along the first polarization rotation direction; a Faraday rotator, receiving and rotating the polarization state of the sixth signal light emitted by the second half-wave plate by a first angle along the second polarization rotation direction to obtain the sixth signal light of the first polarization state; the second polarization rotation direction is opposite to the first polarization rotation direction; a third half-wave plate, receiving and rotating the polarization state of the sixth signal light of the first polarization state emitted by the Faraday rotator by a first angle along the first polarization rotation direction The first half-wave plate is configured to rotate the polarization state of the first echo signal by a first angle along the second polarization rotation direction; the first echo signal emitted by the first electrically controlled rotation unit is received, and the polarization state of the echo signal is rotated by a first angle along the second polarization rotation direction to obtain an echo signal of the first polarization state; the Faraday rotator is configured to receive the first echo signal emitted by the third half-wave plate, and rotate the polarization state of the first echo signal by a first angle along the second polarization rotation direction; the second half-wave plate is configured to receive the first echo signal emitted by the Faraday rotator, and rotate the polarization state of the first echo signal by a first angle along the second polarization rotation direction to obtain an echo signal of the second polarization state; the second polarization beam splitter is configured to receive the echo signal of the second polarization state emitted by the second half-wave plate, and reflect the echo signal to the detection port.

[0013] 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 sixth 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 sixth signal light passing through the first electrically controlled rotation unit and deflects the sixth signal light based on the polarization state of the sixth signal light; a fourth half-wave plate, which receives the sixth signal light emitted by the birefringent crystal and rotates the polarization state of the sixth signal light along the first polarization rotation direction by a first angle; a second electrically controlled rotation unit, including a second DC coil, which controls the polarization state of the sixth signal light passing through the first electrically controlled rotation unit by controlling the current direction of the second DC coil. The first electrically controlled rotation unit further 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. The fourth half-wave plate further receives the echo signal emitted by the second electrically controlled rotation unit and rotates the polarization state of the echo signal by a first angle along the second polarization rotation direction. The birefringent crystal further receives the echo signal and deflects the echo signal based on the polarization state of the echo signal. The first electrically controlled rotation unit further 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.

[0014] 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 sixth signal light passing through, but deflects the echo signal passing through; 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 sixth signal light passing through, but does not deflect the echo signal passing through; 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 sixth signal light passing through, but does not deflect the echo signal passing through; 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 sixth signal light passing through, but deflects the echo signal passing through.

[0015] In one embodiment, the beam splitting module includes: a third polarization beam splitter, receiving the seventh signal light; when the seventh signal light is not deflected by the deflection module and has the first polarization state, it is transmitted from the first position of the third polarization beam splitter and incident on the first port; when the seventh signal light is deflected by the deflection module and has the first polarization state, it is transmitted from the second position of the third polarization beam splitter; when the seventh signal light is deflected by the deflection module and has the second polarization state, it is reflected from the second position of the third polarization beam splitter and incident on the third port; when the seventh signal light is not deflected by the deflection module and has the second polarization state, it is reflected from the first position of the third polarization beam splitter; a first folding prism, receiving the seventh signal light from the first polarization beam splitter; The seventh signal light transmitted from the second position is deflected and incident on the second port; the second folding prism receives the seventh signal light reflected from the first position, deflects the seventh signal light 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, and reflects the echo signals to the deflection module.

[0016] In the second aspect, the present application also provides a wind measurement method of a wind measurement lidar, comprising: controlling a first light source component to emit a first signal light; the first signal light has a first polarization state; controlling an acousto-optic device to receive the first signal light, performing pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; controlling a second light source to emit a second laser; receiving the second signal light and the second laser through a first optical fiber, amplifying the second signal light to obtain a third signal light; the third signal light also has amplified spontaneous radiation light; wherein the first optical fiber is a double-clad erbium-ytterbium co-doped optical fiber; receiving the third signal light through a polarization reflection device, filtering out the amplified spontaneous radiation in the third signal light, and filtering out the amplified spontaneous radiation in the third signal light. The method comprises the steps of: generating a large spontaneous radiation light and rotating 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; receiving the fourth signal light by the first optical fiber and amplifying the fourth signal light again to obtain a fifth signal light; receiving the fifth signal light by the acousto-optic device, and performing pulse modulation and frequency shift modulation on the fifth signal light again to obtain a sixth signal light; and controlling the time-division switching device, which includes a deflection module and a beam splitting module, to deflect the sixth signal light by the deflection module so that the sixth signal light is split by the beam splitting module at different times to obtain a seventh signal light, and the seventh signal light is emitted through different ports respectively.

[0017] In the above-mentioned wind measuring lidar and wind measuring method by wind measuring lidar, the second laser emitted by the second light source of the wind measuring lidar is a multimode pump laser, and the second signal light and the second laser are received through the first optical fiber, the second signal light is amplified to obtain the third signal light, and the fourth signal light is subsequently received and the fourth signal light is amplified again to obtain the fifth signal light, thereby achieving a power increase of the dual-pass amplifier with a low-cost pump of hundreds of yuan through multi-mode pumping and a dual-pass amplification structure, thereby meeting the future demand for improved detection distance of wind measuring radars. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 is a structural block diagram of a wind measurement lidar system in one embodiment;

[0020] Figure 2 is a structural block diagram of a wind measurement laser radar system in yet another embodiment;

[0021] Figure 3 This is the curve of the output power of a single-mode double-pass amplified laser varying with pumping in continuous light mode;

[0022] Figure 4 1. A curve showing the output power of a double-clad double-pass amplified laser varying with pumping power in a continuous light operation mode in one embodiment;

[0023] Figure 5 Schematic diagram of the structure of a polarized reflection device in one embodiment;

[0024] Figure 6 The noise curve of wind lidar system changes with the SMSR of laser;

[0025] Figure 7 is the output signal spectrum without spectral filtering;

[0026] Figure 8 is an output signal spectrum based on spectral filtering in one embodiment;

[0027] Figure 9 A schematic structural diagram of a time-division switching device in one embodiment;

[0028] Figure 10 FIG1 is a curve showing the relationship between the SBS threshold and the transmission fiber length in a quartz optical fiber according to an embodiment;

[0029] Figure 11 A curve showing the relationship between the SBS threshold and the optical fiber mode field diameter according to an embodiment;

[0030] Figure 12 Figure 1 is a diagram showing polarization state transformation and path propagation of light emitted through the first port during forward and reverse transmission in one embodiment;

[0031] Figure 13 FIG1 is a diagram showing polarization state transformation and path propagation of light emitted through the second port during forward and reverse transmission in one embodiment;

[0032] Figure 14 Figure 1 is a diagram showing polarization state transformation and path propagation of light emitted through the third port during forward and reverse transmission in one embodiment;

[0033] Figure 15 FIG1 is a diagram showing polarization state transformation and path propagation of light emitted through the fourth port during forward and reverse transmission in one embodiment;

[0034] Figure 16 A schematic flow chart of a wind measurement method using a wind laser radar in one embodiment of the present invention is shown.

[0035] 111. First light source; 112. Beam splitter; 110. First light source assembly; 190. Coupler; 200. Balanced detector; 210. Signal processing device; 113. Fifth port; 131. Sixth port; 121. First port; 122. Second port; 123. Third port; 124. Fourth port; 125. Detection port; 120. Time-division switching device; 130. Acousto-optic device; 140. Second light source; 150. Combiner; 160. First optical fiber; 170. Polarization reflection device; 126. First pre-processing module ; 127. Second pre-processing module; 128. Deflection module; 129. Beam splitting module; 1261. First polarization beam splitter; 1262. First half-wave plate; 1271. Second polarization beam splitter; 1272. Second half-wave plate; 1273. Faraday rotator; 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. DETAILED DESCRIPTION

[0036] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0038] 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 the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0039] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0040] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0041] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate 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 implementation methods.

[0042] See Figure 1 , Figure 1The structure diagram of the wind measurement laser radar in one embodiment of the present invention is shown. The wind measurement laser radar system provided by one embodiment of the present invention includes: a first light source component 110, emitting a first signal light; the first signal light has a first polarization state; an acousto-optic device 130, 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 second light source 140, emitting a second laser; the second laser is a multi-mode pump laser; a first optical fiber 160, 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 has amplified spontaneous radiation light; wherein the first optical fiber 160 is a double-clad erbium-ytterbium co-doped optical fiber; a polarization reflection device 170, receiving the second signal light The three signal lights are filtered out and the amplified spontaneous emission light in 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 160 also receives the fourth signal light and amplifies the fourth signal light again to obtain a fifth signal light; the acousto-optic device 130 also receives the fifth signal light and pulse-modulates and frequency-shifts the fifth signal light again to obtain a sixth signal light; the time-division switching device 120 includes a deflection module 128 and a beam splitting module 129. By controlling the deflection of the sixth signal light by the deflection module 128, the sixth signal light is split by the beam splitting module 129 at different times to obtain a seventh signal light, and the seventh signal light is emitted through different ports.

[0043] Exemplarily, the first light source assembly 110 includes a first light source 111, which emits a first laser beam having a first wavelength; the first laser beam is a continuous laser beam; and a beam splitter 112, which receives the first laser beam and splits the first laser beam into a local oscillator beam and a first signal beam having a first polarization state. For example, the first light source assembly 110 may be a seed module, the first light source 111 may be a 1550 nm single-frequency seed laser, and the beam splitter 112 may be a polarization-maintaining beam splitter.

[0044] In addition, the wind measurement lidar system also includes a telescope, which is a multi-channel telescope. Optionally, the telescope is a four-channel telescope. The telescope receives the seventh signal light, transmits the seventh signal light to the target to be measured, receives the echo signal reflected by the target to be measured, and returns the echo signal to the different port. The time-division switching device 120 also includes a detection port 125, which transmits the echo signals received by different ports to the detection port 125; the wind measurement lidar system also includes a detection module, which receives the echo signal and local oscillator light output by the detection port 125, thereby generating a wind speed signal of the target to be measured 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.

[0045] Further illustratively, the detection module includes a coupler 190 and a balanced detector 200, wherein the coupler 190 may be a 50:50 fiber coupler 190. The time-division switching device 120 may be a hybrid integrated magneto-optical switch. The first optical fiber 160 may be a double-clad erbium-ytterbium co-doped optical fiber. The polarization reflection device 170 may be a Faraday rotation filter mirror.

[0046] In one embodiment, Figure 1The following is a block diagram of the wind lidar system. The first laser light emitted by the first light source 111 is split into two beams by a beam splitter 112. One beam serves as the local oscillator light and is transmitted to the coupler 190 of the detection module, while the other serves as the signal light. Specifically, the signal light split by the beam splitter 112 is the first signal light, which is transmitted to the acousto-optic device 130. Optionally, the first signal light can be transmitted to the acousto-optic device 130 via a time-division switching device 120. For example, the first signal light can be output to the acousto-optic device 130 after passing through the internal polarization beam splitter of the time-division switching device 120. The acousto-optic device 130 comprises an acousto-optic driver and an acousto-optic modulator. It frequency-shifts the continuous light of the input first signal light and chops it into pulses through pulse modulation to generate a second signal light. The wind lidar system also includes a second light source 140 that emits a second laser light; the second laser light is a multimode pump laser. The second signal light and the second laser light are then transmitted to the first optical fiber 160 via a beam combiner 150. The second light source 140, the beam combiner 150, and the first optical fiber 160 form a fiber amplifier. The first optical fiber 160 performs a primary amplification on the second signal light to produce a third signal light. The third signal light also contains amplified spontaneous emission (ASE). The signal light after the primary amplification is transmitted to the polarization reflection device 170, which filters out the ASE in the third signal light and rotates the polarization state of the third signal light to produce a fourth signal light having a second polarization state perpendicular to the first polarization state. The fourth signal light is transmitted to the first optical fiber 160. Exemplarily, the fourth signal light is transmitted to the first optical fiber 160 along the fast axis of the polarization-maintaining fiber. The first optical fiber 160 also receives the fourth signal light and further amplifies it to produce a fifth signal light. The fifth signal light is then transmitted to the beam combiner 150. The acousto-optic device 130 also receives the fifth signal light and performs further pulse modulation and frequency shift modulation on the fifth signal light to produce a sixth signal light. The time-division switching device 120 includes a deflection module 128 and a beam splitting module 129. By controlling the deflection of the sixth signal light by the deflection module 128, the sixth signal light is split by the beam splitting module 129 at different times to obtain a seventh signal light, which is then emitted through different ports. Exemplarily, the output channel of the sixth signal light is controlled by the high and low levels of the time-division switching device 120, thereby achieving a time-division multiplexing effect. The seventh signal light passes through the telescope and enters the atmosphere. After being reflected by the aerosol in the target detection area, it passes through the telescope and the time-division switching device 120 again. Each echo signal is transmitted to the detection module, such as the coupler 190, and then coupled with the local oscillator light. After mixing at the balanced detector 200, an analog signal is obtained. The analog signal is converted to digital by the sampling module in the signal processing device 210, and then a fast Fourier transform (FFT) is performed in the signal processor chip. After cumulative de-noising, the spectrum information of the radial wind speed is obtained.

[0047] In this embodiment, the second laser light emitted by the second light source 140 of the wind laser radar is a multimode pump laser. The second signal light and the second laser light are received by the first optical fiber 160, the second signal light is amplified to obtain the third signal light, and the fourth signal light is subsequently received and further amplified to obtain the fifth signal light. Through multimode pumping and a dual-pass amplification structure, the power of the dual-pass amplifier is increased with a low-cost pump cost of only a few hundred yuan, meeting the demand for improved detection range of future wind radars. Furthermore, by using the acousto-optic device 130 to perform secondary chopping on the first signal light, this not only filters out acousto-optic leakage pulses and improves the system's dynamic extinction ratio, but also further filters out the amplified spontaneous emission (ASE) generated during fiber amplification, thereby improving the side-mode suppression ratio (SMSR) of the laser output. Furthermore, by adopting a multimode pumped dual-pass amplification structure, this embodiment achieves a power increase in the dual-pass amplifier with a low-cost pump cost of only a few hundred yuan, meeting the demand for improved detection range of future wind radars. For a wind lidar with a measurement distance of 300m, the required single-pulse energy is typically 10μJ. For a laser pulse repetition frequency of 10kHz-30kHz, for example, the required average laser power is in the range of 100-300mW.

[0048] Figure 3 This is the curve of the output power of a single-mode double-pass amplified laser varying with pump power in continuous light mode. Figure 4 The output power of the double-clad double-pass amplified laser varies with the pump in continuous light mode. Figure 3 It can be seen that for a single-mode dual-pass amplifier structure, when the output power reaches 100mW, the required single-mode pump power is 700mW, and to achieve an output power of 300mW, a higher power single-mode pump is required. Figure 3 As can be seen, for a double-clad amplification structure, when the pump power is between 1.25W and 3.05W, the output power range is 100mW-300mW, making it more suitable for high-power output. Furthermore, from a cost perspective, single-mode 980nm pumps at 680mW and above have a narrow application range, resulting in a higher price step. In contrast, the price of a commonly used commercial 9W multimode pump is only about 15% of that of a 680mW single-mode pump due to its wide application range. Therefore, the use of a double-clad double-pass amplification structure based on multimode amplification not only ensures the performance of 100-300mW average power output, laying the foundation for high-energy pulsed lasers, but also offers a cost advantage. At high average power output, the cost is only 15% of that of a single-mode pumped double-pass amplification structure, making it more cost-effective and more suitable for mass production.

[0049] For alternatives, please refer to Figure 2 , is a structural block diagram of a wind measurement lidar system in another embodiment of the present application.

[0050] In this embodiment, the signal light and the pump light are transmitted in opposite directions during the first amplification, and are transmitted in the same direction during the second amplification.

[0051] Optionally, the time-division switching device 120 includes a first polarization beam splitter 1261 .

[0052] Exemplarily, the first signal light is incident on the first polarization beam splitter 1261 through the fifth port 113 of the time-division switching device 120, and after being transmitted by the first polarization beam splitter 1261, it is incident on the acousto-optic device 130 through the sixth port 131. The acousto-optic device 130 performs secondary chopping on the first signal light, which not only filters out the acousto-optic leakage pulse and improves the dynamic extinction ratio of the system, but also further filters out the amplified spontaneous emission (ASE) generated during fiber amplification, thereby improving the side-mode suppression ratio (SMSR) of the laser output. At this time, the return light contains amplified signal light and stray light. The stray light is formed by the incident light reflecting off the surface of the acousto-optic modulator and is transmitted along the slow axis of the optical fiber. After the signal light is reflected back by the polarization reflection device 170 for the second time, the polarization state is rotated 90° and is transmitted along the fast axis of the optical fiber. When the two are incident on the first polarization beam splitter 1261 inside the time-division switching device 120, the sixth signal light is transmitted to the telescope along the output direction of different ports of the time-division switching device 120, while the stray light is transmitted out along the direction of the fifth port 113. The two are spatially separated to avoid pulse envelope modulation formed by interference between the signal light and the stray light, which interferes with signal detection.

[0053] In one embodiment, the second light source 140 is configured to have an anti-reflection function.

[0054] Combiner 150 includes a signal arm and a pump arm. The majority of the fifth signal light is transmitted through the signal arm of combiner 150, while a smaller portion is transmitted through the pump arm of combiner 150 to the multimode pump. Therefore, in this solution, the multimode pump is designed with anti-reflection functionality. The typical anti-reflection band is 1400-1600 nm, and the typical anti-reflection isolation is 30 dB.

[0055] In this embodiment, a multimode pump double-pass amplification scheme is used to increase the isolation from the common end to the pump end from 20dB to 60dB, thereby improving laser reliability. Specifically, this embodiment utilizes a multimode pump and a beam combiner 150. The typical isolation of the beam combiner 150 is 30dB, and the typical isolation of the multimode pump in the anti-reflection band is 30dB. As a result, the overall isolation reaches 60dB, effectively resolving the laser reliability issue associated with energy boosting in a single-stage double-pass amplification structure.

[0056] 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 after multiple reflections.

[0057] First optical fiber 160 can be a double-clad erbium-ytterbium co-doped fiber. Pulsed signal light is transmitted within the double-clad fiber core, while multimode pump light is reflected and transmitted multiple times within the inner cladding. As it repeatedly passes through the erbium-doped core, it achieves population inversion, amplifying the signal light as it passes through.

[0058] Double-clad erbium-ytterbium co-doped fiber amplifiers are typically used as the second-stage amplifier in a MOPA (Master Oscillator Power-Amplifier) ​​structure. The input small signal power is typically around 10mW, ensuring both amplification efficiency and the output signal's side-mode suppression ratio (SMSR). This solution uses it directly for pre-amplification, amplifying the input 100uW signal to 10mW. This is then amplified to 100mW through secondary amplification, achieving the effect of a two-stage cascade amplification using a single double-clad amplification stage.

[0059] In one embodiment, the wind measurement laser radar further includes: a beam combiner 150 , through which the second signal light and the second laser are incident into the first optical fiber 160 .

[0060] In one embodiment, the polarization reflection device 170 includes: a polarization rotator, which receives the third signal light and rotates the polarization state of the third signal light along the first polarization rotation direction to obtain a third deflected signal light; and a reflector, which receives the third deflected signal light, transmits and amplifies the spontaneous radiation light and reflects the third deflected signal light back to the polarization rotator; after the third deflected signal light passes 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.

[0061] For example, Figure 5FIG2 is a schematic diagram of the structure of a polarization reflection device 170 according to an embodiment of the present application. The polarization reflection device 170 includes a built-in polarization rotator and a reflector. The polarization rotator can be a 45° polarization rotator, and the polarization rotator can further be a Faraday rotator. When the first light source 111 is a 1550nm single-frequency seed laser, the reflector is a 1550nm passband reflector. The first polarization rotation direction can be clockwise, and the second polarization rotation direction can be counterclockwise.

[0062] In this embodiment, when a double-clad single-stage amplifier is used to achieve the effect of a two-stage cascade amplification, if no other processing is performed, the output signal SMSR is very poor. Figure 5 The structure enables the polarization-maintaining fiber collimator to direct the third signal light onto the polarization rotator, wherein the polarization rotator is composed of an optical rotation crystal and a coil, and can rotate the polarization state of the third signal light along the first polarization rotation direction to obtain a third deflected signal. Exemplarily, the polarization rotator rotates the polarization state of the third signal light by 45° in a clockwise direction. The third signal light comprises two parts: one is the signal light, and the other is the amplified spontaneous emission (ASE). During secondary amplification, the ASE light will compete with the signal light, affecting the amplification efficiency of the signal light, and will also reduce the SMSR of the laser signal output. Therefore, in this embodiment, the reflector is also coated so that the reflector reflects the signal wavelength within the operating bandwidth of the incident seed laser and transmits other wavelengths, thereby improving the SMSR of the incident signal before secondary amplification. The filtered signal light passes through the built-in 45° polarization rotator again, and the polarization state is deflected by 45° again, thereby obtaining a fourth signal light with a second polarization state.

[0063] In this embodiment, a 1550nm bandpass mirror filters out the ASE light generated during the primary amplification process, which serves two purposes: first, it prevents competition between the ASE light and the signal light during the secondary amplification, thereby reducing the amplification efficiency of the signal light; second, it improves the side mode suppression ratio (SMSR) of the amplifier output signal, thereby preventing the interference noise generated by the local oscillator light and the ASE beat frequency between pulses from affecting the signal-to-noise ratio of the wind measurement radar system.

[0064] In this embodiment, a polarization reflector 170 with integrated filtering function is used to filter out the primary amplified ASE, suppress ASE self-excitation, and improve the output signal's side mode suppression ratio. After filtering, ASE self-excitation is eliminated, and the SMSR is increased to 60dB. The laser output side mode suppression ratio affects the radar's noise floor. This is because the ASE noise contained in the output signal, after being reflected from the end face, forms interference noise with the local oscillator light, raising the system noise floor. Figure 5 In this embodiment, a multimode double-clad amplifier structure is used to amplify microwatt (μW) input signal light. If no technical processing is performed, the SMSR is low, which affects the system noise floor.

[0065] In this embodiment, a multimode-pumped double-clad amplifier dual-pass amplification structure is employed. During the first amplification step, a small signal in the μW range is amplified to the 10mW level. Compared to single-mode dual-pass amplification, multimode double-clad amplification requires higher pump power to achieve a higher average power signal. Consequently, the signal light after the first amplification step contains more ASE light. This has two impacts on the system. First, during pulse amplification, due to the chopping of the continuous input light by the pulsed light, the average power of the small-signal pulses during the first amplification step is relatively low, at the μW level, while the pump power is in the watt level. If the ASE generated by the first amplification step is not processed, it can easily self-excite during the second amplification step, affecting the laser's amplification efficiency and even damaging optical components. Second, this ASE light will undergo the second amplification step along with the signal light, resulting in residual ASE light in the output pulse signal, affecting the amplifier's overall output side-mode suppression ratio. Figure 7 This is the output spectrum of the unprocessed pulsed amplified signal. As can be seen from the figure, the side-mode suppression ratio is low, and self-excitation occurs. To address this issue, this embodiment employs a design that modifies the traditional Faraday rotation filter. The reflector is coated to fully reflect the operating wavelength, fully transmit ASE outside the laser's operating wavelength range, and filter out ASE light. Furthermore, when the amplified signal light passes through the acousto-optic device again, it acts as a time-domain pulse switch, further filtering out inter-pulse ASE and ensuring high contrast in the output pulses. Figure 8 The following is a spectrum diagram of the laser pulse output signal based on this design architecture. As can be seen, the ASE light in this spectrum is well suppressed, with a side-mode suppression ratio of 60dB. This minimizes the beat noise between ASE and local oscillator light, ensuring high output power while maintaining a high side-mode suppression ratio and reducing beat noise.

[0066] In one embodiment, the time-division switching device 120 further includes a first preprocessing module 126, a second preprocessing module 127 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 the first preprocessing module 126, the second preprocessing module 127, the deflection module 128 and the beam splitting module 129 are arranged in sequence; the sixth signal light of the second polarization state from the acousto-optic device 130 is preprocessed by the first preprocessing module 126 to obtain the sixth signal light of the first polarization state, and is preprocessed again by the second preprocessing module 127 to obtain the sixth signal light rotated by the first angle along the first polarization rotation direction, and then deflected by the deflection module 128 to obtain the seventh signal light with different deflection states and different exit positions, and the different deflection states The seventh signal light with different exit positions is output from the first port 121, the second port 122, the third port 123 and the fourth port 124 to the target to be measured 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 to be measured, 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 second preprocessing module 127 to obtain an echo signal of a second polarization state, and are transmitted to the detection port 125 via the second preprocessing module 127; the light between the first preprocessing module 126, 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.

[0067] Please refer to Figure 9 , Figure 9This is a structural diagram of a time-division switching device 120 according to an embodiment of the present application. In this embodiment, the time-division switching device 120 integrates a first pre-processing module 126, a second pre-processing module 127, a deflection module 128, and a beam splitting module 129. After the seed laser is split by the beam splitter, the signal light is transmitted to the fifth port 113 of the time-division switching device 120, and is incident on the first pre-processing module 126 through the polarization-maintaining fiber collimator. The polarization direction of the incident light at the fifth port 113 is along the slow axis direction of the polarization-maintaining fiber, and the polarization direction is horizontal, which is defined as P light, and the vertical polarization is defined as S light. The incident light in the P direction passes through the first pre-processing module 126 and is transmitted to the sixth port 131, and is incident on the subsequent acousto-optic module, the first optical fiber 160, and the polarization reflection device 170 through the optical fiber collimator. After secondary deflection by the polarization reflection device 170, the polarization state is rotated by 90°, transmitted along the fast axis of the optical fiber, and transmitted back to the sixth port 131 of the time-division switching device 120. After passing through the polarization-maintaining optical fiber collimator, it is incident on the first pre-processing module 126. At this time, the polarization direction of the light is S light in the vertical direction. After being processed by the first pre-processing module 126, the polarization state of the incident light is rotated by 90°, and it is converted into P polarized light. Afterwards, the sixth signal light is pre-processed again by the second pre-processing module 127 to obtain the sixth signal light rotated by the first angle along the first polarization rotation direction. The exemplary first angle is 45°. The sixth signal light is then deflected by the deflection module 128 to obtain the seventh signal light with a different deflection state and a different output position. Afterwards, the sixth signal light passes through the beam splitting module 129, and the P light is transmitted and output from the first port 121 to the second port 122 respectively. The S light is reflected and emitted from the third port 123 or the fourth port 124, respectively. That is, the seventh signal light with different deflection states and different emission positions is output from the first port 121, the second port 122, the third port 123 and the fourth port 124 to the target to be measured 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 to be measured. 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 second pre-processing module 127 to obtain an echo signal of the second polarization state. The echo signal is then transmitted to the detection port 125 via the second pre-processing module 127. The light between the first pre-processing module 126, the second pre-processing 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.

[0068] When pulsed light is transmitted in an optical fiber, a nonlinear effect occurs when the peak power of the pulse exceeds the fiber's SBS threshold, causing jitter along the pulse trailing edge and affecting signal detection. The theoretical calculation formula for the SBS threshold in an optical fiber is as follows:

[0069]

[0070] In formula (1), R SBST is the SBS threshold in the optical fiber, A eff is the effective mode field area, L eff is the effective length, which can be approximately equivalent to the physical fiber length for short passive optical fibers. B (Ω B ) is the Brillouin gain coefficient of the quartz fiber, with a typical value of 5×10 -11 m / W. From this formula, we can get the relationship curve between the SBS threshold and the transmission fiber length in the quartz fiber, such as Figure 10 shown.

[0071] When the signal light passes through the various components of the wind measuring lidar, passive optical fiber is usually used. Assuming that the length of each section is 20 cm, when the transmission optical fiber length is 1.2 m, the SBS threshold formula shows that the theoretical SBS threshold is 27 W. Taking a pulse width of 200 ns as an example, the single pulse energy that can be tolerated is 5.4 μJ, which does not meet the requirement of 10 μJ single pulse energy at a detection distance of 300 m. The solution of this embodiment adopts a hybrid integration solution that integrates the first pre-processing module, the second pre-processing module, the deflection module and the beam splitting module, shortening the transmission optical fiber length to 0.8 m, and the SBS theoretical threshold is 41.2 W. Taking a pulse width of 200 ns as an example, the single pulse energy that can be tolerated is increased to 8.2 μJ.

[0072] Traditional magneto-optical switches suitable for the optical communications industry mostly adopt a dual-core collimator design, which has some shortcomings when used in wind-measuring lidar systems. The output light of the single-frequency laser of the wind-measuring lidar system is high-peak power pulse light, and the energy density per unit area is very high. Due to the small mode field area of ​​the dual-core collimator, there is a risk of damage during long-term operation. Secondly, high-peak power pulses are very sensitive to SBS and require a large mode field area of ​​the transmission optical fiber. However, due to problems with the manufacturing process, it is difficult to expand the beam or use a large mode field optical fiber structure for the dual-core collimator. Therefore, this embodiment adopts a large-angle spatial separation method to expand the birefringent crystal splitting distance, making it possible to expand the beam with a single-core collimator or use a large mode field optical fiber design. After beam expansion, the mode field area of ​​the incident light spot is increased, the peak power density per unit area is reduced, and the reliability of the device is improved. In addition, after adopting a single-core collimator, it is possible to use a large mode field area optical fiber for the pigtail. Figure 11 The curve of the relationship between SBS threshold and fiber mode field diameter shows that as the fiber mode field diameter increases, the SBS threshold also increases. The commercial large mode field fiber mode field diameter is 12μm and 15μm. Figure 7Based on the length, using a large mode area fiber design, the SBS thresholds for 12μm and 15μm mode field diameter fibers are 59W and 92.7W, respectively. Taking a 200ns pulse width as an example, the corresponding single pulse energies are 11.8μJ and 18.5μJ. At this point, the single pulse energy exceeds 10μJ, which can support the 10μJ single pulse energy requirement at a measurement distance of 300m.

[0073] In this embodiment, by integrating the first preprocessing module 126, the second preprocessing module 127, the deflection module 128 and the splitting module 129, the length of the passive optical fiber is shortened and the SBS effect is weakened. For example, the SBS threshold is increased from 27W to 92.7W, so that the entire system can withstand high peak power pulses, which is beneficial to long-distance radar detection.

[0074] In one embodiment, the first preprocessing module 126 includes: a first polarization beam splitter 1261, which receives and reflects the sixth signal light of the second polarization state from the acousto-optical device 130; a first half-wave plate 1262, which receives the sixth signal light of the second polarization state emitted by the first polarization beam splitter 1261 and modulates the polarization state of the sixth signal light into the first polarization state before emitting it.

[0075] Please refer again Figure 9 After the seed laser is split by the beam splitter, the signal light is transmitted to the fifth port 113 of the time-division switching device 120 and incident on the first polarization beam splitter 1261 via a polarization-maintaining fiber collimator. The incident light at the fifth port 113 is polarized along the slow axis of the polarization-maintaining fiber. This is defined as P light if it is polarized horizontally, while S light if it is polarized vertically. The P light passes through the first polarization beam splitter 1261 and is transmitted to the sixth port 131. It passes through the fiber collimator and is incident on the subsequent acousto-optic module, the first optical fiber 160, and the polarization reflector 170. After secondary deflection by the polarization reflector 170, the polarization state is rotated 90° and transmitted along the fast axis of the optical fiber. It is then transmitted back to the sixth port 131 of the time-division switching device 120 and incident on the first polarization beam splitter 1261 via a polarization-maintaining fiber collimator. The vertical polarization of the light is now S light and is reflected by the first half-wave plate 1262. The first half-wave plate 1262 rotates the polarization state of the incident light by 90°, converting it into P-polarized light.

[0076] In one embodiment, the second pre-processing module 127 includes: a second polarization beam splitter 1271, which receives and transmits the sixth signal light of the first polarization state emitted by the first pre-processing module 126; a second half-wave plate 1272, which receives and rotates the polarization state of the sixth signal light of the first polarization state transmitted by the second polarization beam splitter 1271 by a first angle along the first polarization rotation direction; a Faraday rotator 1273, which receives and rotates the polarization state of the sixth signal light emitted by the second half-wave plate 1272 by a first angle along the second polarization rotation direction to obtain the sixth signal light of the first polarization state; the second polarization rotation direction is opposite to the first polarization rotation direction; a third half-wave plate 1274, which receives and rotates the polarization state of the sixth signal light of the first polarization state emitted by the Faraday rotator 1273 by a first angle along the first polarization rotation direction The first polarization state of the first echo signal is rotated by a first angle in the second polarization rotation direction; the first polarization state of the echo signal is rotated by a first angle in the second polarization rotation direction; the first polarization state of the echo signal is obtained by the first polarization state echo signal; the Faraday rotator 1273 also receives the first echo signal emitted by the third half-wave plate 1274, and rotates the polarization state of the first echo signal by a first angle in the second polarization rotation direction; the second half-wave plate 1272 also receives the first echo signal emitted by the Faraday rotator 1273, and rotates the polarization state of the first echo signal by a first angle in the second polarization rotation direction to obtain an 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.

[0077] Please refer again Figure 9The sixth signal light processed by the first pre-processing module 126 passes through the second polarization beam splitter 1271 and is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light by 45° before it is incident on the Faraday rotator 1273. The Faraday rotator 1273 also rotates the polarization state of the incident light by 45°, in the opposite direction of the second half-wave plate 1272. In this way, after a single pass, the polarization direction of the incident light remains unchanged and remains P light. The third half-wave plate 1274 receives and rotates the polarization state of the sixth signal light of the first polarization state emitted by the Faraday rotator 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 first echo signal emitted by the first electrically controlled rotation unit 1281, rotates the polarization state of the echo signal by a first angle along the second polarization rotation direction, and obtains an echo signal of the first polarization state; the Faraday rotator 1273 also receives the first echo signal emitted by the third half-wave plate 1274, rotates the polarization state of the first echo signal by a first angle along the second polarization rotation direction; the second half-wave plate 1272 also receives the first echo signal emitted by the Faraday rotator 1273, and rotates the polarization state of the first echo signal by a first angle along the second polarization rotation direction, and obtains an 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.

[0078] 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 sixth 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 sixth signal light passing through the first electrically controlled rotation unit 1281 and deflects the sixth signal light based on the polarization state of the sixth signal light; a fourth half-wave plate 1283, which receives the sixth signal light emitted by the birefringent crystal 1282 and rotates the polarization state of the sixth signal light along the first polarization rotation direction by a first angle; a second electrically controlled rotation unit 1284, including a second DC coil, which controls the rotation direction of the sixth signal light passing through the first electrically controlled rotation unit 1281 by controlling the current direction of the second DC coil. The rotation direction of the polarization state of the light is obtained to obtain the seventh signal light; the echo signal transmitted by the beam splitting module 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 by a first angle along the second polarization rotation direction; 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.

[0079] Please continue to refer to Figure 9The first electrically controlled rotation unit 1281, consisting of a Faraday rotator, a magnet, and a first DC coil, rotates the polarization of the incident light by adjusting the positive and negative current directions. When the current is in the positive direction, the incident light rotates by 45°, opposite to the rotation direction of the third half-wave plate 1274. At this time, after passing through the third half-wave plate 1274 and the first electrically controlled rotation unit 1281, the polarization state of the incident light remains unchanged, becoming P light. When the current in the first electrically controlled rotation unit 1281 is in the negative direction, the rotation direction is the same as that of the third half-wave plate 1274, and the polarization state rotates by 90°, becoming 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 to transmit the horizontal P light and deflect the vertical S light downward. The sixth 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 sixth signal light is rotated by controlling the positive and negative direction of the current in the second electrically controlled rotation unit 1284 to obtain the seventh signal light. The second electrically-controlled rotation unit 1284 also receives the echo signal transmitted by the beam splitting 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 by a first angle along the second polarization rotation direction; 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.

[0080] In one embodiment, the beam splitting module 129 includes: a third polarization beam splitter 1291, which receives the seventh signal light; when the seventh signal light is not deflected by the deflection module 128 and has the first polarization state, it is transmitted from the first position of the third polarization beam splitter 1291 and incident on the first port 121; when the seventh signal light is deflected by the deflection module 128 and has the first polarization state, it is transmitted from the second position of the third polarization beam splitter 1291; when the seventh signal light is deflected by the deflection module 128 and has the second polarization state, it is reflected from the second position of the third polarization beam splitter 1291 and incident on the third port 123; when the seventh signal light is not deflected by the deflection module 128 and has the second polarization state, it is reflected from the first position of the third polarization beam splitter 1291; a first folding prism 1292, which receives the seventh signal light from the first polarization beam splitter 1291; The seventh signal light transmitted from the second position is deflected and incident on the second port 122; the second folding prism 1293 receives the seventh signal light reflected from the first position, deflects the seventh signal light 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, and 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, and reflects the echo signals to the deflection module 128.

[0081] 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 sixth signal light passing through, but deflects the echo signal passing through; 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 sixth signal light passing through, but does not deflect the echo signal passing through; 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 sixth signal light passing through, but does not deflect the echo signal passing through; 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 sixth signal light passing through, but deflects the echo signal passing through.

[0082] For example, please refer to Figure 12, which is a diagram showing the polarization state transformation and path propagation of light emitted from the first port 121 in forward and reverse transmission in one embodiment. When the current directions of the first electrically controlled rotating unit 1281 and the second electrically controlled selecting unit are both positive, the input signal of the time-division switching device 120 is output from the first port 121. The implementation method is as follows: Figure 12 As shown. The polarization direction of the incident light at the fifth port 113 is along the slow axis of the polarization-maintaining fiber, with the polarization direction being horizontal, indicating that it is P-polarized light. After passing through the first polarization beam splitter 1261, it is transmitted to the sixth port 131 and incident on the subsequent acousto-optic module, the first optical fiber 160, and the polarization reflection device 170 through the fiber collimator. After secondary deflection by the polarization reflection device 170, the polarization state is rotated 90° and transmitted along the fast axis of the optical fiber. It is transmitted back to the sixth port 131 of the time-division switching device 120 and incident on the first polarization beam splitter 1261 through the polarization-maintaining fiber collimator. At this time, the light polarization direction is vertical S-polarized light and is reflected by the first half-wave plate 1262. The first half-wave plate 1262 rotates the polarization state of the incident light by 90°, converting it into P-polarized light. Subsequently, the signal light passes through the second polarization beam splitter 1271 and is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light by 45° clockwise. The Faraday rotator 1273 rotates the polarization of the incident light counterclockwise by 45°. During a single pass, the polarization direction of the incident light remains unchanged, remaining P-polarized. The third half-wave plate 1274 rotates the polarization of the incident light clockwise by 45°. When the current in the first electrically controlled rotating unit 1281 is positive, the polarization direction rotates counterclockwise by 45°. After passing through the first electrically controlled rotating unit 1281, the polarization direction remains P-polarized. The incident light then passes through the birefringent crystal 1282, where the polarization direction is now P-polarized and parallel to the optical axis of the birefringent crystal 1282. The incident light then passes through the fourth half-wave plate 1283, where the polarization direction rotates clockwise by 45°. After passing through the second electrically controlled rotating unit 1284, where the current direction is positive, the polarization direction rotates counterclockwise by 45°, remaining P-polarized. The incident light then passes through the third polarization beam splitter 1291 and is transmitted to the first port 121. The collimator pigtail at the second port 122 is connected to a polarization-maintaining patch cord and connected to the telescope Faraday disk. The telescope directs the laser light into the target detection area, and after being reflected by the aerosol particles in the target detection area, the return signal light is received by the telescope. The return light is transmitted to the third polarization beam splitter 1291 and then passes through the second electrically controlled rotation unit 1284 and the fourth half-wave plate 1283 again. Due to the difference in the characteristics of the Faraday rotators of the fourth half-wave plate 1283 and the second electrically controlled rotation unit 1284, when it passes through the second electrically controlled rotation unit 1284, the polarization state rotates 45° counterclockwise. After passing through the fourth half-wave plate 1283, the polarization state rotates 45° counterclockwise, and the polarization state direction is converted from P light to S light. Afterwards, the signal light is transmitted to the birefringent crystal 1282, and the polarization state is S light. When passing through the birefringent crystal 1282, it is deflected downward, and the path is as follows. Figure 11As shown by the dotted line. Transmitted to the first electrically controlled rotation unit 1281, the polarization state rotates 45° counterclockwise. Transmitted to the third half-wave plate 1274, the polarization state rotates another 45° counterclockwise, converting the polarization state direction from S light to P light. Transmitted to the Faraday rotator 1273, the polarization state rotates 45° counterclockwise. After passing through the second half-wave plate 1272, the polarization state rotates another 45° counterclockwise, converting the polarization state direction to S light. Transmitted to the second polarization beam splitter 1271, it is reflected to the detection port 125. At this point, the polarization state is vertically oriented S light. Align the slow axis of the fiber collimator on the detection port 125 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.

[0083] For example, please refer to Figure 13 , which is a polarization state preference and path propagation diagram of light emitted through the second port 122 in forward and reverse transmission in one embodiment. When the current directions of the first electrically controlled rotating unit 1281 and the second electrically controlled selecting unit are both negative, the input signal of the time division switching device 120 is output from the second port 122. Figure 13As shown. The incident light at the fifth port 113 is polarized horizontally along the slow axis of the polarization-maintaining fiber, representing P-polarization. After passing through the first polarization beam splitter 1261, it is transmitted to the sixth port 131 and, through the fiber collimator, is incident on the subsequent acousto-optic module, the first optical fiber 160, and the polarization reflector 170. After secondary deflection by the polarization reflector 170, the polarization state is rotated 90° and transmitted along the fast axis of the optical fiber. It is then transmitted back to the sixth port 131 of the time-division switching device 120 and, through the polarization-maintaining fiber collimator, is incident on the first polarization beam splitter 1261. At this point, the light is polarized vertically as S-polarization and is reflected by the first half-wave plate 1262. The first half-wave plate 1262 rotates the polarization state of the incident light by 90°, converting it into P-polarization light. The signal light then passes through the second polarization beam splitter 1271 and is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light by 45° clockwise. The Faraday rotator 1273 rotates the polarization of the incident light counterclockwise by 45°. During a single pass, the polarization direction of the incident light remains unchanged, remaining P-polarized. The third half-wave plate 1274 rotates the polarization of the incident light clockwise by 45°. When the current in the first electrically controlled rotating unit 1281 is negative, the polarization is rotated 45° clockwise. After passing through the first electrically controlled rotating unit 1281, the polarization is S-polarized. The light then passes through the birefringent crystal 1282, where the polarization is now S-polarized and deflected downward as shown. The light then passes through the fourth half-wave plate 1283, where the polarization is rotated 45° clockwise. After passing through the second electrically controlled rotating unit 1284, where the current is negative, the polarization is rotated 45° clockwise, becoming P-polarized. The light then passes through the third polarization beam splitter 1291, transmits through the first folding prism 1292, and transmits the polarized light to the second port 122. The second port 122 collimator pigtail is connected to the polarization-maintaining jumper head and is connected to the Farah disk of the telescope. The telescope injects the laser into the target detection area, and after being reflected by the aerosol particles in the target detection area, the return signal light is received by the telescope. The return light is transmitted to the first folding prism 1292 and the third polarization beam splitter 1291, and then transmitted through the second electrically controlled rotation unit 1284 and the fourth half-wave plate 1283 again. When it passes through the second electrically controlled rotation unit 1284, the polarization state rotates 45° clockwise. After passing through the fourth half-wave plate 1283, the polarization state rotates 45° counterclockwise, and the direction of the polarization state remains unchanged. Afterwards, the signal light is transmitted to the birefringent crystal 1282, and the polarization state is P light. It passes through the birefringent crystal 1282 without deflection. The path is as follows. Figure 12The dotted lines within the birefringent crystal 1282 are shown. The light is transmitted to the first electrically controlled rotation 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 maintaining its direction. The light is then transmitted to the Faraday rotator 1273, where the polarization state rotates 45° counterclockwise. After passing through the second half-wave plate 1272, the polarization state is also rotated 45° counterclockwise, converting the polarization state to S light. The light is then transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125, where the polarization state is now vertically oriented S light. The slow axis of the fiber collimator in the detection port 125 is aligned with the polarization state of the incident light to ensure that the signal is transmitted along the slow axis of the polarization-maintaining fiber.

[0084] For example, please refer to Figure 14 , which is a polarization state preference and path propagation diagram of light emitted through the third port 123 in forward and reverse transmission in one embodiment. When the current direction of the first electrically controlled rotating unit 1281 is negative and the current direction of the second electrically controlled selecting unit is positive, the input signal of the time division switching device 120 is output from the third port 123. Figure 14As shown. The incident light at the fifth port 113 is polarized horizontally along the slow axis of the polarization-maintaining fiber, representing P-polarization. After passing through the first polarization beam splitter 1261, it is transmitted to the sixth port 131 and, through the fiber collimator, is incident on the subsequent acousto-optic module, the first optical fiber 160, and the polarization reflector 170. After secondary deflection by the polarization reflector 170, the polarization state is rotated 90° and transmitted along the fast axis of the optical fiber. It is then transmitted back to the sixth port 131 of the time-division switching device 120 and, through the polarization-maintaining fiber collimator, is incident on the first polarization beam splitter 1261. At this point, the light is polarized vertically as S-polarization and is reflected by the first half-wave plate 1262. The first half-wave plate 1262 rotates the polarization state of the incident light by 90°, converting it into P-polarization light. The signal light then passes through the second polarization beam splitter 1271 and is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light by 45° clockwise. The Faraday rotator 1273 rotates the polarization of the incident light counterclockwise by 45°. During a single pass, the polarization direction of the incident light remains unchanged, remaining P-polarized. The second half-wave plate 1272 rotates the polarization of the incident light clockwise by 45°. When the current in the first electrically controlled rotating unit 1281 is negative, the polarization is rotated 45° clockwise. After passing through the first electrically controlled rotating unit 1281, the polarization is S-polarized. The light then passes through the birefringent crystal 1282, where the polarization is now S-polarized and deflected downward as shown. The light then passes through the fourth half-wave plate 1283, where the polarization is rotated 45° clockwise. After passing through the second electrically controlled rotating unit 1284, where the current is positive, the polarization is rotated 45° counterclockwise. The polarized light output from the second electrically controlled rotating unit 1284 remains S-polarized. The light then passes through the third polarization beam splitter 1291, where it is reflected and transmitted to the third port 123. The slow axis direction of the collimator of the third port 123 is aligned with the polarization state of the incident light direction, and the output pigtail of the collimator of the third port 123 is connected to the polarization-maintaining jumper head, which is connected to the Farah disk of the telescope. The telescope injects the laser into the target detection area, and after being reflected by the aerosol particles in the target detection area, the return signal light is received by the telescope. The return light is transmitted to the third polarization beam splitter 1291 and then reflected back to the second electrically controlled rotation unit 1284. When it passes through the second electrically controlled rotation unit 1284, the polarization state rotates 45° counterclockwise, and after passing through the fourth half-wave plate 1283, the polarization state rotates 45° counterclockwise, and the polarization state direction changes by 90°, becoming P polarized light. Afterwards, the signal light is transmitted to the birefringent crystal 1282, and the polarization state is P light. It passes through the birefringent crystal 1282 without deflection, and the path is as follows. Figure 14The dotted line inside the birefringent crystal 1282 is shown. The signal is transmitted to the first electrically controlled rotation 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. The polarization direction remains unchanged, remaining P light. The signal is transmitted to the Faraday rotator 1273, where the polarization state rotates 45° counterclockwise. After passing through the second half-wave plate 1272, the polarization state rotates 45° counterclockwise, converting the polarization state to S light. The signal is transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125. At this point, the polarization state is vertically oriented as S light. Align the slow axis of the fiber collimator in the detection port 125 with the polarization state of the incident light to ensure that the signal is transmitted along the slow axis of the polarization-maintaining fiber.

[0085] For example, please refer to Figure 15 , which is a diagram showing the polarization state transformation and path propagation of light emitted through the fourth port 124 in forward and reverse transmission in one embodiment. When the current direction of the first electrically controlled rotating unit 1281 is positive and the current direction of the second electrically controlled selecting unit is negative, the input signal of the time division switching device 120 is output from the fourth port 124. Figure 15As shown. The incident light at the fifth port 113 is polarized horizontally along the slow axis of the polarization-maintaining fiber, representing P-polarization. After passing through the first polarization beam splitter 1261, it is transmitted to the sixth port 131 and, through the fiber collimator, is incident on the subsequent acousto-optic module, the first optical fiber 160, and the polarization reflector 170. After secondary deflection by the polarization reflector 170, the polarization state is rotated 90° and transmitted along the fast axis of the optical fiber. It is then transmitted back to the sixth port 131 of the time-division switching device 120 and, through the polarization-maintaining fiber collimator, is incident on the first polarization beam splitter 1261. At this point, the light is polarized vertically as S-polarization and is reflected by the first half-wave plate 1262. The first half-wave plate 1262 rotates the polarization state of the incident light by 90°, converting it into P-polarization light. The signal light then passes through the second polarization beam splitter 1271 and is transmitted to the second half-wave plate 1272. The second half-wave plate 1272 rotates the polarization state of the incident light by 45° clockwise. The Faraday rotator 1273 rotates the polarization of the incident light counterclockwise by 45°. During a single pass, the polarization direction of the incident light remains unchanged, remaining P-polarized. The third half-wave plate 1274 rotates the polarization of the incident light clockwise by 45°. The current in the first electrically controlled rotating unit 1281 is positive, rotating the polarization 45° counterclockwise. After passing through the first electrically controlled rotating unit 1281, the polarization remains P-polarized. The incident light then passes through the birefringent crystal 1282, where its polarization is now P-polarized and parallel to the optical axis of the birefringent crystal 1282. It then passes through the birefringent crystal 1282 without path deflection. The incident light then passes through the fourth half-wave plate 1283, rotating its polarization 45° clockwise. After passing through the second electrically controlled rotating unit 1284, where the current is negative, the polarization is rotated 45° clockwise, remaining S-polarized. The incident light then passes through the third polarization beam splitter 1291, where it is reflected and transmitted to the second folding prism 1293. After deflection, it is transmitted to the fourth port 124, and the slow axis direction of the polarization-maintaining fiber collimator of the fourth port 124 is aligned with the polarization state of the incident light. Its output pigtail is connected to the polarization-maintaining jumper head, which is connected to the Farah disk of the telescope. The telescope injects the laser into the target detection area, and after being reflected by the aerosol particles in the target detection area, the return signal light is received by the telescope. The return light is reflected by the second folding prism 1293 and then returned to the original path and transmitted to the third polarization beam splitter 1291, and then reflected, and passes through the second electrically controlled rotation unit 1284 and the fourth half-wave plate 1283 again. When passing through the second electrically controlled rotation unit 1284, the polarization state rotates 45° clockwise, and after passing through the fourth half-wave plate 1283, the polarization state rotates 45° counterclockwise, and the direction of the polarization state remains unchanged, and it is still S light. Afterwards, the signal light is transmitted to the birefringent crystal 1282, and the polarization state is S light. When passing through the birefringent crystal 1282, it is deflected downward, and the path is as follows. Figure 15The dotted line inside the birefringent crystal 1282 is shown. The light is transmitted to the first electrically controlled rotation unit 1281, where the polarization state rotates 45° counterclockwise. It is then transmitted to the third half-wave plate 1274, where the polarization state rotates another 45° counterclockwise, converting the polarization state from S light to P light. The light is then transmitted to the Faraday rotator 1273, where the polarization state rotates 45° counterclockwise. After passing through the second half-wave plate 1272, the polarization state rotates another 45° counterclockwise, converting the polarization state to S light. The light is then transmitted to the second polarization beam splitter 1271 and reflected to the detection port 125. At this point, the polarization state is vertically oriented as S light. The slow axis of the fiber collimator in the detection port 125 is aligned with the polarization state of the incident light to ensure that the signal is transmitted along the slow axis of the polarization-maintaining fiber.

[0086] Based on the same inventive concept, the present application also provides a wind lidar wind measurement method applied to the aforementioned wind lidar system. The solution provided by this method is similar to the solution described in the aforementioned system. Therefore, the specific limitations of one or more of the following method embodiments can be found in the above-mentioned limitations on the wind lidar system and will not be further elaborated here.

[0087] Please refer to Figure 16 , Figure 16 A flow chart of a wind measurement method using a wind laser radar in an embodiment of the present invention is shown. In some embodiments, the wind measurement method using a wind laser radar includes the following steps 1602 to 1608 .

[0088] Step 1602: Control the first light source assembly to emit a first signal light; the first signal light has a first polarization state.

[0089] Step 1604: Control the acousto-optic device to receive the first signal light, perform pulse modulation and frequency shift modulation on the first signal light, and obtain a second signal light.

[0090] Step 1606: Control the second light source to emit a second laser; receive the second signal light and the second laser through the first optical fiber, amplify the second signal light to obtain a third signal light; the third signal light also includes amplified spontaneous emission light; receive the third signal light through the polarization reflection device, filter out the amplified spontaneous emission light in the third signal light, and rotate the polarization state of the third signal light to obtain a fourth signal light having 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 a fifth signal light; the acousto-optic device also receives the fifth signal light, and pulse modulates and frequency-shift modulates the fifth signal light again to obtain a sixth signal light.

[0091] Step 1608: Control the time-division switching device, which includes a deflection module and a beam splitting module. By controlling the deflection module to deflect the sixth signal light, the sixth signal light is split by the beam splitting module at different times to obtain seventh signal light. The seventh signal light is emitted through different ports respectively.

[0092] For example, please refer to Figure 1, controlling the first light source assembly to emit a first laser having a first wavelength; the first laser is a continuous laser; the first light source can be a 1550nm single-frequency seed laser. The single-frequency seed laser is split into two beams by a beam splitter, such as a polarization-maintaining beam splitter. One beam serves as the local oscillator light and is transmitted to a coupler, such as a 50:50 fiber coupler, while the other beam serves as the signal light and is transmitted to the fifth port of the time-division switching device. The signal light passes through the first polarization beam splitter of the time-division switching device and is output from the sixth port and transmitted to the acousto-optic module. The acousto-optic device is composed of an acousto-optic driver and an acousto-optic modulator. The acousto-optic device is controlled to frequency-shift and chop the input continuous light into pulsed light. The signal light is then transmitted through a beam combiner, such as a fiber combiner, to a first optical fiber, such as a double-clad erbium-ytterbium co-doped fiber. The double-clad erbium-ytterbium co-doped fiber amplifier is composed of a multimode pump, a beam combiner, and a double-clad erbium-ytterbium co-doped fiber. A second laser is emitted from a second light source. The pulsed signal light propagates through the double-clad fiber core, while the multimode pump light undergoes multiple reflections in the inner cladding. As it repeatedly passes through the erbium- and ytterbium-doped core, it achieves population inversion, amplifying the signal light as it passes through. The amplified signal light is then transmitted to a polarization-reflecting device, such as a Faraday rotation filter. The Faraday rotation filter incorporates a built-in 45° polarization rotator and a 1550nm passband mirror. The 1550nm passband mirror filters out ASE light generated during the primary amplification process, serving two purposes: first, preventing competition between ASE light and the signal light during secondary amplification, which would reduce the amplification efficiency of the signal light; and second, improving the side-mode suppression ratio (SMSR) of the amplifier output signal, thereby preventing interference noise generated by the local oscillator light and the inter-pulse ASE beat frequency from degrading the signal-to-noise ratio of the wind radar system. The filtered signal light then passes through the built-in 45° polarization rotator, shifting its polarization state by another 45°. The signal light is then transmitted along the fast axis of the polarization-maintaining fiber into the double-clad gain fiber. After secondary amplification, the signal light is transmitted to the combiner. The main part of the signal light is transmitted through the signal arm of the combiner, and a small part is transmitted to the multimode pump through the pump arm of the combiner. Therefore, in this embodiment, the multimode pump is designed with an anti-reflection function, the typical anti-reflection band is 1400-1600nm, and the typical anti-reflection isolation is 30dB. The pulse light after secondary amplification is subjected to secondary frequency shifting and chopping by the acousto-optic module. On the one hand, the secondary chopping filters out the acousto-optic leakage pulses to improve the dynamic extinction ratio of the system, and on the other hand, it further filters out the spontaneous emission light (ASE) generated during fiber amplification, thereby improving the side mode suppression ratio (SMSR) of the laser output. At this time, the return light contains amplified signal light and stray light. The stray light is formed by the reflection of the incident light on the surface of the acousto-optic modulator and is transmitted along the slow axis of the optical fiber. After the signal light is reflected back by the polarization reflection device for the second time, the polarization state is rotated 90° and transmitted along the fast axis of the optical fiber.When the two signals are incident on the sixth polarization beam splitter through the sixth port of the time-division switching device, the signal light is transmitted to the telescope along the output directions of the first, second, third, and fourth ports of the time-division switching device, while the stray light is transmitted outward along the fifth port. The signal light and stray light are spatially separated to prevent interference between the signal and stray light, resulting in pulse envelope modulation that interferes with signal detection. The signal light output channel is controlled by the high and low levels of the time-division switching device, thus achieving a time-division multiplexing effect. The outgoing signal light passes through the four-way telescope and enters the atmosphere. After being reflected by aerosols in the target detection area, it passes through the telescope and the time-division switching device again. Each return signal light is transmitted from the detection port to a coupler, such as a 50:50 optical coupler, where it is optically coupled with the local oscillator and mixed at a balanced detector to produce an analog signal. The analog signal is converted to digital by the sampling module in the signal processing module and then undergoes a fast Fourier transform (FFT) in the signal processor chip. After cumulative de-noising, the spectral information of the radial wind speed is obtained.

[0093] This embodiment utilizes a hybrid dual-pass solution combining a single acousto-optic module with multimode double-clad dual-pass amplification and a polarization reflector. This achieves high-efficiency amplification of a single-stage, double-pass amplified laser at a low cost. This hybrid dual-pass solution, employing a single acousto-optic module and a polarization reflector, combines spectral filtering with time-domain switching filtering. This addresses the issue of double-clad amplifiers easily generating high ASE when amplifying weak signals. This prevents the effects of ASE self-excitation on laser amplification and the impact of low SMSR values ​​on wind radar signal detection. Furthermore, the time-division switching device shortens the transmission fiber length, increases the SBS threshold of the pulsed light, and mitigates the SBS effect.

[0094] The hybrid integrated magneto-optical switch adopts a large spatial separation optical path, making it suitable for the design based on a large mode field fiber collimator, increasing the mode field area of ​​the transmission fiber, improving the SBS threshold of the pulsed light, and weakening the SBS effect.

[0095] It should be understood that, although the various steps in the flowcharts involved in the various embodiments described above are displayed in sequence according to the instructions of the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the flowcharts involved in the various embodiments described above can include multiple steps or multiple stages, and these steps or stages are not necessarily executed and completed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of steps or stages in other steps.

[0096] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, 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.

[0097] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A wind measurement laser radar system, characterized in that: include: A first light source assembly emits a first signal light having a first polarization state; an acousto-optic device, receiving the first signal light, performing pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; A second light source emits a second laser; the second laser is a multi-mode pump 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 includes amplified spontaneous emission light; wherein the first optical fiber is a double-clad erbium-ytterbium co-doped optical fiber; a polarization reflection device, receiving the third signal light, filtering out the amplified spontaneous emission light in the third signal light, and rotating the polarization state of the third signal light to obtain a fourth signal light having a second polarization state; the second polarization state is perpendicular to the first polarization state; The first optical fiber further receives the fourth signal light and amplifies the fourth signal light again to obtain a fifth signal light; the acousto-optic device further receives the fifth signal light and performs pulse modulation and frequency shift modulation on the fifth signal light again to obtain a sixth signal light; The time-division switching device includes a deflection module and a beam splitting module. By controlling the deflection module to deflect the sixth signal light, the sixth signal light is split by the beam splitting module at different times to obtain seventh signal light, and the seventh signal light is emitted through different ports respectively.

2. The wind measurement laser radar system according to claim 1, characterized in that: The first optical fiber comprises: a fiber core in which the second signal light is transmitted; and The second laser light is transmitted through the inner cladding after multiple reflections.

3. The wind measurement laser radar system according to claim 1, characterized in that: Also includes: A beam combiner, through which the second signal light and the second laser light are incident into the first optical fiber.

4. The wind measurement laser radar system according to claim 1, characterized in that: The polarized reflection device comprises: a polarization rotator, receiving the third signal light and rotating the polarization state of the third signal light along the first polarization rotation direction to obtain a third deflected signal light; and a reflector that receives the third deflected signal light, transmits the amplified spontaneous emission light, and reflects the third deflected signal light back to the polarization rotator; after passing through the polarization rotator, the polarization state of the third deflected signal light is rotated again along the first polarization rotation direction to obtain a fourth signal light with a second polarization state.

5. The wind measurement laser radar system according to claim 1, characterized in that: The time-division switching device further includes a first preprocessing module, a second 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 first preprocessing module, the second preprocessing module, the deflection module and the beam splitting module are arranged in sequence; The sixth signal light of the second polarization state from the acousto-optic device is preprocessed by the first preprocessing module to obtain the sixth signal light of the first polarization state, and is preprocessed again by the second preprocessing module to obtain the sixth signal light rotated by the first angle along the first polarization rotation direction, and then deflected by the deflection module to obtain the seventh signal light with different deflection states and different exit positions. The seventh signal light with different deflection states and different exit positions is output from the first port, the second port, the third port and the fourth port to the target to be measured respectively through the beam splitting module; the first port, the second port, the third port and the fourth port respectively receive the echo signals reflected from the target to be measured, and the echo signals are again incident on the deflection module through the beam splitting module for deflection processing and then incident on the second preprocessing module to obtain the echo signals of the second polarization state, and are transmitted to the detection port through the second preprocessing module; the light between the first preprocessing module, the second 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.

6. The wind measurement laser radar system according to claim 5, characterized in that: The first preprocessing module includes: a first polarization beam splitter, receiving and reflecting a sixth signal light of the second polarization state from the acousto-optic device; The first half-wave plate receives the sixth signal light in the second polarization state emitted by the first polarization beam splitter and modulates the polarization state of the sixth signal light into the first polarization state before emitting the sixth signal light.

7. The wind measurement laser radar system according to claim 5, characterized in that: The second preprocessing module includes: a second polarization beam splitter, receiving and transmitting the sixth signal light of the first polarization state emitted by the first pre-processing module; a second half-wave plate, receiving and rotating the polarization state of the sixth signal light of the first polarization state transmitted by the second polarization beam splitter by a first angle along the first polarization rotation direction; a Faraday rotator, receiving and rotating the polarization state of the sixth signal light emitted by the second half-wave plate by a first angle along a second polarization rotation direction to obtain a sixth signal light of the first polarization state; wherein the second polarization rotation direction is opposite to the first polarization rotation direction; a third half-wave plate, configured to receive and rotate the polarization state of the sixth signal light of the first polarization state emitted by the Faraday rotator by a first angle along the first polarization rotation direction; and further receive the first echo signal emitted by the first electrically controlled rotation unit, and rotate the polarization state of the echo signal by a first angle along the second polarization rotation direction to obtain an echo signal of the first polarization state; The Faraday rotator further receives the first echo signal emitted by the third half-wave plate, and rotates the polarization state of the first echo signal by a first angle along a second polarization rotation direction; The second half-wave plate further receives the first echo signal emitted by the Faraday rotator, and rotates the polarization state of the first echo signal by a first angle along a second polarization rotation direction to obtain an echo signal of a second polarization state; The second polarization beam splitter further 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.

8. The wind measurement laser radar system according to claim 5, characterized in that: The deflection module comprises: a first electrically controlled rotating unit, comprising a first DC coil, configured to control a rotation direction of a polarization state of a sixth signal light passing through the first electrically controlled rotating unit by controlling a current direction of the first DC coil; a birefringent crystal, receiving the sixth signal light passing through the first electrically controlled rotation unit, and deflecting the sixth signal light based on a polarization state of the sixth signal light; a fourth half-wave plate, receiving the sixth signal light emitted by the birefringent crystal, and rotating the polarization state of the sixth signal light by a first angle along the first polarization rotation direction; a second electrically controlled rotation unit, comprising a second DC coil, configured to control the rotation direction of the polarization state of the sixth signal light passing through the first electrically controlled rotation unit by controlling the current direction of the second DC coil to obtain a seventh signal light; and further configured to receive the echo signal transmitted by the beam splitting module, and control 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 further receives the echo signal emitted by the second electrically controlled rotation unit, and rotates the polarization state of the echo signal by a first angle along a second polarization rotation direction; The birefringent crystal further 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.

9. The wind measurement laser radar system according to claim 8, characterized in that: When the current directions of the first DC coil and the second DC coil are both set to the first direction, the birefringent crystal does not deflect the passing sixth signal light, but deflects the passing echo signal; When the current directions of the first DC coil and the second DC coil are both set to the second direction, the birefringent crystal deflects the passing sixth signal light and 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 sixth signal light and does not deflect the passing echo signal; When the current direction of the first DC coil is set to a first direction and the current direction of the second DC coil is set to a second direction, the birefringent crystal does not deflect the passing sixth signal light, but deflects the passing echo signal.

10. The wind measurement laser radar system according to claim 5, characterized in that: The beam splitting module includes: a third polarization beam splitter, receiving the seventh signal light; when the seventh signal light is not deflected by the deflection module and has the first polarization state, transmitting the seventh signal light from the first position of the third polarization beam splitter and being incident on the first port; when the seventh signal light is deflected by the deflection module and has the first polarization state, transmitting the seventh signal light from the second position of the third polarization beam splitter; when the seventh signal light is deflected by the deflection module and has the second polarization state, reflecting the seventh signal light from the second position of the third polarization beam splitter and being incident on the third port; when the seventh signal light is not deflected by the deflection module and has the second polarization state, reflecting the seventh signal light from the first position of the third polarization beam splitter; a first folding prism, receiving the seventh signal light transmitted from the second position, deflecting the seventh signal light and then incident on the second port; a second folding prism, receiving the seventh signal light reflected from the first position, deflecting the seventh signal light and then causing it to be incident on the fourth port; and receiving the echo signal passing through the fourth port, deflecting the echo signal and then causing it to be incident on the third polarization beam splitter; The first folding prism further receives the echo signal passing through the second port, deflects the echo signal and then makes it incident on the third polarization beam splitter; The third polarization beam splitter also receives the echo signals respectively from the first port and the first folding prism, and transmits the echo signals to the deflection module; and also receives the echo signals respectively from the third port and the second folding lens, and reflects the echo signals to the deflection module.

11. A wind measurement method using a wind laser radar, characterized in that: include: Controlling the first light source assembly to emit a first signal light; the first signal light has a first polarization state; controlling the acousto-optic device to receive the first signal light, and performing pulse modulation and frequency shift modulation on the first signal light to obtain a second signal light; Controlling a second light source to emit a second laser; receiving the second signal light and the second laser through a first optical fiber, amplifying 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; receiving the third signal light through a polarization reflection device, filtering out the amplified spontaneous emission light in the third signal light, and rotating the polarization state of the third signal light to obtain a fourth signal light having 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 a fifth signal light; the acousto-optic device also receives the fifth signal light, and pulse-modulates and frequency-shifts the fifth signal light again to obtain a sixth signal light; A time-division switching device is controlled, wherein the time-division switching device includes a deflection module and a beam splitting module. By controlling the deflection module to deflect the sixth signal light, the sixth signal light is split by the beam splitting module at different times to obtain a seventh signal light, and the seventh signal light is emitted through different ports respectively.

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