Laser wind sounding radar system and method based on double-clad cascaded double-pass amplification

Abstract

The application aims to provide a laser wind measurement radar system and method based on double-clad cascaded double-pass amplification. The system comprises a seed source, a cascaded double-pass pre-amplifier, a main amplifier, a telescope and a pump source. The cascaded double-pass pre-amplifier comprises a first double-pass amplification unit and a second double-pass amplification unit connected in sequence. An optical signal passes through the first double-pass amplification unit and the second double-pass amplification unit in sequence, and is used for two-stage double-pass amplification of an optical signal output by the seed source. The method comprises the following steps: S1, continuous light generation and beam splitting; S2, cascaded double-pass amplification; S3, pulse modulation; S4, main power amplification; S5, emission and reception; and S6, coherent detection. The application is applied to the technical field of laser radar.

Description

Technical Field

[0001] This invention relates to the field of lidar technology, and in particular to an all-fiber lidar system and amplification method suitable for medium-range coherent wind measurement, specifically a lidar wind measurement system and method based on double-clad cascaded double-pass amplification. Background Technology

[0002] Mid-range coherent wind lidar places stringent demands on the performance of pulsed light sources, requiring narrow pulse widths, high repetition rates, and relatively high single-pulse energy. In the amplification stage of the pulsed light source, single-stage pulse amplifiers, limited by physical constraints, cannot simultaneously achieve high conversion efficiency and high energy / power gain. Therefore, pulsed fiber amplifier chains have become the preferred solution to overcome this bottleneck, especially suitable for MOPA (Master Oscillator Power Amplifier) ​​systems. This series structure, consisting of a preamplifier and a power amplifier, theoretically can simultaneously achieve high gain and high efficiency.

[0003] However, existing pulsed fiber amplifier chains suffer from numerous technical drawbacks: on the one hand, fiber nonlinearity and amplified spontaneous emission (ASE) generated during small-signal amplification severely limit the performance of the preamplifier; on the other hand, although power amplifiers with large core sizes and low numerical apertures using back-pumped configurations can suppress nonlinear effects to some extent, the input pulse energy is much lower than the signal saturation energy, and the laser has miniaturization and integration requirements, making it difficult to adapt the power amplifier to large-mode-field fibers, resulting in a significant decrease in efficiency. These factors together make it difficult to realize efficient, high-power, and compact fiber amplifiers.

[0004] To improve the performance of fiber optic amplifiers, a two-way amplification scheme has been proposed, which can increase the small-signal amplification output gain from 8-10 dB in the single-way scheme to 20 dB. In the two-way scheme, the input signal is amplified in the first pass and then reflected back through a high-reflectivity mirror. The sufficient pulse energy carried by the reflected signal is used to effectively extract the fiber gain in the return pass. However, in laser wind radar systems, frequency shifting is required through an acousto-optic modulator. This modulation process causes a 3-6 dB attenuation of the continuous optical signal power, resulting in a small signal at the µW level. This small signal is highly likely to excite spontaneous emission (ASE) self-pulses in the amplifier in a single-way configuration, limiting the single-stage safe gain to only 20-25 dB, which is insufficient to meet the effective amplification requirements of the preamplifier.

[0005] Existing two-way amplification techniques primarily amplify small-signal signals from modulated pulse signals at the microsecond level, neglecting the impact of continuous optical power on the modulated signal. Furthermore, they require additional single-mode pumping, complicating the circuitry and hindering laser integration and miniaturization. Therefore, a two-way amplification technique that balances amplification efficiency, noise suppression, and system compactness is urgently needed to overcome the technical bottlenecks of existing mid-range laser wind-measuring radars. Summary of the Invention

[0006] The purpose of this invention is to provide a laser wind radar system and method based on double-clad cascaded double-pass amplification. By implementing cascaded double-pass amplification of continuous light and pulsed light in the pre-amplification stage, ASE noise is effectively suppressed, the system signal-to-noise ratio and output pulse energy are improved, and a single 940nm multimode pump source is used to complete the pumping of the entire optical path, avoiding multiple pumps and temperature control modules, and achieving high integration and high stability.

[0007] The technical solution adopted in this invention is a laser wind measurement radar system based on double-clad cascaded two-way amplification, the system comprising:

[0008] Seed source, used to output continuous wave single-frequency laser;

[0009] A cascaded double-pass preamplifier includes a first double-pass amplification unit and a second double-pass amplification unit connected in sequence. The optical signal passes through the first double-pass amplification unit and the second double-pass amplification unit in sequence to perform two-stage double-pass amplification on the optical signal output from the seed source.

[0010] The main amplifier is used to perform single-pass high-power amplification on the signal that has been pre-amplified by the cascaded two-way preamplifier.

[0011] A telescope is used to emit amplified laser pulses and receive echo signals.

[0012] The pump source outputs pump light, which is split by a multi-stage beam splitter to provide pump energy to the first double-pass amplification unit, the second double-pass amplification unit, and the main amplifier, respectively.

[0013] The first two-way amplification unit includes a first polarization-maintaining circulator, a first combiner, a first erbium-doped ytterbium double-clad fiber, and a first fiber Bragg grating. The second two-way amplification unit includes a bandpass filter polarization-maintaining circulator, a second combiner, a second erbium-doped ytterbium double-clad fiber, and a second fiber Bragg grating. The first two-way amplification unit uses the first fiber Bragg grating to reflect the forward-amplified signal light back to the first erbium-doped ytterbium double-clad fiber for reverse secondary amplification. The second two-way amplification unit uses the second fiber Bragg grating to reflect the forward-amplified signal light back to the second erbium-doped ytterbium double-clad fiber for reverse secondary amplification.

[0014] Furthermore, the seed source is a distributed feedback laser diode with an output wavelength of 1551.76 nm and a linewidth of less than 150 kHz, the pump source is a multimode pump laser with an output wavelength of 940 nm, and the core / inner cladding diameters of the first erbium-doped ytterbium double-clad fiber and the second erbium-doped ytterbium double-clad fiber are both 10 μm / 128 μm, with a numerical aperture (NA) of 0.2.

[0015] Furthermore, a first acousto-optic modulator is connected between the third port of the first polarization-maintaining circulator and the first port of the bandpass filter polarization-maintaining circulator. The first acousto-optic modulator is used to modulate the intensity of the continuous light output from the third port of the first polarization-maintaining circulator and maintain system safety. The bandpass filter polarization-maintaining circulator is used to filter out the sideband noise generated by modulation and block the backflow to the ASE.

[0016] Furthermore, the main amplifier employs a reverse pumping method. The main amplifier is used to strip residual pump light and perform single-pass power amplification to suppress nonlinear effects. The main amplifier includes a cladding mode stripper, a third beam combiner, and a third erbium-doped ytterbium double-clad fiber. A second acousto-optic modulator is connected between the cladding mode stripper and the third terminal of the bandpass filter polarization-maintaining circulator. The second acousto-optic modulator chops the continuous light output from the third terminal of the bandpass filter polarization-maintaining circulator into pulsed light and sends it to the main amplifier. A second polarization-maintaining circulator is connected between the third beam combiner and the telescope.

[0017] Furthermore, the pump source distributes the pump light to the cascaded two-way preamplifier and the main amplifier via a 25 / 75 beam splitter. The 25 / 75 beam splitter is connected to the third beam combiner via an optical path, and another path of the 25 / 75 beam splitter is connected to a 20 / 80 beam splitter. The 20 / 80 beam splitter is connected to the first beam combiner and the second beam combiner, respectively. The pump light power supplied to the cascaded two-way preamplifier is less than the pump light power supplied to the main amplifier.

[0018] Furthermore, the system also includes a photoelectric detection component, which includes a balanced detector for coherently beating the echo signal received by the telescope with the local oscillator light split from the seed source, calculating the Doppler frequency shift to obtain the wind speed. The input end of the balanced detector is connected to a 50 / 50 beam splitter, and a 30 / 70 beam splitter is provided between the seed source and the first polarization-maintaining circulator. One input port of the 50 / 50 beam splitter is connected to the third port of the second polarization-maintaining circulator, and the other input port of the 50 / 50 beam splitter is connected to the second port of the 30 / 70 beam splitter.

[0019] Furthermore, the first fiber Bragg grating and the second fiber Bragg grating have a bandwidth of 2 nanometers and an output end face with a corner-cut structure to accommodate the seed emission wavelength tolerance and avoid parasitic oscillations.

[0020] A method for laser wind measurement using the system described above includes the following steps:

[0021] S1. Continuous light generation and beam splitting: A continuous wave single-frequency laser is output from the seed source and split into two paths: signal light and local oscillator light.

[0022] S2. Cascaded two-way amplification: In the cascaded two-way preamplifier, the optical signal passes through the first two-way amplification unit and the second two-way amplification unit in sequence. In each unit, the optical signal is amplified in the forward direction through the erbium-doped ytterbium double-clad fiber, then reflected by the fiber Bragg grating, and then amplified again in the reverse direction through the erbium-doped ytterbium double-clad fiber to achieve high gain and low noise amplification.

[0023] S3. Pulse Modulation: The double-pass amplified optical signal is input into the second acousto-optic modulator to generate a Gaussian pulse with a repetition frequency;

[0024] S4. Main power amplification: The Gaussian pulse is input into the main amplifier and power amplification is performed using a single-pass reverse pumping method;

[0025] S5. Transmission and reception: The amplified pulsed laser is transmitted to the area under test through a telescope, and the echo signal reflected from the area under test is received;

[0026] S6. Coherent detection: The echo signal is coherently beatd with the local oscillator light separated in step S1, and the Doppler frequency shift is demodulated by the balanced detector to obtain the wind speed information.

[0027] Furthermore, in step S4, a single-pass reverse pumping structure is adopted, so that the signal light and the pump light are transmitted in opposite directions in the optical fiber to smooth the power density distribution in the optical fiber, thereby suppressing the nonlinear effect of stimulated Brillouin scattering.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. High gain and high signal-to-noise ratio: This invention adopts a cascaded two-way pre-amplification structure. Compared with the traditional single-way amplification (gain of about 20-25dB) or single-stage two-way amplification, this invention improves the gain to more than 50dB through two-stage two-way amplification. At the same time, by utilizing the filtering characteristics of fiber Bragg gratings and the high efficiency of the two-way structure, the signal-to-noise ratio reaches 60dB, and there is no significant ASE noise at 1535nm. The signal-to-noise ratio is improved by 7dB compared with the original structure.

[0030] 2. Effective suppression of ASE self-pulse: This invention completes the main pre-amplification process in the continuous light stage (before the second acousto-optic modulator). Due to the high power of the continuous light, the small signal amplification region is effectively avoided, fundamentally suppressing the ASE self-pulse phenomenon caused by small signal amplification and ensuring signal stability;

[0031] 3. Compact structure and high integration: This invention uses erbium-ytterbium co-doped double-clad fiber and 940nm multimode pump light. The pre-amplification and main amplification requirements can be met simultaneously by a single pump source (3W) and a beam splitter. Compared with the existing technology that requires multiple single-mode pump sources, this invention eliminates the need for additional temperature control circuits, simplifies circuit design, and is conducive to the miniaturization of lidar.

[0032] 4. Power and nonlinearity balance: The main amplifier stage adopts a reverse-pumped single-pass structure, which avoids the doubling of the effective interaction length caused by the two-pass structure, thereby effectively suppressing nonlinear effects and enabling the pulse peak power to reach 38uJ (without SBS jitter), which is far better than the original structure's 20uJ. Attached Figure Description

[0033] Figure 1 This is a simplified structural diagram of the system of the present invention;

[0034] Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0035] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0036] Overall system architecture reference Figure 1 (System overall structure diagram), the laser wind measurement radar system of the present invention mainly includes:

[0037] Seed source 100 is used to output continuous wave single-frequency laser;

[0038] The cascaded double-pass preamplifier includes a first double-pass amplification unit and a second double-pass amplification unit connected in sequence. The optical signal passes through the first double-pass amplification unit and the second double-pass amplification unit in sequence to perform two-stage double-pass amplification on the optical signal output by the seed source 100.

[0039] The main amplifier is used to perform single-pass high-power amplification on the signal that has been pre-amplified by the cascaded two-way preamplifier.

[0040] Telescope 116 is used to emit amplified laser pulses and receive echo signals;

[0041] Pump source 200, the pump light output from the pump source is split by a multi-stage beam splitter, and provides pump energy to the first double-pass amplification unit, the second double-pass amplification unit and the main amplifier respectively;

[0042] The first two-way amplification unit includes a first polarization-maintaining circulator 102, a first combiner 105, a first erbium-doped ytterbium double-clad fiber 106, and a first fiber Bragg grating 107. The second two-way amplification unit includes a bandpass filter polarization-maintaining circulator 104, a second combiner 108, a second erbium-doped ytterbium double-clad fiber 109, and a second fiber Bragg grating 110. The first two-way amplification unit uses the first fiber Bragg grating 107 to reflect the forward-amplified signal light back to the first erbium-doped ytterbium double-clad fiber 106 for reverse secondary amplification. The second two-way amplification unit uses the second fiber Bragg grating 110 to reflect the forward-amplified signal light back to the second erbium-doped ytterbium double-clad fiber 109 for reverse secondary amplification.

[0043] Specifically, the seed source 100 is a distributed feedback laser diode with an output wavelength of 1551.76 nm and a linewidth of less than 150 kHz. The pump source 200 is a multimode pump laser with an output wavelength of 940 nm. The core / inner cladding diameters of the first erbium-doped ytterbium double-clad fiber 106 and the second erbium-doped ytterbium double-clad fiber 109 are both 10 μm / 128 μm, and the numerical aperture (NA) is 0.2. The bandwidth of the first fiber Bragg grating 107 and the second fiber Bragg grating 110 is 2 nanometers, and their output end faces are corner-cut to accommodate the seed emission wavelength tolerance and avoid parasitic oscillations.

[0044] A first acousto-optic modulator 103 is connected between the third port of the first polarization-maintaining circulator 102 and the first port of the bandpass filter polarization-maintaining circulator 104. The first acousto-optic modulator 103 is used to modulate the intensity of the continuous light output from the third port of the first polarization-maintaining circulator 102 and maintain system safety. The bandpass filter polarization-maintaining circulator 104 is used to filter out the sideband noise generated by modulation and block the backflow to the ASE. The main amplifier employs a reverse pumping method. It is used to strip residual pump light and perform single-pass power amplification to suppress nonlinear effects. The main amplifier includes a cladding mode stripper 112, a third combiner 113, and a third erbium-doped ytterbium double-clad fiber 114. A second acousto-optic modulator 111 is connected between the cladding mode stripper 112 and the third end of the bandpass filter polarization-maintaining circulator 104. The second acousto-optic modulator 111 chops the continuous light output from the third end of the bandpass filter polarization-maintaining circulator 104 into pulsed light and sends it to the main amplifier. A second polarization-maintaining circulator 115 is connected between the third combiner 113 and the telescope 116. The pump source 200 distributes the pump light to the cascaded two-way preamplifier and the main amplifier via a 25 / 75 beam splitter 201. The 25 / 75 beam splitter 201 is connected to the third beam combiner 113 via an optical path. Another path of the 25 / 75 beam splitter 201 is connected to a 20 / 80 beam splitter 202. The 20 / 80 beam splitter 202 is connected to the first beam combiner 105 and the second beam combiner 108, respectively. The pump light power supplied to the cascaded two-way preamplifier is less than the pump light power supplied to the main amplifier.

[0045] The system also includes a photoelectric detection component, which includes a balanced detector 118 for coherently beating the echo signal received by the telescope 116 with the local oscillator light split from the seed source 100, and calculating the Doppler frequency shift to obtain the wind speed. The input end of the balanced detector 118 is connected to a 50 / 50 beam splitter 117. A 30 / 70 beam splitter 101 is provided between the seed source 100 and the first polarization-maintaining circulator 102. One input port of the 50 / 50 beam splitter 117 is connected to the third port of the second polarization-maintaining circulator 115, and the other input port of the 50 / 50 beam splitter 117 is connected to the second port of the 30 / 70 beam splitter 101.

[0046] The method for laser wind measurement using the above system includes the following steps:

[0047] S1. Continuous light generation and beam splitting: A continuous wave single-frequency laser is output from the seed source and split into two paths: signal light and local oscillator light.

[0048] S2. Cascaded two-way amplification: In the cascaded two-way preamplifier, the optical signal passes through the first two-way amplification unit and the second two-way amplification unit in sequence. In each unit, the optical signal is amplified in the forward direction through the erbium-doped ytterbium double-clad fiber, then reflected by the fiber Bragg grating, and then amplified again in the reverse direction through the erbium-doped ytterbium double-clad fiber to achieve high gain and low noise amplification.

[0049] S3. Pulse Modulation: The double-pass amplified optical signal is input into the second acousto-optic modulator to generate a Gaussian pulse with a repetition frequency;

[0050] S4. Main power amplification: The Gaussian pulse is input into the main amplifier and power amplification is performed using a single-pass reverse pumping method;

[0051] S5. Transmission and reception: The amplified pulsed laser is transmitted to the area under test through a telescope, and the echo signal reflected from the area under test is received;

[0052] S6. Coherent detection: The echo signal is coherently beatd with the local oscillator light separated in step S1, and the Doppler frequency shift is demodulated by the balanced detector to obtain the wind speed information.

[0053] Specifically, in step S4, a single-pass reverse pumping structure is adopted, so that the signal light and the pump light are transmitted in opposite directions in the optical fiber to smooth the power density distribution in the optical fiber, thereby suppressing the nonlinear effect of stimulated Brillouin scattering.

[0054] The present invention will now be described in more detail.

[0055] The optical path of the first two-way amplification unit is as follows: seed source → 30 / 70 beam splitter → first polarization-maintaining circulator → first beam combiner → first erbium-doped ytterbium double-clad fiber → first fiber Bragg grating. After reflection, the light returns to the first erbium-doped ytterbium double-clad fiber for secondary amplification, and then sequentially passes through the first beam combiner and the first polarization-maintaining circulator before being output to the first acousto-optic modulator. The first acousto-optic modulator modulates the intensity of the optical signal and acts as an optical switch to protect the entire system. Specifically, the first acousto-optic modulator 103 is located between the first two-way amplification unit and the second two-way amplification unit. The first two-way amplification unit amplifies the seed light from 30mW to 386mW of continuous light through a two-way structure. At this point, the first acousto-optic modulator serves two purposes: firstly, it modulates the continuous light intensity (power matching and anti-saturation): if 386mW of continuous light is directly fed into the second two-way amplifier unit, it is highly likely that the gain fiber of the second two-way amplifier unit will quickly enter a saturated operating state, which will not only fail to effectively increase the power but may also induce strong nonlinear effects (such as stimulated Brillouin scattering, SBS). Therefore, the first acousto-optic modulator acts as a high-precision continuous attenuator here, attenuating 386mW to a more suitable intermediate value (e.g., around 100mW), ensuring that the second two-way amplifier unit can efficiently extract gain while always operating within a safe linear amplification range. The light output from the first acousto-optic modulator enters the second two-way amplifier unit through a bandpass filter polarization-maintaining circulator, is combined by a second bundler, amplified by a second erbium-doped ytterbium double-clad fiber, and then amplified by a second fiber Bragg grating reflection before being output to the second acousto-optic modulator by a bandpass filter polarization-maintaining circulator.

[0056] The pump source is a 3W 940nm multimode pump laser; the pump light is sequentially split by a 25 / 75 beam splitter and a 20 / 80 beam splitter to provide pump light for the first and second double-pass amplification units, respectively, and the other output of the 25 / 75 beam splitter provides reverse pump light for the main amplifier.

[0057] The main amplifier adopts a reverse-pumped single-pass amplification structure; the cladding mode stripper removes the residual pump light, and the third erbium-doped ytterbium double-clad fiber performs high-power amplification. The amplified light is then guided into the telescope for outward emission via the second polarization-maintaining circulator.

[0058] The specific process of the optical path of this invention is as follows:

[0059] 1. Seed photogeneration and beam splitting

[0060] The seed source (SEED) outputs a 1551.76nm continuous wave single-frequency laser with a linewidth <150 kHz. The seed light is split into two paths by a 30 / 70 beam splitter: 70% is used as probe light and enters the pre-amplification link, while 30% is used as local oscillator light and directly enters a 50 / 50 beam combiner to await coherent beat frequency.

[0061] 2. Optical path of the first two-way amplification unit

[0062] The probe light enters through port 1 and exits through port 2 of the first polarization-maintaining circulator, reaching the first combiner. A 100mW 940nm pump light split by the 20 / 80 beam splitter is injected into the first combiner, combined with the signal light, and then enters the first erbium-doped ytterbium double-clad fiber for the first forward amplification. The amplified light reaches the first fiber Bragg grating, is reflected, and returns along the original optical path to the first erbium-doped ytterbium double-clad fiber for the second reverse amplification. The second amplified light is then output from port 3 through the first combiner and the first polarization-maintaining circulator, entering the first acousto-optic modulator. The first fiber Bragg grating has a bandwidth of 2nm and is used to filter out ASE noise; its end face is diced to avoid parasitic feedback.

[0063] 3. Optical path of the second double-pass amplification unit

[0064] The 386mW continuous light is attenuated to a safe level (such as 100mW continuous light) in the first acousto-optic modulator for the next stage of amplification.

[0065] The signal light modulated by the first acousto-optic modulator enters the bandpass filter polarization-maintaining circulator, and after filtering and unidirectional conduction, it enters the second beam combiner. Another pump light from the 20 / 80 beam splitter is injected into the second beam combiner, and the combined light enters the second erbium-doped ytterbium double-clad fiber for amplification. After reflection by the second fiber Bragg grating, double-pass amplification is achieved. The amplified light is output from port 3 of the bandpass filter polarization-maintaining circulator to the second acousto-optic modulator. The second acousto-optic modulator chops the continuous light into pulsed light and precisely controls the average power to 5mW.

[0066] 4. Main amplification and emission optical path

[0067] The output light from the second acousto-optic modulator enters the cladding mode stripper (CPS) to strip the residual 940nm pump light from the fiber cladding; it then enters the third combiner; the 1.5W 940nm reverse pump light split by the 25 / 75 beam splitter is injected into the third combiner, combined with the signal light, and then enters the third erbium-doped ytterbium double-clad fiber in the reverse direction to perform single-pass high-power amplification; the amplified light is then guided through the third combiner and the second polarization-maintaining circulator to the telescope and emitted to the target under test.

[0068] 5. Coherent detection and wind speed calculation

[0069] The backscattered echo signal from the target is received by the telescope, enters the 50 / 50 beam combiner through the second polarization-maintaining circulator, and is then combined with the local oscillator light before being input into the balanced detector. The balanced detector coherently beats the signal light with the local oscillator light, calculates the Doppler frequency shift, and outputs the wind speed information.

[0070] The present invention will now be described in comparison with specific embodiments.

[0071] Comparative Example 1: Traditional Single-Cloak EDFA Two-Way Amplification System

[0072] It employs 976nm single-mode pumping and single-clad erbium-doped fiber, requiring multiple pumps and TEC temperature control; the signal-to-noise ratio is 53dB, with significant 1535nm ASE noise; the single-pulse energy is 20μJ, with pulse jitter caused by SBS; the system is large in size and has complex circuitry.

[0073] Embodiment of the present invention: The present invention's double-clad cascaded two-way amplification system

[0074] It employs a 940nm multimode single-pump, erbium-doped ytterbium double-clad fiber cascaded two-way amplification, eliminating the need for TEC; it boasts a signal-to-noise ratio of 60dB with no significant ASE noise; a single-pulse energy of 38μJ with no pulse jitter; and features single-pump drive, compact structure, and high integration.

[0075] Comparative conclusion: This invention is significantly superior to traditional single-cladding two-way amplification systems in terms of gain, noise suppression, pulse energy, system simplification, and miniaturization, and is more suitable for engineering applications of medium-range coherent laser wind radar.

[0076] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser wind-measuring radar system based on double-clad cascaded two-way amplification, characterized in that, The system includes: Seed source (100) is used to output continuous wave single-frequency laser; The cascaded double-pass preamplifier includes a first double-pass amplification unit and a second double-pass amplification unit connected in sequence. The optical signal passes through the first double-pass amplification unit and the second double-pass amplification unit in sequence to perform two-stage double-pass amplification on the optical signal output by the seed source (100). The main amplifier is used to perform single-pass high-power amplification on the signal that has been pre-amplified by the cascaded two-way preamplifier. Telescope (116) for emitting amplified laser pulses and receiving echo signals; The pump source (200) outputs pump light which is split by a multi-stage beam splitter to provide pump energy to the first double-pass amplification unit, the second double-pass amplification unit and the main amplifier respectively. The first two-way amplification unit includes a first polarization-maintaining circulator (102), a first bundler (105), a first erbium-doped ytterbium double-clad fiber (106), and a first fiber Bragg grating (107). The second two-way amplification unit includes a bandpass filter polarization-maintaining circulator (104), a second bundler (108), a second erbium-doped ytterbium double-clad fiber (109), and a second fiber Bragg grating (110). The first two-way amplification unit uses the first fiber Bragg grating (107) to reflect the forward-amplified signal light back to the first erbium-doped ytterbium double-clad fiber (106) for reverse secondary amplification. The second two-way amplification unit uses the second fiber Bragg grating (110) to reflect the forward-amplified signal light back to the second erbium-doped ytterbium double-clad fiber (109) for reverse secondary amplification. A first acousto-optic modulator (103) is connected between the third port of the first polarization-maintaining circulator (102) and the first port of the bandpass filter polarization-maintaining circulator (104). The first acousto-optic modulator (103) is used to modulate the intensity of the continuous light output from the third port of the first polarization-maintaining circulator (102) and maintain system safety. The bandpass filter polarization-maintaining circulator (104) is used to filter out the sideband noise generated by modulation and block the backflow to the ASE. The main amplifier adopts a reverse pumping method. The main amplifier is used to strip the residual pump light and perform single-pass power amplification to suppress nonlinear effects. The main amplifier includes a cladding mode stripper (112), a third beam combiner (113), and a third erbium-doped ytterbium double-clad fiber (114). A second acousto-optic modulator (111) is connected between the cladding mode stripper (112) and the third end of the bandpass filter polarization-maintaining circulator (104). The second acousto-optic modulator (111) chops the continuous light output from the third end of the bandpass filter polarization-maintaining circulator (104) into pulse light and sends it to the main amplifier. A second polarization-maintaining circulator (115) is connected between the third beam combiner (113) and the telescope (116). The pump source (200) distributes the pump light to the cascaded two-way preamplifier and the main amplifier through a 25 / 75 beam splitter (201). The 25 / 75 beam splitter (201) is connected to the third beam combiner (113) via an optical path. The 25 / 75 beam splitter (201) is also connected to a 20 / 80 beam splitter (202). The 20 / 80 beam splitter (202) is connected to the first beam combiner (105) and the second beam combiner (108) respectively. The pump light power supplied to the cascaded two-way preamplifier is less than the pump light power supplied to the main amplifier.

2. The system according to claim 1, characterized in that, The seed source (100) is a distributed feedback laser diode with an output wavelength of 1551.76nm and a linewidth of less than 150kHz. The pump source (200) is a multimode pump laser with an output wavelength of 940nm. The core / inner cladding diameters of the first erbium-doped ytterbium double-clad fiber (106) and the second erbium-doped ytterbium double-clad fiber (109) are both 10μm / 128μm, and the numerical aperture (NA) is 0.

2.

3. The system according to claim 1, characterized in that, The system also includes a photoelectric detection component, which includes a balanced detector (118) for coherently beating the echo signal received by the telescope (116) with the local oscillator light split from the seed source (100) to calculate the Doppler frequency shift and obtain the wind speed. The input end of the balanced detector (118) is connected to a 50 / 50 beam splitter (117). A 30 / 70 beam splitter (101) is provided between the seed source (100) and the first polarization-maintaining circulator (102). One of the input ports of the 50 / 50 beam splitter (117) is connected to the third port of the second polarization-maintaining circulator (115), and the other input port of the 50 / 50 beam splitter (117) is connected to the second port of the 30 / 70 beam splitter (101).

4. The system according to claim 1, characterized in that, The first fiber Bragg grating (107) and the second fiber Bragg grating (110) have a bandwidth of 2 nanometers and an output end face with a corner-cut structure to accommodate the seed emission wavelength tolerance and avoid parasitic oscillations.

5. A method for laser wind measurement using the system as described in claim 3, characterized in that, The method includes the following steps: S1. Continuous light generation and beam splitting: A continuous wave single-frequency laser is output from a seed source and split into two paths: signal light and local oscillator light; S2. Cascaded two-way amplification: In the cascaded two-way preamplifier, the optical signal passes through the first two-way amplification unit and the second two-way amplification unit in sequence. In each unit, the optical signal is amplified in the forward direction through the erbium-doped ytterbium double-clad fiber, then reflected by the fiber Bragg grating, and then amplified again in the reverse direction through the erbium-doped ytterbium double-clad fiber to achieve high gain and low noise amplification. S3. Pulse Modulation: The double-pass amplified optical signal is input into the second acousto-optic modulator to generate a Gaussian pulse with a repetition frequency; S4. Main power amplification: The Gaussian pulse is input into the main amplifier and power amplification is performed using a single-pass reverse pumping method; S5. Transmission and reception: The amplified pulsed laser is transmitted to the area under test through a telescope, and the echo signal reflected from the area under test is received; S6. Coherent detection: The echo signal is coherently beatd with the local oscillator light separated in step S1, and the Doppler frequency shift is demodulated by the balanced detector to obtain the wind speed information.

6. The method according to claim 5, characterized in that, In step S4, a single-pass reverse pumping structure is adopted, which makes the signal light and pump light propagate in opposite directions in the optical fiber to smooth the power density distribution in the optical fiber, thereby suppressing the nonlinear effect of stimulated Brillouin scattering.

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