A U-band high-energy square-wave pulse Raman light source module

Abstract

This invention provides a U-band high-energy square-wave pulsed Raman light source module. It first achieves initial stable amplification of the seed light through forward pumping with a 100-watt pump source, followed by high-energy main amplification through reverse pumping with a kilowatt-level pump source. Both stages of Raman amplification utilize highly nonlinear optical fibers as the gain medium to significantly enhance the stimulated Raman scattering effect, efficiently converting pump light energy into signal light and improving overall Raman gain and energy conversion efficiency. Simultaneously, it balances the stability of the amplification process with the integrity of the pulse waveform, thereby achieving a smooth, step-by-step amplification of the U-band pulsed seed light. Ultimately, it stably outputs high-energy U-band square-wave pulsed light with a single pulse energy ≥5μJ and a pulse width of 80–120ns, significantly improving the light source's output performance and better meeting the application requirements of long-distance fiber optic communication expansion and atmospheric methane remote sensing.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and in particular to a U-band high-energy square wave pulse Raman light source module. Background Technology

[0002] With the rapid development of modern computer networks, the demand for communication capacity in long-distance optical fiber communication systems continues to surge, and traditional communication window resources are becoming increasingly scarce. The available spectrum resources in the currently widely used C-band (1520–1565 nm) and L-band (1565–1620 nm) are about to be exhausted, and there is an urgent need to expand new communication bands to meet the growing capacity demand. Therefore, the development of U-band (around 1645 nm) optical fiber communication light sources has become a key issue that urgently needs to be addressed.

[0003] However, the 1645nm operating wavelength exceeds the gain spectrum range of traditional erbium-doped fiber (EDF), making it difficult for conventional erbium-doped fiber amplifiers and lasers to directly achieve effective optical amplification and laser output in this band. Raman fiber lasers (RFLs) based on stimulated Raman scattering (SRS) can overcome this wavelength limitation. By selecting a pump source with an appropriate wavelength and combining it with a nonlinear fiber medium, laser output in any target band can be achieved. For example, using a 1550nm erbium-doped fiber laser to pump a silica-based fiber can produce a 1645nm Raman laser. Furthermore, Raman fiber lasers offer advantages such as simple structure, high output power, excellent beam quality, and flexible tunable lasing wavelength, making them suitable for fiber optic communication system applications.

[0004] Meanwhile, 1645nm lasers have significant application value in gas sensing and detection, especially in the remote sensing of atmospheric methane (CH4). Satellite remote sensing of CH4 is mainly divided into two categories: passive remote sensing and active remote sensing. Passive remote sensing relies on the 1645nm and 2.3μm short-wave infrared bands and the approximately 8μm thermal infrared band, corresponding to short-wave infrared and thermal infrared sensors. Short-wave infrared sensors detect CH4 by detecting atmospheric backscattering, making them more sensitive to changes in near-surface CH4 concentration. This has become the mainstream technology for atmospheric methane satellite detection, creating an urgent need for high-performance 1645nm light sources. Summary of the Invention

[0005] The purpose of this invention is to provide a U-band high-energy square wave pulse Raman light source module to solve the technical problems in the prior art where the gain medium of traditional erbium-doped fiber cannot cover the U-band, making it difficult to generate high-energy square wave pulse lasers in this band, and the lack of a suitable high-performance U-band pulse light source for long-distance optical fiber communication and atmospheric methane remote sensing.

[0006] To address the aforementioned technical problems, this invention provides a U-band high-energy square-wave pulse Raman light source module, comprising an initial seed source, a Raman pre-amplification unit, and a Raman main amplification unit sequentially connected along the signal transmission direction; the initial seed source is used to output U-band pulse seed light; the Raman pre-amplification unit is used to pre-amplify the U-band pulse seed light to obtain pre-amplified pulse light; the Raman main amplification unit is used to main amplify the pre-amplified pulse light to output high-energy U-band square-wave pulse light with a single pulse energy ≥5μJ and a pulse width of 80~120ns; The Raman pre-amplification unit employs a forward-pumped structure, with its pump source being a 100-900W peak power pump source; the Raman main amplification unit employs a reverse-pumped structure, with its pump source being a 1-9kW peak power pump source; the gain fibers of both the Raman pre-amplification unit and the Raman main amplification unit have a nonlinear coefficient ≥10W. -1 km -1 Highly nonlinear optical fibers.

[0007] Specifically, this invention constructs a U-band high-energy square-wave pulse Raman light source module by sequentially connecting an initial seed source, a Raman pre-amplification unit, and a Raman main amplification unit. The Raman pre-amplification unit uses a 100-watt pump source with a forward pumping structure to achieve stable and efficient pre-amplification of the U-band pulse seed light, providing a moderately powerful and stable foundation signal light for subsequent main amplification, avoiding pulse distortion caused by direct high-power pumping. The Raman main amplification unit uses a kilowatt-level pump source with a reverse pumping structure, enabling high-power energy loading with low signal light damage risk, significantly improving the overall efficiency. The final output is optical pulse energy; at the same time, both amplification units use highly nonlinear optical fibers as gain media, which can significantly enhance the stimulated Raman scattering effect, improve Raman gain and optical energy conversion efficiency, shorten the required gain fiber length, and further improve the module integration and stability. The three work together to achieve regular U-band high-energy square wave pulse light output, effectively solving the technical problem that traditional light sources are difficult to achieve high-energy square wave pulse output in the U-band. The overall amplification efficiency is high, the pulse waveform is controllable, and the output performance is stable, which can better meet the application needs of long-distance optical fiber communication and atmospheric methane remote sensing detection.

[0008] Preferably, the U-band high-energy square wave pulse Raman light source module further includes a pump seed source, a pre-amplification sub-unit, a first optical coupler, a 100-watt-level amplification sub-unit, and a kilowatt-level amplification sub-unit; the first pump light output by the 100-watt-level amplification sub-unit constitutes a 100-watt-level pump source, and the second pump light output by the kilowatt-level amplification sub-unit constitutes a kilowatt-level pump source. The input end of the pre-amplification subunit is connected to the pump seed source, and the output end is connected to the 100-watt-level amplification subunit and the kilowatt-level amplification subunit respectively through the first optical coupler. The pump seed source is used to output continuous pump seed light, and the pre-amplification subunit is used to pre-amplify the continuous pump seed light to obtain pump light that is compatible with the 100-watt-level amplification subunit and the kilowatt-level amplification subunit.

[0009] Specifically, this preferred structure utilizes a single pump seed source in conjunction with a pre-amplification subunit to pre-amplify the continuous pump seed light. The amplified pump light is then synchronously distributed to the 100-watt and kilowatt-level amplification subunits via a first optical coupler. This achieves synchronous driving of the two pump sources, ensuring wavelength consistency, timing synchronization, and power stability between the 100-watt and kilowatt-level pump light, avoiding wavelength mismatch and phase jitter problems introduced by multiple pump sources. On the other hand, it simplifies the overall pump link structure design, reduces the number of independent seed sources, and lowers module complexity and cost. Simultaneously, the pre-amplification process provides power-matched, high-quality input light for subsequent 100-watt and kilowatt-level amplification, improving the amplification efficiency and output reliability of the two pump sources.

[0010] Preferably, the power splitting ratio between the first output terminal and the second output terminal of the first optical coupler is 1:(3-6). This design can save amplification costs without affecting the quality of the subsequent amplified beam.

[0011] Specifically, the aforementioned power splitting ratio can reasonably allocate optical power according to the actual power requirements of the 100-watt-level amplification subunit and the kilowatt-level amplification subunit. While meeting the pump power supply of the 100-watt level, it provides sufficient optical power support for the kilowatt-level high-power amplification. This ratio design can save pump optical power loss, reduce the device cost and energy consumption of subsequent amplification links, and ensure that each level of amplification link operates in the optimal gain range, without adversely affecting the beam quality, spectral purity and pulse waveform stability of subsequent amplification.

[0012] Preferably, the pump seed source includes a seed amplification subunit, a circulator, a first optical isolator, a second optical coupler, and a fiber Bragg grating; The seed amplifier subunit, circulator, first optical isolator and second optical coupler are connected in sequence to form a closed resonant ring optical path, and the fiber Bragg grating is connected to the second port of the circulator; the second optical coupler is a 1×2 fiber coupler, whose first output end is connected to the input end of the seed amplifier subunit, and the second output end is used to output continuous pump seed light.

[0013] Specifically, the pump seed source utilizes a circulator and fiber Bragg grating to achieve precise selection and narrowband filtering of the output wavelength, effectively ensuring the stability and spectral purity of the pump seed light output wavelength and avoiding stray wavelength interference with subsequent pump amplification and Raman amplification processes. The first optical isolator suppresses reflection and oscillation of the back-propagating optical signal in the optical path, preventing feedback light from damaging the seed amplification subunit and improving the reliability of the resonant loop. The second optical coupler, on the one hand, feeds back a portion of the optical signal to the input of the seed amplification subunit to maintain stable resonance, and on the other hand, achieves stable output of continuous pump seed light. The overall ring resonant structure significantly improves the output power stability, beam quality, and wavelength accuracy of the pump seed source, providing consistent, low-noise, and high-performance initial pump light for subsequent pre-amplification subunits, 100-watt-level amplification subunits, and kilowatt-level amplification subunits.

[0014] Preferably, the seed amplification subunit includes a first pump source, a first wavelength division multiplexer, and a first gain fiber; the input end of the first wavelength division multiplexer is connected to the first output end of the second optical coupler, the pump end is connected to the first pump source, and the output end is fused to the first end of the first gain fiber; the second end of the first gain fiber is fused to the first port of the circulator, and the third port of the circulator is connected to the input end of the first optical isolator.

[0015] Specifically, the seed amplification subunit can stably and reliably amplify the optical signal in the resonant loop, providing continuous gain compensation for the ring resonant optical path and ensuring that the pump seed source achieves continuous and stable laser output.

[0016] Preferably, the pre-amplification subunit includes a second pump source, a second wavelength division multiplexer, a second gain fiber, a second optical isolator, and a first bandpass filter; The input of the second wavelength division multiplexer is connected to the second output of the second optical coupler, the pump end is connected to the second pump source, and the output is fused to the first end of the second gain fiber. The second end of the second gain fiber is connected to the input of the second optical isolator, the output of the second optical isolator is connected to the input of the first bandpass filter, and the output of the first bandpass filter is connected to the input of the first optical coupler.

[0017] Specifically, the pre-amplification subunit utilizes a second wavelength division multiplexer to efficiently couple the continuous pump seed light output from the pump seed source and the pump light from the second pump source into the second gain fiber, thereby achieving stable power enhancement and preliminary amplification of the seed light and providing power-matched input light for the subsequent 100-watt and kilowatt-level amplification subunits. The second optical isolator can suppress backlight reflection and oscillation, preventing feedback light from causing impact damage to the front-end devices. The first bandpass filter can filter out stray light and noise generated during amplification, ensuring the spectral purity and beam quality of the output pump light.

[0018] Preferably, the 100-watt amplification subunit includes a first acousto-optic modulator, a third optical isolator, a 100-watt pump first-stage amplification component, and a 100-watt pump second-stage amplification component, which are sequentially optically connected along the signal transmission direction. The 100W pump-stage amplification assembly includes a third pump source, a first forward combiner, a third gain fiber, a second bandpass filter, and a fourth optical isolator. The input end of the first forward combiner is connected to the third optical isolator, the pump end is connected to the third pump source, and the output end is fused to the first end of the third gain fiber. The second end of the third gain fiber is fused to the input end of the second bandpass filter, and the output end of the second bandpass filter is connected to the input end of the fourth optical isolator. The 100W pump-secondary amplification assembly includes a fourth pump source, a second forward combiner, a fourth gain fiber, a fifth optical isolator, and a third optical coupler. The input end of the second forward combiner is connected to the output end of the fourth optical isolator, the pump end is connected to the fourth pump source, and the output end is fused to the first end of the fourth gain fiber. The second end of the fourth gain fiber is fused to the input end of the fifth optical isolator, the output end of the fifth optical isolator is connected to the input end of the third optical coupler, and the first output end of the third optical coupler outputs the first pump light to the Raman pre-amplification unit.

[0019] Specifically, the 100-watt amplification subunit pulse-modulates the input optical signal through a first acousto-optic modulator (AOM). With the help of the host computer, the pulse signal is pre-compensated, which can precisely control the pulse timing and waveform shape, effectively suppressing pulse distortion and edge jitter, and laying the foundation for obtaining a stable and regular U-band square wave pulse. The modulated optical signal is then sequentially input into the 100-watt pump first-stage amplification component and the 100-watt pump second-stage amplification component for two-stage forward cascade amplification. By progressively increasing the optical power and using filtering and optical isolation measures, a stable and reliable 100-watt power output is achieved while ensuring beam quality and spectral purity.

[0020] Preferably, the kilowatt-level amplification subunit includes a second acousto-optic modulator, a sixth optical isolator, a kilowatt pump first-stage amplification component, a kilowatt pump second-stage amplification component, and a kilowatt pump third-stage amplification component, which are sequentially optically connected along the signal transmission direction. The kilowatt pump-stage amplification assembly includes a fifth pump source, a third forward combiner, a fifth gain fiber, a third bandpass filter, and a seventh optical isolator. The input end of the third forward combiner is connected to the sixth optical isolator, the pump end is connected to the fifth pump source, and the output end is fused to the first end of the fifth gain fiber. The second end of the fifth gain fiber is connected to the input end of the third bandpass filter, and the output end of the third bandpass filter is connected to the input end of the seventh optical isolator. The kilowatt-pumped second-stage amplifier assembly includes a sixth gain fiber, a reverse combiner, a sixth pump source, a fourth bandpass filter, and an eighth optical isolator. The first end of the sixth gain fiber is fused to the output end of the seventh optical isolator, and the second end is fused to the input end of the reverse combiner. The pump end of the reverse combiner is connected to the sixth pump source, and the output end is connected to the input end of the fourth bandpass filter. The output end of the fourth bandpass filter is connected to the input end of the eighth optical isolator. The kilowatt-pumped three-stage amplification assembly includes a seventh pump source, a fourth forward combiner, a seventh gain fiber, a mode field adapter, a ninth optical isolator, and a fourth optical coupler. The input end of the fourth forward combiner is connected to the output end of the eighth optical isolator, the pump end is connected to the seventh pump source, and the output end is fused to the first end of the seventh gain fiber. The second end of the seventh gain fiber is connected to the input end of the mode field adapter. The output end of the mode field adapter is connected to the input end of the ninth optical isolator, the output end of the ninth optical isolator is connected to the input end of the fourth optical coupler, and the first output end of the fourth optical coupler outputs the second pump light to the Raman main amplification unit.

[0021] Specifically, the kilowatt-level amplification subunit independently modulates the pulse signal using a second acousto-optic modulator (AOM), and works with the host computer to pre-compensate the pulse waveform, precisely controlling the pulse shape and timing to ensure a stable and regular square wave pulse output, avoiding distortion and jitter. The modulated signal is then amplified in three stages: a kilowatt-pumped first-stage amplification component, a kilowatt-pumped second-stage amplification component, and a kilowatt-pumped third-stage amplification component. The first-stage amplification provides initial power enhancement and noise filtering, the second stage uses a reverse beam-combining pump structure to further improve gain and reduce the risk of signal damage, and the third stage completes the final kilowatt-level power amplification through forward pumping. The gain fibers, bandpass filters, and optical isolators at each stage work together to improve amplification efficiency and spectral purity, effectively suppress back-reflection light protection devices, and optimize beam quality with a mode field adapter. The final output is a second pump light with sufficient power, stable waveform, and excellent beam quality, providing reliable high-power pump support for the Raman main amplification unit.

[0022] Preferably, the first and second gain fibers are both erbium-doped fibers, each with a length of 0.5 to 5 m; the third, fourth, fifth, sixth, and seventh gain fibers are all erbium-ytterbium co-doped fibers, each with a length of 1 to 5 m.

[0023] Specifically, erbium-doped fiber of 0.5–2 m can achieve low-noise, high-beam-quality linear signal amplification in the seed source and pre-amplification stage, providing stable base gain while avoiding nonlinear interference and waveform degradation caused by excessively long fiber. Erbium-ytterbium co-doped fiber of 1–5 m can significantly improve pump absorption efficiency and saturated output power by relying on the efficient sensitization effect of ytterbium ions on erbium ions, adapting to the high-power amplification requirements from hundreds of watts to kilowatts. At the same time, with reasonable fiber length control, it can ensure sufficient pump absorption and signal gain, and effectively suppress nonlinear effects such as stimulated Raman scattering and self-phase modulation during the amplification process, reduce pulse distortion and spectral broadening, so that each stage of the pump amplification link can achieve high power output while maintaining signal purity, waveform stability and optical path reliability.

[0024] Preferably, the second optical coupler is a 1×2 fiber optic coupler, and the power splitting ratio between its first output end and the second output end is 1:(1~2); the third and fourth optical couplers are both 1×2 fiber optic couplers, and their first output end with a 99% splitting ratio is used to output the corresponding pump light, and their second output end with a 1% splitting ratio is used to monitor the waveform and spectrum of the corresponding pump light.

[0025] Specifically, a power splitting ratio of 1:(1~2) can achieve a reasonable distribution of optical power between the resonant loop and the output link, ensuring that the resonant loop has sufficient feedback optical power to maintain stable laser oscillation, and providing continuous pump seed light with intensity matching for the subsequent pre-amplification unit. At the same time, the third and fourth optical couplers adopt a 99:1 splitting structure, so that 99% of the high proportion of optical power is used as pump light for efficient output to the Raman amplification unit, ensuring sufficient pump energy supply. Only 1% of the low proportion of optical power is needed to achieve real-time online monitoring of the pump light waveform and spectrum, which does not affect the power transmission and amplification efficiency of the main optical path, and can monitor the working status of the pump source in real time. This facilitates pulse pre-compensation and waveform calibration with the host computer, further improving the pump output stability and the regularity of the U-band square wave pulse, achieving the dual effect of efficient pump output and accurate status monitoring.

[0026] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a U-band high-energy square-wave pulse Raman light source module. It employs a two-stage amplification architecture consisting of an initial seed source, a Raman pre-amplification unit, and a Raman main amplification unit, sequentially connected along the signal transmission direction. A 100-watt pump source forward pumps the seed light for initial stable amplification, while a kilowatt-level pump source reverse pumps the high-energy main amplification. Furthermore, highly nonlinear optical fibers are used as the gain medium in both stages of the Raman amplification unit to significantly enhance the stimulated Raman scattering effect, efficiently converting pump light energy into signal light and improving the overall Raman scattering performance. By balancing erbium gain and energy conversion efficiency, while also ensuring the stability of the amplification process and the integrity of the pulse waveform, a step-by-step, stable amplification of U-band pulse seed light is achieved. This effectively avoids pulse distortion, nonlinear distortion, and device damage under high-power amplification, thus overcoming the technical shortcomings of traditional erbium-doped fiber light sources that cannot cover the U-band and are difficult to output high-energy square wave pulses. Ultimately, it stably outputs high-energy U-band square wave pulse light with a single pulse energy ≥5μJ and a pulse width of 80–120ns, significantly improving the output performance of the light source and better meeting the application requirements of long-distance fiber optic communication expansion and atmospheric methane remote sensing. Attached Figure Description

[0027] Figure 1 This is a connection diagram of the U-band high-energy square wave pulse Raman light source module provided in Embodiment 1. Figure 2 This is a schematic diagram showing the connection between the 100-watt pump source and the kilowatt pump source in the U-band high-energy square wave pulse Raman light source module provided in Embodiment 1. Figure 3 The host computer waveform pre-compensation signal diagrams for the 100-watt and kilowatt-level pump channels in the U-band high-energy square wave pulse Raman light source module provided in Embodiment 1 are shown. Figure 4 This is a diagram of the standard square wave signal output by the acousto-optic modulator in the U-band high-energy square wave pulse Raman light source module provided in Embodiment 1. Figure 5 The image shows the U-band Raman pulse waveform before phase and timing calibration in the U-band high-energy square wave pulse Raman source module provided in Embodiment 1. Figure 6 The U-band square wave pulse waveform diagram of the U-band high-energy square wave pulse Raman source module provided in this embodiment 1, after phase adjustment and timing optimization, achieves the maximum Raman gain. In the attached diagram: 100—U-band high-energy square-wave pulse Raman source module; 11—Initial seed source; 12—Raman pre-amplification unit; 121—Hundred-watt pump source; 122—Third wavelength division multiplexer; 123—First high nonlinear fiber; 13—Raman main amplification unit; 131—Tenth optical isolator; 132—Second high nonlinear fiber; 133—Fourth wavelength division multiplexer; 134—Kilometer-level pump source; 20—Pump seed source; 201—First pump source; 202—First wavelength division multiplexer; 203—First gain fiber; 204—Optical circulator; 205—Fiber Bragg grating; 20 6—First optical isolator; 207—Second optical coupler; 30—Pre-amplification subunit; 301—Second pump source; 302—Second wavelength division multiplexer; 303—Second gain fiber; 304—Second optical isolator; 305—First bandpass filter; 40—First optical coupler; 501—First acousto-optic modulator; 502—Third optical isolator; 503—100W pump first-stage amplifier assembly; 5031—Third pump source; 5032—First forward combiner; 5033—Third gain fiber; 5034—Second bandpass filter; 5035—Fourth optical isolator; 504—100W pump second-stage amplifier assembly; 5041—Fourth pump source; 5042—Second forward combiner; 5043—Fourth gain fiber; 5044—Fifth optical isolator; 5045—Third optical coupler; 601—Second acousto-optic modulator; 602—Sixth optical isolator; 603—Kilometer-pumped first-stage amplifier assembly; 6031—Fifth pump source; 6032—Third forward combiner; 6033—Fifth gain fiber; 6034—Third bandpass filter; 6035—Seventh optical isolator; 604—Kilowatt pump second-stage amplifier assembly; 6041—Sixth gain fiber; 6042—Reverse combiner; 6043—Sixth pump source; 6044—Fourth bandpass filter; 6045—Eighth optical isolator; 605—Kilowatt pump third-stage amplifier assembly; 6051—Seventh pump source; 6052—Fourth forward combiner; 6053—Seventh gain fiber; 6054—Mode field adapter; 6055—Ninth optical isolator; 6056—Fourth optical coupler. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] The purpose of this invention is to address the shortcomings of existing technologies by providing a U-band high-energy square-wave pulse Raman light source module. This module employs a two-stage cascade structure consisting of an initial seed source, a forward-pumped Raman pre-amplification unit, and a reverse-pumped Raman main amplification unit. This is achieved with a 100-900W pump source for stable pre-amplification of the seed light and a 1-9kW pump source for high-energy main amplification. Highly nonlinear optical fiber is used as the gain medium to efficiently couple the pump energy into U-band signal light gain. This progressively increases the pulse power while maintaining a flat and stable square-wave waveform. This effectively solves the problems of traditional erbium-doped fiber gain media not being able to cover the U-band and the tendency for pulse distortion during high-power amplification. Ultimately, this achieves high-efficiency and high-stability Raman pulse amplification, outputting high-energy U-band square-wave pulse light, meeting the requirements for high-performance U-band pulse light sources in long-distance optical fiber communication and atmospheric methane remote sensing.

[0030] The technical solution of the present invention will now be described in conjunction with specific embodiments.

[0031] Example 1: Please see Figure 1 Embodiment 1 of this invention provides a U-band high-energy square-wave pulse Raman light source module 100, which adopts a bidirectional pumping architecture. Two highly nonlinear optical fibers are pumped collaboratively by a 100-watt pump source 121 and a kilowatt pump source 134 to achieve higher Raman gain and higher power signal output. The 100-watt pump source 121 drives the Raman pre-amplification unit 12, and the kilowatt pump source 134 drives the Raman main amplification unit 13. The specific structure is as follows: Figure 1 As shown.

[0032] Specifically, the U-band high-energy square wave pulse Raman light source module 100 provided in this embodiment 1 includes an initial seed source 11, a Raman pre-amplification unit 12, and a Raman main amplification unit 13 connected sequentially along the signal transmission direction; the initial seed source 11 (Signal) is used to output U-band pulse seed light; the Raman pre-amplification unit 12 is used to pre-amplify the U-band pulse seed light to obtain pre-amplified pulse light; the Raman main amplification unit 13 is used to main amplify the pre-amplified pulse light to output high-energy U-band square wave pulse light.

[0033] Specifically, the Raman preamplification unit 12 adopts a forward pumping structure, which includes a 100-watt pump source 121, a third wavelength division multiplexer 122 (WDM), and a first high nonlinear fiber 123 (HNLF). The input end of the third wavelength division multiplexer 122 is connected to the initial seed source 11, the pump end is connected to the 100-watt pump source 121, and the output end is fused to the first end of the first high nonlinear fiber 123.

[0034] Specifically, the Raman main amplification unit 13 adopts a reverse pumping structure, which includes a tenth optical isolator 131, a second highly nonlinear fiber 132, a fourth wavelength division multiplexer 133, and a kilowatt-level pump source 134. The input end of the tenth optical isolator 131 is fused to the second end of the first highly nonlinear fiber 123, and the output end is fused to the first end of the second highly nonlinear fiber 132. The input end of the fourth wavelength division multiplexer 133 is fused to the second end of the second highly nonlinear fiber 132, the pump end is connected to the kilowatt-level pump source 134, and the output end is used to output high-energy U-band square wave pulse light with a single pulse energy ≥5μJ and a pulse width of 80~120ns.

[0035] In Example 1, the initial seed source 11 is a continuous seed light with a wavelength of 1645nm and a maximum power of 20mW; the parameters of the 100-watt pump source 121 are pulse pumping with a peak power of 100-900W, and the parameters of the kilowatt-level pump source 134 are pulse pumping with a peak power of 1kW-9kW; the nonlinear coefficient of the first highly nonlinear fiber 123 is ≥10W. -1 km -1 The fiber core diameter is 3μm, the mode field diameter is 4μm, and the length is 20m; the second highest nonlinear fiber 132 has a nonlinear coefficient ≥10W. -1 km -1 The fiber core has a diameter of 3μm, the mode field diameter is 4μm, and the length is 6m.

[0036] Specifically, the length of the second high nonlinear fiber 132 is greater than that of the first high nonlinear fiber 123, mainly because it needs to achieve a higher Raman gain to output a high-energy pulse of ≥5μJ. The reverse pump structure can avoid pulse distortion and nonlinear distortion caused by long fibers. At the same time, a longer fiber can disperse high power density to reduce the risk of device damage. The Raman pre-amplification unit 12 only needs a small gain and to ensure waveform stability. In conjunction with the forward pump structure, a shorter fiber is required to prevent premature signal distortion.

[0037] Please see Figure 2 The U-band high-energy square wave pulse Raman light source module 100 provided in this embodiment 1 also includes a pump seed source 20, a pre-amplification sub-unit 30, a first optical coupler 40 (OC), a 100-watt-level amplification sub-unit, and a kilowatt-level amplification sub-unit; the first pump light output by the 100-watt-level amplification sub-unit constitutes a 100-watt-level pump source 121, and the second pump light output by the kilowatt-level amplification sub-unit constitutes a kilowatt-level pump source 134; The input end of the pre-amplification subunit 30 is connected to the pump seed source 20, and the output end is connected to the 100-watt-level amplification subunit and the kilowatt-level amplification subunit respectively through the first optical coupler 40. The pump seed source 20 is used to output continuous pump seed light, and the pre-amplification subunit 30 is used to pre-amplify the continuous pump seed light to obtain pump light that is compatible with the 100-watt-level amplification subunit and the kilowatt-level amplification subunit.

[0038] Specifically, the first optical coupler 40 is a 1×2 fiber optic coupler with a power split ratio of 20:80 at its two output ends. 20% of the optical power is output from the first output end to the 100-watt-level amplification subunit, and the remaining 80% of the optical power is output from the second output end to the kilowatt-level amplification subunit.

[0039] In Embodiment 1, the pump seed source 20 includes a seed amplification subunit, a circulator 204 (CIR), a first optical isolator 206 (ISO), a second optical coupler 207, and a fiber Bragg grating 205 (FBG). The seed amplification subunit, circulator 204, first optical isolator 206, and second optical coupler 207 are sequentially connected to form a closed resonant ring optical path. The fiber Bragg grating 205 is connected to the second port of the circulator 204. The second optical coupler 207 is a 1×2 fiber coupler with a power split ratio of 50:50 at its two outputs. 50% of the optical power is fed back from the first output to the input of the seed amplification subunit to maintain resonance, and the remaining 50% of the optical power is output from the second output as continuous pump seed light to provide a light source for subsequent links.

[0040] Specifically, the seed amplification subunit includes a first pump source 201, a first wavelength division multiplexer 202, and a first gain fiber 203; the input end of the first wavelength division multiplexer 202 is connected to the first output end of the second optical coupler 207, the pump end is connected to the first pump source 201, and the output end is fused to the first end of the first gain fiber 203; the second end of the first gain fiber 203 is fused to the first port of the circulator 204, and the third port of the circulator 204 is connected to the input end of the first optical isolator 206.

[0041] In the pump seed source 20 provided in Example 1: the first gain fiber 203 is an erbium-doped fiber (EDF) with a length of 4m; the first pump source 201 is a 976nm butterfly laser with a maximum power of 500mW; the second optical coupler 207 is a 1×2 fiber coupler with a power splitting ratio of 50:50 at its two output ends; the circulator 204 ensures that the laser enters the second port (port 2) from the first port (port 1), and at port 2, the fiber Bragg grating 205 is used to straighten the laser to the desired wavelength and provides filtering and narrow linewidth. After reflection by the fiber Bragg grating 205, the laser enters the third port (port 3) from port 2; the fiber Bragg grating 205 has a bandwidth of 0.8nm and a center wavelength of 1550nm.

[0042] In Embodiment 1, the pre-amplification subunit 30 includes a second pump source 301, a second wavelength division multiplexer 302, a second gain fiber 303, a second optical isolator 304, and a first bandpass filter 305 (BPF). The input of the second wavelength division multiplexer 302 is connected to the second output of the second optical coupler 207, the pump end is connected to the second pump source 301, and the output is fused to the first end of the second gain fiber 303; the second end of the second gain fiber 303 is connected to the input of the second optical isolator 304, the output of the second optical isolator 304 is connected to the input of the first bandpass filter 305, and the output of the first bandpass filter 305 is connected to the input of the first optical coupler 40.

[0043] In the pre-amplification subunit 30 provided in Example 1: the second pump source 301 is a 976nm butterfly laser with a maximum power of 500mW; the second gain fiber 303 is an erbium-doped fiber with a length of 2.5m; and the bandwidth of the first bandpass filter 305 is within 2nm.

[0044] In Embodiment 1, the 100-watt amplification subunit includes a first acousto-optic modulator 501 (AOM), a third optical isolator 502, a 100-watt pump first-stage amplification component 503, and a 100-watt pump second-stage amplification component 504, which are sequentially optically connected along the signal transmission direction. The 100W pump-stage amplifier 503 includes a third pump source 5031, a first forward combiner 5032, a third gain fiber 5033, a second bandpass filter 5034, and a fourth optical isolator 5035. The input end of the first forward combiner 5032 is connected to the third optical isolator 502, the pump end is connected to the third pump source 5031, and the output end is fused to the first end of the third gain fiber 5033. The second end of the third gain fiber 5033 is fused to the input end of the second bandpass filter 5034, and the output end of the second bandpass filter 5034 is connected to the input end of the fourth optical isolator 5035. The 100W pump secondary amplification assembly 504 includes a fourth pump source 5041, a second forward combiner 5042, a fourth gain fiber 5043, a fifth optical isolator 5044, and a third optical coupler 5045. The input end of the second forward combiner 5042 is connected to the output end of the fourth optical isolator 5045, the pump end is connected to the fourth pump source 5041, and the output end is fused to the first end of the fourth gain fiber 5043. The second end of the fourth gain fiber 5043 is fused to the input end of the fifth optical isolator 5044, the output end of the fifth optical isolator 5044 is connected to the input end of the third optical coupler 5045, and the first output end of the third optical coupler 5045 outputs the first pump light to the Raman pre-amplification unit 12.

[0045] In the 100-watt amplification subunit provided in Example 1: the third pump source 5031 is a 940nm semiconductor laser with a maximum output power of 30W; the third gain fiber 5033 is an erbium-ytterbium co-doped fiber with a length of 2.5m; the second bandpass filter 5034 has a bandwidth of less than 2nm; the fourth pump source 5041 is a 940nm semiconductor laser with a maximum output power of 30W; the fourth gain fiber 5043 is an erbium-ytterbium co-doped fiber with a length of 3m; the third optical coupler 5045 is a 1×2 fiber coupler, whose first output end with a 99% splitting ratio is used to output the corresponding first pump light, and its second output end with a 1% splitting ratio is used to monitor the waveform and spectrum of the first pump light.

[0046] In Embodiment 1, the kilowatt-level amplification subunit includes a second acousto-optic modulator 601, a sixth optical isolator 602, a kilowatt pump first-stage amplification component 603, a kilowatt pump second-stage amplification component 604, and a kilowatt pump third-stage amplification component 605, which are sequentially optically connected along the signal transmission direction. The kilowatt pump-stage amplifier assembly 603 includes a fifth pump source 6031, a third forward combiner 6032, a fifth gain fiber 6033, a third bandpass filter 6034, and a seventh optical isolator 6035. The input end of the third forward combiner 6032 is connected to the sixth optical isolator 602, the pump end is connected to the fifth pump source 6031, and the output end is fused to the first end of the fifth gain fiber 6033. The second end of the fifth gain fiber 6033 is connected to the input end of the third bandpass filter 6034. The output end of the third bandpass filter 6034 is connected to the input end of the seventh optical isolator 6035. The kilowatt-pumped second-stage amplifier assembly 604 includes a sixth gain fiber 6041, a reverse combiner 6042, a sixth pump source 6043, a fourth bandpass filter 6044, and an eighth optical isolator 6045. The first end of the sixth gain fiber 6041 is fused to the output end of the seventh optical isolator 6035, and the second end is fused to the input end of the reverse combiner 6042. The pump end of the reverse combiner 6042 is connected to the sixth pump source 6043, and its output end is connected to the input end of the fourth bandpass filter 6044. The output end of the fourth bandpass filter 6044 is connected to the input end of the eighth optical isolator 6045. The kilowatt-pumped three-stage amplifier assembly 605 includes a seventh pump source 6051, a fourth forward combiner 6052, a seventh gain fiber 6053, a mode field adapter 6054, a ninth optical isolator 6055, and a fourth optical coupler 6056. The input end of the fourth forward combiner 6052 is connected to the output end of the eighth optical isolator 6045, the pump end is connected to the seventh pump source 6051, and the output end is fused to the first end of the seventh gain fiber 6053. The second end of the seventh gain fiber 6053 is connected to the input end of the mode field adapter 6054 (MFA). The output end of the mode field adapter 6054 is connected to the input end of the ninth optical isolator 6055, the output end of the ninth optical isolator 6055 is connected to the input end of the fourth optical coupler 6056, and the first output end of the fourth optical coupler 6056 outputs the second pump light to the Raman main amplifier unit 13.

[0047] Specifically, the mode field adapter 6054 matches fibers with excessively large core-to-core differences, reducing splice loss and ensuring efficient output of optical power and energy. It is important to note that to obtain high-efficiency, high-quality pump-end output, the power of each stage should be set below the saturation power as much as possible to avoid nonlinear effects that prevent power enhancement.

[0048] In the kilowatt-level amplification subunit provided in Example 1: the fifth pump source 6031 is a 940nm semiconductor laser with a maximum output power of 30W; the fifth gain fiber 6033 is an erbium-ytterbium co-doped fiber with a length of 2.5m; the third bandpass filter 6034 has a bandwidth within 2nm; the sixth gain fiber 6041 is an erbium-ytterbium co-doped fiber with a length of 3m; the sixth pump source 6043 is a 940nm semiconductor laser with a maximum output power of 30W; the fourth bandpass filter 6044 has a bandwidth within 2nm; the seventh pump source 6051 is a 940nm semiconductor laser. The laser has a maximum output power of 30W; the seventh gain fiber 6053 is an erbium-ytterbium co-doped fiber with a length of 3m; the mode field adapter 6054 is an optical device operating in the 1550nm band, used to connect a 25 / 300 specification large mode field double-clad fiber to a standard SMF-28e single-mode communication fiber with low loss and high efficiency; the fourth optical coupler 6056 is a 1×2 fiber coupler, whose first output end with a 99% split ratio is used to output the corresponding second pump light, and its second output end with a 1% split ratio is used to monitor the waveform and spectrum of the second pump light.

[0049] Reference Figure 1 and Figure 2 As shown, the specific working process of the U-band high-energy square wave pulse Raman light source module 100 provided in Example 1 is as follows: First, the pump seed source 20 starts working: the first pump source 201 couples the pump light into the first gain fiber 203 through the first wavelength division multiplexer 202. The generated amplified optical signal enters the fiber Bragg grating 205 through port 2 of the circulator 204. After wavelength selection, narrowband filtering and reflection, it is output from port 3 of the circulator 204 to the first optical isolator 206. Then it enters the second optical coupler 207 with 50:50 beam splitting. 50% of the optical power is fed back to the input of the seed amplification subunit to maintain closed-loop resonance and stable oscillation. The other 50% of the optical power is output as continuous pump seed light to the pre-amplification subunit 30.

[0050] Subsequently, the pre-amplification subunit 30 processes the continuous pump seed light: the second pump source 301 couples the pump light into the second gain fiber 303 through the second wavelength division multiplexer 302 to pre-amplify the input continuous pump seed light. The amplified optical signal is suppressed by the second optical isolator 304, and then the first bandpass filter 305 filters out stray noise and amplified spontaneous emission to obtain a pure and power-matched pre-amplified pump light, which is then input to the first optical coupler 40 with a 20:80 split. 20% of the optical power enters the hundred-watt-level amplification subunit, and 80% of the optical power enters the kilowatt-level amplification subunit, providing the basic optical signal for the two-stage pump amplification.

[0051] Next, the 100-watt amplification subunit operates: the pre-amplified pump light is first pulse-modulated by the first acousto-optic modulator 501 (AOM), and the waveform pre-compensation of the pulse signal is performed by the host computer (the pre-compensation signal is as follows). Figure 3 As shown), to ensure that subsequent square wave pulses are flat and stable, the modulated optical signal (output square wave signal as shown) is... Figure 4 (As shown) After passing through the third optical isolator 502, the light sequentially enters the 100W pump first-stage amplification component 503 and the 100W pump second-stage amplification component 504. Through the third pump source 5031 and the fourth pump source 5041, respectively, in conjunction with the forward combiner and the erbium-ytterbium co-doped gain fiber, two stages of stable power amplification are achieved. During the amplification process, the spectrum is purified by the second bandpass filter 5034, and the reverse light interference is suppressed by the multi-stage optical isolator. Finally, the light is output through the third optical coupler 5045 with a 99:1 beam splitting. 99% of the optical power is used as the first pump light input to the Raman pre-amplification unit 12, and 1% of the optical power is used for real-time monitoring of the waveform and spectrum of the first pump light.

[0052] Simultaneously, the kilowatt-level amplification subunit operates synchronously: the pump light from the second output terminal of the first optocoupler 40 is first pulse-modulated by the second acousto-optic modulator 601, and then the upper computer performs waveform pre-compensation on the pulse signal (the pre-compensation signal is as follows). Figure 3 As shown), to ensure that subsequent square wave pulses are flat and stable, the modulated optical signal (output square wave signal as shown) is... Figure 4 (As shown) After passing through the sixth optical isolator 602, the light sequentially passes through the kilowatt-pumped first-stage amplification component 603, the kilowatt-pumped second-stage amplification component 604, and the kilowatt-pumped third-stage amplification component 605. The first-stage amplification achieves initial power enhancement and noise filtering. The second-stage amplification uses a reverse beam-combining pump structure to improve gain and reduce signal impairment. The third-stage amplification achieves kilowatt-level power amplification through forward pumping. The beam quality is optimized in conjunction with the bandpass filters, optical isolators, and mode field adapters 6054 at each stage. Finally, the light is output through the fourth optical coupler 6056 with a 99:1 beam splitting. 99% of the optical power is used as the second pump light input to the Raman main amplification unit 13, and 1% of the optical power is used to monitor the status of the second pump light in real time.

[0053] Finally, the main optical path is amplified and the pulse is output: the initial seed source 11 outputs a U-band pulse seed light, which enters the Raman pre-amplification unit 12 with a forward-pumped structure. The third wavelength division multiplexer 122 couples the U-band pulse seed light with the first pump light output from the 100-watt pump source 121 into the first high nonlinear fiber 123, utilizing the strong Raman effect of the high nonlinear fiber to complete the pre-amplification of the seed light, resulting in a pre-amplified pulse light. The pre-amplified pulse light enters the Raman main amplification unit 13 with a reverse-pumped structure after passing through the tenth optical isolator 131. The fourth wavelength division multiplexer 133 couples it with the second pump light output from the kilowatt pump source 134 into the second high nonlinear fiber 132, further realizing high-energy Raman amplification and outputting a U-band square wave pulse light before phase modulation. The pulse timing deviation between the 100-watt and kilowatt pumps will cause the output to produce two different pulse Raman waveforms, corresponding to the U-band square wave pulse light waveform before phase modulation as follows: Figure 5 As shown. At this point, the waveform superposition effect can be optimized through phase adjustment and timing calibration to obtain the maximum Raman gain output. The optimized waveform is shown below. Figure 6 As shown. Using this structure, a stable U-band Raman source output with a center wavelength of 1645nm, a pulse width of 100ns, a single pulse energy of 10μJ, and a repetition frequency of 20kHz can be achieved.

[0054] This invention addresses the design challenges of the pump end in U-band high-energy Raman pulse light sources by innovatively employing... Figure 2 The overall pump architecture shown effectively overcomes the technical bottleneck of insufficient pump energy due to stimulated Brillouin scattering (SBS) in traditional amplification links. It constructs the overall pump link by combining a self-developed seed source with a multi-stage pre-amplification structure and achieves high-energy Raman pulse output in the 1645nm band using an all-fiber structure. The pulse energy performance is among the leading levels of similar all-fiber U-band Raman light sources in China. Specific advantages are reflected in the following aspects: (1) The self-developed seed source is used, with accurate output wavelength, high spectral purity and low noise, providing a stable and reliable initial light source for subsequent multi-stage pump amplification and Raman conversion, suppressing nonlinear distortion and SBS effect from the source.

[0055] (2) The pulse waveforms of the pump light at the hundred-watt and kilowatt levels are pre-modulated by a dual-channel acousto-optic modulator (AOM) and the phase is precisely controlled by the host computer. This can effectively compensate for timing deviations, optimize the pulse flatness, and obtain regular and stable square wave pulses and maximum Raman gain.

[0056] (3) Different types and lengths of gain fibers are selected for the graded stages. Short-length erbium-doped fibers are used in the seed stage and preamplifier stage to achieve low-noise linear amplification. Erbium-ytterbium co-doped fibers of appropriate length are used in the high-power amplification stage from 100 watts to kilowatts to balance high pump absorption efficiency and high power output capability, while suppressing nonlinear effects.

[0057] (4) A single seed source is used for spectral splitting and hierarchical amplification architecture. By optimizing the spectral splitting ratio, the 100-watt pump and the kilowatt pump can be independently controlled and work together, which not only improves the pump power utilization rate, but also ensures the timing and waveform matching of the two pump stages. (5) The number of pump sources can be flexibly configured. Single or multiple pumps can be used to drive the amplifier stage according to its power requirements. This simplifies the structure, reduces costs, and improves system reliability while ensuring output power.

[0058] (6) Reasonably select high nonlinear optical fiber and optimize its length. Relying on the high nonlinear coefficient, achieve efficient Raman frequency shift and signal amplification. While controlling nonlinear degradation, improve the U-band Raman conversion efficiency. Finally, achieve stable output of high-energy U-band Raman pulse with center wavelength of 1645nm, pulse width of 100ns, single pulse energy of 10μJ, and repetition frequency of 20kHz. The all-fiber structure is compact, reliable, and highly practical for engineering.

[0059] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0060] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A U-band high-energy square wave pulse Raman light source module, characterized in that, It includes an initial seed source, a Raman pre-amplification unit, and a Raman main amplification unit, which are sequentially optically connected along the signal transmission direction; the initial seed source is used to output U-band pulsed seed light. The Raman pre-amplification unit is used to pre-amplify the U-band pulse seed light to obtain pre-amplified pulse light; the Raman main amplification unit is used to main amplify the pre-amplified pulse light to output high-energy U-band square wave pulse light with a single pulse energy ≥5μJ and a pulse width of 80~120ns. The Raman pre-amplification unit employs a forward-pumped structure, with its pump source being a 100-900W peak power pump source; the Raman main amplification unit employs a reverse-pumped structure, with its pump source being a 1-9kW peak power pump source; the gain fibers of both the Raman pre-amplification unit and the Raman main amplification unit have a nonlinear coefficient ≥10W. -1 km -1 Highly nonlinear optical fibers.

2. The U-band high-energy square wave pulse Raman light source module according to claim 1, characterized in that, The U-band high-energy square wave pulse Raman light source module also includes a pump seed source, a pre-amplification subunit, a first optical coupler, a 100-watt-level amplification subunit, and a kilowatt-level amplification subunit; the first pump light output by the 100-watt-level amplification subunit constitutes the 100-watt-level pump source, and the second pump light output by the kilowatt-level amplification subunit constitutes the kilowatt-level pump source. The input end of the pre-amplification subunit is connected to the pump seed source, and the output end is connected to the 100-watt-level amplification subunit and the kilowatt-level amplification subunit respectively through the first optical coupler. The pump seed source is used to output continuous pump seed light, and the pre-amplification subunit is used to pre-amplify the continuous pump seed light to obtain pump light that is compatible with the 100-watt-level amplification subunit and the kilowatt-level amplification subunit.

3. The U-band high-energy square wave pulse Raman light source module according to claim 2, characterized in that, The power splitting ratio between the first output terminal and the second output terminal of the first optical coupler is 1:(3~6).

4. The U-band high-energy square wave pulse Raman light source module according to claim 2, characterized in that, The pump seed source includes a seed amplification subunit, a circulator, a first optical isolator, a second optical coupler, and a fiber Bragg grating; The seed amplification subunit, the circulator, the first optical isolator, and the second optical coupler are sequentially connected to form a closed resonant ring optical path, and the fiber Bragg grating is connected to the second port of the circulator; the second optical coupler is a 1×2 fiber coupler, whose first output end is connected to the input end of the seed amplification subunit, and its second output end is used to output continuous pump seed light.

5. The U-band high-energy square wave pulse Raman light source module according to claim 4, characterized in that, The seed amplification subunit includes a first pump source, a first wavelength division multiplexer, and a first gain fiber; the input end of the first wavelength division multiplexer is connected to the first output end of the second optical coupler, the pump end is connected to the first pump source, and the output end is fused to the first end of the first gain fiber; the second end of the first gain fiber is fused to the first port of the circulator, and the third port of the circulator is connected to the input end of the first optical isolator.

6. The U-band high-energy square wave pulse Raman light source module according to claim 5, characterized in that, The pre-amplification subunit includes a second pump source, a second wavelength division multiplexer, a second gain fiber, a second optical isolator, and a first bandpass filter; The input end of the second wavelength division multiplexer is connected to the second output end of the second optical coupler, the pump end is connected to the second pump source, and the output end is fused to the first end of the second gain fiber; the second end of the second gain fiber is connected to the input end of the second optical isolator, the output end of the second optical isolator is connected to the input end of the first bandpass filter, and the output end of the first bandpass filter is connected to the input end of the first optical coupler.

7. The U-band high-energy square wave pulse Raman light source module according to claim 6, characterized in that, The 100-watt amplification subunit includes a first acousto-optic modulator, a third optical isolator, a 100-watt pump first-stage amplification component, and a 100-watt pump second-stage amplification component, which are sequentially optically connected along the signal transmission direction. The 100-watt pump-stage amplification assembly includes a third pump source, a first forward combiner, a third gain fiber, a second bandpass filter, and a fourth optical isolator. The input end of the first forward combiner is connected to the third optical isolator, the pump end is connected to the third pump source, and the output end is fused to the first end of the third gain fiber. The second end of the third gain fiber is fused to the input end of the second bandpass filter, and the output end of the second bandpass filter is connected to the input end of the fourth optical isolator. The 100W pump-secondary amplification assembly includes a fourth pump source, a second forward combiner, a fourth gain fiber, a fifth optical isolator, and a third optical coupler. The input end of the second forward combiner is connected to the output end of the fourth optical isolator, the pump end is connected to the fourth pump source, and the output end is fused to the first end of the fourth gain fiber. The second end of the fourth gain fiber is fused to the input end of the fifth optical isolator, the output end of the fifth optical isolator is connected to the input end of the third optical coupler, and the first output end of the third optical coupler outputs the first pump light to the Raman pre-amplification unit.

8. The U-band high-energy square wave pulse Raman light source module according to claim 7, characterized in that, The kilowatt-level amplification subunit includes a second acousto-optic modulator, a sixth optical isolator, a kilowatt pump first-stage amplification component, a kilowatt pump second-stage amplification component, and a kilowatt pump third-stage amplification component, which are sequentially optically connected along the signal transmission direction. The kilowatt pump-stage amplification assembly includes a fifth pump source, a third forward combiner, a fifth gain fiber, a third bandpass filter, and a seventh optical isolator. The input end of the third forward combiner is connected to the sixth optical isolator, the pump end is connected to the fifth pump source, and the output end is fused to the first end of the fifth gain fiber. The second end of the fifth gain fiber is connected to the input end of the third bandpass filter, and the output end of the third bandpass filter is connected to the input end of the seventh optical isolator. The kilowatt-pump secondary amplification assembly includes a sixth gain fiber, a reverse combiner, a sixth pump source, a fourth bandpass filter, and an eighth optical isolator. The first end of the sixth gain fiber is fused to the output end of the seventh optical isolator, and the second end is fused to the input end of the reverse combiner. The pump end of the reverse combiner is connected to the sixth pump source, and its output end is connected to the input end of the fourth bandpass filter. The output end of the fourth bandpass filter is connected to the input end of the eighth optical isolator. The kilowatt-pump three-stage amplification assembly includes a seventh pump source, a fourth forward combiner, a seventh gain fiber, a mode field adapter, a ninth optical isolator, and a fourth optical coupler. The input end of the fourth forward combiner is connected to the output end of the eighth optical isolator, the pump end is connected to the seventh pump source, and the output end is fused to the first end of the seventh gain fiber. The second end of the seventh gain fiber is connected to the input end of the mode field adapter. The output end of the mode field adapter is connected to the input end of the ninth optical isolator, the output end of the ninth optical isolator is connected to the input end of the fourth optical coupler, and the first output end of the fourth optical coupler outputs the second pump light to the Raman main amplification unit.

9. The U-band high-energy square wave pulse Raman light source module according to claim 8, characterized in that, The first and second gain fibers are both erbium-doped fibers, each with a length of 0.5 to 5 m; the third, fourth, fifth, sixth, and seventh gain fibers are all erbium-ytterbium co-doped fibers, each with a length of 1 to 5 m.

10. The U-band high-energy square wave pulse Raman light source module according to claim 8, characterized in that, The second optical coupler is a 1×2 fiber optic coupler, and the power splitting ratio between its first output end and the second output end is 1:(1~2); the third optical coupler and the fourth optical coupler are both 1×2 fiber optic couplers, and their first output end with a 99% splitting ratio is used to output the corresponding pump light, and their second output end with a 1% splitting ratio is used to monitor the waveform and spectrum of the corresponding pump light.

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