A continuous U-band high-gain Raman fiber amplification module

Abstract

This invention provides a continuous U-band high-gain Raman fiber amplification module. It utilizes a Raman gain fiber with a dedicated gain peak at a 13 THz frequency shift, coupled with a broadband pump source with a 3 dB spectral width of at least 10 nm. A pump signal combiner is used to achieve efficient fusion coupling between the pump light and the U-band signal, ensuring that the broadband pump energy is precisely matched to the amplification requirements of the U-band signal. This achieves efficient high-gain amplification of the U-band signal, filling the amplification capability gap in this band of traditional amplifiers, ensuring the stability and efficiency of the amplification process, and ultimately outputting a high-purity, high-gain U-band laser signal. Compared with traditional Raman methods, this invention's Thraman fiber amplification module has advantages such as simple structure, high gain, and low cost, and has significant practical value and application prospects.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and in particular to a continuous U-band high-gain Raman fiber amplification module. Background Technology

[0002] Fiber lasers, due to their outstanding advantages such as simple structure, high beam quality, and high conversion efficiency, have been widely used in many important fields such as optical communication, industrial processing, biomedicine, and sensing. With the continuous improvement of fiber fabrication technology and the rapid development of high-brightness semiconductor laser diode pump sources, the output power of fiber lasers has been increased rapidly, further expanding their application scenarios.

[0003] However, most conventional high-power fiber lasers currently rely on rare-earth ion-doped fibers for gain. Limited by the energy level structure of rare-earth ions, these lasers can only operate in specific wavelength bands and cannot achieve wide-range wavelength tuning, making it difficult to meet the application requirements of specific wavelength lasers in specialized fields such as sodium guide stars and atmospheric remote sensing. Meanwhile, the traditional erbium-doped fiber amplifiers widely used in existing fiber optic communication systems can only amplify the C-band (1530–1565 nm) or L-band (1565–1625 nm) separately, making it difficult to amplify the U-band (1625–1675 nm). Even if amplification is possible, the gain effect is poor, exhibiting significant limitations in band amplification.

[0004] The aforementioned technical limitations not only severely restrict the application expansion of fiber lasers in specialized fields such as sodium guiding stars and atmospheric remote sensing, but also limit the further upgrading of communication transmission. Meanwhile, the demand gap for U-band related applications makes the development of related equipment capable of achieving high-gain amplification in the U-band an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous U-band high-gain Raman fiber amplification module to solve the technical problem that existing fiber amplification modules have poor gain performance in U-band amplification.

[0006] To solve the above technical problems, the present invention provides a continuous U-band high-gain Raman fiber amplification module, comprising a U-band signal source, a Raman amplification unit and a filtering unit connected sequentially along the signal transmission direction; the Raman amplification unit includes a broadband pump source, a pump signal combiner and a Raman gain fiber, wherein the 3dB spectral width of the broadband pump source is not less than 10nm. The pump signal combiner includes multiple input terminals and one output terminal. The number of input terminals is equal to the sum of the number of output terminals of the broadband pump source and the number of output terminals of the U-band signal source. The input terminals of the pump signal combiner are fused to the broadband pump source and the U-band signal source, respectively, and the output terminal is fused to the first end of the Raman gain fiber. The Raman gain fiber is an fiber with a Raman gain peak at a frequency shift of 13 THz to match the U-band signal and achieve dedicated amplification.

[0007] Specifically, the continuous U-band high-gain Raman fiber amplification module provided by this invention optimizes the adaptation design of the pump signal combiner, allowing the number of input ends of the combiner to be flexibly adjusted according to the number of output ends of the broadband pump source and the U-band signal source, without being limited by fixed input ports. It is compatible with different pump configurations such as single pump and multi-pump, and the input structure can be flexibly adjusted according to actual power and gain requirements. When combined with a broadband pump source with a spectral width of not less than 10nm and a Raman gain fiber with a dedicated gain peak at a 13THz frequency shift, it can accurately convert pump energy into U-band signal gain, breaking through the inherent limitation of traditional erbium-doped amplifiers that can only cover the C / L band, and efficiently achieving high-gain amplification of U-band signals. It effectively fills the capability gap of traditional amplification schemes in the U-band, taking into account both the adaptability of the scheme and the amplification efficiency, and can flexibly meet the application needs of different scenarios.

[0008] Preferably, the broadband pump source includes a broadband seed source, an optical isolator, an optical filter, and an amplification subunit; the input end of the optical isolator is connected to the broadband seed source, its output end is connected to the input end of the optical filter, and the output end of the optical filter is connected to the amplification subunit.

[0009] Specifically, the broadband seed source provides a stable initial signal, the optical isolator effectively blocks backlight interference, prevents signal reflection from damaging the module, and ensures stable transmission of pump energy; the optical filter removes interference signals such as pump light and stray light, improving signal purity; and the amplification subunit further enhances the pump energy, providing sufficient power for U-band signal amplification.

[0010] Preferably, the amplification subunit includes a pump amplification component and an optical fiber coupler; the input end of the pump amplification component is connected to the output end of the optical filter, its output end is connected to the first input end of the optical fiber coupler, and the first output end of the optical fiber coupler is connected to the input end of the pump signal combiner.

[0011] Specifically, the pump amplification component, as the core internal structure of the broadband pump source, is responsible for providing stable and continuous pump energy to provide sufficient power for U-band signal amplification; the fiber optic coupler is responsible for separating and transmitting the pump signal from the U-band signal to avoid signal interference.

[0012] Preferably, the pump amplification component is any one of a forward pumping structure, a reverse pumping structure, or a bidirectional pumping structure.

[0013] Specifically, the forward pump structure can provide higher gain efficiency and is suitable for scenarios with high amplification rate requirements; the reverse pump structure can effectively suppress spontaneous emission noise during amplification and improve the spectral purity of the output signal, making it suitable for high-precision detection applications; while the bidirectional pump structure can balance high gain and low noise characteristics.

[0014] Preferably, the fiber optic coupler is a 2×2 fiber optic coupler with a splitting ratio of 1:99, and the splitting ratios corresponding to the first input end and the first output end of the fiber optic coupler are both 99%. The forward monitoring port of the fiber optic coupler has a splitting ratio of 1% and is used to monitor the output laser of the pump amplifier component in real time; the reverse monitoring port of the fiber optic coupler has a splitting ratio of 1% and is used to monitor the stimulated Brillouin scattering signal generated in the main optical path in real time.

[0015] Specifically, this invention employs a 2×2 fiber coupler with a splitting ratio of 1:99. This ensures that the vast majority of pump energy is efficiently input into the main optical path through a 99% main path splitting ratio, avoiding pump energy loss and providing ample power support for U-band Raman amplification. Furthermore, it achieves dual-path real-time monitoring through two 1% splitting ports: the forward monitoring port can collect the output laser status of the pump amplification component in real time, facilitating real-time adjustment of pump power and ensuring the stability of U-band gain; the reverse monitoring port can capture the stimulated Brillouin scattering signal generated in the main optical path in real time, enabling timely warning of nonlinear effects risks under high-power operation and preventing scattering signals from interfering with the amplification process or damaging devices. This achieves full-time monitoring of the module's operating status without affecting the main optical path amplification efficiency.

[0016] Preferably, the Raman fiber amplification module further includes a fiber circulator and a chirped grating; the first port of the fiber circulator is fused to the second end of the Raman gain fiber, its second port is connected to the chirped grating, and its third port is connected to the filtering unit.

[0017] Specifically, the fiber optic circulator guides the amplified signal output from the Raman gain fiber from the first port to the second port, which then feeds it into the chirped grating. The target signal reflected back from the chirped grating is then guided from the third port to the subsequent filtering unit. At the same time, it completely blocks the reverse injection of reflected light into the Raman gain fiber, avoiding interference from reverse stray light in the amplification process and damage to the front-end devices, thus ensuring stable unidirectional transmission of the optical path. The chirped grating, relying on its broadband high reflectivity, reflects almost all of the Raman signal in the entire U-band back to the fiber optic circulator. At the same time, it allows stray light such as residual pump light and broadband spontaneous emission noise from outside the band to be directly transmitted and dissipated, completing the first-stage broadband coarse filtering and completely screening out the effective target U-band signal, laying the foundation for subsequent narrowband fine filtering.

[0018] Preferably, the chirped grating has a peak reflectivity of ≥99%, a center wavelength of 1625~1675nm, and a reflection bandwidth of ≥40nm.

[0019] Specifically, the peak reflectivity of the chirped grating is set to no less than 99%, which allows almost all effective signals in the U-band to be reflected back to the fiber optic circulator, greatly reducing the transmission loss of the target signal and ensuring the energy utilization rate of the high-gain Raman signal. The center wavelength of the chirped grating can be precisely matched with the wavelength range of the target Raman signal in the U-band, ensuring that the response band of the grating is completely aligned with the effective signal to be amplified, avoiding signal leakage or mis-filtering caused by band offset. The reflection bandwidth is set to no less than 40nm, which can completely cover the entire signal range of the U-band, ensuring that all effective Raman signals in the U-band can be responded to by the grating.

[0020] Preferably, the filtering unit is a U-band narrowband fiber optic filter with an operating wavelength of 1625nm to 1675nm, a 3dB bandwidth of 1nm to 10nm, an out-of-band rejection ratio of ≥35dB, and an insertion loss of ≤1.5dB.

[0021] Specifically, the 1625nm–1675nm U-band range perfectly matches the target signal band selected by the pre-amplifier, ensuring the complete transmission of the effective signal; the 3dB bandwidth range enables fine signal gating within the U-band, effectively filtering out in-band spontaneous emission (ASE) noise generated during Raman amplification and significantly improving the spectral purity of the output signal; the high out-of-band suppression ratio can deeply suppress out-of-band interference such as residual pump light and stimulated Brillouin scattering stray light that were not completely filtered out by the pre-amplifier, thoroughly purifying the output signal; the low insertion loss can maximize the retention of the high gain obtained by the pre-amplifier Raman amplification, avoiding additional signal energy loss, and ultimately outputting a high-purity, high-power U-band laser signal.

[0022] Preferably, the matrix material of the Raman gain fiber is selected from one of quartz, phosphate, silicate, tellurite or fluoride.

[0023] Specifically, quartz-based optical fibers have mature technology and low transmission loss, making them suitable for conventional U-band optical communication scenarios; phosphate and tellurate-based optical fibers have higher Raman gain coefficients, enabling high-gain amplification of U-band signals with shorter fiber lengths, which is beneficial for miniaturized module design and suitable for detection scenarios with size requirements; fluoride-based optical fibers have a wider infrared transmission range, which can further reduce the transmission loss of U-band signals and meet the needs of high-precision, long-distance signal transmission.

[0024] Preferably, the U-band signal source is selected from one of fiber lasers, semiconductor lasers, and gas lasers.

[0025] Specifically, semiconductor lasers are inexpensive and compact, meeting the application needs of low-cost commercial communication scenarios; fiber lasers have excellent beam quality and stable output power, making them suitable for medium-to-high power industrial processing and conventional optical communication scenarios; while gas lasers have the advantages of narrow linewidth and high wavelength accuracy, meeting the application needs of high-precision special fields such as sodium guiding stars and atmospheric remote sensing.

[0026] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a continuous U-band high-gain Raman fiber amplification module. It utilizes a Raman gain fiber with a dedicated gain peak at a 13 THz frequency shift, coupled with a broadband pump source with a 3 dB spectral width of not less than 10 nm. A pump signal combiner is used to achieve efficient fusion coupling between the pump light and the U-band signal, ensuring that the broadband pump energy precisely matches the amplification requirements of the U-band signal. This achieves efficient high-gain amplification of the U-band (1625~1675 nm) signal, filling the amplification capability gap in this band of traditional amplifiers. It effectively solves the technical pain points of insufficient U-band signal gain and poor band adaptability in existing technologies, ensuring the stability and efficiency of the amplification process. The final output is a high-purity, high-gain U-band laser signal suitable for special fields such as methane detection, atmospheric remote sensing, and optical communication capacity expansion. Compared with traditional Raman methods, this invention's Thyraman fiber amplification module has advantages such as simple structure, high gain, and low cost, and has significant practical value and application prospects. Attached Figure Description

[0027] Figure 1 A schematic diagram of the structure of the continuous U-band high-gain Raman fiber amplifier module provided by the present invention; Figure 2 This is a schematic diagram of the structure of the continuous U-band high-gain Raman fiber amplifier module provided in Embodiment 1; Figure 3 This is a schematic diagram of the structure of the continuous U-band high-gain Raman fiber amplifier module provided in Embodiment 2; In the attached diagram: 100—Raman fiber amplification module; 10—U-band signal source; 20—Broadband pump source; 30—Pump signal combiner; 40—Raman gain fiber; 50—Filtering unit; 60—Fiber circulator; 70—Chirped grating. 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] To address the shortcomings of existing technologies, this invention aims to provide a continuous U-band high-gain Raman fiber amplification module. This module relies on stimulated Raman scattering and boasts unique advantages such as a wide Raman gain spectrum, cascaded operation, and no need for phase matching. It only requires matching a pump laser of the corresponding wavelength to achieve flexible wavelength adaptation within the fiber's transparent range, effectively compensating for the limited band coverage of traditional amplification schemes. This U-band (1625–1675 nm) high-gain amplification scheme, which can fill the gaps in specialized fields such as methane detection and network maintenance, possesses extremely high research value and broad application prospects.

[0030] Specifically, the structure of the continuous U-band high-gain Raman fiber amplification module 100 provided by the present invention is as follows: Figure 1 As shown, it includes a U-band signal source 10, a Raman amplification unit, and a filtering unit 50 connected sequentially along the signal transmission direction; the Raman amplification unit includes a broadband pump source 20, a pump signal combiner 30, and a Raman gain fiber 40, and the 3dB spectral width of the broadband pump source 20 is not less than 10nm. The input end of the pump signal combiner 30 is fused to the broadband pump source 20 and the U-band signal source 10, respectively, and the output end is fused to the first end of the Raman gain fiber 40. The Raman gain fiber 40 is selected from fibers with Raman gain peaks at a frequency shift of 13 THz, in order to match the U-band signal and achieve dedicated amplification.

[0031] Specifically, the Raman fiber amplification module 100 provides a target broadband signal through a U-band signal source 10, and outputs high-power pump light through a self-made broadband pump source 20. The two optical signals are coupled and injected into the Raman gain fiber 40 via a pump signal combiner 30. The pump energy is converted into U-band Raman light by relying on the dedicated Raman gain peak near the 13THz mid-frequency shift of the Raman gain fiber 40. Finally, the high-purity, high-gain U-band Raman signal is obtained by filtering through a filter unit 50. Compared with traditional Raman amplification schemes, this scheme has a simple structure, excellent gain performance, and low deployment cost, and has extremely high practical value and broad application prospects.

[0032] The technical solution of the present invention will now be described in conjunction with specific embodiments.

[0033] Example 1: Please see Figure 2 Example 1 provides a continuous U-band high-gain Raman fiber amplification module 100, including a U-band signal source 10, a Raman amplification unit and a filtering unit 50 connected sequentially along the signal transmission direction; the Raman amplification unit includes a broadband pump source 20, a pump signal combiner 30 and a Raman gain fiber 40, and the 3dB spectral width of the broadband pump source 20 is not less than 10nm. Among them, the pump signal combiner 30 is a (1+1)×1 type combiner, which is used to connect the pump light and the signal light respectively; the input end of the pump signal combiner 30 is fused to the broadband pump source 20 and the U-band signal source 10 respectively, and the output end is fused to the first end of the Raman gain fiber 40; the Raman gain fiber 40 is selected to have a Raman gain peak at a frequency shift of 13THz, so as to match the U-band signal to achieve dedicated amplification.

[0034] In Example 1, the broadband design in the broadband pump source 20 can increase the Brillouin scattering threshold and effectively suppress the adverse effects of stimulated Brillouin scattering on Raman amplification under long-distance transmission conditions, thereby obtaining high-gain Raman light. The broadband pump source 20 includes a broadband seed source, an optical isolator, an optical filter, and an amplification subunit; the input of the optical isolator is connected to the broadband seed source, its output is connected to the input of the optical filter, and the output of the optical filter is connected to the amplification subunit.

[0035] Specifically, the amplification subunit includes a pump amplification component and an optical fiber coupler; the input end of the pump amplification component is connected to the output end of the optical filter, its output end is connected to the first input end of the optical fiber coupler, and the first output end of the optical fiber coupler is connected to the input end of the pump signal combiner 30.

[0036] In this embodiment 1, the pump amplification component is a forward pumping structure, including a semiconductor laser, a wavelength division multiplexer, and a pump gain fiber; wherein, the pump end of the wavelength division multiplexer is connected to the semiconductor laser, the input end is connected to the output end of the optical filter, and the output end is fused to the first end of the pump gain fiber; the second end of the pump gain fiber is connected to the first input end of the fiber coupler.

[0037] In this embodiment 1, the fiber coupler is a 2×2 fiber coupler with a splitting ratio of 1:99. The splitting ratios corresponding to the first input end and the first output end of the fiber coupler are both 99%. The splitting ratio of the forward monitoring port of the fiber coupler is 1%, which is used to monitor the output laser of the pump amplification component in real time. The splitting ratio of the reverse monitoring port of the fiber coupler is 1%, which is used to monitor the stimulated Brillouin scattering signal generated in the main optical path in real time.

[0038] In this embodiment 1, the Raman fiber amplification module 100 further includes a fiber circulator 60 and a chirped grating 70; the first port of the fiber circulator 60 is fused to the second end of the Raman gain fiber 40, the second port is connected to the chirped grating 70, and the third port is connected to the filter unit 50. The Raman light signal enters from the first port, is output to the chirped grating 70 from the second port, is reflected by the chirped grating 70, returns to the circulator from the second port, and is then output to the filter unit 50 from the third port. The chirped grating 70 is used to filter out the U-band Raman light.

[0039] In this embodiment 1, the detailed parameters of each component of the Raman fiber amplification module 100 are as follows: The broadband pump source 20 includes a broadband seed source, an optical isolator, an optical filter, and an amplification subunit. The broadband seed source has a laser power of not less than 6W and a side-mode rejection ratio (SMSR) greater than 55dB. The optical filter has a bandwidth of not less than 10nm. The amplification subunit consists of a semiconductor laser, a wavelength division multiplexer, a pump gain fiber, and a fiber coupler. The semiconductor laser operates at a wavelength of 940nm and has an output power of 30W. The pump gain fiber is an erbium-ytterbium co-doped double-clad fiber with an absorption coefficient of 75dB. The fiber coupler is a 2×2 fiber coupler with a splitting ratio of 1:99. The U-band signal source 10 uses a narrow-linewidth semiconductor laser with a working wavelength of 1645nm and a maximum output power of 30mW. Raman gain fiber 40 is a single-mode fiber with a matrix material of quartz and a Raman gain density of 1.2 / (W·km); The chirped grating 70 has a peak reflectivity of 99% (which can improve the Raman light gain effect), a center wavelength that is matched to the target U-band output wavelength (1645nm), and a reflection bandwidth of 40nm; The filter unit 50 is a U-band narrowband fiber optic filter with a working wavelength of 1645nm, a 3dB bandwidth of 5nm, an out-of-band rejection ratio of 10dB, and an insertion loss of ≤1dB.

[0040] Furthermore, the specific working process of the continuous U-band high-gain Raman fiber amplification module 100 provided in Example 1 is as follows: (1) Start the broadband pump source 20. The broadband seed source outputs the initial broadband signal. This signal is isolated by the optical isolator to avoid the interference of the reverse stray light with the subsequent link. Then, the irrelevant clutter is filtered out by the optical filter to obtain a pure pump signal. After the pump signal enters the amplification subunit, the pump energy is provided by the semiconductor laser. After being integrated by the wavelength division multiplexer and amplified by the pump gain fiber, it is sent to the 2×2 fiber coupler with a split ratio of 1:99 to output broadband pump light (laser power above 6W, SMSR greater than 55dB).

[0041] (2) The fiber coupler inputs 99% of the pump energy into the main optical path for subsequent signal amplification, and at the same time realizes the operation status monitoring through the 1% beam splitting part; at the same time, the U-band signal source 10 (semiconductor laser) outputs the initial U-band signal (1645nm, maximum power 30mw, narrow linewidth), which, together with the pump signal processed by the fiber coupler, is connected to the pump signal combiner 30. The pump signal combiner 30 integrates the two signals into one and accurately injects it into the Raman gain fiber 40.

[0042] (3) Within the Raman gain fiber 40, relying on its quartz matrix characteristics and 1.2 / (W With a Raman gain density of (km), the pump signal energy is efficiently transferred to the initial U-band signal, achieving high-gain amplification of the U-band signal. The amplified Raman optical signal is output from the Raman gain fiber 40 and fused to the first port (port 1) of the fiber optic circulator 60. The fiber optic circulator 60 follows a unidirectional transmission rule, allowing the signal to propagate only along the direction from the first port to the third port (port 3), effectively blocking reverse light transmission and avoiding reverse interference.

[0043] (4) The Raman light signal is transmitted from the first port of the fiber optic circulator 60 to the second port (port 2) and then output to the chirped grating 70. With a peak reflectivity of 99% and a reflection bandwidth of 40nm, the chirped grating 70 accurately filters out out-of-band clutter in the Raman light, retaining only the U-band Raman light that meets the requirements and reflecting it back to the second port of the fiber optic circulator 60. The pure U-band Raman light after reflection continues to be directionally transmitted inside the fiber optic circulator 60 to the third port for output and enters the filtering unit 50.

[0044] (5) The U-band narrowband fiber optic filter, designed for a working wavelength of 1625nm to 1675nm, utilizes a 3dB bandwidth of 5nm, an out-of-band rejection ratio of 10dB, and an insertion loss of ≤1dB to further filter out residual clutter and interference signals, maximizing signal energy retention and ultimately outputting a high-purity, high-gain target U-band signal (1645nm). The third port of the fiber optic circulator 60 is the system's main signal output port, used to connect to the filter unit 50. Throughout the process, the monitoring function of the fiber optic coupler operates synchronously, providing real-time feedback on the equipment's operating status to ensure the stability and reliability of the entire amplification link.

[0045] Example 2: Please see Figure 3 This embodiment 2 provides a continuous U-band high-gain Raman fiber amplification module 100, whose structure is roughly the same as that of the Raman fiber amplification module 100 provided in embodiment 1, with the only difference being: The Raman gain fiber 40 provided in Example 2 is a phosphorus-doped fiber with phosphate as the matrix material and a Raman gain density of 1.9 / (W·km). In this case, Example 2 finally outputs a target U-band signal of 1645nm, and its final amplification power is approximately 1.58 times that of Example 1.

[0046] Compared with existing technologies, this invention has the following advantages: Compared with the limitations of traditional rare-earth ion-doped fiber amplifiers, which are restricted by energy level structure and can only cover specific wavebands, and the problems of insufficient gain and poor adaptability of traditional Raman amplification schemes, this invention relies on stimulated Raman scattering effect. By using a broadband pump source 20 and a Raman gain fiber 40 with a dedicated gain peak at a 13THz frequency shift, it can accurately achieve high-gain amplification of U-band signals, filling the technological gap in special fields such as methane detection and atmospheric remote sensing. At the same time, the optimized structural design adopts a pump signal combiner 30 that can flexibly adapt to the number of input ports, combined with a fiber coupler with monitoring function and a high-efficiency filter unit 50. This effectively suppresses Brillouin scattering and avoids backlight interference, while also being simple in structure, low in cost, and highly adaptable. Moreover, it can flexibly meet the needs of different scenarios by using a variety of selectable matrix materials and signal source types, making it highly practical and with broad application prospects.

[0047] 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.

[0048] 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 continuous U-band high-gain Raman fiber amplification module, characterized in that, It includes a U-band signal source, a Raman amplification unit, and a filtering unit connected sequentially along the signal transmission direction; the Raman amplification unit includes a broadband pump source, a pump signal combiner, and a Raman gain fiber, and the 3dB spectral width of the broadband pump source is not less than 10nm; The pump signal combiner includes multiple input terminals and one output terminal. The number of input terminals is equal to the sum of the number of output terminals of the broadband pump source and the number of output terminals of the U-band signal source. The input terminals of the pump signal combiner are fused to the broadband pump source and the U-band signal source, respectively, and the output terminal is fused to the first end of the Raman gain fiber. The Raman gain fiber is an optical fiber with a Raman gain peak at a 13THz frequency shift to match the U-band signal and achieve dedicated amplification.

2. The continuous U-band high-gain Raman fiber amplification module according to claim 1, characterized in that, The broadband pump source includes a broadband seed source, an optical isolator, an optical filter, and an amplification subunit; the input end of the optical isolator is connected to the broadband seed source, its output end is connected to the input end of the optical filter, and the output end of the optical filter is connected to the amplification subunit.

3. The continuous U-band high-gain Raman fiber amplification module according to claim 2, characterized in that, The amplification subunit includes a pump amplification component and an optical fiber coupler; the input end of the pump amplification component is connected to the output end of the optical filter, its output end is connected to the first input end of the optical fiber coupler, and the first output end of the optical fiber coupler is connected to the input end of the pump signal combiner.

4. The continuous U-band high-gain Raman fiber amplification module according to claim 3, characterized in that, The pump amplification component can be any one of a forward pumping structure, a reverse pumping structure, or a bidirectional pumping structure.

5. The continuous U-band high-gain Raman fiber amplification module according to claim 3, characterized in that, The fiber optic coupler is a 2×2 fiber optic coupler with a splitting ratio of 1:99, and the splitting ratios corresponding to the first input end and the first output end of the fiber optic coupler are both 99%. The forward monitoring port of the fiber optic coupler has a splitting ratio of 1% and is used to monitor the output laser of the pump amplification component in real time; the reverse monitoring port of the fiber optic coupler has a splitting ratio of 1% and is used to monitor the stimulated Brillouin scattering signal generated in the main optical path in real time.

6. The continuous U-band high-gain Raman fiber amplification module according to claim 1, characterized in that, The Raman fiber amplification module further includes a fiber circulator and a chirped grating; the first port of the fiber circulator is fused to the second end of the Raman gain fiber, its second port is connected to the chirped grating, and its third port is connected to the filtering unit.

7. The continuous U-band high-gain Raman fiber amplification module according to claim 6, characterized in that, The chirped grating has a peak reflectivity of ≥99%, a center wavelength of 1625~1675nm, and a reflection bandwidth of ≥40nm.

8. The continuous U-band high-gain Raman fiber amplification module according to claim 6, characterized in that, The filtering unit is a U-band narrowband fiber optic filter with a working wavelength of 1625nm to 1675nm, a 3dB bandwidth of 1nm to 10nm, an out-of-band rejection ratio of ≥35dB, and an insertion loss of ≤1.5dB.

9. The continuous U-band high-gain Raman fiber amplification module according to claim 1, characterized in that, The matrix material of the Raman gain fiber is selected from one of quartz, phosphate, silicate, tellurite or fluoride.

10. The continuous U-band high-gain Raman fiber amplification module according to claim 1, characterized in that, The U-band signal source is selected from one of fiber lasers, semiconductor lasers, and gas lasers.

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