Intermediate infrared polarization-maintaining wavelength broadband tunable Raman soliton laser light source

Abstract

The invention discloses a mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser light source which comprises a polarization-maintaining laser, a polarization-maintaining cascade structure and a polarization-maintaining optical fiber amplifier which are connected in sequence. The polarization-maintaining laser outputs 2-micron femtosecond pulses; the polarization-maintaining cascade structure comprises a second pumping source LD, a second wavelength division multiplexer WDM, a second polarization-maintaining thulium-doped fiber PM-TDF and a polarization-maintaining germanium-doped silica fiber; and the polarization-maintaining optical fiber amplifier comprises a third pumping source LD, a third wavelength division multiplexer WDM and a polarization-maintaining erbium-doped fluorotellurite optical fiber. According to the invention, a full polarization-maintaining structure is adopted, so that low-noise and high-stability laser output is realized; through a cascade structure and a special optical fiber material, broadband tunable Raman soliton output in a wave band of 2-5 microns is realized; an all-fiber structure is adopted, a thulium-doped fiber laser light source is used for directly pumping a high-nonlinearity fiber, and an erbium-doped fiber amplifier and fluorotellurite are combined into the polarization-maintaining erbium-doped fluorotellurite fiber amplifier, so that the integration level and the stability of a system are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of laser light sources, and particularly to a mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser light source. Background Art

[0002] Mid-infrared band (2 - 5μm) laser light sources have important application values in fields such as molecular spectroscopy, environmental monitoring, medical surgery, material processing, and national defense security. For example, many gas molecules have characteristic absorption peaks in the mid-infrared band, which can be used for highly sensitive gas detection; at the same time, the absorption characteristics of mid-infrared lasers in biological tissues make them ideal tools for precise medical surgery. In recent years, fiber-based Raman soliton laser technology has become a research hotspot for mid-infrared laser light sources due to its wide tuning range, high beam quality, and compact structure.

[0003] Raman soliton laser technology uses the nonlinear effects in optical fibers (such as soliton self-frequency shift) to achieve wavelength tuning, and can cover a wide band from near-infrared to mid-infrared. Among them, thulium-doped fiber lasers (2μm band) and erbium-doped fluorotellurite fiber lasers (2.8 - 5μm band) have become key technologies for realizing broadband tunable laser output due to their excellent performance in the mid-infrared band.

[0004] However, the prior art still faces many challenges in the realization of mid-infrared laser light sources:

[0005] (1) Poor system stability and low Raman conversion efficiency: The stability of mid-infrared fiber lasers is affected by factors such as environmental temperature, fiber polarization state, and pump light source fluctuations. In the prior art, there is a lack of effective polarization-maintaining design and dispersion compensation mechanism, resulting in low stability and signal-to-noise ratio of laser output, and it is difficult to meet the requirements of high-precision applications. Unstable seed sources will lead to unstable power during the subsequent amplification and frequency shift processes of the system, and further cause unstable frequency shift wavelengths. The soliton self-frequency shift effect is mainly driven by the nonlinear effects in optical fibers (such as Raman scattering). The polarization state will affect the nonlinear response of light in the optical fiber, and different polarization states may lead to different intensities of nonlinear effects, thus affecting the efficiency and rate of soliton self-frequency shift.

[0006] (2) Limited wavelength tuning range: Existing mid-infrared fiber lasers usually rely on a single gain medium (such as thulium-doped or erbium-doped fiber), and their wavelength tuning range is limited by the energy level structure of the gain medium and the nonlinear characteristics of the optical fiber. The tuning range of thulium-doped fiber lasers is usually limited to 1.9 - 2.1μm, while that of erbium-doped fiber lasers is between 2.8 - 3.5μm, and it is difficult to cover a wider mid-infrared band. The Raman soliton self-frequency shift effect can expand the wavelength tuning range, but its efficiency is limited by the nonlinear coefficient and dispersion characteristics of the optical fiber.

[0007] (3) Lack of broadband tunable integrated solution: In the existing technology, discrete devices or multi-stage amplification structures are usually adopted to achieve mid-infrared laser output, resulting in a complex system, large volume and high cost. There is a lack of a broadband tunable integrated solution from 2μm to 5μm, which limits the flexibility and applicability of mid-infrared laser light sources in practical applications. Summary of the Invention

[0008] The object of the present invention is to overcome the deficiencies of the existing technology and provide a mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser light source.

[0009] The object of the present invention is achieved by the following technical solutions:

[0010] In the first aspect of the present invention, a mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser light source is provided, which includes a polarization-maintaining laser, a polarization-maintaining cascaded structure and a polarization-maintaining fiber amplifier connected in sequence;

[0011] The polarization-maintaining laser outputs femtosecond pulses of 2μm;

[0012] The polarization-maintaining cascaded structure includes a second pump source LD, a second wavelength division multiplexer WDM, a second polarization-maintaining thulium-doped fiber PM-TDF and a polarization-maintaining germanium-doped silica fiber; the 1570nm pump of the second pump source LD is connected to the pump end of the second wavelength division multiplexer WDM, the signal end of the second wavelength division multiplexer WDM is connected to the 2μm femtosecond pulses, and the common end of the second wavelength division multiplexer WDM is sequentially connected to the second polarization-maintaining thulium-doped fiber PM-TDF and the polarization-maintaining germanium-doped silica fiber, and outputs broadband tunable laser output of 2 - 2.8μm;

[0013] The polarization-maintaining fiber amplifier includes a third pump source LD, a third wavelength division multiplexer WDM, and a polarization-maintaining erbium-fluorotellurite fiber; the 980nm pump of the third pump source LD is connected to the pump end of the third wavelength division multiplexer WDM, the signal end of the third wavelength division multiplexer WDM is connected to the 2 - 2.8μm broadband tunable laser output, and the common end of the third wavelength division multiplexer WDM is connected to the polarization-maintaining erbium-fluorotellurite fiber, and outputs broadband tunable Raman solitons of 2.8 - 5μm.

[0014] Furthermore, the polarization-maintaining laser includes a first pump source LD, a first wavelength division multiplexer WDM, a first polarization-maintaining thulium-doped fiber PM-TDF, a polarization-maintaining phase shifter, a coupler OC, a polarization-maintaining single-mode fiber PM-SMF, and a dispersion-tunable chirped fiber grating CFBG; the 1570 nm pump of the first pump source LD is connected to the pump end of the first wavelength division multiplexer WDM, the common end of the first wavelength division multiplexer WDM is connected to the first coupling arm of the coupler OC through the first polarization-maintaining thulium-doped fiber PM-TDF, the signal end of the first wavelength division multiplexer WDM is connected to the second coupling arm of the coupler OC through the polarization-maintaining phase shifter and the polarization-maintaining single-mode fiber PM-SMF, and the output end of the coupler OC is connected to the dispersion-tunable chirped fiber grating CFBG to output 2-μm femtosecond pulses.

[0015] Furthermore, the output end of the polarization-maintaining erbium-fluorotellurite fiber is processed with an 8° bevel angle.

[0016] The beneficial effects of the present invention are as follows:

[0017] In an exemplary embodiment of the present invention, the present exemplary embodiment adopts a fully polarization-maintaining structure to achieve low-noise and high-stability laser output; through a cascaded structure and special optical fiber materials (such as polarization-maintaining germanium-doped silica fiber and polarization-maintaining erbium-fluorotellurite fiber), broadband tunable Raman soliton output in the 2-5 μm band can be achieved. This wide wavelength tuning range enables the laser source to cover a wider wavelength range and meet the requirements of different application scenarios; adopting a fully fiber-optic structure, directly pumping a highly nonlinear fiber (polarization-maintaining erbium-fluorotellurite fiber) with a thulium-doped fiber laser light source, combining an erbium-doped fiber amplifier and fluorotellurite into a polarization-maintaining erbium-fluorotellurite fiber amplifier simplifies the system structure and significantly improves the integration and stability of the system. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of a mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser light source provided by an exemplary embodiment of the present invention. Detailed Embodiments

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, terms such as "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0021] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] See Figure 1 , Figure 1 which shows a schematic structural diagram of a mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser source provided by an exemplary embodiment of the present invention, including a polarization-maintaining laser, a polarization-maintaining cascaded structure and a polarization-maintaining fiber amplifier connected in sequence;

[0024] The polarization-maintaining laser outputs femtosecond pulses of 2 μm;

[0025] The polarization-maintaining cascaded structure includes a second pump source LD, a second wavelength division multiplexer WDM, a second polarization-maintaining thulium-doped fiber PM-TDF and a polarization-maintaining germanium-doped silica fiber; the 1570 nm pump of the second pump source LD is connected to the pump end of the second wavelength division multiplexer WDM, the signal end of the second wavelength division multiplexer WDM is connected to the 2 μm femtosecond pulses, and the common end of the second wavelength division multiplexer WDM is sequentially connected to the second polarization-maintaining thulium-doped fiber PM-TDF and the polarization-maintaining germanium-doped silica fiber to output broadband tunable laser output of 2 - 2.8 μm;

[0026] The polarization-maintaining fiber amplifier includes a third pump source LD, a third wavelength division multiplexer WDM, and a polarization-maintaining erbium-doped fluorotellurite fiber. The 980 nm pump of the third pump source LD is connected to the pump end of the third wavelength division multiplexer WDM. The signal end of the third wavelength division multiplexer WDM is connected to the output of the 2 - 2.8 μm broadband tunable laser. The common end of the third wavelength division multiplexer WDM is connected to the polarization-maintaining erbium-doped fluorotellurite fiber to output a 2.8 - 5 μm broadband tunable Raman soliton.

[0027] Specifically, in this exemplary embodiment, first, a polarization-maintaining laser outputs a 2 μm femtosecond pulse. Then, in the polarization-maintaining cascade structure, the 2 μm femtosecond pulse and the 1570 nm pump light of the second pump source LD are coupled into the gain fiber (i.e., the second polarization-maintaining thulium-doped fiber PM-TDF) through the second wavelength division multiplexer WDM. The gain fiber is directly cascaded with a polarization-maintaining germanium-doped silica fiber. Among them, 2 - 3 μm is located in the large negative dispersion region of the polarization-maintaining germanium-doped silica fiber, which meets the conditions for generating SSFS. Moreover, the polarization-maintaining germanium-doped silica fiber has high nonlinear characteristics and low loss characteristics at 2 - 3 μm, which can effectively drive the generation and frequency shift of Raman solitons. By gradually increasing the pump power of the polarization-maintaining thulium-doped fiber amplifier, the threshold for exciting the soliton self-frequency shift (SSFS) effect is reached. Under the action of the in-pulse Raman scattering effect, the short-wave energy in the spectrum of the pulse will gradually transfer to the long-wave direction, realizing the output of a 2 - 2.8 μm broadband tunable laser. The polarization-maintaining fiber can effectively maintain the polarization state of light and reduce the random change of the polarization state, thus significantly improving the stability and signal-to-noise ratio of the laser output. This structure is used to generate a 2 - 2.8 μm polarization-maintaining broadband tunable Raman soliton and provides a 2.8 μm Raman soliton signal light for the subsequent system.

[0028] Finally, the signal light of the polarization-maintaining fiber amplifier is a Raman soliton with a wavelength of 2.8 μm output from the polarization-maintaining germanium-doped silica fiber. The pump of the third pump source LD is a 30 W 980 nm LD. The third wavelength division multiplexer WDM is used to combine the pump light and the signal light. The polarization-maintaining erbium-doped fluorotellurite fiber is fused behind the third wavelength division multiplexer WDM. Among them, 2.8 - 5 μm is located in the large negative dispersion region of the polarization-maintaining erbium-doped fluorotellurite fiber, which meets the conditions for generating SSFS. Moreover, the polarization-maintaining erbium-doped fluorotellurite fiber has high nonlinear characteristics and low loss characteristics at 2.8 - 5 μm, which can effectively drive the generation and frequency shift of Raman solitons. By gradually increasing the pump power of the polarization-maintaining erbium-doped fluorotellurite fiber amplifier, the threshold for exciting the soliton self-frequency shift (SSFS) effect is reached. Under the action of the in-pulse Raman scattering effect, the short-wave energy in the spectrum of the pulse will gradually transfer to the long-wave direction, and finally, a 2.8 - 5 μm broadband tunable Raman soliton can be output after the polarization-maintaining erbium-doped fluorotellurite fiber.

[0029] It should be noted that fluorotellurite fiber has a wide transparent window, capable of covering the 2 - 5μm band; fluorotellurite fiber has low transmission loss in the 2 - 5μm band; the nonlinear coefficient of fluorotellurite fiber is significantly higher than that of germanium - doped silica fiber, enabling the erbium - doped fluorotellurite fiber to achieve a significant soliton self - frequency shift effect within a shorter fiber length, thereby achieving a more significant frequency shift; while polarization - maintaining erbium - doped fluorotellurite fiber can achieve a high concentration of erbium ion doping, usually reaching 10mol%. The high - concentration doping significantly improves the gain efficiency of the fiber, enabling the fiber amplifier to achieve efficient laser output under low - power pumping conditions. The polarization - maintaining fiber amplifier constructed by combining the erbium - doped fiber amplifier and the polarization - maintaining fluorotellurite fiber has significant advantages in this exemplary embodiment. Its wide transparent window, high nonlinear coefficient, low - loss transmission, and high - concentration doping characteristics enable the laser system to achieve efficient soliton self - frequency shift and broadband tunable laser output.

[0030] In summary, compared with the prior art:

[0031] (1) High stability and high Raman conversion efficiency: This exemplary embodiment adopts a fully polarization - maintaining structure. The polarization - maintaining laser generates the seed pulse of the entire system, and the polarization - maintaining fiber can effectively maintain the polarization state of light, reducing the random change of the polarization state and improving the stability of laser output from the source. The thulium - doped fiber amplifier, germanium - doped silica fiber, and erbium - doped fluorotellurite fiber also adopt a polarization - maintaining structure, enhancing the stability during the amplification and frequency - shift processes. The nonlinear effect of linearly polarized light in the fiber is usually stronger because its electric - field vector remains unchanged in a certain direction of the fiber and can more effectively excite the nonlinear process. Therefore, in the polarization - maintaining structure system, the Raman conversion efficiency of soliton self - frequency shift is higher and the frequency - shift amplitude is larger. Some prior - art fibers are not polarization - maintaining fibers, while all fibers used in this exemplary embodiment are polarization - maintaining fibers, so low - noise and high - stability laser output (mode - locked pulse signal - to - noise ratio ≥ 90dB) can be achieved.

[0032] (2) Wide wavelength tuning range: This exemplary embodiment uses a cascaded structure and special fiber materials (such as polarization - maintaining germanium - doped silica fiber and polarization - maintaining erbium - doped fluorotellurite fiber). Such fibers have high nonlinear coefficients and low - loss characteristics, enabling a significant soliton self - frequency shift effect to be achieved within a shorter fiber length. In the mid - infrared laser output, the high - nonlinear effect and low - loss characteristics enable the laser source to achieve more efficient energy conversion and more stable output. Based on the above two high - nonlinear fibers, broadband tunable Raman soliton output in the 2 - 5μm band can be achieved. This wide wavelength tuning range enables the laser source to cover a wider wavelength range, meeting the requirements of different application scenarios.

[0033] (3) Compact structure and high integration: The present invention adopts an all-fiber structure. By directly pumping a highly nonlinear fiber (polarization-maintaining erbium-doped fluorotellurite fiber) with a thulium-doped fiber laser light source, an erbium-doped fiber amplifier and fluorotellurite are combined into a polarization-maintaining erbium-doped fluorotellurite fiber amplifier, which simplifies the system structure and significantly improves the integration and stability of the system. Wavelength-tunable output can be achieved by directly controlling the pump power, and it has a relatively simplified wavelength tuning mechanism. This compact design not only reduces the system cost and maintenance difficulty, but also improves the portability and reliability of the system. Moreover, it is convenient for further expansion and upgrade, such as adding new fiber materials or optimizing the cavity structure, and has good scalability.

[0034] The output power of a mode-locked thulium laser in some prior arts is 30.2 mW, without power amplification, and only supports a tuning range of 1860 - 2155 nm. However, the highly doped germanium dioxide nonlinear fiber used in this prior art can support wavelength tuning to 3000 nm but is only tuned to 2155 nm, indicating that the output power of the mode-locked thulium laser is too low, and the tuning range of directly pumping the highly doped germanium dioxide nonlinear fiber is limited. In the multi-fiber cascading and amplification method adopted in this exemplary embodiment, a 2-μm seed source can achieve a broadband tunable range of 1950 - 2800 nm through a thulium-doped fiber amplifier and a highly doped germanium dioxide nonlinear fiber, and the tuning range can reach 850 nm. Subsequently, a fiber amplifier with a polarization-maintaining erbium-doped fluorotellurite fiber is cascaded. Due to the power amplification of the rare earth ion erbium ion for the 2.8-μm light, and the low loss and high nonlinearity of fluorotellurite in the range of 2 - 5 μm, a tuning range of 2.8 - 5 μm can be achieved. And we adopt an all-polarization-maintaining structure. The nonlinear effect of light in the fiber is usually stronger because its electric field vector remains unchanged in a certain direction of the fiber, which can more effectively stimulate the nonlinear process, and the soliton self-frequency shift Raman conversion efficiency is higher (>80%). This cascading method of an optical amplifier and a highly nonlinear fiber can output a tunable Raman soliton laser with high power and high conversion efficiency.

[0035] More preferably, in an exemplary embodiment, as Figure 1 shown, the polarization-maintaining laser includes a first pump source LD, a first wavelength division multiplexer WDM, a first polarization-maintaining thulium-doped fiber PM-TDF, a polarization-maintaining phase shifter, a coupler OC, a polarization-maintaining single-mode fiber PM-SMF, and a dispersion-tunable chirped fiber grating CFBG; the 1570-nm pump of the first pump source LD is connected to the pump end of the first wavelength division multiplexer WDM. The common end of the first wavelength division multiplexer WDM is connected to the first coupling arm of the coupler OC through the first polarization-maintaining thulium-doped fiber PM-TDF. The signal end of the first wavelength division multiplexer WDM is connected to the second coupling arm of the coupler OC through the polarization-maintaining phase shifter and the polarization-maintaining single-mode fiber PM-SMF. The output end of the coupler OC is connected to the dispersion-tunable chirped fiber grating CFBG to output 2-μm femtosecond pulses.

[0036] Specifically, in this exemplary embodiment, the 1570 nm pump of the first pump source LD is coupled into the laser cavity through the first wavelength division multiplexer WDM. The first wavelength division multiplexer WDM, the first polarization-maintaining thulium-doped fiber PM-TDF, the 2x2 coupler OC, and the polarization-maintaining single-mode fiber PM-SMF are sequentially fused, and a dispersion-tunable chirped fiber grating CFBG is fused to one end of the 2x2 coupler OC. This structure uses a nonlinear amplifying loop mirror NALM as an equivalent saturable absorber for mode locking, and uses a dispersion-tunable chirped fiber grating CFBG as a dispersion compensation element and an output coupler to output stable femtosecond pulses. This 2-μm polarization-maintaining nine-word cavity laser is used as the seed source of the entire system. The all-polarization-maintaining structure is adopted to improve the system stability and the signal-to-noise ratio of the output pulses. The dispersion-tunable chirped fiber grating CFBG is used for dispersion management to adjust the laser cavity dispersion to near zero chromatic compression of the pulse width, so that the output pulses have higher peak power and narrower pulse width, providing a high-quality seed source for the subsequent soliton self-frequency shift process to output broadband tunable Raman solitons.

[0037] That is to say, in this exemplary embodiment, a 2-μm polarization-maintaining nine-word cavity laser is used to generate the seed pulses of the entire system. The polarization-maintaining fiber can effectively maintain the polarization state of light, reduce the random change of the polarization state, and improve the stability of laser output from the source. Through dispersion compensation technology (such as dispersion-tunable chirped fiber grating), the dispersion characteristics in the laser cavity are optimized, the noise is further reduced, and the output of femtosecond pulses with high signal-to-noise ratio is realized.

[0038] It should be noted that some existing technologies use a real saturable absorber (black phosphorus) for mode locking and use positive dispersion fiber for dispersion compensation, which will cause the entire cavity length to be too long and is not suitable for the case of high laser repetition frequency. In this exemplary embodiment, the nine-word cavity uses a nonlinear amplifying loop mirror NALM mode locking mechanism. NALM is an equivalent saturable absorber, which has advantages such as high damage threshold, fast saturation recovery time, and high output power. The dispersion-tunable chirped fiber grating CFBG is used for intracavity dispersion compensation to precisely compensate and control the dispersion in the oscillator, supporting the generation of stable femtosecond pulses with narrow pulse width (stable mode-locked pulses with a pulse width < 300 fs can be output). The dispersion-tunable chirped fiber grating CFBG can achieve dispersion compensation with a shorter fiber, can significantly shorten the laser cavity length, and improve the laser repetition frequency.

[0039] More preferably, in an exemplary embodiment, the output end of the polarization-maintaining erbium-fluorotellurite fiber is processed with an 8° bevel angle to prevent harmful self-excited oscillation of the amplifier.

[0040] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. Mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser source, characterized by: It includes a polarization-maintaining laser, a polarization-maintaining cascade structure and a polarization-maintaining fiber amplifier connected in sequence; The polarization-maintaining laser outputs 2 μm femtosecond pulses; The polarization-maintaining cascade structure includes a second pump source LD, a second wavelength division multiplexer WDM, a second polarization-maintaining thulium-doped optical fiber PM-TDF and a polarization-maintaining germanium-doped quartz optical fiber; the 1570nm pump of the second pump source LD is connected to the pump end of the second wavelength division multiplexer WDM, the signal end of the second wavelength division multiplexer WDM is connected to the 2μm femtosecond pulse, and the common end of the second wavelength division multiplexer WDM is connected to the second polarization-maintaining thulium-doped optical fiber PM-TDF and the polarization-maintaining germanium-doped quartz optical fiber in sequence, outputting a broadband tunable laser output of 2 to 2.8μm; The polarization-maintaining fiber amplifier comprises a third pump source LD, a third wavelength division multiplexer WDM, and a polarization-maintaining erbium-doped fluorotellurate fiber; the 980nm pump of the third pump source LD is connected to the pump end of the third wavelength division multiplexer WDM, the signal end of the third wavelength division multiplexer WDM is connected to the 2-2.8μm broadband tunable laser output, the common end of the third wavelength division multiplexer WDM is connected to the polarization-maintaining erbium-doped fluorotellurate fiber, and outputs 2.8-5μm broadband tunable Raman solitons.

2. The mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser source according to claim 1, characterized in that: The polarization-maintaining laser comprises a first pump source LD, a first wavelength division multiplexer WDM, a first polarization-maintaining thulium-doped optical fiber PM-TDF, a polarization-maintaining phase shifter, a coupler OC, a polarization-maintaining single-mode optical fiber PM-SMF and a dispersion-adjustable chirped optical fiber grating CFBG; the 1570nm pump of the first pump source LD is connected to the pump end of the first wavelength division multiplexer WDM, the common end of the first wavelength division multiplexer WDM is connected to the first coupling arm of the coupler OC through the first polarization-maintaining thulium-doped optical fiber PM-TDF, the signal end of the first wavelength division multiplexer WDM is connected to the second coupling arm of the coupler OC through the polarization-maintaining phase shifter and the polarization-maintaining single-mode optical fiber PM-SMF, the output end of the coupler OC is connected to the dispersion-adjustable chirped optical fiber grating CFBG, and a 2μm femtosecond pulse is output.

3. The mid-infrared polarization-maintaining wavelength broadband tunable Raman soliton laser source according to claim 1, characterized in that: The output end of the polarization-maintaining erbium-doped fluorotellurate optical fiber is processed with an 8° bevel angle.

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