Tunable raman fiber laser

Abstract

The application relates to a tunable Raman fiber laser, wherein the output end of a pulse seed source unit is connected with a beam splitter one, one-way output end of the beam splitter one is connected with the input end of a combiner one, the output end of a pump source one is connected with the input end of the combiner one, the output end of the combiner one is connected with a gain fiber one, the gain fiber one is connected with an n-order Raman gain fiber, the n-order Raman gain fiber is connected with the input end of an isolator one; the other-way output end of the beam splitter one is connected with the input end of a combiner two, the output end of a pump source two is connected with the input end of the combiner two, the output end of the combiner two is connected with a gain fiber two, the gain fiber two is connected with an n-1-order Raman gain fiber, the n-1-order Raman gain fiber is connected with the input end of an isolator two, the output end of the isolator one and the output end of the isolator two are connected with the input end of an energy combiner; the output end of the energy combiner is connected with a Raman gain fiber, and the output light path of the Raman gain fiber is provided with a filter one. The pulse width and wavelength can be adjusted.

Description

Technical Field

[0001] This invention relates to a tunable Raman fiber laser, belonging to the field of laser technology. Background Technology

[0002] Applications such as lidar, laser displays, atmospheric remote sensing, and nonlinear frequency conversion have a clear demand for pulsed lasers with specific wavelengths. However, the emission spectral ranges of conventional gain fibers (Yb and Er) are limited to 900–1100 nm and 1530–1610 nm, respectively, which is insufficient to meet the needs of some specialized applications. The Raman effect in optical fibers can transfer energy from one optical field to another. Therefore, the nonlinear effects generated by laser transmission in optical fibers can be used to extend the wavelength of lasers. For example, the Raman gain bandwidth in silica optical fibers can reach up to 40 THz. By selecting an appropriate pump wavelength, the desired wavelength can be obtained within the Raman gain bandwidth range.

[0003] Currently, Raman lasers mainly employ two methods:

[0004] 1) Emits using semiconductor materials, such as gallium arsenide, with an emission wavelength range of 970–1340 nm. However, such semiconductor output cannot simultaneously meet the requirements of high power and basic mode output. Generally, basic mode only supports output of hundreds of milliwatts, while output of watts and above can only support multi-mode output. The process is complex and costly.

[0005] 2) Special crystals such as diamond are used as Raman media. However, due to limitations in diamond manufacturing processes and application requirements, the transverse area of ​​the diamond crystals used is relatively small, which places extremely stringent requirements on the input spot size and optical design. Furthermore, the laser requires a spatial resonant cavity structure for oscillation output, with the cavity coated with a special wavelength film, resulting in high costs and poor long-term stability of the spatial cavity structure. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a tunable Raman fiber laser that enables adjustable pulse width and wavelength.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A tunable Raman fiber laser is characterized by comprising a pulsed seed source unit, pump source one, pump source two, beam splitter one, beam combiner one, beam combiner two, an n-order Raman gain fiber, an n-1 order Raman gain fiber, and an energy combiner. The output of the pulsed seed source unit is connected to beam splitter one, which splits the laser into two seed beams with different powers. One output of beam splitter one is connected to the input of beam combiner one. The output of pump source one is connected to the input of beam combiner one. The output of beam combiner one is connected to gain fiber one, which is then connected to the n-order Raman gain fiber. The gain fiber is connected to the input of isolator one, and the output of isolator one is connected to the input of the energy combiner. The other output of beam splitter one is connected to the input of combiner two. The output of pump source two is connected to the input of combiner two. The output of combiner two is connected to gain fiber two. Gain fiber two is connected to n-1 order Raman gain fiber. The n-1 order Raman gain fiber is connected to the input of isolator two. The output of isolator two is connected to the input of the energy combiner. The output of the energy combiner is connected to Raman gain fiber. Filter one is installed on the output optical path of the Raman gain fiber.

[0009] Furthermore, in the aforementioned tunable Raman fiber laser, the gain fiber is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a double-clad core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm.

[0010] Gain fiber 2 is a double-clad fiber with a core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, which is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber.

[0011] n-order Raman gain fiber is a pure silica or germanium-, boron-, or phosphorus-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10µm, 20µm, or 30µm.

[0012] n-1 order Raman gain fiber is pure silica or germanium, boron, or phosphorus doped polarization-maintaining fiber or non-polarization-maintaining fiber with a core diameter of 10µm, 20µm, or 30µm.

[0013] Raman gain fiber is a pure silica or germanium-, boron-, or phosphorus-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10µm, 20µm, or 30µm.

[0014] Furthermore, in the aforementioned tunable Raman fiber laser, the filter is a bandwidth filter with a center wavelength of nth-order Raman laser, and the center wavelengths are 1116nm, 1168nm, 1175nm, 1220nm, 1128nm, 1189nm, 1400nm, 1514nm, 1739nm, etc., with a bandwidth of 0.1 to 10nm.

[0015] Furthermore, in the aforementioned tunable Raman fiber laser, the pulse seed source unit includes a laser resonant cavity and a modulator 1 placed outside the cavity. The laser resonant cavity includes a pump source 3, a beam combiner 3, a gain fiber 3, a beam splitter 2, a collimator 1, a filter 2, and an isolator 3. The output end of the pump source 3 is connected to the input end of the beam combiner 3, and the output end of the beam combiner 3 is connected to the gain fiber 3. The gain fiber 3 is connected to the beam splitter 2, and part of the laser light from the beam splitter 2 is used as the output laser end. The other end of the beam splitter 2 is connected to the collimator 1. The filter 2 is placed inside the collimator 1, and the collimator 1 is connected to the isolator 3. The isolator 3 controls the unidirectional transmission of light, and the modulator 1 modulates the pulse output.

[0016] Furthermore, in the aforementioned tunable Raman fiber laser, the gain fiber is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a double-clad core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm.

[0017] Furthermore, in the aforementioned tunable Raman fiber laser, the collimator is a U-shaped collimator with a distance of 38mm, 89mm, or 96mm between its two ends, and the anti-reflection coatings at both ends have a wavelength range of 600nm to 1050nm or 1050nm to 1620nm.

[0018] Isolator type 3 is an isolator with a center wavelength range of 600nm to 1620nm and an isolation level greater than 25dB;

[0019] The modulator is either an acousto-optic modulator or an electro-optic modulator.

[0020] Furthermore, in the aforementioned tunable Raman fiber laser, filter two is a mirror filter or grating filter with a center wavelength range of 600nm to 1620nm and bandwidths of 0.1nm, 1nm, 2nm, and 3nm.

[0021] Furthermore, in the aforementioned tunable Raman fiber laser, the pulse seed source unit includes a laser resonant cavity and a modulator II placed outside the cavity. The laser resonant cavity includes a pump source IV, a beam combiner IV, a gain fiber IV, a collimator II, and a filter III. The output end of the pump source IV is connected to the input end of the beam combiner IV, and the output end of the beam combiner IV is connected to the gain fiber IV. The gain fiber IV is connected to the collimator II. The filter III is placed inside the collimator II. A high-reflection film is deposited on one end of the fiber of the beam combiner IV, and a low-reflection film is deposited on one end of the collimator II. The high-reflection film and the low-reflection film form a resonant cavity to cause the laser to oscillate and amplify. The modulator II modulates the continuous light into pulsed light.

[0022] Furthermore, in the aforementioned tunable Raman fiber laser, the high-reflectivity film is a reflective film with a bandwidth of 600nm to 1620nm and a reflectivity of >99%; the low-reflectivity film is a reflective film with a bandwidth of 600nm to 1620nm and a reflectivity of 10% to 90% selectable.

[0023] Furthermore, in the aforementioned tunable Raman fiber laser, the gain fiber 4 is a double-clad ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm.

[0024] Collimator 2 is a U-shaped collimator with a distance of 38mm, 89mm and 96mm between its two ends. The anti-reflection coatings at both ends have a wavelength range of 600nm~1050nm or 1050nm~1620nm.

[0025] Modulator type 2 is an acousto-optic modulator or an electro-optic modulator;

[0026] The third type of filter is a lens filter or grating filter with a center wavelength of 600nm to 1620nm and a bandwidth of 0.1nm, 1nm, 2nm, or 3nm.

[0027] Compared with the prior art, the present invention has significant advantages and beneficial effects, specifically reflected in the following aspects:

[0028] This invention provides a Raman fiber laser with adjustable pulse width and wavelength. When the pulse peak reaches the fiber Raman threshold, the energy of the optical field will be converted from fundamental frequency light into Raman light. By selecting a suitable filter, wavelength, and modulator, pulses of different widths are selected as fundamental frequency seed light. After power amplification, Raman pulse light outside the gain fiber spectrum is obtained through Raman frequency shift. This achieves adjustable wavelength and pulse width, and has the advantages of high power, high conversion efficiency, and low thermal effect.

[0029] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing specific embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1: A schematic diagram of the structure of the tunable Raman fiber laser of the present invention;

[0032] Figure 2 : A schematic diagram of one structure of a pulse seed source unit;

[0033] Figure 3 : Schematic diagram of another structure of the pulse seed source unit. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, directional and ordinal terms are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0036] like Figure 1As shown, the tunable Raman fiber laser includes a pulsed seed source unit 1, a pump source 3, a pump source 2 6, a beam splitter 2, a beam combiner 4, a beam combiner 2 11, an n-order Raman gain fiber 7, an n-1 order Raman gain fiber 13, and an energy beam combiner 9. The output of the pulsed seed source unit 1 is connected to the beam splitter 2, which splits the light into two seed beams with different powers. One output of the beam splitter 2 is connected to the input of the beam combiner 4. The output of the pump source 3 is connected to the input of the beam combiner 4. The output of the beam combiner 4 is connected to the gain fiber 5, which is connected to the n-order Raman gain fiber 7. The input of isolator 8 is connected, and the output of isolator 8 is connected to the input of energy combiner 9. The other output of beam splitter 2 is connected to the input of combiner 11. The output of pump source 6 is connected to the input of combiner 11. The output of combiner 11 is connected to gain fiber 12. Gain fiber 12 is connected to n-1 order Raman gain fiber 13. n-1 order Raman gain fiber 13 is connected to the input of isolator 14. The output of isolator 14 is connected to the input of energy combiner 9. The output of energy combiner 9 is connected to Raman gain fiber 10. Filter 15 is provided on the output optical path of Raman gain fiber 10.

[0037] Gain Fiber 15 is a double-clad fiber with a core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm, and is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber.

[0038] Gain fiber 2.12 is a double-clad fiber with a core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm, and is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber.

[0039] n-order Raman gain fiber 7 is a pure silica or germanium-, boron-, or phosphorus-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10µm, 20µm, or 30µm.

[0040] n-1 order Raman gain fiber 13 is a pure silica or germanium, boron, or phosphorus doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10µm, 20µm, or 30µm.

[0041] Raman gain fiber 10 is a pure silica or germanium-, boron-, or phosphorus-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10µm, 20µm, or 30µm.

[0042] Filter 15 is a bandwidth filter for nth-order Raman lasers with center wavelengths of 1116nm, 1168nm, 1175nm, 1220nm, 1128nm, 1189nm, 1400nm, 1514nm, and 1739nm, with bandwidths ranging from 0.1 to 10nm.

[0043] The fundamental frequency seed light 1 of the pulse seed source unit 1 is split into beams by beam splitter 2 with a splitting ratio of 50%:50%. One beam splitting optical path of beam splitter 2 and the optical path of pump source 3 are combined into gain fiber 5 through beam combiner 4, so that the pump light and seed light are amplified in gain fiber 5 to obtain high-power fundamental frequency signal light. The fundamental frequency signal light is converted into energy in n-order Raman gain fiber 7 to obtain n-order Raman laser output.

[0044] The other beam splitting optical path of beam splitter 2 and the optical path of pump source 6 enter gain fiber 2 12 through beam combiner 2 11, so that the pump light and seed light are amplified in gain fiber 2 12 to obtain high-power fundamental frequency signal light. The fundamental frequency signal light is converted into energy in n-1 order Raman gain fiber 13 to obtain n-1 order Raman laser output.

[0045] The obtained n-order Raman laser and n-1-order Raman laser are respectively passed through isolators and then combined by energy combiner 9 into Raman gain fiber 10. The n-1-order Raman light is used as the pump for the n-order Raman light, thereby amplifying the n-order Raman light. The amplified n-order Raman light is then filtered by filter 15 to remove the residual pump light, and the n-order Raman light output is obtained.

[0046] Among them, such as Figure 2 The pulse seed source unit 1 includes a laser resonant cavity and a modulator 108 placed outside the cavity. The laser resonant cavity includes a pump source 3 101, a beam combiner 3 102, a gain fiber 3 103, a beam splitter 2 104, a collimator 1 105, a filter 2 106, and an isolator 3 107. The output end of the pump source 3 101 is connected to the input end of the beam combiner 3 102. The output end of the beam combiner 3 102 is connected to the gain fiber 3 103. The gain fiber 3 103 is connected to the beam splitter 2 104. Part of the laser light from the beam splitter 2 104 is used as the output laser end. The other end of the beam splitter 2 104 is connected to the collimator 1 105. The filter 2 106 is placed inside the collimator 1 105. The collimator 1 105 is connected to the isolator 3 107. The isolator 3 107 controls the unidirectional transmission of light. The modulator 1 108 modulates the pulse output.

[0047] The light emitted from pump source 3 101 is input into gain fiber 3 103 via beam combiner 3 102, causing population inversion within the gain fiber. A portion of the laser light from beam splitter 2 104 serves as the output laser, with the other end connected to collimator 1 105. Isolator 3 107 controls the unidirectional transmission of light. By replacing filters 2 106 with different center wavelength bandwidths and controlling external modulator 1 108, a smooth, unmodulated Gaussian pulse can be obtained. This pulsed laser light serves as the fundamental frequency seed pulse.

[0048] Gain fiber 3103 is a double-clad fiber with a core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm, and is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber.

[0049] Collimator-105 is a U-shaped collimator with a distance of 38mm, 89mm and 96mm between its two ends. The anti-reflection coatings at both ends have a wavelength range of 600nm to 1050nm or 1050nm to 1620nm.

[0050] Isolator 3107 is an isolator with a center wavelength in the range of 600-1620nm and an isolation of greater than 25dB;

[0051] Modulator-108 is an acousto-optic modulator or an electro-optic modulator;

[0052] Filter 2 106 is a lens filter or grating filter with a center wavelength in the range of 600 to 1620 nm and a bandwidth of 0.1 nm, 1 nm, 2 nm, or 3 nm.

[0053] Or, such as Figure 3 The pulse seed source unit 1 includes a laser resonant cavity and a modulator 208 placed outside the cavity. The laser resonant cavity includes a pump source 4 201, a beam combiner 4 203, a gain fiber 4 204, a collimator 2 205, and a filter 3 206. The output end of the pump source 4 201 is connected to the input end of the beam combiner 4 203, and the output end of the beam combiner 4 203 is connected to the gain fiber 4 204. The gain fiber 4 204 is connected to the collimator 2 205. The filter 3 206 is placed inside the collimator 2 205. A high-reflection film 202 is deposited on one end of the fiber of the beam combiner 4 203, and a low-reflection film 207 is deposited on one end of the collimator 2 205. The high-reflection film 202 and the low-reflection film 207 form a resonant cavity to amplify the laser beam. The modulator 2 208 modulates the continuous light into pulsed light. The high-reflectivity film 202 is a reflective film with a bandwidth of 900nm to 1100nm and a reflectivity of >99%; the low-reflectivity film 207 is a reflective film with a bandwidth of 900nm to 1100nm and a reflectivity of 10% to 90% selectable.

[0054] Gain fiber 4204 is a double-clad fiber with a core diameter of 10 / 125µm, 20 / 130µm, or 30 / 250µm, and is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber.

[0055] Collimator 205 is a U-shaped collimator with a distance of 38mm, 89mm and 96mm between its two ends. The anti-reflection coatings at both ends have a wavelength range of 600nm to 1050nm or 1050nm to 1620nm.

[0056] Modulator 208 is an acousto-optic modulator or an electro-optic modulator;

[0057] Filter 3206 is a lens filter or grating filter with a center wavelength in the range of 600 to 1620 nm and bandwidths of 0.1 nm, 1 nm, 2 nm, and 3 nm.

[0058] The light emitted from pump source 4 201 is input into gain fiber 4 204 through combiner 4 203, causing population inversion within the gain fiber. One end of the fiber in combiner 4 203 is coated with a high-reflectivity film 202. Gain fiber 4 204 is connected to collimator 2 205. Filter 3 206 is placed in collimator 2 205. By changing filters 3 206 with different center wavelengths and bandwidths, different wavelength bands of laser output can be controlled. One end of collimator 2 205 is coated with a low-reflectivity film 207. The high-reflectivity film 202 and the low-reflectivity film 207 form a resonant cavity, causing the laser to oscillate and amplify. By changing different filters, different wavelengths of laser output can be obtained. External modulator 2 208 modulates the continuous light into pulsed light, thereby obtaining the fundamental frequency seed pulse.

[0059] Yb-gain fiber emission spectrum ranges from 900nm to 1100nm. Within this range, a bandpass filter is used for filtering. Outside the bandwidth, optical loss is high, suppressing laser formation; while within the filter's spectral bandwidth, laser light has low loss and high gain. When the gain within the laser cavity exceeds the loss, laser light within the filter's bandwidth is formed. Therefore, filters with different center wavelengths and bandwidths can be selected to obtain seed lasers of different wavelengths. By placing a modulator outside the resonant cavity, such as an electro-optic modulator or an acousto-optic modulator, pulsed light outputs with different pulse widths can be obtained.

[0060] During laser transmission through optical fibers, when the peak power of the laser or the fiber is long enough, a portion of the power is transferred from one optical field to another with a lower frequency. Typically, the Raman frequency shift in silica optical fibers is 50–60 nm, thus enabling laser output with wavelengths of 1120–1200 nm outside the Yb gain spectrum.

[0061] In summary, this invention provides a Raman fiber laser with adjustable pulse width and wavelength. When the pulse peak reaches the fiber Raman threshold, the energy of the optical field is converted from fundamental frequency light into Raman light. By selecting a suitable filter, wavelength is selected, and a modulator is used to modulate pulses of different widths as fundamental frequency seed light. After power amplification, Raman pulse light outside the gain fiber spectrum is obtained through Raman frequency shifting. This achieves adjustable wavelength and adjustable pulse width, and features high power, high conversion efficiency, and low thermal effect.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0063] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

[0064] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A tunable Raman fiber laser, characterized in that: The system includes a pulse seed source unit (1), a pump source one (3), a pump source two (6), a beam splitter one (2), a beam combiner one (4), a beam combiner two (11), an n-order Raman gain fiber (7), an n-1 order Raman gain fiber (13), and an energy beam combiner (9). The output end of the pulse seed source unit (1) is connected to the beam splitter one (2). The fundamental frequency seed light of the pulse seed source unit (1) is split by the beam splitter one (2) with a splitting ratio of 50%:50%. One output end of the beam splitter one (2) is connected to the input end of the beam combiner one (4). The output end of the pump source one (3) is connected to the input end of the beam combiner one (4). The output end of the beam combiner one (4) is connected to the gain fiber one (5). The gain fiber one (5) is connected to the n-order Raman gain fiber (7). The gain fiber (7) is connected to the input end of isolator 1 (8), and the output end of isolator 1 (8) is connected to the input end of energy combiner (9); the other output end of beam splitter 1 (2) is connected to the input end of combiner 2 (11), the output end of pump source 2 (6) is connected to the input end of combiner 2 (11), the output end of combiner 2 (11) is connected to gain fiber 2 (12), gain fiber 2 (12) is connected to n-1 order Raman gain fiber (13), n-1 order Raman gain fiber (13) is connected to the input end of isolator 2 (14), the output end of isolator 2 (14) is connected to the input end of energy combiner (9); the output end of energy combiner (9) is connected to Raman gain fiber (10), and filter 1 (15) is provided on the output optical path of Raman gain fiber (10).

2. The tunable Raman fiber laser according to claim 1, characterized in that: Gain fiber 1 (5) is a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a double-clad core diameter of 10 / 125 μm, 20 / 130 μm, or 30 / 250 μm. Gain fiber 2 (12) is a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a double-clad core diameter of 10 / 125 μm, 20 / 130 μm, or 30 / 250 μm. n-order Raman gain fiber (7) is a pure silica or germanium-, boron-, or phosphorus-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10 μm, 20 μm, or 30 μm. n-1 order Raman gain fiber (13) is pure silica or germanium, boron, or phosphorus ion-doped polarization-maintaining fiber or non-polarization-maintaining fiber with a core diameter of 10 μm, 20 μm, or 30 μm. Raman gain fiber (10) is a pure silica or germanium, boron, or phosphorus ion-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a core diameter of 10 μm, 20 μm, or 30 μm.

3. The tunable Raman fiber laser according to claim 1, characterized in that: Filter 1 (15) is a bandwidth filter for an nth-order Raman laser with center wavelengths of 1116nm, 1168nm, 1175nm, 1220nm, 1128nm, 1189nm, 1400nm, 1514nm, and 1739nm, and a bandwidth of 0.1 to 10nm.

4. The tunable Raman fiber laser according to claim 1, characterized in that: The pulse seed source unit (1) includes a laser resonant cavity and a modulator (108) placed outside the cavity. The laser resonant cavity includes a pump source (101), a beam combiner (102), a gain fiber (103), a beam splitter (104), a collimator (105), a filter (106), and an isolator (107). The output end of the pump source (101) is connected to the input end of the beam combiner (102), and the output end of the beam combiner (102) is connected to... The gain fiber 3 (103) is connected to the beam splitter 2 (104). Part of the laser from the beam splitter 2 (104) is used as the output laser. The other end of the beam splitter 2 (104) is connected to the collimator 1 (105). The filter 2 (106) is placed inside the collimator 1 (105). The collimator 1 (105) is connected to the isolator 3 (107). The isolator 3 (107) controls the unidirectional transmission of light. The modulator 1 (108) modulates the pulse output.

5. The tunable Raman fiber laser according to claim 4, characterized in that: Gain fiber 3 (103) is a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber with a double-clad core diameter of 10 / 125 μm, 20 / 130 μm, or 30 / 250 μm.

6. The tunable Raman fiber laser according to claim 4, characterized in that: Collimator 1 (105) is a U-shaped collimator with a distance of 38mm, 89mm and 96mm between its two ends. The wavelength range of the anti-reflection coatings at both ends is 600nm~1050nm or 1050nm~1620nm. Isolator 3 (107) is an isolator with a center wavelength range of 600nm to 1620nm and an isolation greater than 25 dB; Modulator 1 (108) is an acousto-optic modulator or an electro-optic modulator.

7. The tunable Raman fiber laser according to claim 4, characterized in that: Filter 2 (106) is a lens filter or grating filter with a center wavelength range of 600nm to 1620nm and bandwidths of 0.1nm, 1nm, 2nm, and 3nm.

8. The tunable Raman fiber laser according to claim 1, characterized in that: The pulse seed source unit (1) includes a laser resonant cavity and a modulator two (208) placed outside the cavity. The laser resonant cavity includes a pump source four (201), a beam combiner four (203), a gain fiber four (204), a collimator two (205), and a filter three (206). The output end of the pump source four (201) is connected to the input end of the beam combiner four (203). The output end of the beam combiner four (203) is connected to the gain fiber four (204). The gain fiber four (204) is connected to the collimator two (205). The filter three (206) is placed inside the collimator two (205). A high-reflection film (202) is deposited on one end of the fiber of the beam combiner four (203), and a low-reflection film (207) is deposited on one end of the collimator two (205). The high-reflection film (202) and the low-reflection film (207) form a resonant cavity to make the laser oscillate and amplify. The modulator two (208) modulates the continuous light into pulse light.

9. The tunable Raman fiber laser according to claim 8, characterized in that: The high-reflectivity film (202) is a reflective film with a bandwidth of 600nm to 1620nm and a reflectivity of >99%; the low-reflectivity film (207) is a reflective film with a bandwidth of 600nm to 1620nm and a reflectivity of 10% to 90%.

10. The tunable Raman fiber laser according to claim 8, characterized in that: Gain Fiber 4 (204) is a double-clad fiber with a core diameter of 10 / 125 μm, 20 / 130 μm, or 30 / 250 μm, and is either a ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber. Collimator 2 (205) is a U-shaped collimator with a distance of 38mm, 89mm and 96mm between its two ends. The wavelength range of the anti-reflection coatings at both ends is 600nm~1050nm or 1050nm~1620nm. Modulator 2 (208) is an acousto-optic modulator or an electro-optic modulator; Filter 3 (206) is a lens filter or grating filter with a center wavelength range of 600nm to 1620nm and bandwidths of 0.1nm, 1nm, 2nm, and 3nm.

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