Tunable raman fiber laser

Abstract

The present invention relates to a tunable Raman fiber laser, wherein an output end of a pulse seed source unit is connected to a first beam splitter, one output end of the first beam splitter is connected to an input end of a first beam combiner, an output end of a first pump source is connected to the input end of the first beam combiner, an output end of the first beam combiner is connected to a first gain optical fiber, the first gain optical fiber is connected to an nth-order Raman gain optical fiber, and the nth-order Raman gain optical fiber is connected to an input end of a first isolator; the other output end of the first beam splitter is connected to an input end of a second beam combiner, an output end of a second pump source is connected to the input end of the second beam combiner, an output end of the second beam combiner is connected to a second gain optical fiber, the second gain optical fiber is connected to an (n-1)th-order Raman gain optical fiber, the (n-1)th-order Raman gain optical fiber is connected to an input end of a second isolator, and an output end of the first isolator and an output end of the second isolator are connected to an input end of an energy beam combiner; and an output end of the energy beam combiner is connected to a Raman gain optical fiber, and an output optical path of the Raman gain optical fiber is provided with a first filter. The pulse width and the wavelength can be adjusted.

Description

Tunable Raman fiber laser Technical Field

[0001] The invention relates to a tunable Raman fiber laser, belonging to the technical field of lasers. Background Art

[0002] Fields such as lidar, laser display, atmospheric remote sensing, and nonlinear frequency conversion have a clear demand for pulsed lasers with specific wavelengths. However, the emission spectra of conventional gain fibers, Yb and Er, range from 900 to 1100 nm and 1530 to 1610 nm, respectively, with limited wavelength coverage, making it difficult 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 of laser transmission in optical fibers can be exploited to extend the wavelength of lasers. For example, the frequency bandwidth of Raman gain in quartz optical fibers is as high as 40 THz. Simply selecting the appropriate pump wavelength allows the desired wavelength to be obtained within the Raman gain bandwidth.

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

[0004] 1) Using semiconductor materials for emission, such as gallium arsenide, which emits in the wavelength range of 970 to 1340 nm. However, this type of semiconductor output cannot meet both high power and fundamental mode output requirements. Generally, the fundamental mode output only supports hundreds of milliwatts, while outputs above the watt level can only support multi-mode output, resulting in complex processes and high costs.

[0005] 2) Special crystals such as diamond are used as Raman media, but the diamond manufacturing process and application requirements are limited. The cross-sectional area of ​​the diamond crystal used is small, and the requirements for the input spot size and optical design are extremely stringent. Secondly, the laser needs to use a spatial resonant cavity structure for oscillation output, and the cavity is coated with a special wavelength film, which is costly and has poor long-term stability of the spatial cavity structure.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a tunable Raman fiber laser that can adjust the pulse width and wavelength.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] The tunable Raman fiber laser is characterized by comprising a pulse seed source unit, a pump source 1, a pump source 2, a beam splitter 1, a beam combiner 1, a beam combiner 2, an n-order Raman gain fiber, an n-1-order Raman gain fiber, and an energy combiner. The output end of the pulse seed source unit is connected to the beam splitter 1, which is divided into two beams of seed light with different powers by the beam splitter 1. One output end of the beam splitter 1 is connected to the input end of the beam combiner 1. The output end of the pump source 1 is connected to the input end of the beam combiner 1. The output end of the beam combiner 1 is connected to the gain fiber 1. The gain fiber 1 is connected to the n-order Raman gain fiber. The n-order Raman The gain fiber is connected to the input end of isolator 1, and the output end of isolator 1 is connected to the input end of the energy combiner; the other output end of beam splitter 1 is connected to the input end of combiner 2, the output end of pump source 2 is connected to the input end of combiner 2, the output end of combiner 2 is connected to gain fiber 2, gain fiber 2 is connected to n-1 order Raman gain fiber, n-1 order Raman gain fiber is connected to the input end of isolator 2, and the output end of isolator 2 is connected to the input end of the energy combiner; the output end of the energy combiner is connected to the Raman gain fiber, and filter 1 is provided on the output optical path of the Raman gain fiber.

[0010] Furthermore, in the above-mentioned tunable Raman fiber laser, the gain fiber is a double-clad fiber with a core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, which is a polarization-maintaining fiber doped with ytterbium or erbium ions, or a non-polarization-maintaining fiber;

[0011] The second gain fiber is a double-clad core diameter of 10 / 125um, 20 / 130um, 30 / 250um ytterbium-doped or erbium-doped polarization-maintaining fiber or non-polarization-maintaining fiber;

[0012] The n-order Raman gain fiber is pure quartz or germanium, boron, phosphorus ion-doped polarization-maintaining fiber or non-polarization-maintaining fiber with a core diameter of 10um, 20um, or 30um;

[0013] The n-1 order Raman gain fiber is pure quartz or germanium, boron, phosphorus ion doped polarization maintaining fiber or non-polarization maintaining fiber with a core diameter of 10um, 20um, 30um;

[0014] Raman gain fiber is pure quartz or germanium, boron, phosphorus ion doped polarization maintaining fiber or non-polarization maintaining fiber with a core diameter of 10um, 20um, 30um.

[0015] Furthermore, in the above-mentioned tunable Raman fiber laser, filter 1 is a bandwidth filter with a central wavelength of n-order Raman laser, and the central wavelengths are 1116nm, 1168nm, 1175nm, 1220nm, 1128nm, 1189nm, 1400nm, 1514nm, 1739nm, and the bandwidth is 0.1 to 10nm.

[0016] Furthermore, the above-mentioned tunable Raman fiber laser, wherein 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, 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, part of the laser of 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 in the collimator 1, 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.

[0017] Furthermore, in the above-mentioned tunable Raman fiber laser, the gain fiber three is a double-clad fiber with a core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, which is a polarization-maintaining fiber doped with ytterbium or erbium ions, or a non-polarization-maintaining fiber.

[0018] Furthermore, in the above-mentioned tunable Raman fiber laser, the collimator is a U-shaped collimator with a distance between the two ends of 38mm, 89mm, and 96mm, and the two ends are coated with an anti-reflection film with a wavelength range of 600nm to 1050nm or 1050nm to 1620nm;

[0019] Isolator three is an isolator with a central wavelength range of 600nm to 1620nm and an isolation greater than 25dB;

[0020] The modulator is either an acousto-optic modulator or an electro-optic modulator.

[0021] Furthermore, in the above-mentioned tunable Raman fiber laser, the second filter is a lens filter or a grating filter with a central wavelength range of 600nm to 1620nm and a bandwidth of 0.1nm, 1nm, 2nm, or 3nm.

[0022] Furthermore, in the above-mentioned tunable Raman fiber laser, the pulse seed source unit includes a laser resonant cavity and a modulator 2 placed outside the cavity. The laser resonant cavity includes a pump source 4, a combiner 4, a gain fiber 4, a collimator 2 and a filter 3. The output end of the pump source 4 is connected to the input end of the combiner 4, the output end of the combiner 4 is connected to the gain fiber 4, the gain fiber 4 is connected to the collimator 2, the filter 3 is placed in the collimator 2, the optical fiber at one end of the combiner 4 is coated with a high-reflection film, and one end of the collimator 2 is coated with a low-reflection film. The high-reflection film and the low-reflection film form a resonant cavity to oscillate and amplify the laser, and the modulator 2 modulates the continuous light into pulsed light.

[0023] Furthermore, in the above-mentioned tunable Raman fiber laser, the high-reflection film is a reflective film with a bandwidth of 600nm to 1620nm and a reflectivity greater than 99%; the low-reflection film is a reflective film with a bandwidth of 600nm to 1620nm and a reflectivity of 10% to 90%.

[0024] Furthermore, in the above-mentioned tunable Raman fiber laser, the gain fiber 4 is a double-clad fiber core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, ytterbium-doped or erbium-doped polarization-maintaining fiber or a non-polarization-maintaining fiber;

[0025] The second collimator is a U-shaped collimator with a spacing of 38mm, 89mm, and 96mm at both ends, and an anti-reflection coating at both ends with a wavelength range of 600nm to 1050nm or 1050nm to 1620nm;

[0026] Modulator 2 is an acousto-optic modulator or an electro-optic modulator;

[0027] The third filter is a lens filter or a grating filter with a central wavelength of 600 nm to 1620 nm and a bandwidth of 0.1 nm, 1 nm, 2 nm, or 3 nm.

[0028] Compared with the prior art, the present invention has significant advantages and beneficial effects, which are specifically reflected in the following aspects:

[0029] The present 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 light field will be converted from fundamental frequency light to Raman light. By selecting a suitable filter to select the wavelength and a modulator to modulate pulses of different widths as fundamental frequency seed light, Raman pulse light outside the gain fiber spectrum is obtained after power amplification and Raman frequency shift, thereby achieving adjustable wavelength and pulse width, and having the advantages of high power, high conversion efficiency, and low thermal effect.

[0030] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the specific embodiments of the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0032] FIG1 is a schematic structural diagram of a tunable Raman fiber laser according to the present invention;

[0033] Figure 2: Schematic diagram of a structure of a pulse seed source unit;

[0034] Figure 3: Schematic diagram of another structure of the pulse seed source unit. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0036] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of the present invention, directional terms and order terms are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0037] As shown in Figure 1, the tunable Raman fiber laser includes a pulse 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 combiner 9. The output end of the pulse seed source unit 1 is connected to the beam splitter 2, which is divided into two beams of seed light with different powers by the beam splitter 2. One output end of the beam splitter 2 is connected to the input end of the beam combiner 4, the output end of the pump source 3 is connected to the input end of the beam combiner 4, the output end of the beam combiner 4 is connected to the gain fiber 5, the gain fiber 5 is connected to the n-order Raman gain fiber 7, and the n-1-order Raman gain fiber 7 is connected to the input end of isolator 18, and the output end of isolator 18 is connected to the input end of energy combiner 9; the other output end of beam splitter 12 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, and 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 a filter 15 is provided on the output optical path of Raman gain fiber 10.

[0038] The gain fiber 15 is a double-clad fiber core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, and is a polarization-maintaining fiber doped with ytterbium or erbium ions, or a non-polarization-maintaining fiber;

[0039] The gain fiber 2 12 is a double-clad fiber core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, and is a polarization-maintaining fiber doped with ytterbium or erbium ions, or a non-polarization-maintaining fiber;

[0040] The n-order Raman gain fiber 7 is pure quartz or germanium, boron, phosphorus ion-doped polarization-maintaining fiber or non-polarization-maintaining fiber with a core diameter of 10um, 20um, or 30um;

[0041] The n-1 order Raman gain fiber 13 is pure quartz or germanium, boron, phosphorus ion doped polarization maintaining fiber or non-polarization maintaining fiber with a core diameter of 10um, 20um, or 30um;

[0042] The Raman gain fiber 10 is a pure quartz fiber or a polarization-maintaining fiber doped with germanium, boron, or phosphorus ions or a non-polarization-maintaining fiber with a core diameter of 10 μm, 20 μm, or 30 μm.

[0043] Filter 15 is a bandwidth filter with a central wavelength of n-order Raman laser, including central wavelengths of 1116nm, 1168nm, 1175nm, 1220nm, 1128nm, 1189nm, 1400nm, 1514nm, and 1739nm, and a bandwidth of 0.1 to 10nm.

[0044] The fundamental frequency seed light 1 of the pulse seed source unit 1 is split by a beam splitter 2 at a splitting ratio of 50%:50%. One beam splitting path of the beam splitter 2 and the light path of the pump source 3 enter the gain fiber 5 through a beam combiner 4, so that the pump light and the seed light are amplified in the gain fiber 5 to obtain a high-power fundamental frequency signal light. The fundamental frequency signal light undergoes energy conversion in an n-order Raman gain fiber 7 to obtain an n-order Raman laser output;

[0045] The other split light path of the beam splitter 2 and the light path of the pump source 2 6 enter the gain fiber 2 12 through the beam combiner 2 11, so that the pump light and the seed light are amplified in the gain fiber 2 12 to obtain a high-power fundamental frequency signal light. The fundamental frequency signal light undergoes energy conversion in the n-1 order Raman gain fiber 13 to obtain an n-1 order Raman laser output;

[0046] The obtained n-order Raman laser and n-1-order Raman laser are respectively combined by the energy combiner 9 after passing through the isolator into the Raman gain fiber 10, wherein the n-1-order Raman light is used as the pump of the n-order Raman light, thereby amplifying the n-order Raman light. The amplified n-order Raman light is then filtered out by the filter 15 to remove the residual pump light, and the n-order Raman light output is obtained.

[0047] As shown in 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 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 of 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 105, the filter 2 106 is placed in the collimator 105, the collimator 105 is connected to the isolator 3 107, the isolator 3 107 controls the unidirectional transmission of light, and the modulator 108 modulates the pulse output.

[0048] Light from pump source 3 101 is input into gain fiber 3 103 through beam combiner 3 102, inverting the population within the gain fiber. A portion of the laser light from beam splitter 2 104 serves as the output laser. The other end of beam splitter 2 104 is connected to collimator 1 105. Isolator 3 107 controls unidirectional light transmission. By replacing filter 2 106 with different central wavelength bandwidths and controlling extracavity modulator 1 108, smooth, unmodulated Gaussian pulses can be generated. The resulting pulsed laser serves as the fundamental frequency seed pulse.

[0049] Gain fiber 3 103 is a double-clad fiber with a core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, and is a polarization-maintaining fiber or a non-polarization-maintaining fiber doped with ytterbium or erbium ions.

[0050] Collimator 105 is a U-shaped collimator with two end spacings of 38mm, 89mm, and 96mm. Both ends are coated with anti-reflection coatings with a wavelength range of 600nm to 1050nm or 1050nm to 1620nm.

[0051] Isolator 3 107 is an isolator with a central wavelength in the range of 600 to 1620 nm and an isolation greater than 25 dB;

[0052] Modulator 108 is an acousto-optic modulator or an electro-optic modulator;

[0053] The second filter 106 is a lens filter or a grating filter with a central wavelength in the range of 600 to 1620 nm and a bandwidth of 0.1 nm, 1 nm, 2 nm, or 3 nm.

[0054] Alternatively, as shown in 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 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 combiner 4 203, the output end of the combiner 4 203 is connected to the gain fiber 4 204, the gain fiber 4 204 is connected to the collimator 2 205, and the filter 3 206 is placed in the collimator 2 205. A high-reflection film 202 is coated on the optical fiber at one end of the combiner 4 203, and a low-reflection film 207 is coated on one end of the collimator 2 205. The high-reflection film 202 and the low-reflection film 207 form a resonant cavity to cause the laser to oscillate and amplify, and the modulator 208 modulates the continuous light into pulsed light. The high-reflection film 202 is a reflective film with a bandwidth of 900 nm to 1100 nm and a reflectivity greater than 99%. The low-reflection film 207 is a reflective film with a bandwidth of 900 nm to 1100 nm and a reflectivity selectable between 10% and 90%.

[0055] The gain fiber 204 is a double-clad fiber core diameter of 10 / 125um, 20 / 130um, or 30 / 250um, and is a polarization-maintaining fiber doped with ytterbium or erbium ions, or a non-polarization-maintaining fiber;

[0056] Collimator 205 is a U-shaped collimator with two end spacings of 38mm, 89mm, and 96mm. Both ends are coated with anti-reflection coatings with a wavelength range of 600nm to 1050nm or 1050nm to 1620nm.

[0057] Modulator 208 is an acousto-optic modulator or an electro-optic modulator;

[0058] The third filter 206 is a lens filter or a grating filter with a central wavelength in the range of 600 to 1620 nm and a bandwidth of 0.1 nm, 1 nm, 2 nm, or 3 nm.

[0059] The light emitted by the pump source 4 201 is input into the gain fiber 4 204 through the combiner 4 203, so that the particle number in the gain fiber is reversed. A high-reflection film 202 is coated on the optical fiber at one end of the combiner 4 203. The gain fiber 4 204 is connected to the collimator 2 205. A filter 3 206 is placed in the collimator 2 205. By replacing the filter 3 206 with different central wavelengths and bandwidths, the output of lasers in different bands is controlled. A low-reflection film 207 is coated on one end of the collimator 2 205. The high-reflection film 202 and the low-reflection film 207 form a resonant cavity to oscillate and amplify the laser. By replacing different filters, laser output of different wavelengths is obtained. The extracavity modulator 208 modulates the continuous light into pulsed light, thereby obtaining a fundamental frequency seed pulse.

[0060] The Yb gain fiber's emission spectrum ranges from 900nm to 1100nm. Selecting a bandpass filter within this range results in significant light loss outside the bandwidth, inhibiting lasing. Lasers within the filter's spectral bandwidth, however, experience minimal loss and exhibit significant gain. When the intracavity gain exceeds the loss, lasing occurs within the filter's bandwidth. Therefore, filters with different center wavelengths and bandwidths are selected to generate seed lasers of varying wavelengths. By placing a modulator outside the resonant cavity, such as an electro-optic modulator or an acousto-optic modulator, pulsed light output with varying pulse widths can be generated.

[0061] During optical fiber transmission, when the laser's peak power is high or the fiber is long enough, a portion of the power will be transferred from one optical field to another optical field with a lower frequency. The Raman frequency shift in typical quartz fibers is 50 to 60 nm, allowing for laser output at wavelengths of 1120 to 1200 nm outside the Yb gain spectrum.

[0062] In summary, the present 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 light field will be converted from fundamental frequency light to Raman light. By selecting a suitable filter to select the wavelength and a modulator to modulate pulses of different widths as fundamental frequency seed light, Raman pulse light outside the gain fiber spectrum is obtained after power amplification and Raman frequency shift, achieving adjustable wavelength and pulse width, and having the characteristics of high power, high conversion efficiency, and low thermal effect.

[0063] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, and the like made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention. It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it need not be further defined or explained in subsequent figures.

[0064] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0065] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

Claims

1. Tunable Raman fiber laser, characterized in that: It includes a pulsed seed source unit (1), a first pump source (3), a second pump source (6), a first beam splitter (2), a first combiner (4), a second combiner (11), an n - order Raman gain fiber (7), an n - 1 - order Raman gain fiber (13), and an energy combiner (9). The output end of the pulsed seed source unit (1) is connected to the first beam splitter (2), and the first beam splitter (2) divides it into two seed lights with different powers. One output end of the first beam splitter (2) is connected to the input end of the first combiner (4), the output end of the first pump source (3) is connected to the input end of the first combiner (4), the output end of the first combiner (4) is connected to the first gain fiber (5), the first gain fiber (5) is connected to the n - order Raman gain fiber (7), the input end of the n - order Raman gain fiber (7) is connected to the input end of the first isolator (8), and the output end of the first isolator (8) is connected to the input end of the energy combiner (9); The other output end of the first beam splitter (2) is connected to the input end of the second combiner (11), the output end of the second pump source (6) is connected to the input end of the second combiner (11), the output end of the second combiner (11) is connected to the second gain fiber (12), the second gain fiber (12) is connected to the n - 1 - order Raman gain fiber (13), the input end of the n - 1 - order Raman gain fiber (13) is connected to the input end of the second isolator (14), and the output end of the second isolator (14) is connected to the input end of the energy combiner (9); The output end of the energy combiner (9) is connected to the Raman gain fiber (10), and a first filter (15) is provided on the output optical path of the Raman gain fiber (10).

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

3. The tunable Raman fiber laser according to claim 1, characterized in that: The first filter (15) is a bandwidth filter with a central wavelength of the n - order Raman laser, and the central wavelengths are 1116nm, 1168nm, 1175nm, 1220nm, 1128nm, 1189nm, 1400nm, 1514nm, 1739nm, etc., and the bandwidth is 0.1 - 10nm filter.

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

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

6. The tunable Raman fiber laser according to claim 4, characterized in that: The first collimator (105) is a U-shaped collimator with a distance of 38mm, 89mm, or 96mm between the two ends, and the wavelength range of the anti-reflection coating on the two ends is 600nm to 1050nm or 1050nm to 1620nm; The third isolator (107) is an isolator with a central wavelength range of 600nm to 1620nm and an isolation degree greater than 25dB; The first modulator (108) is an acousto-optic modulator or an electro-optic modulator.

7. The tunable Raman fiber laser according to claim 4, characterized in that: The second filter (106) is a lens filter or a grating filter with a central wavelength range of 600nm to 1620nm and a bandwidth of 0.1nm, 1nm, 2nm, or 3nm 8. The tunable Raman fiber laser according to claim 1, characterized in that: The pulsed seed source unit (1) includes a laser resonator and a second modulator (208) placed outside the cavity. The laser resonator includes a fourth pump source (201), a fourth beam combiner (203), a fourth gain fiber (204), a second collimator (205), and a third filter (206). The output end of the fourth pump source (201) is connected to the input end of the fourth beam combiner (203). The output end of the fourth beam combiner (203) is connected to the fourth gain fiber (204). The fourth gain fiber (204) is connected to the second collimator (205). The third filter (206) is placed inside the second collimator (205). A high-reflection film (202) is coated on one end of the fiber of the fourth beam combiner (203). A low-reflection film (207) is coated on one end of the second collimator (205). The high-reflection film (202) and the low-reflection film (207) form a resonator to enable the laser to oscillate and amplify. The second modulator (208) modulates the continuous light into pulsed light.

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

10. The tunable Raman fiber laser according to claim 8, characterized in that: The gain fiber four (204) is a ytterbium- and erbium-ion-doped polarization-maintaining or non-polarization-maintaining fiber with a double-clad core diameter of 10 / 125 um, 20 / 130 um, or 30 / 250 um; The collimator two (205) is a U-shaped collimator with a distance between the two ends of 38 mm, 89 mm, or 96 mm, and the wavelength range of the antireflection film plated on both ends is 600 nm to 1050 nm or 1050 nm to 1620 nm; The modulator two (208) is an acousto-optic modulator or an electro-optic modulator; The filter three (206) is a lens filter or a grating filter with a central wavelength range of 600 nm to 1620 nm and a bandwidth of 0.1 nm, 1 nm, 2 nm, or 3 nm.

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