A high power single mode fiber laser

Abstract

The application discloses a high-power single-mode optical fiber laser, which comprises an oscillator and an amplifier, wherein the oscillator comprises a forward pumping module (1), a high-reflection fiber grating (2), a low-doped large-mode-field low-numerical-aperture gain optical fiber (3), a low-reflection fiber grating (4), a backward pumping module (5) and a laser output module (6); the amplifier comprises a seed source (7), the forward pumping module (1), the low-doped large-mode-field low-numerical-aperture gain optical fiber (3), the backward pumping module (5) and the laser output module (6); the low-doped large-mode-field low-numerical-aperture gain optical fiber is a rare earth ion doped optical fiber with low absorption coefficient, large core mode field diameter and small numerical aperture at the maximum absorption coefficient wavelength. The application simultaneously suppresses mode instability effect and stimulated Raman scattering effect, and has lower photon darkening effect.

Description

Technical Field

[0001] This invention belongs to the field of high-power fiber laser technology and relates to a new solution for a high-power single-mode fiber laser. Background Technology

[0002] High-power single-mode fiber lasers are crucial light sources for industrial processing applications. Currently, the improvement of high-brightness single-channel power is mainly limited by transverse mode instability (TMI) and stimulated Raman scattering (SRS). TMI reduces beam quality, limits power increases, and even threatens laser safety; while SRS induces TMI and reduces system efficiency, spectral purity, and beam quality. Traditionally, increasing the fiber absorption coefficient is thought to shorten the gain fiber length, thus reducing the impact of nonlinear effects. However, for high-power fiber lasers, the TMI threshold is typically lower, and TMI occurs first rather than nonlinear effects. Therefore, continuing to use traditional gain fibers to build high-power fiber lasers cannot achieve high-beam-quality laser output. Furthermore, high absorption can lead to photon darkening, reducing the long-term reliability of the fiber. Theoretical research suggests that TMI mainly originates from mode coupling caused by thermal load; therefore, reducing thermal load is beneficial for suppressing TMI. To effectively suppress the TMI effect, some researchers have used semiconductor pump sources with low absorption coefficient wavelengths to reduce heat generation per unit length. However, this method requires increasing the fiber length to obtain sufficient absorption, which enhances the nonlinear effect. Therefore, the contradiction between increasing the power of traditional high-power single-mode fiber lasers is very acute. Summary of the Invention

[0003] This invention provides a high-power single-mode fiber laser, which includes at least: a forward pump module (1), a low-doped large-mode-field low-numerical-aperture gain fiber (3), a backward pump module (5), and a laser output module (6); wherein the forward pump module (1) and the backward pump module (5) each include an output fiber and an input fiber, and the output fiber of the forward pump module (1) is connected to one end of the low-doped large-mode-field low-numerical-aperture gain fiber (3) by fiber fusion splicing; the output fiber of the backward pump module (5) is connected to the low-doped large-mode-field low-numerical-aperture gain fiber (6) by fiber fusion splicing. The other end of the fiber is connected by optical fiber fusion splicing, and the input fiber of the back pump module (5) and the laser output module (6) are connected by optical fiber fusion splicing. The low-doped large mode field low numerical aperture gain fiber (3) is a quartz glass fiber doped with a single rare earth ion. The cladding absorption coefficient of the low-doped large mode field low numerical aperture gain fiber (3) at the strongest pump absorption wavelength is 0.3dB / m-0.8dB / m, the core diameter is 25μm-50μm, the cladding diameter is 400μm-1000μm, and the core numerical aperture is 0.03-0.055.

[0004] Furthermore, the rare earth ions include ytterbium ions, erbium ions, thulium ions, and holmium ions.

[0005] Furthermore, the single-mode fiber laser can be used as a laser oscillator. When used as a laser oscillator, a high-reflectivity fiber grating (2) is inserted on the fiber between the forward pump module (1) and the low-doped large-mode-field low-numerical-aperture gain fiber (3); and a low-reflectivity fiber grating (4) is inserted between the low-doped large-mode-field low-numerical-aperture gain fiber (3) and the backward pump module (5).

[0006] Furthermore, the center wavelength of the high reflectivity fiber grating (2) corresponds to the wavelength range in which the gain of the low-doped large-mode-field low-numerical-aperture gain fiber is the largest. The reflectivity of the high reflectivity fiber grating (2) is >99%, the reflection bandwidth is 1nm-3nm, and the fiber core, cladding diameter and numerical aperture parameters are the same as those of the low-doped large-mode-field low-numerical-aperture gain fiber (3). The center wavelength of the low reflectivity fiber grating (4) is the same as that of the high reflectivity fiber grating (1). The reflectivity of the low reflectivity fiber grating is 15%-5%, the reflection bandwidth is 0.1nm-2nm, and the fiber core, cladding diameter and numerical aperture parameters are the same as those of the low-doped large-mode-field low-numerical-aperture gain fiber (3). Both fiber gratings are connected to the low-doped large-mode-field low-numerical-aperture gain fiber (3) and the forward pump module (1) or the backward pump module (5) respectively through fiber fusion splicing.

[0007] Furthermore, the center wavelength range of the low reflectivity fiber grating (4) and the high reflectivity fiber grating (1) is 1060nm-1090nm.

[0008] Furthermore, the single-mode fiber laser can be used as a laser amplifier, which includes: a seed source (7); the output fiber of the seed source (7) is fused with the input fiber of the forward pump module (1); the center wavelength of the seed source (7) corresponds to the wavelength range of the low-doped large-mode-field low-numerical-aperture gain fiber (3) with the maximum gain, and the output power of the seed source is 50W-300W.

[0009] Furthermore, the laser output module (6) includes a cladding light filter and an optical fiber output cap. The laser output module (6) uses an optical fiber whose core diameter and numerical aperture are not less than the core diameter and numerical aperture of the signal light output optical fiber of the back pump module (5).

[0010] Furthermore, the forward pump module (1) and the backward pump module (5) have the same optical structure, including an output optical fiber, an input optical fiber, and a pump signal coupler. The pump light is injected into the inner cladding of the output optical fiber through the pump signal coupler and then conducted into the low-doped large-mode-field low-numerical-aperture gain optical fiber (3). The input optical fiber can conduct the signal light output from the seed source or conduct the light output of the low-doped large-mode-field low-numerical-aperture gain optical fiber (3) to the laser output module (6) through the core of the input optical fiber. The core numerical aperture and core diameter of the input optical fiber are not less than the core numerical aperture and core diameter of the low-doped large-mode-field low-numerical-aperture gain optical fiber (3).

[0011] Furthermore, the center wavelength of the output light from the forward pumping module (1) and the backward pumping module (5) is 976 nm.

[0012] The following technical effects can be achieved by adopting this solution:

[0013] Low-doped gain fibers can easily achieve low core numerical apertures. Combined with a large core diameter design, the threshold for mode instability in gain fibers can be increased without significantly increasing the number of supported modes. Simultaneously, the increased core diameter effectively mitigates the increase in fiber length caused by weakened absorption. This scheme suppresses mode instability effects through the low absorption coefficient resulting from low doping; and balances nonlinear effects such as stimulated Raman scattering through a large mode field and low numerical aperture. This design effectively alleviates the two major problems limiting the power increase of single-mode fiber lasers without increasing the difficulty of fiber fabrication, and also significantly improves the shortcomings of highly doped fibers, such as photonic darkening. Attached Figure Description

[0014] Figure 1 This is one of the structural schematic diagrams of a new high-power single-mode fiber laser design.

[0015] Figure 2 This is the second schematic diagram of a new high-power single-mode fiber laser design.

[0016] The diagram is labeled as follows: 1-Forward pump module, 2-High reflectivity fiber grating, 3-Low-doped large mode field low numerical aperture gain fiber, 4-Low reflectivity fiber grating, 5-Backward pump module, 6-Laser output module, 7-Seed source. Detailed Implementation

[0017] The purpose of this invention is to disclose a novel scheme for a high-power single-mode fiber laser. From the perspective of fiber fabrication, it simultaneously suppresses mode instability and stimulated Raman scattering (SRS) by designing a low-doped fiber with a large mode area and low numerical aperture. Firstly, the absorption intensity of the pump light is controlled using a low-doped fiber, thereby mitigating the thermal load on the gain fiber. The gain fiber growth caused by reducing the absorption coefficient and the enhancement of nonlinear effects (SRS) are controlled by increasing the mode area. Compared to traditional gain fibers, low doping naturally results in a low numerical aperture. Low-doped fibers can easily have a smaller core numerical aperture, such as 0.04, thus increasing the mode area without significantly increasing the number of modes supported by the core. This weakens nonlinear effects while maintaining beam quality, achieving simultaneous suppression of both physical limitations. The manufacturing process is also simpler than traditional low-numerical-aperture gain fiber manufacturing methods. Furthermore, the reduced doping concentration weakens photon darkening, which also enhances the reliability of the laser.

[0018] The technical solution of the present invention is as follows:

[0019] A novel high-power single-mode fiber laser design includes two structures: an oscillator and an amplifier. The oscillator structure comprises a forward pump module connected to a high-reflectivity fiber grating, a high-reflectivity fiber grating connected to a low-doped, large-mode-field, low-numerical-aperture gain fiber, a low-reflectivity fiber grating connected to a low-reflectivity fiber grating, a low-reflectivity fiber grating connected to a backward pump module, and a backward pump module connected to a laser output module. All connections are achieved through fiber fusion splicing.

[0020] The low-doped large-mode-field low-numerical-aperture gain fiber is a silica glass fiber doped with a single rare-earth ion, including ytterbium, erbium, thulium, holmium, etc. The cladding absorption coefficient of the fiber at the strongest pump absorption wavelength is 0.3dB / m-0.8dB / m (for example, the strongest absorption wavelength of ytterbium-doped fiber is 976nm), the core diameter is 25μm-50μm, the cladding diameter is 400μm-1000μm, and the core numerical aperture is 0.03-0.055.

[0021] The forward pumping module injects pump light into the fiber cladding of a high-reflectivity fiber grating through a pump coupling device, such as a pump signal coupler. The two devices have the same fiber parameters, and the pump wavelength of the forward pumping module is the strongest absorption wavelength of the low-doped large-mode-field low-numerical-aperture gain fiber.

[0022] The center wavelength of the high reflectivity fiber grating corresponds to the wavelength range in which the gain of the low-doped large-mode-field low-numerical-aperture gain fiber is maximized. For example, for ytterbium-doped fiber, the wavelength range is 1060nm-1090nm. The reflectivity of the high reflectivity fiber grating is >99%, and the reflection bandwidth is 1nm-3nm. The fiber core, cladding diameter, and numerical aperture parameters are the same as those of the low-doped large-mode-field low-numerical-aperture gain fiber, ensuring low-loss fusion splicing.

[0023] The center wavelength of the low-reflectivity fiber grating is the same as that of the high-reflectivity fiber grating; the reflectivity of the low-reflectivity fiber grating is 15%-5%, the reflection bandwidth is 0.1nm-2nm, and the fiber core, cladding diameter, and numerical aperture parameters are the same as those of the low-doped large-mode-field low numerical aperture gain fiber, ensuring low-loss fusion splicing.

[0024] The backward pumping module injects pump light into the inner cladding of a low-reflectivity fiber grating using a pump coupling device, such as a pump signal coupler. The combined end of the pump signal coupler has the same diameter as the outer cladding of the low-reflectivity fiber grating. The backward pumping module also has a signal light transmission function, which can transmit the generated signal light through the fiber core to the laser output module. The numerical aperture of the fiber core for transmitting the signal light is not less than the corresponding parameters of the low-doped large-mode-field low-numerical-aperture gain fiber. The pump wavelength of the backward pumping module is the strongest absorption wavelength of the low-doped large-mode-field low-numerical-aperture gain fiber.

[0025] The laser output module is a structure that outputs the generated high-power laser. It includes a cladding optical filter and an optical fiber output cap. The core diameter and numerical aperture of the optical fiber used are not less than the corresponding parameters of the signal light output optical fiber of the back pump module.

[0026] The amplifier structure consists of: a seed source connected to the forward pump module; the forward pump module connected to a low-doped, large-mode-field, low-numerical-aperture gain fiber; the low-doped, large-mode-field, low-numerical-aperture gain fiber connected to the backward pump module; and the backward pump module connected to the laser output module. All connections are achieved through fiber fusion splicing.

[0027] The low-doped large-mode-field low-numerical-aperture gain fiber is a silica glass fiber doped with a single rare-earth ion, including ytterbium, erbium, thulium, holmium, etc. The cladding absorption coefficient of the fiber at the strongest pump absorption wavelength is 0.3dB / m-0.8dB / m (for example, the strongest absorption wavelength of ytterbium-doped fiber is 976nm), the core diameter is 25μm-50μm, the cladding diameter is 400μm-1000μm, and the core numerical aperture is 0.03-0.055.

[0028] The center wavelength of the seed source corresponds to the wavelength range in which the gain of a low-doped, large-mode-field, low-numerical-aperture-gain fiber is maximized. For example, for ytterbium-doped fiber, the wavelength range is 1060nm-1090nm; the output power of the seed source is 50W-300W.

[0029] The forward pumping module injects pump light into the cladding of a low-doped large-mode-field low-numerical-aperture gain fiber using a pump coupling device, such as a pump signal coupler, and injects seed light into the core of the low-doped large-mode-field low-numerical-aperture gain fiber. The output fiber cladding of the pump signal coupler has the same diameter as the cladding of the low-doped large-mode-field low-numerical-aperture gain fiber, and the core diameter is not greater than the core diameter of the low-doped large-mode-field low-numerical-aperture gain fiber. The pump wavelength of the forward pumping module is the strongest absorption wavelength of the low-doped large-mode-field low-numerical-aperture gain fiber.

[0030] The backward pumping module injects pump light into the cladding of a low-doped large-mode-field low-numerical-aperture gain fiber using a pump coupling device, such as a pump signal coupler. The combined end of the pump signal coupler has the same diameter as the cladding of the low-doped large-mode-field low-numerical-aperture gain fiber. The backward pumping module has a signal light transmission function, which can transmit the amplified signal light through the fiber core to the laser output module. The numerical aperture and diameter of the fiber core for transmitting the signal light are not less than the corresponding parameters of the low-doped large-mode-field low-numerical-aperture gain fiber. The pump wavelength of the backward pumping module is the strongest absorption wavelength of the low-doped large-mode-field low-numerical-aperture gain fiber.

[0031] The laser output module is a structure that outputs the generated high-power laser. It includes a cladding optical filter and an optical fiber output cap. The core diameter and numerical aperture of the optical fiber used are not less than the corresponding parameters of the signal light output optical fiber of the back pump module.

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] The innovation of this invention lies in the use of low-doped, large-mode-field, low-numerical-aperture gain fiber, which can simultaneously suppress mode instability and stimulated Raman scattering. The invention will be further explained below with reference to the figures.

[0034] Figure 1This is a schematic diagram of a new high-power single-mode fiber laser scheme, commonly referred to as an oscillator structure, which includes (1) a forward pump module with a center wavelength of 976nm, a power of 1300W, and an inner cladding of 400μm for the output fiber. (2) a high-reflectivity fiber grating with a center wavelength of 1080nm, a reflectivity of 99%, and a reflection bandwidth of 4nm, with a fiber diameter of 30 / 400μm and a core numerical aperture of 0.05. (3) a low-doped, large-mode-field, low-numerical-aperture ytterbium-doped fiber with an absorption coefficient of 0.6dB / m at a wavelength of 976nm, a core diameter of 30μm, a numerical aperture of 0.05, a cladding diameter of 400μm, and a length of 25m. (4) a low-reflectivity fiber grating with a center wavelength of 1080nm, a reflectivity of 10%, and a reflection bandwidth of 2nm, with a fiber diameter of 30 / 400μm and a core numerical aperture of 0.05. (5) A back-pumping module with a center wavelength of 976nm, a power of 5000W, and an output fiber of 30 / 400μm with a core numerical aperture of 0.05. (6) The laser output module includes a cladding optical filter and an optical fiber output cap, using a 30 / 400μm optical fiber with a core numerical aperture of 0.05. The forward pump module couples the pump light into the inner cladding of the high reflectivity fiber grating (2). After passing through the high reflectivity fiber grating (2), the pump light enters the cladding of the low-doped large-mode-field low-numerical-aperture ytterbium-doped fiber (3) and is continuously absorbed by the fiber core. The high reflectivity fiber grating (2), the low-doped large-mode-field low-numerical-aperture gain fiber (3), and the low reflectivity fiber grating (4) form a fiber resonant cavity, which converts the absorbed pump light into laser light in the fiber core. The backward pump module (5) can also inject pump light on the one hand, and transmit the generated laser light to the laser output module (6) through the signal arm on the other hand. The laser output module (6) includes a cladding light filter and a fiber output cap.

[0035] Figure 2This is the second schematic diagram of a new high-power single-mode fiber laser scheme, usually referred to as an amplifier structure, which includes (1) a forward pump module with a center wavelength of 976nm, (3) a low-doped large-mode low-numerical-aperture ytterbium-doped fiber with an absorption coefficient of 0.6dB / m, a core diameter of 30μm, a numerical aperture of 0.05, and a length of 25m, (5) a backward pump module with a center wavelength of 976nm, (6) a laser output module, and (7) a seed source with a center wavelength of 1080nm and a power of 80W. The laser from the seed source (1) and the pump light from the forward pump module (2) are injected into the low-doped large-mode-field low-numerical-aperture ytterbium-doped fiber (3) through the signal arm and pump arm of the forward pump module (1). The pump light from the backward pump module (5) is also injected into the cladding of the low-doped large-mode-field low-numerical-aperture ytterbium-doped fiber (3). After absorbing the pump light, the low-doped large-mode-field low-numerical-aperture gain fiber (3) continuously amplifies the seed light and outputs it to the laser output module (6) through the signal arm of the backward pump module (5). The laser output module (6) includes a cladding light filter and an fiber output cap.

[0036] Example 1

[0037] The following is a schematic diagram of the structure of the present invention. Figure 1 The corresponding specific embodiment: A new scheme for a high-power single-mode fiber laser includes a forward pumping module (1), a high-reflectivity fiber grating (2), a low-doped large-mode-field low numerical aperture gain fiber (3), a low-reflectivity fiber grating (4), a backward pumping module (5), and a laser output module (6).

[0038] Furthermore, the forward pump module (1) has a pump light center wavelength of 976nm and a power of 1300W.

[0039] The high reflectivity fiber grating (2) has a center wavelength of 1080nm, a reflectivity of 99%, and a reflection bandwidth of 4nm.

[0040] The low-doped large-mode-field low numerical aperture gain fiber (3) is a ytterbium-doped fiber with an absorption coefficient of 0.6 dB / m at 976 nm, a core diameter of 30 μm, a numerical aperture of 0.05, and a length of 25 m.

[0041] The low-reflectivity fiber grating (4) has a center wavelength of 1080nm, a reflectivity of 10%, and a reflection bandwidth of 2nm.

[0042] The back pump module (5) has a pump light center wavelength of 976nm and a power of 5000W.

[0043] The laser output module (6) includes a cladding optical filter and an optical fiber output cap.

[0044] Using this embodiment, a single-mode 1080nm band laser output with a forward output power greater than 5kW can be obtained.

[0045] Example 2

[0046] The following is a schematic diagram of the structure of the present invention. Figure 2 The corresponding specific embodiment: A new scheme for a high-power single-mode fiber laser includes a seed source (7), a forward pumping module (1), a low-doped large-mode-field low numerical aperture gain fiber (3), a backward pumping module (5), and a laser output module (6).

[0047] Furthermore, the seed source (7) has a center wavelength of 1080nm, single-mode input, power of 80W, and output fiber of 20 / 400μm.

[0048] The forward pump module (1) has a pump light center wavelength of 976nm and a power of 1300W. The signal input and output optical fibers are both 20 / 400μm optical fibers.

[0049] The low-doped large-mode-field low numerical aperture gain fiber (3) is a ytterbium-doped fiber with an absorption coefficient of 0.6 dB / m at 976 nm, a core diameter of 30 μm, a cladding diameter of 400 μm, a numerical aperture of 0.05, and a length of 25 m.

[0050] The back pump module (5) has a pump light center wavelength of 976nm and a power of 5000W.

[0051] The laser output module (6) includes a cladding optical filter and an optical fiber output cap. The optical fiber is a 30 / 400μm double-clad optical fiber with a core numerical aperture of 0.05.

[0052] Using this embodiment, a single-mode 1080nm band laser output with a forward output power greater than 5kW can be obtained.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and are not intended to limit them. Although the embodiments of the present invention have been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the embodiments of the present invention should not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-power single-mode fiber laser, characterized in that, The single-mode fiber laser includes at least: a forward pump module (1), a low-doped large-mode-field low-numerical-aperture gain fiber (3), a backward pump module (5), and a laser output module (6); wherein the forward pump module (1) and the backward pump module (5) both include an output fiber and an input fiber, the output fiber of the forward pump module (1) and one end of the low-doped large-mode-field low-numerical-aperture gain fiber (3) are connected together by fiber fusion splicing; the other end of the output fiber of the backward pump module (5) and the low-doped large-mode-field low-numerical-aperture gain fiber (3) are connected together by fiber fusion splicing, and the input fiber of the backward pump module (5) and the laser output module (6) are connected together by fiber fusion splicing; The optical output power of the backward pumping module (5) is greater than that of the forward pumping module (1); The forward pump module (1) and the backward pump module (5) have the same optical structure, including an output optical fiber, an input optical fiber, and a pump signal coupler. The pump light is injected into the inner cladding of the output optical fiber through the pump signal coupler and then conducted into the low-doped large-mode-field low-numerical-aperture gain optical fiber (3). The input optical fiber can conduct the signal light output from the seed source or conduct the light output of the low-doped large-mode-field low-numerical-aperture gain optical fiber (3) to the laser output module (6) through the core of the input optical fiber. The core numerical aperture and core diameter of the input optical fiber are not less than the core numerical aperture and core diameter of the low-doped large-mode-field low-numerical-aperture gain optical fiber (3). The low-doped large-mode-field low numerical aperture gain fiber (3) is a silica glass fiber doped with a single rare earth ion. The cladding absorption coefficient of the low-doped large-mode-field low numerical aperture gain fiber (3) at the strongest pump absorption wavelength is 0.3dB / m-0.8dB / m, the core diameter is 25μm-50μm, the cladding diameter is 400μm-1000μm, and the core numerical aperture is 0.03-0.

055. The laser output module (6) includes a cladding light filter and an optical fiber output cap. The laser output module (6) uses an optical fiber whose core diameter and numerical aperture are not less than the core diameter and numerical aperture of the signal light output optical fiber of the back pump module (5).

2. The single-mode fiber laser as described in claim 1, characterized in that, The rare earth ions mentioned include ytterbium ions, erbium ions, thulium ions, and holmium ions.

3. The single-mode fiber laser as described in claim 1, characterized in that, The single-mode fiber laser can be used as a laser oscillator. When used as a laser oscillator, a high reflectivity fiber grating (2) is inserted on the fiber between the forward pump module (1) and the low-doped large-mode-field low-numerical-aperture gain fiber (3); and a low reflectivity fiber grating (4) is inserted between the low-doped large-mode-field low-numerical-aperture gain fiber (3) and the backward pump module (5).

4. The single-mode fiber laser as described in claim 3, characterized in that, The center wavelength of the high reflectivity fiber grating (2) corresponds to the wavelength range in which the gain of the low-doped large-mode-field low numerical aperture gain fiber is the largest. The reflectivity of the high reflectivity fiber grating (2) is >99%, and the reflection bandwidth is 1nm-3nm. The fiber core, cladding diameter and numerical aperture parameters are the same as those of the low-doped large-mode-field low numerical aperture gain fiber (3). The center wavelength of the low reflectivity fiber grating (4) is the same as that of the high reflectivity fiber grating (2). The reflectivity of the low reflectivity fiber grating is 15%-5%, and the reflection bandwidth is 0.1nm-2nm. The fiber core, cladding diameter and numerical aperture parameters are the same as those of the low-doped large-mode-field low numerical aperture gain fiber (3). Both fiber gratings are connected to the low-doped large-mode-field low numerical aperture gain fiber (3) and the forward pump module (1) or the backward pump module (5) respectively by fiber fusion splicing.

5. The single-mode fiber laser as described in claim 4, characterized in that, The center wavelengths of the low-reflectivity fiber grating (4) and the high-reflectivity fiber grating (2) range from 1060nm to 1090nm.

6. The single-mode fiber laser as described in claim 1, characterized in that, The single-mode fiber laser can be used as a laser amplifier, which includes: a seed source (7); the output fiber of the seed source (7) is fused with the input fiber of the forward pump module (1); the center wavelength of the seed source (7) corresponds to the wavelength range of the low-doped large-mode-field low-numerical-aperture gain fiber (3) with the maximum gain, and the output power of the seed source is 50W-300W.

7. The single-mode fiber laser as described in claim 1, characterized in that, The center wavelength of the output light from the forward pumping module (1) and the backward pumping module (5) is 976 nm.

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