High-beam-quality 980nm-waveband ytterbium-doped fiber laser with expandable power

Abstract

The invention discloses a 980nm-waveband ytterbium-doped fiber laser with expandable power and high beam quality. The 980nm-waveband ytterbium-doped fiber laser is composed of a single-mode seed source, a K-level fiber amplifier and an output coupling end. The single-mode seed source adopts an optical fiber oscillator and is composed of a first gain optical fiber, a first pumping signal beam combiner, a first pumping module, a first cladding light filter, a second cladding light filter, a high-reflectivity optical fiber grating, a low-reflectivity optical fiber grating, a first filter and a mode field adapter. The K-stage optical fiber amplifier is composed of K single-stage optical fiber amplifiers and K-1 filters, and except the last single-stage optical fiber amplifier, the output end of each single-stage optical fiber amplifier is connected with one filter. Each of the K single-stage optical fiber amplifiers comprises a section of gain optical fiber, two pumping signal beam combiners, two pumping modules and two cladding light filters, and the gain optical fiber is a step double-cladding ytterbium-doped optical fiber. According to the invention, high beam quality output can be ensured, and the total output power can be improved.

Description

Technical Field

[0001] The present invention relates to an optical fiber laser, and in particular to an optical fiber laser having an operating band of about 980 nm (975 nm to 985 nm) and a high beam quality (beam quality M 2 Factor is less than or equal to 2) Ytterbium-doped fiber laser. Background Art

[0002] High beam quality 980nm band fiber lasers have broad application prospects. First, high beam quality 980nm band fiber lasers can be used as core pump light sources for ultrafast fiber lasers, which is beneficial to shorten the cavity length, thereby suppressing nonlinear effects, and has important application prospects in industrial processing, material processing and other fields. Secondly, high beam quality 980nm band fiber lasers can also generate new band light sources through frequency conversion. For example, blue-green light in the 490nm band can be generated by frequency doubling, which can be used in fields such as ocean exploration and underwater communications; near-ultraviolet lasers in the 320nm band can be generated by frequency tripling, which can be used in biology, medicine, spectroscopy and other fields.

[0003] At present, the gain fiber that can be used for 980nm band fiber lasers is ytterbium-doped fiber, which is also the preferred gain fiber for high-power fiber lasers at this stage. However, it is not easy to achieve a high-power and high-beam quality 980nm band fiber laser, which is determined by the energy level characteristics of ytterbium ions. The energy level structure of ytterbium ions determines that the 980nm band fiber laser is a three-level laser, which means that while generating a 980nm band light field, it also generates strong amplified spontaneous radiation in the 1030nm band. To suppress the amplified spontaneous radiation in the 1030nm band, the conventional method is to increase the core-cladding ratio of the ytterbium-doped fiber. But this brings new contradictions: First, to achieve high-power laser output, sufficient pump light power is essential, which makes the cladding size not too small, so it is necessary to increase the core diameter to improve the core-cladding ratio, and the increase in core diameter will cause the beam quality to decrease; conversely, to achieve high beam quality output, the core diameter cannot be too large, and the cladding diameter must also be reduced, which in turn limits the coupling of pump light, thereby limiting the increase in output power. Therefore, although the "all-fiber structure 980nm band high-power fiber oscillator" with patent number "ZL201710102903.4" proposes the use of ytterbium-doped fiber with a large core-cladding ratio to achieve a kilowatt-level 980nm band fiber laser, the use of ytterbium-doped fiber with a large core-cladding ratio is not conducive to achieving high beam quality for 980nm band fiber lasers. In addition, the cost of drawing large core cladding is higher than that of ytterbium-doped optical fiber, and related passive components (such as fiber pump combiners, mode field adapters, etc.) also need to be customized or self-developed, which greatly increases the development cost of the system.

[0004] At present, one solution for realizing high beam quality 980nm band fiber lasers is to use microstructured fibers or fibers with special structure designs. Among them, microstructured fibers include photonic crystal fibers, air hole outer cladding fibers, photonic bandgap fibers, multi-core fibers, etc.; fibers with special structure designs include tapered fibers, saddle-shaped fibers, W-shaped fibers, etc. These fibers achieve high beam quality 980nm band fiber laser output through microstructure design or special structure design. The maximum output power is 151W. However, the structures of these fibers are relatively complex, the fiber preparation is difficult, and the development cost is high, which is not conducive to the commercial promotion and application of the laser.

[0005] In order to realize a cost-controlled high-beam-quality 980nm band fiber laser, a feasible solution is to use single-mode or few-mode step-index ytterbium-doped fiber as the gain fiber. The step-index ytterbium-doped fiber used in this type of solution has a simple structure, which greatly reduces the difficulty of fiber drawing and the development cost of the system. The "all-fiber structure 980nm band composite cavity single-mode fiber laser" with patent number "ZL201310749840.3" achieves high beam quality output by using single-mode single-clad ytterbium-doped fiber. However, the core pumping method adopted in this solution greatly limits the pump light power, so that the output power is limited to the watt level. In order to solve the problem of limited pump power in core pumping, the "a kind of all-fiber structure 980nm band high-power fiber oscillator" with patent number "ZL202011314846.4" proposes a high-beam-quality 980nm band fiber oscillator based on double-clad ytterbium-doped fiber. This solution is based on a step-index double-clad ytterbium-doped fiber with a core diameter of 20 microns and a cladding diameter of 125 microns. Through cladding pumping, the pump light power is greatly improved (the pump light power reaches 230W) while ensuring high beam quality. However, the output power of the laser is still limited because the oscillator structure limits the pump light power.

[0006] Summarizing the existing high beam quality 980nm band fiber laser solutions, the core problem is the limited pump module, which greatly limits the power of the pump light, which is very unfavorable for further power expansion. Therefore, under the premise of ensuring cost control, how to achieve further power expansion based on few-mode step double-clad ytterbium-doped fiber is a problem of great concern to technicians in this field. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing 980nm band fiber lasers and provide a power-scalable high-beam quality 980nm band fiber laser based on step double-clad ytterbium-doped fiber. Through the design of ytterbium-doped fiber, the problems faced by the existing solutions in power improvement are solved, so that the laser has a good power expansion output capability while ensuring high beam quality output.

[0008] The technical solution of the present invention is:

[0009] The present invention consists of a single-mode seed source, a K-class optical fiber amplifier and an output coupling end. The output end of the single-mode seed source is connected to the input end of the K-class optical fiber amplifier. The output end of the K-class optical fiber amplifier is connected to the input end of the output coupling end. The output end of the output coupling end serves as the output end of the present invention. The connection between different devices in the present invention is achieved by optical fiber fusion splicing. K is the number of single-stage optical fiber amplifiers in the K-class optical fiber amplifier, and K is a positive integer. The total output power of the present invention is related to K, and the total output power P is equal to the output power of the single-stage optical fiber amplifier multiplied by K. Therefore And K ≥ 2;

[0010] The single-mode seed source of the present invention adopts a fiber oscillator, and the fiber oscillator adopts a backward pumping structure. The single-mode seed source is composed of a first gain fiber, a first pump signal combiner, a first pump module, a first cladding light filter, a second cladding light filter, a high-reflection fiber grating, a low-reflection fiber grating, a first filter and a mode field adapter. Among them, the first pump signal combiner 102 includes N (N is a positive integer) pump light input ends, a signal light input end and an output end. It is required that the core diameter of the output end fiber and the signal light input end fiber of the first pump signal combiner is equal to the core diameter of the first gain fiber; the cladding diameter of the output end fiber and the signal light input end fiber of the first pump signal combiner is equal to the cladding diameter of the first gain fiber. The output end of the first pump signal combiner is connected to one end of the first gain fiber. The pump light input end of the first pump signal combiner is connected to the output fiber of the first pump module. The signal light input end of the first pump signal combiner is connected to the input end of the second cladding light filter. The input end of the first cladding optical filter is connected to the other end of the first gain optical fiber. The output end of the first cladding optical filter is connected to the input end of the high-reflection fiber Bragg grating. The output end of the second cladding optical filter is connected to the input end of the low-reflection fiber Bragg grating. The output end of the low-reflection fiber Bragg grating is connected to the input end of the first filter. The output end of the first filter is connected to the input end of the mode field adapter. The output end of the mode field adapter is the output end of the single-mode seed source, which is connected to the input end of the K-class optical fiber amplifier.

[0011] The first pump module of the present invention includes N1 pump sub-modules, N1≤N. The pump sub-module uses a semiconductor laser with a pigtail output in the 900nm to 960nm band. In this case, the pigtail of the semiconductor laser is the output optical fiber of the pump sub-module. The output optical fiber of all the pump sub-modules constituting the first pump module is the output optical fiber of the first pump module, and is connected to the N1 pump light input ends of the first pump signal combiner. The output optical fiber diameter of the first pump module should be ≤ the diameter of the optical fiber at the pump light input end of the first pump signal combiner; the numerical aperture of the output optical fiber of the first pump module should be ≤ the numerical aperture of the optical fiber at the pump light input end of the first pump signal combiner.

[0012] The first gain fiber of the present invention is a single-mode step-index double-clad ytterbium-doped fiber. The core diameter of the step-index double-clad ytterbium-doped fiber is not less than 10 microns, the normalized frequency is less than 2.405, and the cladding diameter is not less than 125 microns. The length should be ≤ the fiber length corresponding to the single-mode seed source 1 when no self-excited oscillation in the 1030nm band is generated.

[0013] The first cladding optical filter and the second cladding optical filter of the present invention are mainly used to filter out residual pump light. It is required that the core diameter of the first cladding optical filter and the second cladding optical filter is equal to the core diameter of the first gain optical fiber; the cladding diameter of the first cladding optical filter and the second cladding optical filter is equal to the cladding diameter of the first gain optical fiber.

[0014] The central wavelength of the high-reflection fiber Bragg grating of the present invention is between 976 and 980 nm, and the reflectivity at the central wavelength is ≥99%. The output fiber of the high-reflection fiber Bragg grating should suppress the reflection of the optical field by the fiber end face, and can adopt but not limited to the common bevel cutting. The core of the high-reflection fiber Bragg grating is equal to the core diameter of the first gain fiber, and the cladding diameter is equal to the cladding diameter of the first gain fiber.

[0015] The center wavelength of the low-reflection fiber grating of the present invention is approximately equal to the center wavelength of the high-reflection fiber grating (the deviation should be less than 1nm), and the reflectivity at the center wavelength is ≥5%. The core of the low-reflection fiber grating is equal to the core diameter of the first gain fiber, and the cladding diameter is equal to the cladding diameter of the first gain fiber.

[0016] The first filter of the present invention is used to filter out amplified spontaneous radiation in the 1030nm band. The loss in the 1030nm band should be greater than or equal to 50dB. The core diameters of the input and output optical fibers of the first filter are equal to the core diameters of the output optical fibers of the low-reflection fiber grating; the cladding diameters of the input and output optical fibers of the first filter are equal to the cladding diameters of the output optical fibers of the low-reflection fiber grating.

[0017] The mode field adapter of the present invention is used to connect a single-mode seed source and a K-class optical fiber amplifier to ensure near-diffraction-limited transmission of the single-mode seed source. The core diameter of the input optical fiber of the mode field adapter is equal to the core diameter of the output optical fiber of the first filter, and the cladding diameter is equal to the cladding diameter of the output optical fiber of the first filter. The core diameter of the output optical fiber of the mode field adapter is equal to the core diameter of the input end optical fiber of the K-class optical fiber amplifier, and the cladding diameter is equal to the cladding diameter of the input end optical fiber of the K-class optical fiber amplifier.

[0018] The K-stage optical fiber amplifier of the present invention is composed of K single-stage optical fiber amplifiers and K-1 filters. The first-stage optical fiber amplifier, the second filter, ..., the k-th stage optical fiber amplifier, the k+1-th filter, ..., the K-th stage optical fiber amplifier are connected in sequence, 2≤k≤K. Except for the last single-stage optical fiber amplifier (i.e., the K-th stage optical fiber amplifier), the output end of each single-stage optical fiber amplifier is connected to a filter (e.g., Figure 2 The output end of the first-stage optical fiber amplifier is connected to the second filter, the output end of the k-th optical fiber amplifier is connected to the k+1-th filter, and the output end of the K-th optical fiber amplifier is not connected to the filter).

[0019] The K single-stage fiber amplifiers of the present invention (i.e., the first-stage fiber amplifier, ..., the k-th-stage fiber amplifier, ..., the K-th-stage fiber amplifier) ​​have the same structure, and all include 1 section of gain fiber, 2 pump signal combiners, 2 pump modules, and 2 cladding light filters. Among them, the first-stage fiber amplifier is composed of a second gain fiber, a second pump signal combiner, a third pump signal combiner, a second pump module, a third pump module, a third cladding light filter, and a fourth cladding light filter. The second pump signal combiner and the third pump signal combiner both include multiple pump light input ends, 1 signal light input end, and 1 output end, the second pump signal combiner includes M pump light input ends, and the third pump signal combiner includes U pump light input ends. The core diameters of the output fiber of the second pump signal combiner, the signal light input fiber of the second pump signal combiner, the output fiber of the third pump signal combiner, and the signal light input fiber of the third pump signal combiner are all equal to the core diameter of the second gain fiber; the cladding diameters of the output fiber of the second pump signal combiner, the signal light input fiber of the second pump signal combiner, the output fiber of the third pump signal combiner, and the signal light input fiber of the third pump signal combiner are all equal to the cladding diameter of the second gain fiber. The output end of the second pump signal combiner and the output end of the third pump signal combiner are respectively connected to the two ends of the second gain fiber. The signal light input end of the second pump signal combiner is connected to the input end of the third cladding light filter. The pump light input end of the second pump signal combiner is connected to the output fiber of the second pump module. The signal light input end of the third pump signal combiner is connected to the input end of the fourth cladding light filter, and the pump light input end of the third pump signal combiner is connected to the output fiber of the third pump module. The output end of the third cladding optical filter is connected to the output end of the mode field adapter, which is the input end of the first-stage optical amplifier and also the input end of the K-class optical amplifier. The output end of the fourth cladding optical filter is the output end of the first-stage optical amplifier and is connected to the input end of the second filter.

[0020] The second pump module of the present invention comprises M1 pump submodules, and the third pump module comprises U1 pump submodules, M1≤M, U1≤U. The pump submodule selects a semiconductor laser with a pigtail output in the wavelength band of 900nm to 960nm. When a semiconductor laser is selected, the pigtail of the M1 semiconductor laser is the output optical fiber of the pump submodule. The output optical fiber of the M1 pump submodules constituting the second pump module is the output optical fiber of the second pump module, and is connected to the M1 pump light input ends of the second pump signal combiner. The output optical fiber of the U1 pump submodules constituting the third pump module is the output optical fiber of the third pump module, and is connected to the U1 pump light input ends of the third pump signal combiner. The output optical fiber diameter of the second pump module should be ≤ the diameter of the optical fiber at the pump light input end of the second pump signal combiner; the numerical aperture of the output optical fiber of the second pump module should be ≤ the numerical aperture of the optical fiber at the pump light input end of the second pump signal combiner. The output fiber diameter of the third pump module should be ≤ the diameter of the fiber at the pump light input end of the third pump signal combiner; the numerical aperture of the output fiber of the third pump module should be ≤ the numerical aperture of the fiber at the pump light input end of the third pump signal combiner.

[0021] The second gain fiber of the present invention is a step-index double-clad ytterbium-doped fiber. The core diameter of the step-index double-clad ytterbium-doped fiber is required to be ≤20 microns, and the cladding diameter is required to be ≤125 microns. The total cladding absorption of the ytterbium-doped fiber for pump light is required to be ≤3dB, which is the core design of the technical solution. This design can ensure that when the seed light generated by the single-mode seed source is injected into the first-stage optical fiber amplifier, no self-excited oscillation in the 1030nm band is generated.

[0022] The third cladding optical filter and the fourth cladding optical filter of the present invention are mainly used to filter out residual pump light. The core diameter of the third cladding optical filter and the fourth cladding optical filter is equal to the core diameter of the second gain optical fiber; the cladding diameter of the third cladding optical filter and the fourth cladding optical filter is equal to the cladding diameter of the second gain optical fiber 2101.

[0023] The k-th optical fiber amplifier of the present invention is composed of a k+1-th gain optical fiber, a 2k-th pump signal combiner, a 2k+1-th pump signal combiner, a 2k-th pump module, a 2k+1-th pump module, a 2k+1-th cladding optical filter and a 2k+2-th cladding optical filter. The core diameter of the k+1-th gain optical fiber is equal to the core diameter of the second gain optical fiber, and the cladding diameter is equal to the cladding diameter of the second gain optical fiber. The total cladding absorption requirement of the k+1-th gain optical fiber for pump light is required to be ≤3dB, so as to ensure that when the high-power signal light output by the first k-1 single-stage amplifier enters the k-th optical fiber amplifier, no self-excited oscillation in the 1030nm band is generated, so as to ensure the safe operation of the laser. The remaining device parameter requirements in the k-th optical fiber amplifier are the same as those of the first optical fiber amplifier. The output end of the 2k+1-th cladding optical filter is connected to the output end of the previous filter (i.e., the k-th filter) and is the input end of the k-th optical fiber amplifier. The output end of the 2k+2 cladding optical filter is connected to the input end of the next filter (i.e., the k+1 filter), which is the output end of the k-th fiber amplifier. The connection of the remaining components in the k-th fiber amplifier is the same as that of the first-stage fiber amplifier.

[0024] The K-th optical fiber amplifier of the present invention is composed of the K+1-th gain optical fiber, the 2K-th pump signal combiner, the 2K+1 pump signal combiner, the 2K-th pump module, the 2K+1 pump module, the 2K+1 cladding optical filter and the 2K+2 cladding optical filter. The device parameter requirements of the K-th optical fiber amplifier are the same as those of the k-th optical fiber amplifier. The output end of the 2K+1 cladding optical filter is connected to the input end of the previous filter (i.e., the K-th filter) and is the input end of the K-th optical fiber amplifier. The output end of the 2K+2 cladding optical filter is the output end of the K-th optical fiber amplifier and is also the output end of the K-th optical fiber amplifier. The connection conditions of the remaining devices in the K-th optical fiber amplifier are the same as those of the first-stage optical fiber amplifier.

[0025] The K-1 filters in the K-class optical fiber amplifier of the present invention are used to filter out the amplified spontaneous radiation in the 1030nm band. The loss in the 1030nm band should be greater than 50dB. The output beam quality M 2 The factor should not be greater than 1.8. The core diameter of the optical fiber at the input end of each filter should be equal to the core diameter of the cladding light filter connected to it, and the cladding diameter should be equal to the cladding diameter of the cladding light filter connected to it (such as Figure 2The core diameter of the optical fiber at the input end of the second filter shown is equal to the core diameter of the fourth cladding optical filter in the first-stage optical fiber amplifier, and the cladding diameter is equal to the cladding diameter of the fourth cladding optical filter in the first-stage optical fiber amplifier; ...; the core diameter of the optical fiber at the input end of the k+1th filter is equal to the core diameter of the 2k+2th cladding optical filter in the k-th optical fiber amplifier, and the cladding diameter is equal to the cladding diameter of the 2k+2th cladding optical filter in the k-th optical fiber amplifier; ...; the core diameter of the optical fiber at the input end of the Kth filter is equal to the core diameter of the 2K cladding optical filter in the K-1th optical fiber amplifier, and the cladding diameter is equal to the cladding diameter of the 2K cladding optical filter in the K-1th optical fiber amplifier).

[0026] The core diameter of the input optical fiber of the output coupling end of the present invention is equal to the core diameter of the optical fiber of the output end of the K-class optical fiber amplifier, and the cladding diameter is equal to the cladding diameter of the optical fiber of the output end of the K-class optical fiber amplifier. Its structure can adopt an optical fiber output end cap.

[0027] The working process of the present invention is:

[0028] The single-mode seed source 1 is used to generate a single-mode seed light in the 980nm band. The single-mode seed light in the 980nm band enters the optical fiber amplifier 2 for power amplification and then is output through the output coupling end 3. The specific description is as follows: In the single-mode seed source 1, the first pump signal combiner 102 couples the pump light generated by the first pump module 103 into the first gain optical fiber 101, and pumps the ytterbium ions of the first gain optical fiber 101, thereby generating a signal light in the 980nm band. The light field in the 980nm band forms laser oscillation in the resonant cavity formed by the high-reflection fiber grating 106 and the low-reflection fiber grating 107, and is transmitted and output by the low-reflection fiber grating 107. Then, the laser transmitted by the low-reflection fiber grating 107 is filtered out by the first filter 108 to remove the amplified spontaneous radiation in the 1030nm band, and then enters the first-stage optical fiber amplifier through the mode field adapter 109. In the first-stage optical fiber amplifier 210, the second pump signal combiner 2102 and the third pump signal combiner 2103 couple the pump light generated by the second pump module 2104 and the third pump module 2105 into the second gain optical fiber 2101, and pump the ytterbium ions of the second gain optical fiber 2101, thereby amplifying the seed light passing through the core of the second gain optical fiber 2101. After the amplified seed light is filtered out by the second filter 211 to remove the amplified spontaneous radiation in the 1030nm band, it enters the next-stage optical fiber amplifier for amplification. The amplified seed light then enters the subsequent optical fiber amplifier for amplification, and so on. The signal light amplified by the first-stage optical fiber amplifier 210 will be amplified step by step through each single-stage optical fiber amplifier in turn, and finally output from the output coupling end 3. In this process, all cladding light filters are used to filter out residual pump light.

[0029] The following technical effects can be achieved by adopting the present invention:

[0030] 1. The present invention designs the total pump absorption of the ytterbium-doped fiber in the amplifier, making the multi-stage amplification structure of the fiber laser feasible;

[0031] 2. The present invention adopts a multi-stage amplifier structure, and the output power can be expanded by increasing the number of amplifier stages, thereby providing a 980nm band ytterbium-doped fiber laser with scalable power and high beam quality;

[0032] 3. The design of the present invention can give full play to the power bearing capacity of optical fibers and devices. The higher the power bearing capacity of optical fibers and devices, the higher the expandable power;

[0033] 4. The present invention ensures high beam quality output of the laser by adopting a single-mode seed source, a filter with a beam quality factor less than 1.8, and a double-clad ytterbium-doped optical fiber with a core diameter not greater than 20 microns, and the beam quality factor is not greater than 2;

[0034] 5. The present invention greatly reduces the difficulty of drawing ytterbium-doped optical fiber and the manufacturing cost of the system by adopting a step-index double-clad ytterbium-doped optical fiber with a core diameter of no more than 20 microns and a cladding diameter of no less than 125 microns. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the overall structure of the 980nm-band optical fiber laser with expandable power and high beam quality according to the present invention.

[0036] Figure 2 for Figure 1 Schematic diagram of the specific structure of each component. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] like Figure 1 As shown, the present invention consists of a single-mode seed source 1, a K-class fiber amplifier 2 and an output coupling end 3. The output end of the single-mode seed source 1 is connected to the input end of the K-class fiber amplifier 2. The output end of the K-class fiber amplifier 2 is connected to the input end of the output coupling end 3. The output end of the output coupling end 3 serves as the output end of the present invention. The connection between different devices in the present invention is achieved by fiber fusion splicing. K is the number of single-stage fiber amplifiers in the K-class fiber amplifier 2, and K is a positive integer. The total output power of the present invention is related to K, and the total output power is equal to the output power of the single-stage fiber amplifier multiplied by K. Therefore, if it is necessary to prepare a power-expandable, high-beam-quality 980nm band ytterbium-doped fiber laser with a total output power of P, then

[0039] like Figure 2 As shown, the single-mode seed source 1 of the present invention adopts a fiber oscillator, and the fiber oscillator adopts a backward pumping structure. The single-mode seed source 1 is composed of a first gain fiber 101, a first pump signal combiner 102, a first pump module 103, a first cladding light filter 104, a second cladding light filter 105, a high-reflection fiber grating 106, a low-reflection fiber grating 107, a first filter 108 and a mode field adapter 109. Among them, the first pump signal combiner 102 includes N (N is a positive integer) pump light input ends (the pump light input ends are numbered 102-1 to 102-N), a signal light input end 1022 and an output end 1021. It is required that the core diameter of the output optical fiber 1021 and the signal light input optical fiber 1022 of the first pump signal combiner 102 is equal to the core diameter of the first gain optical fiber 101; the cladding diameter of the output optical fiber 1021 and the signal light input optical fiber 1022 of the first pump signal combiner 102 is equal to the cladding diameter of the first gain optical fiber 101. The output end 1021 of the first pump signal combiner 102 is connected to one end of the first gain optical fiber 101. The pump light input end of the first pump signal combiner 102 is connected to the output optical fiber of the first pump module 103. The signal light input end 1022 of the first pump signal combiner 102 is connected to the input end of the second cladding light filter 105. The input end of the first cladding light filter 104 is connected to the other end of the first gain optical fiber 101. The output end of the first cladding light filter 104 is connected to the input end of the high-reflection fiber grating 106. The output end of the second cladding light filter 105 is connected to the input end of the low-reflection fiber Bragg grating 107. The output end of the low-reflection fiber Bragg grating 107 is connected to the input end of the first filter 108. The output end of the first filter 108 is connected to the input end of the mode field adapter 109. The output end of the mode field adapter 109 is the output end of the single-mode seed source 1, which is connected to the input end of the K-class fiber amplifier 2.

[0040] The first pump module 103 includes N1 pump submodules (numbered 103-1 to 103-N1), N1≤N. The pump submodule uses a semiconductor laser with a pigtail output in the 900nm to 960nm band. At this time, the pigtail of the semiconductor laser is the output fiber of the pump submodule. The output fiber of all the pump submodules constituting the first pump module 103 is the output fiber of the first pump module 103, and is connected to the N1 pump light input ends of the first pump signal combiner 102. The output fiber diameter of the first pump module 103 should be ≤ the diameter of the fiber at the pump light input end of the first pump signal combiner 102; the numerical aperture of the output fiber of the first pump module 103 should be ≤ the numerical aperture of the fiber at the pump light input end of the first pump signal combiner 102.

[0041] The first gain fiber 101 of the present invention is a single-mode step-index double-clad ytterbium-doped fiber. The core diameter of the single-mode step-index double-clad ytterbium-doped fiber is not less than 10 microns, the normalized frequency is less than 2.405, and the cladding diameter is not less than 125 microns. The length should be ≤ the fiber length corresponding to the single-mode seed source 1 when no self-excited oscillation in the 1030nm band is generated.

[0042] The first cladding optical filter 104 and the second cladding optical filter 105 of the present invention are mainly used to filter out residual pump light. The core diameter of the first cladding optical filter 104 and the second cladding optical filter 105 is equal to the core diameter of the first gain optical fiber 101; the cladding diameter of the first cladding optical filter 104 and the second cladding optical filter 105 is equal to the cladding diameter of the first gain optical fiber 101.

[0043] The central wavelength of the high-reflection fiber grating 106 of the present invention is between 976 and 980 nm, and the reflectivity at the central wavelength is ≥99%. The core diameter of the high-reflection fiber grating 106 is equal to the core diameter of the first gain fiber 101, and the cladding diameter is equal to the cladding diameter of the first gain fiber 101. The input end of the high-reflection fiber grating 106 is connected to the output end of the first cladding light filter 104. The output end optical fiber of the high-reflection fiber grating 106 should suppress the reflection of the optical field by the optical fiber end face, and can adopt but is not limited to the common bevel cutting.

[0044] The center wavelength of the low-reflection fiber grating 107 of the present invention is approximately equal to the center wavelength of the high-reflection fiber grating 106 (the deviation should be less than 1nm), and the reflectivity at the center wavelength is ≥5%. The core diameter of the low-reflection fiber grating 107 is equal to the core diameter of the first gain fiber 101, and the cladding diameter is equal to the cladding diameter of the first gain fiber 101.

[0045] The first filter 108 of the present invention is used to filter out the amplified spontaneous radiation in the 1030nm band. The loss in the 1030nm band should be ≥50dB. The core diameters of the input and output optical fibers of the first filter 108 are equal to the core diameters of the output optical fibers of the low-reflection fiber grating 107; the cladding diameters of the input and output optical fibers of the first filter 108 are equal to the cladding diameters of the output optical fibers of the low-reflection fiber grating 107.

[0046] The mode field adapter 109 of the present invention is used to connect the single-mode seed source 1 and the K-class fiber amplifier 2 to ensure the near-diffraction-limited transmission of the single-mode seed source 1. The core diameter of the input fiber of the mode field adapter 109 is equal to the core diameter of the output fiber of the first filter 108, and the cladding diameter is equal to the cladding diameter of the output fiber of the first filter 108. The core diameter of the output fiber of the mode field adapter 109 is equal to the core diameter of the input end fiber of the K-class fiber amplifier 2, and the cladding diameter is equal to the cladding diameter of the input end fiber of the K-class fiber amplifier 2.

[0047] like Figure 2 As shown, the K-stage fiber amplifier 2 is composed of K single-stage fiber amplifiers and K-1 filters. The first-stage fiber amplifier 210, the second filter 211, ..., the k-th stage fiber amplifier 2k0, the k+1-th filter 2k1, ..., the K-th stage fiber amplifier 2K0 are connected in sequence, 2≤k≤K. Except for the last single-stage fiber amplifier (i.e., the K-th stage fiber amplifier 2K0), the output end of each single-stage fiber amplifier is connected to a filter (e.g., Figure 2 The output end of the first-stage optical fiber amplifier 210 is connected to the second filter 211, the output end of the k-th optical fiber amplifier 2k0 is connected to the k+1-th filter 2k1, and the output end of the K-th optical fiber amplifier 2K0 is not connected to the filter).

[0048] The K single-stage fiber amplifiers of the present invention (i.e., the first-stage fiber amplifier 210, ..., the k-th-stage fiber amplifier 2k0, ..., the K-th-stage fiber amplifier 2K0) have the same structure, and all include a section of gain fiber, two pump signal combiners, two pump modules, and two cladding light filters. Among them, the first-stage fiber amplifier 210 is composed of a second gain fiber 2101, a second pump signal combiner 2102, a third pump signal combiner 2103, a second pump module 2104, a third pump module 2105, a third cladding light filter 2106, and a fourth cladding light filter 2107. The second pump signal combiner 2102 and the third pump signal combiner 2103 both include multiple pump light input ends, one signal light input end and one output end. The second pump signal combiner 2102 includes M pump light input ends (the pump light input ends are numbered 2102-1 to 2102-M), and the third pump signal combiner 2103 includes U pump light input ends (the pump light input ends are numbered 2103-1 to 2103-U). The core diameters of the output optical fiber 21021 of the second pump signal combiner 2102, the signal light input optical fiber 21022 of the second pump signal combiner 2102, the output optical fiber 21031 of the third pump signal combiner 2103 and the signal light input optical fiber 21032 of the third pump signal combiner 2103 are all equal to the core diameter of the second gain fiber 2101; the cladding diameters of the output optical fiber 21021 of the second pump signal combiner 2102, the signal light input optical fiber 21022 of the second pump signal combiner 2102, the output optical fiber 21031 of the third pump signal combiner 2103 and the signal light input optical fiber 21032 of the third pump signal combiner 2103 are all equal to the cladding diameter of the second gain fiber 2101. The output end 21021 of the second pump signal combiner 2102 and the output end 21031 of the third pump signal combiner 2103 are respectively connected to the two ends of the second gain fiber 2101. The signal light input end 21022 of the second pump signal combiner 2102 is connected to the input end of the third cladding light filter 2106. The pump light input end of the second pump signal combiner 2102 is connected to the output optical fiber of the second pump module 2104. The signal light input end 21032 of the third pump signal combiner 2103 is connected to the input end of the fourth cladding light filter 2107, and the pump light input end of the third pump signal combiner 2103 is connected to the output optical fiber of the third pump module 2105. The output end of the third cladding light filter 2106 is connected to the output end of the mode field adapter 109, which is the input end of the first-stage optical amplifier 210, and is also the input end of the K-class optical amplifier 2. The output end of the fourth cladding optical filter 2107 is the output end of the first-stage optical fiber amplifier 210 , and is connected to the input end of the second filter 211 .

[0049] like Figure 2As shown, the second pump module 2104 of the present invention includes M1 pump submodules (numbered 2104-1 to 2104-M1), and the third pump module 2105 includes U1 pump submodules (numbered 2105-1 to 2015-U1), M1≤M, U1≤U. The pump submodule uses a pigtail to output a semiconductor laser in the 900nm to 960nm band. When a semiconductor laser is selected, the pigtail of the M1 semiconductor laser is the output fiber of the pump submodule. The output fiber of the M1 pump submodules constituting the second pump module 2104 is the output fiber of the second pump module 2104, and is connected to the M1 pump light input end of the second pump signal combiner 2102. The output fiber of the U1 pump submodules constituting the third pump module 2105 is the output fiber of the third pump module 2105, and is connected to the U1 pump light input end of the third pump signal combiner 2103. The output fiber diameter of the second pump module 2104 should be ≤ the diameter of the fiber at the pump light input end 21022 of the second pump signal combiner 2102; the numerical aperture of the output fiber of the second pump module 2104 should be ≤ the numerical aperture of the fiber 21022 at the pump light input end of the second pump signal combiner 2102. The output fiber diameter of the third pump module 2105 should be ≤ the diameter of the fiber at the pump light input end 21032 of the third pump signal combiner 2103; the numerical aperture of the output fiber of the third pump module 2105 should be ≤ the numerical aperture of the fiber at the pump light input end 21032 of the third pump signal combiner 2103.

[0050] The second gain fiber 2101 of the present invention is a step-index double-clad ytterbium-doped fiber. The core diameter of the step-index double-clad ytterbium-doped fiber is required to be ≤20 microns, and the cladding diameter is required to be ≤125 microns. The total cladding absorption of the ytterbium-doped fiber for pump light is required to be ≤3dB, which is the core design of the present technical solution. This design can ensure that when the seed light generated by the single-mode seed source 1 is injected into the first-stage optical fiber amplifier 210, no self-excited oscillation in the 1030nm band is generated.

[0051] The third cladding optical filter 2106 and the fourth cladding optical filter 2107 of the present invention are mainly used to filter out residual pump light. The core diameter of the third cladding optical filter 2106 and the fourth cladding optical filter 2107 is equal to the core diameter of the second gain optical fiber 2101; the cladding diameter of the third cladding optical filter 2106 and the fourth cladding optical filter 2107 is equal to the cladding diameter of the second gain optical fiber 2101.

[0052] The k-th fiber amplifier 2k0 of the present invention is composed of a k+1-th gain fiber 2k01, a 2k-th pump signal combiner 2k02, a 2k+1-th pump signal combiner 2k03, a 2k-th pump module 2k04, a 2k+1-th pump module 2k05, a 2k+1-th cladding light filter 2k06, and a 2k+2-th cladding light filter 2k07. The core diameter of the k+1-th gain fiber 2k01 is equal to the core diameter of the second gain fiber 2101, and the cladding diameter is equal to the cladding diameter of the second gain fiber 2101. It is required that the total cladding absorption of the k+1-th gain fiber 2k01 for the pump light is ≤3dB, so as to ensure that when the high-power signal light output by the first k-1 single-stage amplifiers enters the k-th fiber amplifier 2k0, no self-excited oscillation in the 1030nm band is generated, so as to ensure the safe operation of the laser. The parameter requirements of the remaining components in the k-th fiber amplifier 2k0 are the same as those of the first-stage fiber amplifier 210. The output end of the 2k+1-th cladding optical filter 2k06 is connected to the output end of the previous filter (i.e., the k-th filter 2(k-1)1), which is the input end of the k-th fiber amplifier 2k0. The output end of the 2k+2-th cladding optical filter 2k07 is connected to the input end of the next filter (i.e., the k+1-th filter 2k1), which is the output end of the k-th fiber amplifier 2k0. The connection conditions of the remaining components in the k-th fiber amplifier 2k0 are the same as those of the first-stage fiber amplifier 210.

[0053] The Kth optical fiber amplifier 2K0 of the present invention is composed of the K+1th gain optical fiber 2K01, the 2Kth pump signal combiner 2K02, the 2K+1th pump signal combiner 2K03, the 2Kth pump module 2K04, the 2K+1th pump module 2K05, the 2K+1th cladding optical filter 2K06 and the 2K+2th cladding optical filter 2K07. The device parameter requirements of the Kth optical fiber amplifier 2K0 are the same as those of the kth optical fiber amplifier 2k0. The output end of the 2K+1th cladding optical filter 2K06 is connected to the input end of the previous filter (i.e., the Kth filter 2(K-1)1), which is the input end of the Kth optical fiber amplifier 2K0. The output end of the 2K+2th cladding optical filter 2K07 is the output end of the Kth optical fiber amplifier 2K0, and is also the output end of the Kth optical fiber amplifier 2. The connection conditions of the remaining components in the K-th stage optical fiber amplifier 2K0 are the same as those of the first stage optical fiber amplifier 210 .

[0054] The K-1 filters (such as Figure 2 The second filter 211, ..., the kth filter 2(k-1)1, the k+1th filter 2k1, ..., the Kth filter 2(K-1)1) shown in the figure are all used to filter out the amplified spontaneous radiation in the 1030nm band, and the loss in the 1030nm band is required to be greater than 50dB. Output beam quality M 2The factor should not be greater than 1.8. The core diameter of the optical fiber at the input end of each filter should be equal to the core diameter of the cladding light filter connected to it, and the cladding diameter should be equal to the cladding diameter of the cladding light filter connected to it (such as Figure 2 The core diameter of the optical fiber at the input end of the second filter 211 shown is equal to the core diameter of the fourth cladding optical filter 2106 in the first-stage optical fiber amplifier 210, and the cladding diameter is equal to the cladding diameter of the fourth cladding optical filter 2106 in the first-stage optical fiber amplifier 210; ...; the core diameter of the optical fiber at the input end of the k+1 filter 2k1 is equal to the core diameter of the 2k+2 cladding optical filter 2k06 in the k-stage optical fiber amplifier 2k0, and the cladding diameter is equal to the cladding diameter of the fourth cladding optical filter 2106 in the first-stage optical fiber amplifier 210. The diameter is equal to the cladding diameter of the 2k+2 cladding optical filter 2k06 in the k-th optical fiber amplifier 2k0; ...; the core diameter of the optical fiber at the input end of the K-th filter 2(K-1)1 is equal to the core diameter of the 2k cladding optical filter 2(K-1)06 in the K-1-th optical fiber amplifier 2(K-1)0, and the cladding diameter is equal to the cladding diameter of the 2K cladding optical filter 2(K-1)06 in the K-1-th optical fiber amplifier 2(K-1)0).

[0055] The core diameter of the input fiber of the output coupling end 3 of the present invention is equal to the core diameter of the output fiber of the K-class fiber amplifier 2, and the cladding diameter is equal to the cladding diameter of the output fiber of the K-class fiber amplifier 2. Its structure can adopt a fiber output end cap.

[0056] The working process of the present invention is:

[0057] The single-mode seed source 1 is used to generate a single-mode seed light in the 980nm band. The single-mode seed light in the 980nm band enters the optical fiber amplifier 2 for power amplification and then is output through the output coupling end 3. The specific description is as follows: In the single-mode seed source 1, the first pump signal combiner 102 couples the pump light generated by the first pump module 103 into the first gain optical fiber 101, and pumps the ytterbium ions of the first gain optical fiber 101, thereby generating a signal light in the 980nm band. The light field in the 980nm band forms laser oscillation in the resonant cavity formed by the high-reflection fiber grating 106 and the low-reflection fiber grating 107, and is transmitted and output by the low-reflection fiber grating 107. Then, the laser transmitted by the low-reflection fiber grating 107 is filtered out by the first filter 108 to remove the amplified spontaneous radiation in the 1030nm band, and then enters the first-stage optical fiber amplifier through the mode field adapter 109. In the first-stage optical fiber amplifier 210, the second pump signal combiner 2102 and the third pump signal combiner 2103 couple the pump light generated by the second pump module 2104 and the third pump module 2105 into the second gain optical fiber 2101, and pump the ytterbium ions of the second gain optical fiber 2101, thereby amplifying the seed light passing through the core of the second gain optical fiber 2101. After the amplified seed light is filtered out by the second filter 211 to remove the amplified spontaneous radiation in the 1030nm band, it enters the next-stage optical fiber amplifier for amplification. The amplified seed light then enters the subsequent optical fiber amplifier for amplification, and so on. The signal light amplified by the first-stage optical fiber amplifier 210 will be amplified step by step through each single-stage optical fiber amplifier in turn, and finally output from the output coupling end 3. In this process, all cladding light filters are used to filter out residual pump light.

[0058] In order to test the effect of the present invention, Figure 2 The selection and parameters of the components shown are as follows:

[0059] The selection and parameters of each component in the single-mode seed source 1 are as follows: the core diameter of the first gain fiber 101 is 10 microns, the normalized frequency is 2.405, and the cladding diameter is 125 microns; the first pump signal combiner 102 has two pump light input ports (i.e., N=2). The first pump module 103 includes two pump submodules 103-1 to 103-2 (i.e., N1=2), each of which is composed of a semiconductor laser with a pigtail. The first cladding light filter 104 and the second cladding light filter 105 are used to filter out residual pump light. The central wavelength of the high-reflection fiber grating 106 is 979nm, and the reflectivity of the central wavelength is 99.5%; the central wavelength of the low-reflection fiber grating 107 is 979nm, and the reflectivity of the central wavelength is 10%. The output end of the high-reflection fiber grating 106 is cut into an oblique angle to suppress end face feedback. The loss of 1030nm band amplified spontaneous emission of the first filter 108 is 50dB. The core and cladding diameters of the input optical fiber of the mode field adapter 109 are 10 microns and 125 microns respectively, and the core and cladding diameters of the output optical fiber are 20 microns and 125 microns respectively.

[0060] The selection and parameters of the components of the first-stage fiber amplifier 210 in the K-class fiber amplifier 2 are as follows: the core diameter of the second gain fiber 2101 is 20 microns, the cladding diameter is 125 microns, and the total pump light absorption is 3dB; the second pump signal combiner 2102 and the third pump signal combiner 2103 both have two pump light input ports (i.e., M=U=2). The second pump module 2104 and the third pump module 2105 both include two pump submodules 2104-1 to 2104-2 and 2105-1 to 2105-2 (i.e., M1=U1=2), and each pump submodule is composed of a semiconductor laser with a pigtail. The third cladding light filter 2106 and the second cladding light filter 2107 are used to filter out residual pump light. The loss of the second filter 211 at the 1030nm band is 50dB.

[0061] The selection and parameters of each component in the other K-1 level optical fiber amplifier in the K level optical fiber amplifier 2 are the same as those of each component in the first level amplifier 210, and the loss of the remaining K-2 filters in the 1030nm band is 50dB.

[0062] The output coupling end 3 uses a fiber end cap. When the single-mode seed source 1 provides 10W seed light power and the single-stage fiber amplifier in the K-class fiber amplifier 2 provides 600W pump light power, the single-stage fiber amplifier can achieve a power output of the order of 100W (calculated based on a pump efficiency of 17%). If a two-stage fiber amplifier structure is used (i.e., K=2, the number of filters is 1), a beam quality M of the order of 200W can be achieved. 2The 980nm band laser output has a factor less than 2; if a three-stage fiber amplifier structure is used (i.e. K = 3, the number of filters is 2), a beam quality of 300W can be achieved. 2 The 980nm band laser output has a factor less than 2; if a K-class fiber amplifier structure is used (the number of filters is K-1), a beam quality of M at the order of K*100W can be achieved 2 The laser output in the 980nm band has a factor of less than 2. This also reflects the power scalability of this laser, and the power expansion limit of this laser is determined by the power tolerance of the optical fiber and the device.

Claims

1. A 980nm band ytterbium-doped fiber laser with scalable power and high beam quality, characterized in that The power-scalable high-beam-quality 980nm-band ytterbium-doped fiber laser comprises a single-mode seed source (1), a K-class fiber amplifier (2) and an output coupling end (3); the output end of the single-mode seed source (1) is connected to the input end of the K-class fiber amplifier (2); the output end of the K-class fiber amplifier (2) is connected to the input end of the output coupling end (3); the output end of the output coupling end (3) serves as the output end of the power-scalable high-beam-quality 980nm-band ytterbium-doped fiber laser; different devices in the power-scalable high-beam-quality 980nm-band ytterbium-doped fiber laser are connected by fiber fusion splicing; K is the number of single-stage fiber amplifiers in the K-class fiber amplifier (2), and K is a positive integer. And K ≥ 2, P is the total output power of the 980nm band ytterbium-doped fiber laser with scalable power and high beam quality; A single-mode seed source (1) of a 980nm band ytterbium-doped fiber laser with scalable power and high beam quality adopts a fiber oscillator. The single-mode seed source (1) is composed of a first gain fiber (101), a first pump signal combiner (102), a first pump module (103), a first cladding light filter (104), a second cladding light filter (105), a high-reflection fiber grating (106), a low-reflection fiber grating (107), a first filter (108) and a mode field adapter (109); the first pump signal combiner (102) comprises N pump light input ends (102-1 to 102-N), a signal light input end (1022) and an output end (1021), wherein N is a positive integer; the output end (1021) of the first pump signal combiner (102) is connected to one end of the first gain fiber (101); the first pump signal combiner (102) The pump light input end of the first pump signal combiner (102) is connected to the output optical fiber of the first pump module (103); the signal light input end (1022) of the first pump signal combiner (102) is connected to the input end of the second cladding optical filter (105); the input end of the first cladding optical filter (104) is connected to the other end of the first gain optical fiber (101); the output end of the first cladding optical filter (104) is connected to the input end of the high-reflection fiber grating (106); the output end of the second cladding optical filter (105) is connected to the input end of the low-reflection fiber grating (107); the output end of the low-reflection fiber grating (107) is connected to the input end of the first filter (108); the output end of the first filter (108) is connected to the input end of the mode field adapter (109); the output end of the mode field adapter (109) is the output end of the single-mode seed source (1), and is connected to the input end of the K-class optical fiber amplifier (2); The first pump module (103) comprises N1 pump submodules (103-1 to 103-N1); N1≤N; the pump submodule uses a semiconductor laser with a pigtail output in the 900nm to 960nm band, and the pigtail of the semiconductor laser is the output optical fiber of the pump submodule; the output optical fibers of all the pump submodules constituting the first pump module (103) are the output optical fibers of the first pump module (103), and are connected to N1 pump light input ends of the first pump signal combiner (102); The first gain optical fiber (101) is a single-mode step-index double-clad ytterbium-doped optical fiber; The first cladding light filter (104) and the second cladding light filter (105) are used to filter out residual pump light; The central wavelength of the high-reflection fiber Bragg grating (106) is between 976 and 980 nm, the input end of the high-reflection fiber Bragg grating (106) is connected to the output end of the first cladding light filter (104), and the output end optical fiber of the high-reflection fiber Bragg grating (106) suppresses the reflection of the optical field by the optical fiber end face; The deviation between the central wavelength of the low-reflection fiber grating (107) and the central wavelength of the high-reflection fiber grating (106) is less than 1 nm; The first filter (108) is used to filter out amplified spontaneous emission in the 1030 nm band; The mode field adapter (109) is used to connect the single-mode seed source (1) and the K-class optical fiber amplifier (2) to ensure near-diffraction-limited transmission of the single-mode seed source (1); The K-stage optical fiber amplifier (2) is composed of K single-stage optical fiber amplifiers and K-1 filters, wherein the first-stage optical fiber amplifier (210), the second filter (211), ..., the k-th stage optical fiber amplifier (2k0), the k+1-th filter (2k1), ..., and the K-th stage optical fiber amplifier (2K0) are connected in sequence, 2≤k≤K; except for the K-th stage optical fiber amplifier (2K0), the output end of each single-stage optical fiber amplifier is connected to a filter, that is, the output end of the first-stage optical fiber amplifier (210) is connected to the second filter (211), the output end of the k-th stage optical fiber amplifier (2k0) is connected to the k+1-th filter (2k1), ..., and the output end of the K-th stage optical fiber amplifier (2K0) is not connected to a filter; The first-stage optical fiber amplifier (210), ..., the k-th optical fiber amplifier (2k0), ..., and the K-th optical fiber amplifier (2K0) have the same structure, and all include a gain optical fiber, two pump signal combiners, two pump modules, and two cladding optical filters; wherein the first-stage optical fiber amplifier (210) includes a second gain optical fiber (2101), a second pump signal combiner (2102), a third pump signal combiner (2103), a second pump module (2104), a third pump module (2105), and a third cladding optical filter. The optical filter (2106) and the fourth cladding optical filter (2107) are composed; the second pump signal combiner (2102) and the third pump signal combiner (2103) each include a plurality of pump light input ends, a signal light input end and an output end, the second pump signal combiner (2102) includes M pump light input ends (2102-1 to 2102-M), and the third pump signal combiner (2103) includes U pump light input ends (2103-1 to 2103-U); the output end of the second pump signal combiner (2102) The output end (21031) of the third pump signal combiner (2103) and the second gain optical fiber (2101) are respectively connected; the signal light input end (21022) of the second pump signal combiner (2102) is connected to the input end of the third cladding optical filter (2106); the pump light input end of the second pump signal combiner (2102) is connected to the output optical fiber of the second pump module (2104); the signal light input end (21032) of the third pump signal combiner (2103) is connected to the input end of the fourth cladding optical filter (2106). The first optical fiber amplifier (210) and the second optical fiber amplifier (211) are connected to the input end of the optical fiber amplifier (210), and the second optical fiber amplifier (211) is connected to the input end of the optical fiber amplifier (210). The third pump signal combiner (2103) is connected to the output optical fiber of the third pump module (2105); the output end of the third cladding optical filter (2106) is connected to the output end of the mode field adapter (109), which is the input end of the first optical fiber amplifier (210), and is also the input end of the K-class optical fiber amplifier (2); the output end of the fourth cladding optical filter (2107) is the output end of the first optical fiber amplifier (210), and is connected to the input end of the second filter (211); The second pump module (2104) comprises M1 pump submodules (2104-1 to 2104-M1), and the third pump module (2105) comprises U1 pump submodules (2105-1 to 2015-U1); M1≤M; U1≤U; the pump submodule uses a semiconductor laser with a pigtail output in the 900nm to 960nm band, and the pigtails of the M1 semiconductor lasers are the output optical fibers of the pump submodule; the output optical fibers of the M1 pump submodules constituting the second pump module (2104) are the output optical fibers of the second pump module (2104), and are connected to the M1 pump light input ends of the second pump signal combiner (2102); the output optical fibers of the U1 pump submodules constituting the third pump module (2105) are the output optical fibers of the third pump module (2105), and are connected to the U1 pump light input ends of the third pump signal combiner (2103); The second gain optical fiber (2101) is a step-index double-clad ytterbium-doped optical fiber; the core diameter of the step-index double-clad ytterbium-doped optical fiber is ≤20 microns, and the cladding diameter is ≤125 microns; the total cladding absorption of the ytterbium-doped optical fiber for pump light is ≤3 dB, ensuring that when the seed light generated by the single-mode seed source (1) is injected into the first-stage optical fiber amplifier (210), no self-excited oscillation in the 1030 nm band is generated; The third cladding light filter (2106) and the fourth cladding light filter (2107) of the 980nm band ytterbium-doped fiber laser with scalable power and high beam quality are used to filter out residual pump light; The k-th optical fiber amplifier (2k0) is composed of a k+1-th gain optical fiber (2k01), a 2k-th pump signal combiner (2k02), a 2k+1-th pump signal combiner (2k03), a 2k-th pump module (2k04), a 2k+1-th pump module (2k05), a 2k+1-th cladding light filter (2k06) and a 2k+2-th cladding light filter (2k07); the total cladding absorption of the k+1-th gain optical fiber (2k01) for the pump light is ≤3dB, ensuring that when the high-power signal light output by the first k-1 single-stage amplifiers enters the k-th optical fiber amplifier (2k0), no self-excitation in the 1030nm band is generated. Oscillation; the parameter requirements of the remaining components in the k-th optical fiber amplifier (2k0) are the same as those of the first-stage optical fiber amplifier (210); the output end of the 2k+1-th cladding optical filter (2k06) is connected to the output end of the previous filter, i.e., the k-th filter (2(k-1)1), and is the input end of the k-th optical fiber amplifier (2k0); the output end of the 2k+2-th cladding optical filter (2k07) is connected to the input end of the next filter, i.e., the k+1-th filter (2k1), and is the output end of the k-th optical fiber amplifier (2k0); the connection conditions of the remaining components in the k-th optical fiber amplifier (2k0) are the same as those of the first-stage optical fiber amplifier (210); The Kth optical fiber amplifier (2K0) is composed of a K+1th gain optical fiber (2K01), a 2Kth pump signal combiner (2K02), a 2K+1th pump signal combiner (2K03), a 2Kth pump module (2K04), a 2K+1th pump module (2K05), a 2K+1th cladding light filter (2K06) and a 2K+2nd cladding light filter (2K07); the device parameter requirements of the Kth optical fiber amplifier (2K0) are the same as those of the kth optical fiber amplifier (2k0). The output end of the 2K+1 cladding optical filter (2K06) is connected to the input end of the previous filter, i.e., the K filter (2(K-1)1), and is the input end of the K-th optical fiber amplifier (2K0); the output end of the 2K+2 cladding optical filter (2K07) is the output end of the K-th optical fiber amplifier (2K0), and is also the output end of the K-th optical fiber amplifier (2); the connection conditions of the remaining components in the K-th optical fiber amplifier (2K0) are the same as those of the first-stage optical fiber amplifier (210); In a K-class fiber amplifier (2) of a 980nm band ytterbium-doped fiber laser with scalable power and high beam quality, K-1 filters, namely the second filter (211), ..., the kth filter (2(k-1)1), the k+1th filter (2k1), ..., the Kth filter (2(K-1)1), are all used to filter out amplified spontaneous radiation in the 1030nm band; The core diameter of the optical fiber at the input end of the output coupling end (3) is equal to the core diameter of the optical fiber at the output end of the K-class optical fiber amplifier (2), the cladding diameter is equal to the cladding diameter of the optical fiber at the output end of the K-class optical fiber amplifier (2), and the output coupling end (3) adopts an optical fiber output end cap.

2. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The fiber oscillator used in the single-mode seed source (1) adopts a backward pumping structure; the core diameters of the output end fiber (1021) and the signal light input end fiber (1022) of the first pump signal combiner (102) are equal to the core diameter of the first gain fiber (101); the cladding diameters of the output end fiber (1021) and the signal light input end fiber (1022) of the first pump signal combiner (102) are equal to the cladding diameter of the first gain fiber (101); the first gain fiber (101) adopts a single-mode step-index double-cladding ytterbium-doped The core diameter of the optical fiber is not less than 10 microns, the normalized frequency is less than 2.405, and the cladding diameter is not less than 125 microns; the length is less than or equal to the length of the optical fiber corresponding to the absence of self-excited oscillation in the 1030 nm band in the single-mode seed source (1); the core diameters of the first cladding optical filter (104) and the second cladding optical filter (105) are equal to the core diameter of the first gain optical fiber (101); and the cladding diameters of the first cladding optical filter (104) and the second cladding optical filter (105) are equal to the cladding diameter of the first gain optical fiber (101).

3. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The output optical fiber diameter of the first pump module (103) is less than or equal to the diameter of the optical fiber at the pump light input end of the first pump signal combiner (102); and the numerical aperture of the output optical fiber of the first pump module (103) is less than or equal to the numerical aperture of the optical fiber at the pump light input end of the first pump signal combiner (102).

4. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The reflectivity of the high-reflection fiber grating (106) at the central wavelength is ≥99%; the optical fiber at the output end of the high-reflection fiber grating (106) is cut at an angle; the core diameter of the high-reflection fiber grating (106) is equal to the core diameter of the first gain optical fiber (101), and the cladding diameter is equal to the cladding diameter of the first gain optical fiber (101); the reflectivity of the low-reflection fiber grating (107) at the central wavelength is ≥5%; the core diameter of the low-reflection fiber grating (107) is equal to the core diameter of the first gain optical fiber (101), and the cladding diameter is equal to the cladding diameter of the first gain optical fiber (101).

5. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The loss of the first filter (108) in the 1030nm band is ≥50dB; the core diameters of the input optical fiber and the output optical fiber of the first filter (108) are equal to the core diameter of the output optical fiber of the low-reflection fiber grating (107); the cladding diameters of the input optical fiber and the output optical fiber of the first filter (108) are equal to the cladding diameter of the output optical fiber of the low-reflection fiber grating (107); the core diameter of the input optical fiber of the mode field adapter (109) is equal to the core diameter of the output optical fiber of the first filter (108), and the cladding diameter is equal to the cladding diameter of the output optical fiber of the first filter (108); the core diameter of the output optical fiber of the mode field adapter (109) is equal to the core diameter of the input optical fiber of the K-class optical fiber amplifier (2), and the cladding diameter is equal to the cladding diameter of the input optical fiber of the K-class optical fiber amplifier (2).

6. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The core diameters of the optical fiber (21021) at the output end of the second pump signal combiner (2102), the optical fiber (21022) at the signal light input end of the second pump signal combiner (2102), the optical fiber (21031) at the output end of the third pump signal combiner (2103), and the optical fiber (21032) at the signal light input end of the third pump signal combiner (2103) are all equal to the core diameter of the second gain optical fiber (2101); the cladding diameters of the optical fiber (21021) at the output end of the second pump signal combiner (2102), the optical fiber (21022) at the signal light input end of the second pump signal combiner (2102), the optical fiber (21031) at the output end of the third pump signal combiner (2103), and the optical fiber (21032) at the signal light input end of the third pump signal combiner (2103) are all equal to the cladding diameter of the second gain optical fiber (2101).

7. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The output fiber diameter of the second pump module (2104) is ≤ the diameter of the fiber at the pump light input end 21022 of the second pump signal combiner (2102); the numerical aperture of the output fiber of the second pump module (2104) is ≤ the numerical aperture of the fiber (21022) at the pump light input end of the second pump signal combiner (2102); the output fiber diameter of the third pump module (2105) is ≤ the diameter of the fiber at the pump light input end (21032) of the third pump signal combiner (2103); the numerical aperture of the output fiber of the third pump module (2105) is ≤ the numerical aperture of the fiber at the pump light input end (21032) of the third pump signal combiner (2103).

8. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The core diameters of the third cladding optical filter (2106) and the fourth cladding optical filter (2107) are equal to the core diameter of the second gain optical fiber (2101); the cladding diameters of the third cladding optical filter (2106) and the fourth cladding optical filter (2107) are equal to the cladding diameter of the second gain optical fiber (2101).

9. The scalable power, high beam quality 980 nm band ytterbium-doped fiber laser according to claim 1, characterized in that The core diameter of the k+1th gain optical fiber (2k01) is equal to the core diameter of the second gain optical fiber (2101), and the cladding diameter is equal to the cladding diameter of the second gain optical fiber (2101).

10. The 980nm band ytterbium-doped fiber laser with scalable power and high beam quality as claimed in claim 1, characterized in that The loss of the second filter (211), ..., the kth filter (2(k-1)1), the k+1th filter (2k1), ..., the Kth filter (2(K-1)1) in the 1030nm band is greater than 50dB; the output beam quality M 2 The factor is not greater than 1.8; the core diameters of the input optical fibers of the second filter (211), ..., the kth filter (2(k-1)1), the k+1th filter (2k1), ..., and the Kth filter (2(K-1)1) are equal to the core diameters of the cladding optical filters connected thereto, and the cladding diameters are equal to the cladding diameters of the cladding optical filters connected thereto, that is, the core diameter of the input optical fiber of the second filter (211) is equal to the core diameter of the fourth cladding optical filter (2106) in the first-stage optical fiber amplifier (210), and the cladding diameter is equal to the cladding diameter of the fourth cladding optical filter (2106) in the first-stage optical fiber amplifier (210); ...; the kth filter (2(K-1)1) is equal to the core diameters of the input optical fibers of the second filter (211), and the cladding diameters are equal to the cladding diameters of the fourth cladding optical filter (2106) in the first-stage optical fiber amplifier (210); The core diameter of the optical fiber at the input end of the Kth filter (2(K-1)1) is equal to the core diameter of the 2kth cladding optical filter (2(K-1)06) in the Kth optical fiber amplifier (2(K-1)0), and the cladding diameter is equal to the cladding diameter of the 2kth cladding optical filter (2(K-1)06) in the K-1th optical fiber amplifier (2(K-1)0).

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