A high-brightness kilowatt-level 980nm waveband fiber laser

Abstract

The application discloses a high-brightness kilowatt 980nm waveband optical fiber laser, and aims at solving the contradiction between power and beam quality improvement of the prior art.The application is composed of U optical fiber laser unit modules, an optical fiber signal beam combiner, an output cladding light filter and an output coupling end.The optical fiber laser unit modules, the optical fiber signal beam combiner, the output cladding light filter and the output coupling end are connected in series.The optical fiber laser unit module is composed of a single-mode seed source and a K-stage optical fiber amplifier, and the single-mode seed source adopts a fiber oscillator.The K-stage optical fiber amplifier is composed of K single-stage optical fiber amplifiers.The optical fiber signal beam combiner performs power beam combination on the laser output by the optical fiber laser unit module, the output cladding light filter filters cladding light, and the output coupling end couples the laser.The application can make the laser have kilowatt power output, and realize beam quality optimization and brightness improvement.

Description

Technical Field

[0001] This invention relates to a fiber laser, and more particularly to one operating in the vicinity of 980 nm (975 nm to 985 nm) with a beam quality M 2 High-power, high-brightness fiber lasers with a factor of 5 or less and an output power in the kilowatt range. Background Technology

[0002] High-power, high-brightness 980nm fiber lasers have broad application prospects. Firstly, they can serve as pump sources for near-diffraction-limited rare-earth-doped (e.g., erbium, ytterbium) fiber lasers, which helps suppress nonlinear effects and increase output power, making them promising for industrial processing and materials handling. Secondly, high-power, high-brightness 980nm fiber lasers can also generate novel wavelength light sources through frequency conversion. For example, frequency doubling can generate 490nm blue-green light, applicable to marine exploration and underwater communication; frequency triharmonicization can generate 320nm near-ultraviolet laser light, applicable to biology, medicine, and spectroscopy.

[0003] Currently, ytterbium-doped fiber is the preferred gain fiber for 980nm fiber lasers, and it remains the preferred gain fiber for high-power fiber lasers. However, achieving a high-power, high-brightness 980nm fiber laser is not easy. This is because high-power, high-brightness fiber lasers require not only increased output power but also good beam quality to ensure high brightness. The energy level characteristics of ytterbium ions significantly increase the difficulty of simultaneously improving power and beam quality in 980nm lasers. The energy level structure of ytterbium ions determines that a 980nm fiber laser is a three-level laser, meaning that while generating a 980nm light field, it also produces strong amplified spontaneous emission in the 1030nm band. A common method to suppress this amplified spontaneous emission in the 1030nm band is to increase the core-cladding ratio of the ytterbium-doped fiber. However, this brings new contradictions: First, to achieve high-power laser output, sufficient pump light power is essential, which means that the cladding size cannot be too small. Therefore, the core diameter needs to be increased to improve the core-cladding ratio, but the increase in core diameter will reduce the beam quality. Conversely, to achieve high beam quality output, the core diameter cannot be too large, and the cladding diameter must be reduced accordingly. This limits the coupling of the pump light, thus limiting the improvement of output power. Therefore, although the "All-Fiber Structure 980nm Band High-Power Fiber Oscillator" patent number "ZL201710102903.4" proposes to use ytterbium-doped fiber with a large core-to-cladding ratio (core-to-cladding diameter ratio greater than or equal to 30%) to realize a kilowatt-level 980nm band fiber laser, the use of ytterbium-doped fiber with a large core-to-cladding ratio is not conducive to improving the beam quality of the 980nm band fiber laser. Moreover, the patent does not mention beam quality, and its two implementation schemes only specify power of 990W and 812W respectively. Reference [1] (Maoni Chen, Optics Letter, 2021, 46(21), 5340-5343) also reported a kilowatt-level 980nm band fiber laser. This laser achieved a power output of 1.11 kW by using ytterbium-doped fiber with a large core-to-cladding ratio (core / cladding diameter of 105 / 250 μm). However, the beam quality was poor. 2 The factor has reached 16, which greatly affects the improvement of the laser's brightness. In addition, the drawing cost of large core-to-cladding ratio ytterbium-doped fiber is high, and related passive devices (such as fiber pump combiners, mode field adapters, etc.) also need to be customized or developed in-house, which greatly increases the development cost of the system.

[0004] Currently, one approach to achieving high beam quality 980nm fiber lasers is to use microstructured fibers or fibers with specially designed structures. Microstructured fibers include photonic crystal fibers, air-hole cladding fibers, photonic bandgap fibers, and multi-core fibers; specially designed fibers include tapered fibers, saddle-shaped fibers, and W-shaped fibers. These fibers achieve high beam quality 980nm fiber laser output through microstructure or special structure design. However, a common problem with these approaches is the difficulty in increasing output power; the highest output power currently available is only in the 300W range, significantly lower than kilowatt-level output power. Furthermore, the complex structures of these fibers make fabrication difficult and costly, hindering the commercialization and application of this laser.

[0005] To reduce the development cost of 980nm fiber lasers and achieve cost control, a feasible solution is to use single-mode or few-mode step-index ytterbium-doped fiber as the gain fiber. This approach uses simple ytterbium-doped fiber structures, significantly reducing the difficulty of fiber drawing and system development costs. Patent No. ZL201310749840.3, "All-fiber structure 980nm band composite cavity single-mode fiber laser," achieves high beam quality output by using single-mode, single-clad ytterbium-doped fiber. However, the core-pumping method used in this approach severely limits the pump power, confining the output power to the watt level. To address the pump power limitation problem in core-pumping, patent No. ZL202011314846.4, "An all-fiber structure 980nm band high-power fiber oscillator," proposes a 980nm band fiber oscillator based on double-clad ytterbium-doped fiber. This scheme is based on a step-index double-clad ytterbium-doped fiber with a core diameter of 20 micrometers and a cladding diameter of 125 micrometers. By using cladding pumping, it significantly increases the pump power (reaching 230W) while maintaining high beam quality. However, due to the limitation imposed by the oscillator structure on the pump power, the output power of this laser is still limited, making it difficult to achieve kilowatt-level power output.

[0006] The core issue with existing 980nm fiber laser solutions is the difficulty in simultaneously improving output power and beam quality. While kilowatt-level output has been achieved in 980nm fiber lasers, poor beam quality significantly hinders brightness enhancement. Conversely, existing high-beam-quality 980nm fiber laser solutions struggle to meet kilowatt-level power output requirements. Therefore, under the premise of cost control, how to further improve beam quality based on few-mode step-index double-clad ytterbium-doped fiber, while maintaining kilowatt-level power output, and thus enhance the brightness of kilowatt-level 980nm fiber lasers, is a crucial concern for those skilled in the art. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome the shortcomings of existing 980nm band fiber lasers and provide a high-brightness kilowatt-level 980nm band fiber laser based on step-index double-clad ytterbium-doped fiber. This invention resolves the contradiction between power and beam quality improvement in existing solutions, enabling the laser to optimize beam quality and improve brightness while ensuring kilowatt-level power output.

[0008] The technical solution of this invention is: This invention comprises U fiber laser unit modules (U being a positive integer), a fiber signal combiner, an output cladding optical filter, and an output coupling terminal. The U fiber laser unit modules, the fiber signal combiner, the output cladding optical filter, and the output coupling terminal are connected in series: the fiber signal combiner has N input terminals and 1 output terminal (N being a positive integer). The output terminal of each fiber laser unit module is connected to one input terminal of the fiber signal combiner. Therefore, the number of fiber laser unit modules U should be less than or equal to the number of input terminals N of the fiber signal combiner, i.e., U ≤ N. The output terminal of the fiber signal combiner is connected to the input terminal of the output cladding optical filter. The output terminal of the output cladding optical filter is connected to the input terminal of the output coupling terminal, and the output terminal of the output coupling terminal serves as the output terminal of this invention. Connections between different devices in this invention are achieved through fiber optic fusion splicing. The total output power of this invention... Related to the number U of fiber laser unit modules, P su Given the power of the u-th fiber laser unit module, the required efficiency of the fiber signal combiner is... ≥95%. The target beam quality M of this invention 2 Factor (using M) t 2 (represented by) the beam quality M of the fiber laser unit module 2 Factor (using M) s 2 (representation), U and beam quality retention factor The relationship is The beam quality retention factor of the fiber optic signal combiner is required. ≥70%.

[0009] The U fiber laser unit modules of this invention are identical. The u-th fiber laser unit module consists of a single-mode seed source and a K-stage fiber amplifier. The output of the single-mode seed source is connected to the input of the K-stage fiber amplifier. The K-stage fiber amplifier consists of K single-stage fiber amplifiers (i.e., the first-stage fiber amplifier, ..., the k-th-stage fiber amplifier, ..., the K-th-stage fiber amplifier). The output of the K-th-stage fiber amplifier is the output of the K-stage fiber amplifier, and also the output of the u-th fiber laser unit module. K is the number of single-stage fiber amplifiers in the K-stage fiber amplifier, and K is a positive integer. The output power P of the u-th fiber laser unit module is... su Related to K, P su It equals the sum of the seed optical power P0 and the power that the K-class fiber amplifier can provide, that is: Where P0 represents the power that a single-mode seed source can provide, P k This represents the power that the k-th single-stage fiber amplifier can provide. Therefore, the output power increases with the number of fiber amplifier stages K, which gives the fiber laser unit module good power scalability. The upper limit of its output power is determined by the power handling capability of the fiber and the device.

[0010] The single-mode seed source in the u-th fiber laser unit module uses a fiber optic oscillator with a bidirectional pumping structure. The single-mode seed source consists of a first gain fiber, a first pump signal combiner, a first pump module, a second pump signal combiner, a second pump module, a first cladding optical filter, a second cladding optical filter, a high-reflection fiber grating, a low-reflection fiber grating, a first filter, and a mode field adapter. The first pump signal combiner includes N1 pump light inputs (N1 is a positive integer), one signal light input, and one output. The second pump signal combiner includes N2 pump light inputs (N2 is a positive integer), one signal light input, and one output. The core diameters of the output fiber, signal input fiber, and output / input fiber of the second pump signal combiner are all equal to the core diameter of the first gain fiber. The cladding diameters of these fibers are also equal to the cladding diameter of the first gain fiber. The outputs of the first and second pump signal combiners are connected to the two ends of the first gain fiber, respectively. The pump input of the first pump signal combiner is connected to the output fiber of the first pump module. The signal input of the first pump signal combiner is connected to the input of the first cladding optical filter. The pump input of the second pump signal combiner is connected to the output fiber of the second pump module. The signal input of the second pump signal combiner is connected to the input of the second cladding optical filter. The output of the first cladding optical filter is connected to the input of the high-reflection fiber Bragg grating. The output of the second cladding optical filter is connected to the input of the low-reflection fiber Bragg grating. The output of the low-reflection fiber Bragg grating is connected to the input of the first filter. The output of the first filter is connected to the input of the mode field adapter. The output of the mode field adapter, which is the output of the single-mode seed source, is connected to the input of the K-class fiber amplifier.

[0011] The first pump module in the single-mode seed source of the u-th fiber laser unit module contains N3 pump sub-modules (N3 is a positive integer), and the second pump module contains N4 pump sub-modules (N4 is a positive integer). N3 ≤ N1, N4 ≤ N2. The pump sub-modules use semiconductor lasers with output wavelengths of 900nm–960nm via fiber optic pigtails. When semiconductor lasers are used, the pigtails of the N3 semiconductor lasers serve as the output fibers of the pump sub-modules. The output fibers of the N3 pump sub-modules constituting the first pump module are the output fibers of the first pump module and are connected to the N3 pump light inputs of the first pump signal combiner. The output fibers of the N4 pump sub-modules constituting the second pump module are the output fibers of the second pump module and are connected to the N4 pump light inputs of the second pump signal combiner. The diameter of the output fiber of the first pump module should be less than or equal to the diameter of the pump light input fiber of the first pump signal combiner; the numerical aperture of the output fiber of the first pump module should be less than or equal to the numerical aperture of the pump light input fiber of the first pump signal combiner. The diameter of the output fiber of the second pump module should be less than or equal to the diameter of the pump light input fiber of the second pump signal combiner; the numerical aperture of the output fiber of the second pump module should be less than or equal to the numerical aperture of the pump light input fiber of the second pump signal combiner.

[0012] The first gain fiber in the single-mode seed source of the u-th fiber laser unit module is a single-mode step-index double-clad ytterbium-doped fiber. It is required that the core diameter is not less than 10 micrometers, the normalized frequency is not greater than 2.405, the cladding diameter is not less than 125 micrometers, and the length is ≤ the fiber length corresponding to the absence of 1030nm band self-excited oscillation in the single-mode seed source (which can be obtained by the truncation method, specifically by continuously truncating an excessively long fiber while monitoring the output spectrum in real time until the 1030nm band self-excited oscillation is no longer generated in the output spectrum, at which point the fiber length is the optimal length).

[0013] The first and second cladding optical filters in the single-mode seed source of the u-th fiber laser unit module are mainly used to filter out cladding light. It is required that the core diameters of the first and second cladding optical filters are equal to the core diameter of the first gain fiber; and that the cladding diameters of the first and second cladding optical filters are equal to the cladding diameter of the first gain fiber.

[0014] The center wavelength of the high-reflectivity fiber grating in the single-mode seed source of the u-th fiber laser unit module is between 975-985 nm (preferably between 976-980 nm), and the reflectivity at the center wavelength is ≥99%. The output fiber of the high-reflectivity fiber grating should suppress the reflection of the optical field by the fiber end face, which can be achieved by, but is not limited to, common bevel cuts. The core diameter of the high-reflectivity 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.

[0015] The center wavelength of the low-reflectivity fiber grating in the single-mode seed source of the u-th fiber laser unit module is approximately equal to the center wavelength of the high-reflectivity fiber grating (the deviation should be less than 1 nm), and the reflectivity at the center wavelength is ≥5%. The core diameter of the low-reflectivity 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 in the single-mode seed source of the u-th fiber laser unit module is used to filter out amplified spontaneous emission in the 1030nm band. The first filter is required to have a loss ≥50dB and a beam quality retention factor ≥90% in the 1030nm band. The core diameters of the input and output fibers of the first filter are equal to the core diameter of the output fiber of the low-reflection fiber Bragg grating; the cladding diameters of the input and output fibers of the first filter are also equal to the cladding diameter of the output fiber of the low-reflection fiber Bragg grating.

[0017] The mode field adapter in the single-mode seed source of the u-th fiber laser unit module is connected to a K-level fiber amplifier to ensure near-diffraction-limited transmission of the single-mode seed source. The core diameter of the input fiber of the mode field adapter is equal to the core diameter of the output fiber of the first filter, and the cladding diameter is also equal to the cladding diameter of the output fiber of the first filter. The core diameter of the output fiber of the mode field adapter is equal to the core diameter of the input fiber of the K-level fiber amplifier, and the cladding diameter is also equal to the cladding diameter of the input fiber of the K-level fiber amplifier.

[0018] The K-stage fiber amplifier in the u-th fiber laser unit module consists of K single-stage fiber amplifiers, with the first-stage fiber amplifier, ..., the k-th stage fiber amplifier, ..., the K-th stage fiber amplifier connected sequentially, where 1 ≤ k ≤ K. The K single-stage fiber amplifiers (i.e., the first-stage fiber amplifier, ..., the k-th stage fiber amplifier, ..., the K-th stage fiber amplifier) ​​have identical structures.

[0019] The first-stage fiber amplifier of the K-th fiber amplifier in the u-th fiber laser unit module consists of a second gain fiber, a third pump signal combiner, a fourth pump signal combiner, a third pump module, a fourth pump module, a third cladding optical filter, a fourth cladding optical filter, and a second filter. Both the third and fourth pump signal combiners contain multiple pump light inputs, one signal light input, and one output. The third pump signal combiner contains M1 pump light inputs (M1 is a positive integer), and the fourth pump signal combiner contains M2 pump light inputs (M2 is a positive integer). The core diameters of the output fiber, signal input fiber, and output fiber of the fourth pump signal combiner are all equal to the core diameter of the second gain fiber. The cladding diameters of the output fiber, signal input fiber, and output fiber of the fourth pump signal combiner are also equal to the cladding diameter of the second gain fiber. The outputs of the third and fourth pump signal combiners are connected to the two ends of the second gain fiber, respectively. The signal input of the third pump signal combiner is connected to the input of the third cladding optical filter. The pump input of the third pump signal combiner is connected to the output fiber of the third pump module. The signal input of the fourth pump signal combiner is connected to the input of the fourth cladding optical filter, and the pump input of the fourth pump signal combiner is connected to the output fiber of the fourth pump module. The output of the third cladding optical filter is connected to the output of the mode field adapter, serving as the input of the first-stage fiber amplifier and also the input of the K-stage fiber amplifier. The output of the fourth cladding optical filter is connected to the input of the second filter. The output of the second filter is the output of the first-stage fiber amplifier and is connected to the input of the next-stage fiber amplifier (i.e., the second-stage fiber amplifier).

[0020] The third pump module of the K-level fiber amplifier in the u-th fiber laser unit module contains M3 pump sub-modules (M3 is a positive integer), and the fourth pump module contains M4 pump sub-modules (M4 is a positive integer). M3 ≤ M1, M4 ≤ M2. The pump sub-modules use semiconductor lasers with output wavelengths of 900nm–960nm via fiber optic pigtails. When semiconductor lasers are used, the pigtails of the M3 semiconductor lasers serve as the output fibers of the pump sub-modules. The output fibers of the M3 pump sub-modules constituting the third pump module are the output fibers of the third pump module itself, connected to the M3 pump light inputs of the third pump signal combiner. The output fibers of the M4 pump sub-modules constituting the fourth pump module are the output fibers of the fourth pump module, and connected to the M4 pump light inputs of the fourth pump signal combiner. The diameter of the output fiber of the third pump module should be less than or equal to the diameter of the pump light input fiber of the third pump signal combiner; the numerical aperture of the output fiber of the third pump module should be less than or equal to the numerical aperture of the pump light input fiber of the third pump signal combiner. The diameter of the output fiber of the fourth pump module should be less than or equal to the diameter of the pump light input fiber of the fourth pump signal combiner; the numerical aperture of the output fiber of the fourth pump module should be less than or equal to the numerical aperture of the pump light input fiber of the fourth pump signal combiner.

[0021] The second gain fiber of the K-stage fiber amplifier in the u-th fiber laser unit module is a step-index double-clad ytterbium-doped fiber. It is required that the core diameter is not less than 20 micrometers, the normalized frequency is not greater than 5, the cladding diameter is not less than 125 micrometers, the cladding pump light absorption coefficient is not less than 0.5dB / m, and the length is ≤ the fiber length corresponding to the absence of 1030nm band self-excited oscillation in the first-stage fiber amplifier.

[0022] The third and fourth cladding optical filters in the K-level fiber amplifier of the u-th fiber laser unit module are mainly used to filter out cladding light. The core diameters of the third and fourth cladding optical filters are equal to the core diameter of the second gain fiber; the cladding diameters of the third and fourth cladding optical filters are equal to the cladding diameter of the second gain fiber.

[0023] The second filter in the K-level fiber amplifier of the u-th fiber laser unit module is used to filter out amplified spontaneous emission in the 1030nm band. The second filter is required to have a loss ≥50dB and a beam quality retention factor ≥90% in the 1030nm band. The core diameters of the input and output fibers of the second filter are equal to the core diameter of the output fiber of the fourth cladding optical filter, and the cladding diameter is equal to the cladding diameter of the output fiber of the fourth cladding optical filter.

[0024] The structure of the k-th stage fiber amplifier in the k-th stage fiber amplifier of the u-th fiber laser unit module is exactly the same as that of the first stage fiber amplifier. The input of the k-th stage fiber amplifier is connected to the output of the previous stage fiber amplifier (i.e., the (k-1)-th stage fiber amplifier), and the output of the k-th stage fiber amplifier is connected to the input of the next stage fiber amplifier (i.e., the (k+1)-th stage fiber amplifier). The connection of the remaining components in the k-th stage fiber amplifier is the same as that of the first stage fiber amplifier.

[0025] The structure, device parameter requirements, and device connections of the K-th stage fiber amplifier in the u-th fiber laser unit module are the same as those of the k-th stage fiber amplifier. The input of the K-th stage fiber amplifier is connected to the output of the previous stage fiber amplifier (i.e., the (K-1)-th stage fiber amplifier), and the output of the K-th stage fiber amplifier is the output of the K-th stage fiber amplifier, which is also the output of the fiber laser unit module.

[0026] This invention relates to an optical fiber signal combiner used to combine the laser outputs of U fiber laser unit modules. The core diameters of the N input optical fibers of the optical fiber signal combiner are equal, and equal to the core diameter of the output optical fiber of the fiber laser unit module; the cladding diameters of the N input optical fibers of the optical fiber signal combiner are also equal, and equal to the cladding diameter of the output optical fiber of the fiber laser unit module. The core diameter of the output optical fiber of the optical fiber signal combiner should not exceed 50 micrometers. The efficiency of the optical fiber signal combiner is required. ≥95%, beam quality retention factor of fiber optic signal combiner ≥70%.

[0027] The output cladding light filter of this invention is mainly used to filter out the cladding light generated after passing through the optical fiber signal combiner. The core diameter of the cladding light filter is equal to the core diameter of the optical fiber at the output end of the optical fiber signal combiner, and the cladding diameter is equal to the cladding diameter of the optical fiber at the output end of the optical fiber signal combiner.

[0028] In this invention, the core diameter of the input fiber at the output coupling end is equal to the core diameter of the output fiber of the cladding optical filter, and the cladding diameter is equal to the cladding diameter of the output fiber of the cladding optical filter. Its structure can employ an optical fiber output cap. The output coupling end couples the 980nm band laser transmitted in the fiber core from the cladding optical filter.

[0029] The working process of this invention is as follows: The first step involves U fiber laser unit modules operating in parallel to generate U amplified 980nm wavelength laser beams. Specifically, the single-mode seed source in the u-th fiber laser unit module generates a single-mode seed beam in the 980nm wavelength range, and the fiber amplifier amplifies the power of this seed beam. The method by which the u-th fiber laser unit module generates the amplified 980nm wavelength laser beam is as follows: Step 1.1 The first pump signal combiner couples the pump light generated by the first pump module into the first gain fiber, while the second pump signal combiner couples the pump light generated by the second pump module into the first gain fiber. The pump light coupled into the first gain fiber excites the ytterbium ions in the first gain fiber, causing population inversion, thereby generating a signal light in the 980nm band.

[0030] Step 1.2: The 980nm optical field generates laser oscillation within a resonant cavity composed of a high-reflectivity fiber grating and a low-reflectivity fiber grating. The high-reflectivity fiber grating provides strong optical feedback to maintain efficient laser oscillation; the low-reflectivity fiber grating acts as an output coupler, providing partial feedback while transmitting the laser beam. During this process, a first cladding light filter and a second cladding light filter are used to filter out cladding light.

[0031] Step 1.3 The first filter filters the laser transmitted from the low-reflection fiber grating to filter out the 1030nm band amplified spontaneous emission, and obtains pure 980nm band signal light.

[0032] Step 1.4 The mode field adapter performs mode field matching on the pure 980nm band signal light output from the first filter, and injects the seed light into the first-stage fiber amplifier with low loss.

[0033] Step 1.5: The third pump signal combiner in the first-stage fiber amplifier couples the pump light generated by the third pump module into the second gain fiber, while the fourth pump signal combiner couples the pump light generated by the fourth pump module into the second gain fiber. The pump light coupled into the second gain fiber excites ytterbium ions in the second gain fiber, causing population inversion, thereby amplifying the seed light passing through the core of the second gain fiber. During this process, the third and fourth cladding light filters are used to filter out the cladding light.

[0034] Step 1.6 The second filter filters the amplified seed light from the fourth cladding optical filter to remove the amplified spontaneous emission in the 1030nm band, obtaining a pure amplified 980nm band signal light, which is used as the output of the first-stage fiber amplifier.

[0035] Step 1.7 The second-stage fiber amplifier amplifies and filters the clean 980nm band signal light output from the first-stage fiber amplifier, ..., the k-th-stage fiber amplifier amplifies and filters the clean 980nm band signal light output from the (k-1)-th-stage fiber amplifier, ..., the K-th-stage fiber amplifier amplifies and filters the clean signal light output from the (K-1)-th-stage fiber amplifier. The signal light amplified by the first-stage fiber amplifier is sequentially amplified and filtered stage by stage K fiber amplifiers, ultimately outputting a clean, amplified 980nm band laser as the output of the u-th fiber laser unit module. During this process, all cladding light filters are used to filter out cladding light.

[0036] The second step involves the fiber optic signal combiner performing power combining on the U amplified 980nm band lasers received from the U fiber laser unit modules to obtain the combined 980nm band laser.

[0037] The third step involves the output cladding optical filter removing the combined 980nm band laser output from the fiber signal combiner to obtain the 980nm band laser transmitted in the fiber core.

[0038] The fourth step involves coupling the 980nm wavelength laser transmitted through the fiber core from the cladding optical filter at the output coupling end. Its main function is to suppress optical feedback while efficiently and with low loss coupling the laser within the fiber core, thus obtaining the final 980nm wavelength output laser.

[0039] The following technical effects can be achieved by using this invention: 1. By designing the number of fiber optic signal combiner inputs, signal power loss, and output power of the fiber laser unit modules, the laser achieves a power boost capability in the kilowatt range. 2. Through the design of the fiber optic signal combiner beam quality preservation coefficient and the fiber laser unit module, the laser achieves the beam quality target M. 2 High brightness output capability with a factor of less than 5; 3. By designing the single-mode seed source, the normalized frequency of the ytterbium-doped fiber in the single-stage fiber amplifier, and the beam quality preservation coefficient of the filter, the fiber laser unit module can meet the design requirements for beam quality.

[0040] 4. By designing the core diameter, cladding diameter, and fiber length of ytterbium-doped fiber, the single-stage fiber amplifier has a good power boosting capability, further enabling the fiber laser unit module to meet the design requirements in terms of power level. 5. By employing step-index double-clad optical fiber, this invention greatly reduces the difficulty of optical fiber drawing and the manufacturing cost of the system. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the high-brightness kilowatt-level 980nm band fiber laser structure of the present invention.

[0042] Figure 2 This is a schematic diagram of the fiber laser unit module of the present invention.

[0043] Figure 3 This is a schematic diagram of the single-mode seed source of the present invention.

[0044] Figure 4 This is a schematic diagram of the specific structure of the single-stage fiber amplifier of the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0046] like Figure 1 As shown, this invention consists of U fiber laser unit modules (U being a positive integer) (each fiber laser unit module is numbered 1-1 to 1-U, where the u-th fiber laser unit module is numbered 1-u, 1≤u≤U), a fiber signal combiner 2, an output cladding optical filter 3, and an output coupling terminal 4. The U fiber laser unit modules, fiber signal combiner 2, output cladding optical filter 3, and output coupling terminal 4 are connected in series: the fiber signal combiner 2 has N input terminals and 1 output terminal (N being a positive integer). The output terminal of each fiber laser unit module is connected to one input terminal of the fiber signal combiner 2. Therefore, the number of fiber laser unit modules U should be less than or equal to the number of input terminals N of the fiber signal combiner 2, i.e., U≤N. The output terminal of the fiber signal combiner 2 is connected to the input terminal of the output cladding optical filter 3. The output terminal of the output cladding optical filter 3 is connected to the input terminal of the output coupling terminal 4, and the output terminal of the output coupling terminal 4 serves as the output terminal of this invention. In this invention, the connection between different devices is achieved through fiber optic fusion splicing. The total output power of this invention... Related to the number U of fiber laser unit modules, P su Given the power of the u-th fiber laser unit module 1-u, the required efficiency of fiber signal combiner 2 is... ≥95%. The target beam quality M of this invention 2 Factor (using M) t 2 (represented by) the beam quality M of the fiber laser unit module 2 Factor (using M) s 2 (representation), U and beam quality retention factor The relationship is The beam quality retention factor of fiber optic signal combiner 2 is required to be [percentage missing]. ≥70%.

[0047] like Figure 2 As shown, the U fiber laser unit modules of this invention are identical. The u-th fiber laser unit module 1-u consists of a single-mode seed source 11 and a K-stage fiber amplifier 12. The output of the single-mode seed source 11 is connected to the input of the K-stage fiber amplifier 12. The K-stage fiber amplifier 12 consists of K single-stage fiber amplifiers (i.e., first-stage fiber amplifier 121, ..., k-th-stage fiber amplifier 12k, ..., K-th-stage fiber amplifier 12K). The output of the K-th-stage fiber amplifier 12K is the output of the K-stage fiber amplifier 12, and also the output of the u-th fiber laser unit module 1-u. K is the number of single-stage fiber amplifiers in the K-stage fiber amplifier 12, and K is a positive integer. The output power P of the u-th fiber laser unit module 1-u is... su Related to K, P su It is equal to the sum of the seed optical power P0 and the power that the K-class fiber amplifier 12 can provide, that is: Where P0 represents the power that the single-mode seed source 11 can provide, P k This represents the power that the k-th single-stage fiber amplifier 12k can provide. Therefore, the output power increases with the number of fiber amplifier stages K, which gives the fiber laser unit module good power scalability. The upper limit of its output power is determined by the power handling capability of the fiber and the device.

[0048] like Figure 3As shown, the single-mode seed source 11 in the u-th fiber laser unit module 1-u adopts an fiber optic oscillator with a bidirectional pumping structure. The single-mode seed source 11 consists of a first gain fiber 11-0, a first pump signal combiner 11-1, a first pump module 11-2, a second pump signal combiner 11-3, a second pump module 11-4, a first cladding optical filter 11-5, a second cladding optical filter 11-6, a high-reflection fiber grating 11-7, a low-reflection fiber grating 11-8, a first filter 11-9, and a mode field adapter 11-10. The first pump signal combiner 11-1 includes N1 pump light inputs (N1 is a positive integer), one signal light input, and one output. The second pump signal combiner 11-3 includes N2 pump light inputs (N2 is a positive integer), one signal light input, and one output. The core diameters of the output optical fibers of the first pump signal combiner 11-1, the signal light input optical fibers of the first pump signal combiner 11-1, the output optical fibers of the second pump signal combiner 11-3, and the signal light input optical fibers of the second pump signal combiner 11-3 are all equal to the core diameter of the first gain optical fiber 11-0. The cladding diameters of the output optical fibers of the first pump signal combiner 11-1, the signal light input optical fibers of the first pump signal combiner 11-1, the output optical fibers of the second pump signal combiner 11-3, and the signal light input optical fibers of the second pump signal combiner 11-3 are all equal to the cladding diameter of the first gain optical fiber 11-0. The output ends of the first pump signal combiner 11-1 and the second pump signal combiner 11-3 are respectively connected to the two ends of the first gain optical fiber 11-0. The pump light input end of the first pump signal combiner 11-1 is connected to the output optical fiber of the first pump module 11-2. The signal light input of the first pump signal combiner 11-1 is connected to the input of the first cladding optical filter 11-5. The pump light input of the second pump signal combiner 11-3 is connected to the output fiber of the second pump module 11-4. The signal light input of the second pump signal combiner 11-3 is connected to the input of the second cladding optical filter 11-6. The output of the first cladding optical filter 11-5 is connected to the input of the high-reflection fiber grating 11-7. The output of the second cladding optical filter 11-6 is connected to the input of the low-reflection fiber grating 11-8. The output of the low-reflection fiber grating 11-8 is connected to the input of the first filter 11-9. The output of the first filter 11-9 is connected to the input of the mode field adapter 11-10. The output of the mode field adapter 11-10 is the output of the single-mode seed source 11 and is connected to the input of the K-class fiber amplifier 12.

[0049] The first pump module 11-2 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u contains N3 pump sub-modules (N3 is a positive integer) (numbered 11-2-1 to 11-2-N3), and the second pump module 11-4 contains N4 pump sub-modules (N4 is a positive integer) (numbered 11-4-1 to 11-4-N4). N3 ≤ N1. N4 ≤ N2. The pump sub-modules use semiconductor lasers with a 900nm to 960nm wavelength band output via fiber optic pigtails. When semiconductor lasers are used, the pigtails of the N3 semiconductor lasers are the output fibers of the pump sub-modules. The output fibers of the N3 pump sub-modules constituting the first pump module 11-2 are the output fibers of the first pump module 11-2, and are connected to the N3 pump light input terminals of the first pump signal combiner 11-1. The output optical fibers of the N4 pump sub-modules constituting the second pump module 11-4 are the output optical fibers of the second pump module 11-4, and are connected to the N4 pump light input terminals of the second pump signal combiner 11-3. The diameter of the output optical fiber of the first pump module 11-2 should be less than or equal to the diameter of the pump light input fiber of the first pump signal combiner 11-1; the numerical aperture of the output optical fiber of the first pump module 11-2 should be less than or equal to the numerical aperture of the pump light input fiber of the first pump signal combiner 11-1. The diameter of the output optical fiber of the second pump module 11-4 should be less than or equal to the diameter of the pump light input fiber of the second pump signal combiner 11-3; the numerical aperture of the output optical fiber of the second pump module 11-4 should be less than or equal to the numerical aperture of the pump light input fiber of the second pump signal combiner 11-3.

[0050] The first gain fiber 11-0 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u is a single-mode step-index double-clad ytterbium-doped fiber. It is required that the core diameter is not less than 10 micrometers, the normalized frequency is not greater than 2.405, the cladding diameter is not less than 125 micrometers, and the length is ≤ the fiber length corresponding to the absence of 1030nm band self-excited oscillation in the single-mode seed source 11 (which can be obtained by the truncation method, specifically by continuously truncating an excessively long fiber while monitoring the output spectrum in real time until the 1030nm band self-excited oscillation is no longer generated in the output spectrum, at which point the fiber length is the optimal length).

[0051] The first cladding optical filter 11-5 and the second cladding optical filter 11-6 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u are mainly used to filter out cladding light. It is required that the core diameter of the first cladding optical filter 11-5 and the second cladding optical filter 11-6 is equal to the core diameter of the first gain fiber 11-0; and that the cladding diameter of the first cladding optical filter 11-5 and the second cladding optical filter 11-6 is equal to the cladding diameter of the first gain fiber 11-0.

[0052] The center wavelength of the high-reflectivity fiber grating 11-7 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u is between 975-985nm (preferably between 976-980nm), and the reflectivity at the center wavelength is ≥99%. The output fiber of the high-reflectivity fiber grating 11-7 should suppress the reflection of the optical field by the fiber end face, and can be cut at an angle, but is not limited to common methods. The core diameter of the high-reflectivity fiber grating 11-7 is equal to the core diameter of the first gain fiber 11-0, and the cladding diameter is equal to the cladding diameter of the first gain fiber 11-0.

[0053] The center wavelength of the low-reflectivity fiber grating 11-8 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u is approximately equal to the center wavelength of the high-reflectivity fiber grating 11-7 (the deviation should be less than 1 nm), and the reflectivity at the center wavelength is ≥5%. The core diameter of the low-reflectivity fiber grating 11-8 is equal to the core diameter of the first gain fiber 11-0, and the cladding diameter is equal to the cladding diameter of the first gain fiber 11-0.

[0054] The first filter 11-9 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u is used to filter out amplified spontaneous emission in the 1030nm band. The first filter 11-9 is required to have a loss ≥50dB and a beam quality retention factor ≥90% in the 1030nm band. The core diameters of the input and output fibers of the first filter 11-9 are equal to the core diameter of the output fiber of the low-reflection fiber grating 11-8; the cladding diameters of the input and output fibers of the first filter 11-9 are equal to the cladding diameter of the output fiber of the low-reflection fiber grating 11-8.

[0055] The mode field adapter 11-10 in the single-mode seed source 11 of the u-th fiber laser unit module 1-u is connected to the K-level fiber amplifier 12 to ensure near-diffraction-limited transmission of the single-mode seed source 11. The core diameter of the input fiber of the mode field adapter 11-10 is equal to the core diameter of the output fiber of the first filter 11-9, and the cladding diameter is equal to the cladding diameter of the output fiber of the first filter 11-9. The core diameter of the output fiber of the mode field adapter 11-10 is equal to the core diameter of the input fiber of the K-level fiber amplifier 12, and the cladding diameter is equal to the cladding diameter of the input fiber of the K-level fiber amplifier 12.

[0056] The K-stage fiber amplifier 12 in the u-th fiber laser unit module 1-u consists of K single-stage fiber amplifiers. The first-stage fiber amplifiers 121, ..., the k-th stage fiber amplifiers 12k, ..., and the K-th stage fiber amplifiers 12K are connected sequentially, where 1 ≤ k ≤ K. The K single-stage fiber amplifiers (i.e., the first-stage fiber amplifiers 121, ..., the k-th stage fiber amplifiers 12k, ..., and the K-th stage fiber amplifiers 12K) have identical structures.

[0057] like Figure 4 As shown, the first-stage fiber amplifier 121 of the K-stage fiber amplifier 12 in the u-th fiber laser unit module 1-u consists of a second gain fiber 121-0, a third pump signal combiner 121-1, a fourth pump signal combiner 121-2, a third pump module 121-3, a fourth pump module 121-4, a third cladding optical filter 121-5, a fourth cladding optical filter 121-6, and a second filter 121-7. Both the third pump signal combiner 121-1 and the fourth pump signal combiner 121-2 include multiple pump light inputs, one signal light input, and one output. The third pump signal combiner 121-1 includes M1 pump light inputs (M1 is a positive integer), and the fourth pump signal combiner 121-2 includes M2 pump light inputs (M2 is a positive integer). The core diameters of the output optical fibers of the third pump signal combiner 121-1, the signal input optical fibers of the third pump signal combiner 121-1, the output optical fibers of the fourth pump signal combiner 121-2, and the signal input optical fibers of the fourth pump signal combiner 121-2 are all equal to the core diameter of the second gain optical fiber 121-0. The cladding diameters of the output optical fibers of the third pump signal combiner 121-1, the signal input optical fibers of the third pump signal combiner 121-1, the output optical fibers of the fourth pump signal combiner 121-2, and the signal input optical fibers of the fourth pump signal combiner 121-2 are all equal to the cladding diameter of the second gain optical fiber 121-0. The output ends of the third pump signal combiner 121-1 and the fourth pump signal combiner 121-2 are respectively connected to the two ends of the second gain optical fiber 121-0. The signal light input of the third pump signal combiner 121-1 is connected to the input of the third cladding optical filter 121-5. The pump light input of the third pump signal combiner 121-1 is connected to the output fiber of the third pump module 121-3. The signal light input of the fourth pump signal combiner 121-2 is connected to the input of the fourth cladding optical filter 121-6, and the pump light input of the fourth pump signal combiner 121-2 is connected to the output fiber of the fourth pump module 121-4. The output of the third cladding optical filter 121-5 is connected to the output of the mode field adapter 11-10, serving as the input of the first-stage fiber amplifier 121 and also the input of the K-stage fiber amplifier 12. The output of the fourth cladding optical filter 121-6 is connected to the input of the second filter 121-7. The output of the second filter 121-7 is the output of the first-stage fiber amplifier 121, and is connected to the input of the next-stage fiber amplifier (i.e., the second-stage fiber amplifier 122).

[0058] The third pump module 121-3 of the K-level fiber amplifier 12 in the u-th fiber laser unit module 1-u contains M3 pump sub-modules (M3 is a positive integer) (numbered 121-3-1 to 121-3-M3), and the fourth pump module 121-4 contains M4 pump sub-modules (M4 is a positive integer) (numbered 121-4-1 to 121-4-M4). M3 ≤ M1. M4 ≤ M2. The pump sub-modules use semiconductor lasers with a 900nm to 960nm wavelength band output via fiber optic pigtails. When semiconductor lasers are used, the pigtails of the M3 semiconductor lasers are the output fibers of the pump sub-modules. The output fibers of the M3 pump sub-modules constituting the third pump module 121-3 are the output fibers of the third pump module 121-3, and are connected to the M3 pump light input terminals of the third pump signal combiner 121-1. The output optical fibers of the M4 pump sub-modules constituting the fourth pump module 121-4 are the output optical fibers of the fourth pump module 121-4, and are connected to the M4 pump light input terminals of the fourth pump signal combiner 121-2. The diameter of the output optical fiber of the third pump module 121-3 should be less than or equal to the diameter of the pump light input fiber of the third pump signal combiner 121-1; the numerical aperture of the output optical fiber of the third pump module 121-3 should be less than or equal to the numerical aperture of the pump light input fiber of the third pump signal combiner 121-1. The diameter of the output optical fiber of the fourth pump module 121-4 should be less than or equal to the diameter of the pump light input fiber of the fourth pump signal combiner 121-2; the numerical aperture of the output optical fiber of the fourth pump module 121-4 should be less than or equal to the numerical aperture of the pump light input fiber of the fourth pump signal combiner 121-2.

[0059] The second gain fiber 121-0 of the K-level fiber amplifier 12 in the u-th fiber laser unit module 1-u is a step-index double-clad ytterbium-doped fiber. It is required that the core diameter is not less than 20 micrometers, the normalized frequency is not greater than 5, the cladding diameter is not less than 125 micrometers, the cladding pump light absorption coefficient is not less than 0.5dB / m, and the length is ≤ the fiber length corresponding to the absence of 1030nm band self-excited oscillation in the first-stage fiber amplifier.

[0060] The third cladding optical filter 121-5 and the fourth cladding optical filter 121-6 of the K-class fiber amplifier 12 in the u-th fiber laser unit module 1-u are mainly used to filter out cladding light. The core diameter of the third cladding optical filter 121-5 and the fourth cladding optical filter 121-6 is equal to the core diameter of the second gain fiber 121-0; the cladding diameter of the third cladding optical filter 121-5 and the fourth cladding optical filter 121-6 is equal to the cladding diameter of the second gain fiber 121-0.

[0061] The second filter 121-7 of the K-class fiber amplifier 12 in the u-th fiber laser unit module 1-u is used to filter out amplified spontaneous emission in the 1030nm band. The second filter 121-7 is required to have a loss ≥50dB and a beam quality retention factor ≥90% in the 1030nm band. The core diameters of the input and output fibers of the second filter 121-7 are equal to the core diameter of the output fiber of the fourth cladding optical filter 121-5, and the cladding diameter is equal to the cladding diameter of the output fiber of the fourth cladding optical filter 121-5.

[0062] The structure and device parameters of the k-th stage fiber amplifier 12k in the k-th stage fiber amplifier 12 of the u-th fiber laser unit module 1-u are exactly the same as those of the first stage fiber amplifier 121. The input terminal of the k-th stage fiber amplifier 12k is connected to the output terminal of the previous stage fiber amplifier (i.e., the (k-1)-th stage fiber amplifier 12(k-1)), and the output terminal of the k-th stage fiber amplifier 12k is connected to the input terminal of the next stage fiber amplifier (i.e., the (k+1)-th stage fiber amplifier 12(k+1)). The connection of the remaining devices in the k-th stage fiber amplifier 12k is the same as that of the first stage fiber amplifier.

[0063] The structure and device parameters of the K-stage fiber amplifier 12K in the u-th fiber laser unit module 1-u are the same as those of the k-th fiber amplifier 120k. The input terminal of the K-stage fiber amplifier 12K is connected to the output terminal of the previous stage fiber amplifier (i.e., the K-1 stage fiber amplifier 12(K-1)), and the output terminal of the K-stage fiber amplifier 12K is the output terminal of the K-stage fiber amplifier 12, which is also the output terminal of the fiber laser unit module.

[0064] The fiber optic signal combiner 2 of this invention is used to combine the laser outputs of U fiber laser unit modules. The core diameters of the N input fibers of the fiber optic signal combiner 2 are equal, and equal to the core diameter of the output fiber of the fiber laser unit module; the cladding diameters of the N input fibers of the fiber optic signal combiner 2 are also equal, and equal to the cladding diameter of the output fiber of the fiber laser unit module. The core diameter of the output fiber of the fiber optic signal combiner 2 should not exceed 50 micrometers. The efficiency of the fiber optic signal combiner 2 is required to be ≥95%, and the beam quality retention factor is required to be ≥70%.

[0065] The output cladding light filter 3 of this invention is mainly used to filter out the cladding light generated after passing through the optical fiber signal combiner 2. The core diameter of the cladding light filter 3 is equal to the core diameter of the optical fiber at the output end of the optical fiber signal combiner 2, and the cladding diameter is equal to the cladding diameter of the optical fiber at the output end of the optical fiber signal combiner 2.

[0066] The core diameter of the input optical fiber of the output coupling end 4 of this invention is equal to the core diameter of the output optical fiber of the cladding optical filter 3, and the cladding diameter is equal to the cladding diameter of the output optical fiber of the cladding optical filter 3. Its structure can employ an optical fiber output cap. The output coupling end 4 couples the 980nm band laser output from the cladding optical filter 3, which is transmitted in the fiber core, to the output.

[0067] The working process of this invention is as follows: The first step involves U fiber laser unit modules operating in parallel to generate U amplified 980nm wavelength laser beams. Specifically, the single-mode seed source 11 in the u-th fiber laser unit module 1-u generates a single-mode seed light in the 980nm wavelength range, and the fiber amplifier 12 amplifies the power of this seed light. The method by which the u-th fiber laser unit module 1-u generates the amplified 980nm wavelength laser beam is as follows: Step 1.1 The first pump signal combiner 11-1 couples the pump light generated by the first pump module 11-2 into the first gain fiber 11-0, while the second pump signal combiner 11-3 couples the pump light generated by the second pump module 11-4 into the first gain fiber 11-0. The pump light coupled into the first gain fiber 11-0 excites the ytterbium ions in the first gain fiber 11-0, causing population inversion, thereby generating a signal light in the 980nm band.

[0068] Step 1.2: The 980nm optical field generates laser oscillation within the resonant cavity formed by the high-reflectivity fiber grating 11-7 and the low-reflectivity fiber grating 11-8. The high-reflectivity fiber grating 11-7 provides strong optical feedback to maintain efficient laser oscillation; the low-reflectivity fiber grating 11-8 acts as an output coupler, providing partial feedback while transmitting the laser beam. During this process, the first cladding light filter 11-5 and the second cladding light filter 11-6 filter out the cladding light.

[0069] Step 1.3 The first filter 11-9 filters the laser transmitted from the low-reflection fiber grating 11-8, filtering out the 1030nm band amplified spontaneous emission, and obtaining pure 980nm band signal light.

[0070] Step 1.4 The mode field adapter 11-10 performs mode field matching on the pure 980nm band signal light output from the first filter 11-9, and injects the seed light into the first-stage fiber amplifier 121 with low loss.

[0071] Step 1.5: In the first-stage fiber amplifier 121, the third pump signal combiner 121-1 couples the pump light generated by the third pump module 121-3 into the second gain fiber 121-0, while the fourth pump signal combiner 121-2 couples the pump light generated by the fourth pump module 121-4 into the second gain fiber 121-0. The pump light coupled into the second gain fiber 121-0 excites the ytterbium ions in the second gain fiber 121-0, causing population inversion, thereby amplifying the seed light passing through the core of the second gain fiber 121-0. During this process, the third cladding light filter 121-5 and the fourth cladding light filter 121-6 are used to filter out the cladding light.

[0072] Step 1.6 The second filter 121-7 filters the amplified seed light from the fourth cladding optical filter 121-6 to filter out the amplified spontaneous emission in the 1030nm band, and obtains a pure amplified 980nm band signal light, which is used as the output of the first-stage fiber amplifier 121.

[0073] Step 1.7 The second-stage fiber amplifier 122 amplifies and filters the pure 980nm band signal light output from the first-stage fiber amplifier 121, ..., the k-th stage fiber amplifier 12k amplifies and filters the pure 980nm band signal light output from the (k-1)-th stage fiber amplifier 12(k-1), ..., the K-th stage fiber amplifier 12K amplifies and filters the pure signal light output from the (K-1)-th stage fiber amplifier 12(K-1). The signal light amplified by the first-stage fiber amplifier 121 is amplified and filtered stage by stage K fiber amplifiers, finally outputting a pure amplified 980nm band laser as the output of the u-th fiber laser unit module 1-u. During this process, all cladding light filters are used to filter out cladding light.

[0074] In the second step, the fiber optic signal combiner 2 performs power combining on the U amplified 980nm band lasers received from the U fiber laser unit modules to obtain the combined 980nm band laser.

[0075] The third step is to perform cladding light filtering on the synthesized 980nm band laser output from the fiber signal combiner 2 to obtain the 980nm band laser transmitted in the fiber core.

[0076] The fourth step is to couple the 980nm band laser output from the cladding optical filter 3 that is transmitted in the fiber core to the output. That is, while suppressing optical feedback, the laser in the fiber core is coupled out with high efficiency and low loss, so as to obtain the final 980nm band output laser.

[0077] To verify the effectiveness of the present invention, three embodiments are provided.

[0078] like Figure 1 As shown, the high-brightness kilowatt-level 980nm band fiber laser of this invention consists of U identical fiber laser unit modules (1-1 to 1-U), a fiber signal combiner 2, an output cladding optical filter 3, and an output coupling terminal 4. Figure 2 As shown, each fiber laser unit module contains a single-mode seed source 11 and a K-class fiber amplifier 12.

[0079] like Figure 3 As shown, the components and parameters of the single-mode seed source 11 are as follows: the core diameter of the first gain fiber 11-1 is 10 micrometers, the normalized frequency is 2.405, and the cladding diameter is 125 micrometers; the first pump signal combiner 11-1 and the second pump signal combiner 11-3 each have two pump light input terminals (i.e., N1=N2=2). The first pump module 11-2 contains two pump sub-modules 11-2-1 and 11-2-2, and the second pump module 11-4 contains two pump sub-modules 11-4-1 and 11-4-2 (i.e., N3=N4=2). Each pump sub-module consists of a semiconductor laser with a pigtail. The first cladding light filter 11-5 and the second cladding light filter 11-6 are used to filter out cladding light. The high-reflectivity fiber grating 11-7 has a center wavelength of 979 nm and a reflectivity of 99.5% at that wavelength; the low-reflectivity fiber grating 11-8 has a center wavelength of 979 nm and a reflectivity of 10% at that wavelength. The output end of the high-reflectivity fiber grating 11-7 is cut at an angle to suppress end-face feedback. The loss of the first filter 11-9 in amplifying spontaneous emission at 1030 nm is 50 dB, and the beam quality retention factor is 90%. The input fiber of the mode field adapter 11-10 has a core diameter of 10 μm and a cladding diameter of 125 μm, while the output fiber has a core diameter of 20 μm and a cladding diameter of 125 μm.

[0080] like Figure 4As shown, the selection and parameters of each component in the first-stage fiber amplifier 121 of the K-class fiber amplifier 12 are as follows: the core diameter of the second gain fiber 121-0 is 20 micrometers, the cladding diameter is 125 micrometers, the normalized frequency is 5, and the cladding pump light absorption coefficient is 0.5 dB / m; the third pump signal combiner 121-1 and the fourth pump signal combiner 121-2 each have two pump light input terminals (i.e., M1=M2=2). The third pump module 121-3 contains two pump sub-modules 121-3-1 to 121-3-2, and the fourth pump module 121-4 contains two pump sub-modules 121-4-1 to 121-4-2 (i.e., M3=M4=2), each pump sub-module consisting of a semiconductor laser with a pigtail. The third cladding light filter 121-5 and the second cladding light filter 121-6 are used to filter out cladding light. The second filter 121-7 has a loss of 50dB at the 1030nm band and a beam quality retention factor of 90%. The selection and parameters of each component in the other K-1 stage fiber amplifier in the K-stage fiber amplifier 12 are the same as those of each component in the first stage amplifier 121.

[0081] Fiber optic signal combiner 2 has U input ends and one output end. The core diameter of each of the U input fibers is 20 micrometers, and the cladding diameter is 125 micrometers. The core diameter of the output fiber is 50 micrometers, and the cladding diameter is 400 micrometers. The efficiency of fiber optic signal combiner 2... The beam quality retention rate is 95%. The efficiency is 70%. The core diameter of the output cladding optical filter 3 is 50 micrometers, and the cladding diameter is 400 micrometers. The output coupling end 4 uses an optical fiber output cap. The core diameter of the input optical fiber of the optical fiber output cap is 50 micrometers, and the cladding diameter is 400 micrometers.

[0082] A single-mode seed source 11 provides a seed optical power of P0 = 20W (beam quality M). 2 With a factor not greater than 1.1, the single-stage fiber amplifier in the K-class fiber amplifier 12 provides 660W of pump optical power, and the single-stage fiber amplifier can provide =132W of power (calculated based on a pump efficiency of 20%), then the power that the u-th fiber laser unit module can provide is... for( )W.

[0083] By adjusting the number U of fiber laser unit modules and the amplification stage K of the K-stage fiber amplifier 12 in the fiber laser unit module, a variety of feasible parameter combinations can be achieved under the condition of satisfying the predetermined output power and beam quality.

[0084] Formula (1) represents the total output power P of the high-brightness kilowatt-level 980nm band fiber laser of this invention. t With the power of U fiber laser unit modules (P) su The relationship between the power of the u-th fiber laser unit module and the efficiency η of the fiber signal combiner 2.

[0085] , formula (1) Formula (2) represents the target beam quality M of the high-brightness kilowatt-level 980nm band fiber laser of this invention. 2 Factor (using M) t 2 (represented by) the beam quality M of the fiber laser unit module 2 Factor (using M) s 2 (representation), U and beam quality retention factor The relationship.

[0086] , formula (2) The efficiency of fiber optic signal combiner 2 ( (95%) and beam quality retention factor ( Substituting 70% into formulas (1) and (2), in "P t >1kW, M t 2 With the target value set at <5", the range of U can be solved. Combined with P su M s 2 By understanding the relationship between U and K, feasible (U,K) combinations can be obtained. Example 1 is U=7, K=1; Example 2 is U=4, K=2; Example 3 is U=3, K=3.

[0087] Example 1 (U=7, K=1) consists of 7 such Figure 2The fiber laser unit modules shown (1-1 to 1-7) consist of a fiber signal combiner 2, an output cladding optical filter 3, and an output coupling terminal 4. The fiber signal combiner 2 has U input ends, i.e., 7 input ends. The core diameter of each of the 7 input fibers in the fiber signal combiner 2 is 20 micrometers, and the cladding diameter is 125 micrometers. The core diameter of the output fiber in the fiber signal combiner 2 is 50 micrometers, and the cladding diameter is 400 micrometers. The efficiency of the fiber signal combiner 2 is 95%, and the beam quality retention factor is 70%. The core diameter of the output cladding optical filter 3 is 50 micrometers, and the cladding diameter is 400 micrometers. The output coupling terminal 4 uses a fiber output cap. The core diameter of the input fiber in the fiber output cap is 50 micrometers, and the cladding diameter is 400 micrometers. Each fiber laser unit module consists of a single-mode seed source 11 and a K-class fiber amplifier 12. The K-level fiber amplifier 12 adopts a single-stage fiber amplifier structure (i.e., K=1), consisting of a first-stage fiber amplifier 121. It provides 20W of seed optical power (beam quality M) to the single-mode seed source 11. 2 With a factor not greater than 1.1, and the first-stage fiber amplifier 121 in the K-class fiber amplifier 12 providing 660W of pump power, each fiber laser unit module has an output power of 152W in the 980nm band, and the beam quality M 2 Factor (i.e., M) s 2 The 152W laser output from the seven fiber laser unit modules is synchronously input into the fiber signal combiner 2 for power combining. The combined laser then passes through the output cladding optical filter 3 and the output coupling terminal 4 before being output, ultimately yielding a power of 1.01kW (measured using a power meter) and a beam quality M. 2 A 980nm band laser output with a factor of 4.9 (measured using a beam quality analyzer) achieved "P" t >1kW, M t 2 The target is set at "<5".

[0088] Example 2 (U=4, K=2) consists of 4 such Figure 2The fiber laser unit modules shown (1-1 to 1-4) consist of a fiber signal combiner 2, an output cladding optical filter 3, and an output coupling terminal 4. The fiber signal combiner 2 has four input terminals, N equal to U. The core diameter of each of the four input fibers in the fiber signal combiner 2 is 20 micrometers, and the cladding diameter is 125 micrometers. The core diameter of the output fiber in the fiber signal combiner 2 is 50 micrometers, and the cladding diameter is 400 micrometers. The efficiency of the fiber signal combiner 2 is 95%, and the beam quality retention factor is 70%. The core diameter of the output cladding optical filter 3 is 50 micrometers, and the cladding diameter is 400 micrometers. The output coupling terminal 4 uses a fiber output cap. The core diameter of the input fiber in the fiber output cap is 50 micrometers, and the cladding diameter is 400 micrometers. Each fiber laser unit module consists of a single-mode seed source 11 and a K-class fiber amplifier 12. The K-stage fiber amplifier 12 employs a two-stage fiber amplifier structure (K=2), consisting of a first-stage fiber amplifier 121 and a second-stage fiber amplifier 122. It provides 20W of seed optical power (beam quality M) to the single-mode seed source 11. 2 With a factor not greater than 1.1, and the first-stage fiber amplifier 121 and the second-stage fiber amplifier 122 in the K-class fiber amplifier 12 providing 660W pump power, each fiber laser unit module has an output power of 284W in the 980nm band, and the beam quality M 2 Factor (i.e., M) s 2 The 284W laser output from the four fiber laser unit modules is synchronously input into the fiber signal combiner 2 for power combining. The combined laser then passes through the output cladding optical filter 3 and the output coupling terminal 4 before being output, ultimately yielding a power of 1.08kW (measured using a power meter) and a beam quality M. 2 A 980nm band laser output with a factor of 4.6 (measured using a beam quality analyzer) achieved "P" t >1kW, M t 2 The target is set at "<5".

[0089] Example 3 (U=3, K=3) consists of 3 such Figure 2The fiber laser unit modules shown (1-1 to 1-3) consist of a fiber signal combiner 2, an output cladding optical filter 3, and an output coupling terminal 4. The number of input terminals N of the fiber signal combiner 2 is equal to U, i.e., the number of input terminals is 3. The core diameter of each of the three input fibers of the fiber signal combiner 2 is 20 micrometers, and the cladding diameter is 125 micrometers. The core diameter of the output fiber of the fiber signal combiner 2 is 50 micrometers, and the cladding diameter is 400 micrometers. The efficiency of the fiber signal combiner 2 is 95%, and the beam quality retention factor is 70%. The core diameter of the output cladding optical filter 3 is 50 micrometers, and the cladding diameter is equal to 400 micrometers. The output coupling terminal 4 uses a fiber output end cap. The core diameter of the input fiber of the fiber output end cap is 50 micrometers, and the cladding diameter is equal to 400 micrometers. Each fiber laser unit module consists of a single-mode seed source 11 and a K-class fiber amplifier 12. The K-stage fiber amplifier 12 employs a three-stage fiber amplifier structure (K=3), consisting of a first-stage fiber amplifier 121, a second-stage fiber amplifier 122, and a third-stage fiber amplifier 123. It provides 20W of seed optical power (beam quality M) to the single-mode seed source 11. 2 With a factor not greater than 1.1, and the first-stage fiber amplifier 121, second-stage fiber amplifier 122, and third-stage fiber amplifier 123 in the K-class fiber amplifier 12 providing 660W pump power, each fiber laser unit module has an output power of 416W in the 980nm band, and the beam quality M... 2 Factor (i.e., M) s 2 The 416W laser output from the three fiber laser unit modules is synchronously input into the fiber signal combiner 2 for power combining. The combined laser then passes sequentially through the output cladding optical filter 3 and the output coupling terminal 4 before being output, ultimately yielding a power of 1.18kW (measured using a power meter) and a beam quality M of 1.9. 2 A 980nm wavelength laser output with a factor of 4.7 (measured using a beam quality analyzer) achieved "P" t >1kW, M t 2 The target is set at "<5".

[0090] It should be noted that the above composition is only an example of several specific implementation methods to verify the feasibility of the technical solution of the present invention. The present invention is not a system with fixed parameters, but provides a complete set of design freedoms. Those skilled in the art can, according to specific target power and target beam quality requirements, use the system power and beam quality model disclosed in the present invention (i.e., formula (1) and formula (2)) to determine the power (P) of the fiber laser unit module. sThe number of amplification stages (K) in the fiber laser unit module, the number of fiber laser unit modules (U), and the performance of the fiber signal combiner 2 ( , By flexibly matching and optimizing these key parameters, a variety of specific technical solutions can be derived. For example, embodiments 1, 2, and 3 can all achieve an output power greater than 1kW while maintaining a beam quality M² factor of less than 5. All such technical solutions derived under the guidance of the aforementioned model that can achieve specific target power and beam quality fall within the protection scope of this invention. This flexible and controllable design concept opens up a new technical path for achieving high-brightness kilowatt-level 980nm band fiber laser output.

Claims

1. A high-brightness kilowatt-level 980nm band fiber laser, characterized in that... A high-brightness kilowatt-level 980nm band fiber laser consists of U fiber laser unit modules, a fiber signal combiner (2), an output cladding optical filter (3), and an output coupling terminal (4), where U is a positive integer. The fiber signal combiner (2) has N input terminals and 1 output terminal, where N is a positive integer. The output terminal of each fiber laser unit module is connected to one input terminal of the fiber signal combiner (2), where U ≤ N. The output terminal of the fiber signal combiner (2) is connected to the input terminal of the output cladding optical filter (3). The output of the output cladding optical filter (3) has a U input terminal and a U output terminal. The output end is connected to the input end of the output coupling end (4), and the output end of the output coupling end (4) serves as the output end of a high-brightness kilowatt-level 980nm band fiber laser. The connection between different devices is achieved through fiber fusion splicing. U fiber laser unit modules work in parallel to generate U amplified 980nm band lasers: the single-mode seed source (11) in the u-th fiber laser unit module (1-u) generates a single-mode seed light in the 980nm band, and the K-level fiber amplifier (12) amplifies the power of the single-mode seed light in the 980nm band. U fiber laser unit modules are identical. The u-th fiber laser unit module (1-u) consists of a single-mode seed source (11) and a K-level fiber amplifier (12), where 1≤u≤U. The output of the single-mode seed source (11) is connected to the input of the K-level fiber amplifier (12). The K-level fiber amplifier (12) consists of K single-level fiber amplifiers, namely the first-level fiber amplifier (121), ..., the k-th-level fiber amplifier (12k), ..., the K-th-level fiber amplifier (12K). The output of the K-th-level fiber amplifier (12K) is the output of the u-th fiber laser unit module (1-u), where K is a positive integer. The single-mode seed source (11) in the u-th fiber laser unit module (1-u) adopts a fiber optic oscillator with a bidirectional pumping structure. The single-mode seed source (11) consists of a first gain fiber (11-0), a first pump signal combiner (11-1), a first pump module (11-2), a second pump signal combiner (11-3), a second pump module (11-4), a first cladding optical filter (11-5), a second cladding optical filter (11-6), a high-reflection fiber grating (11-7), a low-reflection fiber grating (11-8), a first filter (11-9), and a mode field adapter (11-10). The first pump signal combiner (11-1) includes N1 pump light inputs, one signal light input, and one output. The second pump signal combiner (11-3) includes N2 pump light input terminals, one signal light input terminal, and one output terminal, where N1 and N2 are both positive integers. The core diameters of the output fiber of the first pump signal combiner (11-1), the signal light input fiber of the first pump signal combiner (11-1), the output fiber of the second pump signal combiner (11-3), and the signal light input fiber of the second pump signal combiner (11-3) are all equal to the core diameter of the first gain fiber (11-0). The cladding diameters of the output fiber of the first pump signal combiner (11-1), the signal input fiber of the first pump signal combiner (11-1), the output fiber of the second pump signal combiner (11-3), and the signal input fiber of the second pump signal combiner (11-3) are all equal to the cladding diameter of the first gain fiber (11-0); the output ends of the first pump signal combiner (11-1) and the second pump signal combiner (11-3) are respectively connected to the two ends of the first gain fiber (11-0); the first pump signal combiner... The pump light input of the first pump signal combiner (11-1) is connected to the output fiber of the first pump module (11-2); the signal light input of the first pump signal combiner (11-1) is connected to the input of the first cladding optical filter (11-5); the pump light input of the second pump signal combiner (11-3) is connected to the output fiber of the second pump module (11-4); the signal light input of the second pump signal combiner (11-3) is connected to the input of the second cladding optical filter (11-6); the first cladding optical filter (11-5)... The output end of the second cladding optical filter (11-6) is connected to the input end of the high-reflection fiber grating (11-7); the output end of the second cladding optical filter (11-6) is connected to the input end of the low-reflection fiber grating (11-8); the output end of the low-reflection fiber grating (11-8) is connected to the input end of the first filter (11-9); the output end of the first filter (11-9) is connected to the input end of the mode field adapter (11-10), and the output end of the mode field adapter (11-10) is the output end of the single-mode seed source (11), which is connected to the input end of the K-level fiber amplifier (12); The first pump signal combiner (11-1) couples the pump light generated by the first pump module (11-2) into the first gain fiber (11-0), and the second pump signal combiner (11-3) couples the pump light generated by the second pump module (11-4) into the first gain fiber (11-0). The pump light coupled into the first gain fiber (11-0) excites the ytterbium ions in the first gain fiber (11-0), causing population inversion and generating a signal light in the 980nm band. The first cladding light filter (11-5) and the second cladding light filter (11-5) in the single-mode seed source 11 of the u-th fiber laser unit module (1-u) -6) is used to filter out cladding light; the output fiber of the high-reflectivity fiber grating (11-7) suppresses the reflection of the optical field by the fiber end face, and the low-reflectivity fiber grating (11-8) is used as an output coupler to output the laser in a transmission manner while providing partial feedback; the first filter (11-9) in the single-mode seed source (11) of the u-th fiber laser unit module (1-u) is used to filter out the amplified spontaneous emission of the 1030nm band, and the mode field adapter (11-10) performs mode field matching on the pure 980nm band signal light output by the first filter (11-9) and injects the seed light into the first-stage fiber amplifier (121) with low loss; The K-stage fiber amplifier (12) in the u-th fiber laser unit module (1-u) is composed of K single-stage fiber amplifiers. The first-stage fiber amplifier (121), ..., the k-th stage fiber amplifier (12k), ..., the K-th stage fiber amplifier (12K) are connected in sequence, 1≤k≤K; the K single-stage fiber amplifiers have the same structure. The first-stage fiber amplifier (121) of the K-stage fiber amplifier (12) in the u-th fiber laser unit module (1-u) consists of a second gain fiber (121-0), a third pump signal combiner (121-1), a fourth pump signal combiner (121-2), a third pump module (121-3), a fourth pump module (121-4), a third cladding optical filter (121-5), a fourth cladding optical filter (121-6), and a second filter (121-7). The third pump signal combiner (121-1) couples the pump light generated by the third pump module (121-3) into the second gain fiber (121-0), and the fourth pump signal combiner (121-2) couples the pump light generated by the fourth pump module (121-4) into the second gain fiber (121-0); the third cladding light filter (121-5) and the fourth cladding light filter (121-6) are used to filter out cladding light; the second filter (121-7) in the first-stage fiber amplifier (121) of the u-th fiber laser unit module (1-u) is used to filter out amplified spontaneous emission in the 1030nm band; The structure of the k-th fiber amplifier (12k) in the k-th fiber amplifier (12) of the u-th fiber laser unit module (1-u) is the same as that of the first-th fiber amplifier (121); the input terminal of the k-th fiber amplifier (12k) is connected to the output terminal of the (k-1)-th fiber amplifier (12(k-1)), and the output terminal of the k-th fiber amplifier (12k) is connected to the input terminal of the (k+1)-th fiber amplifier (12(k+1)). The structure of the K-th fiber amplifier (12K) in the u-th fiber laser unit module (1-u) is the same as that of the k-th fiber amplifier (12k); the input terminal of the K-th fiber amplifier (12K) is connected to the output terminal of the (K-1)-th fiber amplifier (12(K-1)), and the output terminal of the K-th fiber amplifier (12K) is the output terminal of the K-th fiber amplifier (12), which is also the output terminal of the fiber laser unit module; The fiber signal combiner (2) is used to combine the laser output from U fiber laser unit modules; the output cladding light filter (3) is used to filter out the cladding light generated after passing through the fiber signal combiner (2); the output coupling end (4) couples the 980nm band laser output from the cladding light filter (3) that is transmitted in the fiber core.

2. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... The method for determining the number U of the fiber laser unit modules and the number K of the fiber amplifier (12) is as follows: the total output power of the high-brightness kilowatt-level 980nm band fiber laser , For the efficiency of the fiber optic signal combiner, the requirements are... ≥95%, Let u be the output power of the u-th fiber laser unit module (1-u). P0 represents the power provided by the single-mode seed source (11), P k M represents the power provided by the k-th single-stage fiber amplifier (12k); the target beam quality M of a high-brightness kilowatt-level 980nm band fiber laser. 2 Factor M t 2 With fiber laser unit module beam quality M 2 Factor M s 2 Beam quality retention coefficient of U and fiber optic signal combiner satisfy ,Require ≥70%; and Substitution and , in "P t >1kW, M t 2 Under the target setting of "<5", the range of U is solved, and then P is combined. su M s 2 The relationship between K and U yields the (U,K) combination.

3. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... The first pump module (11-2) in the single-mode seed source (11) of the u-th fiber laser unit module (1-u) contains N3 pump sub-modules, where N3 is a positive integer; the second pump module (11-4) contains N4 pump sub-modules, where N4 is a positive integer; N3≤N1; N4≤N2; the pump sub-modules are selected from semiconductor lasers with a fiber optic output in the 900nm~960nm band, and the fiber optics of the N3 semiconductor lasers are the output fibers of the pump sub-modules; the output fibers of the N3 pump sub-modules constituting the first pump module (11-2) are the output fibers of the first pump module (11-2), and are connected to the N3 pump light input ends of the first pump signal combiner (11-1); the N4 pump sub-modules constituting the second pump module (11-4) The output fiber of the block is the output fiber of the second pump module (11-4), which is connected to the N4 pump light input ends of the second pump signal combiner (11-3); the diameter of the output fiber of the first pump module (11-2) is less than or equal to the diameter of the pump light input fiber of the first pump signal combiner (11-1); the numerical aperture of the output fiber of the first pump module (11-2) is less than or equal to the numerical aperture of the pump light input fiber of the first pump signal combiner (11-1); the diameter of the output fiber of the second pump module (11-4) is less than or equal to the diameter of the pump light input fiber of the second pump signal combiner (11-3); the numerical aperture of the output fiber of the second pump module (11-4) is less than or equal to the numerical aperture of the pump light input fiber of the second pump signal combiner (11-3).

4. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... The first gain fiber (11-0) in the single-mode seed source (11) of the u-th fiber laser unit module (1-u) is a single-mode step-index double-clad ytterbium-doped fiber, requiring a core diameter of not less than 10 micrometers, a normalized frequency of not more than 2.405, a cladding diameter of not less than 125 micrometers, and a length ≤ the fiber length corresponding to the absence of 1030nm band self-excited oscillation in the single-mode seed source (11); the core diameters of the first cladding optical filter (11-5) and the second cladding optical filter (11-6) are equal to the core diameter of the first gain fiber (11-0), and the first cladding optical filter ( The cladding diameter of the first gain fiber (11-0) is equal to that of the second cladding optical filter (11-5) and the second cladding optical filter (11-6); the center wavelength of the high-reflectivity fiber grating (11-7) is between 975-985nm, and the reflectivity at the center wavelength is ≥99%; the high-reflectivity fiber grating (11-7) is cut at an angle, but not limited to an oblique angle, and the core diameter of the high-reflectivity fiber grating (11-7) is equal to the core diameter of the first gain fiber (11-0), and the cladding diameter is equal to that of the first gain fiber (11-0); the center wavelength of the low-reflectivity fiber grating (11-8) is similar to that of the high-reflectivity fiber grating (11-0). The center wavelengths of the fiber gratings (11-7) are approximately equal, and the reflectivity at the center wavelength is ≥5%; the core diameter of the low-reflection fiber grating (11-8) is equal to the core diameter of the first gain fiber (11-0), and the cladding diameter is equal to the cladding diameter of the first gain fiber (11-0); the loss of the first filter (11-9) in the 1030nm band is ≥50dB, the beam quality retention factor is ≥90%, and the core diameters of the input and output fibers of the first filter (11-9) are equal to the core diameter of the output fiber of the low-reflection fiber grating (11-8). The cladding diameters of the input and output optical fibers of (11-9) are equal to the cladding diameter of the output optical fiber of the low-reflection fiber grating (11-8); the core diameter of the input optical fiber of the mode field adapter (11-10) is equal to the core diameter of the output optical fiber of the first filter (11-9), and the cladding diameter is equal to the cladding diameter of the output optical fiber of the first filter (11-9); the core diameter of the output optical fiber of the mode field adapter (11-10) is equal to the core diameter of the input optical fiber of the K-class fiber amplifier (12), and the cladding diameter is equal to the cladding diameter of the input optical fiber of the K-class fiber amplifier (12).

5. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 4, characterized in that... The center wavelength of the high-reflectivity fiber grating (11-7) is between 976-980nm; the deviation between the center wavelength of the low-reflectivity fiber grating (11-8) and the center wavelength of the high-reflectivity fiber grating (11-7) is less than 1nm.

6. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... Both the third pump signal combiner (121-1) and the fourth pump signal combiner (121-2) include multiple pump light inputs, one signal light input, and one output. The third pump signal combiner (121-1) includes M1 pump light inputs, where M1 is a positive integer, and the fourth pump signal combiner (121-2) includes M2 pump light inputs, where M2 is a positive integer. The output fiber of the third pump signal combiner (121-1), the signal light input fiber of the third pump signal combiner (121-1), and the output fiber of the fourth pump signal combiner (121-2) are all included. The core diameters of the output fiber and the signal input fiber of the fourth pump signal combiner (121-2) are all equal to the core diameter of the second gain fiber (121-0); the cladding diameters of the output fiber of the third pump signal combiner (121-1), the signal input fiber of the third pump signal combiner (121-1), the output fiber of the fourth pump signal combiner (121-2), and the signal input fiber of the fourth pump signal combiner (121-2) are all equal to the cladding diameter of the second gain fiber (121-0); the output fiber of the third pump signal combiner (121-1)... The output ends of the fourth pump signal combiner (121-2) and the second gain fiber (121-0) are respectively connected to both ends of the second gain fiber (121-0); the signal light input end of the third pump signal combiner (121-1) is connected to the input end of the third cladding optical filter (121-5); the pump light input end of the third pump signal combiner (121-1) is connected to the output fiber of the third pump module (121-3); the signal light input end of the fourth pump signal combiner (121-2) is connected to the input end of the fourth cladding optical filter (121-6); the fourth pump signal combiner (121-2)... The pump light input is connected to the output fiber of the fourth pump module (121-4); the output of the third cladding optical filter (121-5) is connected to the output of the mode field adapter (11-10), which is the input of the first-stage fiber amplifier (121) and also the input of the K-stage fiber amplifier (12); the output of the fourth cladding optical filter (121-6) is connected to the input of the second filter (121-7); the output of the second filter (121-7) is the output of the first-stage fiber amplifier (121) and is connected to the input of the second-stage fiber amplifier (122).

7. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... The third pump module (121-3) of the K-level fiber amplifier (12) in the u-th fiber laser unit module (1-u) contains M3 pump sub-modules, where M3 is a positive integer; the fourth pump module (121-4) contains M4 pump sub-modules, where M4 is a positive integer; M3≤M1; M4≤M2; the pump sub-modules use semiconductor lasers with a 900nm~960nm wavelength band output via pigtails. When semiconductor lasers are used, the pigtails of the M3 semiconductor lasers are the output fibers of the pump sub-modules; the output fibers of the M3 pump sub-modules constituting the third pump module (121-3) are the output fibers of the third pump module (121-3), and are combined with the third pump signal combiner ( The M3 pump light inputs of the third pump module (121-1) are connected; the output fibers of the M4 pump sub-modules constituting the fourth pump module (121-4) are the output fibers of the fourth pump module (121-4), and are connected to the M4 pump light inputs of the fourth pump signal combiner (121-2); the diameter of the output fiber of the third pump module (121-3) is less than or equal to the diameter of the pump light input fiber of the third pump signal combiner (121-1); the numerical aperture of the output fiber of the third pump module (121-3) is less than or equal to the numerical aperture of the pump light input fiber of the third pump signal combiner (121-1); the diameter of the output fiber of the fourth pump module (121-4) is less than or equal to the numerical aperture of the pump light input fiber of the fourth pump signal combiner (121-2). The diameter of the pump light input fiber of 121-2); the numerical aperture of the output fiber of the fourth pump module (121-4) is less than or equal to the numerical aperture of the pump light input fiber of the fourth pump signal combiner (121-2); the second gain fiber (121-0) of the K-level fiber amplifier (12) in the u-th fiber laser unit module (1-u) is a step-index double-clad ytterbium-doped fiber with a core diameter of not less than 20 micrometers, a normalized frequency of not more than 5, a cladding diameter of not less than 125 micrometers, a cladding pump light absorption coefficient of not less than 0.5dB / m, and a length less than or equal to the fiber length corresponding to the absence of 1030nm band self-excited oscillation in the first-stage fiber amplifier; the third cladding light filter (121-5) The core diameters of the second filter (121-7) and the fourth cladding optical filter (121-6) are equal to the core diameter of the second gain fiber (121-0); the cladding diameters of the third cladding optical filter (121-5) and the fourth cladding optical filter (121-6) are equal to the cladding diameter of the second gain fiber (121-0); the second filter (121-7) has a loss ≥50dB in the 1030nm band and a beam quality retention factor ≥90%; the core diameters of the input and output fibers of the second filter (121-7) are equal to the core diameter of the output fiber of the fourth cladding optical filter (121-5), and the cladding diameter is equal to the cladding diameter of the output fiber of the fourth cladding optical filter (121-5).

8. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... The fiber core diameters of the N input fiber ends of the fiber signal combiner (2) are equal, which is equal to the fiber core diameter of the output fiber end of the fiber laser unit module; the cladding diameters of the N input fiber ends of the fiber signal combiner (2) are equal, which is equal to the cladding diameter of the output fiber end of the fiber laser unit module; the fiber core diameter of the output fiber end of the fiber signal combiner (2) is not greater than 50 micrometers; the efficiency of the fiber signal combiner (2) is ≥95%, and the beam quality retention coefficient of the fiber signal combiner (2) is ≥70%; the fiber core diameter of the cladding optical filter (3) is equal to the fiber core diameter of the output fiber end of the fiber signal combiner (2), and the cladding diameter is equal to the cladding diameter of the output fiber end of the fiber signal combiner (2); the fiber core diameter of the input fiber end of the output coupling end (4) is equal to the fiber core diameter of the output fiber end of the cladding optical filter (3), and the cladding diameter is equal to the cladding diameter of the output fiber end of the cladding optical filter (3), and an optical fiber output cap is used.

9. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 1, characterized in that... The operation process of the high-brightness kilowatt-level 980nm band fiber laser is as follows: In the first step, U fiber laser unit modules work in parallel to generate U amplified 980nm band lasers: the single-mode seed source (11) in the u-th fiber laser unit module (1-u) generates a single-mode seed light in the 980nm band, and the fiber amplifier (12) amplifies the power of the single-mode seed light in the 980nm band. The second step is that the fiber optic signal combiner (2) performs power combining on the U amplified 980nm band lasers received from the U fiber laser unit modules to obtain the combined 980nm band laser. The third step is to use the output cladding light filter (3) to perform cladding light filtering on the synthesized 980nm band laser output by the fiber signal combiner (2) to obtain the 980nm band laser transmitted in the fiber core. The fourth step is to couple the 980nm band laser transmitted in the fiber core to the output of the cladding optical filter (3) at the output coupling end (4). That is, while suppressing optical feedback, the laser in the fiber core is coupled out with high efficiency and low loss to obtain the final 980nm band output laser.

10. A high-brightness kilowatt-level 980nm band fiber laser as described in claim 9, characterized in that... The method described in the first step for the u-th fiber laser unit module (1-u) to generate amplified 980nm band laser is as follows: Step 1.1 The first pump signal combiner (11-1) couples the pump light generated by the first pump module (11-2) into the first gain fiber (11-0), while the second pump signal combiner (11-3) couples the pump light generated by the second pump module (11-4) into the first gain fiber (11-0). The pump light coupled into the first gain fiber (11-0) excites the ytterbium ions in the first gain fiber (11-0), causing population inversion, thereby generating signal light in the 980nm band. Step 1.2 The optical field in the 980nm band forms laser oscillation in the resonant cavity composed of a high-reflectivity fiber grating (11-7) and a low-reflectivity fiber grating (11-8); wherein, the high-reflectivity fiber grating (11-7) is used to provide strong optical feedback to maintain efficient laser oscillation; the low-reflectivity fiber grating (11-8) is used as an output coupler to output the laser in a transmission manner while providing partial feedback; in this process, the first cladding light filter (11-5) and the second cladding light filter (11-6) are used to filter out cladding light; Step 1.3 The first filter (11-9) filters the laser transmitted from the low-reflection fiber grating (11-8), filtering out the amplified spontaneous emission in the 1030nm band, and obtaining pure signal light in the 980nm band. Step 1.4 The mode field adapter (11-10) performs mode field matching on the pure 980nm band signal light output from the first filter (11-9) and injects the seed light into the first-stage fiber amplifier (121) with low loss. Step 1.5 In the first-stage fiber amplifier (121), the third pump signal combiner (121-1) couples the pump light generated by the third pump module (121-3) into the second gain fiber (121-0), while the fourth pump signal combiner (121-2) couples the pump light generated by the fourth pump module (121-4) into the second gain fiber (121-0). The pump light coupled into the second gain fiber (121-0) excites the ytterbium ions in the second gain fiber (121-0), causing population inversion, thereby amplifying the seed light passing through the core of the second gain fiber (121-0). During this process, the third cladding light filter (121-5) and the fourth cladding light filter (121-6) are used to filter out the cladding light. Step 1.6 The second filter (121-7) filters the amplified seed light from the fourth cladding optical filter (121-6) to filter out the amplified spontaneous emission in the 1030nm band and obtain pure amplified 980nm band signal light, which is used as the output of the first-stage fiber amplifier 121. Step 1.7 The second-stage fiber amplifier (122) amplifies and filters the pure 980nm band signal light output from the first-stage fiber amplifier (121), ..., the k-th stage fiber amplifier (12k) amplifies and filters the pure 980nm band signal light output from the (k-1)-th stage fiber amplifier (12(k-1)), ..., the K-th stage fiber amplifier (121K) amplifies and filters the pure 980nm band signal light output from the (K-1)-th stage fiber amplifier (12(K-1)). The signal light amplified by the first-stage fiber amplifier (121) is amplified and filtered stage by stage by stage by stage of K fiber amplifiers, and finally outputs the amplified 980nm band laser as the output of the u-th fiber laser unit module (1-u); in this process, all cladding light filters are used to filter out cladding light.

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