All-fiber amplifier with improved performance against photon darkening

Abstract

In order to solve the problem of output performance attenuation of the existing fiber laser amplifier in a high radiation environment, especially the problem of laser efficiency reduction and beam quality degradation caused by radiation-induced defects, the application provides a kind of all-fiber amplifier with improved anti-photonic darkening performance, which is characterized in that a bleaching light circulator is connected behind the gain fiber of the amplifier, so that the bleaching light can enter the gain fiber of the amplifier in a loop mode, thereby realizing the cyclic bleaching of the gain fiber, which can not only effectively improve the bleaching efficiency, but also enhance the energy density of the bleaching light in the gain fiber, and significantly improve the anti-darkening performance and working life of the all-fiber amplifier in a high radiation environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber lasers, in particular to a full-fiber amplifier with improved anti-photonic darkening performance. BACKGROUND

[0002] With the continuous exploration of space by mankind and the rapid development of space technology, the application scope and scene of fiber lasers in the space field have greatly increased, such as space laser communication, laser radar, space debris disposal, fiber laser gyro, etc. However, the space environment is very harsh, mainly manifested in that the fiber laser will be irradiated by high-energy electromagnetic radiation (X-ray, gamma ray) and charged particles (positive and negative electrons, protons, alpha particles, etc.). The most affected by the laser is the high-energy rays such as gamma rays and X-rays. Rare earth-doped active fibers will produce various types of defects (or called "color centers") under space irradiation conditions, resulting in increased loss and reduced output power and service life of the fiber laser.

[0003] For high-power fiber lasers used in space, they are not only affected by the radiation-induced darkening effect, but also affected by the photonic darkening effect. With the increase of the running time of high-power lasers, the core background loss of the doped fiber increases, the output power of the fiber laser decreases rapidly and gradually reaches a stable state, which is the photonic darkening effect. The photonic darkening effect will cause the laser output threshold to increase, the system stability to decrease, and the working life to be shortened, which limits the industrial application and development of high-power fiber lasers.

[0004] As a potential solution to realize anti-darkening fiber lasers, the basic principle of the photobleaching technology is to use light of a specific wavelength to irradiate the fiber to reduce or repair ion defects induced by radiation or photonic darkening. However, the efficiency and practicability of the existing photobleaching technology are limited by the injection method and energy density of the bleaching light. When low-power density bleaching light is injected into the laser system, due to the inherent loss of the bleaching light in the fiber device, the low-power density bleaching light has limited ability to repair ion defects caused by darkening, and it is difficult to achieve a high-efficiency and stable bleaching effect. SUMMARY

[0005] In order to solve the problem of output performance attenuation of the existing fiber laser amplifier in a high radiation environment, especially the problem of laser efficiency reduction and beam quality degradation caused by radiation-induced defects, the present application provides a full-fiber amplifier with improved anti-photonic darkening performance. The laser is connected with a bleaching light circulator behind the gain fiber of the amplifier, so that the bleaching laser can circulate into the gain fiber of the amplifier, thereby realizing efficient bleaching of the gain fiber and improving the anti-darkening performance of the full-fiber amplifier in the radiation environment and under the condition of photonic darkening.

[0006] To achieve the above technical purposes, the technical scheme adopted by the present application is:

[0007] In one aspect, the present application provides a kind of all-fiber amplifier for improving the performance of anti-light subversion, including seed laser, bleaching light source, wavelength division multiplexer, forward pumping signal combiner, gain optical fiber, fiber-coupled semiconductor laser, bleaching light circulator;Forward pumping signal combiner has a signal input fiber, a signal output fiber and at least one pump energy transmission fiber;

[0008] Seed laser, bleaching light source connects wavelength division multiplexer, and the energy transmission fiber of wavelength division multiplexer is connected to the signal input fiber of forward pumping signal combiner, and each pump energy transmission fiber of the forward pumping signal combiner is connected to the fiber-coupled semiconductor laser;One end of the gain optical fiber is connected to the signal output fiber of the forward pumping signal combiner, and the other end is connected to the signal input fiber of the bleaching light circulator, and the bleaching laser output by the bleaching light source and the pump light output by the plurality of fiber-coupled semiconductor lasers are transmitted in the cladding of the gain optical fiber, and the signal laser output by the seed laser is transmitted in the core of the gain optical fiber;

[0009] The bleaching light circulator has a pump energy transmission fiber closed loop, and the bleaching laser that is not completely absorbed and is output to the bleaching light circulator through the fiber cladding of the gain optical fiber reenters the gain optical fiber through the pump energy transmission fiber closed loop in the bleaching light circulator, to realize the circulation bleaching of the gain optical fiber, and the signal laser output through the core of the gain optical fiber is output through the signal output fiber of the bleaching light circulator.

[0010] Preferably, the bleaching light circulator includes a fiber combiner end, a signal fiber and at least one pair of pump energy transmission fibers, the signal fiber includes a signal input fiber and a signal output fiber, and the two pump energy transmission fibers in each pair are fused to form a pump energy transmission fiber closed loop, and the fusion points of the pump energy transmission fibers in each pair form pump energy transmission fiber fusion points, the gain optical fiber is connected to the signal input fiber of the bleaching light circulator, the signal laser output through the core of the gain optical fiber is output through the signal input fiber and the signal output fiber of the bleaching light circulator, and the laser output through the cladding of the gain optical fiber reenters the gain optical fiber through the pump energy transmission fiber closed loop of the bleaching light circulator.Further, it also includes a cladding light filter and a fiber end cap, the signal output fiber of the bleaching light circulator is connected to the cladding light filter, the cladding light filter is connected to the fiber end cap, and the core and cladding diameters of the cladding light filter are greater than or equal to the core and cladding diameters of the signal output fiber of the bleaching light circulator.

[0011] Preferably, the bleaching light circulator can be composed of a backward-pumped signal combiner, the core / cladding diameters of the signal input fiber of the backward-pumped signal combiner match the core / cladding diameters of the gain fiber, the number n of the pump energy transfer fibers of the backward-pumped signal combiner satisfies 2≤n≤36, and n is an even number, and the pump energy transfer fibers are fused to form a plurality of pump energy transfer fiber closed loops.

[0012] As another preferred embodiment, the present application also includes a backward-pumped signal combiner, the signal output fiber of the bleaching light circulator is connected to the backward-pumped signal combiner, the backward-pumped signal combiner has one signal input fiber, one signal output fiber, and at least one pump energy transfer fiber, the signal input fiber of the backward-pumped signal combiner is connected to the signal output fiber of the bleaching light circulator, the signal output fiber of the backward-pumped signal combiner is connected to a cladding light filter, each pump energy transfer fiber of the backward-pumped signal combiner is connected to a fiber-coupled semiconductor laser, the signal output fiber of the backward-pumped signal combiner is connected to the cladding light filter, and the cladding light filter is connected to a fiber end cap, the core and cladding diameters of the cladding light filter are greater than or equal to the core and cladding diameters of the signal output fiber of the backward-pumped signal combiner.

[0013] Preferably, the gain fiber of the present application is a step-index fiber doped with one or more of ytterbium ions, erbium ions, neodymium ions, thulium ions, and holmium ions, and the cross-sectional structure of the gain fiber is one of single-clad, double-clad, triple-clad, or preform with a specific layer structure.

[0014] Preferably, the bleaching light source of the present application generates bleaching laser with a wavelength range of 360nm-780nm and an output power of 1mW-10W, and the bleaching laser generated by the bleaching light source is single-wavelength laser, dual-wavelength laser, or a combination of multiple wavelengths.

[0015] Preferably, the fiber-coupled semiconductor laser of the present application is an excitation source of upper-level particles generated by the gain fiber, and the output wavelength of the fiber-coupled semiconductor laser matches the absorption peak of the doped rare earth ions in the gain fiber, and the output wavelength of the fiber-coupled semiconductor laser is one or a combination of multiple of 808nm, 915nm, 940nm, and 976nm.

[0016] Preferably, the output mode of the seed laser of the present application is fiber output, the core diameter of the output fiber ranges from 5μm to 50μm, and the wavelength of the signal laser generated by the seed laser ranges from 950nm to 1200nm.

[0017] The above-mentioned all-fiber amplifier with improved anti-photodarkening performance can be used in a γ-ray, X-ray or ultraviolet radiation environment or a photon darkening environment, and can achieve online bleaching in a γ-ray, X-ray or ultraviolet radiation environment or offline bleaching after working in a γ-ray, X-ray or ultraviolet radiation environment.

[0018] Compared with the prior art, the present invention can produce the following technical effects:

[0019] The present invention injects bleaching light generated by a bleaching light source into the gain fiber of the amplifier to bleach the gain fiber. A bleaching light circulator is connected behind the gain fiber, which has a closed loop of pump-energy transmission fiber. This allows the incompletely absorbed bleaching laser output by the amplifier to circulate back and forth into the gain fiber of the amplifier, achieving cyclic bleaching of the gain fiber. This not only effectively improves the photobleaching efficiency but also enhances the energy density of the bleaching light within the gain fiber cladding, significantly improving the anti-darkening performance and operating life of the fiber amplifier in high-radiation environments. The present method can effectively improve the bleaching efficiency of all-fiber amplifiers and greatly enhance the anti-darkening performance of the amplifier.

[0020] The laser in the present invention has an all-fiber structure, and the bleaching light source can achieve both online bleaching effects and offline time-sharing bleaching. It has a simple structure and is easy to operate, which can greatly expand the application of fiber lasers in different radiation environments and photodarkening environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0022] Figure 1 This is a schematic structural diagram of an all-fiber amplifier with improved anti-photon darkening performance provided by Example 1 of the present invention;

[0023] Figure 2 This is a schematic structural diagram of a bidirectionally pumped all-fiber amplifier with improved anti-photon darkening performance provided by Example 2 of the present invention;

[0024] Figure 3 1 is a schematic structural diagram of a bleaching light circulator provided by one embodiment of the present invention;

[0025] Figure 4 1 is a schematic structural diagram of a bleaching light circulator provided by one embodiment of the present invention;

[0026] Figure annotation:

[0027] 1, gain fiber; 2, forward pumping signal combiner; 3, pump energy transfer fiber; 4, fiber coupled semiconductor laser; 5, wavelength division multiplexer; 6, wavelength division multiplexer energy transfer fiber; 7, bleaching light source; 8, seed laser; 9, bleaching light circulator; 10, signal input fiber; 11, fiber combiner end; 12, pump energy transfer fiber closed loop; 13, pump energy transfer fiber splicing point; 14, signal output fiber; 15, cladding light filter; 16, fiber end cap; 17, reverse pumping signal combiner;

[0028] 12-1, first pump energy transfer fiber; 12-2, second pump energy transfer fiber; 12-3, third pump energy transfer fiber; 12-4, fourth pump energy transfer fiber; 12-5, fifth pump energy transfer fiber; 12-6, sixth pump energy transfer fiber; 13-1, first pump energy transfer fiber splicing point; 13-2, second pump energy transfer fiber splicing point; 13-3, third pump energy transfer fiber splicing point. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] The principle of the all-fiber amplifier with improved anti-photodarkening performance conceived by the present application is that: by introducing a bleaching light circulator behind the gain fiber in the all-fiber amplifier, the bleaching laser injected into the cladding of the gain fiber in the amplifier passes through the pump energy transfer fiber closed loop of the bleaching light circulator, and returns to the cladding of the gain fiber in the amplifier, realizing the circulation of the gain fiber bleaching, improving the power density of the bleaching laser in the cladding of the gain fiber, and thus improving the photodarkening bleaching effect.

[0031] Reference Figure 1 Fig. 1 is a structure schematic diagram of an all-fiber amplifier with improved anti-photodarkening performance provided by Embodiment 1 of the present application, comprising a seed laser 8, a bleaching light source 7, a wavelength division multiplexer 5, a forward pumping signal combiner 2, a gain fiber 1, a fiber coupled semiconductor laser 4, a bleaching light circulator 9, a cladding light filter 15, and a fiber end cap 16.

[0032] The seed laser 8 and the bleaching light source 7 are connected with the wavelength division multiplexer 5, and the wavelength division multiplexer transmission fiber 6 is connected with the signal input fiber of the forward pumping signal combiner 2. The signal laser output by the seed laser 8 and the bleaching laser output by the bleaching light source 7 are coupled into the amplifier through the wavelength division multiplexer transmission fiber 6, and the bleaching laser is used for bleaching the photon darkening and the radiation-induced darkening of the gain fiber.

[0033] One end of the gain fiber 1 of the amplifier is connected with the signal output fiber of the forward pumping signal combiner 2, and the other end is connected with the signal input fiber of the bleaching light circulator 9.

[0034] The bleaching light circulator 9 comprises a fiber combiner end 11, a signal fiber and at least one pair of pump transmission fibers, the signal fiber comprises a signal input fiber 10 and a signal output fiber 14, and two pump transmission fibers in each pair are fused to form a pump transmission fiber closed loop 12, and the fusion of the two pump transmission fibers forms a pump transmission fiber fusion point 13. The gain fiber 1 is connected with the signal input fiber 10 of the bleaching light circulator 9, the signal laser output through the core of the gain fiber 1 is output through the signal input fiber 10 and the signal output fiber 14 of the bleaching light circulator 9, and the laser output through the cladding of the gain fiber 1 reenters the gain fiber 1 through the pump transmission fiber closed loop 12 of the bleaching light circulator 9.

[0035] The signal output fiber 14 of the bleaching light circulator 9 is connected with the cladding light filter 15, the cladding light filter 15 is connected with the fiber end cap 16, and the laser output by the gain fiber 1 is filtered through the cladding light filter 15 to remove residual pump light and other component light, and then is expanded and output through the fiber end cap 16. The core and cladding diameters of the cladding light filter 15 are greater than or equal to the core and cladding diameters of the signal output fiber 14 of the bleaching light circulator 9.

[0036] The bleaching laser generated by the bleaching light source 7 is coupled into the forward pumping signal combiner 2 through the wavelength division multiplexer transmission fiber 6, and then is injected into the cladding of the gain fiber 1 of the amplifier through the signal output fiber of the forward pumping signal combiner 2, so as to bleach the photon darkening and the radiation-induced darkening of the gain fiber. The bleaching laser which is not completely absorbed reenters the gain fiber cladding of the amplifier through the pump transmission fiber closed loop 12 of the bleaching light circulator 9, thereby forming a circulating bleaching effect.

[0037] The bleaching light circulator 9 can be composed of a reverse pumping signal combiner, the signal input fiber 10 of the reverse pumping signal combiner is connected with one end of the gain fiber 1, and the core / cladding diameters of the signal input fiber 10 match the core / cladding diameters of the gain fiber 1. The number n of the pump transmission fibers of the reverse pumping signal combiner satisfies 2≤n≤36, and n is an even number, and the pump transmission fibers are fused in pairs to form a plurality of pump transmission fiber closed loops.

[0038] The output of the seed laser 8 is fiber output, and the core diameter of the output fiber ranges from 5 μm to 50 μm; the signal laser generated by the seed laser 8 has a wavelength ranging from 950 nm to 1200 nm, and preferably, a 1080 nm laser with a core diameter of 10 μm is used to realize single-mode output.

[0039] The bleaching laser generated by the bleaching light source 7 has a wavelength ranging from 360 nm to 780 nm and an output power ranging from 1 mW to 10 W, and includes single-wavelength laser, double-wavelength laser or multiple-wavelength combination, and is used for light darkening bleaching of the gain fiber; preferably, the bleaching light source 7 uses a 450 nm blue laser with an output power of 100 mW.

[0040] The bleaching laser generated by the bleaching light source 7 is transmitted in the cladding, and the transmission path is: bleaching laser generated by the bleaching light source 7→wavelength division multiplexer 5→forward pumping signal combiner 2→gain fiber 1→bleaching light circulator 9→pump energy transmission fiber closed loop 12 in the bleaching light circulator 9→bleaching light circulator 9→gain fiber 1→forward pumping signal combiner 2.

[0041] The signal laser generated by the seed laser 8 is transmitted in the core, and the transmission path is: signal laser generated by the seed laser 8→wavelength division multiplexer 5→forward pumping signal combiner 2→gain fiber 1→bleaching light circulator 9→signal output fiber 14 of the bleaching light circulator 9→cladding light filter 15→fiber end cap 16.

[0042] Referring to Figure 2 is a full-fiber amplifier structure schematic diagram provided by Embodiment 2 of the application for improving the anti-light darkening performance, and the full-fiber amplifier of Embodiment 2 is a bidirectional pumping structure, Figure 2 The structure schematic diagram of the embodiment shown in the figure is basically the same as that of the embodiment shown in the figure Figure 1 , and includes a seed laser 8, a bleaching light source 7, a wavelength division multiplexer 5, a forward pumping signal combiner 2, a gain fiber 1, a fiber-coupled semiconductor laser 4, a bleaching light circulator 9, a cladding light filter 15, a fiber end cap 16 and a reverse pumping signal combiner 17.

[0043] Figure 2 The embodiment shown in the figure is basically the same as that of the embodiment shown in the figure Figure 1The difference of the embodiment shown is that the signal output fiber 14 of the bleaching light circulator 9 is connected to a backward pumped signal combiner 17, the backward pumped signal combiner 17 has one signal input fiber, one signal output fiber and at least one pump energy transfer fiber 3, the signal input fiber of the backward pumped signal combiner 17 is connected to the signal output fiber 14 of the bleaching light circulator 9, each pump energy transfer fiber 3 of the backward pumped signal combiner 17 is connected to a fiber coupled semiconductor laser 4, the signal output fiber of the backward pumped signal combiner 17 is connected to a cladding light filter 15, the cladding light filter 15 is connected to a fiber end cap 16, the core and cladding diameters of the cladding light filter 15 are equal to or greater than the core and cladding diameters of the signal output fiber of the backward pumped signal combiner 17.

[0044] Increasing the backward pumped signal combiner 17 injection backward pumped power can further improve the output power of the all fiber amplifier, in order to enable the pump power injected by the fiber coupled semiconductor laser 4 connected to the backward pumped signal combiner 17 to smoothly pass through the bleaching light circulator 9 into the amplifier gain fiber, the size of the signal input fiber 10 of the bleaching light circulator 9 is consistent with the size of the signal output fiber 14.

[0045] The bleaching light circulator 9 can be a side pumped signal combiner, including a fiber combiner end 11, a signal input fiber 10, a signal output fiber 14 and at least one pump energy transfer fiber closed loop 12. One pump energy transfer fiber closed loop 12 is formed by two pump energy transfer fibers through fusion splicing, and the fusion splicing points of the two pump energy transfer fibers form pump energy transfer fiber fusion splicing points 13. The two ends of the pump energy transfer fiber closed loop 12 are thinned and attached to the cladding of the signal fiber to form the fiber combiner end 11, the signal input fiber 10 and the signal output fiber 14 of the bleaching light circulator 9 are the same fiber, and do not need to be thinned by fusion splicing.

[0046] In any of the above embodiments:

[0047] The gain fiber 1 is a step index fiber doped with rare earth ions, the rare earth ions are one or more of ytterbium ions, erbium ions, neodymium ions, thulium ions and holmium ions; the cross-sectional structure of the gain fiber 1 is one of single cladding, double cladding, triple cladding or preform with a specific layer structure.

[0048] The forward pumped signal combiner 2 has one signal input fiber, one signal output fiber and at least one pump energy transfer fiber 3; the at least one pump energy transfer fiber 3 of the forward pumped signal combiner 2 is connected to a fiber coupled semiconductor laser 4.

[0049] The fiber-coupled semiconductor laser 4 is an excitation source of the upper energy level particles generated by the gain fiber 1, and the output wavelength thereof matches the absorption peak of the rare earth ion doped in the gain fiber 1, and can be one or a combination of 808 nm, 915 nm, 940 nm, 976 nm.

[0050] The present application is suitable for various radiation environments, including gamma ray, X ray, ultraviolet radiation environment, and is also suitable for photon darkening environment, and the present application can realize online bleaching and offline bleaching. The online bleaching refers to that in the gamma ray, X ray, ultraviolet radiation environment or photon darkening environment, the bleaching light source is turned on synchronously during the working process of the all-fiber amplifier, and the bleaching light source bleaches the gain fiber irradiated in the working process of the all-fiber amplifier. The offline bleaching refers to that after the all-fiber amplifier works in the gamma ray, X ray, ultraviolet radiation environment or photon darkening environment, the loss of the all-fiber amplifier increases, and the output power and service life of the all-fiber amplifier decrease. For the all-fiber amplifier working in the gamma ray, X ray, ultraviolet radiation environment or photon darkening environment, the bleaching light source 7 is turned on in the non-radiation environment according to the scheme of the present application, the bleaching laser is injected into the cladding of the gain fiber 1 of the amplifier by using the bleaching light source 7, the gain fiber 1 is bleached by the bleaching laser, and the output performance of the all-fiber amplifier after bleaching returns to the state before radiation or darkening, so as to repeat the use and bleaching.

[0051] Reference Figure 3The structural diagram of the bleaching light circulator provided by an embodiment of the present application is specifically a (6+1) x 1 reverse pumping signal combiner constituted bleaching light circulator. The bleaching light circulator 9 has a fiber combiner end 11, a signal input fiber 10, a signal output fiber 14 and a 3-pump energy transfer fiber closed loop 12, the 3-pump energy transfer fiber closed loop 12 includes 6 pump energy transfer fibers, specifically a first pump energy transfer fiber 12-1, a second pump energy transfer fiber 12-2, a third pump energy transfer fiber 12-3, a fourth pump energy transfer fiber 12-4, a fifth pump energy transfer fiber 12-5 and a sixth pump energy transfer fiber 12-6, wherein the first pump energy transfer fiber 12-1 and the sixth pump energy transfer fiber 12-6 are fused to form a first pump energy transfer fiber fusion point 13-1, the second pump energy transfer fiber 12-2 and the fifth pump energy transfer fiber 12-5 are fused to form a second pump energy transfer fiber fusion point 13-2, and the third pump energy transfer fiber 12-3 and the fourth pump energy transfer fiber 12-4 are fused to form a third pump energy transfer fiber fusion point 13-3. Specifically, the signal input fiber size of the reverse pumping signal combiner includes common 20 / 400 μm, 25 / 400 μm, 30 / 400 μm, 30 / 600 μm and the like, the signal output fiber size includes 20 / 250 μm, 25 / 250 μm, 30 / 250 μm, 42 / 250 μm and the like, and the pump energy transfer fiber size includes 105 / 125 μm, 135 / 155 μm, 220 / 242 μm and the like.

[0052] Referring to Figure 4 The structural diagram of the bleaching light circulator provided by an embodiment of the present application is specifically a (2+1) x 1 side pumping signal combiner constituted bleaching light circulator. The bleaching light circulator 9 has a fiber combiner end 11, a signal input fiber 10, a signal output fiber 14 and a pump energy transfer fiber closed loop 12. The pump energy transfer fiber closed loop 12 includes 2 pump energy transfer fibers, a first pump energy transfer fiber 12-1 and a second pump energy transfer fiber 12-2, and the first pump energy transfer fiber 12-1 and the second pump energy transfer fiber 12-2 are fused to form a first pump energy transfer fiber fusion point 13-1. The signal input fiber 10 and the signal output fiber 14 of the side pumping signal combiner are the same fiber, and the core / cladding size is consistent, which can be applied to backward pumping and bidirectional pumping fiber lasers to realize the injection of reverse pumping power. Specifically, the signal input fiber size of the side pumping signal combiner includes common 20 / 400 μm, 25 / 400 μm, 30 / 400 μm and the like, the signal output fiber size includes 20 / 400 μm, 25 / 400 μm, 30 / 400 μm and the like, and the pump energy transfer fiber size includes 105 / 125 μm, 135 / 155 μm, 220 / 242 μm and the like.

[0053] Any technical features in the above embodiments can be combined, and for the sake of brevity, not all possible combinations are described above, however, as long as the combinations of technical features do not contradict each other, they shall be considered within the scope of the present disclosure.

[0054] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the scope of the present application. It should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. An all-fiber optical amplifier with improved resistance to photodarkening, characterized in that, The application relates to a laser device, which comprises a seed laser, a bleaching light source, a wavelength division multiplexer, a forward pumping signal combiner, a gain optical fiber, a fiber-coupled semiconductor laser and a bleaching light circulator. The seed laser and the bleaching light source are connected with the wavelength division multiplexer, the wavelength division multiplexer is connected with a signal input fiber of the forward pumping signal combiner, each pump energy transmission fiber of the forward pumping signal combiner is connected with the fiber-coupled semiconductor laser, one end of the gain optical fiber is connected with a signal output fiber of the forward pumping signal combiner, and the other end of the gain optical fiber is connected with a signal input fiber of the bleaching light circulator; the bleaching laser output by the bleaching light source and the pump light output by the multiple fiber-coupled semiconductor lasers are transmitted in the cladding layer of the gain optical fiber, and the signal laser output by the seed laser is transmitted in the core of the gain optical fiber. The bleaching light circulator has a pump energy transmission fiber closed loop, the bleaching laser which is not completely absorbed and is output from the fiber cladding of the gain optical fiber reenters the gain optical fiber through the pump energy transmission fiber closed loop in the bleaching light circulator, the gain optical fiber is circulated and bleached, and the signal laser which is output from the core of the gain optical fiber is output through the signal output fiber of the bleaching light circulator.

2. The all-fiber optical amplifier of claim 1, wherein the gain fiber is a double- clad fiber. The bleaching light circulator comprises a fiber combiner end, a signal fiber and at least one pair of pump energy transmission fibers, the signal fiber comprises a signal input fiber and a signal output fiber, two pump energy transmission fibers in each pair are fused to form a pump energy transmission fiber closed loop, and the fusion points of the two pump energy transmission fibers in each pair form pump energy transmission fiber fusion points; the gain optical fiber is connected with the signal input fiber of the bleaching light circulator, the signal laser which is output from the core of the gain optical fiber is output through the signal input fiber and the signal output fiber of the bleaching light circulator, and the laser which is output from the cladding layer of the gain optical fiber reenters the gain optical fiber through the pump energy transmission fiber closed loop of the bleaching light circulator.

3. The all-fiber optical amplifier of claim 1, wherein the gain fiber is a double- clad fiber. The bleaching light circulator further comprises a cladding light filter and a fiber end cap, the signal output fiber of the bleaching light circulator is connected with the cladding light filter, the cladding light filter is connected with the fiber end cap, and the core and cladding diameters of the cladding light filter are greater than or equal to the core and cladding diameters of the signal output fiber of the bleaching light circulator.

4. The all-fiber optical amplifier of claim 2, wherein the gain fiber is a double- clad fiber. The bleaching light circulator is composed of a reverse pumping signal combiner, the core / cladding diameters of the signal input fiber of the reverse pumping signal combiner match the core / cladding diameters of the gain optical fiber, the number n of the pump energy transmission fibers of the reverse pumping signal combiner satisfies 2<=n<=36, and n is an even number, and the two pump energy transmission fibers in each pair are fused to form multiple pump energy transmission fiber closed loops.

5. The all-fiber optical amplifier of claim 1, wherein the gain fiber is a double- clad fiber. The bleaching light source comprises a reverse pumping signal combiner, a signal output fiber of the bleaching light circulator is connected to the reverse pumping signal combiner, the reverse pumping signal combiner has a signal input fiber, a signal output fiber and at least one pump energy transfer fiber, the signal input fiber of the reverse pumping signal combiner is connected to the signal output fiber of the bleaching light circulator, each pump energy transfer fiber of the reverse pumping signal combiner is connected to a fiber-coupled semiconductor laser, the signal output fiber of the reverse pumping signal combiner is connected to a cladding light filter, the cladding light filter is connected to a fiber end cap, and the core and cladding diameters of the cladding light filter are greater than or equal to the core and cladding diameters of the signal output fiber of the reverse pumping signal combiner.

6. The all-fiber optical amplifier of any of claims 1 to 5, wherein the gain fiber is a double-clad fiber. The gain fiber is a step-index fiber doped with rare earth ions, and the rare earth ions are one or more of ytterbium ions, erbium ions, neodymium ions, thulium ions and holmium ions; and the gain fiber has a cross-sectional structure of single cladding, double cladding, triple cladding or a specific layer structure.

7. The all-fiber optical amplifier of any of claims 1-5, wherein the fiber Bragg grating is a fiber Bragg grating having a period of 1.5 pm and a refractive index modulation of 1.5 x 10"4. The bleaching light source generates bleaching laser with a wavelength ranging from 360 nm to 780 nm and an output power ranging from 1 mW to 10 W; and the bleaching light source generates single-wavelength laser, dual-wavelength laser or multiple-wavelength combinations.

8. The all-fiber optical amplifier of any of claims 1-5, wherein the fiber is a double-clad fiber. The fiber-coupled semiconductor laser is an excitation source of upper-level particles generated by the gain fiber, and the output wavelength of the fiber-coupled semiconductor laser matches the absorption peak of the rare earth ions doped in the gain fiber; and the output wavelength of the fiber-coupled semiconductor laser is one or more combinations of 808 nm, 915 nm, 940 nm and 976 nm.

9. The all-fiber optical amplifier of claim 1 or 2 or 3 or 4 or 5 or 7 or 8, wherein, The seed laser has a fiber output, and the core diameter of the output fiber ranges from 5 μm to 50 μm; and the signal laser generated by the seed laser has a wavelength ranging from 950 nm to 1200 nm.

10. The all-fiber amplifier with improved anti-photodarkening performance according to claim 1 can be applied in a gamma ray, X-ray or ultraviolet radiation environment or a photodarkening environment, and can realize online bleaching in the gamma ray, X-ray or ultraviolet radiation environment or offline bleaching after working in the gamma ray, X-ray or ultraviolet radiation environment.

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