All-fiber laser for improving photon darkening bleaching effect

Abstract

The invention discloses an all-fiber laser capable of improving a photon darkening bleaching effect, which comprises a fiber laser oscillator, a bleaching light source and a bleaching light circulator, and is characterized in that the bleaching light source generates bleaching light and injects the bleaching light into a fiber laser resonant cavity to bleach a gain fiber. The bleaching light circulator is provided with a pumping energy transmission optical fiber closed loop, so that bleaching laser which is output by the optical fiber laser resonant cavity and is not completely absorbed can enter the optical fiber laser resonant cavity in a circulating and reciprocating mode, circulating bleaching of gain optical fibers is achieved, and therefore the light bleaching efficiency can be effectively improved; and the energy density of bleaching light in the gain fiber can be enhanced, and the anti-darkening performance and the working life of the fiber laser in a high-radiation environment can be obviously improved and prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, and in particular to an all-optical fiber laser capable of improving the photon darkening and bleaching effect. Background Art

[0002] With the continuous exploration of space by human beings and the rapid development of space technology, the application breadth and scenarios of fiber lasers in the space field have greatly increased, such as space laser communications, lidar, space waste disposal, fiber laser gyroscopes, etc. However, the space environment is very harsh, mainly manifested in that fiber lasers will be irradiated by high-energy electromagnetic radiation (X-rays, gamma rays) and charged particles (positrons, protons, alpha particles, etc.). The highest-energy rays such as gamma rays and X-rays have the greatest impact on the active optical fiber in the laser. Rare earth-doped active optical fibers will produce various types of defects (or "color centers") under space irradiation conditions, resulting in increased losses and reduced output power and service life of fiber lasers.

[0003] High-power fiber lasers for space applications are affected not only by the radiation-induced darkening effect, but also by the photon darkening effect. As the operation time of high-power lasers increases, the output power of the fiber laser decreases rapidly and gradually reaches a stable state due to the increase in background loss in the doped fiber core. This phenomenon is the photon darkening effect. The photon darkening effect will cause the laser light threshold to increase, the system stability to decrease, and the working life to shorten, which limits the industrial application and development of high-power fiber lasers.

[0004] As a potential solution to achieve anti-darkening fiber lasers, photobleaching technology is based on the principle of using light of a specific wavelength to irradiate the optical fiber to reduce or repair ion defects induced by radiation or photon darkening. However, the efficiency and practicality of 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 optical fiber device, the low-power-density bleaching light has limited ability to repair ion defects caused by darkening, making it difficult to achieve efficient and stable bleaching effects. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention proposes an all-fiber laser with improved photon darkening bleaching effect. The laser connects a bleaching light circulator behind the laser resonant cavity so that the bleaching laser can circulate back and forth into the fiber laser resonant cavity, thereby achieving efficient cyclic bleaching of the gain fiber and improving the anti-darkening performance of the fiber laser in a radiation environment and under photon darkening conditions.

[0006] In order to achieve the above technical purpose, the technical solution adopted by the present invention is:

[0007] In one aspect, the present invention provides an all-fiber laser for improving the photon darkening bleaching effect, comprising a fiber laser oscillator, a bleaching light source, and a bleaching light circulator;

[0008] In the fiber laser oscillator, a high-reflection fiber Bragg grating, a gain fiber, and a low-reflection fiber Bragg grating are sequentially connected to form a fiber laser resonant cavity;

[0009] The bleaching light source injects bleaching laser into the fiber laser oscillator from the side of the high-reflection fiber grating of the fiber laser resonant cavity, and the bleaching laser is transmitted in the fiber cladding of the fiber laser resonant cavity to bleach the gain fiber;

[0010] A bleaching light circulator is connected to one side of the low-reflection fiber Bragg grating. The bleaching light circulator has a pump energy transmission fiber closed loop. The incompletely absorbed bleaching laser output to the bleaching light circulator through the fiber cladding of the low-reflection fiber Bragg grating re-enters the fiber laser resonant cavity through the pump energy transmission fiber closed loop in the bleaching light circulator, thereby realizing cyclic bleaching of the gain fiber. The signal laser output through the core of the low-reflection fiber Bragg grating is output through the signal fiber of the bleaching light circulator.

[0011] Preferably, the fiber laser oscillator comprises a gain fiber, a high-reflection fiber Bragg grating, a low-reflection fiber Bragg grating, a fiber-coupled semiconductor laser, and a forward pump signal combiner;

[0012] A plurality of fiber-coupled semiconductor lasers are respectively connected to the pump energy transmission fibers of the forward pump signal combiner; the bleaching light source is connected to the signal input fiber of the forward pump signal combiner through the bleaching light source energy transmission fiber, and the pump light generated by the fiber-coupled semiconductor laser and the bleaching laser generated by the bleaching light source are coupled into the fiber cladding of the fiber laser resonant cavity through the forward pump signal combiner for transmission.

[0013] Preferably, the bleaching light circulator comprises a fiber bundle combining 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, the two pairs of pump energy transmission fibers are fused in pairs to form a pump energy transmission fiber closed loop, the pump energy transmission fibers are fused in pairs to form a pump energy transmission fiber fusion point, the low-reflection fiber grating is connected to the signal input fiber of the bleaching light circulator, the signal laser output through the core of the low-reflection fiber grating 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 low-reflection fiber grating re-enters the fiber laser resonant cavity through the pump energy transmission fiber closed loop of the bleaching light circulator.

[0014] Preferably, the bleaching light circulator can be composed of a reverse pump signal combiner, the core / cladding diameter of the signal input fiber of the reverse pump signal combiner matches the core / cladding diameter of the low-reflection fiber grating, the number n of pump energy transmission fibers of the reverse pump signal combiner satisfies 2≤n≤36, and n is an even number, and the pump energy transmission fibers are fused in pairs to form a plurality of pump energy transmission fiber closed loops.

[0015] Preferably, the fiber laser oscillator also includes a reverse pump signal combiner, the signal output fiber of the bleaching light circulator is connected to the reverse pump signal combiner, the reverse pump signal combiner has a signal input fiber, a signal output fiber and at least one pump energy transmission fiber, the signal input fiber of the reverse pump signal combiner is connected to the signal output fiber of the bleaching light circulator, each pump energy transmission fiber of the reverse pump signal combiner is connected to a fiber-coupled semiconductor laser, the signal output fiber of the reverse pump signal combiner is connected to a cladding light filter, and the cladding light filter is connected to a fiber end cap.

[0016] The all-fiber laser for improving the photon darkening bleaching effect can adapt to various radiation environments, can be used in gamma-ray, X-ray or ultraviolet radiation environments or photon darkening environments, can realize online bleaching in gamma-ray, X-ray or ultraviolet radiation environments, or realize offline bleaching after working in gamma-ray, X-ray or ultraviolet radiation environments.

[0017] Compared with the prior art, the technical effects that the present invention can produce are:

[0018] The present invention injects the bleaching light generated by the bleaching light source into the gain fiber in the fiber laser resonant cavity to bleach the gain fiber. Since a bleaching light circulator is connected behind the fiber laser resonant cavity, and the bleaching light circulator has a pump energy transmission fiber closed loop, the bleaching laser output by the fiber laser resonant cavity that is not completely absorbed can circulate back and forth into the gain fiber in the fiber laser resonant cavity to achieve cyclic bleaching of the gain fiber, which can not only effectively improve the light bleaching efficiency, but also enhance the energy density of the bleaching light in the gain fiber cladding, significantly improving the anti-darkening performance and working life of the fiber laser in a high radiation environment. The method of the present invention can effectively improve the bleaching efficiency of the all-fiber laser and maximize the anti-darkening performance of the fiber laser.

[0019] The laser in the present invention is 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, and can greatly expand the application of fiber lasers in different radiation environments and photodarkening environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0021] Figure 1 This is a schematic diagram of the structure of an all-fiber laser for improving the photon darkening and bleaching effect provided by Example 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of the structure of a bidirectionally pumped all-fiber laser for improving the photon darkening and bleaching effect provided by Example 2 of the present invention;

[0023] Figure 3 is a schematic structural diagram of a bleaching light circulator provided by an embodiment of the present invention;

[0024] Figure 4 is a schematic structural diagram of a bleaching light circulator provided by an embodiment of the present invention;

[0025] Figure 5 It is a schematic diagram of the structure of scheme A in a pair of proportions;

[0026] Figure 6 This is a comparison chart of the output power of schemes A and B in a pair of ratios.

[0027] Figure annotation:

[0028] 1. Gain fiber; 2. High reflection fiber Bragg grating; 3. Low reflection fiber Bragg grating; 4. Fiber coupled semiconductor laser; 5. Pump energy transmission fiber; 6. Forward pump signal combiner; 7. Bleaching light source; 8. Bleaching light source energy transmission fiber; 9. Bleaching light circulator; 10. Signal input fiber; 11. Fiber beam combining end; 12. Pump energy transmission fiber closed loop; 13. Pump energy transmission fiber fusion point; 14. Signal output fiber; 15. Cladding light filter; 16. Fiber end cap; 17. Reverse pump signal combiner;

[0029] 12-1, first pump energy transmission fiber; 12-2, second pump energy transmission fiber; 12-3, third pump energy transmission fiber; 12-4, fourth pump energy transmission fiber; 12-5, fifth pump energy transmission fiber; 12-6, sixth pump energy transmission fiber; 13-1, fusion point of first pump energy transmission fiber; 13-2, fusion point of second pump energy transmission fiber; 13-3, fusion point of third pump energy transmission fiber. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The principle of the all-fiber laser for improving the photon darkening bleaching effect conceived by the present invention is: by introducing a bleaching light circulator in the all-fiber laser, the bleaching laser injected into the fiber laser resonant cavity passes through the pump energy transmission fiber closed loop of the bleaching light circulator and returns to the fiber laser resonant cavity to achieve cyclic reciprocating bleaching, thereby improving the power density of the bleaching light in the resonant cavity, thereby improving the photon darkening bleaching effect of the fiber laser.

[0032] In one embodiment, an all-fiber laser for improving the photon darkening bleaching effect is provided, comprising a fiber laser oscillator, a bleaching light source 7, and a bleaching light circulator 9;

[0033] In the fiber laser oscillator, a high-reflection fiber Bragg grating 2, a gain fiber 1, and a low-reflection fiber Bragg grating 3 are sequentially connected to form a fiber laser resonant cavity;

[0034] The bleaching light source 7 injects bleaching laser into the fiber laser oscillator from one side of the high-reflection fiber grating 2 of the fiber laser resonant cavity, and the bleaching laser is transmitted in the fiber cladding of the fiber laser resonant cavity to bleach the gain fiber 1;

[0035] One side of the low-reflection fiber Bragg grating 3 is connected to a bleaching light circulator 9, which has a pump energy transmission fiber closed loop 12. The incompletely absorbed bleaching laser output to the bleaching light circulator 9 through the fiber cladding of the low-reflection fiber Bragg grating 3 re-enters the fiber laser resonant cavity through the pump energy transmission fiber closed loop 12 in the bleaching light circulator 9, thereby realizing cyclic bleaching of the gain fiber 1. The signal laser output through the core of the low-reflection fiber Bragg grating 3 is output through the signal fiber of the bleaching light circulator 9.

[0036] Reference Figure 1 , is a schematic diagram of the structure of an all-fiber laser for improving the photon darkening bleaching effect provided in Example 1 of the present invention, including a gain fiber 1, a high-reflection fiber grating 2, a low-reflection fiber grating 3, a fiber-coupled semiconductor laser 4, a forward pump signal combiner 6, a bleaching light source 7, a bleaching light circulator 9, a cladding light filter 15 and a fiber end cap 16.

[0037] The forward pump signal combiner 6 has a signal input fiber, a signal output fiber and at least one pump power transmission fiber 5. Each pump power transmission fiber 5 of the forward pump signal combiner 6 is connected to a fiber-coupled semiconductor laser 4. The bleaching light source 7 is connected to the signal input fiber of the forward pump signal combiner 6 through the bleaching light source power transmission fiber 8. The signal output fiber of the forward pump signal combiner 6 is connected to the high-reflection fiber grating 2. The high-reflection fiber grating 2, the gain fiber 1, and the low-reflection fiber grating 3 are sequentially connected to form a fiber laser resonant cavity. The pump light generated by the fiber-coupled semiconductor laser 4 and the bleaching laser generated by the bleaching light source 7 are coupled into the fiber cladding of the fiber laser resonant cavity through the forward pump signal combiner 6 for transmission, and the gain fiber 1 is bleached.

[0038] exist Figure 1 In the illustrated embodiment, the bleaching light circulator 9 may be a reverse pump signal combiner, comprising a fiber combining end 11, a signal input fiber 10, a signal output fiber 14, and a plurality of pump energy transmission fiber closed loops 12, each pump energy transmission fiber closed loop 12 being formed by two-by-two fusion splicing of pump energy transmission fibers, and the two-by-two fusion splicing of pump energy transmission fibers forming pump energy transmission fiber fusion splicing points 13. The number n of the pump energy transmission fibers satisfies 2≤n≤36, and n is an even number.

[0039] The low-reflection fiber Bragg grating 3 is connected to the signal input fiber 10 of the bleaching light circulator 9. The signal laser output from the core of the low-reflection fiber Bragg grating 3 is output through the core of the signal input fiber 10 of the bleaching light circulator 9 and the core of the signal output fiber. The laser output from the cladding of the low-reflection fiber Bragg grating 3 re-enters the fiber laser resonant cavity through the pump energy transmission fiber closed loop 12 of the bleaching light circulator 9.

[0040] The signal output optical fiber 14 of the bleaching light circulator 9 is connected to a cladding light filter 15 , and the cladding light filter 15 is connected to an optical fiber end cap 16 , wherein the cladding light filter 15 is used to filter out light of other wavelengths except the signal light.

[0041] The transmission path of the bleaching laser generated by the bleaching light source 7 is: bleaching light source 7 → bleaching light source energy transmission fiber 8 → forward pump signal combiner 6 → high reflection fiber Bragg grating 2 → gain fiber 1 → low reflection fiber Bragg grating 3 → bleaching light circulator 9 → pump energy transmission fiber closed loop 12 → bleaching light circulator 9 → low reflection fiber Bragg grating 3 → gain fiber 1 → high reflection fiber Bragg grating 2.

[0042] Reference Figure 2, is a schematic diagram of the structure of an all-fiber laser for improving the photon darkening bleaching effect provided in Example 2 of the present invention. The all-fiber laser in this embodiment is a bidirectional pumping structure, including a gain fiber 1, a high-reflection fiber grating 2, a low-reflection fiber grating 3, a fiber-coupled semiconductor laser 4, a forward pump signal combiner 6, a bleaching light source 7, a bleaching light circulator 9, a reverse pump signal combiner 17, a cladding light filter 15 and a fiber end cap 16.

[0043] The forward pump signal combiner 6 has a signal input fiber, a signal output fiber and at least one pump power transmission fiber 5. Each pump power transmission fiber 5 of the forward pump signal combiner 6 is connected to a fiber-coupled semiconductor laser 4. The bleaching light source 7 is connected to the signal input fiber of the forward pump signal combiner 6 through the bleaching light source power transmission fiber 8. The signal output fiber of the forward pump signal combiner 6 is connected to the high-reflection fiber grating 2. The high-reflection fiber grating 2, the gain fiber 1, and the low-reflection fiber grating 3 are sequentially connected to form a fiber laser resonant cavity. The pump light generated by the fiber-coupled semiconductor laser 4 and the bleaching laser generated by the bleaching light source 7 are coupled into the fiber cladding of the fiber laser resonant cavity through the forward pump signal combiner 6 for transmission, and the gain fiber 1 is bleached.

[0044] The bleaching light circulator 9 can be a side pump signal combiner, including a fiber combining end 11, a signal input fiber 10, a signal output fiber 14 and at least one pump energy transmission fiber closed loop 12. A pump energy transmission fiber closed loop 12 is formed by fusion splicing two pump energy transmission fibers, wherein the pump energy transmission fibers are fused to form a pump energy transmission fiber fusion point 13. The signal input fiber 10 of the bleaching light circulator 9 is consistent in size with the signal output fiber 14, ensuring that the reversely injected pump power smoothly passes through the signal fiber of the bleaching light circulator 9 into the laser resonant cavity. The two ends of the pump energy transmission fiber closed loop 12 are stretched and attached to the cladding of the signal fiber to form a fiber combining end 11. The signal input fiber 10 and the signal output fiber 14 are the same fiber, and there is no need to melt and taper to thin it.

[0045] The signal output fiber 14 of the bleaching light circulator 9 is connected to the signal input fiber of the reverse pumping signal combiner 17. The reverse pumping signal combiner 17 has a signal input fiber, a signal output fiber and at least one pumping energy transmission fiber 5. The signal input fiber of the reverse pumping signal combiner 17 is connected to the signal output fiber 14 of the bleaching light circulator 9. Each pumping energy transmission fiber 5 of the reverse pumping signal combiner 17 is connected to a fiber-coupled semiconductor laser 4. The signal output fiber of the reverse pumping signal combiner 17 is connected to a cladding light filter 15, and the cladding light filter 15 is connected to a fiber end cap 16. The cladding light filter 15 is used to filter out residual pump light and other component lights in the output laser. The signal laser is expanded and output after passing through the fiber end cap 16.

[0046] Furthermore, in any of the above embodiments:

[0047] The gain fiber is a step-refractive-index fiber doped with rare earth ions, wherein the doped 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 is one of single cladding, double cladding, triple cladding, or a prefabricated specific stacked structure.

[0048] The reflectivity of the high-reflection fiber Bragg grating is greater than 90%, the reflectivity of the low-reflection fiber Bragg grating is between 1% and 30%, the central wavelength of the high-reflection fiber Bragg grating matches the central wavelength of the low-reflection fiber Bragg grating, and the central wavelength range is 950nm to 1200nm. The core / cladding diameters of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating are the same as the core / cladding diameters at both ends of the gain optical fiber.

[0049] The fiber-coupled semiconductor laser is an excitation source for the gain fiber to generate upper-level particles, and its output wavelength matches the absorption peak of the rare earth ions doped in the gain fiber, which can be one or more combinations of 808nm, 915nm, 940nm, and 976nm.

[0050] Furthermore, the bleaching laser wavelength range generated by the bleaching light source is between 360nm and 780nm, including single wavelength laser, dual wavelength laser or a combination of multiple wavelengths, which is used for photo-darkening bleaching of the gain fiber. Preferably, the bleaching light source is a 450nm blue light laser.

[0051] The present invention is applicable to various radiation environments, including radiation environments such as gamma rays, X-rays, ultraviolet rays, and photon darkening environments. The present invention can realize both online bleaching and offline bleaching. Online bleaching means that in a radiation environment such as gamma rays, X-rays, ultraviolet rays, or a photon darkening environment, the all-fiber laser (i.e., fiber laser oscillator) synchronously turns on a bleaching light source during operation, and the bleaching light source bleaches the irradiated gain fiber online during the operation of the all-fiber laser (i.e., fiber laser oscillator). Offline bleaching means that an all-fiber laser (i.e., fiber laser oscillator) that works in a radiation environment such as gamma rays, X-rays, ultraviolet rays, or a photon darkening environment will cause an increase in loss, thereby reducing the output power and service life of the all-fiber laser (i.e., fiber laser oscillator). For an all-fiber laser that has been working in a radiation environment such as gamma rays, X-rays, ultraviolet rays, or a photon darkening environment, the solution proposed in the present invention is used to inject bleaching laser light from the side of the high-reflection fiber grating 2 of the fiber laser resonant cavity into the fiber laser oscillator in a radiation-free environment using a bleaching light source 7. The bleaching laser bleaches the gain fiber 1. After bleaching, the output performance of the all-fiber laser is restored to the state before radiation or darkening, and it can be repeatedly used and bleached.

[0052] Reference Figure 3 , is a schematic diagram of the structure of a bleaching light circulator provided in one embodiment of the present invention, specifically a bleaching light circulator composed of a (6+1)ⅹ1 reverse pump signal combiner. The bleaching light circulator 9 has a fiber bundle end 11, a signal input fiber 10, a signal output fiber 14 and three pump energy transmission fiber closed loops 12, the three pump energy transmission fiber closed loops 12 include six pump energy transmission fibers, specifically a first pump energy transmission fiber 12-1, a second pump energy transmission fiber 12-2, a third pump energy transmission fiber 12-3, a fourth pump energy transmission fiber 12-4, a fifth pump energy transmission fiber 12-5 and a sixth pump energy transmission fiber 12-6, wherein the first pump energy transmission fiber 12-1 and the sixth pump energy transmission fiber 12-6 are fused to form a first pump energy transmission fiber fusion point 13-1, the second pump energy transmission fiber 12-2 and the fifth pump energy transmission fiber 12-5 are fused to form a second pump energy transmission fiber fusion point 13-2, and the third pump energy transmission fiber 12-3 and the fourth pump energy transmission fiber 12-4 are fused to form a third pump energy transmission fiber fusion point 13-3. Specifically, the signal input fiber sizes of the reverse pump signal combiner include the common 20 / 400μm, 25 / 400μm, 30 / 400μm, 30 / 600μm, etc., the signal output fiber sizes include 20 / 250μm, 25 / 250μm, 30 / 250μm, 42 / 250μm, etc., and the pump energy transmission fiber sizes include 105 / 125μm, 135 / 155μm, 220 / 242μm, etc.

[0053] Reference Figure 4 , is a schematic diagram of the structure of a bleaching light circulator provided in one embodiment of the present invention, specifically a bleaching light circulator composed of a (2+1)ⅹ1 side pump signal combiner. The bleaching light circulator 9 has a fiber combining end 11, a signal input fiber 10, a signal output fiber 14 and a pump energy transmission fiber closed loop 12. The pump energy transmission fiber closed loop 12 includes two pump energy transmission fibers, a first pump energy transmission fiber 12-1 and a second pump energy transmission fiber 12-2, and the first pump energy transmission fiber 12-1 and the second pump energy transmission fiber 12-2 are fused to form a first pump energy transmission fiber fusion point 13-1. The signal input fiber 10 and the signal output fiber 14 of the side pump signal combiner are the same fiber, and their core / cladding sizes are consistent, which can be applied to backward pumping and bidirectional pumping fiber lasers to achieve reverse pump power injection. Specifically, the signal input fiber sizes of the side-pumped signal combiner include the common 20 / 400μm, 25 / 400μm, 30 / 400μm, etc., the signal output fiber sizes include 20 / 400μm, 25 / 400μm, 30 / 400μm, etc., and the pump energy transmission fiber sizes include 105 / 125μm, 135 / 155μm, 220 / 242μm, etc.

[0054] In order to prove the superiority of the solution proposed by the present invention, a comparative demonstration is carried out:

[0055] In the comparative example, scheme A is a scheme without using a bleaching light circulator, and the structural schematic diagram of scheme A is as follows: Figure 5 As shown, the optical path structure of scheme A is Figure 1 The only difference between the optical path structures shown is that the optical path structure of scheme A does not include a bleaching light circulator, the low-reflection fiber grating 3 is connected to the cladding light filter 15 , and the cladding light filter 15 is connected to the optical fiber end cap 16 .

[0056] In the comparative example, scheme B is a scheme using a bleaching light circulator, and the structural schematic diagram of scheme B is as follows: Figure 1 As shown, a (6+1)ⅹ1 reverse pump signal combiner is used as a bleaching light circulator, wherein the signal input fiber size of the (6+1)ⅹ1 reverse pump signal combiner is 30 / 400μm, the signal output fiber size is 30 / 250μm, the pump energy transmission fiber size is 220 / 242μm, and the six pump energy transmission fibers are fused in pairs to form three pump energy transmission fiber closed loops.

[0057] Except for whether or not to use a bleaching light circulator, the selection, parameters and connection methods of other devices in Plan A and Plan B are the same. The gain fiber uses a 30 / 400μm double-clad ytterbium-doped fiber, and the central wavelength of the fiber laser resonator is 1080nm. In Plan A and Plan B, the fiber laser is irradiated with gamma rays with an irradiation dose rate of 1.04mGy / s and a total irradiation dose of 11.3Gy before the bleaching experiment. In the bleaching experiment, a 450nm blue light laser was used as the bleaching light source, and the bleaching laser output power was about 70mW. In the scheme using the bleaching light circulator, when the bleaching light source is turned on to inject the bleaching laser, the output power of the laser gradually increases from 71W to 105.8W within the same bleaching time. The laser output power of the scheme without the bleaching light circulator only increases from 71W to 95.4W. The comparison results are shown as follows. Figure 6 The results show that the all-fiber laser with improved photon darkening bleaching effect proposed in the present invention can achieve an 11% improvement in bleaching efficiency.

[0058] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. An all-fiber laser for improving the photon darkening and bleaching effect, characterized in that: Including fiber laser oscillator, bleaching light source, bleaching light circulator; In the fiber laser oscillator, a high-reflection fiber Bragg grating, a gain fiber, and a low-reflection fiber Bragg grating are sequentially connected to form a fiber laser resonant cavity; The bleaching light source injects bleaching laser into the fiber laser oscillator from the side of the high-reflection fiber grating of the fiber laser resonant cavity, and the bleaching laser is transmitted in the fiber cladding of the fiber laser resonant cavity to bleach the gain fiber; A bleaching light circulator is connected to one side of the low-reflection fiber Bragg grating. The bleaching light circulator has a pump energy transmission fiber closed loop. The incompletely absorbed bleaching laser output to the bleaching light circulator through the fiber cladding of the low-reflection fiber Bragg grating re-enters the fiber laser resonant cavity through the pump energy transmission fiber closed loop in the bleaching light circulator, thereby realizing cyclic bleaching of the gain fiber. The signal laser output through the core of the low-reflection fiber Bragg grating is output through the signal fiber of the bleaching light circulator.

2. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 1, characterized in that: The fiber laser oscillator includes a gain fiber, a high-reflection fiber Bragg grating, a low-reflection fiber Bragg grating, a fiber-coupled semiconductor laser, and a forward pump signal combiner; A plurality of fiber-coupled semiconductor lasers are respectively connected to the pump energy transmission fibers of the forward pump signal combiner; the bleaching light source is connected to the signal input fiber of the forward pump signal combiner through the bleaching light source energy transmission fiber, and the pump light generated by the fiber-coupled semiconductor laser and the bleaching laser generated by the bleaching light source are coupled into the fiber cladding of the fiber laser resonant cavity through the forward pump signal combiner for transmission.

3. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 2, characterized in that: The bleaching light circulator comprises an optical fiber bundle combining end, a signal optical fiber and at least one pair of pumping energy transmission optical fibers, wherein the signal optical fiber comprises a signal input optical fiber and a signal output optical fiber, and the two paired pumping energy transmission optical fibers are fused in pairs to form a pumping energy transmission optical fiber closed loop, and the pumping energy transmission optical fiber fusion point is formed at the place where the pumping energy transmission optical fibers are fused in pairs, and the low-reflection optical fiber grating is connected to the signal input optical fiber of the bleaching light circulator, and the signal laser output through the core of the low-reflection optical fiber grating is output through the signal input optical fiber and the signal output optical fiber of the bleaching light circulator, and the laser output through the cladding of the low-reflection optical fiber grating re-enters the optical fiber laser resonant cavity through the pumping energy transmission optical fiber closed loop of the bleaching light circulator.

4. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 3, characterized in that: It also includes a cladding light filter and an optical fiber end cap. The signal output optical fiber of the bleaching light circulator is connected to the cladding light filter, and the cladding light filter is connected to the optical fiber end cap.

5. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 3 or 4, characterized in that: The bleaching light circulator is composed of a reverse pump signal combiner, the core / cladding diameter of the signal input optical fiber of the reverse pump signal combiner matches the core / cladding diameter of the low-reflection fiber grating, the number n of the pump energy transmission optical fibers of the reverse pump signal combiner satisfies 2≤n≤36, and n is an even number, and the pump energy transmission optical fibers are fused in pairs to form a plurality of pump energy transmission optical fiber closed loops.

6. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 3, characterized in that: The fiber laser oscillator comprises a reverse pump signal combiner, the signal output fiber of the bleaching light circulator is connected to the reverse pump signal combiner, the reverse pump signal combiner has a signal input fiber, a signal output fiber and at least one pump energy transmission fiber, the signal input fiber of the reverse pump signal combiner is connected to the signal output fiber of the bleaching light circulator, each pump energy transmission fiber of the reverse pump signal combiner is connected to a fiber-coupled semiconductor laser, the signal output fiber of the reverse pump signal combiner is connected to a cladding light filter, and the cladding light filter is connected to a fiber end cap.

7. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 1, 2, 3, 4 or 6, characterized in that: The gain fiber is a step-refractive-index fiber doped with rare earth ions, wherein the doped 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 is one of single cladding, double cladding, triple cladding, or a prefabricated specific stacked structure.

8. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 1, 2, 3, 4 or 6, characterized in that: The wavelength range of the bleaching laser generated by the bleaching light source is between 360nm and 780nm, including single-wavelength laser, dual-wavelength laser or a combination of multiple wavelengths, and is used for photo-darkening bleaching of the gain optical fiber.

9. The all-fiber laser for improving the photon darkening and bleaching effect according to claim 8, characterized in that: The reflectivity of the high-reflection fiber Bragg grating is greater than 90%, the reflectivity of the low-reflection fiber Bragg grating is between 1% and 30%, the central wavelength of the high-reflection fiber Bragg grating matches the central wavelength of the low-reflection fiber Bragg grating, and the central wavelength range is 950nm to 1200nm. The core / cladding diameter of the high-reflection fiber Bragg grating and the core / cladding diameter of the low-reflection fiber Bragg grating are respectively the same as the core / cladding diameters at both ends of the gain optical fiber.

10. The all-fiber laser for improving the photon darkening bleaching effect as claimed in claim 1 can be used in a γ-ray, X-ray or ultraviolet radiation environment or a photon darkening environment, and can realize online bleaching in a γ-ray, X-ray or ultraviolet radiation environment or realize offline bleaching after working in a γ-ray, X-ray or ultraviolet radiation environment.

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