All-fiber lasers to improve photon darkening and bleaching effects

Abstract

This invention discloses an all-fiber laser for improving photonic darkening and bleaching effects, comprising a fiber laser oscillator, a bleaching source, and a bleaching optical circulator. The bleaching source generates bleaching light and injects it into the fiber laser resonator to bleach the gain fiber. Since the bleaching optical circulator is connected after the fiber laser resonator, and the bleaching optical circulator has a closed loop for pumping the energy transfer fiber, the bleaching laser light that is not completely absorbed from the fiber laser resonator can be repeatedly injected into the fiber laser resonator to achieve cyclic bleaching of the gain fiber. This not only effectively improves the optical bleaching efficiency but also enhances the energy density of the bleaching light in the gain fiber, significantly improving the anti-darkening performance and operating life of the fiber laser in high-radiation environments.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and in particular to an all-fiber laser that improves the photon darkening and bleaching effect. Background Technology

[0002] With the continuous exploration of space and the rapid development of space technology, the application scope and scenarios of fiber lasers in the space field have greatly increased, such as space laser communication, lidar, space debris disposal, and fiber laser gyroscopes. However, the space environment is extremely harsh, mainly manifested in the fact that fiber lasers are exposed to high-energy electromagnetic radiation (X-rays, gamma rays) and charged particles (positrons, electrons, protons, alpha particles, etc.). High-energy rays such as gamma rays and X-rays have the greatest impact on the active fiber in the laser. Rare-earth-doped active fibers will develop various types of defects (or "color centers") under space irradiation conditions, leading to increased losses and reducing the output power and lifespan of the fiber laser.

[0003] In addition to radiation-induced darkening, high-power fiber lasers for space applications are also affected by photonic darkening. As the operating time of a high-power laser increases, the output power rapidly decreases and gradually reaches a stable state due to the increased background loss in the doped fiber core; this phenomenon is known as photonic darkening. Photonic darkening leads to an increase in the laser's output threshold, reduced system stability, and a shorter operating life, thus limiting the industrial application and development of high-power fiber lasers.

[0004] Optical bleaching technology, as a potential solution for achieving anti-darkening fiber lasers, works by irradiating optical fibers with light of a specific wavelength to reduce or repair ion defects induced by radiation or photon darkening. However, the efficiency and practicality of existing optical bleaching technologies are limited by the injection method and energy density of the bleaching light. When low-power-density bleaching light is injected into a laser system, its ability to repair darkening-induced ion defects is limited due to the inherent losses of the bleaching light within the fiber optic device, making it difficult to achieve efficient and stable bleaching results. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention proposes an all-fiber laser that improves the photon darkening bleaching effect. This laser connects a bleaching optical circulator after the laser resonator, allowing the bleaching laser to repeatedly enter the fiber laser resonator, thereby achieving efficient cyclic bleaching of the gain fiber and improving the anti-darkening performance of the fiber laser under radiation and photon darkening conditions.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0007] On the one hand, the present invention provides an all-fiber laser for improving the photon darkening bleaching effect, including a fiber laser oscillator, a bleaching light source, and a bleaching optical circulator;

[0008] In a fiber laser oscillator, a high-reflectivity fiber grating, a gain fiber, and a low-reflectivity fiber grating are connected in sequence to form a fiber laser resonant cavity.

[0009] The bleaching light source injects bleaching laser into the fiber laser oscillator from the high-reflectivity fiber grating side of the fiber laser resonator. The bleaching laser propagates in the fiber cladding of the fiber laser resonator and bleachs the gain fiber.

[0010] A bleaching optical circulator is connected to one side of the low-reflection fiber grating. The bleaching optical circulator has a closed loop of pumping power transfer fiber. The bleached laser that is not completely absorbed and is output to the bleaching optical circulator through the fiber cladding of the low-reflection fiber grating is re-entered into the fiber laser resonator through the closed loop of pumping power transfer fiber in the bleaching optical circulator, thereby realizing the cyclic bleaching of the gain fiber. The signal laser output from the fiber core of the low-reflection fiber grating is output through the signal fiber of the bleaching optical circulator.

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

[0012] Multiple fiber-coupled semiconductor lasers are respectively connected to the pump power 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 power transmission fiber; 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 resonator through the forward pump signal combiner for transmission.

[0013] Preferably, the bleaching optical circulator includes an optical fiber bundle-over end, a signal optical fiber, and at least one pair of pump power transmission fibers. The signal optical fiber includes a signal input fiber and a signal output fiber. The two pump power transmission fibers in the pair are fused together to form a closed loop of pump power transmission fibers. The fusion points of the two pump power transmission fibers form fusion splices of pump power transmission fibers. The low-reflection fiber grating is connected to the signal input fiber of the bleaching optical circulator. The signal laser output from the core of the low-reflection fiber grating is output through the signal input fiber and the signal output fiber of the bleaching optical circulator. The laser output from the cladding of the low-reflection fiber grating re-enters the fiber laser resonator through the closed loop of the pump power transmission fibers of the bleaching optical circulator.

[0014] Preferably, the bleached optical 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 is matched with the core / cladding diameter of the low-reflection fiber grating. The number n of the pump power transmission fibers of the reverse pump signal combiner satisfies 2≤n≤36, and n is an even number. The pump power transmission fibers are fused together in pairs to form multiple pump power transmission fiber closed loops.

[0015] Preferably, the fiber laser oscillator further includes a reverse pump signal combiner, the signal output fiber of the bleached optical 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 power transmission fiber, the signal input fiber of the reverse pump signal combiner is connected to the signal output fiber of the bleached optical circulator, each pump power 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 optical filter, and the cladding optical filter is connected to an optical fiber end cap.

[0016] The aforementioned all-fiber laser that improves the photon darkening bleaching effect can adapt to various radiation environments and can be used in gamma-ray, X-ray, or ultraviolet radiation environments or photon darkening environments. It can achieve online bleaching in gamma-ray, X-ray, or ultraviolet radiation environments or offline bleaching after working in gamma-ray, X-ray, or ultraviolet radiation environments.

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

[0018] This invention injects bleaching light generated by a bleaching source into the gain fiber of a fiber laser resonator to bleach the gain fiber. Because a bleaching light circulator is connected after the fiber laser resonator, and this circulator has a closed loop for pumping the energy transfer fiber, the incompletely absorbed bleaching laser light output from the fiber laser resonator can repeatedly enter the gain fiber within the resonator, achieving cyclic bleaching of the gain fiber. This not only effectively improves the optical bleaching efficiency but also enhances the energy density of the bleaching light within the gain fiber cladding, significantly improving the anti-darkening performance and lifespan of the fiber laser in high-radiation environments. Using this method, the bleaching efficiency of all-fiber lasers can be effectively improved, maximizing their anti-darkening performance.

[0019] The laser in this invention is an all-fiber structure. The bleaching light source can achieve both online bleaching and offline time-division 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 light darkening environments. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of an all-fiber laser structure for improving photon darkening and bleaching effects, provided in Embodiment 1 of the present invention.

[0022] Figure 2 This is a schematic diagram of a bidirectional pumped all-fiber laser structure for improving photon darkening and bleaching effects, provided in Embodiment 2 of the present invention.

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

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

[0025] Figure 5 This is a schematic diagram of scheme A in a proportional representation;

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

[0027] Attached image captions:

[0028] 1. Gain fiber; 2. High-reflectivity fiber grating; 3. Low-reflectivity fiber grating; 4. Fiber-coupled semiconductor laser; 5. Pump power fiber; 6. Forward pump signal combiner; 7. Bleached light source; 8. Bleached light source power fiber; 9. Bleached optical circulator; 10. Signal input fiber; 11. Fiber combiner end; 12. Pump power fiber closed loop; 13. Pump power fiber fusion splice; 14. Signal output fiber; 15. Cladding optical filter; 16. Fiber end cap; 17. Reverse pump signal combiner;

[0029] 12-1, First pump power transmission fiber; 12-2, Second pump power transmission fiber; 12-3, Third pump power transmission fiber; 12-4, Fourth pump power transmission fiber; 12-5, Fifth pump power transmission fiber; 12-6, Sixth pump power transmission fiber; 13-1, First pump power transmission fiber fusion splice; 13-2, Second pump power transmission fiber fusion splice; 13-3, Third pump power transmission fiber fusion splice. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] The principle of the all-fiber laser with improved photonic darkening and bleaching effect conceived in this invention is as follows: by introducing a bleaching light circulator into the all-fiber laser, the bleaching laser injected into the fiber laser resonator passes through the closed loop of the pump power transfer fiber of the bleaching light circulator and returns to the fiber laser resonator to achieve cyclic bleaching, thereby increasing the power density of the bleaching light in the resonator and thus improving the photonic darkening and bleaching effect of the fiber laser.

[0032] In one embodiment, an all-fiber laser for improving photon darkening and bleaching effects is provided, including a fiber laser oscillator, a bleaching light source 7, and a bleaching optical circulator 9.

[0033] In a fiber laser oscillator, a high-reflectivity fiber grating 2, a gain fiber 1, and a low-reflectivity fiber grating 3 are connected in sequence to form a fiber laser resonant cavity.

[0034] The bleaching light source 7 injects bleaching laser into the fiber laser oscillator from the high-reflectivity fiber grating 2 side of the fiber laser resonator. The bleaching laser propagates in the fiber cladding of the fiber laser resonator and bleachs the gain fiber 1.

[0035] One side of the low-reflection fiber grating 3 is connected to a bleaching optical circulator 9. The bleaching optical circulator 9 has a pump power transfer fiber closed loop 12. The bleached laser that is not completely absorbed and is output to the bleaching optical circulator 9 through the fiber cladding of the low-reflection fiber grating 3 re-enters the fiber laser resonator through the pump power transfer fiber closed loop 12 in the bleaching optical circulator 9, thereby realizing the cyclic bleaching of the gain fiber 1. The signal laser output from the fiber core of the low-reflection fiber grating 3 is output through the signal fiber of the bleaching optical circulator 9.

[0036] Reference Figure 1 This is a schematic diagram of an all-fiber laser structure for improving photon darkening and bleaching effects, provided in Embodiment 1 of the present invention. It includes 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 optical circulator 9, a cladding optical filter 15, and an optical fiber end cap 16.

[0037] The forward pump signal combiner 6 has one signal input fiber, one 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 a high-reflectivity fiber grating 2. The high-reflectivity fiber grating 2, the gain fiber 1, and the low-reflectivity fiber grating 3 are sequentially connected to form a fiber laser resonator. 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 resonator through the forward pump signal combiner 6 and transmitted to bleach the gain fiber 1.

[0038] exist Figure 1 In the illustrated embodiment, the bleached optical circulator 9 can be a reverse pump signal combiner, including an optical fiber combiner end 11, a signal input optical fiber 10, a signal output optical fiber 14, and multiple pump power transmission fiber closed loops 12. Each pump power transmission fiber closed loop 12 is formed by fusion splicing two pump power transmission fibers in pairs, and the fusion splices between the two pump power transmission fibers form pump power transmission fiber fusion splice points 13. The number of pump power transmission fibers n satisfies 2 ≤ n ≤ 36, and n is an even number.

[0039] The low-reflection fiber grating 3 is connected to the signal input fiber 10 of the bleached optical circulator 9. The signal laser output from the core of the low-reflection fiber grating 3 is output through the core of the signal input fiber 10 and the core of the signal output fiber of the bleached optical circulator 9. The laser output from the cladding of the low-reflection fiber grating 3 re-enters the fiber laser resonator through the pump power transfer fiber closed loop 12 of the bleached optical circulator 9.

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

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

[0042] Reference Figure 2This is a schematic diagram of an all-fiber laser structure for improving photonic darkening and bleaching effects, provided in Embodiment 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 one signal input fiber, one 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 a high-reflectivity fiber grating 2. The high-reflectivity fiber grating 2, the gain fiber 1, and the low-reflectivity fiber grating 3 are sequentially connected to form a fiber laser resonator. 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 resonator through the forward pump signal combiner 6 and transmitted to bleach the gain fiber 1.

[0044] The bleached optical circulator 9 can be a side-pump signal combiner, including an optical fiber combiner end 11, a signal input optical fiber 10, a signal output optical fiber 14, and at least one pump power transfer optical fiber closed loop 12. One pump power transfer optical fiber closed loop 12 is formed by fusion splicing two pump power transfer optical fibers, with the fusion points of the two pump power transfer optical fibers forming pump power transfer optical fiber fusion splices 13. The signal input optical fiber 10 and the signal output optical fiber 14 of the bleached optical circulator 9 have the same dimensions, ensuring that the reverse-injected pump power smoothly passes through the signal optical fiber of the bleached optical circulator 9 into the laser resonant cavity. The two ends of the pump power transfer optical fiber closed loop 12 are thinned and attached to the cladding of the signal optical fiber to form the optical fiber combiner end 11. The signal input optical fiber 10 and the signal output optical fiber 14 are the same optical fiber, eliminating the need for fusion tapering.

[0045] The signal output fiber 14 of the bleached optical circulator 9 is connected to the signal input fiber of the reverse pump signal combiner 17. The reverse pump signal combiner 17 has one signal input fiber, one signal output fiber, and at least one pump power transmission fiber 5. The signal input fiber of the reverse pump signal combiner 17 is connected to the signal output fiber 14 of the bleached optical circulator 9. Each pump power transmission fiber 5 of the reverse pump signal combiner 17 is connected to an fiber-coupled semiconductor laser 4. The signal output fiber of the reverse pump signal combiner 17 is connected to the cladding optical filter 15, which is connected to an fiber end cap 16. The cladding optical filter 15 is used to filter out residual pump light and other component light 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-index fiber doped with rare-earth ions, wherein 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 is one of single-clad, double-clad, triple-clad, or prefabricated with a specific layered structure.

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

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

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

[0051] This invention is applicable to various radiation environments, including those with gamma rays, X-rays, and ultraviolet radiation, as well as photon darkening environments. It can achieve both online and offline bleaching. Online bleaching refers to the simultaneous activation of a bleaching source during the operation of the all-fiber laser (i.e., fiber laser oscillator) in environments with gamma rays, X-rays, ultraviolet radiation, or photon darkening. The bleaching source bleaches the irradiated gain fiber online during the operation of the all-fiber laser (i.e., fiber laser oscillator). Offline bleaching addresses the increased losses in all-fiber lasers (i.e., fiber laser oscillators) after operation in environments with gamma rays, X-rays, ultraviolet radiation, or photon darkening, which reduces their output power and lifespan. For all-fiber lasers that have been operating in radiation environments such as gamma rays, X-rays, and ultraviolet rays, or in photon darkening environments, the proposed solution of this invention allows for the injection of bleaching laser light from the high-reflectivity fiber grating 2 side of the fiber laser resonator into the fiber laser oscillator using a bleaching light source 7 in a radiation-free environment. The bleaching laser bleaches the gain fiber 1, and after bleaching, the output performance of the all-fiber laser is restored to its state before radiation or darkening. This process of reuse and bleaching can be repeated.

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

[0053] Reference Figure 4 This is a schematic diagram of a bleaching optical circulator provided in an embodiment of the present invention, specifically a bleaching optical circulator composed of a (2+1)×1 side pump signal combiner. The bleaching optical circulator 9 has an optical fiber combiner end 11, a signal input optical fiber 10, a signal output optical fiber 14, and a pump power transfer fiber closed loop 12. The pump power transfer fiber closed loop 12 includes two pump power transfer fibers: a first pump power transfer fiber 12-1 and a second pump power transfer fiber 12-2. The first pump power transfer fiber 12-1 and the second pump power transfer fiber 12-2 are fused together to form a first pump power transfer fiber fusion splice point 13-1. The signal input fiber 10 and the signal output fiber 14 of the side pump signal combiner are the same fiber with identical core / cladding dimensions, making it suitable for backward-pumped and bidirectional-pumped fiber lasers to achieve reverse pump power injection. Specifically, the signal input fiber size of the side-pumped signal combiner includes common sizes such as 20 / 400μm, 25 / 400μm, and 30 / 400μm, the signal output fiber size includes sizes such as 20 / 400μm, 25 / 400μm, and 30 / 400μm, and the pump power transmission fiber size includes sizes such as 105 / 125μm, 135 / 155μm, and 220 / 242μm.

[0054] To demonstrate the superiority of the proposed solution, the following comparative analysis is conducted:

[0055] In the comparative example, scheme A is the scheme that does not use a bleaching light circulator. The structural diagram of scheme A is as follows: Figure 5 As shown, the optical path structure of scheme A is similar to... Figure 1 The only difference in the optical path structure shown is that the optical path structure of scheme A does not have a bleached optical circulator, the low-reflection fiber grating 3 is connected to the cladding optical filter 15, and the cladding optical filter 15 is connected to the fiber end cap 16.

[0056] In the comparative example, scheme B uses a bleaching light circulator. The structural diagram of scheme B is shown below. Figure 1 As shown, a (6+1)×1 reverse pump signal combiner is used as the bleaching optical circulator. The signal input fiber of the (6+1)×1 reverse pump signal combiner has a size of 30 / 400μm, the signal output fiber has a size of 30 / 250μm, and the pump power transmission fiber has a size of 220 / 242μm. The six pump power transmission fibers are fused together in pairs to form three pump power transmission fiber closed loops.

[0057] Schemes A and B are identical in all aspects except for the use of a bleaching optical circulator; all other components, parameters, and connection methods are the same. The gain fiber is a 30 / 400μm double-clad ytterbium-doped fiber, and the center wavelength of the fiber laser resonator is 1080nm. Before the bleaching experiment, the fiber laser in both schemes is irradiated with gamma rays at a dose rate of 1.04mGy / s, with a total dose of 11.3Gy. In the bleaching experiment, a 450nm blue laser is used as the bleaching source, with an output power of approximately 70mW. In the scheme using the bleaching optical circulator, when the bleaching source is turned on and the bleaching laser is injected, the laser output power gradually increases from 71W to 105.8W within the same bleaching time. In the scheme without the bleaching optical circulator, the laser output power only increases from 71W to 95.4W. The comparison results are as follows: Figure 6 As shown. The results indicate that the all-fiber laser proposed in this invention for improving photonic darkening bleaching can achieve an 11% improvement in bleaching efficiency.

[0058] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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 embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. An all-fiber laser for improving photon darkening and bleaching effects, characterized in that, Includes fiber laser oscillators, bleaching light sources, and bleaching optical circulators; In a fiber laser oscillator, a high-reflectivity fiber grating, a gain fiber, and a low-reflectivity fiber grating are connected in sequence to form a fiber laser resonant cavity. The bleaching light source injects bleaching laser into the fiber laser oscillator from the high-reflectivity fiber grating side of the fiber laser resonator. The bleaching laser propagates in the fiber cladding of the fiber laser resonator and bleachs the gain fiber. A bleaching optical circulator is connected to one side of the low-reflection fiber grating. The bleaching optical circulator has a closed loop of pumping power transfer fiber. The bleached laser that is not completely absorbed and is output to the bleaching optical circulator through the fiber cladding of the low-reflection fiber grating is re-entered into the fiber laser resonator through the closed loop of pumping power transfer fiber in the bleaching optical circulator, thereby realizing the cyclic bleaching of the gain fiber. The signal laser output from the fiber core of the low-reflection fiber grating is output through the signal fiber of the bleaching optical circulator.

2. The all-fiber laser for improving photon darkening and bleaching effects according to claim 1, characterized in that, A fiber laser oscillator includes a gain fiber, a high-reflectivity fiber grating, a low-reflectivity fiber grating, a fiber-coupled semiconductor laser, and a forward pump signal combiner. Multiple fiber-coupled semiconductor lasers are respectively connected to the pump power 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 power transmission fiber; 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 resonator through the forward pump signal combiner for transmission.

3. The all-fiber laser for improving photon darkening and bleaching effect according to claim 2, characterized in that, The bleached optical circulator includes an optical fiber combiner, a signal optical fiber, and at least one pair of pump power transmission fibers. The signal optical fiber includes a signal input fiber and a signal output fiber. The two pump power transmission fibers in the pair are fused together to form a closed loop of pump power transmission fibers. The fusion points of the two pump power transmission fibers form fusion splices of pump power transmission fibers. The low-reflection fiber grating is connected to the signal input fiber of the bleached optical circulator. The signal laser output from the core of the low-reflection fiber grating is output through the signal input fiber and the signal output fiber of the bleached optical circulator. The laser output from the cladding of the low-reflection fiber grating re-enters the fiber laser resonator through the closed loop of the pump power transmission fibers of the bleached optical circulator.

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

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

6. The all-fiber laser for improving photon darkening and bleaching effect according to claim 3, characterized in that, The fiber laser oscillator includes a reverse pump signal combiner. The signal output fiber of the bleached optical circulator is connected to the reverse pump signal combiner. The reverse pump signal combiner has one signal input fiber, one signal output fiber, and at least one pump power transmission fiber. The signal input fiber of the reverse pump signal combiner is connected to the signal output fiber of the bleached optical circulator. Each pump power 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 optical filter. The cladding optical filter is connected to an optical fiber end cap.

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

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

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

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

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