Large mode field photonic crystal fiber amplifier and preparation method thereof

Abstract

A large-mode-field photonic crystal fiber amplifier and its fabrication method are disclosed. The amplifier comprises a bundled cladding fiber, a mode-matched solid photonic crystal fiber, a rare-earth-doped silica gain photonic crystal fiber, and an output fiber connected in sequence. This large-mode-field photonic crystal fiber amplifier can be readily used in all-fiber pulsed lasers to achieve high beam quality and high-energy output. The output fiber has a flexible bending mechanism and requires no additional processing of the output end face, thus improving the practicality of fiber pulsed lasers.

Description

Technical Field

[0001] The invention relates to a large mode field photonic crystal fiber amplification system, in particular to a large mode field photonic crystal fiber amplifier and a preparation method thereof. Background Art

[0002] Rare earth doped silica optical fiber has been successfully applied in industrial processing, medical treatment, energy, military and other fields due to its advantages such as high output laser power and good thermomechanical properties. For rare earth doped silica cladding optical fiber (core size is generally less than 20 microns), the main factor limiting the further improvement of its laser performance is the nonlinear effect and laser damage caused by the increased power density at the fiber end face. In order to solve this problem, large mode field optical fiber has been developed and has become a research hotspot in recent years.

[0003] Since 2004, the University of Southampton in the UK (Optics Express, 2004, Vol. 12, No. 25, pp. 6088-6092), the Institute of Photonic Technology of Jena University in Germany and Heraeus (SPIE Conference Proceedings, Vol. 6873, 2008, pp. 687311-1-9) have carried out Yb 3+ Research and development of doped large mode field special optical fiber. In recent years, domestic institutions such as Shanghai Institute of Optics and Fine Mechanics, Xi'an Institute of Optics and Fine Mechanics, Yanshan University, National University of Defense Technology, Huazhong University of Science and Technology and Changfei Optical Fiber and Cable Co., Ltd. have also invested a lot of energy in the development of large mode field photonic crystal fiber. Compared with double-clad fiber, rare earth doped large mode field photonic crystal fiber has many microstructures, usually air holes arranged in a certain pattern. These specially arranged structures give photonic crystal fiber unique optical properties, such as: ultra-large core single-mode characteristics, special dispersion characteristics, etc.

[0004] Although rare earth doped large mode field photonic crystal fiber has excellent performance, its products and application units are still limited to foreign countries. The reasons are: 1. It is difficult to prepare rare earth doped large mode field photonic crystal fiber, and 2. Photonic crystal fiber is difficult to use. Photonic crystal fiber has a large mode field size, and it has a large mode mismatch when it is fused with the cladding fiber, resulting in large fusion loss. Conventional mode field adaptation is to taper the cladding fiber to "loosen the center", destroy the core waveguide of the cladding fiber, and diffuse the signal light into the cladding. This method will reduce the polarization degree of the signal light and require additional polarizing elements to increase the polarization degree, reducing the effective power of the laser. The core numerical aperture of photonic crystal fiber is small and cannot meet the use requirements of small bending radius. Therefore, current ultrafast fiber lasers usually use spatial output, which increases the difficulty of using fiber ultrafast lasers.

[0005] The preparation of photonic crystal fiber amplifiers is also a difficult problem, and there is no corresponding preparation process flow to refer to. The first is the end face processing of photonic crystal fiber. Compared with traditional cladding fiber, air holes will increase the difficulty of cutting, increase the cutting angle, and make the cut end face incomplete. When the end face is processed by grinding, the grinding powder will enter the structural holes of the optical fiber, making it difficult to clean. 2 The cutting machine can obtain a good end face when processing small-sized photonic crystal fibers, but when the outer diameter of the fiber is greater than 400 microns, its end face will be curved due to its light spot. The second is the fusion splicing of photonic crystal fibers. An inappropriate fusion splicing process will cause the collapse of the photonic crystal fiber structure hole, change the performance of the photonic crystal fiber, and increase the fusion loss. Patent CN101571611B provides a method for fusion splicing with other optical fibers while tolerating the collapse of the photonic crystal fiber structure, but this method requires matching refractive index gradient fibers and coreless fibers. These are usually not met in actual use. Patent CN104297849B proposes a technical process for achieving low-loss fusion splicing of photonic crystal fibers, but the patent only targets optical fibers with an outer diameter of 125. But in reality, the outer diameter of a photonic crystal fiber is usually quite different from the outer diameter of a traditional optical fiber that needs to be fused.

[0006] Currently, there is no photonic crystal fiber amplifier structure similar to cladding fiber and the corresponding preparation process. Summary of the invention

[0007] In view of the shortcomings and defects of the prior art, the present invention proposes a rare earth doped large mode field photonic crystal fiber amplifier and a preparation method thereof. The amplifier can be conveniently used in an all-fiber pulse amplification laser to achieve high beam quality and high energy output. The output fiber has a flexible bending mode and does not require additional processing of the output end face, thereby improving the practicality of the fiber pulse laser. The ability to generate and transmit high-energy, high beam quality ultrashort pulses far exceeds that of existing cladding fiber pulse amplifiers. In addition, a hollow photonic crystal fiber is used as the output fiber, which has large mode field characteristics, ultra-low nonlinear characteristics, and good bending resistance, which can greatly improve the flexibility of the use of the pulse laser.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A large mode field photonic crystal fiber amplifier is characterized in that it comprises a beam combining cladding fiber, a mode matching photonic crystal fiber, a rare earth doped quartz gain photonic crystal fiber and an output fiber which are connected in sequence, wherein the mode matching photonic crystal fiber is a pure quartz core photonic crystal fiber with an air hole structure, the output end of the mode matching photonic crystal fiber has the same mode field size as the gain photonic crystal fiber, and the input end has the same mode field size as the cladding beam combining fiber, the output fiber is a hollow core quartz photonic crystal fiber, and the output fiber has a mode field diameter equivalent to that of the gain photonic crystal fiber.

[0010] The cladding beam combining optical fiber is a conventional commercial quartz cladding optical fiber and can be directly connected to a commercial beam combiner.

[0011] The mode-matched photonic crystal fiber is a pure quartz core photonic crystal fiber with an air hole structure. The mode field is changed by taper or changing the air hole size. The output end cladding size is greater than or equal to the cladding size of the combiner fiber.

[0012] The gain photonic crystal fiber is a rare earth doped quartz photonic crystal fiber, which is an air hole structure or a full solid structure.

[0013] The length of the output optical fiber is not limited. The coating layer of the hollow-core photonic crystal optical fiber is a high-refractive-index organic material for realizing cladding light stripping.

[0014] The method for preparing the large mode field photonic crystal fiber amplifier comprises the following steps:

[0015] 1) According to the mode field size of the cladding combiner, the pure quartz photonic crystal fiber is tapered to obtain the cladding combined fiber, the mode field size of the cladding combined fiber after tapering matches the mode field size of the cladding combiner, and the "adiabatic" transmission condition of the fiber fundamental mode is met during tapering;

[0016] 2) Use commercial Vytran LDC401 to process the end faces of all optical fibers to ensure that the cut end faces are clean, free of cracks and debris, and the end face inclination angle is less than 1 degree. All optical fibers are cut with a small tension, which is 30%-50% less than that of cladding optical fibers of the same size;

[0017] 3) Clean the end faces of all cut optical fibers with an ultrasonic alcohol mixture and 2 Short-time, low-power heating on the welding machine;

[0018] 4) Select the appropriate heating method for welding according to the difference in the size of the optical fiber to be welded: when the size difference between the mode-matched photonic crystal fiber and the cladding combiner is less than 200 microns, select the thermal conduction heating method for welding; when the size difference between the photonic crystal fiber and the combiner fiber is greater than 200 microns, select the laser absorption heating method for welding; use small-size optical fiber for welding power correction, and reduce the welding power by at least 30% based on the correction power. The welding is carried out in a low-temperature, short-time, and multiple manner;

[0019] 5) Fusion of the mode-matching photonic crystal fiber and the gain photonic crystal fiber: Select the heating method according to the outer diameter of the optical fiber. When the outer diameter exceeds 500 microns, select laser absorption heating for welding. When the outer diameter is less than 500 microns, any heating method can be selected. The welding power setting is the same as step 3), and it is carried out in a low temperature, short time, and multiple times manner.

[0020] 6) The fusion splicing of the gain photonic crystal fiber and the output fiber, i.e., the hollow-core photonic crystal fiber, should be performed under the monitoring of a CCD camera to ensure better core alignment and improve coupling efficiency. The selection of the fusion splicing power is the same as in step 3). At the same time, the heating source should be deviated from the center and the process should be performed at a low temperature, for a short time, and multiple times.

[0021] 7) The prepared amplifier includes long cladding fiber, mode-matched photonic crystal fiber, Yb 3+ Doped large mode field quartz photonic crystal fiber and hollow core energy transfer fiber, the long cladding fiber is connected to the pump combiner;

[0022] 8) The strength of the fusion point of the photonic crystal fiber is relatively weak and cannot be protected by re-coating. The fusion point of the photonic crystal fiber is placed in a quartz tube or a metal groove, and then the optical fiber is fixed to the quartz tube or the metal groove with optical glue to protect the fusion point. When the photonic crystal fiber is used in a low-power amplification system with a pump power less than 50W, a quartz tube protection method can be adopted. When the pump power is greater than 50W, a metal groove cooling protection method is adopted, which is conducive to the control of the fusion point temperature; the prepared large mode field photonic crystal fiber amplifier is placed on a metal disk for fixing, which can be a curved groove or a straight groove. The winding diameter is determined according to the core size and core numerical aperture of the optical fiber, and its fundamental mode loss is not increased as a principle.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. The present invention can effectively prepare a rare earth doped large mode field photonic crystal fiber amplifier with an all-fiber structure, which has the ability to generate and transmit high-energy, high beam quality ultra-short pulses, far exceeding the existing cladding fiber pulse amplifiers. The use of hollow-core transmission photonic crystal fibers greatly improves the flexibility of pulse fiber lasers and expands their scope of use.

[0025] 2. It provides a specific reference range for the processing and fusion process optimization of photonic crystal fibers, which can effectively optimize the process, improve the fusion quality, reduce the fusion loss, and effectively reduce the difficulty of using photonic crystal fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the end face diagram of the combined cladding fiber;

[0027] Figure 2 This is the end face diagram of the mode field matched photonic crystal fiber;

[0028] Figure 3 It's Yb 3+ End-face view of doped large mode field photonic crystal fiber;

[0029] Figure 4 This is the end view of the hollow core output photonic crystal light;

[0030] Figure 5 It's Yb 3+ Pulse amplification curve of doped large mode field photonic crystal fiber amplifier;

[0031] Figure 6 It's Yb 3+ The pulse amplified output spot of the doped large mode field photonic crystal fiber amplifier. DETAILED DESCRIPTION

[0032] This case implementation includes the following optical fibers:

[0033] The combined cladding optical fiber has a core size of 20 microns, a mode field diameter of 18 microns, and a cladding diameter of 125 microns. Figure 1 As shown,

[0034] The mode matching optical fiber is a pure quartz air hole structure photonic crystal optical fiber with a core of 40 microns, a mode field diameter of 30 microns, a cladding diameter of 200 microns, an outer diameter of 450 microns, and a structure as follows: Figure 2 As shown;

[0035] The Yb 3+ The core of doped silica photonic crystal fiber is 40 microns, the mode field diameter is 30 microns, and the cladding diameter is 260 microns. Figure 3 As shown;

[0036] The hollow core energy transfer photonic crystal fiber has a core of 40 microns, a mode field diameter of 32 microns, an outer diameter of 125 microns, and a structure as follows: Figure 4 As shown;

[0037] A large mode field photonic crystal fiber amplifier comprises a beam combining cladding fiber, a mode matching photonic crystal fiber, a rare earth doped quartz gain photonic crystal fiber and an output fiber which are connected in sequence. The mode matching photonic crystal fiber is a pure quartz core photonic crystal fiber with an air hole structure. The output end of the mode matching photonic crystal fiber has the same mode field size as the gain photonic crystal fiber, and the input end has the same mode field size as the cladding beam combining fiber. The output fiber is a hollow core quartz photonic crystal fiber, and the output fiber has a mode field diameter equivalent to that of the gain photonic crystal fiber.

[0038] The cladding beam combining optical fiber is a conventional commercial quartz cladding optical fiber and can be directly connected to a commercial beam combiner.

[0039] The mode-matched photonic crystal fiber is a pure quartz core photonic crystal fiber with an air hole structure. The mode field is changed by taper or changing the air hole size. The output end cladding size is greater than or equal to the cladding size of the combiner fiber.

[0040] The gain photonic crystal fiber is a rare earth doped quartz photonic crystal fiber, which is an air hole structure or a full solid structure.

[0041] The output optical fiber is a hollow core quartz photonic crystal optical fiber, the length of the hollow core photonic crystal optical fiber is not limited, and the coating layer of the hollow core photonic crystal optical fiber is a high refractive index organic material for realizing cladding light stripping.

[0042] The method for preparing the large mode field photonic crystal fiber amplifier comprises the following steps:

[0043] 1) According to the mode field size of the cladding combiner, the pure quartz photonic crystal fiber is tapered to obtain the cladding combined fiber, the mode field size of the cladding combined fiber after tapering matches the mode field size of the cladding combiner, and the "adiabatic" transmission condition of the fiber fundamental mode is met during tapering;

[0044] 2) Use commercial Vytran LDC401 to process the end faces of all optical fibers to ensure that the cut end faces are clean, free of cracks and debris, and the end face inclination angle is less than 1 degree. All optical fibers are cut with a small tension, which is 30%-50% less than that of cladding optical fibers of the same size;

[0045] 3) Clean the end faces of all optical fibers after cutting with an ultrasonic alcohol mixture and 2 Short-time, low-power heating on the welding machine;

[0046] 4) The fusion splicing of the mode-matched photonic crystal fiber and the cladding beam-combining fiber: select a suitable heating method for fusion splicing according to the difference in the size of the optical fibers to be fused: when the size difference between the mode-matched photonic crystal fiber and the cladding beam-combining fiber is less than 200 microns, select the thermal conduction heating method for fusion splicing; when the size difference between the photonic crystal fiber and the beam-combining fiber is greater than 200 microns, select the laser absorption heating method for fusion splicing; use a small-size optical fiber for fusion power correction, and reduce the fusion power by at least 30% based on the correction power. The fusion splicing is performed in a low-temperature, short-time, and multiple manner;

[0047] 5) Fusion of the mode-matching photonic crystal fiber and the gain photonic crystal fiber: Select the heating method according to the outer diameter of the optical fiber. When the outer diameter exceeds 500 microns, select laser absorption heating for welding. When the outer diameter is less than 500 microns, any heating method can be selected. The welding power setting is the same as step 3), and it is carried out in a low temperature, short time, and multiple times manner.

[0048] 6) The fusion splicing of the gain photonic crystal fiber and the output fiber, i.e., the hollow-core photonic crystal fiber, should be performed under the monitoring of a CCD camera to ensure better core alignment and improve coupling efficiency. The selection of the fusion splicing power is the same as in step 3). At the same time, the heating source should be deviated from the center and the process should be performed at a low temperature, for a short time, and multiple times.

[0049] 7) The prepared amplifier includes 15cm long cladding bundled fiber, 3-5cm mode-matched photonic crystal fiber, 2m long Yb 3+ Doped large mode field quartz photonic crystal fiber and 2m long hollow core energy transfer fiber, the long cladding fiber is connected to the pump combiner;

[0050] 8) The strength of the fusion point of the photonic crystal fiber is relatively weak and cannot be protected by re-coating. The fusion point of the photonic crystal fiber is placed in a quartz tube or a metal groove, and then the optical fiber is fixed to the quartz tube or the metal groove with optical glue to protect the fusion point. When the photonic crystal fiber is used in a low-power amplification system with a pump power less than 50W, a quartz tube protection method can be adopted. When the pump power is greater than 50W, a metal groove cooling protection method is adopted, which is conducive to the control of the fusion point temperature; the prepared large mode field photonic crystal fiber amplifier is placed on a metal disk for fixing, which can be a curved groove or a straight groove. The winding diameter is determined according to the core size and core numerical aperture of the optical fiber, and its fundamental mode loss is not increased as a principle.

[0051] Example

[0052] The specific preparation process of the large mode field photonic crystal fiber amplifier of the present invention is as follows:

[0053] 1) Select the 450 μm outer diameter taper program on the Vytran 3000 fusion splicer, and use the 450 μm outer diameter mode-matched photonic crystal fiber for power calibration. On the basis of the calibration power, reduce the heating power by half to perform taper: pull the pure quartz photonic crystal fiber with an outer diameter of 450 μm and a cladding of 200 μm to an outer diameter of 280 μm, a cladding of 125 μm, a taper length of 7 mm, and a waist length of 10 mm;

[0054] 2) Using a Vytran LDC400 cleaver and selecting a 250 μm cleaving program to cleave the photonic crystal fiber, or using a CT105 cleaver to cleave the combined cladding fiber and reducing the cleaving tension by 25%, the thimble of the cleaver is rotated to a state where it just touches the fiber, and the waist region of the fiber prepared in step 1) is cleaved to obtain an ideal end face;

[0055] The optical fiber is cut by using a Vytran LDC400 cutter and selecting a 450-micron cutting program, and the cutting tension is reduced by 50%. The cutting needle of the cutter is rotated to a state where it just touches the optical fiber, and the cutting is performed in the unprocessed area of ​​the mode-matched photonic crystal fiber to obtain an ideal end face.

[0056] The Vytran LDC400 cleaver was used to select a 250-micron cleaving program to cleave the optical fiber, and the cleaving tension was reduced by 25%. The thimble of the cleaver was rotated to a state where it just touched the optical fiber. 3+ Doped silica large mode field photonic crystal fiber can be cut to obtain an ideal end face;

[0057] 3) All the cut optical fibers were ultrasonically cleaned in an alcohol-acetone mixture for 10 ms, and then placed in a CO 2 On the welding machine, it is heated quickly and at low temperature (100ms, 10Bit) to cause the mixed liquid to evaporate from the microstructure pores;

[0058] 4) The fusion of the mode-matched photonic crystal fiber and the cladding combiner: put the processed optical fiber into the Fujikura 100P+ fusion splicer, place the photonic crystal fiber on the right fixture of the fusion splicer, and place the 125-micron cladding fiber on the left fixture of the fusion splicer; select the 125-micron fusion splicing program, set the main heating power to 140 Bit, set the heating source to the center, the heating time to 1000 ms, and the fusion overlap to 10 microns; set 3 reheating programs respectively: heating power 140 bit, heating time 1000 ms, heating power 140 bit, heating time 800 ms, heating power 140 bit, heating time 500 ms, select the manual alignment of the polarization axis, under this process condition, the photonic crystal fiber structure does not collapse, the fusion strength is high, and the fusion point is protected in the metal groove;

[0059] 5) Fusion of the mode-matched photonic crystal fiber and the gain photonic crystal fiber: Place the treated optical fiber into the Fujikura 100P+ fusion splicer, place the mode-matched photonic crystal fiber on the right fixture of the fusion splicer, and place the 260 μm Yb 3+ Place the doped quartz photonic crystal fiber on the left fixture of the fusion splicer, select the 250 micron fusion program, the heating source is 50 microns to the right, the main heating power is set to 190Bit, the heating source is set in the center, the heating time is 1700ms, and the fusion overlap is set to 10 microns. Use the heating power of 200bit and the heating time of 1700ms to strengthen the fusion point 3 times, and select the manual polarization axis alignment method. Under this process condition, the photonic crystal fiber structure does not collapse and the fusion strength is high. Protect the fusion point in the metal groove;

[0060] 6) The Yb 3+ Doped photonic crystal fiber and the hollow core photonic crystal fiber are fused: the optical fiber is placed in the Fujikura 100P+ fusion splicer, and the Yb 3+ The doped photonic crystal fiber is placed on the right fixture of the fusion splicer, and the 125-micron hollow-core photonic crystal fiber is placed on the left fixture of the fusion splicer. The 125-micron fusion splicing program is selected, and the output end of the hollow-core photonic crystal fiber is imaged on the CCD through a lens to select the best alignment position. The main heating power is set to 70 bits, the heating source is offset to the right by 150 microns, the heating time is 200 ms, the fusion overlap is set to 5 microns, and the heating power is 170 bits. The heating time is 700 ms to strengthen the fusion point 80 times. Under this process condition, the photonic crystal fiber structure does not collapse, the fusion strength is high, and the fusion point is protected in the metal groove;

[0061] 7) The prepared amplifier includes 15cm long cladding bundled fiber, 3-5cm mode-matched photonic crystal fiber, 2m long Yb 3+ Doped large mode field quartz photonic crystal fiber and 2m long hollow core energy transfer fiber, the long cladding fiber is connected to the pump combiner;

[0062] 8) The strength of the fusion point of the photonic crystal fiber is relatively weak and cannot be protected by re-coating. The fusion point of the photonic crystal fiber is placed in a quartz tube or a metal groove, and then the optical fiber and the quartz tube or the metal groove are fixed with optical glue to protect the fusion point. When the photonic crystal fiber is used in a low-power amplification system with a pump power less than 50W, a quartz tube protection method can be adopted. When the pump power is greater than 50W, a metal groove cooling protection method is adopted, which is conducive to the control of the temperature of the fusion point; Yb 3+ The doped large mode field photonic crystal fiber is coiled on a water cooling plate with a bending diameter of 23 cm, the fusion point is placed in a straight groove, and the bending diameter of the hollow core fiber is not less than 16 cm.

[0063] The 1W, 1030nm wavelength, 30ps, 41MHz pulse light is amplified, and the light-to-light conversion efficiency is 68.5%. The curve of amplified power changing with pump power is shown in Figure 5 As shown, the output spot is Figure 6 shown.

[0064] Experiments show that the large mode field photonic crystal fiber amplifier of the present invention can be conveniently used in all-fiber pulse amplification lasers to achieve high beam quality and high energy output. The output optical fiber has a flexible bending mode and does not require additional processing of the output end face, thereby improving the practicality of the fiber pulse laser.

Claims

1. A large mode field photonic crystal fiber amplifier, characterized in that: It comprises a cladding beam combining fiber, a mode matching photonic crystal fiber, a rare earth doped quartz gain photonic crystal fiber and an output fiber which are connected in sequence. The mode matching photonic crystal fiber is a pure quartz core photonic crystal fiber with an air hole structure. The output end of the mode matching photonic crystal fiber has the same mode field size as the gain photonic crystal fiber, and the input end has the same mode field size as the cladding beam combining fiber. The output fiber is a hollow core quartz photonic crystal fiber, and the output fiber has a mode field diameter equivalent to that of the gain photonic crystal fiber. The cladding beam combining optical fiber is a commercial quartz photonic crystal optical fiber, which is directly connected to a commercial cladding beam combiner; The mode-matching photonic crystal fiber achieves the change of mode field by taper or changing the size of the air hole, and the cladding size of the output end is greater than or equal to the cladding size of the cladding beam-combining fiber; The gain photonic crystal fiber is a rare earth doped quartz photonic crystal fiber, which is an air hole structure or a fully solid structure; The length of the hollow core quartz photonic crystal optical fiber is not limited. The coating layer of the hollow core quartz photonic crystal optical fiber is a high refractive index organic material for realizing cladding light stripping.

2. The large mode area photonic crystal fiber amplifier according to claim 1, characterized in that: Contains 15cm long cladding bundled fiber, 3-5cm mode-matched photonic crystal fiber, 2m long Yb 3+ Doped large mode area silica photonic crystal fiber and 2m long hollow core energy transfer fiber.

3. The method for preparing the large mode field photonic crystal fiber amplifier according to claim 1, characterized in that: The preparation method comprises the following steps: 1) According to the mode field size of the cladding combiner, the quartz photonic crystal fiber is tapered to obtain the cladding combined fiber, the mode field size of the cladding combined fiber after tapering matches the mode field size of the cladding combiner, and the "adiabatic" transmission condition of the fiber fundamental mode is met during tapering; 2) Process the end faces of all optical fibers to ensure that the cut end faces are clean, free of cracks and debris, and the end face inclination angle is less than 1 degree; 3) The end face of the cut photonic crystal fiber is cleaned with an ultrasonic alcohol mixture and heated for a short time and at a low power on a CO2 fusion splicer; 4) Selecting a suitable heating method for welding according to the difference in the size of the optical fibers to be welded: When the size difference between the mode-matched photonic crystal fiber and the cladding beam-combining fiber is less than 200 microns, a heat conduction heating method is selected for welding; when the size difference between the photonic crystal fiber and the cladding beam-combining fiber is greater than 200 microns, a laser absorption heating method is selected for welding; welding is performed in a low temperature, short time, and multiple times; 5) Fusion of the mode-matching photonic crystal fiber and the gain photonic crystal fiber: Select a heating method according to the outer diameter of the optical fiber. When the outer diameter exceeds 500 microns, select laser absorption heating for fusion splicing; use low temperature, short time, and multiple times; 6) The fusion splicing of the gain photonic crystal fiber and the output fiber, i.e., the hollow-core quartz photonic crystal fiber, should be performed under the monitoring of a CCD camera to align the fiber core and improve the coupling efficiency. At the same time, the heating source should be deviated from the center and the process should be performed at a low temperature, for a short time, and multiple times; 7) The prepared amplifier includes cladding beam combining fiber, mode matching photonic crystal fiber, Yb 3+ Doped large mode field quartz photonic crystal fiber and hollow core energy transfer fiber, the cladding beam combining fiber is connected to the pump combiner; 8) Place the fusion point of the photonic crystal fiber in a quartz tube or metal groove, and then use optical glue to fix the fiber and the quartz tube or metal groove to protect the fusion point. When the photonic crystal fiber is used in a low-power amplification system with a pump power less than 50W, a quartz tube protection method is adopted. When the pump power is greater than 50W, a metal groove cooling protection method is adopted; place the prepared large mode field photonic crystal fiber amplifier on a curved groove or straight groove metal disk for fixation, and the winding diameter is determined according to the core size and core numerical aperture of the optical fiber.

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