A method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier and an amplifier

Abstract

The invention relates to a method for manufacturing a fully-fiberized 40μm core diameter photonic crystal fiber amplifier and the amplifier, belonging to the technical field of high-power lasers. A plurality of input optical fibers are respectively connected to the input port of a beam combiner, wherein the input optical fibers include a signal polarization-maintaining optical fiber with a core diameter of 10μm and a plurality of pump optical fibers. The input end of an output polarization-maintaining optical fiber is connected to the output port of the beam combiner, wherein the core diameter of the output polarization-maintaining optical fiber is 20μm. The output end of the output polarization-maintaining optical fiber is fused to the input end of a photonic crystal gain optical fiber with a core diameter of 40μm, and the output end of the photonic crystal gain optical fiber with a core diameter of 40μm is fused to an end cap. The invention adopts a forward pumping method to amplify signal light, and injects pump light from the input port of the beam combiner to realize the full fiberization of the amplifier, and the overall architecture is simpler.

Description

Technical Field

[0001] The invention belongs to the technical field of high-power lasers, and in particular relates to a method for manufacturing a fully-fiberized 40-μm core diameter photonic crystal optical fiber amplifier and the amplifier. Background Art

[0002] As the laser processing market's demand for processing efficiency and processing quality continues to increase, the demand for ultrashort pulse lasers with high power and high beam quality is also increasing. In ultrashort pulse fiber lasers, the nonlinear effects, thermal damage and other physical mechanisms in the optical fiber limit the continuous increase in power. Therefore, it is necessary to expand the core diameter to effectively reduce the nonlinear effect. However, when the mode field area becomes larger, ordinary optical fibers can no longer maintain the single-mode transmission characteristics, resulting in a decrease in the beam quality of the laser output light. Large mode field photonic crystal fibers can maintain single-mode transmission characteristics while increasing the core diameter. Therefore, large mode field photonic crystal fibers have been increasingly widely used in high-power fiber lasers.

[0003] At present, in order to meet the requirements of high power, most of the 40μm photonic crystal fiber amplifiers on the market use reverse pumping, injecting spatial pump light from the tail end of the fiber into the fiber through a lens to avoid the impact of poor fusion quality, but this greatly sacrifices the flexibility, stability and reliability of the system. Compared with reverse pumping, co-directional pumping injects the pump light into the gain fiber through the front-end fiber combiner, which can realize the full fiberization of the system and greatly improve the flexibility, stability and reliability of the system. It can be seen that all-fiber fusion coupling is a necessary condition for the practical application of large-core photonic crystal fiber amplifiers.

[0004] Since there is no mode field adapter that can match 40μm photonic crystal fiber on the market, the only way is to use optical fibers with different diameters to fuse with 40μm photonic crystal fiber. However, there is a special air hole structure in the core of 40μm photonic crystal fiber, which is easy to collapse during the welding process, resulting in reduced coupling efficiency. The pump light is easy to leak after passing through the welding point, causing severe heating near the welding point under high power conditions, causing damage to the amplifier, and it is difficult to output high-power and high-beam quality lasers. Summary of the invention

[0005] In view of the various deficiencies in the prior art and in order to solve the above problems, a method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier and an amplifier that can meet high power requirements are proposed.

[0006] In a first aspect, the present invention further provides a method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier, comprising:

[0007] Connecting a plurality of input optical fibers to the input port of the beam combiner respectively, wherein the input optical fibers include a signal polarization-maintaining optical fiber with a core diameter of 10 μm and a plurality of pump optical fibers; connecting the input end of the output polarization-maintaining optical fiber to the output port of the beam combiner, wherein the core diameter of the output polarization-maintaining optical fiber is 20 μm;

[0008] The output end of the output polarization-maintaining optical fiber is fused to the input end of the photonic crystal gain optical fiber with a core diameter of 40 μm, and the output end of the photonic crystal gain optical fiber with a core diameter of 40 μm is fused to the end cap.

[0009] The technical solution is further configured to fuse the output end of the output polarization-maintaining optical fiber with the input end of the photonic crystal gain optical fiber with a core diameter of 40 μm, specifically:

[0010] Performing end-face cutting on the output end of the output polarization-maintaining optical fiber;

[0011] Perform end-face cutting on the input end of the photonic crystal gain fiber with a core diameter of 40 μm;

[0012] The first main melting power P1, the first main melting time T1, the first pre-melting power P2, the first pre-melting time T2 and the overlap amount are set, and the output end of the output polarization-maintaining optical fiber and the input end of the photonic crystal gain optical fiber with a core diameter of 40 μm are welded 2 to 4 times to form a first welding point.

[0013] The technical solution is further configured as follows: the first main melting power P1 is 500-580 bits, the first main melting time T1 is 1500-2000 ms, the first pre-melting power P2 is 520-590 bits, the first pre-melting time T2 is 100-300 ms, and the overlap amount is 7-14 μm.

[0014] The technical solution is further configured to fuse the output end of the photonic crystal gain fiber with a core diameter of 40 μm with the end cap, specifically:

[0015] Perform end-face cutting on the output end of a photonic crystal gain fiber with a core diameter of 40 μm;

[0016] Place the end cap in the end cap fixture;

[0017] The second main melting power P3, the second main melting time T3, the second pre-melting power P4 and the second pre-melting time T4 are set, and the output end of the photonic crystal gain fiber with a core diameter of 40 μm is welded with the end cap 2 to 4 times to form a second welding point.

[0018] The technical solution is further configured as follows: the second main melting power P3 is 620-700 bits, the second main melting time T3 is 3500-4500 ms, the second pre-melting power P4 is 660-740 bits, and the second pre-melting time T4 is 1200-2000 ms.

[0019] The technical solution is further configured such that the tension value for end-face cutting of the input end and the output end of the photonic crystal gain fiber with a core diameter of 40 μm is 880 to 920 g, and the rotation angle is 0°.

[0020] The technical solution is further configured to include applying glue to protect the first welding point and the second welding point, specifically:

[0021] The first welding point and the second welding point are respectively placed in the U-shaped groove, UV curing glue is coated in the U-shaped groove, and the UV curing glue is irradiated with a UV lamp until it is cured, and the first welding point and the second welding point are respectively fixed in the U-shaped groove.

[0022] The technical solution is further configured to provide a U-shaped groove on the surface of a metal plate through which a cooling medium flows, wherein the U-shaped groove is a curved groove or a straight groove.

[0023] In a second aspect, the present invention provides a fully fiberized 40 μm core diameter photonic crystal fiber amplifier, comprising:

[0024] An input optical fiber, comprising a signal polarization-maintaining optical fiber with a core diameter of 10 μm and a plurality of pump optical fibers, wherein the signal polarization-maintaining optical fiber is used to transmit signal light, and the pump optical fiber is used to transmit pump light;

[0025] A beam combiner, whose input ports are respectively connected to the signal polarization-maintaining optical fiber and the pump optical fiber, and is used to couple the signal light and the pump light;

[0026] And an output polarization-maintaining optical fiber with a core diameter of 20 μm, whose input end is connected to the output port of the beam combiner, whose output end is fused to the input end of a photonic crystal gain optical fiber with a core diameter of 40 μm, and whose output end is fused to an end cap.

[0027] The technical solution is further configured as follows: six pump optical fibers are provided, and the core diameter of the pump optical fibers is 105 μm, and the beam combiner is a (6+1)×1 beam combiner.

[0028] The beneficial effects of the present invention are:

[0029] 1. The signal light is amplified by forward pumping, and the pump light is injected from the input port of the combiner to realize the full fiberization of the amplifier, making the overall architecture simpler.

[0030] 2. The cutting parameters and welding parameters of the photonic crystal gain fiber with a core diameter of 40μm are optimized to improve the welding quality, reduce the welding loss, avoid the degradation of the beam quality, and effectively reduce the difficulty of using the photonic crystal gain fiber with a core diameter of 40μm.

[0031] 3. Apply UV curing glue in the U-shaped groove to fully cover the optical fiber near the first fusion point and the second fusion point, and confine all the transmitted light inside the optical fiber to avoid the leakage of the transmitted light and the heating of the optical fiber near the first fusion point and the second fusion point, so as to meet the high power requirements.

[0032] 4. The signal polarization-maintaining fiber with a core diameter of 10μm is the fiber with the largest core diameter among the fibers that ensure single-mode characteristics and can obtain higher output power. At the same time, the output polarization-maintaining fiber with a core diameter of 20μm and the photonic crystal gain fiber with a core diameter of 40μm have low fusion loss and can meet the use requirements without the need to transition to 40μm ordinary polarization-maintaining fiber.

[0033] 5. The production method is simple, the cost is low, and it is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of a method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier in the present invention;

[0035] Figure 2 (a) is a schematic diagram showing the uneven end face of the optical fiber after cutting;

[0036] Figure 2 (b) is a schematic diagram showing that the optical fiber end face has obvious scratches covering the fiber core after cutting;

[0037] Figure 3 It is a schematic diagram of the fully fiberized 40 μm core diameter photonic crystal fiber amplifier of the present invention.

[0038] In the attached figure: 1-signal polarization-maintaining fiber, 2-pump fiber, 3-beam combiner, 4-output polarization-maintaining fiber, 5-first fusion point, 6-photonic crystal gain fiber, 7-second fusion point, 8-end cap. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings of the present invention. Based on the embodiments in this application, other similar embodiments obtained by ordinary technicians in this field without making creative work should all fall within the scope of protection of this application. In addition, the directional words mentioned in the following embodiments, such as "up", "down", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional words used are used to illustrate rather than limit the invention.

[0040] Embodiment 1:

[0041] like Figure 1 As shown, a method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier comprises the following steps:

[0042] S100, connect multiple input optical fibers to the input port of the combiner respectively, wherein the input optical fibers include a signal polarization-maintaining optical fiber with a core diameter of 10 μm and multiple pump optical fibers, and connect the input end of the output polarization-maintaining optical fiber to the output port of the combiner, wherein the core diameter of the output polarization-maintaining optical fiber is 20 μm.

[0043] The specific steps include:

[0044] S101, performing end-face cutting on the output end of the output polarization-maintaining optical fiber and placing the optical fiber into a fusion splicer.

[0045] S102, cutting the input end of the photonic crystal gain fiber with a core diameter of 40 μm and placing it in a fusion splicer.

[0046] S103, setting the first main melting power P1, the first main melting time T1, the first pre-melting power P2, the first pre-melting time T2 and the overlap amount, and performing 2 to 4 weldings on the output end of the output polarization-maintaining optical fiber and the input end of the photonic crystal gain optical fiber with a core diameter of 40 μm to form a first welding point.

[0047] During the fiber fusion splicing process, pre-fusion splicing is performed first to soften the fiber slightly, and then the main fusion splicing is performed. The pre-fusion power and pre-fusion time are mutually restricted. The product of the pre-fusion time and the pre-fusion power can be used to obtain the energy generated by the laser during the pre-fusion process. If the pre-fusion power is too large and the pre-fusion time is too short, the fiber will melt and deform instantly. If the pre-fusion power is too small, even if the pre-fusion time is long, the melting threshold will not be reached, and the fiber cannot be melted or fusion spliced. Therefore, these two parameters are mutually restricted, and it is also necessary to find the appropriate setting value based on experience. The same is true for the main fusion power and main fusion time.

[0048] To this end, the inventor conducted multiple welding experiments, first setting the first main melting time T1 at 1800ms, and increasing the welding power from small to large. When the welding power setting value is 500bit, the photonic crystal gain fiber with a core diameter of 40μm can be softened before welding. When the welding power is set to 590bit, the welding process will cause the photonic crystal gain fiber with a core diameter of 40μm to soften too severely, the internal air hole structure collapses, and the welding loss increases sharply. When the welding power is greater than 650bit, the photonic crystal gain fiber with a core diameter of 40μm is completely softened, causing the fiber end face to deform and be pulled into a spherical shape, making it unusable. When the welding power is between 500bit and 590bit, the photonic crystal gain fiber with a core diameter of 40μm can be softened and the air hole collapse is not obvious. In this range, further experiments are conducted, combined with the adjustment of the welding time, and the optimal welding power and time parameters are obtained based on the welding effect. Preferably, the first main melting power P1 is 500-580 bits, the first main melting time T1 is 1500-2000 ms, the first pre-melting power P2 is 520-590 bits, and the first pre-melting time T2 is 100-300 ms.

[0049] The value of the overlap determines the length of overlap of two optical fibers when they are squeezed against each other. If the overlap is too large, the optical fibers that are not softened enough may be misaligned or deformed when they are pushed together, resulting in large losses. In addition, when the photonic crystal gain fiber with a core diameter of 40 μm is welded, the air hole collapses slightly, and the end face will also produce a certain degree of concave. At this time, increasing the overlap can reduce the additional loss caused by this. Therefore, the overlap should not be too small. Based on this, the inventor proposed the invention of low welding power, small overlap, and multiple welding, and selected a relatively small overlap for multiple welding accumulation. During the experiment, it was found that when the overlap was less than 7 μm, the optical fiber could not be welded due to the small amount of advancement; when the overlap was greater than 14 μm, the optical fiber would be misaligned. Preferably, the overlap is 7 to 14 μm, and the welding loss is minimal.

[0050] S200, the output end of the output polarization-maintaining optical fiber is fused to the input end of the photonic crystal gain optical fiber with a core diameter of 40 μm, and the output end of the photonic crystal gain optical fiber with a core diameter of 40 μm is fused to the end cap.

[0051] The specific steps include:

[0052] S201, perform end-face cutting on the output end of the photonic crystal gain fiber with a core diameter of 40 μm and place it into a fusion splicer.

[0053] S202, placing the end cap in the end cap fixture, and then placing the fixture into the welding machine.

[0054] S203, setting a second main melting power P3, a second main melting time T3, a second pre-melting power P4 and a second pre-melting time T4, and performing 2 to 4 weldings on the output end of the photonic crystal gain fiber with a core diameter of 40 μm and the end cap to form a second welding point.

[0055] Preferably, the second main melting power P3 is 620-700 bits, the second main melting time T3 is 3500-4500 ms, the second pre-melting power P4 is 660-740 bits, and the second pre-melting time T4 is 1200-2000 ms.

[0056] Preferably, due to the special air hole structure inside the photonic crystal gain fiber, its fiber characteristics are quite different from those of ordinary 40μm optical fibers. Therefore, it is necessary to reasonably adjust the tension value and rotation angle of the end face cutting to make the fiber end face after cutting relatively smooth and without cracks, so as to facilitate the subsequent fiber fusion splicing operation. The inventors have found through multiple cutting experiments that: when the tension value is less than 780g, the optical fiber cannot be tightened during the cutting process and thus cannot be cut; when the tension value is greater than 780g and less than 880g, the optical fiber will bend to a certain extent while being pressed by the blade, resulting in the cutting angle being too large after the optical fiber is cut, and the optical fiber end face obtained after cutting is uneven, such as Figure 2 (a) As shown; when the tension value is set between 880g and 920g, the cutting can obtain a better end face and the fiber core has no scratches; when the tension value is greater than 920g, the fiber end face obtained after cutting has obvious scratches and covers the fiber core, as shown in Figure 2 Therefore, the tension value for end-face cutting of the input end and the output end of the photonic crystal gain fiber with a core diameter of 40 μm is 880 to 920 g, and the rotation angle is 0°, which can ensure that the cross section obtained after cutting is flat.

[0057] Preferably, the method further includes applying glue to protect the first welding point and the second welding point, specifically:

[0058] The first welding point and the second welding point are respectively placed in the U-shaped groove, UV curing glue is coated in the U-shaped groove, and the UV curing glue is irradiated with a UV lamp until it is cured, and the first welding point and the second welding point are respectively fixed in the U-shaped groove.

[0059] Preferably, a U-shaped groove is provided on the surface of a metal plate having a cooling medium (such as cooling water) flowing therein, and the U-shaped groove is a curved groove or a straight groove. The first fusion point and the second fusion point are placed in the U-shaped grooves respectively, and the optical fibers near the first fusion point and the second fusion point are ensured to be in a relaxed state without any bending, and the UV curing glue is evenly applied to the first fusion point and the second fusion point in the U-shaped groove and an area about 10 cm in length near the area.

[0060] like Figure 3 As shown, the present invention provides a fully fiberized 40 μm core diameter photonic crystal fiber amplifier, comprising:

[0061] An input optical fiber, comprising a signal polarization-maintaining optical fiber 1 with a core diameter of 10 μm and a plurality of pump optical fibers 2, wherein the signal polarization-maintaining optical fiber 1 is used to transmit signal light, and the pump optical fibers 2 are used to transmit pump light;

[0062] A beam combiner 3, whose input ports are respectively connected to the signal polarization-maintaining optical fiber 1 and the pump optical fiber 2, and is used for coupling the signal light and the pump light;

[0063] And an output polarization-maintaining optical fiber 4 with a core diameter of 20 μm, whose input end is connected to the output port of the combiner 3, whose output end is fused to the input end of the photonic crystal gain optical fiber 6 with a core diameter of 40 μm, and whose output end is fused to the end cap 8.

[0064] Preferably, the specification of the signal polarization-maintaining fiber 1 is 10 / 125, and its input end is connected to the output fiber of the signal light so that the signal light can be injected, and its output end is connected to the combiner 3 to inject the signal light into the combiner 3. Six pump fibers 2 are provided, and the specification of the pump fibers 2 is 105 / 125 fibers, and its input end is used to be connected to the laser amplifier pump so that the pump light can be injected into the amplifier, and its output end is connected to the combiner 3 to inject the pump light into the combiner 3. The combiner 3 is a (6+1)×1 combiner, which is used to couple the signal light and the pump light injected at the front end into the same optical fiber, so that the light injected from 7 different optical fibers can be output from one optical fiber. The specification of the output polarization-maintaining fiber 4 is 20 / 130, and its input end is connected to the beam combiner 3, which plays the role of transmitting signal light and pump light. Its output end is fused with the input end of the photonic crystal gain fiber 6 with a core diameter of 40μm to form a first fusion point 5, ensuring a good fusion effect so that the pump light and signal light can be injected into the photonic crystal gain fiber. The photonic crystal gain fiber 6 with a core diameter of 40μm is used as a gain medium in the amplifier, which can amplify the power of the injected signal light. Its output end is fused with the end cap 8 to form a second fusion point 7, ensuring a good fusion effect so that the amplified laser can be smoothly output from the end cap 8. The end cap 8 is used to protect the output end face of the optical fiber to prevent the end face of the optical fiber from being damaged due to excessive power density or contamination of the optical fiber end face, thereby affecting the output light quality.

[0065] The thicker the fiber core diameter, the higher its nonlinear threshold, and the greater the power that can be amplified. The 10μm amplifier is a relatively mature fiber amplifier, and the signal polarization-maintaining fiber 1 with a core diameter of 10μm is the fiber with the largest core diameter among ordinary optical fibers that can guarantee single-mode characteristics, and can obtain higher output power, so the 10μm amplifier is used as the preamplifier of the 40μm photonic crystal fiber amplifier. If the signal polarization-maintaining fiber with a core diameter of 10μm is directly fused with the photonic crystal gain fiber with a core diameter of 40μm, due to the large difference in the fiber core diameter, the fusion is not reliable, it is more difficult to ensure the effect and quality of the fusion point, and the NA (numerical aperture) is more mismatched. Therefore, a beam combiner or mode field adapter is used to transition the fiber core diameter to 20μm, and then it is fused with the photonic crystal gain fiber with a core diameter of 40μm.

[0066] When optical fibers with different core diameters are fused together, the mode field mismatch will cause Among them, ω1 and ω2 represent the mode field diameter of the optical fiber to be fused. The mode field diameter of the 10 / 125 specification optical fiber is 10.7μm, the mode field diameter of the 20 / 130 specification optical fiber is 16μm, and the mode field diameter of the photonic crystal gain fiber with a core diameter of 40μm is 31μm. According to the formula, it can be calculated that when the 10μm core diameter optical fiber and the 40μm core diameter optical fiber are fused, the fusion loss caused by the mode field mismatch is 4.66dB, and the signal light loss is about 2 / 3. When the 20 / 130 specification optical fiber and the 40μm core diameter optical fiber are fused, the fusion loss caused by the mode field mismatch is only 1.77dB, and the signal light loss is less than 1 / 3, which can meet the use requirements. Generally speaking, for special fusion points, a fusion loss of less than 3dB is acceptable. Therefore, the fusion of the output polarization-maintaining optical fiber 4 with a core diameter of 20μm and the photonic crystal gain optical fiber 6 with a core diameter of 40μm can meet the use requirements without the need to transition to a 40μm ordinary polarization-maintaining optical fiber. In addition, since the inner cladding diameter of the photonic crystal gain fiber with a core diameter of 40μm is 200μm, and the inner cladding diameter of the commonly used 30 / 250 specification fiber is 250μm, which is larger than the inner cladding diameter of the 40μm photonic crystal gain fiber, if the 30 / 250 specification fiber and the 40μm photonic crystal gain fiber are fused, it will cause the pump light propagating in the inner cladding to leak, so it is not applicable.

[0067] Embodiment 2:

[0068] The same parts of this embodiment as those of the first embodiment are not described in detail, except that:

[0069] The length of the photonic crystal gain fiber with a core diameter of 40μm is 2m, the cutting tension is 900g, and the rotation angle is 0°. During the fusion splicing of the photonic crystal gain fiber with a core diameter of 40μm and the output polarization-maintaining fiber with a core diameter of 20μm, the main melting power is set to 540bit, the main melting time is 1800ms, the pre-melting power is set to 560bit, the pre-melting time is 200ms, and the overlap is 10μm.

[0070] During the fusion splicing of the photonic crystal gain fiber with a core diameter of 40 μm and the end cap, the main melting power was 660 bits, the main melting time was 4000 ms, the pre-melting power was 700 bits, and the pre-melting time was 1600 ms.

[0071] When a seed light with an average power of 0.8W, a repetition rate of 40MHz, and a pulse width of 500ps is injected into the front end of the amplifier and a 160W pump light is injected, the output optical power reaches 100W and the beam quality M 2 =1.1.

[0072] The present invention has been described in detail above. The above description is only a preferred embodiment of the present invention and should not limit the scope of implementation of the present invention. That is, all equivalent changes and modifications made within the scope of this application should still fall within the scope of the present invention.

Claims

1. A method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier, characterized in that: include: Connecting a plurality of input optical fibers to the input port of the beam combiner respectively, wherein the input optical fibers include a signal polarization-maintaining optical fiber with a core diameter of 10 μm and a plurality of pump optical fibers; connecting the input end of the output polarization-maintaining optical fiber to the output port of the beam combiner, wherein the core diameter of the output polarization-maintaining optical fiber is 20 μm; The output end of the output polarization-maintaining fiber is fused with the input end of the photonic crystal gain fiber with a core diameter of 40 μm, and the output end of the photonic crystal gain fiber with a core diameter of 40 μm is fused with the end cap. The photonic crystal gain fiber with a core diameter of 40 μm is used as the gain medium in the amplifier. The mode field diameters of the photonic crystal gain fiber with a core diameter of 40 μm and the output polarization-maintaining fiber with a core diameter of 20 μm are different.

2. The method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 1, characterized in that: The output end of the output polarization-maintaining fiber is fused with the input end of the photonic crystal gain fiber with a core diameter of 40 μm, specifically: Performing end-face cutting on the output end of the output polarization-maintaining optical fiber; Perform end-face cutting on the input end of a photonic crystal gain fiber with a core diameter of 40 μm; The first main melting power P1, the first main melting time T1, the first pre-melting power P2, the first pre-melting time T2 and the overlap amount are set, and the output end of the output polarization-maintaining optical fiber and the input end of the photonic crystal gain optical fiber with a core diameter of 40 μm are welded 2 to 4 times to form a first welding point.

3. The method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 2, characterized in that: The first main melting power P1 is 500-580 bits, the first main melting time T1 is 1500-2000 ms, the first pre-melting power P2 is 520-590 bits, the first pre-melting time T2 is 100-300 ms, and the overlap amount is 7-14 μm.

4. The method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 2, characterized in that: The output end of the photonic crystal gain fiber with a core diameter of 40 μm is fused to the end cap, specifically: Perform end-face cutting on the output end of a photonic crystal gain fiber with a core diameter of 40 μm; Place the end cap in the end cap fixture; The second main melting power P3, the second main melting time T3, the second pre-melting power P4 and the second pre-melting time T4 are set, and the output end of the photonic crystal gain fiber with a core diameter of 40 μm is welded with the end cap 2 to 4 times to form a second welding point.

5. The method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 4, characterized in that: The second main melting power P3 is 620-700 bits, the second main melting time T3 is 3500-4500 ms, the second pre-melting power P4 is 660-740 bits, and the second pre-melting time T4 is 1200-2000 ms.

6. A method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 4 or 5, characterized in that: The tensile force for end-cutting the input and output ends of a photonic crystal gain fiber with a core diameter of 40 μm is 880-920 g, and the rotation angle is 0°.

7. The method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 6, characterized in that: The method further includes applying glue to protect the first welding point and the second welding point, specifically: The first welding point and the second welding point are respectively placed in the U-shaped groove, UV curing glue is coated in the U-shaped groove, and the UV curing glue is irradiated with a UV lamp until it is cured, and the first welding point and the second welding point are respectively fixed in the U-shaped groove.

8. The method for manufacturing a fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 7, characterized in that: A U-shaped groove is provided on the surface of a metal plate through which a cooling medium flows. The U-shaped groove is a curved groove or a straight groove.

9. A fully fiberized 40 μm core diameter photonic crystal fiber amplifier, characterized in that: include: An input optical fiber, comprising a signal polarization-maintaining optical fiber with a core diameter of 10 μm and a plurality of pump optical fibers, wherein the signal polarization-maintaining optical fiber is used to transmit signal light, and the pump optical fiber is used to transmit pump light; A beam combiner, whose input ports are respectively connected to the signal polarization-maintaining optical fiber and the pump optical fiber, and is used to couple the signal light and the pump light; And an output polarization-maintaining fiber with a core diameter of 20 μm, whose input end is connected to the output port of the combiner, whose output end is fused to the input end of a photonic crystal gain fiber with a core diameter of 40 μm, and the output end of the photonic crystal gain fiber with a core diameter of 40 μm is fused to the end cap, and the mode field diameters of the photonic crystal gain fiber with a core diameter of 40 μm and the output polarization-maintaining fiber with a core diameter of 20 μm are different.

10. A fully fiberized 40 μm core diameter photonic crystal fiber amplifier according to claim 9, characterized in that: The pump optical fibers are provided with six pieces, and the core diameter of the pump optical fibers is 105 μm. The beam combiner is a (6+1)×1 beam combiner.

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