Reverse pumping / signal beam combiner, preparation method and application

Abstract

The invention provides a reverse pumping / signal beam combiner, a preparation method and application, a hollow-core optical fiber is used as a signal optical fiber of the beam combiner, the same ends of the signal optical fiber and a plurality of pumping optical fibers form a beam combining end of an optical fiber bundle through fused biconical taper beam combination, and the signal optical fiber is located in the center of the optical fiber bundle. The other pumping optical fibers are evenly distributed on the periphery of the signal optical fiber, the output optical fiber is welded to the beam combining end of the optical fiber bundle, fiber cores of the hollow-core optical fiber and the output optical fiber in the optical fiber bundle are aligned, Fresnel reflection can occur at a melting point formed by close welding of the end faces of the hollow-core optical fiber and the output optical fiber, and the output optical fiber is matched with a mode field of the hollow-core optical fiber. The prepared reverse pumping / signal beam combiner can be applied to an optical fiber laser system and simultaneously undertakes the tasks of the reverse pumping / signal beam combiner and a low-reflectivity grating, and the hollow-core optical fiber can more flexibly control the output light mode and the light beam quality.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of optical fiber devices, and in particular to a reverse pump / signal combiner, a preparation method and an application thereof. Background Art

[0002] Hollow-core optical fiber can confine light to the hollow core by virtue of its unique structure, providing a propagation environment in near-free space. Compared with traditional solid-core optical fiber, it has a higher damage threshold, lower optical nonlinear effects, and lower waveguide dispersion, and has broad application prospects in sensing, communications, fiber gas lasers, and high-power laser transmission. In order to apply hollow-core optical fibers with excellent performance in traditional fiber laser systems, two methods have been developed: spatial optical path coupling and fiber fusion splicing to achieve high-efficiency coupling between solid-core optical fiber and hollow-core optical fiber. Among them, the fiber fusion splicing method has developed technical means that can achieve mode field matching, withstand high-power lasers, and have low losses, and is expected to achieve miniaturization and all-fiber integration.

[0003] Fiber lasers have the advantages of compact structure, high conversion efficiency, good beam quality and flexible transmission. They have been widely used in many fields such as industrial processing, scientific research, biomedicine, etc. With the improvement of pumping schemes and the improvement of the performance of fiber passive devices, the output power of fiber laser systems has been continuously improved. However, with the increase of optical power, the nonlinear effect in the system becomes more obvious, which limits the increase of the output power of the fiber laser system and affects the beam quality of the output light. Studies have found that the nonlinear threshold of the system can be effectively improved by adopting a reverse pumping scheme, reducing the fiber length and using optical fibers with large mode field diameters. The reverse pump / signal combiner is the core device for realizing reverse pumping in fiber lasers. It is responsible for efficiently coupling the pump light into the active fiber cladding and transmitting the signal light with high quality. Its performance directly determines the pumping capacity of the laser system and the output optical power level.

[0004] The input signal fiber of the reverse pump / signal combiner is generally used as the output fiber of the entire fiber laser system. In order to reduce the nonlinear effect, the length of the signal fiber of the reverse pump / signal combiner is relatively short, usually only 2-3 m, which limits the application scenarios of high-power fiber lasers. In addition, the important fiber components in the all-fiber structure fiber laser system include fiber gratings, pump / signal combiners, cladding light filters, end caps, etc., which are connected by melting points. Too many melting points will affect the stability of the system and the output beam quality to a certain extent. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a reverse pump / signal combiner, a preparation method and an application thereof.

[0006] Specifically, the technical solution of the present invention is: On the one hand, a method for preparing a reverse pump / signal combiner is proposed, comprising the following steps: According to the specific application scenario requirements, solid core fiber and hollow core fiber are selected as the output fiber and signal fiber of the reverse pump / signal combiner respectively; The output optical fiber is obtained by heating and expanding the solid core optical fiber or performing a fusion taper operation and then cutting it at a flat angle, so that the output optical fiber and the hollow core optical fiber can achieve mode field matching; Prepare pump optical fibers and placeholder optical fibers, use a multi-hole tube optical fiber fixture to assist in bundling the pump optical fibers and the placeholder optical fibers, and obtain a first optical fiber bundle, wherein a certain length of coating layer is stripped off one end of each pump optical fiber and the placeholder optical fiber, and multiple pump optical fibers are evenly arranged on the periphery of the placeholder optical fiber; The first optical fiber bundle is passed through the pre-tapered glass tube to obtain the second optical fiber bundle of the sleeve; Extracting the placeholder optical fiber from the second optical fiber bundle to obtain a third optical fiber bundle; Melting and taper-forming the third optical fiber bundle to obtain a fourth optical fiber bundle, wherein a center hole is maintained at the center of the fourth optical fiber bundle; Using an optical fiber cutter to cut the waist region of the fourth optical fiber bundle obtained after the fusion taper, ensuring that the waist region of the optical fiber bundle has a certain length after cutting and the end face of the waist region is flat and of good quality, to obtain a fifth optical fiber bundle, wherein the center of the fifth optical fiber bundle maintains a center hole; Stripping a certain length of coating layer from one end of the hollow-core optical fiber, and at the same time, etching the cladding layer of the end of the hollow-core optical fiber from which the coating layer is stripped according to the size of the central hole of the fifth optical fiber bundle and performing a flat-angle cutting after etching, so that the hollow-core optical fiber can be inserted into the central hole; Inserting the hollow-core optical fiber after the corrosion treatment into the central hole of the fifth optical fiber bundle to complete the bundle assembly, thereby obtaining a sixth optical fiber bundle; The sixth fiber bundle is fused with the output fiber: first, the hollow-core fiber and the output fiber core are aligned by using the beam quality feedback alignment system, and then the hollow-core fiber is moved away from the melting point (i.e., the melting point when the fifth fiber bundle is fused with the output fiber) by using a precision translation stage, and the fifth fiber bundle is fused with the output fiber by using a fiber fusion splicer, and finally, the hollow-core fiber is moved by using a precision translation stage to bring the end faces of the hollow-core fiber in the sixth fiber bundle and the output fiber close together and then fused; Complete the fabrication of the reverse pump / signal combiner.

[0007] The hollow-core fiber in the sixth fiber bundle is fused with the output fiber: first, the beam quality feedback alignment system is used to align the cores of the hollow-core fiber and the output fiber, and then the precision translation stage is used to move the hollow-core fiber away from the melting point to avoid deformation of the microstructure of the hollow-core fiber when the fifth fiber bundle is fused with the output fiber. The fifth fiber bundle is fused with the output fiber using a fiber fusion splicer, and finally, the precision translation stage is used to close the end faces of the hollow-core fiber in the sixth fiber bundle and the output fiber and then fused. During the fusion process, the discharge amount is controlled so that the microstructure of the hollow-core fiber will not be deformed or collapsed. Complete the fabrication of the reverse pump / signal combiner.

[0008] Furthermore, the present invention also includes: a certain length of hollow-core fiber roughening section is arranged on the signal optical fiber at a certain distance from the combining end of the reverse pump / signal combiner as a cladding light filter, and the hollow-core fiber roughening section is formed by stripping off the coating layer of the hollow-core optical fiber of a certain length and then corroding the roughened hollow-core optical fiber cladding with a corrosive agent.

[0009] Furthermore, the hollow-core fiber is one of antiresonant hollow-core fiber, kagome fiber, nested antiresonant hollow-core fiber, hollow-core photonic bandgap fiber, capillary fiber, and multi-hollow fiber, and the length of the hollow-core fiber can be flexibly selected according to specific application requirements, and the length can be 3-100 m, or even longer. According to the requirements of the output beam quality of the fiber laser, the number of modes supported by the appropriate hollow-core fiber is selected, such as single-mode hollow-core fiber or few-mode hollow-core fiber, and the mode filtering and selection functions are performed at the reverse pump / signal combiner using the number of modes supported by the hollow-core fiber to achieve precise control of the number of modes and beam quality of the laser output light.

[0010] On the other hand, the present invention provides a reverse pump / signal combiner prepared by the preparation method of a reverse pump / signal combiner, comprising a signal optical fiber, an output optical fiber and multiple pump optical fibers, wherein the signal optical fiber is a hollow core optical fiber, the output optical fiber is a solid core optical fiber, the same end of the signal optical fiber and the multiple pump optical fibers are fused and tapered to form a combined end of the optical fiber bundle, the combined end of the optical fiber bundle has a cone region and a waist region, the signal optical fiber is located at the center of the optical fiber bundle, and the remaining multiple pump optical fibers are evenly arranged on the periphery of the signal optical fiber, the output optical fiber is fused to the combined end of the optical fiber bundle, and the cores of the hollow core optical fiber in the optical fiber bundle and the output optical fiber are aligned and the end faces of the two are tightly fused to form a melting point to form a Fresnel reflection, and the mode field of the output optical fiber is matched with that of the hollow core optical fiber.

[0011] Furthermore, a certain length of hollow-core fiber roughening section is provided on the signal optical fiber at a certain distance from the beam combining end as a cladding light filter, and the hollow-core fiber roughening section is formed by stripping off a certain length of the coating layer of the hollow-core optical fiber and then corroding the roughened hollow-core optical fiber cladding with a corrosive agent.

[0012] The reverse pump / signal combiner prepared by the above-mentioned reverse pump / signal combiner preparation method can be applied to the fiber laser system, and simultaneously undertakes the tasks of the reverse pump / signal combiner and the low reflectivity grating, which can simplify the fiber laser structure, realize high-quality long-distance transmission of the laser in the laser output fiber, meet the needs of some remote operations of high-power fiber lasers, and expand its application scenarios.

[0013] Compared with the conventional reverse pump / signal combiner in which the signal optical fiber is a solid core optical fiber, the beneficial effects of the present invention are as follows: (1) By using hollow-core optical fiber with lower nonlinear effects, the signal fiber length of the reverse pump / signal combiner can be longer in the high-power fiber laser system, and the fiber laser system and output port can be distributed over long distances, which can ensure the remote operation of the laser system in special environments and expand the application scenarios of high-power fiber lasers; (2) According to specific application requirements, flexibly select hollow-core fibers that support different numbers of modes, including single-mode hollow-core fibers, few-mode hollow-core fibers, and multi-mode hollow-core fibers, so as to control the number of modes and beam quality of the output light of the fiber laser system and meet the application requirements of different scenarios; (3) The output fiber and the hollow-core fiber are directly fused at a flat angle. The Fresnel reflection at the melting point can play the role of a low-reflectivity grating and participate in the formation of the resonant cavity of the fiber laser. (4) The reverse pump / signal combiner prepared by the method of the present invention is applied to a fiber laser. Compared with a conventional fiber laser system, the present invention integrates the functions of a conventional reverse pump / signal combiner, a low reflectivity grating, and a cladding light filter into one reverse pump / signal combiner based on a hollow-core fiber, thereby reducing the melting point in the fiber laser system, which is beneficial to improving the stability of the system and reducing the degradation of the output light beam quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0015] Figure 1 A schematic diagram of the structure of a hollow core optical fiber after cladding corrosion, roughening, and cutting in one embodiment; Figure 2 Schematic diagram of the structure of a reverse pump / signal combiner after fusion in one embodiment; Figure 3 A schematic diagram of a fiber laser system constructed in one embodiment; Figure 4 : is a mode field distribution diagram of a light wave mode that can be stably transmitted in a triple-nested anti-resonant hollow-core optical fiber used in an embodiment, wherein Figure 4 (a) is the fundamental mode field distribution diagram of hollow core optical fiber. Figure 4 (b) LP of hollow core fiber 11 Mode field distribution diagram.

[0016] Figure annotation: 1. Hollow-core fiber; 2. Reverse pump / signal combiner; 11. Hollow-core fiber corrosion section; 12. Hollow-core fiber roughening section; 21. Output fiber; 22. Output fiber core expansion area; 23. Waist region; 24. Taper region; 25. Pump fiber; 31. Forward pump combiner; 32. High reflectivity fiber Bragg grating; 33. Gain fiber; 34. End cap. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Reference Figure 1 An embodiment of the present invention provides a method for preparing a reverse pump / signal combiner, comprising the following steps: (1) Prepare materials: According to the specific application scenario requirements, solid core fiber and hollow core fiber are selected as the output fiber and signal fiber of the reverse pump / signal combiner respectively; The output optical fiber is obtained by heating and expanding the solid core optical fiber or performing a fusion taper operation and then cutting it at a flat angle, so that the output optical fiber and the hollow core optical fiber can achieve mode field matching; A pump fiber and a placeholder fiber are prepared, and a multi-hole tube fiber fixture is used to assist in bundling the pump fiber and the placeholder fiber to obtain a first fiber bundle, wherein a certain length of coating layer is stripped off one end of each pump fiber and the placeholder fiber, and multiple pump fibers are evenly arranged on the periphery of the placeholder fiber.

[0019] (2) Bundle: The first optical fiber bundle is passed through the pre-tapered glass tube to obtain the second optical fiber bundle of the sleeve; Extracting the placeholder optical fiber from the second optical fiber bundle to obtain a third optical fiber bundle; Melting and taper-forming the third optical fiber bundle to obtain a fourth optical fiber bundle, wherein a center hole is maintained at the center of the fourth optical fiber bundle; Using an optical fiber cutter to cut the waist region of the fourth optical fiber bundle obtained after the fusion taper, ensuring that the waist region of the optical fiber bundle has a certain length after cutting and the end face of the waist region is flat and of good quality, to obtain a fifth optical fiber bundle, wherein the center of the fifth optical fiber bundle maintains a center hole; Stripping a certain length of coating layer from one end of the hollow-core optical fiber, and at the same time, etching the cladding layer of the end of the hollow-core optical fiber from which the coating layer is stripped according to the size of the central hole of the fifth optical fiber bundle and performing a flat-angle cutting after etching, so that the hollow-core optical fiber can be inserted into the central hole; Inserting the hollow-core optical fiber after the corrosion treatment into the central hole of the fifth optical fiber bundle to complete the bundle assembly, thereby obtaining a sixth optical fiber bundle; The hollow-core fiber in the sixth fiber bundle is fused with the output fiber: first, the beam quality feedback alignment system is used to align the cores of the hollow-core fiber and the output fiber, and then the precision translation stage is used to move the hollow-core fiber away from the melting point to avoid deformation of the microstructure of the hollow-core fiber when the fifth fiber bundle is fused with the output fiber. The fifth fiber bundle is fused with the output fiber using a fiber fusion splicer, and finally, the precision translation stage is used to close the end faces of the hollow-core fiber in the sixth fiber bundle and the output fiber and then fused. During the fusion process, the discharge amount is controlled so that the microstructure of the hollow-core fiber will not be deformed or collapsed. Complete the fabrication of the reverse pump / signal combiner.

[0020] The hollow-core fiber used as the signal fiber of the reverse pump / signal combiner in the present invention has the following advantages: the hollow-core fiber has a lower nonlinear effect, and the reverse pump / signal combiner with the signal fiber as the hollow-core fiber is applied to the high-power fiber laser system. The length of the signal fiber of the reverse pump / signal combiner can be longer, and the fiber laser system and the output port can be distributed over long distances, which can ensure the remote operation of the laser system in special environments and expand the application scenarios of high-power fiber lasers. Flexible selection of hollow-core fibers that support different numbers of modes can realize the control of the number of modes and beam quality of the output light of the fiber laser system, and meet the needs of various application scenarios. The output fiber and the hollow-core fiber are both cut at a flat angle, that is, the cut end faces of the output fiber and the hollow-core fiber are at a flat angle to ensure that Fresnel reflection occurs at the melting point formed by the fusion of the output fiber and the hollow-core fiber. In the process of fusing the hollow-core fiber in the sixth fiber bundle with the output fiber, the end faces (both planes) of the hollow-core fiber and the output fiber are closely fused, and the Fresnel reflection at the melting point can play the role of a low-reflectivity grating and participate in the formation of the resonant cavity of the fiber laser. In this way, the reverse pump / signal combiner and the low reflectivity grating can be integrated into one reverse pump / signal combiner, which reduces the melting point in the fiber laser system, is beneficial to improving the stability of the system and reducing the degradation of the output light beam quality.

[0021] The present invention obtains an output optical fiber by heating and expanding the core or melting and taper-pulling the solid core optical fiber and then cutting it at a flat angle, so that the output optical fiber and the hollow core optical fiber can achieve mode field matching and reduce the loss caused by mode field mismatch. Specifically, the following steps are included: Calculate the mode field diameter of solid core fiber and hollow core fiber; Based on the calculated mode field diameters of the solid core fiber and the hollow core fiber, determine whether to perform heating core expansion or melt taper operation on the solid core fiber. If the mode field diameter of the solid core fiber is larger than the mode field diameter of the hollow core fiber, melt taper is performed on the solid core fiber. If the mode field diameter of the solid core fiber is smaller than the mode field diameter of the hollow core fiber, heat and expand the solid core fiber. Calculate the mode field diameter of the output optical fiber that can achieve mode field matching between the output optical fiber and the hollow-core optical fiber, determine the core diameter of the output optical fiber that achieves mode field matching, and further determine the heating core expansion or fusion taper parameters of the solid-core optical fiber; According to the determined melt taper or heating core expansion parameters, one end of the solid core optical fiber is subjected to heating core expansion or melt taper operation to obtain an output optical fiber, and the output optical fiber and the hollow core optical fiber can achieve mode field matching.

[0022] The fusion taper method uses a taper machine to taper the output optical fiber, uses a torch to heat the optical fiber, and the clamps on both sides of the torch move at different speeds to achieve precise taper of the optical fiber. By setting parameters such as the torch fire volume, the movement speed of the optical fiber clamp, the size and length of the taper zone and waist zone, the shape and size of the optical fiber after taper can be accurately controlled, the size of the cladding and the core can be reduced, and the mode field diameter can be reduced. The taper parameters mainly include: the length and size of the taper waist zone and the taper zone, and the length of the taper zone needs to meet the adiabatic taper conditions.

[0023] The heating core expansion method heats the output optical fiber through a hydrogen-oxygen flame, causing the doping in the optical fiber core to diffuse into the cladding, expanding the core diameter and thus achieving an expansion of the mode field diameter.

[0024] like Figure 1The structure diagram of the hollow-core optical fiber after cladding corrosion, roughening and cutting in one embodiment is shown. A certain length of coating is stripped from one end of the hollow-core optical fiber 1. The hollow-core optical fiber stripped of the coating is the hollow-core optical fiber to be corroded. Before the cladding of the hollow-core optical fiber stripped of the coating is corroded according to the size of the central hole of the fifth optical fiber bundle, a solid-core optical fiber is first fused to the end of the hollow-core optical fiber 1 to be corroded to prevent the corrosive liquid from entering the hollow-core optical fiber and destroying the internal structure. The cladding size of the fused solid-core optical fiber must be larger than the size of the microstructure area of ​​the hollow-core optical fiber. Then, the hollow-core optical fiber cladding is corroded by using a hydrofluoric acid solution. By controlling the corrosion time, a hollow-core optical fiber corrosion segment 11 with an optical fiber cladding size matching the size of the central hole of the fifth optical fiber bundle is obtained. Furthermore, the preparation method of the reverse pump / signal combiner provided in one embodiment, in addition to the steps provided in the above embodiments, further includes: a certain length of hollow-core fiber roughening section 12 is provided on the signal optical fiber at a certain distance from the beam combining end of the reverse pump / signal combiner as a cladding light filter, and the hollow-core fiber roughening section 12 is formed by stripping the coating layer of a certain length of the hollow-core optical fiber and then corroding the hollow-core optical fiber cladding with an etchant. In this way, the functions of the reverse pump / signal combiner, the low reflectivity grating, and the cladding light filter can be integrated into one reverse pump / signal combiner. When the reverse pump / signal combiner is applied to a fiber laser, the melting point in the fiber laser system will be reduced, which is beneficial to improving the stability of the system and reducing the degradation of the output light beam quality.

[0025] Preferably, when the hollow-core optical fiber cladding is corroded by hydrofluoric acid solution, multiple hollow-core optical fibers can be set up as controls at the same time. In the early stage, a control optical fiber is taken out at the same time intervals to measure the diameter to obtain a more accurate corrosion rate and calculate the accurate corrosion time. In the later stage, when the calculated corrosion time is approaching, a fiber is taken out at shorter intervals to measure its diameter until the appropriate optical fiber cladding size is obtained.

[0026] The type of hollow core fiber described in the present invention is not limited, and can be any one of antiresonant hollow core fiber, kagome fiber, nested antiresonant hollow core fiber, hollow core photonic bandgap fiber, capillary fiber, and multi-hollow fiber, and according to specific application requirements, the length of the hollow core fiber can be flexibly selected, and its length can be 3-100 m, or even longer. According to the requirements of the output beam quality of the fiber laser, the number of modes supported by the appropriate hollow core fiber is selected, such as single-mode hollow core fiber or few-mode hollow core fiber, and the mode filtering and selection functions are performed at the reverse pump / signal combiner using the number of modes supported by the hollow core fiber to achieve precise control of the number of modes and beam quality of the laser output light.

[0027] In one embodiment, a double-clad output fiber with a core / cladding size of 20 / 400 μm (NA=0.06 / 0.46), a hollow core fiber of 30 / 250 μm, and 6 double-clad pump fibers with structural parameters of 220 / 242 μm (NA=0.22) are used as examples to illustrate the preparation method of the reverse pump / signal combiner provided by the present invention. The specific steps are as follows: (1) Prepare materials: Prepare output optical fiber, signal optical fiber, pump optical fiber and glass tube, among which the output optical fiber is a 20 / 400 μm (NA=0.06 / 0.46) double-clad solid core optical fiber, the signal optical fiber is a hollow core optical fiber 1 with a core of 30 μm, an inner cladding of 87 μm, an outer cladding of 240 μm, and a capillary thickness of 1.15-1.2 μm, the pump optical fiber 25 uses six 220 / 242 μm (NA=0.22) double-clad solid core optical fibers, and the glass tube is a thin-walled semi-doped fluorine glass tube with an inner / outer diameter of 850 / 1000 μm.

[0028] The mode field diameters of the output fiber and the hollow-core fiber are calculated according to the wavelength to be applied. Taking the wavelength to be applied as 1080 nm as an example, it can be obtained that the mode field diameter of the selected 20 / 400 μm (NA=0.06 / 0.46) double-clad fiber is smaller than the mode field diameter of the hollow-core fiber 1, so the selected 20 / 400 μm (NA=0.06 / 0.46) double-clad fiber needs to be heated and expanded to match the mode fields of the output fiber and the hollow-core fiber. It can be calculated that the core diameter of the 20 / 400 μm (NA=0.06 / 0.46) double-clad fiber used as the output fiber needs to be heated and expanded to about 26 μm. The output fiber core expansion area 22 is obtained by the heating and core expansion method to achieve mode field matching between the solid-core output fiber 21 and the hollow-core fiber 1. The heating core expansion is to discharge the electrode of the fusion splicer on the end face of the optical fiber or heat it with a hydrogen-oxygen flame, so that the doping substances in the optical fiber core diffuse into the cladding, so that the optical fiber mode field increases with the size of the core, and the size of the cladding remains almost unchanged during the heating process. The core diameter of the core expansion area 22 of the output optical fiber changes gradually, and the diameter gradually decreases to the original core diameter size as the distance from the heat source increases. The mode field diameter of the output optical fiber in this embodiment is smaller than the mode field diameter of the hollow core optical fiber. The core diameter of the output optical fiber is expanded to 26 μm by accurately controlling the heating time, and then the output optical fiber is cut in the middle area of ​​the heating core expansion, and the diameter of the cut optical fiber core is observed using a microscope to ensure that the output optical fiber core meets the mode field matching conditions.

[0029] It can be further determined that the hollow-core optical fiber needs to be etched to 133 μm, and the glass tube needs to be pre-tapered to 726 / 854 μm.

[0030] At one end of the hollow-core optical fiber 1, a coating layer of about 8 cm in length is stripped off, and a solid core optical fiber with a cladding diameter of 250 μm is fused to the end from which the coating layer is stripped off, and then a hydrofluoric acid solution is inserted to perform cladding corrosion, and multiple control hollow-core optical fibers are set up to detect the corrosion process. After the corrosion is completed, a flat-angle cut is performed to obtain a hollow-core optical fiber corrosion segment 11 with a diameter of 133 μm. About 1 m before the other end of the hollow-core optical fiber 1, a coating layer of about 5 cm in length is stripped off, and then a corrosive agent made of 55% hydrofluoric acid and glass frosting paste is used to roughen the cladding of the coating stripping segment to obtain a hollow-core optical fiber roughening segment 12 with a length of 3 cm, as shown in FIG. Figure 1 The figure is a schematic diagram of the structure of a hollow core optical fiber after cladding corrosion, roughening and cutting in one embodiment.

[0031] Prepare 7 220 / 242 μm (NA=0.22) double-clad solid-core optical fibers, and insert the 7 optical fibers into a 7-hole optical fiber fixture to obtain the first optical fiber bundle, wherein the optical fiber inserted from the central hole of the 7-hole optical fiber fixture is the placeholder optical fiber, and the other optical fibers inserted from the 6 holes evenly distributed around are pump optical fibers 25, wherein one end of each pump optical fiber and the placeholder optical fiber is stripped of a coating layer of about 8 cm in length, and the placeholder optical fiber inserted into the central hole can also be stripped of a slightly longer length of the coating layer to facilitate the distinction between the pump optical fiber and the placeholder optical fiber, and then wipe it clean with anhydrous ethanol to ensure that the surface of the optical fiber cladding is clean.

[0032] Use anhydrous ethanol to clean the wall of the glass tube, and then pre-tap it to an inner / outer diameter of 726 / 854 μm, a waist length of about 3 cm, and a taper length of about 8 mm at both ends for use.

[0033] (2) Bundle: Align the stripped ends of the fiber coating of the first fiber bundle. At this time, the end face of the pump fiber 25 is flush, while the placeholder fiber is slightly longer. Insert the first fiber bundle into anhydrous ethanol, and continuously shake and twist the 7-hole fiber clamp to make the placeholder fiber in the center. The pump fibers are neatly and straightly arranged around the placeholder fiber to avoid staggered twisting of the pump fibers. Then, slowly pull it out of the anhydrous ethanol and insert it into the pre-tapered glass tube to obtain the second fiber bundle of the sleeve. There is a slight resistance during the process of inserting the fiber bundle, indicating that the inner diameter of the glass tube is close to the diameter of the fiber bundle.

[0034] The placeholder optical fiber is extracted from the second optical fiber bundle, and the optical fiber bundle is placed on a heating table and an exhaust fan is used to extract the residual anhydrous ethanol in the glass tube to prevent the glass tube and the optical fiber bundle from being burned in the subsequent taper drawing process, thereby obtaining a third optical fiber bundle.

[0035] Adjust the taper parameters to taper the fiber bundle, including the amount of fire head, taper speed, taper area and waist area size, etc. The parameters of the taper area 24 and waist area 23 of the fiber bundle need to meet the adiabatic taper conditions. The length of the taper area 24 can be set to 1.5 cm, the length of the waist area 23 can be set to 3 cm, and the waist area diameter can be the same as the output fiber cladding diameter of 400 μm. The third fiber bundle is melt tapered to obtain a fourth fiber bundle, and the center of the fourth fiber bundle maintains a center hole.

[0036] The waist region of the fourth optical fiber bundle obtained after the fusion taper is cut with an optical fiber cutter to ensure that the waist region of the optical fiber bundle has a certain length (about 2 cm) after cutting and the end face of the waist region is flat and of good quality, thereby obtaining a fifth optical fiber bundle, wherein the center of the fifth optical fiber bundle maintains a center hole.

[0037] The hollow-core optical fiber after cladding corrosion, roughening and cutting is inserted into the central hole of the fifth optical fiber bundle to complete the bundle assembly and obtain the sixth optical fiber bundle.

[0038] The sixth fiber bundle is fused with the output fiber: first, the beam quality feedback alignment system is used to align the cores of the hollow-core fiber and the output fiber, and then the precision translation stage is used to move the hollow-core fiber in the sixth fiber bundle, so that the hollow-core fiber is far away from the melting point (i.e., the melting point when the fifth fiber bundle is fused with the output fiber, where the fifth fiber bundle is the fiber bundle outside the hollow-core fiber of the sixth fiber bundle), to avoid deformation of the microstructure of the hollow-core fiber when the fifth fiber bundle is fused with the output fiber, and the fifth fiber bundle is fused with the output fiber using a fiber fusion splicer, and finally, the precision translation stage is used to move the hollow-core fiber in the sixth fiber bundle, so that the end faces of the hollow-core fiber in the sixth fiber bundle and the output fiber are close together, and the discharge amount is controlled during the fusion process so that the microstructure of the hollow-core fiber will not be deformed or collapsed. In the process of fusion of the hollow-core fiber and the output fiber, the beam quality feedback alignment is used to ensure that the cores of the hollow-core fiber in the sixth fiber bundle and the output fiber are aligned, so as to reduce the insertion loss and reduce the impact on the light spot characteristics of the device.

[0039] Finally, the reverse pump / signal combiner is fabricated.

[0040] The present invention adopts a two-step fusion method. After alignment is achieved, the fifth optical fiber bundle is first fused with the output optical fiber, and then the hollow-core optical fiber and the output optical fiber end face are pressed tightly together using a precision translation stage, and a small discharge amount is used for fusion, ensuring that the hollow-core optical fiber microstructure will not deform or collapse during the fusion process.

[0041] like Figure 2As shown, a reverse pump / signal combiner prepared by the preparation method of the reverse pump / signal combiner provided by the above embodiment is provided, comprising a signal fiber, an output fiber 21 and a plurality of pump fibers 25, wherein the signal fiber is a hollow core fiber 1, and the output fiber 21 is a solid core fiber. The same end of the signal fiber and the plurality of pump fibers 25 are fused and tapered to form a combined end of the fiber bundle, and the combined end of the fiber bundle has a cone region 24 and a waist region 23. The signal fiber is located at the center of the fiber bundle, and the remaining plurality of pump fibers 25 are evenly arranged on the periphery of the signal fiber. The output fiber 21 is fused with the combined end of the fiber bundle, and the cores of the hollow core fiber 1 and the output fiber 21 in the fiber bundle are aligned, and the cores of the hollow core fiber 1 and the output fiber 21 in the fiber bundle are aligned, and the end faces of the two are closely fused to form a melting point where Fresnel reflection can occur, and the mode field of the output fiber 21 is matched with that of the hollow core fiber 1. In this embodiment, the output optical fiber 21 has an output optical fiber core expansion region 22 to ensure that the mode field of the output optical fiber 21 matches that of the hollow core optical fiber 1. The cut end faces of the output optical fiber 21 and the hollow core optical fiber 1 are at a flat angle to ensure that Fresnel reflection occurs at the melting point formed by the fusion of the output optical fiber 21 and the hollow core optical fiber 1. Furthermore, a certain length of hollow core optical fiber roughening section 12 is provided on the signal optical fiber at a certain distance from the beam combining end as a cladding light filter, and the hollow core optical fiber roughening section 12 is formed by stripping a certain length of the coating layer of the hollow core optical fiber and then corroding the roughened hollow core optical fiber cladding with an etchant.

[0042] The reverse pump / signal combiner prepared in the above embodiment is applied to a high beam quality fiber laser system, and simultaneously realizes the functions of the reverse pump / signal combiner, the low reflectivity grating and the cladding light filter. Figure 3It is a schematic diagram of a fiber laser system constructed in an embodiment, including a forward pumping combiner 31, a high reflectivity fiber grating 32, a gain fiber 33, a reverse pumping / signal combiner 2 based on a hollow core fiber, and an end cap 34. The forward pumping combiner 31, the high reflectivity fiber grating 32, the gain fiber 33, the reverse pumping / signal combiner 2 and the end cap 34 are connected in sequence, and the signal fiber of the reverse pumping / signal combiner is used as the output fiber of the signal light. The reverse pumping / signal combiner plays the functions of pumping light injection, signal light transmission, forming a resonant cavity, cladding light filtering and long-distance transmission of output light in the fiber laser system. Thanks to the advantage of the low nonlinear effect of the hollow core fiber 1, a relatively long hollow core fiber 1 can be used as the output fiber of the fiber laser system, which expands the application of high-power fiber lasers. The reverse pumping / signal combiner 2 based on the hollow core fiber 1 realizes multi-functional integration, reduces the melting point in the system, and can effectively improve the stability of the system and reduce the risk of beam quality degradation. The output fiber core expansion region 22 in the reverse pump / signal combiner 2 may introduce high-order modes that affect the beam quality of the output light of the fiber laser system. In order to solve this problem, in one embodiment, only the fundamental mode, LP mode, and 1080 nm wavelength are selected to transmit. 11 The three-nested antiresonant hollow-core fiber with the same mode as the 20 / 400 μm solid fiber can effectively filter out the high-order modes introduced by the output fiber core expansion area 22 and ensure low loss and good beam quality, such as Figure 4 As shown, Figure 4 : is a mode field distribution diagram of a light wave mode that can be stably transmitted in the triple-nested anti-resonant hollow-core optical fiber used in this embodiment, wherein Figure 4 (a) is the fundamental mode field distribution diagram of hollow core optical fiber. Figure 4 (b) LP of hollow core fiber 11 Mode field distribution diagram.

[0043] Furthermore, according to specific application requirements, single-mode hollow-core optical fibers, few-mode hollow-core optical fibers, or multi-mode hollow-core optical fibers with different microstructures and sizes can be selected. By selecting the corresponding hollow-core optical fibers, the output light mode and beam quality of the fiber laser system can be controlled more flexibly, and laser output with different beam qualities can be achieved to meet various application requirements. The present invention can simplify the structure of the fiber laser, realize high-power laser high-quality long-distance transmission of the laser in the laser output optical fiber, and effectively control the output light beam quality.

[0044] Matters not covered by the present invention are known technologies.

[0045] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0046] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a reverse pump / signal combiner, characterized in that: The following steps are involved: According to the specific application scenario requirements, solid core fiber and hollow core fiber are selected as the output fiber and signal fiber of the reverse pump / signal combiner respectively; The output optical fiber is obtained by heating and expanding the solid core optical fiber or performing a fusion taper operation and then cutting it at a flat angle, so that the output optical fiber and the hollow core optical fiber can achieve mode field matching; Prepare pump optical fibers and placeholder optical fibers, use a multi-hole tube optical fiber fixture to assist in bundling the pump optical fibers and the placeholder optical fibers, and obtain a first optical fiber bundle, wherein a certain length of coating layer is stripped off one end of each pump optical fiber and the placeholder optical fiber, and multiple pump optical fibers are evenly arranged on the periphery of the placeholder optical fiber; The first optical fiber bundle is passed through the pre-tapered glass tube to obtain the second optical fiber bundle of the sleeve; Extracting the placeholder optical fiber from the second optical fiber bundle to obtain a third optical fiber bundle; Melting and taper-forming the third optical fiber bundle to obtain a fourth optical fiber bundle, wherein a center hole is maintained at the center of the fourth optical fiber bundle; Using an optical fiber cutter to cut the waist region of the fourth optical fiber bundle obtained after the fusion taper, ensuring that the waist region of the optical fiber bundle has a certain length after cutting and the end face of the waist region is flat and of good quality, to obtain a fifth optical fiber bundle, wherein the center of the fifth optical fiber bundle maintains a center hole; Stripping a certain length of coating layer from one end of the hollow-core optical fiber, and at the same time, etching the cladding layer of the end of the hollow-core optical fiber from which the coating layer is stripped according to the size of the central hole of the fifth optical fiber bundle and performing a flat-angle cutting after etching, so that the hollow-core optical fiber can be inserted into the central hole; Inserting the hollow-core optical fiber after the corrosion treatment into the central hole of the fifth optical fiber bundle to complete the bundle assembly, thereby obtaining a sixth optical fiber bundle; The sixth fiber bundle is fused with the output fiber: first, the hollow-core fiber and the output fiber core are aligned by using the beam quality feedback alignment system, then the hollow-core fiber is moved away from the melting point by using the precision translation stage, and the fifth fiber bundle is fused with the output fiber by using the fiber fusion splicer, and finally, the hollow-core fiber is moved by using the precision translation stage to bring the end faces of the hollow-core fiber in the sixth fiber bundle and the output fiber close together and then fused; Complete the fabrication of the reverse pump / signal combiner.

2. The method for preparing the reverse pump / signal combiner according to claim 1, characterized in that: The output optical fiber is obtained by heating and expanding the solid core optical fiber or performing a fusion taper operation and then performing a flat-angle cutting operation so that the output optical fiber and the hollow core optical fiber can achieve mode field matching, including the following steps: Calculate the mode field diameter of solid core fiber and hollow core fiber; Based on the calculated mode field diameters of the solid core fiber and the hollow core fiber, determine whether to perform heating core expansion or melt taper operation on the solid core fiber. If the mode field diameter of the solid core fiber is larger than the mode field diameter of the hollow core fiber, melt taper is performed on the solid core fiber. If the mode field diameter of the solid core fiber is smaller than the mode field diameter of the hollow core fiber, heat and expand the solid core fiber. Calculate the mode field diameter of the output optical fiber that can achieve mode field matching between the output optical fiber and the hollow-core optical fiber, determine the core diameter of the output optical fiber that achieves mode field matching, and further determine the heating core expansion or fusion taper parameters of the solid-core optical fiber; According to the determined melt taper or heating core expansion parameters, one end of the solid core optical fiber is subjected to heating core expansion or melt taper operation to obtain an output optical fiber, and the output optical fiber and the hollow core optical fiber can achieve mode field matching.

3. The method for preparing the reverse pump / signal combiner according to claim 1, characterized in that: Before the cladding of one end of the hollow-core optical fiber stripped of the coating is corroded according to the size of the central hole of the fifth optical fiber bundle, a section of solid optical fiber is first fused to the end of the hollow-core optical fiber to be corroded to prevent the corrosive liquid from entering the hollow-core optical fiber and damaging the internal structure, wherein the cladding size of the fused section of solid optical fiber must be larger than the size of the microstructure area of ​​the hollow-core optical fiber; then the cladding of the hollow-core optical fiber is corroded by using a hydrofluoric acid solution, and by controlling the corrosion time, a hollow-core optical fiber with an optical fiber cladding size matching the size of the central hole of the fifth optical fiber bundle is obtained.

4. The method for preparing the reverse pump / signal combiner according to claim 1, 2 or 3, characterized in that: Also includes: A hollow-core fiber roughening section of a certain length is arranged on the signal optical fiber at a certain distance from the combining end of the reverse pump / signal combiner as a cladding light filter. The hollow-core fiber roughening section is formed by stripping off the coating layer of the hollow-core optical fiber of a certain length and then corroding the roughened hollow-core optical fiber cladding with a corrosive agent.

5. The method for preparing a reverse pump / signal combiner according to claim 1, characterized in that: The hollow-core fiber is one of an antiresonant hollow-core fiber, a kagome fiber, a nested antiresonant hollow-core fiber, a hollow-core photonic bandgap fiber, a capillary fiber, and a multi-hollow fiber. According to the requirements of the output beam quality of the fiber laser, a corresponding hollow-core fiber is selected, and the hollow-core fiber is used in a reverse pump / signal combiner to perform mode selection and filtering functions, so as to realize the control of the mode number and beam quality of the laser output light.

6. The reverse pump / signal combiner prepared by the method for preparing a reverse pump / signal combiner according to claim 1, characterized in that: The invention comprises a signal optical fiber, an output optical fiber and a plurality of pump optical fibers, wherein the signal optical fiber is a hollow core optical fiber, the output optical fiber is a solid core optical fiber, the same end of the signal optical fiber and the plurality of pump optical fibers are fused and tapered to form a combined end of the optical fiber bundle, the combined end of the optical fiber bundle has a cone region and a waist region, the signal optical fiber is located at the center of the optical fiber bundle, and the remaining plurality of pump optical fibers are evenly arranged at the periphery of the signal optical fiber, the output optical fiber is fused with the combined end of the optical fiber bundle, and the cores of the hollow core optical fiber in the optical fiber bundle are aligned with the cores of the output optical fiber, and the end faces of the two are closely fused to form a melting point to enable Fresnel reflection, and the mode field of the output optical fiber is matched with that of the hollow core optical fiber.

7. The reverse pump / signal combiner according to claim 6, characterized in that: The hollow-core fiber is one of an antiresonant hollow-core fiber, a kagome fiber, a nested antiresonant hollow-core fiber, a hollow-core photonic bandgap fiber, a capillary fiber, and a multi-hollow fiber. According to the requirements of the output beam quality of the fiber laser, a corresponding hollow-core fiber is selected, and the hollow-core fiber is used in a reverse pump / signal combiner to perform mode selection and filtering functions, so as to realize the control of the mode number and beam quality of the laser output light.

8. The reverse pump / signal combiner according to claim 6, characterized in that: A certain length of hollow-core fiber roughening section is provided on the signal optical fiber at a certain distance from the beam combining end as a cladding light filter. The hollow-core fiber roughening section is formed by stripping a certain length of the hollow-core optical fiber coating layer and then corroding the roughened hollow-core optical fiber cladding with a corrosive agent.

9. Application of the reverse pump / signal combiner prepared by the method for preparing the reverse pump / signal combiner as claimed in claim 1 in a fiber laser system.

10. The use according to claim 9, characterized in that: The fiber laser system includes a forward pump combiner, a high reflectivity fiber Bragg grating, a gain fiber, a reverse pump / signal combiner and an end cap. The forward pump combiner, the high reflectivity fiber Bragg grating, the gain fiber, the reverse pump / signal combiner and the end cap are connected in sequence, and the signal fiber of the reverse pump / signal combiner serves as the output fiber of the signal light.

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