Hollow Core Fiber Power Combiner

Abstract

The present invention relates to the technical field of optical fiber devices, and proposes a hollow-core fiber power combiner, including an optical fiber bundle and a hollow-core optical fiber, wherein the optical fiber bundle is formed by taper-forming n solid-core optical fibers; the input end of the optical fiber bundle is the large end of the optical fiber bundle, and the output end of the optical fiber bundle is the small end of the optical fiber bundle, wherein one of the n solid-core optical fibers in the optical fiber bundle is located at the center as the central optical fiber, and the remaining n-1 optical fibers are distributed around the center optical fiber; the hollow-core optical fiber is a nested anti-resonant hollow-core optical fiber, which includes an outer cladding, a nested ring and a hollow-core region from the inside to the outside, and n-1 nested rings are distributed around the periphery of the hollow-core region; the laser of the input optical fiber bundle is input into the hollow-core optical fiber through the small end of the optical fiber bundle, and the long-distance transmission of the laser is realized by using the hollow-core optical fiber. The present invention has a simple and compact structure, high coupling efficiency, can better maintain the purity of the beam mode, and has great application value and potential advantages for high-power long-distance transmission of optical fiber lasers.

Description

Technical Field

[0001] The invention mainly relates to the technical field of optical fiber devices, in particular to a hollow-core optical fiber power combiner. Background Art

[0002] In the past few years, with the improvement of fiber drawing process and pump source brightness, the development of fiber lasers has made major breakthroughs, especially in terms of power and brightness. With its excellent beam quality, efficient light-to-electric conversion efficiency and convenient thermal management, fiber lasers have been widely used in fields such as material processing, medical cosmetology, military defense, etc. Despite this, there are still some challenges in increasing the power of fiber lasers. The main difficulty in limiting the power increase of fiber lasers is that under high transmission power conditions, excessive power density will lead to strong nonlinear effects. This can be alleviated by increasing the fiber mode field area and reducing the transmission power density. The contradiction is that increasing the fiber mode field area can certainly weaken the nonlinear effect, but it will inevitably lead to the excitation of high-order modes in the fiber, thereby degrading the beam quality of the output laser. Taking the industrial application of high-power fiber lasers as an example, such as welding and cutting, it requires not only higher laser power, but also better beam quality to ensure processing accuracy. Therefore, how to achieve high-power output while ensuring high beam quality is the biggest challenge facing fiber laser technology. At present, it is difficult to further break through the output power of single-fiber near-single-mode optical fiber, and the maximum output power is in the order of 10,000 watts. For some application scenarios that require higher brightness and high-energy lasers, a single fiber may not be able to meet the application requirements.

[0003] Power combining can break through the bottleneck of increasing the power of a single laser and is a common solution to break through the power increase of a single fiber laser in recent years. However, since the laser is ultimately concentrated on a single optical fiber for transmission, the problem of beam quality degradation due to the larger mode field area is still unavoidable. Summary of the invention

[0004] In view of the defects and shortcomings of the prior art, the purpose of the present invention is to provide a hollow-core fiber power combiner, which realizes high-beam quality transmission of high-power laser by using hollow-core fiber. Hollow-core fiber (HCF) is a fiber with a special structure. In hollow-core fiber, the core part of the traditional optical fiber is replaced by gas / liquid or vacuum. Compared with ordinary solid optical fiber, due to its unique hollow-core structure, the interaction between light and optical fiber material during transmission inside it is greatly reduced, thereby greatly weakening the nonlinear effect. Therefore, even hollow-core fiber (single-mode) with a smaller mode field area can support long-distance transmission of high-power laser. The corresponding power combiner is designed using hollow-core fiber, and the size of the beam-forming fiber matching the hollow-core fiber is simulated and optimized. In order to ensure the transmission coupling efficiency, a smaller taper ratio is required, as well as the matching of the beam-forming fiber mode field and the hollow-core fiber mode field after taper. Such a hollow-core fiber combiner is of great significance for improving the transmission power and beam quality of fiber lasers.

[0005] The technical solution adopted by the present invention is:

[0006] A hollow-core fiber power combiner comprises a fiber bundle and a hollow-core fiber, wherein the fiber bundle is formed by taper-forming n solid-core fibers; the input end of the fiber bundle is the large end of the fiber bundle, and the output end of the fiber bundle is the small end of the fiber bundle, wherein one of the n solid-core fibers in the fiber bundle is located at the center as a central fiber, and the remaining n-1 fibers are distributed around the central fiber in a central manner;

[0007] The hollow core optical fiber is a nested antiresonant hollow core optical fiber, which includes an outer cladding, a nested ring and a hollow core region from the inside to the outside, and n-1 nested rings are distributed around the outer periphery of the hollow core region;

[0008] The laser of the input fiber bundle is input into the hollow core fiber through the small head end of the fiber bundle, and the hollow core fiber is used to realize the long-distance transmission of the laser.

[0009] Furthermore, n solid-core optical fibers are bundled by using a tube-twisted cone to obtain an optical fiber bundle, and the small end of the optical fiber bundle is fused with the hollow-core optical fiber.

[0010] Furthermore, the small end of the optical fiber bundle and the hollow-core optical fiber are connected via a small gas cavity, the small gas cavity is connected to the small end of the optical fiber bundle, the input end of the hollow-core optical fiber is fixed and sealed in the small gas cavity, and the laser of the input optical fiber bundle is input into the hollow-core optical fiber via the small end of the optical fiber bundle.

[0011] Furthermore, the output end of the hollow-core optical fiber is fused with an optical fiber end cap to achieve laser output.

[0012] Furthermore, the output end of the hollow-core optical fiber is fixed and sealed in a small gas cavity, and laser output is achieved through the small gas cavity.

[0013] Furthermore, the outer cladding of the hollow-core optical fiber is processed with cooling gas filling holes by femtosecond laser, and cooling gas is filled into the hollow core area of ​​the hollow-core optical fiber by the cooling gas filling holes, and the cooling gas is carbon dioxide or nitrogen that does not require tail gas treatment.

[0014] Furthermore, before the n solid-core optical fibers are taper-bundled, the core diameter of each solid-core optical fiber is less than 20 μm.

[0015] Furthermore, by controlling the taper ratio of the optical fiber bundle, the optical fiber mode field area at the small end of the optical fiber bundle formed by taper bundling is made to be the same as the mode field area of ​​the hollow-core optical fiber.

[0016] Furthermore, each nested ring of the hollow-core optical fiber is a circular nested ring, each nested ring is provided with m sub-nested rings inside, m is greater than or equal to 0, and each nested ring has the same diameter. The ratio of the nested ring diameter b to the hollow core region diameter a of the hollow-core optical fiber is designed to improve the mode purity of the laser transmitted in the hollow-core optical fiber under high power conditions.

[0017] When the optimal value of the nested ring diameter b / hollow core area diameter a of the hollow core fiber is 30%, the power proportion of the high-order mode in the nested ring is maximized while ensuring that the fundamental mode leakage loss is small, thereby increasing the high-order mode leakage loss.

[0018] When the ratio of the nested ring diameter b to the hollow core region diameter a of the hollow core optical fiber is greater than 30% (such as reaching 35%), the leakage of the higher-order modes is relatively high, and the leakage of the fundamental mode is also relatively high.

[0019] When the nested ring diameter b / hollow core area diameter a of the hollow core fiber is less than or equal to 15%, although the fundamental mode loss in the nested ring is small, the power of the high-order mode is basically not distributed in the nested ring, and the leakage loss is small.

[0020] Furthermore, the wall thickness d of the nested ring / the diameter b of the nested ring is optimized to reduce the leakage of the fundamental mode and increase the proportion of the nested ring of the high-order mode.

[0021] Compared with the prior art, the present invention can produce the following technical effects:

[0022] The present invention designs a hollow-core fiber power combiner, which realizes weak broadening and low nonlinear transmission of high-power laser with high beam quality in the hollow-core fiber by tapering multiple optical fibers into a bundle and then connecting them with the hollow-core fiber with low loss (it can be plug-in, spatial alignment, or fusion splicing, and the specific connection method is determined by whether the optical fiber bundle is sleeved when tapering the bundle).

[0023] Furthermore, the present invention also achieves laser coupling with low loss and low beam quality degradation rate by simulating and designing the bundle structure and taper ratio of the bundled optical fiber. By utilizing femtosecond processing microstructure, low-temperature gas is introduced from the outside into the hollow-core optical fiber to reduce the thermal effect generated by high-power transmission, which can further reduce the nonlinear effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 1 This is a schematic diagram of the structure of a hollow-core fiber power combiner provided by an embodiment of the present invention:

[0026] Figure 2 FIG. 1 is a diagram showing the arrangement of an optical fiber bundle in an embodiment, wherein Figure 2 (a) is the arrangement shape diagram of the non-central surround structure optical fiber bundle formed by three optical fibers; Figure 2 (b) is a diagram showing the arrangement of a center-surround structure optical fiber bundle formed by seven optical fibers;

[0027] Figure 3 is the fundamental mode field distribution diagram of different structures, where Figure 3 (a) is the fundamental mode field distribution diagram when three optical fibers form a surround structure. Figure 3 (b) is the fundamental mode field distribution diagram when 7 optical fibers form a surround structure. Figure 3 (c) is the mode field distribution diagram of the fundamental mode of the hollow-core fiber with six nested rings;

[0028] Figure 4 The relationship diagram of the model diameter of the optical fiber bundle under different taper ratios;

[0029] Figure 5 is the distribution diagram of the fundamental mode field and high-order mode field of hollow-core optical fiber under different parameters, where Figure 5 (a) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 15%. Figure 5 (b) is the high-order mode field distribution diagram of hollow-core optical fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 15%. Figure 5 (c) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30%. Figure 5 (d) is the high-order mode field distribution diagram of the hollow-core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30%. Figure 5(e) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 35%. Figure 5 (f) is the high-order mode field distribution diagram of the hollow-core optical fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 35%. Figure 5 (g) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30% and the ratio of the nested ring wall thickness d to the nested ring diameter b is 0.025. Figure 5 (h) is the mode field distribution diagram of the high-order mode of the hollow-core optical fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30% and the ratio of the nested ring diameter b to the hollow core area diameter a is 0.025.

[0030] Numbers in the figure:

[0031] 1. Fiber bundle; 2. Hollow core fiber; 3. Cooling gas supply unit; 4. Laser. DETAILED DESCRIPTION

[0032] 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.

[0033] Reference Figure 1 An embodiment of the present invention provides a hollow-core fiber power combiner, comprising a fiber bundle 1 and a hollow-core fiber 2, wherein the fiber bundle 1 is formed by taper-forming n solid-core optical fibers; the input end of the fiber bundle 1 is the large end of the fiber bundle, and the output end of the fiber bundle 1 is the small end of the fiber bundle, wherein one of the n solid-core optical fibers in the fiber bundle 1 is located at the center as a central optical fiber, and the remaining n-1 optical fibers are distributed around the central optical fiber in a centrally arranged manner;

[0034] The hollow core optical fiber 2 is a nested antiresonant hollow core optical fiber, which includes an outer cladding, a nested ring and a hollow core region from the inside to the outside, and n-1 nested rings are distributed around the outer periphery of the hollow core region;

[0035] The laser light 4 input into the optical fiber bundle 1 is input into the hollow core optical fiber 2 through the small end of the optical fiber bundle, and the hollow core optical fiber 2 is used to realize the long-distance transmission of the laser light.

[0036] The purpose of the above embodiment is to achieve high beam quality transmission of high-power laser by using hollow core fiber. Hollow core fiber (HCF) is a special structure of optical fiber. Compared with ordinary solid optical fiber, due to its unique hollow core structure, the interaction between light and optical fiber material during transmission inside it is greatly reduced, thereby greatly weakening the nonlinear effect. Therefore, even a hollow core fiber (single mode) with a smaller mode field area can support long-distance transmission of high-power laser.

[0037] Specifically, the fiber bundle formed by taper-forming n solid-core optical fibers (the type and structure of the solid-core optical fibers are the same, and they can be polarization-maintaining optical fibers or non-polarization-maintaining optical fibers) in the above embodiment is a center-surround structure, that is, one optical fiber is located in the center as the center optical fiber, and the remaining n-1 optical fibers are distributed around the center optical fiber in a center-surrounding manner, so as to ensure the excitation of the fundamental mode of the hollow-core optical fiber and increase the coupling efficiency. Further, the number of optical fibers surrounding the center optical fiber should match the number of nested rings, that is, the number of optical fibers surrounding the center optical fiber and the number of nested rings distributed around the periphery of the hollow core area of ​​the hollow-core optical fiber are both n-1, so as to increase the mode field matching. At the same time, by controlling the taper ratio, the mode field area of ​​the fiber bundle formed by taper-forming can be better matched with the hollow-core optical fiber.

[0038] Preferably, the hollow core fiber 2 is a nested anti-resonant hollow core fiber with low bending transmission loss, and the nested anti-resonant hollow core fiber has a large loss at the Raman wavelength of the transmitted signal laser. Further, the leakage loss of the high-order mode is increased by optimizing the ratio of the nested ring wall thickness to the ring diameter.

[0039] Each nested ring of the hollow-core optical fiber 2 is a circular nested ring, and each nested ring is provided with m sub-nested rings inside, where m is greater than or equal to 0, and each nested ring has the same diameter. The ratio of the diameter b of the nested ring to the diameter a of the hollow core area of ​​the hollow-core optical fiber is designed to improve the mode purity of the laser transmitted in the hollow-core optical fiber under high power conditions.

[0040] The above embodiment designs a corresponding power combiner using hollow core optical fiber, and the power combiner is a power combiner without a signal fiber.

[0041] In one embodiment, the core and outer cladding of the solid core optical fiber used for taper bundling are both circular, wherein the cladding is a double cladding structure. Furthermore, the core diameter of the solid core optical fiber used for taper bundling is less than 20 μm before taper bundling, which can have a greater coupling efficiency while ensuring the quality of the laser beam after taper bundling. Preferably, the taper ratio is about 3.75%, so that the mode field area of ​​the optical fiber at the small end of the optical fiber bundle after taper bundling can be well matched with the hollow core optical fiber.

[0042] In a preferred embodiment, it also includes a cooling gas supply unit 3, which is to process cooling gas filling holes in the outer cladding of the hollow-core optical fiber using a femtosecond laser, and use the cooling gas filling holes to fill the hollow core area of ​​the hollow-core optical fiber with cooling gas, and the cooling gas can be selected as carbon dioxide, nitrogen and other pollution-free gases that do not require tail gas treatment. In this way, the outer cladding of the hollow-core optical fiber is hollowed out with a single hole using a femtosecond laser, and through the designed gas cavity connected to the cooling gas filling hole and the filling device, low-temperature gas can be filled into the hollow-core optical fiber to reduce the thermal effect during high-power transmission.

[0043] In the above embodiment, the preferred implementation is: using n solid core optical fibers to form a bundle by using a tube to pull the cone to form a bundle, and fusing the small end of the optical fiber bundle with the hollow core optical fiber, so that there is no sealing problem at the input end of the hollow core optical fiber.

[0044] If the above embodiment does not adopt the tube taper bundle assembly method, the sealing problem of the input end of the hollow-core optical fiber needs to be considered. The problem can be solved by using a small gas cavity in the prior art. Specifically, the small end of the optical fiber bundle and the hollow-core optical fiber are connected through a small gas cavity, the small gas cavity is connected to the small end of the optical fiber bundle, the input end of the hollow-core optical fiber is fixed and sealed in the small gas cavity, and the laser of the input optical fiber bundle is input into the hollow-core optical fiber through the small end of the optical fiber bundle.

[0045] The output end of the hollow core optical fiber can be welded with an optical fiber end cap to achieve laser output. Alternatively, the output end of the hollow core optical fiber is fixed and sealed in a small gas cavity, and the laser output is achieved through a window mirror of the small gas cavity.

[0046] In one embodiment, simulation optimization is performed for the size of the bundled optical fiber that matches the hollow-core optical fiber. In order to ensure the transmission coupling efficiency, a smaller taper ratio is required, as well as the matching of the mode field of the bundled optical fiber after taper and the mode field of the hollow-core optical fiber. Such a hollow-core optical fiber combiner is of great significance for improving the transmission power and beam quality of optical fiber lasers. Specifically, the hollow-core optical fiber power combiner in this embodiment includes an optical fiber bundle 1 and a hollow-core optical fiber 2, wherein the optical fiber bundle 1 is formed by 7 solid-core optical fibers being bundled by tapering with a sleeve; the input end of the optical fiber bundle 1 is the large end of the optical fiber bundle, and the output end of the optical fiber bundle 1 is the small end of the optical fiber bundle, wherein one of the 7 solid-core optical fibers in the optical fiber bundle 1 is located in the center as the central optical fiber, and the remaining six optical fibers are distributed around the center optical fiber. In this embodiment, in order to ensure coupling efficiency / injection power core / increase taper ratio, the core diameter of the solid core fiber before taper must be less than or equal to 20 μm, and the cladding diameter of the solid core fiber is ~400 μm. Specifically, if a solid core fiber with a core-to-cladding ratio of 20 / 400 and NA of 0.065 is used, a too large core diameter will make the taper larger. In addition, a large core diameter and more mode components will lead to greater energy loss after taper. Seven solid core fibers (core-to-cladding ratio of 20 / 400 and NA of 0.065) are used for tapering and bundling. The fiber bundle formed by tapering is a center-surround structure, such as Figure 2 As shown in (b), one optical fiber is located in the center as the central optical fiber, and the remaining six optical fibers are distributed around the central optical fiber in a central surrounding pattern to increase the proportion of central light intensity before tapering and increase the fundamental mode coupling efficiency.

[0047] Reference Figure 4 , is the model diameter relationship diagram of the fiber bundle under different taper ratios. Seven solid core fibers (core-to-clad ratio of 20 / 400, NA of 0.065) are used to form a taper bundle. The fiber bundle formed by taper bundling is a center-surround structure. When the taper ratio (small / large end) is 3.75%, the mode field area of ​​the fiber at the small end of the fiber bundle after taper bundling is equal to the mode field area of ​​the hollow-core fiber. In this way, the fiber bundle after taper bundling is as close to the mode field diameter of the hollow-core fiber as possible, increasing the coupling efficiency.

[0048] Figure 2 FIG. 1 is a diagram showing the arrangement of an optical fiber bundle in an embodiment, wherein Figure 2 (a) is the arrangement shape diagram of the non-central surround structure optical fiber bundle formed by three optical fibers; Figure 2 (b) is the arrangement shape diagram of the center-surround structure optical fiber bundle formed by 7 optical fibers. Figure 3 is the fundamental mode field distribution diagram of different structures, where Figure 3 (a) is the fundamental mode field distribution diagram when three optical fibers form a surround structure. Figure 3 (b) is the fundamental mode field distribution diagram when 7 optical fibers form a surround structure. Figure 3 (c) is the mode field distribution diagram of the hollow-core fiber fundamental mode of six nested rings. Specifically, Figure 2 (a) is the arrangement shape diagram of the non-central surround structure fiber bundle formed by three optical fibers, and its corresponding fundamental mode field distribution diagram is shown in Figure 3 (a) shown. Figure 2 (b) is the arrangement shape diagram of the center-surround structure fiber bundle formed by 7 optical fiber tapers, and its corresponding fundamental mode field distribution diagram is shown in Figure 3 (b) As shown. When the fiber bundle formed by the taper is not a center-surround structure or the number of outer cores is inconsistent with the number of nested rings, its mode field shape is as follows Figure 3 (a) shows, with Figure 3 (c) Inconsistent morphology. If the fiber bundle formed by the taper is a center-surround structure fiber bundle and the number of fibers outside the center fiber is consistent with the number of nested rings, its mode field distribution is as follows: Figure 3 (b) shows that Figure 3 The mode field morphology of the hollow-core optical fiber shown in (c) is similar. For example, when n is 7, it is a hexagonal fundamental mode field, which can greatly improve the coupling efficiency.

[0049] Since the optical fiber bundle is obtained by using 7 solid-core optical fibers to form a bundle by using a tube to pull a cone, the small end of the optical fiber bundle can be fused with the hollow-core optical fiber, so there is no sealing problem at the input end of the hollow-core optical fiber. The output end of the hollow-core optical fiber can achieve laser output by fusing the optical fiber end cap. Alternatively, the output end of the hollow-core optical fiber is fixed and sealed in a small gas cavity, and laser output is achieved through the small gas cavity.

[0050] The hollow-core optical fiber 2 is a nested antiresonant hollow-core optical fiber, which includes an outer cladding, a nested ring, and a hollow-core region from the inside to the outside, and six circular nested rings are distributed around the outer periphery of the hollow-core region. The number of centrally surrounded optical fibers should be consistent with the number of circular nested rings in the hollow-core optical fiber to increase the mode field overlap and increase the fundamental mode coupling ratio. A sub-nested ring is arranged inside each circular nested ring, and each circular nested ring has the same diameter. The ratio of the diameter b of the circular nested ring to the diameter a of the hollow-core region of the hollow-core optical fiber is designed to improve the mode purity of the laser transmitted in the hollow-core optical fiber under high power conditions.

[0051] The outer cladding of the hollow-core optical fiber is processed with cooling gas filling holes by femtosecond laser, and cooling gas is filled into the hollow core area of ​​the hollow-core optical fiber by using the cooling gas filling holes. The cooling gas can be selected as non-polluting gas such as carbon dioxide and nitrogen that does not require tail gas treatment.

[0052] The sealing problem at the cooling gas filling hole can be solved by a gas cavity. A hollow-core optical fiber with a cooling gas filling hole is sealed and passes through the gas cavity. The cooling gas filling hole is located in the gas cavity. A filling pipe for injecting cooling gas is provided in the gas cavity. The filling pipe is connected to a cooling gas source supply device, so that low-temperature gas can be filled into the hollow-core optical fiber to reduce the thermal effect during high-power transmission.

[0053] The purpose of optimizing the b / a ratio is to increase the high-order mode loss. By optimizing the b / a ratio, the fundamental mode mode field can be distributed in the hollow area as much as possible, while many high-order mode mode field components are distributed in the nested rings. Further, by optimizing the nested ring wall thickness d / nested ring diameter b, the fundamental mode leakage can be further reduced and the proportion of high-order mode nested rings can be increased.

[0054] In one embodiment, a hollow-core fiber power combiner is provided, comprising a fiber bundle 1 and a hollow-core fiber 2. The fiber bundle 1 is formed by assembling 7 solid-core fibers (core-to-clad ratio of 20 / 400 and NA of 0.065) through a sleeve and tapering. The fiber bundle formed by tapering is a center-surround structure, such as Figure 2 As shown in (b), one optical fiber is located in the center as the central optical fiber, and the other six optical fibers are distributed around the central optical fiber. The taper ratio is 3.75%, so that the mode field area of ​​the optical fiber at the small end of the optical fiber bundle after taper bundling is equal to the mode field area of ​​the hollow core optical fiber. The hollow core optical fiber 2 is a nested antiresonant hollow core optical fiber, which includes an outer cladding, a nested ring and a hollow core region from the inside to the outside, and 6 nested rings are distributed around the outer periphery of the hollow core region; each nested ring of the hollow core optical fiber 2 is a circular nested ring, and each nested ring is provided with a sub-nested ring inside, and each nested ring has the same diameter. The small end of the optical fiber bundle is fused with the input end of the hollow core optical fiber 2. The laser input to the optical fiber bundle 1 (the laser wavelength transmitted during simulation is in the 1.08 um band) is input to the hollow core optical fiber 2 through the small end of the optical fiber bundle, and the long-distance transmission of the laser is realized by using the hollow core optical fiber 2. The ratio of the diameter b of the nested ring to the diameter a of the hollow core region is designed to improve the mode purity of the laser transmitted in the hollow core optical fiber under high power conditions. Further, by optimizing the nested ring wall thickness d / nested ring diameter b, the fundamental mode leakage can be further reduced and the proportion of high-order mode nested rings can be increased. Figure 5 , Figure 5 is the distribution diagram of the fundamental mode field and high-order mode field of hollow-core optical fiber under different parameters, where Figure 5 (a) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 15%. Figure 5 (b) is the high-order mode field distribution diagram of hollow-core optical fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 15%. Figure 5 (c) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30%. Figure 5 (d) is the high-order mode field distribution diagram of the hollow-core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30%. Figure 5 (e) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 35%. Figure 5 (f) is the high-order mode field distribution diagram of the hollow-core optical fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 35%. Figure 5 (g) is the mode field distribution diagram of the fundamental mode of the hollow core fiber when the ratio of the nested ring diameter b to the hollow core area diameter a is 30% and the ratio of the nested ring wall thickness d to the nested ring diameter b is 0.025. Figure 5 (h) is the high-order mode field distribution diagram of hollow-core optical fiber when the ratio of the nested ring diameter b to the hollow core region diameter a is 30% and the ratio of the nested ring diameter b to the hollow core region diameter a is 0.025. Figure 5 (a) and Figure 5 (b) It can be seen that when the ratio of the nested ring diameter b to the hollow core area diameter a is small (less than or equal to 15%), although the fundamental mode has a small loss in the nested ring, the power of the high-order mode is basically not distributed in the nested ring, and the leakage loss is small. That is, at this time, the distribution of the high-order mode and the fundamental mode in the nested ring is small, and the mode loss is small. Figure 5 (c) and Figure 5 (d) It can be seen that when the nested ring diameter b / hollow core area diameter a is equal to 30% (the optimal value), the fundamental mode is distributed in a smaller nested ring and the mode loss is smaller, while the high-order mode is distributed in a larger nested ring and the mode loss is larger. Figure 5 (e) and Figure 5 (f) It can be seen that when the nested ring diameter b / hollow core area diameter a is equal to 35%, the high-order mode and fundamental mode are both distributed more in the nested ring, and the mode loss is larger. Although the leakage of the high-order mode is higher, the leakage of the fundamental mode is also higher. Figure 5 (g) and Figure 5 (h) It can be seen that, under the premise that the ratio of the nested ring diameter b to the hollow area diameter a is 30%, by optimizing the ratio of the nested ring wall thickness d to the nested ring diameter b, specifically when the nested ring wall thickness d / nested ring diameter b is 0.025, the fundamental mode is basically distributed in the hollow area, while a large part of the high-order mode is distributed in the nested ring. Therefore, the fundamental mode loss is small and the high-order mode loss is large. It can be seen that further optimizing the ratio of the nested ring wall thickness d to the nested ring diameter b can further reduce the fundamental mode leakage and increase the proportion of the high-order mode nested ring.

[0055] By designing the hollow-core fiber structure, the taper ratio, and the bundled fiber surrounding structure, the purity of the laser mode is ensured while ensuring the coupling ratio as much as possible.

[0056] The laser passes through the input end of the fiber bundle (the large end of the fiber bundle) through the cone area and enters the hollow-core fiber from the output end of the fiber bundle (the small end of the fiber bundle) designed with a center surround structure. The hollow-core fiber is used for weak broadening and weak nonlinear transmission of high-power lasers by taking advantage of its low nonlinear and fast transmission characteristics. The hollow-core fiber adopts an anti-resonant nested structure to reduce bending transmission loss and increase high-order mode leakage loss. The cooling gas (environmentally friendly and easily accessible carbon dioxide or nitrogen, etc.) is injected into the hollow-core fiber through the cooling gas filling hole for cooling, which can further reduce the nonlinear effect and self-focusing caused by the photothermal effect. By specially designing the taper ratio of the bundled tapered fiber and the ratio of the nested ring wall thickness to the nested ring diameter of the hollow-core fiber, it can be better ensured that the transmitted laser has a better mode purity under high power conditions.

[0057] Matters not covered by the present invention are known technologies.

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

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

[0060] 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 hollow core fiber power combiner, characterized in that: The invention comprises an optical fiber bundle and a hollow-core optical fiber, wherein the optical fiber bundle is formed by taper-forming n solid-core optical fibers, and the n solid-core optical fibers are taper-formed and connected with the hollow-core optical fiber with low loss; the input end of the optical fiber bundle is the large end of the optical fiber bundle, and the output end of the optical fiber bundle is the small end of the optical fiber bundle, wherein one optical fiber among the n solid-core optical fibers in the optical fiber bundle is located at the center as the central optical fiber, and the remaining n-1 optical fibers are distributed around the central optical fiber in a central surrounding manner; The hollow core optical fiber is a nested antiresonant hollow core optical fiber, which includes an outer cladding, a nested ring and a hollow core region from the inside to the outside, and n-1 nested rings are distributed around the outer periphery of the hollow core region; The laser of the input fiber bundle is input into the hollow core fiber through the small end of the fiber bundle, and the hollow core fiber is used to realize the long-distance transmission of the laser; Each nested ring of the hollow-core optical fiber is a circular nested ring, each nested ring is provided with m sub-nested rings inside, m is greater than or equal to 0, and each nested ring has the same diameter. The ratio of the diameter b of the nested ring to the diameter a of the hollow core region of the hollow-core optical fiber is optimized to improve the mode purity of the laser transmitted in the hollow-core optical fiber under high power conditions; the wall thickness d of the nested ring / the diameter b of the nested ring is optimized to reduce the leakage of the fundamental mode and increase the proportion of the nested ring of the high-order mode, wherein the optical fiber bundle adopts 7 solid-core optical fibers with a core-to-wrapper ratio of 20 / 400 and an NA of 0.

065. The optical fiber bundle is formed by cone-drawing through a sleeve, and the optical fiber bundle formed by cone-drawing is a center-surround structure, wherein the cone-drawing ratio is 3.75%, and the optical fiber mode field area of ​​the small end of the optical fiber bundle after cone-drawing is equal to the mode field area of ​​the hollow-core optical fiber, and 6 nested rings are distributed around the outer periphery of the hollow core area of ​​the hollow-core optical fiber; each nested ring of the hollow-core optical fiber is a circular nested ring, and each nested ring is provided with a sub-nested ring inside, and each nested ring has the same diameter, wherein the ratio of the nested ring diameter b to the hollow core area diameter a is 30%, and the nested ring wall thickness d / nested ring diameter b is 0.

025.

2. The hollow core fiber power combiner according to claim 1, characterized in that: The small end of the optical fiber bundle is fused with the hollow core optical fiber.

3. The hollow core fiber power combiner according to claim 1, characterized in that: The small end of the optical fiber bundle and the hollow-core optical fiber are connected via a small gas cavity, the small gas cavity is connected to the small end of the optical fiber bundle, the input end of the hollow-core optical fiber is fixed and sealed in the small gas cavity, and the laser of the input optical fiber bundle is input into the hollow-core optical fiber via the small end of the optical fiber bundle.

4. The hollow core fiber power combiner according to claim 2 or 3, characterized in that: The output end of the hollow core optical fiber is fused with an optical fiber end cap to achieve laser output.

5. The hollow core fiber power combiner according to claim 4, characterized in that: The outer cladding of the hollow-core optical fiber is processed with a cooling gas charging micro-channel by femtosecond laser, and the cooling gas charging channel is used to charge the hollow core area of ​​the hollow-core optical fiber with cooling gas, and the cooling gas is carbon dioxide or nitrogen.

6. The hollow core fiber power combiner according to claim 2 or 3, characterized in that: The output end of the hollow core optical fiber is fixed and sealed in a small gas cavity, and laser output is achieved through the small gas cavity.

7. The hollow core fiber power combiner according to claim 6, characterized in that: The outer cladding of the hollow-core optical fiber is processed with cooling gas filling holes by femtosecond laser, and cooling gas is filled into the hollow core area of ​​the hollow-core optical fiber by the cooling gas filling holes. The cooling gas is carbon dioxide or nitrogen that does not require tail gas treatment.

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