An integrated fiber coupler with flat-top spot output, preparation and output method

Abstract

The application discloses a one-piece optical fiber coupler with flat-top light spot output, a preparation method and an output method, and relates to the technical field of laser light spot shaping. The one-piece optical fiber coupler with flat-top light spot output comprises an input optical fiber bundle, a multimode output optical fiber and a ball-burning transition structure. The output end of the input optical fiber bundle is formed into a taper fusion zone through tapering. The output end of the taper fusion zone is processed into at least one ball-burning structure through ball-burning, and the diameter of the spherical structure of the ball-burning structure is greater than the core diameter of the input optical fiber in the taper fusion zone, so that the proportion of high-order modes in laser is increased. The input end of the multimode output optical fiber is fusion-spliced with the ball-burning structure formed at the output end of the taper fusion zone of the input optical fiber bundle. The application can perform light spot shaping on a Gaussian-distributed laser beam to obtain flat-top light spot output, and does not need to increase a complex machining part structure, has a simple manufacturing method, a small size, a compact structure and good stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser spot shaping, in particular to an integrated fiber coupler for flat-top spot output, and a preparation and output method. BACKGROUND

[0002] Flat-top light is a widely used light spot pattern, including medical, cosmetic, microscope illumination, machine vision and industrial laser processing fields. Flat-top light beam is a light beam with flat and uniform intensity distribution, sharp edges and rapid energy drop to zero. The output spot of the flat-top light beam can be square, rectangular, straight, circular or any other shape. In industrial applications, flat-top light beams are often obtained by beam shaping methods. Traditional beam shaping can rely on spatial optical systems, such as aspherical lens group method, microlens array shaping method and diffractive optical element method. These methods have good shaping effect and small light energy loss, but in practical applications, they often introduce complex lens optical systems, which affect the integration of the light source system. In addition, the complex lens optical system also has poor shock resistance.

[0003] In some applications in the field of industrial laser processing, it is necessary to uniformly distribute laser energy on the light spot to improve the processing effect and ensure the consistency and stability of the processing effect. In a laser system, beam shaping can be achieved by directly coupling the beam shaping device of the fiber structure with the fiber laser system or the solid laser system.

[0004] There are currently two methods to achieve beam homogenization shaping of fiber structure: 1) directly homogenize the energy distribution of the fundamental mode Gaussian light beam, and transfer part of the energy in the center of the light beam to the edge of the light beam to obtain a flat energy distribution of the fundamental mode output, and finally achieve the purpose of homogenizing the light beam energy; 2) increase the proportion of high-order modes in the output laser to enhance the energy at the edge of the fundamental mode, and finally achieve multi-mode output to achieve the energy distribution of the output spot flat-top, which is simply referred to as high-order mode shaping method. In high-power fiber laser systems, the output fiber is usually a multi-mode fiber, so the high-order mode shaping method is usually used. Among them, the use of rectangular or polygonal core fiber or polygonal fiber for beam homogenization shaping is one of the earliest beam shaping methods. By using rectangular or polygonal waveguide structures to excite high-order modes in the fiber, the beam energy is coupled between the fundamental mode and the high-order mode, achieving the purpose of beam energy redistribution, thereby achieving beam homogenization shaping. This method uses irregular core diameter fiber, which requires the introduction of complex fiber fabrication process, takes more time, has low yield, and poses a great challenge to fiber drawing. Therefore, such fiber often costs hundreds of times more than conventional fiber, which cannot be used on a large scale in the industrial market.

[0005] In view of the problems of the prior art, those skilled in the art urgently need an integrated fiber coupler with a flat-top light spot output, its fabrication and output method. Summary of the Invention

[0006] The purpose of this invention is to provide an integrated fiber coupler with flat-top beam output, its fabrication and output method, to solve the problems existing in the prior art. It can shape the beam of an input Gaussian distributed laser beam to obtain a flat-top beam output, without the need for complex machining components. The fabrication method is simple, the size is small, the structure is compact, and the stability is good.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] In a first aspect, the present invention provides an integrated fiber coupler with flat-top beam output, comprising an input fiber bundle, a multimode output fiber, and a spherical transition structure; the input fiber bundle includes at least two input fibers, the output end of the input fiber bundle being tapered to form a tapered fusion region; the spherical transition structure is formed between the output end of the input fiber bundle in the tapered fusion region and the input end of the multimode output fiber; the output end of the tapered fusion region is spherically treated to form at least one spherical structure, and the diameter of the spherical structure of the spherical structure is larger than the core diameter of the input fiber integrally connected thereto in the tapered fusion region to increase the proportion of higher-order modes in the laser; the input end of the multimode output fiber is fused to the spherical structure formed by the input fiber bundle at the output end of the tapered fusion region; the spherical transition structure includes at least the spherical structure formed by the input fiber bundle at the output end of the tapered fusion region.

[0009] In some embodiments, each input optical fiber is sintered at its output end in the tapered fusion zone to form a first sintered ball structure, and the diameter of the spherical structure of each first sintered ball structure is larger than the core diameter of the corresponding single input optical fiber in the tapered fusion zone; multiple arrays of the first sintered ball structures of multiple input optical fibers are arranged to form a sintered ball array, and the sintered ball transition structure includes the sintered ball array; the input end of the multimode output optical fiber is fused with the spherical structure of the multiple first sintered ball structures to form an integrated structure.

[0010] In some embodiments, all the input optical fibers of the input fiber bundle are sintered at the output end of the tapered fusion region to form a common second sintered sphere structure, and the diameter of the spherical structure of the second sintered sphere structure is larger than the sum of the core diameters of all the input optical fibers in the tapered fusion region; the input end of the multimode output fiber is fused with the spherical structure of the second sintered sphere structure to form an integral structure.

[0011] In some embodiments, the input end of the multimode output fiber is subjected to a sintering process to form a third sintered structure, and the third sintered structure of the multimode output fiber is fused with the second sintered structure to form an integral structure; the sintered transition structure includes the third sintered structure and the second sintered structure.

[0012] In some embodiments, the output end of the input fiber bundle is formed by fused tapering using a sleeve method to create the tapered fusion region, and the sleeve fitted onto the output end of the input fiber bundle is made of a quartz composite material; the radius of curvature R of the sintered sphere structure formed at the output end of the input fiber bundle in the tapered fusion region satisfies the following condition:

[0013]

[0014] Wherein, n1 is the refractive index of the sleeve, n2 is the core refractive index of the multimode output fiber, and α is the incident angle of the laser.

[0015] In some embodiments, the length of the tapered fusion region is 5-15 mm, and the taper angle is 2°-8°; the radius of curvature of the spherical structure formed at the output end of the input fiber bundle in the tapered fusion region is 50-600 μm; the core diameter of the multimode output fiber is 100-1000 μm, and the numerical aperture (NA) of the multimode output fiber is 0.22.

[0016] In some embodiments, the input fiber bundle includes a first input fiber located at the center and a plurality of second input fibers arranged circumferentially around the first input fiber, wherein the total number Q of the first input fiber and the plurality of second input fibers satisfies:

[0017] Q = 3n 2 +3n+1;

[0018] Where n is a positive integer.

[0019] In a second aspect, the present invention provides a method for fabricating an integrated optical fiber coupler with flat-top light spot output, comprising the following steps: tapering the output end of the input optical fiber bundle to form a taper fusion region; performing a sintering process on the output end of the input optical fiber bundle in the taper fusion region to form at least one sintered structure; and fusion splicing the input end of the multimode output optical fiber with the sintered structure formed at the output end of the input optical fiber bundle in the taper fusion region.

[0020] In some embodiments, the step of "tapering the output end of the input fiber bundle to form a tapered fusion region" includes: placing the input fiber bundle into a sleeve to form a prefabricated fiber bundle, and tapering the prefabricated fiber bundle to form the tapered fusion region; the step of "sintering the output end of the input fiber bundle in the tapered fusion region to form at least one sintered structure, and fusion splicing the input end of the multimode output fiber to the sintered structure formed at the output end of the input fiber bundle in the tapered fusion region" includes: cutting the output end of the tapered fusion region, and sintering the cut end face so that each input fiber forms a first sintered structure, and fusion splicing the input end of the multimode output fiber to multiple first sintered structures. A spherical structure is fused together; or all the input fibers of the input fiber bundle are spherically fused at the output end of the tapered fusion region to form a common second spherical structure, and the input end of the multimode output fiber is fused to the spherical structure of the second spherical structure to form an integral structure; or all the input fibers of the input fiber bundle are spherically fused at the output end of the tapered fusion region to form a common second spherical structure, the input end of the multimode output fiber is spherically fused to form a third spherical structure, and the third spherical structure is fused to the second spherical structure; wherein the diameter of the spherical structure of the second spherical structure is larger than the sum of the core diameters of all the input fibers in the tapered fusion region.

[0021] In a third aspect, the present invention provides a method for outputting a flat-top beam, using an integrated fiber coupler with flat-top beam output as described above or a fiber coupler fabricated using the above-described method for fabricating an integrated fiber coupler with flat-top beam output. The fiber coupler includes an input fiber bundle, a multimode output fiber, and at least one spherical structure. The method includes the following steps: a laser beam passes from the input fiber bundle through the spherical structure, and the proportion of higher-order modes in the output laser is increased in the spherical fiber waveguide of the spherical structure. After exiting through the spherical structure, the laser beam is coupled into the multimode output fiber, thereby achieving flat-top energy output.

[0022] The present invention achieves the following technical effects compared to the prior art:

[0023] This invention discloses an integrated fiber coupler with flat-top laser output, its fabrication, and its output method. The fiber bundle input is tapered to form a tapered fusion region in the fiber bundle combining assembly. The output end of the tapered fusion region is then sintered to form a sintered sphere structure. Laser propagation occurs through the sintered sphere region of the fiber bundle combining assembly. The sintering process increases the core diameter of the fiber waveguide, exciting mixed higher-order modes, which are then coupled into the multimode output fiber for transmission. This invention's structure and method can shape the input Gaussian-distributed laser beam to achieve a flat-top laser output. After refraction through the spherical structure, the laser divergence angle is reduced, achieving low-loss coupling and flat-top energy laser output. Furthermore, this invention is an all-fiber integrated structure, not a spatial optical path transmission, requiring no additional complex machined components. The fabrication method is simple, the size is small, the structure is compact, and the stability is good. It is compatible with existing fiber laser processing systems or solid-state laser processing systems. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a flat-top laser beam output via an optical fiber coupler in some embodiments of the present invention;

[0026] Figure 2 This is a schematic diagram of the first embodiment of the integrated fiber optic coupler with flat-top beam output of the present invention;

[0027] Figure 3 for Figure 1 A schematic diagram of the cross-section of AA.

[0028] Figure 4 This is one of the schematic diagrams of a second embodiment of the integrated fiber optic coupler with flat-top light spot output of the present invention;

[0029] Figure 5 This is a second schematic diagram of the second embodiment of the integrated fiber optic coupler with flat-top light spot output of the present invention;

[0030] Figure 6 This is a flowchart illustrating the main steps of the fabrication method of an integrated fiber optic coupler with flat-top light spot output in some embodiments of the present invention.

[0031] In the figure: 10-Input fiber bundle; 11-Tapered fusion region; 12-Sheath; 20-Sintered sphere structure; 21-First sintered sphere structure; 22-Second sintered sphere structure; 30-Multimode output fiber; 31-Multimode output fiber core; 32-Multimode output fiber cladding; 33-Multimode output fiber coating; 34-Third sintered sphere structure; 40-Output spot and its energy distribution. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The purpose of this invention is to provide an integrated fiber coupler with flat-top beam output, its fabrication and output method, to solve the problems existing in the prior art. It can shape the beam of an input Gaussian distributed laser beam to obtain a flat-top beam output, without the need to add complex machined parts. The fabrication method is simple, the size is small, the structure is compact, and the stability is good.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] This invention provides an integrated fiber optic coupler with flat-top beam output, such as... Figures 1 to 3 As shown, it includes an input fiber bundle 10, a multimode output fiber 30, and a burn-ball transition structure; wherein, the input fiber bundle 10 includes two or more input fibers, and the output end of the input fiber bundle 10 is tapered to form a tapered fusion region 11; a burn-ball transition structure is formed between the output end of the input fiber bundle 10 in the tapered fusion region 11 and the input end of the multimode output fiber 30.

[0037] The output end of the tapered fusion region 11 is sintered to form at least one sintered sphere structure 20, and the diameter of the spherical structure of the sintered sphere structure 20 is larger than the core diameter of the input fiber integrally connected to it in the tapered fusion region 11 in order to increase the proportion of higher-order modes in the laser; the input end of the multimode output fiber 30 is fused to the sintered sphere structure 20 formed at the output end of the input fiber bundle 10 in the tapered fusion region 11.

[0038] The burn-ball transition structure includes at least the burn-ball structure 20 formed at the output end of the input fiber bundle 10 in the tapered fusion region 11.

[0039] It should be noted that the input optical fiber and the spherical structure of this invention are an integral structure, and the other end of the spherical structure is connected to the output power transmission optical fiber by fusion splicing; Figure 2 In this structure, the fiber optic bundle assembly, i.e., the input fiber bundle 10, is located on the left side of the structure. The fibers are fused and tapered using a sleeve method. A spherical structure 20 is formed in the fused tapered region using a non-contact electric arc, laser, or flame sintering process. One side of the spherical structure 20 is fused with the multimode output fiber 30 to form an all-fiber integrated structure. Light enters the tapered fusion region 11 from the input fiber bundle 10, passes through the waveguide of the spherical structure after sintering, and is coupled into the multimode output fiber 30 for transmission.

[0040] For optical fibers, a flat-top beam is a superposition of multiple modes. Since the output fiber is often a multimode fiber with a large core diameter, the number of supported guided modes, approximately M, can be expressed as:

[0041]

[0042] The superposition of modes will also improve the uniformity of the beam, achieving a flat-top beam output. V is the normalized frequency of the optical fiber, which can be expressed as:

[0043]

[0044] Where a is the fiber diameter, NA is the fiber numerical aperture, and λ is the incident wavelength; it can be seen that the larger the fiber core, the more modes can exist in the fiber. Traditional beam combiners control tapering loss through adiabatic tapering to avoid mode distortion within the fiber, thus only exciting a portion of the modes, and the output beam distribution is still Gaussian or Gaussian-like. This invention, through an all-fiber integrated beam combiner structure, increases the fiber waveguide core diameter after sintering the fiber in the tapered region, which can excite more higher-order modes. After transmission through the multimode output fiber, a flat-top energy distribution beam spot can be obtained. This structure can achieve beam spot shaping of the input Gaussian distributed laser beam.

[0045] In some embodiments, each input optical fiber is sintered at the output end of the tapered fusion region 11 to form a first sintered ball structure 21, and the diameter of the spherical structure of each first sintered ball structure 21 is larger than the core diameter of the corresponding single input optical fiber in the tapered fusion region 11; multiple first sintered ball structures 21 of multiple input optical fibers are arranged in an array to form a sintered ball array, and the sintered ball transition structure includes the sintered ball array; the input end of the multimode output optical fiber 30 is fused with the spherical structure of multiple first sintered ball structures 21 to form an integrated structure.

[0046] In some embodiments, the input fiber bundle 10 includes a first input fiber located at the center and multiple second input fibers arranged circumferentially around the first input fiber. The multiple second input fibers can be arranged in several layers around the first input fiber, and the total number Q of the first input fiber and the multiple second input fibers satisfies:

[0047] Q = 3n 2 +3n+1; where n is a positive integer.

[0048] In some embodiments, the plurality of first spherical structures 21 are arranged in parallel optical paths. Preferably, the number of first spherical structures 21 is equal to the number of multiple input optical fibers.

[0049] It should be noted that the optical fibers in the fiber bundle assembly are arranged uniformly and axially symmetrically, such as... Figure 2 As shown, the number of optical fibers in the input fiber bundle 10 satisfies the above formula. In the tapered fusion zone 11, each optical fiber inside the fluorine tube is precisely sintered into a ball using a non-contact laser to form an array of sintered ball structures. The sintered ball structures are then fused with the flattened output multimode optical fibers to form an all-fiber integrated structure. Figure 3 AA shows a schematic diagram of the cross-sectional structure of a spherical fiber waveguide integrated in the conical region when n=1. Light enters the tapered fusion region 11 through the fiber combiner, and then propagates in the spherical structure 20 of the fiber waveguide after sphericalization. The core diameter of the fiber waveguide increases after sphericalization, allowing for the excitation of more higher-order modes. After transmission through the multimode output fiber, a flat-top energy distribution spot can be obtained.

[0050] In some embodiments, the length of the tapered fusion region 11 is 5-15 mm, and the taper angle is 2°-8°; the radius of curvature of the spherical structure 20 formed at the output end of the input fiber bundle 10 in the tapered fusion region 11 is 50-600 μm; the core diameter of the multimode output fiber 30 is 100-1000 μm, and the numerical aperture NA of the multimode output fiber 30 is 0.22.

[0051] In some embodiments, the output end of the input fiber bundle 10 is formed into a tapered fusion region 11 by fusion tapering using a sleeve method, and the sleeve 12 fitted onto the output end of the input fiber bundle 10 is made of a quartz composite material. The sleeve 12 of the present invention can be made of a fluorine-doped quartz composite material with a high refractive index.

[0052] In some embodiments, the radius of curvature R of the spherical structure 20 formed at the output end of the input fiber bundle 10 in the tapered fusion region 11 satisfies the following condition:

[0053]

[0054] Where n1 is the refractive index of the sleeve, n2 is the core refractive index of the multimode output fiber 30, and α is the incident angle of the laser.

[0055] It should be noted that if the output end of the tapered fusion region 11 is formed into a spherical structure 20 through spherical treatment, then the radius of curvature R in the above formula is the radius of curvature of the spherical structure of the spherical structure 20; if the output end of the tapered fusion region 11 is formed into two or more spherical structures 20 through spherical treatment, then the radius of curvature R in the above formula is the sum of the radii of curvature of the two or more spherical structures 20; and α in the above formula is the incident angle of the laser entering the multimode output fiber 30.

[0056] In some implementations, such as Figure 1 As shown, the multimode output fiber 30 of the present invention includes a multimode output fiber core 31, a multimode output fiber cladding 32, and a multimode output fiber coating 33; after the laser passes through the fiber coupler of the present invention, it forms an output light spot and its energy distribution 40.

[0057] When using the integrated fiber optic coupler with flat-top beam output of this invention:

[0058] The fiber optic bundle assembly, i.e., the input fiber bundle 10, includes multiple fibers as input ports. The bundling methods include end-face coupling and side-coupled structures. The fiber optic bundle assembly uses a fused taper method to assemble and tape the fibers. The sleeve 12 is made of fluorine-doped quartz composite material. After tapering, the tapered region is cut, and the cut end face undergoes a spherical sintering process. The spherical fiber waveguide integrated in the tapered region is sintered using a non-contact electric arc, laser, or flame process to form a spherical structure. The spherical sintering process increases the core diameter of the fiber waveguide, allowing for the excitation of more higher-order modes. The spherical fiber waveguide structure integrated in the tapered region includes an array arrangement where each individual input fiber is sintered into a roughly circular shape. After the incident laser excites mixed higher-order modes through the spherical structure integrated in the tapered region, it is then coupled into the multimode output fiber 30 for transmission.

[0059] Example 2

[0060] This embodiment provides an integrated fiber optic coupler with flat-top beam output, such as... Figure 4 and Figure 5 As shown, the difference between this embodiment and Embodiment 1 is that:

[0061] All the input optical fibers contained in the input fiber bundle 10 are integrated and sintered at the output end of the tapered fusion region 11 to form a common second sintered sphere structure 22, and the diameter of the spherical structure of the integrated second sintered sphere structure 22 is larger than the sum of the core diameters of all the input optical fibers in the tapered fusion region 11; the input end of the multimode output fiber 30 is fused with the spherical structure of the second sintered sphere structure 22 formed at the output end of all the input optical fibers in the tapered fusion region 11 to form an integrated structure.

[0062] It should be noted that the spherical fiber waveguide structure integrated in the conical region of the present invention includes a fiber waveguide structure formed by integrating fiber bundles and burning them into a sphere.

[0063] In some embodiments, the input end of the multimode output fiber 30 is subjected to a sintering process to form a third sintering structure 34; and the third sintering structure 34 is fused with the second sintering structure 22 formed at the output end of all input fibers in the tapered fusion region 11 to form an integrated structure.

[0064] The burn-ball transition structure of the present invention includes a third burn-ball structure 34 formed at the input end of the multimode output fiber 30 and a common second burn-ball structure 22 formed at the output end of all input fibers in the tapered fusion region 11.

[0065] In some embodiments, the input fiber bundle 10 forms a plurality of second burn-ball structures 22 at the output end of the tapered fusion region 11, and / or forms a plurality of third burn-ball structures 34 at the input end of the multimode output fiber 30, forming a series of second burn-ball structures 22 and / or third burn-ball structures 34, that is, the plurality of burn-ball structures are in a head-to-tail configuration. Preferably, the number of second burn-ball structures 22 and / or third burn-ball structures 34 is 2-10.

[0066] refer to Figure 4 As shown, the fiber bundle assembly is located on the left side of the structure, and the fiber is fused and tapered using the sleeve method. The fused tapered region is sintered using a non-contact electric arc process; at the same time, one end of the multimode output fiber 30 is sintered, and the two sintered structures are fused together in the tapered region to form a sintered transition structure, which excites the incident Gaussian beam in modes, and forms a uniform light field distribution after passing through the multimode output fiber 30.

[0067] refer to Figure 5 As shown, there are two second sintered ball structures 22, and the two second sintered ball structures 22 and one third sintered ball structure 34 form a series optical path connected end to end.

[0068] Example 3

[0069] This invention discloses a method for fabricating an integrated fiber coupler with flat-top beam output, such as... Figure 6 As shown, it includes the following steps:

[0070] Step S1: Taper the output end of the input fiber bundle 10 to form a tapered fusion region 11;

[0071] Step S2: Perform a sintering process on the output end of the input fiber bundle 10 in the tapered fusion region 11 to form at least one sintered ball structure 20.

[0072] Step S3: The input end of the multimode output fiber 30 is fused with the spherical structure 20 formed at the output end of the input fiber bundle 10 in the tapered fusion zone 11.

[0073] In some embodiments, the step of "tapering the output end of the input fiber bundle 10 to form a tapered fusion region 11" includes:

[0074] The input fiber bundle 10 is placed into the sleeve to form a prefabricated fiber bundle, and the prefabricated fiber bundle is tapered to form a tapered fusion zone 11.

[0075] In some embodiments, the step of "performing a sintering process on the output end of the input fiber bundle 10 at the tapered fusion region 11 to form at least one sintered structure 20" includes:

[0076] The output end of the tapered fusion zone 11 is cut, and the cut end face is subjected to a ball-burning process to form at least one ball-burning structure 20.

[0077] In some embodiments, the step of "performing a sintering process on the output end of the input fiber bundle 10 in the tapered fusion region 11 to form at least one sintered structure 20, and fusion splicing the input end of the multimode output fiber 30 with the sintered structure 20 formed at the output end of the input fiber bundle 10 in the tapered fusion region" includes:

[0078] The output end of the tapered fusion region 11 is cut, and the cut end face is sintered to form a first sintered structure 21 for each input fiber. The input end of the multimode output fiber 30 is then fused directly to multiple first sintered structures 21; or

[0079] All input fibers of the input fiber bundle 10 are sintered at the output end of the tapered fusion region 11 to form a common second sintered sphere structure, and the diameter of the spherical structure of the second sintered sphere structure 22 is larger than the sum of the core diameters of all input fibers in the tapered fusion region 11; the input end of the multimode output fiber 30 is fused to the spherical structure of the second sintered sphere structure 22 to form an integrated structure; or

[0080] The output end of the tapered fusion region 11 is cut, and the cut end face is sintered to form a common second sintered structure 22 for all input optical fibers. The input end of the multimode output optical fiber 30 is sintered to form a third sintered structure 34, and the third sintered structure 34 is fused with the second sintered structure 22.

[0081] Based on the above steps, it should be noted that in the preparation method of the present invention, an input fiber bundle 10 and a multimode output fiber 30 are prepared in advance. The input fiber bundle 10 is placed in a fluorine-doped outer tube to form a prefabricated fiber bundle. The prefabricated fiber bundle is tapered, the tapered region is cut, and the end face of the cut tapered region and / or the input end of the multimode output fiber 30 are sintered to prepare a transition structure.

[0082] In some embodiments, the multiple first spherical structures 21 of the tapered fusion region 11 are in a parallel optical path configuration.

[0083] Example 4

[0084] This invention discloses a method for outputting a flat-top light spot. The method uses an integrated fiber optic coupler with flat-top light spot output as described in Embodiment 1 or Embodiment 2, or an integrated fiber optic coupler with flat-top light spot output as described in Embodiment 3. The fiber optic coupler includes an input fiber bundle 10, a multimode output fiber 30, and at least one burnt-ball structure 20.

[0085] The preparation method of this embodiment includes:

[0086] The laser beam originates from the input fiber bundle 10, passes through the spherical structure 20, and increases the proportion of higher-order modes in the output laser in the spherical fiber waveguide of the spherical structure 20. After exiting through the spherical structure, it is coupled into the multimode output fiber 30, thus achieving flat-top energy output.

[0087] The multiple input optical fibers are bundled together through a fluorine-doped tube. The laser is coupled into the tapered region through the input optical fiber bundle 10. The tapered region is subjected to a spherical burning process, or a single input optical fiber is burned to form a spherical array to expand the diameter of the optical fiber waveguide and excite mixed higher-order modes. The excited mixed higher-order modes are coupled into the multimode output optical fiber 30 for transmission, forming a light intensity distribution with a flat top.

[0088] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. An integrated fiber optic coupler with flat-top beam output, characterized in that, Includes an input fiber bundle, a multimode output fiber, and a burn-in ball transition structure; The input fiber bundle includes at least two input fibers, and the output end of the input fiber bundle is tapered to form a tapered fusion region; the input fiber bundle has the burn-ball transition structure formed between the output end of the tapered fusion region and the input end of the multimode output fiber; The output end of the tapered fusion region is subjected to a spherical burning process to form at least one spherical structure, and the diameter of the spherical structure of the spherical structure is larger than the core diameter of the input optical fiber integrally connected to it in the tapered fusion region in order to increase the proportion of higher-order modes in the laser. The input end of the multimode output fiber is fused to the sintered ball structure formed at the output end of the input fiber bundle in the tapered fusion zone. The burnt-ball transition structure includes at least the burnt-ball structure formed by the input fiber bundle at the output end of the tapered fusion region.

2. The integrated fiber optic coupler with flat-top beam output according to claim 1, characterized in that, Each input optical fiber at the output end of the tapered fusion zone is subjected to a spherical burning process to form a first spherical structure. The diameter of the spherical structure of each first spherical structure is larger than the core diameter of the corresponding single input optical fiber in the tapered fusion zone. Multiple first burnt-ball structures of multiple input optical fibers are arranged in an array to form a burnt-ball array, and the burnt-ball transition structure includes the burnt-ball array; The input end of the multimode output optical fiber is fused with the spherical structure of multiple first burnt-ball structures to form an integrated structure.

3. The integrated fiber optic coupler with flat-top beam output according to claim 1, characterized in that, All the input optical fibers of the input fiber bundle are sintered at the output end of the tapered fusion region to form a common second sintered sphere structure, and the diameter of the spherical structure of the second sintered sphere structure is greater than the sum of the core diameters of all the input optical fibers in the tapered fusion region; The input end of the multimode output optical fiber is fused to the spherical structure of the second burnt-ball structure to form an integrated structure.

4. The integrated fiber optic coupler with flat-top beam output according to claim 3, characterized in that, The input end of the multimode output optical fiber is subjected to a sintering process to form a third sintered structure, and the third sintered structure of the multimode output optical fiber is fused with the second sintered structure to form an integral structure. The burnt ball transition structure includes the third burnt ball structure and the second burnt ball structure.

5. The integrated fiber optic coupler with flat-top beam output according to claim 1, characterized in that, The output end of the input fiber bundle is formed by fusion tapering using a sleeve method to create the tapered fusion region. The sleeve fitted onto the output end of the input fiber bundle is made of quartz composite material. The radius of curvature R of the sintered sphere structure formed at the output end of the input fiber bundle in the tapered fusion region satisfies the following: Wherein, n1 is the refractive index of the sleeve, n2 is the core refractive index of the multimode output fiber, and α is the incident angle of the laser.

6. The integrated fiber optic coupler with flat-top beam output according to claim 1, characterized in that, The length of the tapered fusion zone is 5-15mm, and the taper angle is 2°-8°; The radius of curvature of the sintered sphere structure formed at the output end of the tapered fusion region by the input fiber bundle is 50-600 μm. The core diameter of the multimode output fiber is 100-1000 μm, and the numerical aperture (NA) of the multimode output fiber is 0.

22.

7. The integrated fiber optic coupler with flat-top beam output according to claim 2, characterized in that, The input fiber bundle includes a first input fiber located at the center and multiple second input fibers arranged circumferentially around the first input fiber. The total number Q of the first input fiber and the multiple second input fibers satisfies: Q=3n 2 +3n+1; Where n is a positive integer.

8. A method for fabricating an integrated fiber optic coupler with flat-top beam output, characterized in that, Includes the following steps: Taper the output end of the input fiber bundle to form a tapered fusion zone; The input fiber bundle is subjected to a sintering process at the output end of the tapered fusion region to form at least one sintered structure: The input end of the multimode output fiber is fused with the sintered ball structure formed at the output end of the input fiber bundle in the tapered fusion zone.

9. The preparation method according to claim 8, characterized in that, The steps of "tapering the output end of the input fiber bundle to form a tapered fusion zone" include: The input fiber bundle is placed into a sleeve to form a prefabricated fiber bundle, and the prefabricated fiber bundle is tapered to form the tapered fusion region; The steps of "performing a sintering process on the output end of the input fiber bundle in the tapered fusion region to form at least one sintered structure, and then fusion splicing the input end of the multimode output fiber to the sintered structure formed at the output end of the input fiber bundle in the tapered fusion region" include: The output end of the tapered fusion region is cut, and the cut end face is sintered to form a first sintered ball structure for each input fiber. The input end of the multimode output fiber is then fused with multiple first sintered ball structures; or All the input fibers of the input fiber bundle are sintered at their output ends in the tapered fusion region to form a common second sintered-sphere structure. The input ends of the multimode output fibers are then fused to the spherical structure of the second sintered-sphere structure to form an integral structure; or All the input optical fibers of the input fiber bundle are subjected to a sintering process at the output end of the tapered fusion zone to form a common second sintered structure. The input end of the multimode output fiber is subjected to a sintering process to form a third sintered structure, and the third sintered structure is fused with the second sintered structure. Wherein, the diameter of the spherical structure of the second burnt sphere structure is greater than the sum of the core diameters of all the input optical fibers in the tapered fusion region.

10. A method for outputting a flat-top light spot, characterized in that, An integrated fiber optic coupler with flat-top spot output as described in any one of claims 1-7 or an integrated fiber optic coupler with flat-top spot output as described in any one of claims 8-9, wherein the fiber optic coupler comprises an input fiber bundle, a multimode output fiber, and at least one sintered ball structure. The method includes the following steps: The laser beam originates from the input fiber bundle, passes through the spherical structure, and increases the proportion of higher-order modes in the output laser within the spherical fiber waveguide of the spherical structure. After exiting the spherical structure, the laser beam is coupled into the multimode output fiber, achieving flat-top energy output.

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