Manufacturing method of hollow-core optical fiber preform with special-shaped structure

Abstract

The invention provides a manufacturing method of a hollow-core optical fiber preform with a special-shaped structure, and belongs to the technical field of manufacturing of optical fiber preforms. The method comprises the following steps: firstly, providing at least two hollow glass tubes; cutting each hollow glass tube along the axial direction of the hollow glass tube to form a C-shaped section tube with an opening; then, at least two C-shaped section pipes are in butt joint at the openings of the C-shaped section pipes, and a pre-assembly body with a special-shaped section structure is formed through combination; and finally, laser beams are adopted for welding along seams at the butt joint positions of the C-shaped section pipes, so that the C-shaped section pipes are combined into a whole, and the hollow-core optical fiber preform with the special-shaped structure is formed. Through modularized C-shaped pipe butt joint and laser welding, the problem that a complex special-shaped hollow core structure is difficult to manufacture through a traditional method is solved, high-precision forming and stable inheritance of the special-shaped structure are achieved, and a reliable manufacturing basis is provided for space division multiplexing and other frontier optical applications.

Description

Technical Field

[0001] This invention relates to the field of optical fiber preform manufacturing technology, and specifically to a method for manufacturing an irregularly shaped hollow optical fiber preform. Background Technology

[0002] With the increasing application of fiber optic technology in communication, sensing, and laser transmission, the requirements for fiber performance are becoming increasingly stringent. Traditional solid-core optical fibers are limited by material properties, resulting in limitations in transmission power, nonlinear effects, and bandwidth. Hollow-core optical fibers, using air as the primary light-guiding medium, can significantly reduce nonlinear effects and material absorption, making them suitable for high-power transmission and broadband optical communication.

[0003] Currently, structures such as antiresonant hollow-core optical fibers have attracted widespread attention, typically consisting of an outer cladding tube and an internal capillary array. However, existing technologies are mostly limited to circular symmetrical structures, making it difficult to achieve non-circular, multi-core, or irregularly shaped hollow-core designs, which are precisely what multifunctional integrated optical fibers such as space division multiplexing and orbital angular momentum mode transmission require. Existing manufacturing methods, such as tube-rod stacking, are difficult to construct non-circular cavities, and surface tension during fiber drawing can easily cause shape recovery. If multiple irregularly shaped glass tubes are used for assembly, problems such as difficult positioning, complex fixing, and high welding precision requirements arise. In particular, for the three-dimensional spatial curved contact line formed by open butt joints, existing laser welding technology struggles to achieve precise energy control and trajectory tracking. Summary of the Invention

[0004] This invention provides a method for manufacturing irregularly shaped hollow optical fiber preforms, which solves the problems in the prior art, such as the difficulty in constructing complex irregularly shaped hollow structures due to the reliance on stacked circular tubes, and the inability to maintain the preset geometric shape during the fiber drawing process due to the shape restoration effect.

[0005] To achieve the above objectives, one embodiment of the present invention provides a method for manufacturing an irregularly shaped hollow optical fiber preform, comprising: step S1: providing at least two hollow glass tubes; step S2: cutting each of the hollow glass tubes along its axial direction to form a C-shaped cross-section tube with an opening; step S3: joining at least two of the C-shaped cross-section tubes together at their openings to form a pre-assembled body with an irregularly shaped cross-section structure; step S4: using a laser beam to weld along the joint at the joint of the C-shaped cross-section tubes, so that the C-shaped cross-section tubes are combined into one body to form the irregularly shaped hollow optical fiber preform.

[0006] Furthermore, in step S3, the two C-shaped cross-section tubes are joined together to form the pre-assembled body with a figure-eight cross-section.

[0007] Furthermore, in step S3, three or more of the C-shaped cross-section tubes are symmetrically arranged and connected around a center point to form the pre-assembled body with a quincunx or ring array cross-section.

[0008] Furthermore, in step S2, the C-shaped cross-section tube is formed by laser cutting, and the wavelength range of the laser is 9μm to 11μm.

[0009] Furthermore, step S2 also includes: flame polishing or hot annealing the cut edge of the C-shaped cross-section tube.

[0010] Furthermore, in step S3, a positioning mold with a negative cavity is used to align and fix the C-shaped cross-section tube, the shape of which matches the target irregular cross-section structure.

[0011] Furthermore, in step S4, the pre-assembled body is moved by controlling the multi-axis motion platform, and / or the focus of the laser beam is precisely moved along the three-dimensional spatial trajectory of the seam by controlling the deflection of the laser scanning galvanometer.

[0012] Furthermore, in step S4, the laser power or scanning speed is adjusted in real time according to the curvature of the joint.

[0013] On the other hand, a hollow optical fiber preform with an irregular structure is also provided, which is manufactured by the above-mentioned manufacturing method. Its cross-section includes a continuous glass body formed by welding at least two C-shaped hollow glass tubes at the opening. The glass body forms a hollow structure with a cross-section of "8", plum blossom, or ring array.

[0014] On the other hand, a hollow optical fiber is also provided, which is drawn by the aforementioned irregularly shaped hollow optical fiber preform.

[0015] This invention provides a method for manufacturing irregularly shaped hollow optical fiber preforms. By employing an innovative process of C-shaped tube modular docking and laser welding, high-precision and customizable manufacturing of irregularly shaped hollow optical fiber preforms is achieved. This method decomposes complex irregular structures into standardized C-shaped units, fundamentally overcoming the limitation of traditional circular tube stacking technology in constructing non-circular hollow structures. Precision welding along the three-dimensional docking seam using a programmable laser scanning system not only achieves high-strength bonding between C-shaped tubes but, more importantly, effectively suppresses the shape restoration effect during subsequent high-temperature fiber drawing. This ensures that pre-designed complex geometric structures such as figure-eight and cloverleaf shapes can be completely and stably inherited into the final optical fiber product, providing a reliable manufacturing foundation for meeting the stringent requirements of core geometry in cutting-edge applications such as space division multiplexing and orbital angular momentum transmission. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a structural schematic diagram of the manufacturing method of the irregularly shaped hollow optical fiber preform provided in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the final product provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of another final product provided in Embodiment 2 of the present invention.

[0017] Among them, 1. C-shaped cross-section tube; 2. Laser beam; 3. Focusing lens; 4. Laser; 5. Irregularly shaped hollow fiber preform; 6. Hollow-core anti-resonant fiber. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0019] It should be noted that the acquisition, transmission, storage, use, and processing of data in the technical solution of this application all comply with the relevant provisions of national laws and regulations. In the embodiments of this application, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this application, and do not imply that the applicant has already used or necessarily used such solutions.

[0020] As optical fiber technology advances into cutting-edge fields such as space division multiplexing, orbital angular momentum transfer, and high-dimensional signal processing, existing hollow-core optical fiber preform manufacturing technologies face core bottlenecks, including the difficulty in precisely shaping irregularly shaped structures, the susceptibility of complex geometries to deformation due to surface tension during fiber drawing, and the challenge of ensuring the symmetry and consistency of multi-core arrangements. Therefore, developing a novel preform preparation method capable of achieving high-precision manufacturing and stable inheritance of complex irregularly shaped hollow-core structures is crucial.

[0021] To address this issue, this invention proposes a method for manufacturing irregularly shaped hollow fiber preforms. By precisely cutting standard circular tubes into C-shaped basic units as flexible building blocks, the method overcomes the shape limitations of traditional circular tube stacking on the hollow geometry. A multi-axis motion platform is used to control a laser beam to scan and weld along a three-dimensional seam. Its local energy deposition characteristics effectively suppress the shape recovery effect at high temperatures, ensuring the complete inheritance of the irregular structure from preform to fiber. Finally, through various combinations of the number of C-shaped tubes, opening orientation, and docking methods, the method enables the customized and high-precision manufacturing of various complex hollow structures, providing a reliable material basis for space division multiplexing, special mode excitation, and multifunctional integrated optical fibers.

[0022] The following is combined with Figures 1-3 This invention is described in detail.

[0023] Example 1 like Figure 1 As shown, an embodiment of the present invention provides a method for manufacturing an irregularly shaped hollow optical fiber preform, comprising: step S1: providing at least two hollow glass tubes; step S2: cutting each of the hollow glass tubes along its axial direction to form a C-shaped cross-section tube with an opening; step S3: joining at least two of the C-shaped cross-section tubes together at their openings to form a pre-assembled body with an irregularly shaped cross-section structure; step S4: using a laser beam to weld along the joint at the joint of the C-shaped cross-section tubes, so that each of the C-shaped cross-section tubes is integrated into one body to form the irregularly shaped hollow optical fiber preform.

[0024] Specifically, the hollow glass tube can be a quartz glass tube with an outer diameter of 6mm, a wall thickness of 0.6mm, and a length of 1000mm. Using a carbon dioxide laser cutting system, at a wavelength of 10.6μm, a power of 50W, and a cutting speed of 10mm / s, the glass tube is precisely processed axially into a C-shaped cross-section tube with an opening angle of approximately 150°. Subsequently, two C-shaped tubes are placed in a V-shaped positioning groove, and their openings are aligned with each other by a precision motion platform to form an "8"-shaped pre-assembled body. Finally, a continuous wave CO2 laser is used, and a laser beam with a power set to 45W is focused by a lens and controlled by a multi-axis motion platform to scan and weld along the three-dimensional seam of the pre-assembled body at a speed of 5mm / s, thereby achieving the integrated combination of the C-shaped tubes and forming a structurally complete "8"-shaped hollow fiber preform.

[0025] The manufacturing method for irregularly shaped hollow optical fiber preforms provided in this invention, through an innovative process of "providing—cutting—docking—welding," fundamentally overcomes the limitations of traditional circular tube stacking technology in constructing complex irregularly shaped hollow structures, advancing optical fiber preform manufacturing from passive stacking to a new stage of active design. This solution precisely cuts standard circular tubes into C-shaped basic units, providing unprecedented design freedom for flexible combination into pre-defined irregularly shaped structures such as the figure-eight shape. Furthermore, the use of a laser beam for local scanning welding along the three-dimensional docking seam, with its concentrated energy and small heat-affected zone, ensures high-precision forming of the irregularly shaped structure and effectively resists the shape recovery effect during subsequent high-temperature drawing, thus inheriting the complex geometric design completely and stably into the final optical fiber product. This method not only solves the feasibility problem of manufacturing irregularly shaped structures but also significantly improves the reliability and scalability of the process with its modular and standardized characteristics, providing a crucial manufacturing foundation for cutting-edge optical applications such as space division multiplexing and orbital angular momentum transmission.

[0026] Preferably, in step S2, the C-shaped cross-section tube is formed by laser cutting, and the wavelength range of the laser is 9μm to 11μm.

[0027] Specifically, the laser cutting method preferably employs a carbon dioxide laser with a typical output wavelength of 10.6 μm, falling within the 9 μm to 11 μm range. This wavelength of laser light can be effectively absorbed by quartz glass, achieving efficient and clean cutting. During cutting, the laser power can be controlled between 40W and 60W, with the spot diameter focused to approximately 50 μm. A precision rotating fixture drives the glass tube to rotate uniformly at a linear velocity of 5 mm / s to 15 mm / s, thereby cutting away one side along the axial direction to form a C-shaped cross-section tube with an opening angle of 120° to 170°. This laser cutting process results in a narrow kerf and a small heat-affected zone, producing smooth cut edges free of microcracks, laying a solid foundation for subsequent butt welding and welding processes.

[0028] In a preferred embodiment of the present invention, the laser cutting wavelength is limited to the range of 9μm to 11μm, allowing the photon energy of this wavelength to be efficiently absorbed by the quartz glass material, thereby achieving rapid and clean cutting. This efficient linear optical absorption mechanism can generate localized melting and vaporization, forming a precise cut with a narrow kerf and a small heat-affected zone. This not only avoids microcracks and stress concentrations that may be caused by mechanical cutting, but also provides a high-quality, high-precision C-shaped cross-section tube foundation for subsequent butt welding processes, ensuring the structural integrity and geometric accuracy of the final irregular-shaped preform from the source.

[0029] Preferably, step S2 further includes: flame polishing or hot annealing the cut edge of the C-shaped cross-section tube.

[0030] Specifically, flame polishing can be performed using an oxyhydrogen flame or an oxypropane flame. The flame tip sweeps across the cut edge of the C-shaped tube, using high temperature to instantly melt and level the micron-sized thin layer on the glass surface, effectively eliminating microcracks and burrs generated during cutting and forming a smooth and flat welding interface. The thermal annealing process involves placing the cut C-shaped tube in a programmable temperature controlled furnace and slowly heating it at a rate not exceeding 5°C / min to a temperature near the glass strain point, for example, approximately 1050°C for quartz glass. After holding at this temperature for 1 to 2 hours, it is then slowly cooled to room temperature at a rate not exceeding 3°C / min. This process effectively releases the mechanical stress introduced by cutting, improves the structural stability of the edge material, and prevents microcracks from propagating in subsequent processing. Both of these post-treatment methods significantly improve the quality of the cut edge, providing a clean and stable bonding interface for subsequent laser welding, thereby ensuring the overall mechanical strength and long-term reliability of the irregularly shaped preform.

[0031] In a preferred embodiment of the invention, the introduction of a post-treatment step such as flame polishing or hot annealing effectively eliminates micro-cracks on the cut edges of the C-shaped tube and releases its internal stress, thereby significantly improving the smoothness of the cut surface and the structural integrity of the material. This optimization not only enhances the contact tightness of the C-shaped tubes during butt welding but also provides a clean, stable, and high-quality interface for subsequent laser welding, fundamentally ensuring the mechanical strength of the weld joint and the overall structural reliability of the irregularly shaped preform, and ensuring the precise inheritance of complex geometries during the wire drawing process.

[0032] Preferably, in step S3, a positioning mold with a negative cavity is used to align and fix the C-shaped cross-section tube, and the shape of the negative cavity matches the target irregular cross-section structure.

[0033] Specifically, the positioning mold can be made of high-purity graphite or high-temperature resistant ceramic material. Its negative cavity is prepared using precision machining or laser ablation technology based on a precise three-dimensional model of the target irregular structure. Taking the formation of an "8"-shaped preform as an example, the negative cavity of the mold is a standard "8"-shaped groove, whose dimensions have a micron-level interference fit or transition fit relationship with the outer contour of the two C-shaped tubes after docking. During assembly, the pre-prepared C-shaped tubes are precisely embedded into the corresponding positions of the grooves. The mold cavity wall automatically constrains the degrees of freedom of each C-shaped tube in the horizontal and vertical directions, ensuring self-alignment and tight docking at their openings, thereby quickly and accurately forming the required pre-assembled body.

[0034] Preferably, in step S4, the pre-assembled body is moved by controlling the multi-axis motion platform, and / or the focus of the laser beam is precisely moved along the three-dimensional spatial trajectory of the seam by controlling the deflection of the laser scanning galvanometer.

[0035] More preferably, in step S4, the laser power or scanning speed is adjusted in real time according to the curvature of the joint.

[0036] Specifically, the multi-axis motion platform can be a five-axis linkage system, integrating X, Y, and Z linear axes, an A-axis rotating around the X-axis, and a C-axis rotating around the Z-axis. The pre-assembled body is fixed on the platform's fixture. Simultaneously, the laser scanning galvanometer system consists of a pair of high-speed galvanometer mirrors, which can deflect the laser beam angle under computer control. Before welding, based on the butt joint trajectory in the three-dimensional model of the pre-assembled body, a composite control program containing the platform's motion path and galvanometer deflection commands is pre-programmed. During welding, the platform moves the workpiece in macroscopic linear and rotational motions, while the galvanometer performs microscopic, rapid, and precise positioning of the laser focus. The two work together to enable the laser focus to accurately track the complex butt joint in three-dimensional space. During this process, the control system monitors the curvature changes of the motion trajectory in real time. For example, when the turning radius of the welding path decreases, the laser power is automatically reduced from 45W to 42W and the scanning speed is slowed from 5mm / s to 3mm / s to ensure uniform energy deposition on the curved path and avoid excessive ablation of the glass material due to overheating or weak welding due to insufficient heat. When the path returns to straight, the parameters are adjusted accordingly. This dynamic adaptive control strategy, combining macroscopic positioning and microscopic correction, ensures consistent and reliable welding quality along the entire three-dimensional joint.

[0037] Preferably, the hollow-core anti-resonant optical fiber further includes a second anti-resonant layer 3, which is disposed outside the first anti-resonant layer 4 and surrounded by the inner cladding layer 2. The second anti-resonant layer 3 is composed of one or more auxiliary air holes, which are arranged in a ring around the first anti-resonant layer 4 and have a polygonal cross-sectional shape.

[0038] This invention also provides an irregularly shaped hollow optical fiber preform, manufactured by the above-described manufacturing method, the cross-section of which includes a continuous glass body formed by welding at least two C-shaped hollow glass tubes at the opening, the glass body forming a hollow structure with a cross-section of "8", plum blossom, or ring array.

[0039] This invention also provides a hollow optical fiber, which is formed by drawing an irregularly shaped hollow optical fiber preform.

[0040] like Figure 2 As shown, in this embodiment of the invention, the glass body is arranged in a cross-section of the number "8".

[0041] Example 2, The main difference between this embodiment and Embodiment 1 lies in the increased number of C-shaped tubes, the assembly method, and the increased complexity of the corresponding welding path.

[0042] like Figure 3As shown, specifically, this embodiment uses three hollow quartz glass tubes of the same specifications as in Embodiment 1. They are also machined into C-shaped cross-section tubes with an opening angle of approximately 150° using a carbon dioxide laser cutting system, and the cut edges are flame-polished. Subsequently, a positioning mold made of high-purity graphite is used for assembly. The core of this mold is a precision-machined quincunx-shaped negative cavity, the outline of which matches the outer contour of the three C-shaped tubes arranged symmetrically around a central point with their openings facing inwards. The three C-shaped tubes are carefully embedded into the cavity of the mold; the mold's constraint ensures they automatically and precisely align, forming a stable quincunx-shaped pre-assembled body with clear and distinct seams between the three tubes. Laser welding is then performed. The basic parameters of the welding system are the same as in Embodiment 1. Due to the increased number of seams to three and the more complex path, the motion control program was adjusted. Based on the quincunx-shaped geometric model, the three-dimensional spatial trajectory of the laser focus scanning the three seams sequentially is pre-programmed. During welding, the multi-axis motion platform and the laser scanning galvanometer work together. Because the curvature changes more significantly at the corners of the quincunx-shaped structure, an adaptive parameter adjustment strategy was implemented in the control system: when the laser scans to the corner area, the system automatically reduces the scanning speed from 5 mm / s to 3 mm / s and fine-tunes the laser power accordingly to ensure uniform energy deposition along the complex geometric path and avoid overheating or weak welding. Finally, the welding of the three seams is completed sequentially, firmly combining the three C-shaped tubes into a single quincunx-shaped hollow fiber preform. After welding, the same annealing process as in Example 1 is used to eliminate internal stress.

[0043] The embodiments of this invention demonstrate that by using a positioning mold of a specific shape and adaptive laser welding control, a complex quincunx-shaped hollow optical fiber preform was successfully manufactured. This fully proves that the method described in this invention is not only applicable to simple figure-eight structures, but also possesses strong flexibility and reliability in manufacturing various complex irregular structures, providing an effective manufacturing solution for the diverse needs of special optical fibers.

[0044] In summary, the manufacturing method for irregularly shaped hollow optical fiber preforms provided by this invention successfully solves three core challenges in the manufacturing of irregularly shaped hollow optical fiber preforms: difficulty in structural forming, low geometric accuracy, and poor shape inheritance. This method decomposes complex irregular structures into standardized C-shaped units, overcoming the geometric limitations of traditional circular tube stacking technology. It enables flexible design and high-precision manufacturing of various hollow structures, from figure-eight to quincunx shapes. Utilizing localized laser scanning welding, the concentrated and controllable energy significantly reduces thermal deformation, ensuring that the irregular structure is completely and stably inherited into the optical fiber during subsequent high-temperature drawing. This provides a reliable and customizable foundation for the manufacturing of special optical fibers for cutting-edge optical applications such as space division multiplexing and orbital angular momentum transmission.

[0045] The above description is merely a preferred embodiment of the technical solution of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing an irregularly shaped hollow optical fiber preform, characterized in that, include: Step S1: Provide at least two hollow glass tubes; Step S2: Cut each of the hollow glass tubes along its axial direction to form a C-shaped cross-section tube with an opening; Step S3: Connect at least two of the C-shaped cross-section tubes together at their openings to form a pre-assembled body with an irregular cross-section structure; Step S4: Use a laser beam to weld along the joint of the C-shaped cross-section tubes, so that the C-shaped cross-section tubes are combined into one, forming the irregular hollow fiber preform.

2. The manufacturing method according to claim 1, characterized in that, In step S3, the two C-shaped cross-section tubes are joined together to form the pre-assembled body with a figure-eight cross-section.

3. The manufacturing method according to claim 1, characterized in that, In step S3, three or more of the C-shaped cross-section tubes are symmetrically arranged and connected around a center point to form the pre-assembled body with a quincunx or ring array cross-section.

4. The manufacturing method according to claim 1, characterized in that, In step S2, the C-shaped cross-section tube is formed by laser cutting, and the wavelength range of the laser is 9μm to 11μm.

5. The manufacturing method according to claim 1, characterized in that, Step S2 further includes: flame polishing or hot annealing the cut edge of the C-shaped cross-section tube.

6. The manufacturing method according to claim 1, characterized in that, In step S3, a positioning mold with a negative cavity is used to align and fix the C-shaped cross-section tube, and the shape of the negative cavity matches the target irregular cross-section structure.

7. The manufacturing method according to claim 1, characterized in that, In step S4, the pre-assembled body is moved by controlling the multi-axis motion platform, and / or the focus of the laser beam is precisely moved along the three-dimensional spatial trajectory of the seam by controlling the deflection of the laser scanning galvanometer.

8. The manufacturing method according to claim 1, characterized in that, In step S4, the laser power or scanning speed is adjusted in real time according to the curvature of the joint.

9. A hollow optical fiber preform with an irregular structure, characterized in that, Manufactured by the manufacturing method of any one of claims 1 to 8, the cross-section of which comprises a continuous glass body formed by welding at the opening of at least two C-shaped hollow glass tubes, the glass body forming a hollow structure with a cross-section of "8", plum blossom, or annular array.

10. A hollow optical fiber, characterized in that, It is formed by drawing the irregularly shaped hollow optical fiber preform as described in claim 9.

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