Antiresonant hollow core fiber and method of making the same

Abstract

The embodiment of the application provides a kind of anti-resonant hollow optical fiber and its preparation method, belong to optical fiber technical field.Anti-resonant hollow optical fiber includes outer cladding, multiple anti-resonant structures and connecting piece, multiple the anti-resonant structure is spaced in the outer cladding, the anti-resonant structure includes arc part and two straight parts, the arc part and two the straight part are enclosed to form closed cavity, the arc part of multiple the anti-resonant structure jointly defines the core area for light transmission, the straight part extends to the outer cladding in the direction away from the core area, the arc part is protrudingly arranged towards the direction of the core area;The connecting piece one end is connected with the inner wall of the outer cladding, the other end is connected with the straight part, to fix the anti-resonant structure on the outer cladding.The anti-resonant hollow optical fiber provided in the embodiment of the application can effectively constrain the position of anti-resonant structure during optical fiber drawing process, guarantee the uniformity and consistency of optical fiber structure.

Description

Technical Field

[0001] This application relates to optical fiber technology, and more particularly to an anti-resonant hollow optical fiber and its fabrication method. Background Technology

[0002] Antiresonant hollow fiber confines the optical field within a low-refractive-index air core, enabling low-latency and low-loss data transmission. Antiresonant hollow fiber comprises a multi-layered nested structure, consisting of multiple antiresonant tubes nested sequentially from the inside out. The antiresonant reflection effect created by these tubes confines the fiber core's fundamental mode.

[0003] In related technologies, the anti-resonant tube and the outer cladding of the anti-resonant hollow fiber are positioned by direct contact through the tube wall. However, during the fiber drawing process, the anti-resonant tube is blown and deformed by high temperature and gas filling, which can easily lead to contact between multiple anti-resonant tubes and the generation of nodes, causing abnormal fiber attenuation, deterioration of structural uniformity, and severely limiting the yield of anti-resonant hollow fiber. Summary of the Invention

[0004] This application provides an anti-resonant hollow optical fiber and its preparation method to solve the technical problem in related technologies where anti-resonant tubes easily come into contact and generate nodes during optical fiber drawing.

[0005] This application provides an anti-resonant hollow-core optical fiber, comprising:

[0006] Outer layer;

[0007] Multiple anti-resonant structures are spaced apart in the outer cladding layer. Each anti-resonant structure includes an arc-shaped portion and two straight portions, which enclose a closed cavity. The arc-shaped portions of the multiple anti-resonant structures collectively define a fiber core region for optical transmission. The straight portions extend to the outer cladding layer in a direction away from the fiber core region, and the arc-shaped portions protrude toward the fiber core region.

[0008] A connector, one end of which is connected to the inner wall of the outer cladding and the other end of which is connected to the straight section, so as to fix the anti-resonance structure on the outer cladding.

[0009] In some possible implementations, the two straight sections have a first intersection point, and the straight section and the arcuate section have a second intersection point;

[0010] The first intersection point is connected to the inner wall of the outer cladding layer, and the second intersection point is connected to the connector.

[0011] In some possible implementations, the second intersection point has two points located at both ends of the arcuate portion, and the two second intersection points are respectively connected to the outer cladding layer by one of the connectors.

[0012] In some possible implementations, the extension direction of the connector coincides with the tangential direction of the arcuate portion at the second intersection point.

[0013] In some possible implementations, the two straight portions are arranged symmetrically relative to the arcuate portion, and the two connectors are arranged symmetrically relative to the arcuate portion;

[0014] The outer cladding layer, the fiber core region, the first intersection point, and the center of the arc-shaped portion are all located on the same straight line.

[0015] In some possible implementations, the arcuate portion has at least two spaced outwards along the radial direction of the fiber core region, and at least two of the arcuate portions are connected to two of the straight portions; wherein, in the plurality of anti-resonant structures, the arcuate portions on the side away from the outer cladding layer collectively define the fiber core region.

[0016] In some possible implementations, it also includes:

[0017] Multiple gap anti-resonant units are arranged alternately with multiple anti-resonant structures around the fiber core region in a circumferentially spaced manner. The gap anti-resonant units are circular tubes or elliptical tubes.

[0018] Multiple anti-resonant tubes are disposed in the closed cavity. The anti-resonant tubes are tangentially arranged with the two straight sections. Both the anti-resonant tubes and the arc-shaped sections are used to form an anti-resonant reflective surface.

[0019] In some possible implementations, the included angle between the two straight sections is 20° to 170°; the ratio of the length of the straight section to the radius of the fiber core region is 1.2-3;

[0020] The arc length of the arc-shaped portion and the straight portion satisfy the following formula:

[0021] ;

[0022] Where L is the arc length of the arc-shaped portion. Let α be the length of the straight section, and α be the included angle between the two straight sections.

[0023] In some possible implementations, the anti-resonance structure, the gap anti-resonance unit, and the anti-resonance tube are all quartz tubes.

[0024] On the other hand, this application also provides a method for fabricating an anti-resonant hollow-core optical fiber, used to fabricate the anti-resonant hollow-core optical fiber as described in any of the preceding claims. The method for fabricating the anti-resonant hollow-core optical fiber includes the following steps:

[0025] Provide an outer layer;

[0026] Multiple nested tubular components are provided in the outer cladding layer, and the outer cladding layer and the nested tubular components are connected by connectors.

[0027] The nested tubes are adjusted to form an anti-resonance structure, which includes an arc-shaped portion and two straight portions. The arc-shaped portion and the two straight portions enclose a closed cavity. The arc-shaped portions of the multiple anti-resonance structures collectively define a fiber core region for optical transmission. The straight portions extend to the outer cladding layer in a direction away from the fiber core region, and the arc-shaped portions protrude in a direction toward the fiber core region.

[0028] The anti-resonant hollow fiber and its fabrication method provided in this application embodiment have a straight section extending to the cladding in the anti-resonant hollow fiber in a direction away from the fiber core region. One end of the connector is connected to the straight section, and the other end is connected to the inner wall of the cladding. Thus, the anti-resonant structure forms a multi-point connection with the cladding through the connection between the straight section and the cladding, and the connection between the connector and the cladding. Compared with the anti-resonant tube in related technologies that contacts the cladding at a fixed point through the tube wall, the multi-point connection can effectively constrain the spatial position of the anti-resonant structure during the fiber drawing process, and prevent the anti-resonant structure from contacting and generating nodes under high temperature and gas expansion environment. This is beneficial to extend the single drawing length and ensure the uniformity and consistency of the fiber structure.

[0029] In addition, the arc-shaped part protrudes towards the fiber core region, and the arc-shaped part and the two straight parts enclose a closed cavity. The arc-shaped part itself constitutes the anti-resonance reflection surface of the anti-resonance structure. Compared with the anti-resonance tube with a circular cross section, the irregularly shaped closed cavity reduces the area of ​​the air region inside the anti-resonance structure, which is beneficial to suppressing the parasitic coupling between the fiber core fundamental mode and the cladding mode, thereby further reducing the fundamental mode leakage loss and making it easier to obtain a flatter transmission loss spectrum. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] Figure 1 This is a schematic diagram of the structure of the anti-resonant hollow fiber provided in the embodiments of this application;

[0032] Figure 2 A schematic diagram illustrating the fabrication process of the anti-resonant hollow-core optical fiber provided in this application embodiment;

[0033] Figure 3 This is a structural simulation diagram of the anti-resonant hollow fiber provided in Embodiment 1 of this application;

[0034] Figure 4 This is a scanning electron microscope image of the anti-resonant hollow fiber provided in Embodiment 1 of this application;

[0035] Figure 5 This is the transmission loss spectrum of the anti-resonant hollow fiber provided in Embodiment 1 of this application;

[0036] Figure 6 This is a structural simulation diagram of the anti-resonant hollow fiber provided in Embodiment 2 of this application;

[0037] Figure 7 This is the transmission loss spectrum of the anti-resonant hollow-core optical fiber provided in Embodiment 2 of this application;

[0038] Figure 8 This is a scanning electron microscope image of the anti-resonant hollow fiber provided in Embodiment 3 of this application;

[0039] Figure 9 This is a histogram of the single-drawing length distribution of the anti-resonant hollow optical fiber provided in Embodiments 1 and 3 of this application.

[0040] Explanation of reference numerals in the attached figures

[0041] 100. Outer cladding layer; 110. Core area;

[0042] 200. Anti-resonance structure; 210. Arc-shaped section; 220. Straight section; 230. First intersection point; 240. Second intersection point;

[0043] 300. Connectors;

[0044] 400, Gap Anti-Resonant Unit;

[0045] 500, anti-resonant transistor;

[0046] 600. Nested pipe fittings;

[0047] 700. Initial thin-walled tube;

[0048] 800, Quartz mother tube;

[0049] 900. Mold.

[0050] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0053] In this application, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0054] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.

[0055] Unless otherwise stated, the term "multiple" means two or more.

[0056] As mentioned in the background technology, in related technologies, the anti-resonant tube and the outer cladding of the anti-resonant hollow fiber are directly positioned by tube wall contact. However, during the fiber drawing process, the anti-resonant tube is blown and deformed by high temperature and gas filling, which can easily lead to contact between multiple anti-resonant tubes and the generation of nodes, causing abnormal fiber attenuation, deterioration of structural uniformity, and severely limiting the yield of anti-resonant hollow fiber.

[0057] Based on the above description of the relevant technologies, one or more embodiments of this application provide an anti-resonant hollow-core optical fiber and a method for preparing the same. In the anti-resonant hollow-core optical fiber, the straight portion extends to the cladding in a direction away from the fiber core region. One end of the connector is connected to the straight portion, and the other end is connected to the inner wall of the cladding. Thus, the anti-resonant structure forms a multi-point connection with the cladding through the connection of the straight portion to the cladding and the connection of the connector to the cladding. Compared with the anti-resonant tube in the related technology that contacts the cladding at a fixed point through the tube wall, the multi-point connection can effectively constrain the spatial position of the anti-resonant structure during the fiber drawing process, prevent the anti-resonant structure from contacting and generating nodes under high temperature and gas expansion environments, extend the single drawing length, and help ensure the uniformity and consistency of the fiber structure.

[0058] The following description, in conjunction with the accompanying drawings, illustrates the solutions of the embodiments of this application.

[0059] like Figure 1 As shown, the anti-resonant hollow optical fiber provided in this application embodiment includes an outer cladding 100, multiple anti-resonant structures 200, and connectors 300.

[0060] Multiple anti-resonant structures 200 are spaced apart in the outer cladding 100. Each anti-resonant structure 200 includes an arc-shaped portion 210 and two straight portions 220. The arc-shaped portion 210 and the two straight portions 220 enclose a closed cavity. The arc-shaped portions 210 of the multiple anti-resonant structures 200 collectively define the fiber core region 110 for optical transmission. The straight portions 220 extend to the outer cladding 100 in a direction away from the fiber core region 110. The arc-shaped portions 210 protrude toward the fiber core region 110. One end of the connector 300 is connected to the inner wall of the outer cladding 100, and the other end is connected to the straight portion 220 to fix the anti-resonant structure 200 on the outer cladding 100.

[0061] Therefore, the closed cavity formed by the arc-shaped portion 210 and the two straight portions 220 of the anti-resonant structure 200 has a smaller internal air area than that of the circular anti-resonant tube 500. The resonant mode of the fiber core region 110 is more difficult to couple with the mode of the internal region of the anti-resonant structure 200, thereby reducing the leakage loss of the fiber core fundamental mode.

[0062] In this embodiment, the outer cladding 100 is a quartz tubular structure that extends along the axial direction of the optical fiber. The outer cladding 100 has a circular cross-section and provides mechanical support and protection within the optical fiber, as well as a mounting base for the internal anti-resonance structure 200. For example, the outer diameter of the outer cladding 100 is 100~500μm.

[0063] The fiber core region 110 disposed within the outer cladding layer 100 is located in the central region of the outer cladding layer 100. The fiber core region 110 is formed by multiple anti-resonant structures 200. The fiber core region 110 is used to transmit optical signals. Here, the gas filled inside the fiber core region 110 can be air, nitrogen, argon or other inert gas. Since the refractive index of the gas is lower than the refractive index of the anti-resonant structure 200, a refractive index difference is formed. The refractive index difference is used to meet the light guiding conditions of anti-resonant reflected light.

[0064] Since no solid material is placed in the core region 110, the light field is transmitted in the gas medium, which can effectively eliminate the absorption and scattering losses introduced by the solid material. The anti-resonant reflective surface formed by the gas medium core region 110 and the arc-shaped part 210 achieves extremely low transmission loss and near-light speed transmission delay, thereby improving the overall performance of the anti-resonant hollow fiber.

[0065] Depend on Figure 1 It can also be seen that the anti-resonant structure 200 in this embodiment has four anti-resonant structures evenly spaced circumferentially on the inner wall of the outer cladding 100, although other numbers can also be used. The anti-resonant structure 200 confines the light field to the fiber core region 110 for transmission through the anti-resonant reflection effect. Adjacent anti-resonant structures 200 do not contact each other, thus avoiding the formation of parasitic nodes.

[0066] Here, each anti-resonant structure 200 includes an arc-shaped portion 210 and two straight portions 220. The arc-shaped portion 210 bends convex towards the core region 110. The optical field is emitted back to the core region 110 at the interface between the core region 110 and the arc-shaped portion 210, preventing it from being coupled into the arc-shaped portion 210. For example, the cross-sectional area of ​​the closed cavity formed by the arc-shaped portion 210 and the two straight portions 220 is smaller than the cross-sectional area of ​​a circular resonant tube cavity with the same radial dimensions. The smaller cross-sectional area can correspondingly reduce the air region inside the cavity. As a result, the resonant coupling condition between the core fundamental mode and the corresponding cavity mode of the anti-resonant structure 200 is suppressed, which helps to reduce the fundamental mode leakage loss and at the same time reduce the parasitic loss peaks on the transmission spectrum.

[0067] In this embodiment, the two straight sections 220 have a first intersection point 230, and the straight section 220 and the arc section 210 have a second intersection point 240; the first intersection point 230 is connected to the inner wall of the outer cladding layer 100, and the second intersection point 240 is connected to the connector 300.

[0068] As an alternative implementation, the second intersection point 240 has two points at both ends of the arc-shaped portion 210, and the two second intersection points 240 are respectively connected to the outer cladding layer 100 through a connector 300.

[0069] In the above embodiment, two straight sections 220 extend in a direction away from the fiber core region 110 and intersect at their extended ends to form a first intersection point 230. The first intersection point 230 is the junction of the two straight sections 220 and is located on the side of the anti-resonant structure 200 furthest from the fiber core region 110. The first intersection point 230 is connected to the inner wall of the outer cladding layer 100, so that the extended ends of the straight sections 220 are directly positioned on the outer cladding layer 100.

[0070] Here, the connection between the first intersection point 230 and the inner wall of the outer cladding layer 100 can be either direct contact or fusion bonding. When fusion bonding is used, the first intersection point 230 is integrally fixed with the inner wall of the outer cladding layer 100 by means of laser welding or other methods, further enhancing the connection strength between the anti-resonance structure 200 and the outer cladding layer 100.

[0071] The two ends of the arc-shaped portion 210 intersect with the two straight portions 220 respectively, forming two second intersection points 240. The second intersection point 240 is the transition connection between the arc-shaped portion 210 and the straight portion 220. A connector 300 is connected to each second intersection point 240. One end of the connector 300 is fixedly connected to the second intersection point 240, and the other end of the connector 300 is fixedly connected to the inner wall of the outer cladding layer 100.

[0072] Thus, each anti-resonant structure 200 is fixed at three points through the connection between the first intersection point 230 and the inner wall of the outer cladding 100, and the connection between the connectors 300 at the two second intersection points 240 and the inner wall of the outer cladding 100. The first intersection point 230 provides the outermost radial positioning reference, and the two connectors 300 provide auxiliary positioning on both circumferential sides. The three connection points together form a stable triangular fixing structure. Compared with the anti-resonant tube 500 in related technologies, which uses a single-point contact positioning method, the anti-resonant hollow fiber of this embodiment effectively constrains the spatial position of the anti-resonant structure 200 during the fiber drawing process by using multi-point fixing. This prevents the anti-resonant structure 200 from contacting and generating nodes under high temperature and gas expansion conditions, which is beneficial to ensuring the uniformity and consistency of the fiber structure.

[0073] The connector 300 in this embodiment can be made of a solid quartz rod. Compared with a tubular structure, a solid rod has higher compressive strength and is less prone to deformation during wire drawing, thus effectively fixing the anti-resonance structure 200. The connector 300 and the second intersection point 240 are also connected by fusion welding, so that the connector 300 and the straight part 220 form an integrated structure at the second intersection point 240, enhancing the overall connection strength.

[0074] As an alternative implementation, the number of connectors 300 can be flexibly adjusted. For example, when the radial dimension of the anti-resonance structure 200 is small or the inflation pressure is low, one connector 300 can be set at each of the two second intersection points 240 to form a two-point fixation with the first intersection point 230. When the radial dimension of the anti-resonance structure 200 is large or the structural stability requirement is high, two or more connectors 300 can be set at the two second intersection points 240 to form more points of fixation.

[0075] As an alternative implementation, the first intersection point 230 and the inner wall of the outer cladding layer 100 are also indirectly connected by a connector 300. One end of the connector 300 is fused to the first intersection point 230, and the other end is fixedly connected to the inner wall of the outer cladding layer 100. This design allows the anti-resonance structure 200 to be adapted to outer cladding layers 100 of different sizes by adjusting the connection length of the connector 300.

[0076] In some embodiments, the extending direction of the connector 300 coincides with the tangential direction of the arcuate portion 210 at the second intersection 240.

[0077] During the fiber drawing process, the internal air pressure of the anti-resonant structure 200 causes both the arc-shaped portion 210 and the straight portion 220 to bear external forces. The extension direction of the connector 300 coincides with the tangential direction of the arc-shaped portion 210, making the connection constraint force provided by the connector 300 collinear with the force direction of the arc-shaped portion 210. As a result, the connector 300 mainly bears the tensile and compressive forces in the axial direction and is almost unaffected by bending or shear loads. This design makes the force distribution of the connector 300 more stable and effectively avoids the problem of connector 300 breaking and failing.

[0078] When the anti-resonance structure 200 is pressurized, the force on the arc-shaped part 210 is transmitted to the second intersection point 240 at both ends, and then transmitted to the first intersection point 230 through the straight part 220. The connector 300 is connected to the second intersection point 240 of the straight part 220. Compared with other positions on the straight part 220, it can more directly and effectively suppress the deformation of the arc-shaped part 210 from making contact.

[0079] It should be noted that in related technologies, during the production of optical fibers, the larger the diameter of the anti-resonant tube 500, the greater the expansion and deformation of the anti-resonant tube 500 due to high temperature and air blowing, making it more prone to contact and node problems. Therefore, the fiber preform is limited by the diameter of the anti-resonant tube, resulting in a limited drawing length. In this embodiment, the outer cladding and anti-resonant structure are connected by connectors. During high-temperature drawing and air inflation, the anti-resonant structure 200 is fixed and constrained at multiple points. The anti-resonant hollow fiber is less sensitive to the preform diameter, thus allowing the use of larger diameter fiber preforms for drawing, thereby further improving the single drawing length and production efficiency. Figure 1As shown, in some embodiments, in the same anti-resonant structure 200, two straight sections 220 are arranged symmetrically relative to the arc-shaped section 210, and two connectors 300 are arranged symmetrically relative to the arc-shaped section 210; the outer cladding layer 100, the fiber core region 110, the first intersection point 230 and the center of the arc-shaped section 210 are located on the same straight line.

[0080] The aforementioned arc-shaped portion 210 has a symmetry axis a, which passes through the midpoint of the arc-shaped portion 210. The two straight portions 220 and the two connecting members 300 are arranged mirror-symmetrically about the symmetry axis a. The two straight portions 220 and the two connecting members 300 have the same length. This symmetrical design ensures that the anti-resonance structure 200 provides a uniform anti-resonance reflection effect to the fiber core region 110 in the circumferential direction. The structural parameters on both sides of the arc-shaped portion 210 are identical, avoiding the introduction of additional asymmetric mode coupling or polarization loss due to structural asymmetry. Furthermore, the symmetrical design facilitates ensuring consistent deformation on both sides of the arc-shaped portion 210 during subsequent inflation and expansion, maintaining the symmetry of the closed cavity shape, and ensuring that the curvature of the arc-shaped portion 210 is uniformly distributed in the circumferential direction.

[0081] like Figure 2 As shown, it should be noted that in the manufacturing process, symmetrical design can be achieved through the initial placement of the mold 900 for positioning. That is, during the assembly stage, the initial thin-walled tube 700 is placed inside the mold 900, which divides the initial thin-walled tube 700 into equal parts. The nested tube 600 used to form the anti-resonance structure 200 is constrained by the mold 900. The two connecting parts 300 of the same anti-resonance structure 200 are welded and fixed to the inner wall of the initial thin-walled tube 700 in symmetrical positions to ensure positioning and symmetry accuracy. Here, the mold 900 can be a four-part mold as shown in the figure. The shape of the mold 900 can also be adjusted accordingly for different numbers of anti-resonance structures 200.

[0082] By aligning the centers of the cladding 100, core region 110, first intersection point 230, and arc-shaped portion 210 collinearly, the anti-resonant structure 200 is accurately positioned radially, the radial distance between the arc-shaped portion 210 and the core region 110 is determined, and the anti-resonant reflection conditions are kept consistent in all circumferential directions. Furthermore, the symmetrical arrangement combined with the collinear alignment of the components ensures that the anti-resonant structure 200 is completely symmetrical about the radial axis of symmetry, providing a structural basis for the circularly symmetrical light-guiding characteristics of the optical fiber. This helps reduce fundamental mode loss and improve the flatness of the transmission spectrum.

[0083] In some embodiments, the arcuate portion 210 has at least two arcuate portions 210 spaced outward along the radial direction of the fiber core region 110, and each arcuate portion 210 is connected to two straight portions 220 to form a nested annular structure.

[0084] Both of the aforementioned arc-shaped portions 210 are connected to the two straight portions 220. For ease of description, the radial direction of the fiber core region 110 is taken as the reference direction. The arc-shaped portion 210 closer to the fiber core region 110 is the first arc-shaped portion 210, and the arc-shaped portion 210 farther from the fiber core region 110 is the second arc-shaped portion 210. The first arc-shaped portion 210 and the two straight portions 220 enclose to form the outermost first closed cavity. The second arc-shaped portion 210 and the two straight portions 220 enclose to form a smaller second closed cavity. The first closed cavity and the second closed cavity are nested together, and each closed cavity is separated by the arc-shaped portion 210 and is not connected to each other.

[0085] Here, the curvatures of the first and second arc-shaped portions 210 are different. Moving outward along the radial direction of the fiber core region 110, the curvatures of the two arc-shaped portions 210 decrease sequentially, creating a radially gradient anti-resonant reflection structure. The curvature gradient of each layer of arc-shaped portions 210 causes the light field to leak outward from the fiber core region 110, sequentially facing anti-resonant reflecting surfaces with increasing curvature. Different curvatures result in different reflection efficiencies for different spatial frequency components of the light field. The arrangement of curvature gradients makes the reflection characteristics of each arc-shaped portion 210 complementary, collectively covering a wider spatial frequency range.

[0086] In the above embodiments, such as Figure 1 As shown, there are two arc-shaped portions 210. As an alternative implementation, there are three or more arc-shaped portions 210, forming a multi-layer nested structure. The more arc-shaped portions 210 there are, the more levels of anti-resonance reflection, and the stronger the constraint on the fiber core fundamental mode, but the structure is also more complex. Therefore, the number of arc-shaped portions 210 can be adjusted according to the actual application scenario.

[0087] like Figure 1 As shown, in some embodiments, the anti-resonant hollow fiber further includes multiple gap anti-resonant units 400 and multiple anti-resonant tubes 500.

[0088] Multiple gap anti-resonant units 400 and multiple anti-resonant structures 200 are arranged alternately around the fiber core region 110 in a circumferential interval. The gap anti-resonant unit 400 is a circular tube or an elliptical tube. The anti-resonant tube 500 is located in a closed cavity and is tangential to two straight sections 220. Both the anti-resonant tube 500 and the arc-shaped section 210 are used to form an anti-resonant reflective surface.

[0089] In the above embodiments, the multiple gap anti-resonance units 400 and multiple anti-resonance structures 200 are arranged alternately around the circumferential spacing of the fiber core region 110. This means that, with the cross-section of the optical fiber as a reference angle, one anti-resonance structure 200 and one gap anti-resonance unit 400 are arranged sequentially along the circumferential direction of the inner wall of the outer cladding 100. The cross-section of the gap anti-resonance unit 400 is circular or elliptical, and its tube wall is made of thin-walled quartz material. The interior of the gap anti-resonance unit 400 is a hollow region filled with gas. The tube wall thickness of the gap anti-resonance unit 400 meets the anti-resonance condition, enabling it to function as an independent anti-resonance reflecting surface.

[0090] The gap anti-resonance unit 400 supplements the circumferential coverage of the anti-resonance reflecting surface. The gap region between adjacent anti-resonance structures 200 contains a weak point, and higher-order modes in the optical field may leak from this region. Placing the gap anti-resonance unit 400 in the gap region fills the reflection dead zone, ensuring that the anti-resonance effect is covered circumferentially on the inner wall of the cladding 100. Simultaneously, the gap anti-resonance unit 400 and the straight sections 220 of the two anti-resonance structures 200 together define a mode leakage channel. Higher-order modes leak outward through this channel and are reflected or absorbed by the gap anti-resonance unit 400, thereby improving the single-mode characteristics of the optical fiber.

[0091] As an alternative implementation, the number of gap anti-resonant units 400 can be equal to or different from the number of anti-resonant structures 200. When the number is the same, the anti-resonant structures 200 and gap anti-resonant units 400 are arranged alternately in the circumferential direction of the inner wall of the outer cladding layer 100. When the number is different, for example, one gap anti-resonant unit 400 is arranged between every two anti-resonant structures 200.

[0092] As an alternative implementation, the gap anti-resonance unit 400 can also be omitted. For example, when the gap between adjacent anti-resonance structures 200 is small, the leakage in the gap region is within an acceptable range, and the gap anti-resonance unit 400 can be omitted to simplify the overall optical fiber structure.

[0093] Depend on Figure 2 It can also be seen that in the actual preparation process, the anti-resonant tube 500 can be pre-connected to the inner wall of the initial thin-walled tube 700 through the mold 900.

[0094] Figure 3The diagram shows a simulation of the structure of the anti-resonant hollow fiber provided in this application embodiment. The anti-resonant tube 500 is a thin-walled quartz tube filled with gas. The outer wall of the anti-resonant tube 500 is tangent to the inner walls of the two straight sections 220. When viewed from the inside out from the core region 110, the light field first encounters the anti-resonant reflection surface formed by the arc-shaped section 210. The residual light field passes through the arc-shaped section 210 and enters the closed cavity. It then encounters the anti-resonant reflection surface formed by the anti-resonant tube 500. The two arc-shaped sections 210 and the anti-resonant tube 500 together constitute a radial gradient anti-resonant reflection structure. The two are arranged sequentially from the inside out in the radial direction to reflect the leaked light field step by step. This design can suppress leakage loss step by step and further reduce the fundamental mode transmission loss.

[0095] Furthermore, the tangency between the anti-resonant tube 500 and the two straight sections 220 allows the anti-resonant tube 500 to achieve a more stable positioning effect within the closed cavity. During the inflation and drawing process, the contact at the tangent point between the straight section 220 and the anti-resonant tube 500 provides circumferential constraint for the anti-resonant tube 500, preventing it from shifting or rotating during expansion.

[0096] It should be noted that the specific wall thicknesses of the two arc-shaped sections 210, the anti-resonant tube 500, and the gap anti-resonant unit 400 can be determined using the following formula:

[0097] ;

[0098] In the above formula, t1 is the wall thickness of the two arc-shaped parts 210, the anti-resonant tube 500, or the gap anti-resonant unit 400, λ1 is the wavelength of the transmitted light, m1 is the order of the anti-resonant layer, m1 can be 1, 2, 3, 4 or 5, n1 is the refractive index of the material of the fiber core region 110, and n2 is the refractive index corresponding to the two arc-shaped parts 210, the anti-resonant tube 500, or the gap anti-resonant unit 400.

[0099] For example, the wall thickness of the two arc-shaped parts 210, the anti-resonant tube 500 and the gap anti-resonant unit 400 ranges from 0.1 to 3 μm, and the specific values ​​can be adjusted according to the formula and design scenario.

[0100] In some embodiments, the included angle between the two straight portions 220 is 20° to 170°; the ratio of the radius of the straight portion 220 to the radius of the fiber core region 110 is 1.2-3;

[0101] The arc length of the curved portion 210 and the straight portion 220 satisfy the following formula:

[0102] ;

[0103] Where L is the arc length of the arc-shaped portion 210. Let α be the length of the straight section 220, and α be the angle between the two straight sections 220.

[0104] The above formula shows that, given a fixed angle, the arc length of the curved portion 210 is directly proportional to the length of the straight portion 220. Knowing the radius of the target core region 110 and the required arc length of the curved portion 210, the corresponding length of the straight portion 220 and the included angle can be determined using this formula. Conversely, knowing the length of the straight portion 220 and the included angle, the arc length of the curved portion 210 can be calculated. This provides a quantitative basis for the structural parameter design of the preform and the control of the gas filling pressure in the fiber drawing process.

[0105] In the above embodiments, the included angle between the two straight sections 220 determines the opening degree of the anti-resonance structure 200 and the cross-sectional area of ​​the closed cavity. When the included angle between the two straight sections 220 is small, the cross-section of the closed cavity is narrow and long, and the arc length of the arc section 210 is short. When the included angle between the two straight sections 220 is large, the cross-section of the closed cavity is wide and flat, and the arc length of the arc section 210 is long.

[0106] Here, the included angle between the two straight sections 220 is 20°, 120°, or 170°. If the included angle is less than 20°, the enclosed cavity is too narrow, the arc length of the curved section 210 is too short, and the effective area of ​​the anti-resonant reflective surface is insufficient, making it difficult to provide adequate reflection constraint. If the included angle is greater than 170°, the two straight sections 220 are nearly parallel, the first intersection point 230 is too far from the fiber core region 110, and the radial dimension of the anti-resonant structure 200 is too large, potentially exceeding the spatial limitations of the inner cavity of the outer cladding 100. Therefore, within the included angle range of 20° to 170°, the area of ​​the enclosed cavity formed by the curved section 210 and the two straight sections 220 is smaller than the area of ​​a circular tube with the same radial dimension, reducing the internal air region and helping to suppress the resonant coupling between the fiber core fundamental mode and the cavity mode.

[0107] In this embodiment, the length of the straight portion 220 refers to the distance extending from the second intersection point 240 along the straight portion 220 to the first intersection point 230, and the radius of the fiber core region 110 refers to the distance from the center point of the fiber core region 110 to the arc-shaped portion 210. For example, the ratio of the straight portion 220 to the radius of the fiber core region 110 is 1.2, 2, or 3. Within this range, the straight portion 220 has sufficient length to ensure a stable closed cavity is formed between the arc-shaped portion 210 and the inner wall of the outer cladding layer 100. Simultaneously, the connection between the straight portion 220 and the inner wall of the outer cladding layer 100 is stable, which helps to ensure connection strength.

[0108] It should be noted that when two arc-shaped portions 210 are provided, the ratio of the straight line length corresponding to the arc-shaped portion 210 away from the fiber core region 110 to the radius of the fiber core region 110 is 0.6-1.5. Here, the straight line length corresponding to the arc-shaped portion 210 away from the fiber core region 110 refers to the distance from the intersection point of the arc-shaped portion 210 and the straight line portion 220 to the first intersection point 230. For example, the ratio of the straight line corresponding to the arc-shaped portion 210 away from the fiber core region 110 to the radius of the fiber core region 110 is 0.6, 1, or 1.5.

[0109] Another embodiment of this application provides a method for fabricating an anti-resonant hollow fiber, used to fabricate an anti-resonant hollow fiber as described in any of the above embodiments. The method for fabricating the anti-resonant hollow fiber includes the following steps:

[0110] Step 100: Provide an outer layer 100;

[0111] Step 200: Multiple nested pipe fittings 600 are set in the outer cladding layer 100, and the outer cladding layer 100 and the nested pipe fittings 600 are connected by connectors 300;

[0112] Step 300: Adjust the nested tube 600 to form an anti-resonance structure 200. The anti-resonance structure 200 includes an arc-shaped portion 210 and two straight portions 220. The arc-shaped portion 210 and the two straight portions 220 enclose a closed cavity. The arc-shaped portions 210 of the multiple anti-resonance structures 200 jointly define the fiber core region 110 for optical transmission. The straight portions 220 extend to the outer cladding layer 100 in a direction away from the fiber core region 110. The arc-shaped portions 210 protrude in the direction towards the fiber core region 110.

[0113] In some embodiments, in step 200, a plurality of nested tubular components 600 are provided in the outer cladding layer 100, including:

[0114] Step 201: Prepare multiple nested tubular fittings 600;

[0115] Step 202: Insert mold 900 into initial thin-walled tube 700, and preposition multiple nested tubes 600 into initial thin-walled tube 700 through mold 900;

[0116] Step 203: Connect the nested tube 600 to the initial thin-walled tube 700 via the connector 300.

[0117] like Figure 2 The mold 900 is the four-part mold 900 shown in the figure. The four nested tubes 600 are constrained by the mold 900 within the initial thin-walled tube 700, and then the nested tubes 600 are connected by the connectors 300. Here, the mold 900 is also used to pre-position each gap anti-resonance unit 400.

[0118] like Figure 2As shown in the embodiments of this application, an exemplary fabrication process of anti-resonant hollow optical fiber includes:

[0119] First, prepare a quartz mother tube 800. Place the initial mother tube in a graphite heating furnace and raise the temperature in the graphite heating furnace to above 2000℃. After the initial mother tube melts, draw it into a quartz mother tube 800 of the required size.

[0120] When stacking and welding nested tubes 600, and designing two arc-shaped sections 210 and an anti-resonance tube 500, three types of quartz tubes are nested and stacked, and then the tangential nodes of the three quartz tubes are melted and welded using a laser to prepare nested tubes 600. The innermost quartz tube is the subsequent anti-resonance tube 500, and the outer walls of the two quartz tubes opposite to the outer layer are the subsequent two spaced arc-shaped sections 210.

[0121] In the initial thin-walled tube 700, the prepared nested tube 600 is assembled and welded into an intermediate preform using a mold 900. The assembled intermediate preform is then melted in a heating furnace and drawn proportionally into an anti-resonant hollow optical fiber intermediate of the required size.

[0122] The anti-resonant hollow fiber intermediate is inserted into the quartz mother tube 800 and assembled with the gas-filled mold to obtain the secondary preform. This ensures that the gap between the anti-resonant hollow fiber intermediate and the quartz mother tube 800 can be evacuated under negative pressure, and the interior of the inner nested tube 600 can be filled with gas to control the pressure.

[0123] Finally, the anti-resonant hollow fiber is drawn by placing the secondary preform on a drawing tower. A negative pressure is applied between the anti-resonant hollow fiber intermediate and the quartz sleeve. The shape, size, and wall thickness of the nested tube 600 are controlled by adjusting the inflation pressure, ensuring its dimensions change proportionally with other structures. Specifically, by applying positive pressure inside the nested tube 600 or by locally heating a specific area, and using the constraint of the connector 300, the tube wall undergoes directional expansion and deformation at high temperatures, ultimately forming a closed cavity composed of an arc-shaped portion 210 and a straight portion 220, i.e., the anti-resonant structure 200.

[0124] Example 1

[0125] An exemplary structure of the anti-resonant hollow fiber prepared according to the above-described method is as follows: Figure 4 As shown, the core region 110 has a radius of 15.0 μm, and the straight section 220 has a straight length of... 1 is 23.6 μm, the straight line length corresponding to the arc-shaped portion 210 far from the fiber core region 110. The diameter of the two arc-shaped parts 210, the included angle of the two arc-shaped parts 500, and the included angle of the two arc-shaped parts 500 are all 112°. The radius of the anti-resonant tube 500 is 6.5μm, the radius of the gap anti-resonant unit 400 is 7μm, the wall thickness of the two arc-shaped parts 210, the anti-resonant tube 500 and the gap anti-resonant unit 400 are all 1.15μm, and the outer diameter of the outer cladding 100 is 240μm.

[0126] Figure 5 The transmission loss spectrum of the anti-resonant hollow-core optical fiber provided in Embodiment 1 of this application is obtained from... Figure 6 It can be seen that the transmission loss of this antiresonant hollow-core fiber at a wavelength of 1550nm is 0.105dB / km, while the attenuation in the wavelength range of 1525-1620nm is less than 0.13dB / km, exhibiting good flatness. Furthermore, the intermode crosstalk coefficient of this antiresonant hollow-core fiber in the 1550nm band was measured to be -58dB / km.

[0127] Example 2

[0128] An exemplary structure of the anti-resonant hollow fiber prepared according to the above-described method is as follows: Figure 6 As shown, the core region 110 has a radius of 15.0 μm, and the straight section 220 has a straight length of... 1 is 25μm, the straight length corresponding to the arc-shaped portion 210 far from the fiber core region 110. The diameter of the two arc-shaped parts 210, the diameter of the anti-resonant tube 500, and the included angle of the two arc-shaped parts 210, the diameter of the anti-resonant tube 500 and the diameter of the gap anti-resonant unit 400 are all 1.15 μm. The outer diameter of the outer cladding 100 is 240 μm.

[0129] After testing, Figure 7 The transmission loss spectrum of the antiresonant hollow-core optical fiber provided in Embodiment 2 of this application is shown. This antiresonant hollow-core optical fiber exhibits a transmission loss of 0.09 dB / km at a wavelength of 1550 nm, and an attenuation of less than 0.11 dB / km in the wavelength range of 1525-1620 nm, demonstrating good flatness. Because the antiresonant unit 400 with a design gap is omitted in Embodiment 2, the single-pulling length of the optical fiber is reduced to some extent compared to Embodiment 1, but its single-mode characteristic is enhanced, and the intermodal crosstalk coefficient of the optical fiber is -65 dB / km.

[0130] Example 3

[0131] In related technologies, only one exemplary structure of the nested pipe fitting 600 is designed, such as... Figure 8The core region 110 has a radius of 15.0 μm, the outermost anti-resonant tube 500 has a radius of 24 μm, the middle anti-resonant tube 500 has a radius of 16.3 μm, the innermost anti-resonant tube 500 has a radius of 7.0 μm, all anti-resonant tubes 500 have a wall thickness of 1.15 μm, and the outer diameter of the outer cladding 100 is 240 μm.

[0132] During long-distance fiber drawing, the thin-walled quartz layers inside the hollow fiber are prone to contact due to the spacing of less than 7μm, resulting in nodes that cause structural distortion. OTDR is required to locate the fault and remove the defective areas, thus shortening the length of the qualified fiber.

[0133] According to the statistical results of the wire drawing experiment, such as Figure 9 As shown, Figure 9 In the above embodiments, multiple sets of fiber drawing length experiments were conducted, with the vertical axis representing the percentage of different fiber drawing lengths in the corresponding embodiments. In Embodiment 1, the anti-resonant hollow-core fiber with anti-resonant structure 200 had an average qualified fiber length of 49.1 km. In Embodiment 3, the anti-resonant hollow-core fiber with only nested tube fitting 600 had an average qualified fiber length of 36.8 km. This indicates that the anti-resonant hollow-core fiber with anti-resonant structure 200 in Embodiment 1 can effectively avoid contact between the thin-walled quartz cladding layers, thereby increasing the qualified fiber drawing length.

[0134] The technical solutions of this application have been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of this application is obviously not limited to these specific embodiments. The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An anti-resonant hollow-core optical fiber, characterized in that, include: Outer cladding (100); Multiple anti-resonant structures (200) are spaced apart in the outer cladding (100). Each anti-resonant structure (200) includes an arc-shaped portion (210) and two straight portions (220). The arc-shaped portion (210) and the two straight portions (220) enclose a closed cavity. The arc-shaped portions (210) of the multiple anti-resonant structures (200) together define a fiber core region (110) for optical transmission. The straight portions (220) extend to the outer cladding (100) in a direction away from the fiber core region (110). The arc-shaped portions (210) protrude toward the fiber core region (110). A connector (300) is provided, one end of which is connected to the inner wall of the outer cladding layer (100) and the other end of which is connected to the straight section (220) to fix the anti-resonance structure (200) on the outer cladding layer (100).

2. The anti-resonant hollow-core optical fiber according to claim 1, characterized in that, The two straight sections (220) have a first intersection point (230) and the straight section (220) and the arc section (210) have a second intersection point (240). The first intersection (230) is connected to the inner wall of the outer cladding layer (100), and the second intersection (240) is connected to the connector (300).

3. The anti-resonant hollow-core optical fiber according to claim 2, characterized in that, The second intersection (240) has two points located at both ends of the arc-shaped portion (210), and the two second intersections (240) are respectively connected to the outer cladding layer (100) through a connector (300).

4. The anti-resonant hollow-core optical fiber according to claim 2, characterized in that, The extending direction of the connector (300) coincides with the tangential direction of the arcuate portion (210) at the second intersection (240).

5. The anti-resonant hollow-core optical fiber according to claim 3, characterized in that, The two straight sections (220) are arranged symmetrically relative to the arc-shaped section (210), and the two connectors (300) are arranged symmetrically relative to the arc-shaped section (210); The centers of the outer cladding layer (100), the core region (110), the first intersection point (230), and the arc-shaped portion (210) are located on the same straight line.

6. The anti-resonant hollow-core optical fiber according to any one of claims 1 to 5, characterized in that, The arc-shaped portion (210) has at least two spaced apart along the radial direction of the outer cladding layer (100), and each of the at least two arc-shaped portions (210) is connected to two straight portions (220); Among the multiple anti-resonant structures (200), the arc-shaped portion (210) on the side opposite to the outer cladding layer (100) jointly defines the fiber core region (110).

7. The anti-resonant hollow-core optical fiber according to claim 6, characterized in that, Also includes: Multiple gap anti-resonant units (400) are arranged alternately with multiple anti-resonant structures (200) around the fiber core region (110) at circumferential intervals. The gap anti-resonant units (400) are circular tubes or elliptical tubes. Multiple anti-resonant tubes (500) are disposed in the closed cavity. The anti-resonant tubes (500) are tangentially disposed with the two straight sections (220). Both the anti-resonant tubes (500) and the arc-shaped section (210) are used to form an anti-resonant reflective surface.

8. The anti-resonant hollow-core optical fiber according to any one of claims 1 to 5, characterized in that, The included angle between the two straight sections (220) is 20° to 170°; the ratio of the length of the straight section (220) to the radius of the core region (110) is 1.2-3; The arc length of the arc-shaped portion (210) and the straight portion (220) satisfy the following formula: ； Where L is the arc length of the arc-shaped portion (210), α is the length of the straight section (220), and α is the included angle between the two straight sections (220).

9. The anti-resonant hollow-core optical fiber according to claim 7, characterized in that, The anti-resonance structure (200), the gap anti-resonance unit (400), and the anti-resonance tube (500) are all quartz tubes.

10. A method for fabricating an anti-resonant hollow-core optical fiber, characterized in that, The method for preparing an anti-resonant hollow-core optical fiber as described in any one of claims 1 to 9 comprises the following steps: Provide an outer layer (100); Multiple nested pipe fittings (600) are provided in the outer cladding layer (100), and the outer cladding layer (100) and the nested pipe fittings (600) are connected by connectors (300). The nested tube (600) is adjusted to form an anti-resonant structure (200), which includes an arc-shaped portion (210) and two straight portions (220). The arc-shaped portion (210) and the two straight portions (220) enclose a closed cavity. The arc-shaped portions (210) of the multiple anti-resonant structures (200) jointly define a fiber core region (110) for optical transmission. The straight portions (220) extend to the outer cladding layer (100) in a direction away from the fiber core region (110). The arc-shaped portions (210) protrude in a direction toward the fiber core region (110).

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