A small-mode-field thin-core hollow optical fiber and a preparation method thereof

Abstract

The application discloses a kind of small-mode-field hollow core fiber of fine diameter and preparation method thereof, the preparation method includes: using filling pipe to lay multiple compensation tubes and positioning rods on the inner surface of accumulation bottom pipe;Compensation tube and positioning rod are fixed with accumulation bottom pipe respectively, and the pipe body formed by fixed combination is stretched and zoomed into sleeve;Multiple anti-resonance tube preform rods are fixed in each group of positioning rods respectively, to form hollow core fiber preform rod;Hollow core fiber preform rod is stretched and zoomed into intermediate body, and the intermediate body is drawn into wire to form hollow core fiber;Wherein, anti-resonance tube preform rod includes outer anti-resonance tube mother tube located in outermost layer and multiple inner anti-resonance tube mother tubes located in inner layer;After forming hollow core fiber, the thickness of the tube wall of each inner anti-resonance tube is the same, and the thickness of the tube wall of outer anti-resonance tube is greater than the thickness of the tube wall of inner anti-resonance tube;When drawing, negative pressure is applied to the cavity formed by surrounding anti-resonance tube preform rod, positioning rod and the inner surface of intermediate body, and positive pressure is applied to the remaining cavities in intermediate body.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, specifically to a small-diameter, small-mode-field hollow optical fiber and its fabrication method. Background Technology

[0002] Hollow-core optical fiber refers to a new generation of special optical fiber with a gas core, where optical signal transmission is constrained by a microstructure cladding. It possesses a unique light-guiding principle, with optical field energy and solid-state overlap as low as 10⁻⁴, thus unaffected by intrinsic material defects. Transmission loss at 1550 nm has been reduced to below 0.1 dB / km. Compared to solid-core optical fiber, hollow-core optical fiber also exhibits lower dispersion, delay, and a higher nonlinear effect threshold, thus possessing significant industrial value for future long-distance terrestrial backbone networks and transoceanic submarine optical cables.

[0003] Besides long-distance transmission applications spanning large distances, there is also a huge demand for optical fiber in short-distance interconnection and module interconnection within server racks. The low latency and high input power of hollow-core fiber can further drive the development of data centers, such as the evolution towards ultra-high speeds of 1.6T, achieving low-latency, high-bandwidth links. Due to the miniaturization requirements and limitations of short-distance applications, hollow-core fiber needs a smaller outer diameter, macro-bending attenuation comparable to G657 fiber, and higher single-mode purity. However, the core diameter of hollow-core fiber is currently typically controlled between 27-32 μm, while the glass outer diameter is generally above 200 μm. Simply reducing the glass outer diameter without changing the core diameter of the internal microstructure will cause severe macro- and micro-bending losses, and due to the large size of the microstructure, the overall outer diameter reduction is limited. Reducing both the internal microstructure diameter and the overall fiber diameter will result in insufficient tension during fiber drawing, increasing the uncontrollability of structural adjustments. Specifically, the minimum spacing between anti-resonant units may not meet design standards, thus impairing optical performance. The existing technologies cannot achieve structural control of hollow optical fibers under low drawing tension and small diameter.

[0004] Therefore, there is an urgent need for a fabrication method suitable for small-diameter, small-mode-field hollow optical fibers, and it is necessary to keep the internal structure of the hollow optical fiber stable during the drawing process. Summary of the Invention

[0005] The purpose of this invention is to provide a small-diameter, small-mode-field hollow optical fiber and its preparation method, so that the hollow optical fiber has a stable structure during the preparation process.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for fabricating a small-diameter, small-mode-field hollow-core optical fiber, comprising:

[0007] S1. Multiple compensation pipes and positioning rods are laid out on the inner surface of the stacking bottom pipe using filling pipes; the positioning rods are set in groups, and each group of positioning rods and compensation pipes are laid out alternately.

[0008] S2. Fix the compensation pipe and positioning rod to the stacking bottom pipe respectively, and stretch and scale the pipe body formed by the fixed combination into a sleeve.

[0009] S3. Fix multiple anti-resonant tube preforms to each group of positioning rods to form hollow fiber preforms.

[0010] S4. Stretch and scale the hollow fiber preform into an intermediate body, and draw the intermediate body into a hollow fiber.

[0011] The anti-resonant tube preform includes an outer anti-resonant tube mother tube located on the outermost layer and multiple inner anti-resonant tube mother tubes located on the inner layer. During wire drawing, a negative pressure is applied to the cavity formed by the inner surface of the anti-resonant tube preform, positioning rod, and intermediate body, and a positive pressure is applied to the remaining cavities within the intermediate body.

[0012] According to the above scheme, the length of the filling tube is 1 / 12 to 1 / 8 of the length of the compensation tube or positioning rod; the filling tube is located at both ends of the stacking bottom tube.

[0013] According to the above scheme, in step S2, the compensation tube and the positioning rod are fixed to the bottom stacking tube by welding with an oxyhydrogen flame or a carbon dioxide laser.

[0014] According to the above scheme, each set of positioning rods includes two positioning rods.

[0015] According to the above scheme, the hollow fiber preform includes 4 anti-resonant tube preforms, 4 compensation tubes, and 4 sets of positioning rods.

[0016] According to the above scheme, step S3 includes:

[0017] S301. Place the sleeve on the processing platform and rotate the sleeve to make a set of positioning bars located at the lowest point in the vertical direction of the set of positioning bars.

[0018] S302. Weld and fix the anti-resonance tube preform to the positioning rod located at the lowest point;

[0019] S303, Rotate the sleeve to position the other set of positioning bars at the lowest point in the vertical direction of the set of positioning bars;

[0020] S303, repeat steps S301~S302, and fix each anti-resonant tube preform in sequence.

[0021] According to the above scheme, in the anti-resonant tube preform, multiple support rods connect the outer anti-resonant tube mother tube and the adjacent inner anti-resonant tube mother tube.

[0022] According to the above scheme, the number of support rods is two.

[0023] According to the above scheme, the straight line formed by the geometric center of the support rod and the geometric center of the positioning rod on the same side passes through the center of the outer anti-resonance tube mother tube, and the included angle formed by the straight lines on both sides is greater than 30° and less than 55°.

[0024] According to the above scheme, the wire drawing tension in step S4 is 4~6.5N.

[0025] According to the above scheme, in step S4, the outer layer of the hollow fiber is coated during the drawing process, and the outer diameter of the coating formed is 220~250μm.

[0026] The present invention also provides a small-diameter, small-mode-field hollow fiber, comprising an outer cladding and an inner cladding. The inner cladding includes a plurality of anti-resonant units, which are arranged circumferentially along the inner surface of the outer cladding and connected to the inner surface of the outer cladding. The central cavity covered by the inner cladding forms the fiber core. The hollow fiber is prepared by the preparation method described above.

[0027] The anti-resonance unit includes an outer anti-resonance tube located on the outer layer and multiple inner anti-resonance tubes located on the inner layer. The wall thickness of each inner anti-resonance tube is the same, while the wall thickness of the outer anti-resonance tube is greater than that of the inner anti-resonance tube. A compensation structure is provided between adjacent anti-resonance units, and the compensation structure is in contact with the inner surface of the outer cladding layer.

[0028] According to the above scheme, in the same anti-resonant unit, adjacent inner anti-resonant tubes are tangentially connected, the tangent points between different inner anti-resonant tubes are collinear with the geometric center of the hollow fiber, and the position of each tangent point is biased to the side away from the geometric center of the hollow fiber.

[0029] According to the above scheme, in the anti-resonance unit, there is a pair of support structures connecting the outer anti-resonance tube and the outermost inner anti-resonance tube.

[0030] According to the above scheme, the contact arc length at the connection between the external anti-resonant tube and the inner surface of the outer cladding is 0.15 to 0.25 times the outer circumference of the external anti-resonant tube.

[0031] According to the above scheme, the distance between the innermost inner anti-resonant tube and the fitting arc is less than 3μm.

[0032] According to the above scheme, the wall thickness of the external anti-resonant tube is 0.85~1.3μm.

[0033] According to the above scheme, the wall thickness of the internal anti-resonant tube is 0.3~0.5μm.

[0034] According to the above scheme, the outer diameter of the outer cladding layer is 100~150μm.

[0035] According to the above scheme, the diameter of the fiber core is 13~15μm.

[0036] According to the above scheme, the spacing between adjacent anti-resonant units is 2.5~4μm.

[0037] According to the above scheme, the spacing between adjacent anti-resonant units and compensation structures is 2.5~4μm.

[0038] The present invention also provides a hollow optical fiber cable, which is composed of the small-diameter, small-mode-field hollow optical fiber described above.

[0039] Beneficial effects

[0040] In the fabrication process of this invention, a differentiated design is adopted where the outer wall thickness of the anti-resonant unit is greater than that of the inner layer. The anti-resonant tube preform is fixed to each set of positioning rods to form a hollow fiber preform. This preform is then stretched through an intermediate body to the fiber drawing stage. During fiber drawing, a negative pressure is applied to the cavity formed by the anti-resonant tube preform, positioning rods, and the inner surface of the intermediate body, while a positive pressure is applied to the remaining cavities. This precise balance of internal forces effectively controls the morphology of the internal microstructure during the thin-diameter fiber drawing process. It avoids problems such as increased macro- and micro-bending losses, anti-resonant unit adhesion, or uncontrolled spacing that easily occur when simply reducing the outer diameter of the fiber or the diameter of the internal microstructure. This ensures the stability and consistency of the internal microstructure of the thin-diameter, small-mode-field hollow fiber. Furthermore, the outer anti-resonant tube can form suitable reflection conditions for specific wavelengths of light with the inner anti-resonant tube, meeting the requirements for light guiding. This, in turn, ensures the excellent optical performance of the fiber, such as low dispersion, low latency, and high nonlinear effect threshold, meeting the core requirements of short-distance interconnection, modular interconnection, and other miniaturized applications for thin fiber diameter, small mode field, and stable optical performance. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the cross-sectional structure of a small-diameter, small-mode-field hollow fiber according to an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of an anti-resonance unit structure according to an embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram comparing the duty cycles of different anti-resonant units according to an embodiment of the present invention;

[0044] Figure 4 This is a schematic diagram of the sleeve manufacturing process according to an embodiment of the present invention;

[0045] Figure 5 This is a schematic diagram of a sleeve structure according to an embodiment of the present invention;

[0046] Figure 6 This is a schematic diagram of the hollow optical fiber preform manufacturing process according to an embodiment of the present invention;

[0047] Figure 7 This is a schematic diagram of the intermediate fiber drawing process according to an embodiment of the present invention.

[0048] In the figure: 1. Outer cladding; 2. Outer anti-resonant tube; 3. First inner anti-resonant tube; 4. Second inner anti-resonant tube; 5. Compensation structure; 6. Fiber core; 7. Support structure; 8. Filler tube; 9. Positioning rod; 10. Stacking bottom tube; 11. Compensation tube. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0050] This embodiment discloses a method for fabricating a small-diameter, small-mode-field hollow-core optical fiber, including:

[0051] S1. Multiple compensation pipes 11 and positioning rods 9 are arranged on the inner surface of the stacking bottom pipe 10 using the filling pipe 8; the positioning rods 9 are arranged in groups, and each group of positioning rods 9 and compensation pipes 11 are arranged alternately (see...). Figure 4 );

[0052] S2. Fix the compensation pipe 11 and the positioning rod 9 to the stacking bottom pipe 10 respectively, and stretch and scale the pipe body formed by the fixed connection to form a sleeve (see Figure 5 );

[0053] S3. Fix multiple anti-resonant tube preforms to each group of positioning rods 9 to form hollow fiber preforms.

[0054] S4. Stretch and scale the hollow fiber preform into an intermediate body, and draw the intermediate body into a fiber (either by drawing directly or by adding an external sleeve) to form a hollow fiber.

[0055] The anti-resonant tube preform includes an outer anti-resonant tube mother tube located at the outermost layer and multiple inner anti-resonant tube mother tubes located at the innermost layer; during wire drawing, a negative pressure is applied to the cavity formed by the anti-resonant tube preform, positioning rod 9, and the inner surface of the intermediate body (see...). Figure 7 ), applying positive pressure to the remaining cavities within the intermediate body.

[0056] Specifically, the positioning rod 9 serves to separate the anti-resonant unit from the outer surface, preventing the anti-resonant unit from connecting to the inner surface of the outer cladding 1 during intermediate body stretching and fiber drawing, and preventing the arc length of the bonding arc between the anti-resonant unit and the inner surface of the outer cladding 1 from continuing to increase while the fiber is molten in the drawing furnace. In addition, the positioning rod 9 can also position the anti-resonant tube preform during the fabrication of the hollow fiber preform, improving the overall structural uniformity and orientation accuracy of the hollow fiber.

[0057] Furthermore, the length of the filling tube 8 is 1 / 12 to 1 / 8 of the length of the compensation tube 11 or the positioning rod 9; the filling tube 8 is located at both ends of the stacking bottom tube 10.

[0058] Furthermore, in step S2, the compensation tube 11 and the positioning rod 9 are welded and fixed to the stacking bottom tube 10 by an oxyhydrogen flame or a carbon dioxide laser.

[0059] Furthermore, each set of positioning rods 9 includes two positioning rods 9.

[0060] Furthermore, the hollow fiber preform includes four anti-resonant tube preforms, four compensation tubes 11, and four sets of positioning rods 9.

[0061] Further, step S3 includes:

[0062] S301. Place the sleeve on the processing platform and rotate the sleeve to make a set of positioning bars 9 located at the lowest point in the vertical direction of the set of positioning bars 9.

[0063] S302. Weld and fix the anti-resonance tube preform to the positioning rod 9 located at the lowest point;

[0064] S303, Rotate the sleeve to position the other set of positioning rods 9 at the lowest point in the vertical direction of the set of positioning rods 9;

[0065] S303, repeat steps S301~S302, and fix each anti-resonant tube preform in sequence.

[0066] Specifically, when the structure of the formed hollow optical fiber preform is as follows: Figure 6 When shown (i.e., the anti-resonant units in the formed hollow fiber are distributed at 90° intervals), the rotation angle of step S303 is 90°.

[0067] Furthermore, in the anti-resonant tube preform, multiple support rods connect the outer anti-resonant tube 2 mother tube to the adjacent inner anti-resonant tube mother tube.

[0068] Specifically, the support rod serves to separate the outer anti-resonant tube from the adjacent inner anti-resonant tube, preventing direct connection between the anti-resonant tubes when the positioning rod 9 is present, which would cause structural distortion and damage to optical performance. The support rod can also be combined with the positioning rod 9 to stabilize the structure of the anti-resonant unit from both the inner and outer sides, making the shape of the anti-resonant unit closer to the ideal design model.

[0069] Furthermore, the number of support rods is two.

[0070] Furthermore, the straight line formed by the geometric center of the support rod on the same side and the geometric center of the positioning rod 9 passes through the center of the outer anti-resonance tube mother tube, and the included angle formed by the straight lines on both sides is greater than 30° and less than 55°.

[0071] Furthermore, the drawing tension in step S4 is 4~6.5N.

[0072] Furthermore, in step S4, the outer layer of the hollow fiber is coated during the fiber drawing process, and the outer diameter of the coating formed is 220~250μm.

[0073] In this embodiment, the preparation method can achieve continuous filament drawing with a length of more than 10 km.

[0074] The present invention also provides a small-diameter, small-mode-field hollow optical fiber, comprising an outer cladding 1 and an inner cladding, the inner cladding comprising a plurality of anti-resonant units, the plurality of anti-resonant units being arranged circumferentially along the inner surface of the outer cladding 1 and connected to the inner surface of the outer cladding 1, the central cavity covered by the inner cladding forming a fiber core 6, characterized in that the hollow optical fiber is prepared by the preparation method described above.

[0075] The anti-resonance unit includes an outer anti-resonance tube 2 located on the outer layer and multiple inner anti-resonance tubes located on the inner layer. The wall thickness of each inner anti-resonance tube is the same, while the wall thickness of the outer anti-resonance tube 2 is greater than that of the inner anti-resonance tubes. A compensation structure 5 is provided between adjacent anti-resonance units, and the compensation structure 5 is in contact with the inner surface of the outer cladding layer 1.

[0076] Furthermore, in the same anti-resonant unit, adjacent inner anti-resonant tubes are tangentially connected, and the tangent points between different inner anti-resonant tubes are collinear with the geometric center of the hollow fiber, and the positions of each tangent point are all biased away from the geometric center of the hollow fiber.

[0077] Furthermore, in the anti-resonance unit, a pair of support structures 7 connect the outer anti-resonance tube 2 and the outermost inner anti-resonance tube.

[0078] Furthermore, the contact arc length at the connection between the outer anti-resonant tube 2 and the inner surface of the outer cladding 1 is 0.15 to 0.25 times the outer circumference of the outer anti-resonant tube 2.

[0079] Furthermore, the distance between the innermost inner anti-resonant tube and the fitting arc is less than 3μm.

[0080] Furthermore, the wall thickness of the external anti-resonant tube 2 is 0.85~1.3μm.

[0081] Furthermore, the wall thickness of the internal anti-resonant tube is 0.3~0.5μm.

[0082] In the hollow optical fiber obtained by the above preparation method, the wall thickness error of the outer anti-resonant tube 2 of different anti-resonant units is less than 10%, and the wall thickness error of the inner anti-resonant tube of the same level is less than 15%.

[0083] Furthermore, the outer diameter of the outer cladding layer 1 is 100~150μm.

[0084] Furthermore, the diameter of the fiber core 6 is 13~15μm.

[0085] Furthermore, the spacing between adjacent anti-resonant units is 2.5~4μm.

[0086] Furthermore, the spacing between adjacent anti-resonant units and compensation structure 5 is 2.5~4μm.

[0087] In this embodiment, the hollow-core optical fiber operates at wavelengths ranging from 400 to 2000 nm, with attenuation less than 3 dB / km and macrobending loss equal to or better than the macrobending standard of G657.A2 optical fiber at 1550 nm. This hollow-core optical fiber can achieve pure fundamental mode output when its length is less than 20 m. The inner cladding of this hollow-core optical fiber, in addition to solid materials, is composed of one or more of argon, nitrogen, helium, or air. The solid materials are composed of one or more of pure quartz glass, sulfide glass, fluoride glass, plastics, and crystalline materials.

[0088] This embodiment provides a structural example of a small-diameter, small-mode-field hollow fiber. See [link to previous document]. Figure 1 The cross-section of the hollow fiber shown includes an outer cladding 1 and an inner cladding. The inner cladding is composed of four sets of anti-resonance units, which are arranged circumferentially along the inner surface of the outer cladding 1 and connected to the inner surface of the outer cladding 1. The central cavity covered by the inner cladding forms the fiber core 6. Figure 1 The anti-resonance unit shown consists of three layers of anti-resonance tubes, including an outer anti-resonance tube 2, a first inner anti-resonance tube 3, and a second inner anti-resonance tube 4. The first inner anti-resonance tube 3 and the second inner anti-resonance tube 4 are tangent to each other at a point, and the first inner anti-resonance tube 3 is connected to the outer anti-resonance tube 2 through a support structure 7. The connection points of each anti-resonance tube are tangent to the inner surface of the outer cladding layer 1. The wall thicknesses of the first inner anti-resonance tube 3 and the second inner anti-resonance tube 4 in the anti-resonance unit are the same, while the wall thickness of the outer anti-resonance tube 2 is greater than that of the first inner anti-resonance tube 3 and the second inner anti-resonance tube 4. Between each group of anti-resonance units, a compensation structure 5 is arranged circumferentially along the inner surface of the outer cladding layer 1, and the compensation structure 5 is in contact with the inner surface of the outer cladding layer 1. Each anti-resonance tube is a circular hollow tube, wherein the outer anti-resonance tube 2 and the compensation structure 5 are connected to the inner surface of the outer cladding layer 1. During wire drawing, the viscosity of the molten solid material decreases and is subjected to surface tension, resulting in a situation where the connection between the outer anti-resonance tube 2 and the outer cladding layer 1 is subject to surface tension. Figure 2 The arc length shown To adapt to short-distance, miniaturized applications and compact signal transmission systems, the outer diameter of the hollow fiber cladding layer 1 is 100-150 μm, corresponding to a coating outer diameter of 220-250 μm during fiber drawing. Due to the low mechanical strength of thin-diameter fibers, a low drawing tension of 4-6.5 N should be set during drawing to prevent tower breakage. To make the structure approximate the ideal design model (ensuring optical performance), the anti-resonant units are spaced apart... Spacing between the anti-resonant unit and the compensation structure 5 All are 2.5~4μm in diameter, with core 6 having a diameter of 13~15μm. Because... , The fiber is very small, and traditional structures are difficult to control effectively during low-tension, fine-diameter fiber drawing, thus making long-distance fiber take-up impossible. Therefore, this invention differentiates the wall thickness of the outer anti-resonator 2 from that of the first inner anti-resonator 3 and the second inner anti-resonator 4. Specifically, the anti-resonance wall thickness order of the outer anti-resonator 2 relative to the working wavelength is one order higher than that of the first and second inner anti-resonator 4. This reduces the duty cycle and pressure sensitivity of the outer anti-resonator 2 while optimizing the fiber bandwidth, increasing the cavity area inside the anti-resonator unit, and introducing greater parameter margin for structural adjustment, ultimately ensuring the optical performance of the fiber. Combined with the fabrication method of this embodiment, the arc length of the bonding arc between the outer anti-resonator 2 and the inner surface of the cladding 1 can be reduced, further reducing the duty cycle and pressure sensitivity of the outer anti-resonator 2, thereby achieving controllable structural height under conditions of fine-diameter, low-tension fiber drawing and stringent requirements for tube spacing.

[0089] Figure 2 As shown Figure 1 A magnified view of a specific anti-resonant unit in the cross-sectional structure of a hollow-core optical fiber. Under the premise of optimizing fiber optic performance, the outer diameter of the outer anti-resonant tube 2 is 1.43 to 1.7 times the diameter of the fiber core 6. The shortest radial distance between the inner surface of the first inner anti-resonant tube 3 and the outer surface of the second inner anti-resonant tube 4 is... The inner diameter of the second inner anti-resonator tube 4 is 0.5 to 0.6 times the diameter of the fiber core. The shortest radial distance between the inner surface of the second inner anti-resonant tube 4 and the inner surface of the outer anti-resonant tube 2 is 0.4 to 0.55 times the diameter of the fiber core 6. <1.5μm. To minimize the duty cycle of the external anti-resonator 2, the arc length of the contact arc is... The outer perimeter of the external anti-resonant tube 2 is 0.15 to 0.25 times that of the external anti-resonant tube 2, and is achieved by the preparation method described in this embodiment. The function of the support structure 7 in the anti-resonant unit is to stabilize the shape of each anti-resonant tube during preparation and prevent structural distortion caused by the special preparation method.

[0090] See Figure 3 The benefits of minimizing the arc length of the contact arc between the outer anti-resonator 2 and the inner surface of the cladding 1 are explained in this invention. Comparisons using cases A, B, and C approximate the connection between the outer anti-resonator 2 and the inner surface of the cladding 1 during hollow fiber drawing. To achieve the target core 6 size and the desired optical performance, the internal structure of the outer anti-resonator 2 in cases A, B, and C requires positive pressure control, and the maximum radial distance between the outer surface of the outer anti-resonator 2 and the inner surface of the cladding 1 expands to Z. , , The wall thicknesses of the three types of external anti-resonant tubes 2, namely A, B, and C, are respectively. , , The inner diameters of the three types of external anti-resonator tubes 2 are A, B, and C, respectively. , , The bonding lengths between the external anti-resonant tube 2 and the inner surface of the outer cladding layer 1 are respectively for three types: A, B, and C, and they satisfy the following conditions: , , Therefore, it can be deduced that:

[0091]

[0092] That is, the duty cycle of the external anti-resonator 2 decreases in the three cases A, B and C, and the sensitivity to air pressure regulation decreases in the three cases. In other words, the structure of the external anti-resonator is more controllable in case C.

[0093] This embodiment also provides a hollow fiber optic cable, which is composed of the small-diameter, small-mode-field hollow fiber described above.

[0094] The beneficial effects of the present invention include at least the following:

[0095] 1. This invention sets the outer anti-resonator tube 2 to have a wall thickness greater than that of the second / third-order anti-resonator tube of the inner anti-resonator tube, thereby reducing the duty cycle of the outer anti-resonator tube and its pressure sensitivity. During rod fabrication, a positioning rod 9 is placed on the inner wall of the sleeve. Applying a certain degree of negative pressure during wire drawing significantly reduces the contact arc length between the outer anti-resonator tube 2 and the inner surface of the outer cladding layer 1, further reducing the duty cycle of the outer anti-resonator tube 2 during structure forming. This makes the microstructure more stable and controllable under low-tension wire drawing conditions with small diameters. Specifically, under a glass outer diameter of 100-150 μm, a coating outer diameter of 230-250 μm, and a wire drawing tension of 4.5-6.5 N, the spacing between the anti-resonator units can be stably controlled between 2.5-4 μm, and the diameter of the fiber core 6 can be controlled between 13-15 μm. This allows for alignment with design standards, making the optical structure closer to the ideal model.

[0096] 2. This invention sets the internal wall thickness of the anti-resonant unit to be smaller than that of the first / second-order anti-resonant tube of the external anti-resonant tube, thus optimizing the fiber bandwidth, increasing the cavity area inside the anti-resonant unit, and introducing greater parameter margin for structural adjustment, ultimately ensuring the optical performance of the fiber. Specifically, this is reflected in: fiber attenuation <3dB / km, fiber macrobending additional loss comparable to the G657.A2 macrobending standard at 1550nm, and the ability to achieve a fiber length <20m for pure fundamental mode output.

[0097] 3. This invention proposes a structurally controllable, small-diameter, small-mode-field hollow-core optical fiber and its fabrication method. The fiber possesses characteristics such as small mode field, ultra-strong bending resistance, high single-mode purity, and high structural stability during the small-diameter drawing process. It is suitable for short-distance, miniaturized, and compact data transmission applications.

[0098] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0099] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 small-diameter, small-mode-field hollow-core optical fiber, comprising an outer cladding and an inner cladding, the inner cladding comprising a plurality of anti-resonant units, the plurality of anti-resonant units being arranged circumferentially along the inner surface of the outer cladding and connected to the inner surface of the outer cladding, the central cavity covered by the inner cladding forming the fiber core, characterized in that, The anti-resonance unit includes an outer anti-resonance tube located on the outer layer and multiple inner anti-resonance tubes located on the inner layer. The wall thickness of each inner anti-resonance tube is the same, while the wall thickness of the outer anti-resonance tube is greater than that of the inner anti-resonance tube. A compensation structure is provided between adjacent anti-resonance units, and the compensation structure is in contact with the inner surface of the outer cladding layer.

2. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, In the same anti-resonant unit, adjacent inner anti-resonant tubes are tangentially connected, and the tangent points between different inner anti-resonant tubes are collinear with the geometric center of the hollow fiber, and the positions of each tangent point are all biased away from the geometric center of the hollow fiber.

3. The small-diameter, small-mode-field hollow-core optical fiber according to claim 2, characterized in that, In the anti-resonance unit, a pair of support structures connect the outer anti-resonance tube and the outermost inner anti-resonance tube.

4. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The arc length of the contact arc at the connection between the external anti-resonant tube and the inner surface of the outer cladding is 0.15 to 0.25 times the outer circumference of the external anti-resonant tube.

5. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The distance between the innermost inner anti-resonant tube and the fitting arc is less than 3μm.

6. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The wall thickness of the external anti-resonant tube is 0.85~1.3μm.

7. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The wall thickness of the internal anti-resonant tube is 0.3~0.5μm.

8. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The outer diameter of the outer cladding layer is 100~150μm.

9. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The diameter of the fiber core is 13~15μm.

10. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The spacing between adjacent anti-resonant units is 2.5~4μm.

11. The small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The spacing between adjacent anti-resonant units and compensation structures is 2.5~4μm.

12. A method for fabricating a small-diameter, small-mode-field hollow-core optical fiber, characterized in that, The method for fabricating the small-diameter, small-mode-field hollow-core optical fiber of claim 1 includes: S1. Multiple compensation pipes and positioning rods are laid out on the inner surface of the stacking bottom pipe using filling pipes; the positioning rods are set in groups, and each group of positioning rods and compensation pipes are laid out alternately. S2. Fix the compensation pipe and positioning rod to the stacking bottom pipe respectively, and stretch and scale the pipe body formed by the fixed combination into a sleeve. S3. Fix multiple anti-resonant tube preforms to each group of positioning rods to form hollow fiber preforms. S4. Stretch and scale the hollow fiber preform into an intermediate body, and draw the intermediate body into a hollow fiber. The anti-resonant tube preform includes an outer anti-resonant tube mother tube located on the outermost layer and multiple inner anti-resonant tube mother tubes located on the inner layer. During wire drawing, negative pressure is applied to the cavity formed by the inner surface of the anti-resonant tube preform, positioning rod, and intermediate body, while positive pressure is applied to the remaining cavities within the intermediate body.

13. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The length of the filling tube is 1 / 12 to 1 / 8 of the length of the compensation tube or positioning rod; the filling tube is located at both ends of the stacking bottom tube.

14. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, In step S2, the compensation tube and positioning rod are fixed to the bottom stacking tube by welding with an oxyhydrogen flame or a carbon dioxide laser.

15. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, Each set of positioning rods includes two positioning rods.

16. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The hollow fiber preform consists of four anti-resonant tube preforms, four compensation tubes, and four sets of positioning rods.

17. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, Step S3 includes: S301. Place the sleeve on the processing platform and rotate the sleeve to make a set of positioning bars located at the lowest point in the vertical direction of the set of positioning bars. S302. Weld and fix the anti-resonance tube preform to the positioning rod located at the lowest point; S303, Rotate the sleeve to position the other set of positioning bars at the lowest point in the vertical direction of the set of positioning bars; S304, repeat steps S301~S303, and fix each anti-resonant tube preform in sequence.

18. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 15, characterized in that, In the anti-resonant tube preform, multiple support rods connect the outer anti-resonant tube main tube to the adjacent inner anti-resonant tube main tube.

19. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 18, characterized in that, There are two support rods.

20. The method for fabricating a small-diameter, small-mode-field hollow optical fiber according to claim 18, characterized in that, The straight line formed by the geometric center of the support rod and the geometric center of the positioning rod on the same side passes through the center of the outer anti-resonance tube mother tube, and the included angle formed by the straight lines on both sides is greater than 30° and less than 55°.

21. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, In step S4, the wire drawing tension is 4~6.5N.

22. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, In step S4, the outer layer of the hollow fiber is coated during the fiber drawing process, and the outer diameter of the coating formed is 220~250μm.

23. A hollow-core optical fiber cable, characterized in that, It is composed of the small-diameter, small-mode-field hollow optical fiber as described in claim 1.

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