Small-diameter small-mode-field hollow-core optical fiber and preparation method thereof

Abstract

The invention discloses a small-diameter small-mode-field hollow-core optical fiber and a preparation method thereof. The preparation method comprises the following steps: arranging a plurality of compensation tubes and positioning rods on the inner surface of an accumulation bottom tube by using a filling tube; the compensation pipe and the positioning rod are fixed to the stacking bottom pipe, and a pipe body formed through fixed combination is stretched and contracted into a sleeve; respectively fixing a plurality of anti-resonance tube preforms on each group of positioning rods to form a hollow-core optical fiber preform; stretching and zooming the hollow-core optical fiber preform into an intermediate, and drawing the intermediate to form a hollow-core optical fiber; wherein the anti-resonance tube preform comprises an outer anti-resonance tube main tube positioned on the outermost layer and a plurality of inner anti-resonance tube main tubes positioned on the inner layer; after the hollow-core optical fiber is formed, the thicknesses of the tube walls of the inner anti-resonance tubes are the same, and the thickness of the tube wall of the outer anti-resonance tube is greater than that of the tube wall of the inner anti-resonance tube; during wire drawing, negative pressure is applied to a cavity defined by the anti-resonance tube preform, the positioning rod and the inner surface of the intermediate, and positive pressure is applied to other cavities in the intermediate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber technology, in particular to a small-mode-field hollow core optical fiber with a small diameter and a preparation method thereof. BACKGROUND

[0002] Hollow core optical fiber refers to a new generation of special optical fiber with a micro-structured cladding to constrain the transmission of optical signals and a gas as the core. The hollow core optical fiber has a unique light guiding principle, and the overlap of optical field energy and solid is as low as 10-4 order of magnitude, thereby being not limited by intrinsic defects of the material. The transmission loss at 1550 nm has been reduced to below 0.1 dB / km. Compared with solid core optical fiber, the hollow core optical fiber also has lower dispersion, time delay and higher nonlinear effect threshold, and thus has visible industrial value in future long-distance land backbone network and transoceanic submarine cable.

[0003] In addition to long-distance transmission applications with large span, there is a huge demand for optical fibers in short-distance interconnection in cabinets, module interconnection and other businesses. The characteristics of low time delay and high input fiber power of the hollow core optical fiber can further promote the development of data centers, such as the evolution of super-high speed to 1.6T, and the realization of low delay and high bandwidth link characteristics. Due to the miniaturization development demand and limitation of short-distance application scenarios, the hollow core optical fiber needs to have a smaller outer diameter, a macro-bend additional attenuation comparable to G657 optical fiber and higher single-mode purity. However, the core diameter of the hollow core optical fiber is usually controlled between 27-32 μm, and the glass outer diameter is generally above 200 μm. If the internal micro-structure core diameter is not changed and the glass outer diameter is simply reduced, it will cause serious macro-bend and micro-bend loss. Due to the large size of the micro-structure, the degree of reduction of the overall outer diameter is limited. If the internal micro-structure diameter and the overall diameter of the optical fiber are reduced, the tension during the drawing process will be small, which will increase the uncontrollable degree in the structure adjustment process. Specifically, the minimum distance between the anti-resonant units cannot be targeted to the design standard, thereby damaging the optical performance. The scheme adopted in the prior art cannot realize the controllability of the structure of the hollow core optical fiber under low drawing tension in a small diameter.

[0004] Therefore, there is an urgent need for a preparation method suitable for a small-mode-field hollow core optical fiber with a small diameter, and the internal structure of the hollow core optical fiber needs to be kept stable during the drawing process. SUMMARY

[0005] The purpose of the present application is to provide a small-mode-field hollow core optical fiber with a small diameter and a preparation method thereof, so that the structure of the hollow core optical fiber is stable during the preparation process.

[0006] To solve the above technical problems, the present application provides a preparation method of a small-mode-field hollow core optical fiber, comprising: S1, a plurality of compensation tubes and positioning rods are arranged on the inner surface of the accumulated bottom tube by using a filling tube; the positioning rods are arranged in groups, and each group of positioning rods and compensation tubes are arranged alternately; S2, fixing the compensation tube and the positioning rod with the stacking bottom tube respectively, and stretching the tube body formed by the fixed combination into a sleeve tube; S3, fixing the plurality of anti-resonance tube preform rods to the positioning rods in each group respectively to form an air-core optical fiber preform rod; S4, stretching the air-core optical fiber preform rod into an intermediate body, and drawing the intermediate body into an air-core optical fiber; The anti-resonance tube preform rod comprises an outer anti-resonance tube mother tube at the outermost layer and a plurality of inner anti-resonance tube mother tubes at the inner layer. When drawing, negative pressure is applied to the cavity formed by the anti-resonance tube preform rod, the positioning rod, and the inner surface of the intermediate body, and positive pressure is applied to the remaining cavities in the intermediate body.

[0007] According to the above scheme, the length of the filling tube is 1 / 12-1 / 8 of the length of the compensation tube or the positioning rod. The filling tube is located at both ends of the stacking bottom tube.

[0008] According to the above scheme, the compensation tube and the positioning rod are welded and fixed with the stacking bottom tube by hydrogen-oxygen flame or carbon dioxide laser.

[0009] According to the above scheme, each group of positioning rods comprises two positioning rods.

[0010] According to the above scheme, the air-core optical fiber preform rod comprises four anti-resonance tube preform rods, four compensation tubes, and four groups of positioning rods.

[0011] According to the above scheme, step S3 comprises: S301, placing the sleeve tube on a processing platform, and rotating the sleeve tube to make a positioning rod in a group located at the lowest point in the vertical direction of the positioning rod in the group; S302, welding and fixing the anti-resonance tube preform rod with the positioning rod at the lowest point; S303, rotating the sleeve tube to make another positioning rod in a group located at the lowest point in the vertical direction of the positioning rod in the group; S303, repeating steps S301-S302 to fix each anti-resonance tube preform rod in turn.

[0012] According to the above scheme, in the anti-resonance tube preform rod, a plurality of support rods are connected between the outer anti-resonance tube mother tube and the adjacent inner anti-resonance tube mother tube.

[0013] According to the above scheme, the number of support rods is two.

[0014] According to the above scheme, the straight line formed by the geometric center of the support rod on the same side and the geometric center of the positioning rod passes through the center of the outer anti-resonance tube mother tube, and the included angle formed by the two straight lines is greater than 30° and less than 55°.

[0015] According to the above scheme, the drawing tension in step S4 is 4-6.5 N.

[0016] According to the above scheme, the outer layer of the hollow core fiber is coated during the drawing in step S4, and the coating formed has an outer diameter of 220-250 μm.

[0017] The application also provides a small-mode-field hollow core fiber with a small diameter, which comprises an outer cladding and an inner cladding, the inner cladding comprises a plurality of anti-resonant units, the plurality of anti-resonant units are arranged along the inner surface of the outer cladding in a circumferential direction and are connected to the inner surface of the outer cladding, and a central cavity covered by the inner cladding forms a core, and the hollow core fiber is prepared by the preparation method described above. The anti-resonant unit comprises an outer anti-resonant tube located on the outer layer and a plurality of inner anti-resonant tubes located on the inner layer, the wall thickness of each inner anti-resonant tube is the same, the wall thickness of the outer anti-resonant tube is greater than the wall thickness of the inner anti-resonant tube, and a compensation structure is arranged between adjacent anti-resonant units and is connected to the inner surface of the outer cladding.

[0018] According to the above scheme, in the same anti-resonant unit, adjacent inner anti-resonant tubes are connected tangentially, the tangent points between different inner anti-resonant tubes are collinear with the geometric center of the hollow core fiber, and each tangent point is deviated to one side away from the geometric center of the hollow core fiber.

[0019] According to the above scheme, in the anti-resonant unit, a pair of support structures are connected between the outer anti-resonant tube and the outermost inner anti-resonant tube.

[0020] According to the above scheme, the fitting arc length at the connection between the outer anti-resonant tube and the inner surface of the outer cladding is 0.15-0.25 times the outer circumference of the outer anti-resonant tube.

[0021] According to the above scheme, the spacing between the innermost inner anti-resonant tube and the fitting arc is less than 3 μm.

[0022] According to the above scheme, the wall thickness of the outer anti-resonant tube is 0.85-1.3 μm.

[0023] According to the above scheme, the wall thickness of the inner anti-resonant tube is 0.3-0.5 μm.

[0024] According to the above scheme, the outer diameter of the outer cladding is 100-150 μm.

[0025] According to the above scheme, the diameter of the core is 13-15 μm.

[0026] According to the above scheme, the spacing between adjacent different anti-resonant units is 2.5-4 μm.

[0027] According to the above scheme, the spacing between adjacent anti-resonant units and the compensation structure is 2.5-4 μm.

[0028] The application also provides a hollow core fiber cable composed of the small-mode-field hollow core fiber with a small diameter described above.

[0029] Advantages In the preparation process of the present application, by adopting the differential design that the outer layer pipe wall thickness of the anti-resonance unit is greater than the inner layer, the anti-resonance pipe preform rod is fixed to the positioning rods of each group to form an air-core optical fiber preform rod, and then the intermediate body is stretched to the drawing link, and the cavity formed by surrounding the inner surface of the anti-resonance pipe preform rod, the positioning rod and the intermediate body is subjected to negative pressure during drawing, and the remaining cavities are subjected to positive pressure, which can precisely balance the internal stress, effectively control the morphology of the internal microstructure during fine drawing, avoid the problems of increased macro-bending loss, anti-resonance unit adhesion or spacing out of control when simply reducing the fiber outer diameter or internal microstructure diameter, and ensure the stability and consistency of the internal microstructure of the fine small-mode-field air-core optical fiber. The outer anti-resonance pipe can form a matching reflection condition with the inner anti-resonance pipe for specific wavelength light waves, which meets the light guiding requirement. Further, the low dispersion, low time delay and high nonlinear effect threshold of the optical fiber are ensured, which meets the core requirements of small-size application scenarios such as short-distance interconnection and module interconnection for fine small-mode-field air-core optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 1 is a schematic diagram of the cross-sectional structure of a fine small-mode-field air-core optical fiber according to an embodiment of the present application; Figure 2 Fig. 2 is a schematic diagram of the anti-resonance unit structure according to an embodiment of the present application; Figure 3 Fig. 3 is a comparative schematic diagram of the duty cycle of different anti-resonance units according to an embodiment of the present application; Figure 4 Fig. 4 is a schematic diagram of the sleeve making process according to an embodiment of the present application; Figure 5 Fig. 5 is a schematic diagram of the sleeve structure according to an embodiment of the present application; Figure 6 Fig. 6 is a schematic diagram of the air-core optical fiber preform rod making process according to an embodiment of the present application; Figure 7 Fig. 7 is a schematic diagram of the intermediate body drawing process according to an embodiment of the present application.

[0031] In the figure: 1, outer cladding; 2, outer anti-resonance pipe; 3, first inner anti-resonance pipe; 4, second inner anti-resonance pipe; 5, compensation structure; 6, core; 7, support structure; 8, filling pipe; 9, positioning rod; 10, accumulation bottom pipe; 11, compensation pipe. DETAILED DESCRIPTION

[0032] To make the purposes, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some but not all of the embodiments of the present disclosure. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present disclosure.

[0033] The present embodiment discloses a preparation method of a small-mode-field thin-core hollow optical fiber, comprising: S1, a plurality of compensation tubes 11 and positioning rods 9 are arranged on the inner surface of the accumulation base tube 10 by using the filling tube 8; the positioning rods 9 are arranged in groups, and each group of positioning rods 9 and the compensation tubes 11 are arranged alternately (see Figure 4 ); S2, the compensation tubes 11 and the positioning rods 9 are fixed with the accumulation base tube 10 respectively, and the tube body formed by the fixed combination is stretched and zoomed into a sleeve (see Figure 5 ); S3, a plurality of anti-resonance tube preform rods are fixed on each group of positioning rods 9 respectively to form a hollow optical fiber preform rod; S4, the hollow optical fiber preform rod is stretched and zoomed into an intermediate body, and the intermediate body is drawn into a hollow optical fiber in a wire shape (directly drawn or drawn with an additional sleeve); Wherein, the anti-resonance tube preform rod comprises an outer anti-resonance tube mother tube located at the outermost layer and a plurality of inner anti-resonance tube mother tubes located at the inner layer; when drawing, negative pressure is applied to the cavity formed by the anti-resonance tube preform rod, the positioning rod 9, and the inner surface of the intermediate body (see Figure 7 ), and positive pressure is applied to the remaining cavities in the intermediate body.

[0034] Specifically, the positioning rod 9 separates the anti-resonance unit from the outer surface, prevents the anti-resonance unit from being connected to the inner surface of the outer cladding layer 1 during the stretching of the intermediate body and the drawing of the optical fiber, and prevents the arc length of the fitted arc between the anti-resonance unit and the inner surface of the outer cladding layer 1 from continuing to increase in the molten state of the optical fiber in the drawing furnace. In addition, the positioning rod 9 can also position the anti-resonance tube preform rod during the manufacture of the hollow optical fiber preform rod, thereby improving the overall structural uniformity and orientation accuracy of the hollow optical fiber.

[0035] Further, the length of the filling tube 8 is 1 / 12~1 / 8 of the length of the compensation tube 11 or the positioning rod 9; and the filling tube 8 is located at both ends of the accumulation base tube 10.

[0036] Further, the compensation tube 11 and the positioning rod 9 are fixed by hydrogen-oxygen flame or carbon dioxide laser welding in step S2.

[0037] Further, each group of positioning rods 9 comprises two positioning rods 9.

[0038] Further, the hollow core fiber preform includes four anti-resonance tube preforms, four compensation tubes 11 and four sets of positioning rods 9.

[0039] Further, the step S3 includes: S301, placing the sleeve on the processing platform, and rotating the sleeve to make a set of positioning rods 9 be at the lowest point in the vertical direction of the set of positioning rods 9; S302, welding and fixing the anti-resonance tube preform with the positioning rod 9 at the lowest point; S303, rotating the sleeve to make another set of positioning rods 9 be at the lowest point in the vertical direction of the set of positioning rods 9; S303, repeating the steps S301-S302 to fix each anti-resonance tube preform in turn.

[0040] Specifically, when the structure of the formed hollow core fiber preform is as shown in Figure 6 that is, the anti-resonance units in the formed hollow core fiber are distributed at intervals of 90°, the rotation angle of the step S303 is 90°.

[0041] Further, in the anti-resonance tube preform, a plurality of support rods are connected between the outer anti-resonance tube 2 mother tube and the adjacent inner anti-resonance tube mother tube.

[0042] Specifically, the support rods separate the outer anti-resonance tube mother tube and the adjacent inner anti-resonance tube mother tube, preventing the anti-resonance tubes from being directly connected when the positioning rods 9 are present, thereby preventing structural distortion and damaging the optical performance. The support rods can also be combined with the positioning rods 9 to stabilize the structure of the anti-resonance unit from the inner and outer sides of the anti-resonance unit, making the anti-resonance unit form closer to the ideal design model.

[0043] Further, the number of support rods is two.

[0044] Further, the straight line formed by the geometric centers of the support rods 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 two straight lines is greater than 30° and less than 55°.

[0045] Further, the drawing tension in the step S4 is 4-6.5 N.

[0046] Further, the outer layer of the hollow core fiber is coated during the drawing in the step S4, and the outer diameter of the coating formed by the coating is 220-250 μm.

[0047] In this embodiment, the preparation method can realize continuous drawing of more than 10 km in length.

[0048] The application further provides a small-mode-field thin-diameter hollow optical fiber, comprising an outer cladding 1 and an inner cladding, the inner cladding comprises a plurality of anti-resonant units, the plurality of anti-resonant units are arranged along the inner surface of the outer cladding 1 in a circumferential direction and are in contact with the inner surface of the outer cladding 1, and the central cavity covered by the inner cladding forms a core 6, characterized in that the hollow optical fiber is prepared by the preparation method described above. The anti-resonant unit comprises an outer anti-resonant tube 2 located at the outer layer and a plurality of inner anti-resonant tubes located at the inner layer, the wall thickness of each inner anti-resonant tube is the same, the wall thickness of the outer anti-resonant tube 2 is greater than the wall thickness of the inner anti-resonant tube, and a compensation structure 5 is arranged between adjacent anti-resonant units, and the compensation structure 5 is in contact with the inner surface of the outer cladding 1.

[0049] Further, in the same anti-resonant unit, adjacent inner anti-resonant tubes are connected in tangency, the tangent points between different inner anti-resonant tubes are collinear with the geometric center of the hollow optical fiber, and each tangent point is deviated to one side away from the geometric center of the hollow optical fiber.

[0050] Further, in the anti-resonant unit, the outer anti-resonant tube 2 is connected with the outermost inner anti-resonant tube through a pair of support structures 7.

[0051] Further, the fitting arc length of the connection between the outer anti-resonant tube 2 and the inner surface of the outer cladding 1 is 0.15-0.25 times the outer circumference of the outer anti-resonant tube 2.

[0052] Further, the spacing between the innermost inner anti-resonant tube and the fitting arc is less than 3μm.

[0053] Further, the wall thickness of the outer anti-resonant tube 2 is 0.85-1.3μm.

[0054] Further, the wall thickness of the inner anti-resonant tube is 0.3-0.5μm.

[0055] In the hollow optical fiber prepared 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%.

[0056] Further, the outer diameter of the outer cladding 1 is 100-150μm.

[0057] Further, the diameter of the core 6 is 13-15μm.

[0058] Further, the spacing between adjacent different anti-resonant units is 2.5-4μm.

[0059] Further, the spacing between adjacent anti-resonant units and the compensation structure 5 is 2.5-4μm.

[0060] In the embodiment, the hollow core fiber has a working wavelength of 400-2000 nm, an attenuation of less than 3 dB / km, and a macro-bending loss equal to or better than the macro-bending standard of G657.A2 fiber at 1550 nm; the hollow core fiber can achieve pure fundamental mode output when the length is less than 20 m. The inner cladding of the hollow core fiber is composed of one or a mixture of argon, nitrogen, helium or air in addition to solid materials; the solid materials are one or a mixture of pure quartz glass, sulfide glass, fluoride glass, plastic and crystal materials.

[0061] The embodiment provides a structure example of a small-mode-field hollow core fiber with a small diameter, as shown in the cross section of the hollow core fiber. Figure 1 The hollow core fiber includes an outer cladding 1 and an inner cladding composed of four groups of anti-resonant units, which are arranged along the inner surface of the outer cladding 1 and connected to the inner surface of the outer cladding 1, and the central cavity covered by the inner cladding forms a core 6. Figure 1 The anti-resonant unit is composed of three layers of anti-resonant tubes, including an outer anti-resonant tube 2, a first inner anti-resonant tube 3 and a second inner anti-resonant tube 4, the first inner anti-resonant tube 3 and the second inner anti-resonant tube 4 are tangent to each other at a point, and the first inner anti-resonant tube 3 is connected to the outer anti-resonant tube 2 through a support structure 7, and the connection of each anti-resonant tube is tangent to the inner surface of the outer cladding 1. The wall thicknesses of the first inner anti-resonant tube 3 and the second inner anti-resonant tube 4 of the anti-resonant unit are the same, and the wall thickness of the outer anti-resonant tube 2 is greater than that of the first inner anti-resonant tube 3 and the second inner anti-resonant tube 4. Between each group of anti-resonant units, a compensation structure 5 is arranged along the inner surface of the outer cladding 1, and the compensation structure 5 is connected to the inner surface of the outer cladding 1. Each anti-resonant tube is a circular hollow tube, wherein the outer anti-resonant tube 2 and the compensation structure 5 are connected to the inner surface of the outer cladding 1, and the viscosity of the molten solid material decreases and is affected by surface tension during drawing, and there is an arc length Figure 2 as shown in the drawing. To adapt to short-distance miniaturization applications and compact signal transmission systems, the outer diameter of the hollow core fiber outer cladding 1 is 100-150 μm, and the corresponding coating outer diameter during drawing is 220-250 μm. Due to the low mechanical strength of the small-diameter fiber, a low drawing tension of 4-6.5 N should be set to prevent tower breakage during drawing. In order to make the structure close to the ideal design model (ensure optical performance), the spacing between the anti-resonant units is and the spacing between the anti-resonant units and the compensation structure 5 is both 2.5-4 μm, and the diameter of the core 6 is 13-15 μm. Because , The small traditional structure is difficult to effectively control in low tension thin diameter wire drawing, so that long distance fiber collection cannot be realized. Therefore, the wall thickness of the differentiated outer anti-resonance tube 2 and the first inner anti-resonance tube 3 and the second inner anti-resonance tube 4 is set, and the effect of the setting is specifically embodied that the anti-resonance wall thickness order of the outer anti-resonance tube 2 for the working wavelength is larger than that of the first inner anti-resonance tube 3 and the second inner anti-resonance tube 4 for the working wavelength by one order. Therefore, while reducing the duty cycle and the air pressure sensitivity of the outer anti-resonance tube 2, the optical fiber bandwidth is optimized, the cavity area inside the anti-resonance unit is increased, a larger parameter margin is introduced for structure adjustment, and finally the optical performance of the optical fiber can be ensured. In combination with the preparation method of the embodiment, the arc length of the arc of the outer anti-resonance tube 2 and the inner surface of the outer cladding 1 can be reduced, and the duty cycle and the air pressure sensitivity of the outer anti-resonance tube 2 are further reduced, so that the structure is highly controllable under the condition of thin diameter low tension wire drawing and strict tube spacing requirement.

[0062] Figure 2 As shown in Figure 1 The local enlarged view of a certain anti-resonance unit in the cross-sectional structure of the hollow core optical fiber. Under the premise of optimizing the optical performance of the optical fiber, the outer diameter of the outer anti-resonance tube 2 is 1.43-1.7 times the diameter of the core 6, the radial shortest distance between the inner surface of the first inner anti-resonance tube 3 and the outer surface of the second inner anti-resonance tube 4 is 0.5-0.6 times the diameter of the core, the inner diameter of the second inner anti-resonance tube 4 is 0.4-0.55 times the diameter of the core 6, and the radial shortest distance between the inner surface of the second inner anti-resonance tube 4 and the inner surface of the outer anti-resonance tube 2 is less than 1.5 μm. In order to minimize the duty cycle of the outer anti-resonance tube 2, the arc length of the arc is 0.15-0.25 times the outer circumference of the outer anti-resonance tube 2. The preparation method described in the embodiment realizes that the supporting structure 7 in the anti-resonance unit is to stabilize the shape of each anti-resonance tube during preparation, and prevent structural distortion caused by the special preparation method.

[0063] Referring to Figure 3 , the benefits of minimizing the arc length of the arc of the outer anti-resonance tube 2 and the inner surface of the outer cladding 1 of the present application are explained. A, B and C are used for comparison, which can approximately represent the connection between the outer anti-resonance tube 2 and the inner surface of the outer cladding 1 during the drawing of the hollow core optical fiber. In order to achieve the target core 6 size and realize the expected optical performance, the inside of the outer anti-resonance tube 2 of A, B and C needs to be positively controlled, and the maximum radial distance between the outer surface of the outer anti-resonance tube 2 and the inner surface of the outer cladding 1 is expanded to Z. The wall thicknesses of the outer anti-resonance tubes 2 of A, B and C are respectively ​​​​The inner diameter of the outer counter resonant tube 2 is A, B and C respectively, 、 、 The length of the outer counter resonant tube 2 and the inner surface of the outer cladding 1 is A, B and C respectively, and satisfies , , Therefore, it can be deduced that:

[0064] That is, the duty cycle of the outer counter resonant tube 2 in A, B and C cases decreases in turn, and the sensitivity to air pressure control decreases in turn, that is, the structure of the outer counter resonant tube in the C case is more controllable.

[0065] The embodiment also provides a hollow core fiber cable composed of the small-diameter small-mode-field hollow core fiber described above.

[0066] The beneficial effects of the present application at least include: 1. The outer counter resonant tube 2 is provided with a wall thickness greater than the second / third order counter resonant wall thickness of the inner counter resonant tube, which reduces the duty cycle of the outer counter resonant tube and reduces its air pressure sensitivity. When making a rod, a positioning rod 9 is arranged on the inner wall of the sleeve, and a certain degree of negative pressure is applied during wire drawing, which can greatly reduce the fitting arc length of the outer counter resonant tube 2 and the inner surface of the outer cladding 1, further reducing the duty cycle of the outer counter resonant tube 2 during structure forming, thereby making the microstructure more stable and easier to control in the case of small-diameter low-tension wire drawing. Specifically embodied in: 100-150 mu m glass outer diameter, 230-250 coating outer diameter, 4.5-6.5 N wire drawing tension, the counter resonant unit can be stably controlled between 2.5-4 mu m, and the fiber core 6 diameter can be controlled between 13-15 mu m, so that the design standard can be marked, and the optical structure is closer to the ideal model.

[0067] 2. The inner part of the counter resonant unit is provided with a wall thickness smaller than the first / second order counter resonant wall thickness of the outer counter resonant tube, which optimizes the fiber bandwidth, increases the cavity area inside the counter resonant unit, introduces a larger parameter margin for structure adjustment, and finally ensures the optical performance of the fiber. Specifically embodied in: fiber attenuation < 3 dB / km, fiber macro-bend additional loss can be marked as G657.A2 in the macro-bend standard at 1550 nm, and the fiber length of pure mode output can be less than 20 m.

[0068] 3. The present application provides a kind of structure highly controllable small-mode-field hollow core fiber and its preparation method, and the fiber has the characteristics of small-mode-field, super bending resistance, high single-mode purity and structure highly stable in small-diameter wire drawing process. It is suitable for short-distance, miniaturization and compact scene data transmission applications.

[0069] It should be noted that the various steps / components described in the present application can be split 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, as required by implementation, to achieve the objectives of the present application.

[0070] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for fabricating a small-diameter, small-mode-field hollow-core optical fiber, characterized in that, include: 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.

2. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, 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.

3. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, 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.

4. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, Each set of positioning rods includes two positioning rods.

5. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, The hollow fiber preform consists of four anti-resonant tube preforms, four compensation tubes, and four sets of positioning rods.

6. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, 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; S303, repeat steps S301~S302, and fix each anti-resonant tube preform in sequence.

7. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 4, 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.

8. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 7, characterized in that, There are two support rods.

9. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 7, 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°.

10. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, characterized in that, In step S4, the wire drawing tension is 4~6.5N.

11. The method for fabricating a small-diameter, small-mode-field hollow-core optical fiber according to claim 1, 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.

12. 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 hollow optical fiber is prepared by any one of the preparation methods described in claims 1 to 11; 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.

13. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, 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.

14. The small-diameter, small-mode-field hollow-core optical fiber according to claim 13, 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.

15. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, 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.

16. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The distance between the innermost inner anti-resonant tube and the fitting arc is less than 3μm.

17. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The wall thickness of the external anti-resonant tube is 0.85~1.3μm.

18. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The wall thickness of the internal anti-resonant tube is 0.3~0.5μm.

19. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The outer diameter of the outer cladding layer is 100~150μm.

20. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The diameter of the fiber core is 13~15μm.

21. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The spacing between adjacent anti-resonant units is 2.5~4μm.

22. The small-diameter, small-mode-field hollow-core optical fiber according to claim 12, characterized in that, The spacing between adjacent anti-resonant units and compensation structures is 2.5~4μm.

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 12.

Images