Low-loss hollow-core optical fiber and preparation method thereof

Abstract

The invention provides a low-loss hollow-core optical fiber and a preparation method thereof. The hollow-core optical fiber comprises an outer cladding, and a plurality of anti-resonance units and a plurality of cladding supplementing units which are connected to the inner wall of the outer cladding, the anti-resonance units are evenly distributed along the inner wall of the outer cladding at equal intervals, the cladding supplement units are arranged between the adjacent anti-resonance units, and the anti-resonance units surround to form a fiber core area in the outer cladding. The anti-resonance unit comprises an outer anti-resonance tube, a first inner anti-resonance tube, a second inner anti-resonance tube and a substrate; the opening of the substrate faces the center of the outer cladding layer and is tightly attached to the inner wall of the outer cladding layer; the cross sections of the outer anti-resonance tube and the first inner anti-resonance tube are arc-shaped, the openings face the substrate, and the two ends are connected to the two ends of the substrate; the second internal anti-resonance tube is connected to the inner wall of the substrate; the cladding supplementing unit is of a circular or arc-shaped structure. In the drawing process of the optical fiber, the anti-resonance unit of the hollow-core optical fiber has good structural stability.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber communications, and in particular to a low-loss hollow-core optical fiber and a preparation method thereof. Background Art

[0002] Because optical signals are primarily transmitted within their air core, hollow-core microstructured optical fibers significantly reduce the impact of solid-core fiber materials, such as dispersion, high nonlinearity, and low damage thresholds. Hollow-core microstructured optical fibers offer revolutionary solutions for low-latency optical communications, high-precision fiber gyroscopes, nonlinear optics, high-power laser transmission, and quantum optics, and have become a highly anticipated research area in optical fiber technology. After years of rapid iteration and development, their fabrication technology has significantly improved, making them a promising candidate for upgrading solid-core optical fibers. Currently, the newly developed double-nested hollow-core antiresonant fiber can reduce transmission loss to 0.08dB / km, significantly exceeding the level of solid-core fiber and setting a new record for ultra-low loss in hollow-core optical fibers.

[0003] Although hollow-core microstructured fibers have great advantages in application, providing more feasibility and flexibility in structural design and preparation methods to further optimize the performance of hollow-core antiresonant fibers remains an important issue in this field.

[0004] Existing public technologies, such as CN118068479A, disclose an eye-shaped single-polarization antiresonant hollow-core fiber. This fiber achieves geometric birefringence by creating structural asymmetry in two directions through the placement of arc-shaped antiresonant units with different wall thicknesses in orthogonal directions. Furthermore, an additional antiresonant unit is added in one direction to suppress polarization modes, thereby achieving single-polarization output. However, in this technology, the second inner antiresonant tube and the fourth antiresonant unit abut against the inner walls of the outer antiresonant tube and the first inner antiresonant tube, respectively, with their end nodes connected to the end nodes and external regions of the first and first inner antiresonant tubes, respectively. To ensure the tightest possible connection between the second inner antiresonant tube (or the fourth antiresonant unit) and the outer antiresonant tube (or the first inner antiresonant tube), the end faces of the second inner antiresonant tube (or the fourth antiresonant unit) must be cleaved at a specific angle. This ensures that when the second inner antiresonant tube (or the fourth antiresonant unit) abuts the inner wall of the outer antiresonant tube (or the first inner antiresonant tube), the end faces conform as closely to the inner wall as possible. This special cleavage angle increases the difficulty of fiber fabrication. However, even if the end face cutting angle requirements are met, the end face of the second inner antiresonance tube (or the fourth antiresonance unit) and the inner wall of the outer antiresonance tube (or the first inner antiresonance tube) are still a combination of a flat surface and a curved surface, which easily makes the end face of the second inner antiresonance tube (or the fourth antiresonance unit) and the outer antiresonance tube (or the first inner antiresonance tube) loosely connected during fusion splicing, thereby reducing the structural stability of the hollow-core optical fiber.

[0005] CN111474627A reports a low-loss hollow-core antiresonant optical fiber. In some embodiments, the circular elements and arc-shaped elements are not connected to each other, but are directly connected to the inner surface of the cladding tube. This leads to very high requirements for the position arrangement of the antiresonant elements during the manufacturing process, and its deviation may even have a significant negative impact on optical transmission.

[0006] Therefore, proposing an optical fiber structure with low loss and high fabrication feasibility to overcome the defects of existing solutions is a technical problem that needs to be solved. Summary of the Invention

[0007] The object of the present invention is to provide a low-loss hollow-core optical fiber and a preparation method thereof, so as to improve the structural stability of an anti-resonance unit in the hollow-core optical fiber.

[0008] To solve the above technical problems, the present invention provides a low-loss hollow-core optical fiber, comprising an outer cladding, and a plurality of anti-resonance units and a plurality of cladding supplementary units connected to the inner wall of the outer cladding; the anti-resonance units are evenly and equidistantly distributed along the inner wall of the outer cladding, the cladding supplementary units are located between adjacent anti-resonance units, and each anti-resonance unit surrounds a core region within the outer cladding; The anti-resonance unit includes an outer anti-resonance tube, a first inner anti-resonance tube, a second inner anti-resonance tube, and a substrate; The cross section of the base is arc-shaped, the opening is toward the center of the outer cladding and is closely attached to the inner wall of the outer cladding, and the end surfaces at both ends are flat; The cross-sections of the outer anti-resonance tube and the first inner anti-resonance tube are both arc-shaped, the openings are both facing the substrate, the end faces of both ends are both flat, and both ends are connected to the two ends of the substrate; The second inner anti-resonance tube is connected to the inner wall of the substrate, and the cross section of the second inner anti-resonance tube is circular or arc-shaped; The cross section of the cladding supplementary unit is circular or arc-shaped.

[0009] According to the above solution, the centers of the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube and the center of the outer cladding are collinear.

[0010] According to the above scheme, the number of anti-resonance units is 3 to 8.

[0011] According to the above solution, the opening angle of the outer anti-resonance tube is 180-270°, the opening angle of the first inner anti-resonance tube is 120-200°, and the opening angle of the substrate is 100-180°.

[0012] According to the above solution, when the cross section of the second internal anti-resonance tube is arc-shaped, its opening angle is 210-300°.

[0013] According to the above solution, the cladding supplement unit is located on the arc-shaped inner wall of the outer cladding defined by two adjacent substrates, and its angle away from the midpoint of the arc-shaped inner wall of the outer cladding is 0-10 degrees.

[0014] According to the above solution, the wall thickness difference between the outer anti-resonance tube, the first inner anti-resonance tube, and the second inner anti-resonance tube does not exceed 0.1um, and the wall thickness is 0.4-2.0um, and the wall thickness of the base is 4-6um.

[0015] According to the above scheme, the outer diameter ratio of the first inner antiresonance tube and the outer antiresonance tube is 0.5~0.9, the outer diameter ratio of the second inner antiresonance tube and the outer antiresonance tube is 0.1~0.4, the outer diameter ratio of the cladding supplement unit and the outer antiresonance tube is 0.1~0.4, and the diameter ratio of the core region and the outer antiresonance tube is 0.6~0.9.

[0016] According to the above solution, the top of the second internal anti-resonance tube is higher than both side ends of the substrate.

[0017] According to the above solution, when the cross section of the second internal anti-resonance tube is arc-shaped, the second internal anti-resonance tube is connected to the substrate via the auxiliary substrate; The cross section of the subsidiary substrate is arc-shaped, and the opening direction is the same as that of the substrate; the end faces of both ends of the second internal anti-resonance tube and the subsidiary substrate are both planes, and the two ends of the second internal anti-resonance tube are connected to the two ends of the subsidiary substrate.

[0018] The present invention also provides a method for preparing a low-loss hollow-core optical fiber, which is used to prepare the low-loss hollow-core optical fiber described above. The preparation method comprises: S1. Prepare capillaries corresponding to the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube, the substrate, and the cladding supplementary unit; S2. Cut or not cut the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube, and the capillaries corresponding to the substrate according to the structure of the target hollow-core optical fiber to form respective prefabricated structures; S3, combining the prefabricated structure of the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube, and the substrate to form an anti-resonance unit assembly; S4, fixing the plurality of anti-resonance unit assemblies, the capillaries corresponding to the cladding supplementary units, and the filling structure to each other in a prefabricated sleeve to form a microstructure preform; S5. The microstructure preform is drawn and cut to obtain an intermediate transition body without a filling structure, and the intermediate transition body and the sleeve are combined to form a hollow-core optical fiber preform. Finally, the hollow-core optical fiber preform is drawn to obtain a low-loss hollow-core optical fiber.

[0019] According to the above scheme, in step S2, the cutting method is horizontal cutting, and the cut surfaces at both ends are overlapped; the cutting process includes hot cutting and cold cutting, hot cutting uses laser cutting, and cold cutting uses blade cutting.

[0020] According to the above scheme, step S3 includes: S301, placing the substrate on a limiting device, making both ends of the substrate level, and marking the bottom of the substrate; S302, placing the second internal anti-resonance tube at the bottom of the substrate so that the center of the second internal anti-resonance tube is vertically aligned with the center of the substrate; S303, placing both end surfaces of the outer anti-resonance tube and the first inner anti-resonance tube closely on both end surfaces of the substrate; S304 , welding the contact portions of the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube and the substrate to obtain an anti-resonance unit assembly.

[0021] According to the above scheme, in step S301, the limiting device includes a base, a first semicircular slider, a second semicircular slider, and a slider buckle; the first semicircular slider and the second semicircular slider are slidably connected to the base and can slide horizontally on the base, and the slider buckle locks and unlocks the positions of the first semicircular slider and the second semicircular slider. When the slider buckle is locked, an area for placing the substrate is formed between the first semicircular slider and the second semicircular slider.

[0022] According to the above solution, in step S301, the method for leveling both ends of the substrate includes: placing level detection pieces on both end surfaces of the substrate, and adjusting the position of the substrate so that the level detection pieces are displayed in the middle.

[0023] According to the above solution, when the cross section of the second inner anti-resonance tube is circular, step S302 includes: adjusting the position of the second inner anti-resonance tube so that the second inner anti-resonance tube is tangent to the bottom mark of the substrate.

[0024] According to the above scheme, step S304 includes: when the cross-section of the second inner anti-resonance tube is circular, using an external heat source to weld the contact point between the second inner anti-resonance tube and the substrate; when the cross-section of the second inner anti-resonance tube is arc-shaped, first using an external heat source to weld the auxiliary substrate to the bottom of the substrate, and then welding the contact surface between the second inner anti-resonance tube and the auxiliary substrate.

[0025] According to the above scheme, step S4 includes: S401, placing the anti-resonance unit assembly in a prefabricated casing, and making the base tangent to the inner wall of the prefabricated casing; S402, placing circular capillary filling tubes or filling rods on both sides of the anti-resonance unit assembly, and placing a central filling tube or filling rod in the middle of the prefabricated sleeve; the circular capillary filling tubes or filling rods and the central filling tube or filling rod are both arranged at both ends of the prefabricated sleeve; S403, placing the capillary tube corresponding to the cladding supplement unit between adjacent circular capillary filling tubes or filling rods; S404, repeating steps S401 to S403 to form a microstructure preform; S405 , adjusting the orientation of each anti-resonance unit assembly so that the central axis of the anti-resonance unit assembly is aligned with the center of the sleeve.

[0026] According to the above solution, in step S405 , a laser level is used to perform orientation correction on the anti-resonance unit assembly.

[0027] Beneficial effects The present invention provides a substrate, and arranges the end faces of the substrate, the outer anti-resonance tube, and the first inner anti-resonance tube to be flat surfaces. This allows the ends of the outer anti-resonance tube and the first inner anti-resonance tube to be in close contact with the ends of the substrate when manufacturing a microstructure preform rod. The two ends are more closely fitted under the action of an external heat source, thereby improving the stability of the stretching process. By providing a cladding supplement unit between the anti-resonance unit assemblies, the proportion of light energy leaking into the cladding is reduced while the suppression efficiency of high-order modes is also improved, thereby improving the mode purity of the optical signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the hollow-core optical fiber structure of Example 1 in one embodiment of the present invention; Figure 2 A side view of a limiting device according to an embodiment of the present invention; Figure 3 This is an axonometric view of a limiting device according to an embodiment of the present invention; Figure 4 Schematic diagram of the distribution of the support structure inside the hollow-core optical fiber preform according to Example 1 in one embodiment of the present invention; Figure 5 1 is a wavelength-limited loss distribution diagram of a hollow-core optical fiber according to Example 1 in one embodiment of the present invention; Figure 6 Schematic diagram of the support structure distribution inside the hollow-core optical fiber preform according to Example 2 of one embodiment of the present invention; Figure 7 1. The confinement loss and high-order mode suppression ratio of the hollow-core optical fiber of Example 2 in one embodiment of the present invention vary with the deviation angle. Figure 8 Schematic diagram of the hollow-core optical fiber structure of Example 3 in one embodiment of the present invention; Figure 9 This is the limiting loss curve of the hollow-core optical fiber of Example 3 in one embodiment of the present invention.

[0029] In the figure: 1-external antiresonance tube, 2-first internal antiresonance tube, 3-second internal antiresonance tube, 4-substrate, 5-cladding supplementary unit, 6-external cladding, 7-core region, 8-circular capillary filling tube or filling rod, 9-center filling tube or filling rod, 10-nested tube combination, 11-offset angle, 12-attached substrate, 1a-limiting device, 2a-slider buckle, 3a-first semicircular slider, 3b-second semicircular slider. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0031] This embodiment discloses a low-loss hollow-core optical fiber, comprising an outer cladding 6, and a plurality of antiresonance units and a plurality of cladding supplement units 5 connected to the inner wall of the outer cladding 6. The antiresonance units are evenly and equidistantly distributed along the inner wall of the outer cladding 6, and the cladding supplement units 5 are located between adjacent antiresonance units. Each antiresonance unit surrounds a core region 7 within the outer cladding 6. It will be understood that the size of the core region 7 is determined by the size and number of the antiresonance units. The anti-resonance unit includes an outer anti-resonance tube 1, a first inner anti-resonance tube 2, a second inner anti-resonance tube 3, and a substrate 4; The cross section of the base 4 is an arc-shaped structure, with the opening facing the center of the outer cladding 6 and closely attached to the inner wall of the outer cladding 6, and the end surfaces at both ends are flat; The cross-sections of the outer anti-resonance tube 1 and the first inner anti-resonance tube 2 are both arc-shaped, with their openings facing the substrate 4, their end faces at both ends being flat, and both ends being connected to the ends of the substrate 4; The second inner anti-resonance tube 3 is connected to the inner wall of the substrate 4 , and the cross section of the second inner anti-resonance tube 3 is circular or arc-shaped (the circular shape includes a single circular shape and a nested circular shape); The cross section of the cladding supplement unit 5 is circular or arc-shaped.

[0032] Furthermore, the centers of the outer anti-resonance tube 1 , the first inner anti-resonance tube 2 , and the second inner anti-resonance tube 3 are collinear with the center of the outer cladding 6 .

[0033] Furthermore, the number of the anti-resonance units is 3 to 8.

[0034] Furthermore, the number of the anti-resonance units is 4 to 7.

[0035] Furthermore, the number of the anti-resonance units is 4 to 6.

[0036] Furthermore, the opening angle of the outer anti-resonance tube 1 is 180-270°, the opening angle of the first inner anti-resonance tube 2 is 120-200°, and the opening angle of the base 4 is 100-180°. It should be understood that the opening angle of a structure with an arc-shaped cross-section (i.e., an arc-shaped structure) is defined as: the clockwise angle formed by the lines connecting the two end portions of the arc-shaped structure and the center of the arc-shaped structure along the inner side of the arc.

[0037] Furthermore, when the cross section of the second inner anti-resonance tube 3 is arc-shaped, the opening angle thereof is 210-300°.

[0038] Furthermore, the cladding supplement unit 5 is located on the arc-shaped inner wall of the outer cladding 6 defined by two adjacent substrates 4, and its angle of deviation from the midpoint of the arc-shaped inner wall of the outer cladding is 0-10 degrees. Furthermore, the wall thickness difference between the outer anti-resonance tube 1 , the first inner anti-resonance tube 2 , and the second inner anti-resonance tube 3 does not exceed 0.1 μm, and the wall thicknesses are all 0.4-2.0 μm, and the wall thickness of the substrate 4 is 4-6 μm.

[0039] Furthermore, the outer diameter ratio of the first inner antiresonance tube 2 and the outer antiresonance tube 1 is 0.5~0.9, the outer diameter ratio of the second inner antiresonance tube 3 and the outer antiresonance tube 1 is 0.1~0.4, the outer diameter ratio of the cladding supplement unit 5 and the outer antiresonance tube 1 is 0.1~0.4, and the diameter ratio of the core region 7 to the outer antiresonance tube 1 is 0.6~0.9.

[0040] Furthermore, the top of the second inner anti-resonance tube 3 is higher than both side ends of the substrate 4 .

[0041] Furthermore, when the second inner anti-resonance tube 3 is an arc-shaped structure, the second inner anti-resonance tube 3 is connected to the substrate 4 via the auxiliary substrate 12; The cross section of the subsidiary substrate 12 is arc-shaped, and the opening direction is the same as that of the substrate 4; the end faces of the second inner anti-resonance tube 3 and the end faces of the subsidiary substrate 12 are both planes, and the two ends of the second inner anti-resonance tube 3 are connected to the two ends of the subsidiary substrate 12.

[0042] This embodiment further provides a method for preparing a low-loss hollow-core optical fiber, which is used to prepare the low-loss hollow-core optical fiber described above. The preparation method includes: S1, preparing capillaries corresponding to the outer anti-resonance tube 1, the first inner anti-resonance tube 2, the second inner anti-resonance tube 3, the substrate 4, and the cladding supplement unit 5; S2, cutting or not cutting the capillaries corresponding to the outer anti-resonance tube 1, the first inner anti-resonance tube 2, the second inner anti-resonance tube 3, and the substrate 4 according to the structure of the target hollow-core optical fiber to form respective prefabricated structures; S3, combining the prefabricated structure of the outer anti-resonance tube 1, the first inner anti-resonance tube 2, the second inner anti-resonance tube 3, and the substrate 4 to form an anti-resonance unit assembly; S4, fixing the plurality of anti-resonance unit assemblies, the capillaries corresponding to the cladding supplementary units 5, and the filling structure to each other in a prefabricated sleeve to form a microstructure preform; S5. The microstructure preform is drawn and cut to obtain an intermediate transition body without a filling structure, and the intermediate transition body and the sleeve are combined to form a hollow-core optical fiber preform. Finally, the hollow-core optical fiber preform is drawn to obtain a low-loss hollow-core optical fiber.

[0043] In this embodiment, by changing only the size of the first inner anti-resonance tube 2 while keeping the size of the outer anti-resonance tube 1 unchanged, the air area between the outer anti-resonance tube 1 and the first inner anti-resonance tube 2 can be increased, thereby achieving better high-order mode filtering characteristics.

[0044] Furthermore, in step S2, the cutting method is horizontal cutting, and the cut surfaces at both ends are overlapped; the cutting process includes hot cutting and cold cutting, hot cutting uses laser cutting, and cold cutting uses blade cutting.

[0045] Furthermore, step S3 includes: S301, placing the substrate 4 on a limiting device 1a, making both ends of the substrate 4 level, and marking the bottom of the substrate 4; S302, placing the second internal anti-resonance tube 3 at the bottom of the substrate 4, and aligning the center of the second internal anti-resonance tube 3 vertically with the center of the substrate 4; S303, placing both end surfaces of the outer anti-resonance tube 1 and the first inner anti-resonance tube 2 closely on both end surfaces of the substrate 4; S304 , welding the contact portions of the outer anti-resonance tube 1 , the first inner anti-resonance tube 2 , the second inner anti-resonance tube 3 and the substrate 4 to obtain an anti-resonance unit assembly.

[0046] Further, in step S301, see Figure 2~Figure 3 The limiting device 1a includes a base, a first semicircular slider 3a, a second semicircular slider 3b, and a slider buckle 2a; the first semicircular slider 3a and the second semicircular slider 3b are slidably connected to the base and can slide horizontally on the base, and the slider buckle 2a locks and unlocks the positions of the first semicircular slider 3a and the second semicircular slider 3b. When the slider buckle 2a is locked, an area for placing the base 4 is formed between the first semicircular slider 3a and the second semicircular slider 3b; an example of using the limiting device 1a is: placing the base 4 on the base, loosening the slider buckle 2a, sliding the first semicircular slider 3a to the leftmost end of the base, adjusting the second semicircular slider 3b so that the distance between it and the first semicircular slider 3a matches the base 4, and finally locking the slider buckle 2a.

[0047] Furthermore, in step S301 , the method for leveling both ends of the base 4 includes placing level detection pieces on both end surfaces of the base 4 , and adjusting the position of the base 4 so that the level detection pieces are displayed in the middle.

[0048] Furthermore, when the cross-section of the second inner anti-resonance tube 3 is circular, step S302 includes: adjusting the position of the second inner anti-resonance tube 3 so that the bottom marks of the second inner anti-resonance tube 3 and the substrate 4 are tangent; at this time, the distance between the end faces of the second inner anti-resonance tube 3 and the substrate 4 is the same.

[0049] Furthermore, step S304 includes: using an external heat source to weld the contact surfaces of the external anti-resonance tube 1, the first internal anti-resonance tube 2 and the substrate 4; when the cross-section of the second internal anti-resonance tube 3 is circular, using an external heat source to weld the contact points of the second internal anti-resonance tube 3 and the substrate 4; when the cross-section of the second internal anti-resonance tube 3 is arc-shaped, first using an external heat source to weld the auxiliary substrate 12 to the bottom of the substrate 4, and then welding the contact surfaces of the second internal anti-resonance tube 3 and the auxiliary substrate 12.

[0050] Furthermore, step S4 includes: S401, placing the anti-resonance unit assembly in a prefabricated casing, and making the substrate 4 tangent to the inner wall of the prefabricated casing; S402, see Figure 4 Circular capillary filling tubes or filling rods 8 are placed on both sides of the anti-resonance unit assembly, and a central filling tube or filling rod 9 is placed in the middle of the sleeve; the circular capillary filling tubes or filling rods 8 and the central filling tubes or filling rods 9 are tangent to the prefabricated structures corresponding to the outer anti-resonance tubes 1 in the anti-resonance unit assembly, and are used to fix the anti-resonance unit assembly together with the inner wall of the prefabricated sleeve; the circular capillary filling tubes or filling rods 8 and the central filling tubes or filling rods 9 are both arranged at both ends of the prefabricated sleeve; S403, placing the capillary corresponding to the cladding supplement unit 5 between adjacent circular capillary filling tubes or filling rods 8; S404, repeating steps S401 to S403 to form a microstructure preform; S405 , adjusting the orientation of each anti-resonance unit assembly so that the central axis of the anti-resonance unit assembly is aligned with the center of the sleeve.

[0051] Furthermore, in step S405 , a laser level is used to perform orientation correction on the anti-resonance unit assembly.

[0052] The present invention is applicable to a hollow-core optical fiber whose inner anti-resonance unit is an arc-shaped structure, and can significantly improve the structural stability of the hollow-core optical fiber of this structural type.

[0053] This embodiment provides the following structural example of a low-loss hollow-core optical fiber.

[0054] Example 1: See also Figure 1The core diameter of the low-loss hollow-core optical fiber is 28.5 μm. The diameters of the outer antiresonance tube 1, the first inner antiresonance tube 2, and the second inner antiresonance tube 3 are 41.6 μm, 33.7 μm, and 14 μm, respectively, and the wall thickness is 1.1 μm. The opening angles of the outer antiresonance tube 1 and the first inner antiresonance tube 2 are 230° and 110°, respectively. The diameter of the base 4 is 36.1 μm, the wall thickness is 2.5 μm, and the opening angle is 115°. The diameter of the cladding supplement unit 5 is 11.5 μm and is located at the midpoint of the arc-shaped inner wall of the outer cladding 6. Figure 5 As shown in FIG, the low-loss hollow-core optical fiber of this structure has low confinement loss in the C~L band.

[0055] Example 2: See also Figure 6 In this example, the second inner antiresonance tube 3 in the low-loss hollow-core fiber is a nested tube assembly 10, with the nested tube diameters of the second inner antiresonance tube 3 being 16 μm and 7.8 μm, respectively. The diameters of the outer antiresonance tube 1 and the first inner antiresonance tube 2 are 38.7 μm and 30.8 μm, respectively. The diameter of the cladding supplement unit 5 is 11 μm, and the offset angle 11 is 4°. The wall thicknesses of the nested tubes of the outer antiresonance tube 1, the first inner antiresonance tube 2, and the second inner antiresonance tube 3 are all between 1.15 and 1.25 μm. For the curves of the confinement loss and high-order mode suppression ratio of the low-loss hollow-core fiber with this structure as a function of the offset angle, see [ 1 ]. Figure 7 .

[0056] Example 3: See also Figure 8 In the low-loss hollow-core optical fiber of this example, the cross-sections of the second inner anti-resonance tube 3 and the cladding supplement unit 5 are both arc-shaped; their diameters are 12.3um and 15.6um respectively. An auxiliary base 12 is closely attached to the inner bottom of the base 4. The auxiliary base 12 has an arc-shaped cross-section and a diameter of 14.1um. The opening of the auxiliary base 12 faces the center of the outer cladding 6. The opening of the second inner anti-resonance tube 3 faces the auxiliary base 12, and the two ends of the second inner anti-resonance tube 3 are connected to the two ends of the auxiliary base 12. The opening of the cladding supplement unit 5 faces the inner wall of the outer cladding 6. For the limiting loss curve of the low-loss hollow-core optical fiber of this structure, see Figure 9 .

[0057] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0058] It will be easily understood by those skilled in the art 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 in the scope of protection of the present invention.

Claims

1. A low-loss hollow-core optical fiber, characterized in that: The fiber comprises an outer cladding, and a plurality of anti-resonance units and a plurality of cladding supplement units connected to the inner wall of the outer cladding; the anti-resonance units are evenly and equidistantly distributed along the inner wall of the outer cladding, the cladding supplement units are between adjacent anti-resonance units, and each anti-resonance unit surrounds and forms a core region inside the outer cladding; The anti-resonance unit includes an outer anti-resonance tube, a first inner anti-resonance tube, a second inner anti-resonance tube, and a substrate; The cross section of the base is arc-shaped, the opening is toward the center of the outer cladding and is closely attached to the inner wall of the outer cladding, and the end surfaces at both ends are flat; The cross-sections of the outer anti-resonance tube and the first inner anti-resonance tube are both arc-shaped, the openings are both facing the substrate, the end surfaces at both ends are both flat, and both ends are connected to the two ends of the substrate; The second inner anti-resonance tube is connected to the inner wall of the substrate, and the cross section of the second inner anti-resonance tube is circular or arc-shaped; The cross section of the cladding supplementary unit is circular or arc-shaped.

2. The low-loss hollow-core optical fiber according to claim 1, wherein The centers of the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube and the center of the outer cladding are collinear.

3. The low-loss hollow-core optical fiber according to claim 1, wherein The number of anti-resonance units is 3 to 8.

4. The low-loss hollow-core optical fiber according to claim 1, wherein The opening angle of the outer anti-resonance tube is 180-270 degrees, the opening angle of the first inner anti-resonance tube is 120-200 degrees, and the opening angle of the base is 100-180 degrees.

5. The low-loss hollow-core optical fiber according to claim 1, wherein When the cross section of the second internal anti-resonance tube is arc-shaped, the opening angle thereof is 210-300°.

6. The low-loss hollow-core optical fiber according to claim 1, wherein: The cladding supplement unit is located on the arc-shaped inner wall of the outer cladding defined by two adjacent substrates, and the angle of the cladding supplement unit away from the midpoint of the arc-shaped inner wall of the outer cladding is 0-10 degrees.

7. The low-loss hollow-core optical fiber according to claim 1, wherein: The difference in wall thickness between the outer anti-resonance tube, the first inner anti-resonance tube, and the second inner anti-resonance tube does not exceed 0.1 μm, and the wall thicknesses are all 0.4 to 2.0 μm, and the wall thickness of the base is 4 to 6 μm.

8. The low-loss hollow-core optical fiber according to claim 1, wherein: The outer diameter ratio of the first inner antiresonance tube and the outer antiresonance tube is 0.5~0.9, the outer diameter ratio of the second inner antiresonance tube and the outer antiresonance tube is 0.1~0.4, the outer diameter ratio of the cladding supplement unit and the outer antiresonance tube is 0.1~0.4, and the diameter ratio of the core region and the outer antiresonance tube is 0.6~0.

9.

9. The low-loss hollow-core optical fiber according to claim 1 or 8, characterized in that: The top of the second internal anti-resonance tube is higher than both side ends of the substrate.

10. The low-loss hollow-core optical fiber according to claim 1, characterized in that ,When the cross section of the second inner anti-resonance tube is an arc shape, the second inner anti-resonance tube is connected to the substrate through the auxiliary substrate; The cross section of the auxiliary base is arc-shaped, and the opening direction is the same as that of the base; Both end surfaces of the second internal anti-resonance tube and both end surfaces of the subsidiary substrate are planes, and both ends of the second internal anti-resonance tube are connected to both ends of the subsidiary substrate.

11. A method for preparing a low-loss hollow-core optical fiber, characterized in that: For preparing the low-loss hollow-core optical fiber according to claim 1, the preparation method comprises: S1. Prepare capillaries corresponding to the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube, the substrate, and the cladding supplementary unit; S2. Cut or not cut the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube, and the capillaries corresponding to the substrate according to the structure of the target hollow-core optical fiber to form respective prefabricated structures; S3, combining the prefabricated structure of the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube, and the substrate to form an anti-resonance unit assembly; S4, fixing the plurality of anti-resonance unit assemblies, the capillaries corresponding to the cladding supplementary units, and the filling structure to each other in a prefabricated sleeve to form a microstructure preform; S5. The microstructure preform is drawn and cut to obtain an intermediate transition body without a filling structure, and the intermediate transition body and the sleeve are combined to form a hollow-core optical fiber preform. Finally, the hollow-core optical fiber preform is drawn to obtain a low-loss hollow-core optical fiber.

12. The method for preparing a low-loss hollow-core optical fiber according to claim 11, wherein: In step S2, the cutting method is horizontal cutting, and the cut surfaces at both ends are overlapped; the cutting process includes hot cutting and cold cutting, hot cutting uses laser cutting, and cold cutting uses blade cutting.

13. The method for preparing a low-loss hollow-core optical fiber according to claim 11, wherein: Step S3 includes: S301, placing the substrate on a limiting device, making both ends of the substrate level, and marking the bottom of the substrate; S302, placing the second internal anti-resonance tube at the bottom of the substrate so that the center of the second internal anti-resonance tube is vertically aligned with the center of the substrate; S303, placing both end surfaces of the outer anti-resonance tube and the first inner anti-resonance tube closely on both end surfaces of the substrate; S304 , welding the contact portions of the outer anti-resonance tube, the first inner anti-resonance tube, the second inner anti-resonance tube and the substrate to obtain an anti-resonance unit assembly.

14. The method for preparing a low-loss hollow-core optical fiber according to claim 13, wherein: In step S301, the limiting device includes a base, a first semicircular slider, a second semicircular slider, and a slider buckle; the first semicircular slider and the second semicircular slider are slidably connected to the base and can slide horizontally on the base, and the slider buckle locks and unlocks the positions of the first semicircular slider and the second semicircular slider. When the slider buckle is locked, an area for placing the substrate is formed between the first semicircular slider and the second semicircular slider.

15. The method for preparing a low-loss hollow-core optical fiber according to claim 13, wherein: In step S301 , the method for leveling both ends of the substrate includes: placing level detection pieces on both end surfaces of the substrate, and adjusting the position of the substrate so that the level detection pieces are displayed in a center state.

16. The method for preparing a low-loss hollow-core optical fiber according to claim 13, wherein: When the cross section of the second inner anti-resonance tube is circular, step S302 includes: adjusting the position of the second inner anti-resonance tube so that the second inner anti-resonance tube is tangent to the bottom mark of the substrate.

17. The method for preparing a low-loss hollow-core optical fiber according to claim 13, wherein: Step S304 includes: when the cross-section of the second inner anti-resonance tube is circular, using an external heat source to weld the contact point between the second inner anti-resonance tube and the substrate; when the cross-section of the second inner anti-resonance tube is arc-shaped, first using an external heat source to weld the auxiliary substrate to the bottom of the substrate, and then welding the contact surface between the second inner anti-resonance tube and the auxiliary substrate.

18. The method for preparing a low-loss hollow-core optical fiber according to claim 11, wherein: Step S4 includes: S401, placing the anti-resonance unit assembly in a prefabricated casing, and making the base tangent to the inner wall of the prefabricated casing; S402, placing circular capillary filling tubes or filling rods on both sides of the anti-resonance unit assembly, and placing a central filling tube or filling rod in the middle of the prefabricated sleeve; the circular capillary filling tubes or filling rods and the central filling tube or filling rod are both arranged at both ends of the prefabricated sleeve; S403, placing the capillary tube corresponding to the cladding supplement unit between adjacent circular capillary filling tubes or filling rods; S404, repeating steps S401 to S403 to form a microstructure preform; S405 , adjusting the orientation of each anti-resonance unit assembly so that the central axis of the anti-resonance unit assembly is aligned with the center of the sleeve.

19. The method for preparing a low-loss hollow-core optical fiber according to claim 18, wherein: In step S405 , a laser level is used to perform orientation correction on the anti-resonance unit assembly.

Images