Low-loss hollow-core optical fiber and method of making the same

Abstract

This invention provides a low-loss hollow-core optical fiber and its fabrication method. The hollow-core optical fiber includes an outer cladding, and several anti-resonant units and several cladding supplementary units connected to the inner wall of the outer cladding. The anti-resonant units are uniformly and equidistantly distributed along the inner wall of the outer cladding, and the cladding supplementary units are located between adjacent anti-resonant units. Each anti-resonant unit surrounds and forms the core region inside the outer cladding. Each anti-resonant unit includes an outer anti-resonant tube, a first inner anti-resonant tube, a second inner anti-resonant tube, and a substrate. The substrate has an arc-shaped cross-section, with its opening facing the center of the outer cladding and closely attached to the inner wall of the outer cladding. The outer anti-resonant tube and the first inner anti-resonant tube both have arc-shaped cross-sections, with their openings facing the substrate, and both ends connected to the two ends of the substrate. The second inner anti-resonant tube is connected to the inner wall of the substrate. The cladding supplementary units have a circular or arc-shaped structure. During the optical fiber drawing process, the anti-resonant units of the hollow-core optical fiber of this invention exhibit good structural stability.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, specifically to a low-loss hollow-core optical fiber and its preparation method. Background Technology

[0002] Hollow-core microstructured optical fibers, because optical signals are primarily transmitted within their air core, significantly reduce the impact of problems associated with solid fiber fabrication materials, such as dispersion, high nonlinearity, and low damage thresholds, compared to solid-core fibers. This provides revolutionary solutions for low-latency optical communication, high-precision fiber optic gyroscopes, nonlinear optics, high-power laser transmission, and quantum optics, making it a highly anticipated research direction in fiber optic technology. After years of rapid iteration and development, its fabrication technology has significantly improved, making it a key candidate for upgrading solid-core fibers. Currently, the newly developed double-nested hollow-core antiresonant fiber can reduce transmission loss to 0.08 dB / km, significantly better than solid-core fibers, setting a new record for ultra-low loss in hollow-core fibers.

[0003] Although hollow-core microstructured optical fibers have significant advantages in applications, providing more feasibility and flexibility in structural design and fabrication methods to further optimize the performance of hollow-core anti-resonant optical fibers remains an important issue in this field.

[0004] In existing publicly available technologies, such as CN118068479A, an eye-shaped single-polarization anti-resonant hollow-core optical fiber is disclosed. This fiber achieves single-polarization output by creating a structural asymmetry in two directions through wall thickness differences in arc-shaped anti-resonant units along orthogonal directions, thereby introducing geometric birefringence. Furthermore, an additional anti-resonant unit is added in one direction to suppress polarization modes. However, in this technology, the second inner anti-resonant tube and the fourth anti-resonant unit abut against the inner walls of the outer anti-resonant tube and the first inner anti-resonant tube, respectively, and their end nodes are connected to the end nodes of the first and second inner anti-resonant tubes and the external region, respectively. To ensure the second inner anti-resonant tube (or the fourth anti-resonant unit) and the outer anti-resonant tube (or the first inner anti-resonant tube) are as tightly bonded as possible, the end faces of the second inner anti-resonant tube (or the fourth anti-resonant unit) need to have special cutting angles so that when the second inner anti-resonant tube (or the fourth anti-resonant unit) abuts against the inner wall of the outer anti-resonant tube (or the first inner anti-resonant tube), the end faces can fit as closely as possible to the inner wall. Achieving these special cutting angles increases the difficulty of fiber fabrication. However, even if the end face cutting angle requirement is met, the end face of the second inner anti-resonant tube (or the fourth anti-resonant unit) and the inner wall of the outer anti-resonant tube (or the first inner anti-resonant tube) are still a combination of a plane and a curved surface. This makes it easy for the end face of the second inner anti-resonant tube (or the fourth anti-resonant unit) and the outer anti-resonant tube (or the first inner anti-resonant tube) to be loosely connected during fusion splicing, which reduces the structural stability of the hollow fiber.

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

[0006] Therefore, proposing a low-loss and highly feasible optical fiber structure to overcome the shortcomings of existing solutions is a technical problem that needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a low-loss hollow-core optical fiber and its preparation method, so as to improve the structural stability of the anti-resonant unit in the hollow-core optical fiber.

[0008] To solve the above-mentioned technical problems, the present invention provides a low-loss hollow-core optical fiber, including an outer cladding, and a plurality of anti-resonant units and a plurality of cladding supplementary units connected to the inner wall of the outer cladding; the anti-resonant units are evenly and equidistantly distributed along the inner wall of the outer cladding, and the cladding supplementary units are located between adjacent anti-resonant units, with each anti-resonant unit surrounding and forming the fiber core region inside the outer cladding.

[0009] The anti-resonance unit includes an outer anti-resonance transistor, a first inner anti-resonance transistor, a second inner anti-resonance transistor, and a substrate;

[0010] The base has a circular arc cross-section, with the opening facing the center of the outer cladding and closely attached to the inner wall of the outer cladding, and both end faces are flat.

[0011] Both the external anti-resonant tube and the first internal anti-resonant tube have circular arc cross-sections, with their openings facing the substrate. Both end faces are flat, and both ends are connected to the two ends of the substrate.

[0012] The second internal anti-resonant tube is connected to the inner wall of the substrate, and the cross-section of the second internal anti-resonant tube is circular or arc-shaped.

[0013] The cross-section of the cladding supplementary unit is circular or arc-shaped.

[0014] According to the above scheme, the centers of the outer anti-resonant tube, the first inner anti-resonant tube, and the second inner anti-resonant tube are collinear with the center of the outer cladding.

[0015] According to the above scheme, the number of anti-resonance units is 3 to 8.

[0016] According to the above scheme, the opening angle of the external anti-resonant tube is 180~270°, the opening angle of the first internal anti-resonant tube is 120~200°, and the opening angle of the substrate is 100~180°.

[0017] According to the above scheme, when the cross-section of the second internal anti-resonant tube is arc-shaped, its opening angle is 210~300°.

[0018] According to the above scheme, the cladding supplement unit is located on the inner arc of the outer cladding defined by two adjacent bases, and its angle of deviation from the midpoint of the inner arc of the outer cladding is 0~10°.

[0019] According to the above scheme, the wall thickness difference between the outer anti-resonant tube, the first inner anti-resonant tube, and the second inner anti-resonant tube does not exceed 0.1 μm, and the wall thickness of each is 0.4~2.0 μm, while the wall thickness of the substrate is 4~6 μm.

[0020] According to the above scheme, the outer diameter ratio of the first inner anti-resonant tube to the outer anti-resonant tube is 0.5~0.9, the outer diameter ratio of the second inner anti-resonant tube to the outer anti-resonant tube is 0.1~0.4, the outer diameter ratio of the cladding supplement unit to the outer anti-resonant tube is 0.1~0.4, and the diameter ratio of the fiber core region to the outer anti-resonant tube is 0.6~0.9.

[0021] According to the above scheme, the top of the second internal anti-resonant tube is higher than the two ends of the base.

[0022] According to the above scheme, when the cross-section of the second inner anti-resonant tube is arc-shaped, the second inner anti-resonant tube is connected to the base through an auxiliary base;

[0023] The cross-section of the auxiliary 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 inner anti-resonant tube and the end faces of both ends of the auxiliary substrate are planes, and the two ends of the second inner anti-resonant tube are connected to the two ends of the auxiliary substrate.

[0024] This invention also provides a method for preparing low-loss hollow-core optical fiber, used to prepare the low-loss hollow-core optical fiber described above, the method comprising:

[0025] S1. Prepare the outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, the substrate, and the capillary corresponding to the cladding supplementary unit;

[0026] S2. The outer anti-resonator, the first inner anti-resonator, the second inner anti-resonator, and the capillary corresponding to the substrate are cut or not cut according to the structure of the target hollow fiber to form their respective prefabricated structures.

[0027] S3. The outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, and the prefabricated structure of the substrate are combined to form an anti-resonant unit assembly.

[0028] S4. Multiple anti-resonance unit assemblies, capillaries corresponding to cladding supplementary units, and filling structures are fixed together in a prefabricated sleeve to form a microstructure prefabricated rod.

[0029] S5. After the microstructure preform is drawn and cut, an intermediate transition body without filling structure is obtained. The intermediate transition body and the sleeve are then combined to form a hollow fiber preform. Finally, the hollow fiber preform is drawn into a low-loss hollow fiber.

[0030] According to the above scheme, in step S2, the cutting method is horizontal cutting, and the resulting two cut surfaces overlap; the cutting process includes hot cutting and cold cutting, with hot cutting using laser cutting and cold cutting using blade cutting.

[0031] According to the above scheme, step S3 includes:

[0032] S301. Place the base on a limiting device to make both ends of the base horizontal and mark the bottom of the base.

[0033] S302. Place the second internal anti-resonant tube at the bottom of the substrate, so that the center of the second internal anti-resonant tube is vertically aligned with the center of the substrate.

[0034] S303. Place the two end faces of the external anti-resonant tube and the first internal anti-resonant tube tightly against the two end faces of the substrate.

[0035] S304. Weld the contact points of the outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, and the substrate to obtain an anti-resonant unit assembly.

[0036] 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; 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 base is formed between the first semicircular slider and the second semicircular slider.

[0037] According to the above scheme, in step S301, the method of making the two ends of the substrate horizontal includes: placing horizontal detection pieces on the two end faces of the substrate, and adjusting the position of the substrate so that the horizontal detection pieces are displayed in the center state.

[0038] According to the above scheme, when the cross-section of the second inner anti-resonant tube is circular, step S302 includes: adjusting the position of the second inner anti-resonant tube so that the second inner anti-resonant tube is tangent to the bottom mark of the substrate.

[0039] According to the above scheme, step S304 includes: when the cross-section of the second inner anti-resonant tube is circular, an external heat source is used to weld the contact point between the second inner anti-resonant tube and the substrate; when the cross-section of the second inner anti-resonant tube is arc-shaped, an external heat source is first used to weld the auxiliary substrate to the bottom of the substrate, and then the contact surface between the second inner anti-resonant tube and the auxiliary substrate is welded.

[0040] According to the above scheme, step S4 includes:

[0041] S401. Place the anti-resonance unit assembly inside the prefabricated sleeve, and make the base tangent to the inner wall of the prefabricated sleeve.

[0042] S402. Circular capillary filling tubes or filling rods are placed on both sides of the anti-resonance unit assembly, and a central filling tube or filling rod is placed in the middle of the prefabricated sleeve; the circular capillary filling tubes or filling rods and the central filling tube or filling rods are both set at both ends of the prefabricated sleeve.

[0043] S403. Place the capillary corresponding to the cladding supplement unit between adjacent circular capillary filling tubes or filling rods.

[0044] S404. Repeat steps S401 to S403 to form a microstructure preform.

[0045] S405. Adjust 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.

[0046] According to the above scheme, in step S405, a laser level is used to correct the orientation of the anti-resonance unit assembly.

[0047] Beneficial effects

[0048] This invention provides a substrate with flat end faces for the substrate, the outer anti-resonator, and the first inner anti-resonator. This ensures that during the fabrication of the microstructure preform, the ends of the outer and inner anti-resonator are in close contact with the ends of the substrate, resulting in a tighter fit under external heat and improved stability during the stretching process. Furthermore, by adding cladding supplementary units between the anti-resonator unit assemblies, the proportion of light energy leaking into the cladding is reduced, while the suppression efficiency of higher-order modes is improved, thereby enhancing the mode purity of the optical signal. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the hollow optical fiber structure of Example 1 in one embodiment of the present invention;

[0050] Figure 2 This is a side view of a limiting device according to an embodiment of the present invention;

[0051] Figure 3 This is an isometric view of a limiting device according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the distribution of the internal support structure of the hollow optical fiber preform in one embodiment of the present invention.

[0053] Figure 5 This is a wavelength-confinence loss distribution diagram of a hollow-core optical fiber in Example 1 of an embodiment of the present invention;

[0054] Figure 6 This is a schematic diagram of the distribution of the internal support structure of the hollow optical fiber preform in Example 2 of an embodiment of the present invention;

[0055] Figure 7 The curves showing the confinement loss and higher-order mode suppression ratio of the hollow-core optical fiber as a function of deviation angle are shown in Example 2 of this invention.

[0056] Figure 8 This is a schematic diagram of the hollow fiber structure of Example 3 in one embodiment of the present invention;

[0057] Figure 9 This is a confined loss curve of a hollow-core optical fiber in Example 3 of an embodiment of the present invention.

[0058] In the figure: 1-external anti-resonator tube, 2-first internal anti-resonator tube, 3-second internal anti-resonator tube, 4-substrate, 5-cladding supplementary unit, 6-outer cladding, 7-core region, 8-circular capillary filling tube or filling rod, 9-central filling tube or filling rod, 10-nested tube combination, 11-offset angle, 12-attached substrate, 1a-limiting device, 2a-slider buckle, 3a-first semi-circular slider, 3b-second semi-circular slider. Detailed Implementation

[0059] 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.

[0060] This embodiment discloses a low-loss hollow-core optical fiber, including an outer cladding 6, and a plurality of anti-resonant units and a plurality of cladding supplementary units 5 connected to the inner wall of the outer cladding 6; the anti-resonant units are evenly and equidistantly distributed along the inner wall of the outer cladding 6, and the cladding supplementary units 5 are located between adjacent anti-resonant units, and each anti-resonant unit surrounds and forms a core region 7 inside the outer cladding 6; it can be understood that the size of the core region 7 is determined by the size and number of anti-resonant units;

[0061] 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;

[0062] 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 both end faces are flat.

[0063] Both the outer anti-resonant tube 1 and the first inner anti-resonant tube 2 have circular arc-shaped cross sections, with their openings facing the base 4. Both end faces are flat, and both ends are connected to the two ends of the base 4.

[0064] The second inner anti-resonant tube 3 is connected to the inner wall of the base 4. The cross-section of the second inner anti-resonant tube 3 is circular or arc-shaped (circular includes single circles and nested circles).

[0065] The cross-section of the cladding supplement unit 5 is circular or arc-shaped.

[0066] Furthermore, the centers of the outer anti-resonator 1, the first inner anti-resonator 2, and the second inner anti-resonator 3 are collinear with the center of the outer cladding 6.

[0067] Furthermore, the number of anti-resonant units is 3 to 8.

[0068] Furthermore, the number of anti-resonant units is 4 to 7.

[0069] Furthermore, the number of anti-resonant units is 4 to 6.

[0070] Furthermore, the opening angle of the outer anti-resonant tube 1 is 180~270°, the opening angle of the first inner anti-resonant tube 2 is 120~200°, and the opening angle of the substrate 4 is 100~180°. It should be understood that the opening angle of the structure with a circular arc cross-section (i.e., the circular arc structure) is defined as the clockwise angle formed by the lines connecting the two ends of the circular arc structure to the center of the circular arc structure along the inner side of the circular arc.

[0071] Furthermore, when the cross-section of the second internal anti-resonant tube 3 is arc-shaped, its opening angle is 210~300°.

[0072] Furthermore, the cladding supplement unit 5 is located on the arcuate inner wall of the outer cladding 6 defined by two adjacent bases 4, and its angle of deviation from the midpoint of the arcuate inner wall of the outer cladding is 0~10°.

[0073] Furthermore, the wall thickness difference between the outer anti-resonator 1, the first inner anti-resonator 2, and the second inner anti-resonator 3 does not exceed 0.1 μm, and the wall thickness of each is 0.4~2.0 μm, while the wall thickness of the substrate 4 is 4~6 μm.

[0074] Furthermore, the outer diameter ratio of the first inner anti-resonant tube 2 to the outer anti-resonant tube 1 is 0.5~0.9, the outer diameter ratio of the second inner anti-resonant tube 3 to the outer anti-resonant tube 1 is 0.1~0.4, the outer diameter ratio of the cladding supplement unit 5 to the outer anti-resonant tube 1 is 0.1~0.4, and the diameter ratio of the core region 7 to the outer anti-resonant tube 1 is 0.6~0.9.

[0075] Furthermore, the top of the second internal anti-resonant tube 3 is higher than the two ends of the base 4.

[0076] Furthermore, when the second internal anti-resonant tube 3 has an arc-shaped structure, the second internal anti-resonant tube 3 is connected to the base 4 through the auxiliary base 12;

[0077] The cross-section of the auxiliary 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-resonant tube 3 and the end faces of the auxiliary substrate 12 are both planes, and the two ends of the second inner anti-resonant tube 3 are connected to the two ends of the auxiliary substrate 12.

[0078] This embodiment also provides a method for preparing low-loss hollow-core optical fiber, used to prepare the low-loss hollow-core optical fiber described above. The preparation method includes:

[0079] S1. Fabricate the capillary corresponding to the outer anti-resonant tube 1, the first inner anti-resonant tube 2, the second inner anti-resonant tube 3, the substrate 4, and the cladding supplement unit 5.

[0080] S2. The capillaries corresponding to the outer anti-resonator tube 1, the first inner anti-resonator tube 2, the second inner anti-resonator tube 3, and the substrate 4 are cut or not cut according to the structure of the target hollow fiber to form their respective prefabricated structures.

[0081] S3. The prefabricated structure of the outer anti-resonant tube 1, the first inner anti-resonant tube 2, the second inner anti-resonant tube 3, and the substrate 4 is combined to form an anti-resonant unit assembly.

[0082] S4. Multiple anti-resonance unit assemblies, capillaries corresponding to cladding supplementary unit 5, and filling structures are fixed together in the prefabricated sleeve to form a microstructure prefabricated rod.

[0083] S5. After the microstructure preform is drawn and cut, an intermediate transition body without filling structure is obtained. The intermediate transition body and the sleeve are then combined to form a hollow fiber preform. Finally, the hollow fiber preform is drawn into a low-loss hollow fiber.

[0084] This embodiment can achieve better high-order mode filtering characteristics by changing only the size of the first inner anti-resonant tube 2 while keeping the size of the outer anti-resonant tube 1 unchanged, thereby increasing the air area between the outer anti-resonant tube 1 and the first inner anti-resonant tube 2.

[0085] Furthermore, in step S2, the cutting method is horizontal cutting, and the resulting two cut surfaces overlap; the cutting process includes hot cutting and cold cutting, with hot cutting using laser cutting and cold cutting using blade cutting.

[0086] Further, step S3 includes:

[0087] S301. Place the base 4 on a limiting device 1a to make both ends of the base 4 horizontal, and mark the bottom of the base 4.

[0088] S302. Place the second internal anti-resonant tube 3 at the bottom of the base 4, and align the center of the second internal anti-resonant tube 3 perpendicularly with the center of the base 4.

[0089] S303. Place the two end faces of the outer anti-resonant tube 1 and the first inner anti-resonant tube 2 tightly against the two end faces of the substrate 4.

[0090] S304. The contact parts of the outer anti-resonant tube 1, the first inner anti-resonant tube 2, the second inner anti-resonant tube 3 and the substrate 4 are welded to obtain the anti-resonant unit assembly.

[0091] Further, in step S301, see... Figures 2-3 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. 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 as follows: place the base 4 on the base, release the slider buckle 2a, slide the first semicircular slider 3a to the leftmost end of the base, adjust the distance between the second semicircular slider 3b and the first semicircular slider 3a to match the base 4, and finally lock the slider buckle 2a.

[0092] Further, in step S301, the method for making the two ends of the substrate 4 horizontal includes: placing horizontal detection pieces on the two end faces of the substrate 4, and adjusting the position of the substrate 4 so that the horizontal detection pieces are displayed in the center state.

[0093] Furthermore, when the cross-section of the second internal anti-resonant tube 3 is circular, step S302 includes: adjusting the position of the second internal anti-resonant tube 3 so that the second internal anti-resonant tube 3 and the bottom mark of the substrate 4 are tangent; at this time, the distance between the two end faces of the second internal anti-resonant tube 3 and the substrate 4 is the same.

[0094] Further, step S304 includes: using an external heat source to weld the contact surfaces of the external anti-resonant tube 1, the first internal anti-resonant tube 2, and the substrate 4; when the cross-section of the second internal anti-resonant tube 3 is circular, using an external heat source to weld the contact points of the second internal anti-resonant tube 3 and the substrate 4; when the cross-section of the second internal anti-resonant tube 3 is arc-shaped, firstly 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-resonant tube 3 and the auxiliary substrate 12.

[0095] Further, step S4 includes:

[0096] S401. Place the anti-resonance unit assembly inside the prefabricated sleeve, and make the base 4 tangent to the inner wall of the prefabricated sleeve.

[0097] S402, see also Figure 4Circular 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 tube or filling rod 9 are tangent to the prefabricated structure corresponding to the outer anti-resonance tube 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 tube or filling rod 9 are set at both ends of the prefabricated sleeve;

[0098] S403. Place the capillary corresponding to the cladding supplement unit 5 between adjacent circular capillary filling tubes or filling rods 8.

[0099] S404. Repeat steps S401 to S403 to form a microstructure preform.

[0100] S405. Adjust 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.

[0101] Furthermore, in step S405, a laser level is used to correct the orientation of the anti-resonance unit assembly.

[0102] This invention is applicable to hollow optical fibers with an inner anti-resonance unit that is arc-shaped, and can significantly improve the structural stability of this type of hollow optical fiber.

[0103] This embodiment provides the following structural example of a low-loss hollow fiber.

[0104] Example 1:

[0105] See Figure 1 The low-loss hollow-core optical fiber has a core diameter of 28.5 μm. The diameters of the outer anti-resonator 1, the first inner anti-resonator 2, and the second inner anti-resonator 3 are 41.6 μm, 33.7 μm, and 14 μm, respectively, and the wall thickness of each is 1.1 μm. The opening angles of the outer anti-resonator 1 and the first inner anti-resonator 2 are 230° and 110°, respectively. The substrate 4 has a diameter of 36.1 μm, a wall thickness of 2.5 μm, and an opening angle of 115°. The cladding supplementary unit 5 has a diameter of 11.5 μm and is located at the midpoint of the arc-shaped inner wall of the outer cladding 6. Figure 5 As shown, the low-loss hollow fiber of this structure has low confinement loss in the C~L band.

[0106] Example 2:

[0107] See Figure 6In this example, the second inner anti-resonator 3 in the low-loss hollow fiber is a nested tube assembly 10, with nested tube diameters of 16 μm and 7.8 μm, respectively; the outer anti-resonator 1 and the first inner anti-resonator 2 have diameters of 38.7 μm and 30.8 μm, respectively; the cladding supplementary unit 5 has a diameter of 11 μm; and the offset angle 11 is 4°. The wall thicknesses of the different nested tubes of the outer anti-resonator 1, the first inner anti-resonator 2, and the second inner anti-resonator 3 are all between 1.15 and 1.25 μm. The confinement loss and higher-order mode suppression ratio of this low-loss hollow fiber as a function of the offset angle are shown in [reference needed]. Figure 7 .

[0108] Example 3:

[0109] See Figure 8 In this example of a low-loss hollow-core fiber, the cross-sections of the second inner anti-resonator 3 and the cladding supplement unit 5 are both arc-shaped, with diameters of 12.3 μm and 15.6 μm, respectively. An auxiliary substrate 12 is attached tightly to the inner bottom of the substrate 4. The auxiliary substrate 12 has an arc-shaped cross-section with a diameter of 14.1 μm, and its opening faces the center of the outer cladding 6. The opening of the second inner anti-resonator 3 faces the auxiliary substrate 12, and both ends of the second inner anti-resonator 3 are connected to the two ends of the auxiliary substrate 12. The opening of the cladding supplement unit 5 faces the inner wall of the outer cladding 6. The confinement loss curve for this low-loss hollow-core fiber structure is shown in [reference needed]. Figure 9 .

[0110] 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.

[0111] 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 low-loss hollow-core optical fiber, characterized in that, It includes an outer cladding layer, and several anti-resonant units and several cladding supplementary units connected to the inner wall of the outer cladding layer; the anti-resonant units are evenly and equidistantly distributed along the inner wall of the outer cladding layer, and the cladding supplementary units are between adjacent anti-resonant units, and each anti-resonant unit surrounds and forms the core region inside the outer cladding layer. The anti-resonance unit includes an outer anti-resonance transistor, a first inner anti-resonance transistor, a second inner anti-resonance transistor, and a substrate; The base has a circular arc cross-section, with the opening facing the center of the outer cladding and closely attached to the inner wall of the outer cladding, and both end faces are flat. Both the external anti-resonant tube and the first internal anti-resonant tube have circular arc cross-sections, with their openings facing the substrate. Both end faces are flat, and both ends are connected to the two ends of the substrate. The second internal anti-resonant tube is connected to the inner wall of the substrate, and the cross-section of the second internal anti-resonant 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, characterized in that, The centers of the outer anti-resonant tube, the first inner anti-resonant tube, and the second inner anti-resonant tube are collinear with the center of the outer cladding.

3. The low-loss hollow-core optical fiber according to claim 1, characterized in that, The number of anti-resonant units is 3 to 8.

4. The low-loss hollow-core optical fiber according to claim 1, characterized in that, The opening angle of the external anti-resonant tube is 180~270°, the opening angle of the first internal anti-resonant tube is 120~200°, and the opening angle of the substrate is 100~180°.

5. The low-loss hollow-core optical fiber according to claim 1, characterized in that, When the cross-section of the second internal resonant tube is circular, its opening angle is 210~300°.

6. The low-loss hollow-core optical fiber according to claim 1, characterized in that, The cladding supplement unit is located on the inner arc of the outer cladding defined by two adjacent bases, and its angle of deviation from the midpoint of the inner arc of the outer cladding is 0~10°.

7. The low-loss hollow-core optical fiber according to claim 1, characterized in that, The wall thickness difference between the external anti-resonant tube, the first internal anti-resonant tube, and the second internal anti-resonant tube does not exceed 0.1 μm, and the wall thickness of each is 0.4~2.0 μm, while the wall thickness of the substrate is 4~6 μm.

8. The low-loss hollow-core optical fiber according to claim 1, characterized in that, The outer diameter ratio of the first inner anti-resonant tube to the outer anti-resonant tube is 0.5~0.9, the outer diameter ratio of the second inner anti-resonant tube to the outer anti-resonant tube is 0.1~0.4, the outer diameter ratio of the cladding supplement unit to the outer anti-resonant tube is 0.1~0.4, and the diameter ratio of the fiber core region to the outer anti-resonant 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-resonator is higher than the two ends of the base.

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

11. A method for fabricating a low-loss hollow-core optical fiber, characterized in that, The method for preparing the low-loss hollow-core optical fiber according to claim 1 includes: S1. Prepare the outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, the substrate, and the capillary corresponding to the cladding supplementary unit; S2. The outer anti-resonator, the first inner anti-resonator, the second inner anti-resonator, and the capillary corresponding to the substrate are cut or not cut according to the structure of the target hollow fiber to form their respective prefabricated structures. S3. The outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, and the prefabricated structure of the substrate are combined to form an anti-resonant unit assembly. S4. Multiple anti-resonance unit assemblies, capillaries corresponding to cladding supplementary units, and filling structures are fixed together in a prefabricated sleeve to form a microstructure prefabricated rod. S5. After the microstructure preform is drawn and cut, an intermediate transition body without filling structure is obtained. The intermediate transition body and the sleeve are then combined to form a hollow fiber preform. Finally, the hollow fiber preform is drawn into a low-loss hollow fiber.

12. The method for preparing low-loss hollow-core optical fiber according to claim 11, characterized in that, In step S2, the cutting method is horizontal cutting, and the resulting two cut surfaces overlap; the cutting process includes hot cutting and cold cutting, with hot cutting using laser cutting and cold cutting using blade cutting.

13. The method for preparing low-loss hollow-core optical fiber according to claim 11, characterized in that, Step S3 includes: S301. Place the base on a limiting device to make both ends of the base horizontal and mark the bottom of the base. S302. Place the second internal anti-resonant tube at the bottom of the substrate, so that the center of the second internal anti-resonant tube is vertically aligned with the center of the substrate. S303. Place the two end faces of the external anti-resonant tube and the first internal anti-resonant tube tightly against the two end faces of the substrate. S304. Weld the contact points of the outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, and the substrate to obtain an anti-resonant unit assembly.

14. The method for preparing low-loss hollow-core optical fiber according to claim 13, characterized in that, 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; 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 base is formed between the first semicircular slider and the second semicircular slider.

15. The method for preparing low-loss hollow-core optical fiber according to claim 13, characterized in that, In step S301, the method for making the two ends of the substrate horizontal includes: placing horizontal detection pieces on the two end faces of the substrate, and adjusting the position of the substrate so that the horizontal detection pieces are displayed in the center.

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

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

18. The method for preparing low-loss hollow-core optical fiber according to claim 11, characterized in that, Step S4 includes: S401. Place the anti-resonance unit assembly inside the prefabricated sleeve, and make the base tangent to the inner wall of the prefabricated sleeve. S402. Circular capillary filling tubes or filling rods are placed on both sides of the anti-resonance unit assembly, and a central filling tube or filling rod is placed in the middle of the prefabricated sleeve; the circular capillary filling tubes or filling rods and the central filling tube or filling rods are both set at both ends of the prefabricated sleeve. S403. Place the capillary corresponding to the cladding supplement unit between adjacent circular capillary filling tubes or filling rods. S404. Repeat steps S401 to S403 to form a microstructure preform. S405. Adjust 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 low-loss hollow-core optical fiber according to claim 18, characterized in that, In step S405, a laser level is used to correct the orientation of the anti-resonance unit assembly.

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