Small-outer-diameter hollow-core optical fiber with mode field diameter matched with conventional single-mode optical fiber and application of small-outer-diameter hollow-core optical fiber

Abstract

The invention relates to a small-outer-diameter hollow-core optical fiber with a mode field diameter matched with a conventional single-mode optical fiber and application, the small-outer-diameter hollow-core optical fiber comprises an outer cladding and an inner cladding, the inner cladding comprises three groups of anti-resonance structure units, an auxiliary inner cladding is arranged along the circumferential direction of the inner wall of the outer cladding, each anti-resonance structure unit comprises four or more than four layers of anti-resonance tubes with different radiuses, and the anti-resonance tubes are arranged in the outer cladding. Comprising an outer anti-resonance tube and multiple layers of inner anti-resonance tubes, the outer anti-resonance tube and the inner anti-resonance tubes adjacent to the outer anti-resonance tube are arc-shaped, and the rest of the inner anti-resonance tubes comprise arc-shaped anti-resonance tubes and / or circular anti-resonance tubes with different radiuses. When the optical fiber is welded or connected with a conventional single-mode solid-core optical fiber, an intermediate transition optical fiber or a switching device can be omitted, and low-loss and high-quality interconnection is realized. And meanwhile, the small fiber core has the unique macro-bending and micro-bending insensitive characteristic, so that the optical fiber can be allowed to adopt a smaller glass outer diameter and a smaller coating outer diameter, and the fiber accommodating capacity in a single optical cable is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and specifically designs a small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber and its application. Background Art

[0002] Hollow-core antiresonant fiber uses an air core and a specially designed microstructured cladding, achieving low-loss, low-dispersion, single-mode transmission with ultra-low nonlinearity. By creating a three-layer antiresonant barrier within the cladding to suppress radial light leakage, the transmission loss of hollow-core antiresonant fiber in the visible to 2μm band has surpassed the Rayleigh scattering and material absorption limits of solid-core fiber, with an attenuation specification of <0.1dB / km at 1550nm. This breakthrough has made hollow-core antiresonant fiber a promising application in long-haul backbone communications and submarine cables.

[0003] The loss mechanism of hollow-core antiresonant fiber includes intrinsic confinement loss, scattering loss on the surface of the microstructured cladding medium, and absorption loss of the core gas and solid material at specific wavelengths. In addition, in practical applications, macrobending and microbending losses should usually be additionally considered. At a specified operating wavelength, confinement loss, surface scattering loss, and material absorption loss (if any) are inversely proportional to the core diameter, while macrobending and microbending losses are directly proportional to the core diameter. Among them, macrobending and microbending losses are also related to the diameter of the outer cladding and coating layer of the optical fiber. In the most commonly used C+L band, hollow-core antiresonant fiber with 5-unit three-layer antiresonant tubes often uses a core diameter of 30±2μm to minimize overall loss. The main problems include: 1. The mode field diameter is severely mismatched with that of conventional single-mode fiber, necessitating the addition of transition fibers or adapters, which increases the cost, complexity, construction difficulty, and maintenance difficulty of the entire link. 2. Reducing the outer diameter of the cladding and coating increases macrobending and microbending losses. 3. The large outer diameter (generally >200 μm) used to avoid macrobending and microbending interference reduces the fiber capacity within a single cable and the flexibility of the fiber itself. However, if the core diameter of the hollow-core antiresonant fiber is reduced to match its mode field diameter with that of conventional single-mode fiber, the limiting loss will increase dramatically and become the dominant loss mechanism.

[0004] Similar patents, such as CN202010425225, use innovative structures to use cut fan-shaped tubes as the tube wall near the fiber core in the microstructure cladding, and add a nested tube structure inside to reduce optical fiber transmission loss. CN202311478016 uses a cladding composed of one or more layers of arc-shaped microstructure units to confine the light beam to propagate within the fiber core. While ensuring low fiber loss, it effectively reduces the fiber size, making the hollow-core fiber structure highly compatible and suitable for a wider range of applications. The hollow-core fiber comprises an outer cladding and an inner cladding; the outer cladding is a hollow tubular structure, and the inner cladding is disposed within the outer cladding; the inner cladding comprises multiple rotationally symmetrical structures, each of which includes at least one sheet-like structure, and each sheet-like structure is connected to the outer cladding at opposite ends. This can suppress the loss increase on the long-wavelength side of the light-guiding passband due to mode interaction, effectively widening the low-loss passband of the optical fiber.

[0005] Although the above patents propose fan-shaped, arc-shaped or sheet-shaped structures and three-unit rotationally symmetrical designs, the following apply: 1. The mode field diameter for achieving low loss in optical fiber is approximately 20 μm (core diameter is approximately 30 μm); 2. The distance between the core boundary and the outer cladding is difficult to increase further; 3. Considering the single-mode purity and fabrication feasibility, the number of radial antiresonance layers is difficult to increase further; 4. Reducing the outer diameter of the glass and the outer diameter of the coating will increase the macrobend and microbend losses of the optical fiber. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and propose a small outer diameter hollow core optical fiber and its application that can achieve low loss and high quality interconnection and match the mode field diameter of conventional single-mode optical fiber.

[0007] The technical solution adopted in the present invention is: A small outer diameter hollow-core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber comprises an outer cladding and an inner cladding. The inner cladding is composed of antiresonance structural units, which are arranged circumferentially along the inner wall of the outer cladding and in contact with the inner wall of the outer cladding. The central cavity enclosed by the inner cladding forms a fiber core. The invention is characterized in that: the inner cladding comprises three groups of antiresonance structural units, which are evenly spaced along the circumference. An auxiliary inner cladding is provided circumferentially along the inner wall of the outer cladding. The auxiliary inner cladding comprises three auxiliary units, which are arranged circumferentially with the antiresonance structural units at staggered intervals and in contact with the inner wall of the outer cladding. The antiresonance structural units comprise four or more layers of antiresonance tubes of different radii, including an outer antiresonance tube and multiple layers of inner antiresonance tubes. The outer antiresonance tube and the inner antiresonance tube adjacent to the outer antiresonance tube are arc-shaped, and the remaining inner antiresonance tubes comprise arc-shaped antiresonance tubes and / or circular antiresonance tubes of different radii.

[0008] According to the above technical solution, when the remaining inner anti-resonance tubes are circular tubes with different radii, each circular anti-resonance tube forms a double-layer or multi-layer nested structure and is tangent to each other at one point and to the inner wall of the outer cladding.

[0009] According to the above technical solution, a nesting auxiliary unit is provided inside the inner anti-resonance tube adjacent to the outer anti-resonance tube and on both sides of the double-layer or multi-layer nested structure.

[0010] According to the above technical solution, the nested auxiliary unit has a one-layer structure.

[0011] According to the above technical solution, the auxiliary unit and the nested auxiliary unit are anti-resonance tubes with arc-shaped structures or circular tube structures.

[0012] According to the above technical solution, the distance between the auxiliary unit and the outer anti-resonance tube of the adjacent anti-resonance structure unit and the distance between the outer anti-resonance tubes of each group of adjacent anti-resonance structure units are set at 4±1 μm.

[0013] According to the above technical solution, at least one radial distance between adjacent antiresonance tubes of the antiresonance structure unit is 0.5-0.62 times the core diameter, and the radial distance between each adjacent antiresonance tube is no more than 0.62 times the core diameter.

[0014] According to the above technical solution, the radial distance between the outer anti-resonance tube and the inner anti-resonance tube adjacent to the outer anti-resonance tube is no more than 0.5 times the core diameter.

[0015] According to the above technical solution, the diameter of the fiber core is in the range of 15±1 μm, and the corresponding mode field diameter is 10.5±0.7 μm.

[0016] According to the above technical solution, the distance between the core boundary and the outer cladding is 30-35 μm.

[0017] According to the above technical solution, the outer diameter of the outer cladding is 115-180 μm.

[0018] According to the above technical solution, the coating outer diameter of the optical fiber is controlled to be 230-300 μm.

[0019] According to the above technical solution, the arc-shaped anti-resonance tube is obtained by cutting the raw material tube. The cutting angle of the outer anti-resonance tube is 210±10 degrees, and the cutting angle of the remaining inner multi-layer anti-resonance tubes is preferably 190±10 degrees.

[0020] According to the above technical solution, the substrate material of the outer cladding, antiresonance structure unit, auxiliary unit and nested auxiliary unit is any one of pure quartz glass, doped quartz glass, chalcogenide glass, fluoride glass or plastic.

[0021] According to the above technical solution, the core region and other hollow regions within the outer cladding are filled with gas.

[0022] According to the above technical solution, the gas is argon, nitrogen, helium, air or a mixture of multiple gases.

[0023] According to the above technical solution, the wall thickness of each antiresonance tube in the antiresonance structure unit, the auxiliary unit and the nested auxiliary unit is the same, and by changing the wall thickness, the optical fiber can transmit light signals of different bands with low loss.

[0024] According to the above technical solution, the wall thickness of each anti-resonance tube in the anti-resonance structure unit, the auxiliary unit and the nested auxiliary unit is controlled within a tolerance of ±5%.

[0025] According to the above technical solution, when directly interconnected with a conventional single-mode optical fiber, the coupling point loss is ≤0.4dB.

[0026] An application of the above-mentioned small outer diameter hollow-core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber is characterized in that the hollow-core optical fiber is used in the fields of communications, lasers, or sensing.

[0027] The beneficial effects of the present invention are: 1. The present invention increases the number of antiresonance layers and the core-outer cladding distance by providing three groups of antiresonance structural units that are non-contacting and have an arc-shaped outer layer. In combination with auxiliary units, the excess cavity area is filled while the distance between the arc-shaped antiresonance tubes of the outer layers of each group of antiresonance structural units is increased, thereby improving kilometer-level drawing stability. The above design can achieve ultra-low loss and high single-mode purity signal transmission while reducing the core diameter, and the optical fiber has excellent bending resistance. The mode field diameter of the low hollow core antiresonance optical fiber of the present invention is large enough to match conventional G652 optical fiber, reducing the direct interconnection loss between the hollow core antiresonance optical fiber and conventional single-mode optical fiber, thereby saving transition optical fiber or adapter components.

[0028] 2. When fusion splicing or connecting with conventional single-mode solid-core optical fibers, this invention can eliminate intermediate transition fibers or adapters, achieving low-loss, high-quality interconnections. Furthermore, the small core's unique macrobend and microbend insensitivity allows for smaller glass and coating outer diameters, thereby increasing the fiber capacity within a single optical cable.

[0029] 3. The present invention reduces the loss of hollow-core antiresonant optical fiber with a core diameter of 15μm to below 0.15dB / km at 1550nm by increasing the radial distance between the core boundary and the outer cladding, the number of antiresonant layers of the antiresonant structural unit, and combining auxiliary units to fill the excess cavity area, and allows the use of smaller glass and coating outer diameters.

[0030] 4. By setting the distance between the outer arc-shaped antiresonance tubes of each group of antiresonance structural units at 4±1 μm and combining this with the design of auxiliary units, the present invention can suppress the leakage of fundamental mode energy along the gaps. Furthermore, kilometer-scale continuous wire drawing is stable, easy to control, and less likely to form nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a schematic diagram of the structure of a small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber provided in Example 1 of the present invention.

[0033] Figure 2 It is a partially enlarged schematic diagram of the anti-resonance structure unit provided in Example 1 of the present invention.

[0034] Figure 3 This is a schematic diagram of the structure of a small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber provided in Example 2 of the present invention.

[0035] Figure 4 This is a comparison diagram of the limiting losses of Example 1, Example 2, a five-unit three-layer anti-resonance tube, and a four-unit three-layer anti-resonance tube with a gap tube of the present invention.

[0036] Figure 5 This is the loss curve of Example 1 of the present invention when the bending diameter is 6 cm.

[0037] Figure 6 This is a schematic diagram of the structure of a small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber, provided in Example 3 of the present invention.

[0038] Figure 7 This is a schematic diagram of the structure of a small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber provided in Example 4 of the present invention.

[0039] Figure 8 This is a schematic diagram of the structure of a small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber, provided in Example 5 of the present invention.

[0040] Note: The structural change principles of Examples 3-5 based on Example 1 are also applicable to Example 2.

[0041] In the figure: 1-outer cladding, 2-fiber core (the dotted line is only for schematic purpose and does not exist in the actual structure), 3-auxiliary unit, 4-outer antiresonance tube, 5-first inner antiresonance tube, 6-second inner antiresonance tube, 7-third inner antiresonance tube, 8-fourth inner antiresonance tube, g01-minimum spacing between the outer antiresonance tubes of each group of antiresonance structural units, g02-spacing between the outer antiresonance tube and the first inner antiresonance tube, g03-spacing between the first inner antiresonance tube and the second inner antiresonance tube, g04-spacing between the second inner antiresonance tube and the third inner antiresonance tube, g05-spacing between the third inner antiresonance tube and the fourth inner antiresonance tube, g06-inner diameter of the fourth inner antiresonance tube, g07-minimum spacing between the auxiliary unit and the outer antiresonance tube, g08-inner diameter of the auxiliary unit, 9-arc-shaped fourth inner antiresonance tube, 10-arc-shaped auxiliary unit, 11-double-layer nested structure, 12-triple-layer nested structure, 13-nested auxiliary unit. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0043] Example 1: like Figure 1 、 2As shown, this embodiment provides a small outer diameter hollow-core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber, comprising an outer cladding 1 and an inner cladding, wherein the inner cladding is composed of antiresonance structural units, which are arranged circumferentially along the inner wall of the outer cladding and connected to the inner wall of the outer cladding 1. The central cavity covered by the inner cladding forms a core 2, and the inner cladding includes three antiresonance structural units, which are evenly spaced along the circumference. The antiresonance structural units include four or more layers of multilayer antiresonance tubes with different radii, including an outer antiresonance tube and an inner multilayer antiresonance tube. The outer antiresonance tube and the inner antiresonance tube adjacent to the outer antiresonance tube are arc-shaped, and the remaining inner multilayer antiresonance tubes include arc-shaped antiresonance tubes and / or circular tube antiresonance tubes with different radii. That is, the remaining inner multilayer antiresonance tubes can all be arc-shaped antiresonance tubes, or all be circular tube antiresonance tubes, or a combination of arc-shaped antiresonance tubes and circular tube antiresonance tubes. This embodiment uses an antiresonance structure unit comprising five layers of multilayer antiresonance tubes of different radii as an example, including an outer circular arc-shaped antiresonance tube 4, a first inner antiresonance tube 5, a second inner antiresonance tube 6, a third inner antiresonance tube 7, and a fourth inner antiresonance tube 8. The two endpoints of the circular arc-shaped antiresonance tube are connected to the inner wall of the outer cladding 1, while the circular antiresonance tube is tangent to the inner wall of the outer cladding 1. The core region and other cavity regions within the outer cladding are filled with air.

[0044] In Example 1 of the present invention, the optical signal is transmitted in the fiber core 2, and the dotted line approximately represents the fiber core boundary, which has a diameter of 15 μm. In order to increase the radial distance from the fiber core boundary to the outer cladding 1, that is, to increase the path length of the signal leakage in the radial direction, and at the same time ensure that the layers in each inner cladding (anti-resonance microstructure) do not adhere to each other to form harmful nodes, three groups of rotationally symmetrically arranged anti-resonance structural units are used. At this time, the radial distance from the fiber core boundary to the outer cladding 1 can be increased to 30-35 μm, preferably 35 μm. The outer diameter of the outer cladding is controlled to be 115-180 μm, preferably 125 μm. The outer diameter of the coating of the optical fiber is controlled to be 230-300 μm, preferably 245 μm. The outer anti-resonance tube 4 of the three groups of anti-resonance structural units adopts an arc-shaped structure to fill the excess cavity area generated between the groups to avoid leakage of the core fundamental mode energy. The minimum spacing g01 between the anti-resonance tubes 4 outside the group is preferably controlled at 4.5±0.5μm, which is a distance that can suppress the leakage of fundamental mode energy along the gap and is stable, easy to control, and not easy to stick to nodes during kilometer-level continuous drawing. At this time, in order to further fill the excess cavity formed between the groups, an auxiliary unit 3 is provided along the circumference of the inner wall of the outer cladding. The auxiliary unit 3 includes three auxiliary anti-resonance tubes with circular tube structures. The auxiliary unit 3 is arranged at intervals with the anti-resonance structure unit along the circumference of the inner wall of the outer cladding and is connected to the inner wall of the outer cladding. The auxiliary unit is an anti-resonance tube with a single-layer structure, which can ensure that a circular cavity with a diameter greater than 0.62 times the core diameter cannot be generated in this area, thereby avoiding leakage of the core fundamental mode energy.

[0045] like Figure 2 As shown, in order to achieve preparation feasibility, the spacing g01 corresponding to the optical fiber profile given in Example 1 is 4.68μm, g07 is 4.25μm, and the corresponding g08 is 4.7μm. Among them, g07 is preferably 4.5±0.5μm, and g08 is adjusted according to the distance between g01 and g07 and the wall thickness of the auxiliary unit 3. Because the radial distance from the core boundary to the outer cladding 1 is increased, more than three layers of anti-resonance tubes can be added to the channel where the core light signal energy leaks radially to form an anti-resonance barrier. In Example 1, 5 layers of anti-resonance tubes are set, and the anti-resonance tubes do not contact each other and are connected to the inner wall of the outer cladding. Each layer of anti-resonance tubes produces two anti-resonance reflections (the air layer between the solid layers also plays an anti-resonance reflection effect). At this time, the radial leakage of the core energy will pass through 10 anti-resonance barriers. Similarly, in order to fill the excess cavities formed between the solid material structures in the inner cladding, the first inner anti-resonance tube 5, the second inner anti-resonance tube 6, and the third inner anti-resonance tube 7 adopt an arc-shaped structure, and the fourth inner anti-resonance tube 8 can adopt a circular tube structure. In order to ensure effective high-order mode filtering, at least one of the spacings g02, g03, g04, g05, and g06 formed by adjacent anti-resonance tubes (4, 5, 6, 7, 8) in the same group should be 0.5-0.62 times the spacing between the fiber cores, and is preferably set at g03. Figure 2 As shown, in Example 1, g02, g03, g04, g05, and g06 are set to 5, 8.05, 5, 5.35, and 4.7 μm, respectively. In the optical fiber preform corresponding to Example 1, the arc-shaped anti-resonance tubes 4-7 in this embodiment are obtained by cutting the circular mother tube, and the cutting angles are 209°, 195°, 192°, and 191°, respectively. It should be noted that the cutting angle of the outer arc-shaped anti-resonance tube 4 can be further increased, but g01 will be shortened. If g01 is less than 3 μm, the preparation risk will increase. It can also be further reduced, but g01 will be widened. If g01 is greater than 5 μm, the risk of energy leakage in the fiber core fundamental mode will increase. The cutting angles of the first inner anti-resonance tube 5, the second inner anti-resonance tube 6, and the third inner anti-resonance tube 7 can be increased or decreased based on Example 1. Similarly, the preparation feasibility and the risk of energy leakage in the fiber core fundamental mode should be considered comprehensively. In Example 1, the wall thickness of all anti-resonance tubes is set to 1.15 μm, and the material is pure quartz glass. As shown Figure 4 As shown in the simulation calculation results (the core diameter of all optical fiber structures is 15μm), the limiting loss of Example 1 at 1550nm is as low as below 0.01dB / km, which is much lower than that of the five-unit three-layer and four-unit three-layer structures. In addition, in order to increase the distance from the core boundary to the outer cladding, that is, to increase the diameter of the outer nested tube, the minimum gaps between the five-unit and four-unit groups and the outer nested tubes are 2.63 and 3.5μm respectively, which are extremely unstable in actual preparation. In addition, in order to increase the air area available for division in the microstructure cladding, the wall thickness of the anti-resonance tube (anti-resonance layer) of the five-unit three-layer and four-unit three-layer structures corresponds to the first-order light guide passband (the wall thickness is thinner, about 370-515nm), and the structural duty cycle is extremely high, which is extremely unstable in actual preparation. As Figure 5 The simulation results show that the loss of Example 1 at 1550nm is less than 0.02dB / km when the bending diameter is 6cm. 6 In Example 1, because the ratio of the 15μm core diameter to the 1550nm operating wavelength is less than 10, the fiber is extremely insensitive to microbends, and the outer diameter of the outer cladding can be reduced to 125±1μm, matching that of conventional single-mode fiber. Furthermore, the coated outer diameter of the fiber can be reduced to 240±5μm, matching that of conventional single-mode fiber, increasing the fiber capacity within a single optical cable.

[0046] This embodiment also provides an application of a small outer diameter hollow core optical fiber whose mode field diameter matches that of a conventional single-mode optical fiber, which is applied in communications, lasers, and sensors.

[0047] Example 2: Compared with Example 1, Example 2 of the present invention reduces one layer of arc-shaped anti-resonance tubes in the radial direction, and the spacing between adjacent anti-resonance tubes is also slightly adjusted. Figure 4As shown, the loss of Example 2 at 1550nm is less than 0.3dB / km. Because two layers can exist with a radial spacing of 0.5-0.62 times the core diameter, the structure shown in Example 2 cannot observe the existence of core higher-order modes in simulation calculations, and the single-mode performance is better than that of Example 1. Therefore, it is particularly suitable for short-distance data center interconnect applications that require high single-mode performance.

[0048] Example 3: like Figure 6 As shown, the structure of Example 3 is basically the same as that of Example 1, except that: in this embodiment, the auxiliary unit 3 and the fourth inner anti-resonance tube 8 of the circular tube structure are respectively changed into an arc-shaped auxiliary unit 10 and an arc-shaped fourth inner anti-resonance tube 9.

[0049] Example 4: like Figure 7 As shown, the structure of Example 4 is basically the same as that of Example 1, except that the third inner anti-resonance tube 7 is set as a circular tube anti-resonance tube, and is combined with the fourth inner anti-resonance tube 8 to form a double-layer nested structure 11, and the two circular anti-resonance tubes are tangent at one point and tangent to the inner wall of the outer cladding.

[0050] Example 5: like Figure 8 As shown, the structure of Example 5 is basically the same as that of Example 1, except that the second and third anti-resonance tubes in the inner layer are set as circular tube anti-resonance tubes, and the second, third, and fourth nested anti-resonance tubes 6, 7, and 8 in the inner layer are merged into a three-layer nested structure 12. The three circular tube anti-resonance tubes are tangent to each other at one point and are tangent to the inner wall of the outer cladding. At the same time, inside the first inner anti-resonance tube 5, on both sides of the three-layer nested structure 12, and on the inner wall of the outer cladding 1, two additional nested auxiliary units 13 are arranged to fill the excess cavity formed between the three-layer nested structure 12 and the first inner anti-resonance tube 5 to prevent the core fundamental mode energy from leaking. In Example 5, the nested auxiliary unit 13 is a nested auxiliary anti-resonance tube with a circular structure, but it can also be a nested auxiliary anti-resonance tube with an arc-shaped structure.

[0051] It should be noted that the structural change principles of Examples 3-5 based on Example 1 are also applicable to Example 2.

[0052] It should be noted that based on design principles, theoretical expectations and Figure 4 、 5 The simulation results show that Examples 3-5 have optical properties similar to that of Example 1. The structural and theoretical descriptions in Example 1 are also applicable to Examples 2-5.

[0053] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A small outer diameter hollow-core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber, comprising an outer cladding and an inner cladding, wherein the inner cladding is composed of antiresonant structural units arranged circumferentially along and in contact with the inner wall of the outer cladding, and wherein a central cavity enclosed by the inner cladding forms a fiber core, characterized in that: The inner cladding includes three groups of antiresonance structural units, which are evenly spaced along the circumferential direction. An auxiliary inner cladding is provided circumferentially along the inner wall of the outer cladding, and the auxiliary inner cladding includes three auxiliary units. The auxiliary units are arranged circumferentially with the antiresonance structural units in an alternating manner and in contact with the inner wall of the outer cladding. The antiresonance structural units include four or more layers of antiresonance tubes of different radii, including outer antiresonance tubes and multiple layers of inner antiresonance tubes. The outer antiresonance tubes and inner antiresonance tubes adjacent to the outer antiresonance tubes are arc-shaped, and the remaining inner antiresonance tubes include arc-shaped antiresonance tubes and / or circular antiresonance tubes of different radii.

2. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1, characterized in that: When the remaining inner anti-resonance tubes are all circular tubes with different radii, each circular anti-resonance tube forms a double-layer or multi-layer nested structure and is tangent to each other at one point and is tangent to the inner wall of the outer cladding.

3. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 2, characterized in that: A nesting auxiliary unit is provided inside the inner anti-resonance tube adjacent to the outer anti-resonance tube and on both sides of the double-layer or multi-layer nested structure.

4. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 3, characterized in that: The nested auxiliary unit has a one-layer structure.

5. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 3, characterized in that: The auxiliary unit and the nested auxiliary unit are anti-resonance tubes with an arc structure or a circular tube structure.

6. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The distance between the external anti-resonance tubes of the auxiliary unit and the adjacent anti-resonance structure unit and the distance between the external anti-resonance tubes of each group of adjacent anti-resonance structure units are set at 4±1 μm.

7. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: At least one radial distance between adjacent anti-resonance tubes of the anti-resonance structure unit is 0.5-0.62 times the core diameter, and the radial distance between each adjacent anti-resonance tube is no greater than 0.62 times the core diameter.

8. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The radial distance between the outer anti-resonance tube and the inner anti-resonance tube adjacent to the outer anti-resonance tube is no more than 0.5 times the core diameter.

9. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The diameter of the fiber core is in the range of 15±1 μm, and the corresponding mode field diameter is 10.5±0.7 μm.

10. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The distance between the core boundary and the outer cladding is 30-35 μm.

11. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The outer diameter of the outer cladding is 115-180 μm.

12. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The outer diameter of the optical fiber coating is controlled to be 230-300 μm.

13. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The arc-shaped anti-resonance tube is obtained by cutting the raw material tube. The cutting angle of the outer anti-resonance tube is 210±10 degrees, and the cutting angle of the remaining inner multi-layer anti-resonance tubes is preferably 190±10 degrees.

14. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 3, characterized in that: The substrate material of the outer cladding, the anti-resonance structure unit, the auxiliary unit and the nested auxiliary unit is any one of pure quartz glass, doped quartz glass, chalcogenide glass, fluoride glass or plastic.

15. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: The core region and other hollow regions within the outer cladding are filled with gas.

16. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 15, characterized in that: The gas is argon, nitrogen, helium, air or a mixture of multiple gases.

17. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 3, characterized in that: The wall thickness of each anti-resonance tube in the anti-resonance structure unit, the auxiliary unit and the nested auxiliary unit is the same, and by changing the wall thickness, the optical fiber can transmit light signals of different bands with low loss.

18. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 3, characterized in that: The wall thickness of each anti-resonance tube in the anti-resonance structure unit, the auxiliary unit and the nested auxiliary unit is controlled within a tolerance of ±5%.

19. The small outer diameter hollow core optical fiber with a mode field diameter matching that of a conventional single-mode optical fiber according to claim 1 or 2, characterized in that: When directly interconnected with conventional single-mode optical fiber, it has a coupling point loss of ≤0.4dB.

20. An application of a small outer diameter hollow core optical fiber having a mode field diameter matching that of a conventional single-mode optical fiber according to any one of claims 1 to 19, characterized in that: The hollow-core optical fiber is used in the fields of communication, laser or sensing.

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