Small outer diameter hollow core fiber matching mode field diameter of conventional single mode fiber and application thereof

Abstract

The application relates to a small-outer-diameter hollow core fiber matched with a mode field diameter of a conventional single-mode optical fiber and application, which 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 on the inner wall of the outer cladding in a circumferential direction, the anti-resonance structure unit comprises four layers or more than four layers of anti-resonance tubes with different radii, the anti-resonance tube comprises an outer anti-resonance tube and a multi-layer inner anti-resonance tube, the outer anti-resonance tube and the inner anti-resonance tube adjacent to the outer anti-resonance tube are circular arc-shaped, and the rest of the inner anti-resonance tubes comprise circular arc-shaped anti-resonance tubes with different radii and / or circular anti-resonance tubes. When the application is fused or connected with a conventional single-mode solid core fiber, an intermediate transition optical fiber or an adapter device can be omitted, low-loss and high-quality interconnection is realized. Meanwhile, the unique macro-bend and micro-bend insensitivity of the small fiber core can allow the optical fiber to adopt a smaller glass outer diameter and coating outer diameter, so that the fiber capacity in a single optical cable is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber communication, and specifically designs a small outer diameter hollow core optical fiber matching a mode field diameter of a conventional single-mode optical fiber and an application thereof. BACKGROUND

[0002] The hollow core anti-resonant optical fiber takes air as the core and combines a specially designed microstructure cladding to realize low loss, low dispersion, single-mode transmission and super-low nonlinear effect. By establishing three layers of anti-resonant barriers in the cladding to inhibit the radial leakage of light waves, the transmission loss of the hollow core anti-resonant optical fiber in the visible light to 2 μm band has exceeded the Rayleigh scattering and material absorption limit of solid core optical fibers, and the 1550 nm attenuation index has been realized to be <0.1 dB / km. This breakthrough makes the hollow core anti-resonant optical fiber have visible application value in long-distance backbone network communication and submarine optical cables.

[0003] The loss mechanism of the hollow core anti-resonant optical fiber includes intrinsic confinement loss, scattering loss of the microstructure cladding medium surface, and absorption loss of the core gas and solid material at a specific wavelength. In addition, in actual application, macro-bending and micro-bending loss should be additionally considered. In the case of a specified working wavelength, the confinement loss, surface scattering loss and material absorption loss (if present) are inversely proportional to the core diameter, while the macro-bending and micro-bending loss is proportional to the core diameter. The macro-bending and micro-bending loss is also related to the diameter of the outer cladding and the coating layer of the optical fiber. In the most commonly used C+L band, the hollow core anti-resonant optical fiber with a 5-unit three-layer anti-resonant tube usually adopts a core diameter of 30±2 μm to minimize the total loss. The existing problems mainly include: 1. The mode field diameter is seriously mismatched with the conventional single-mode optical fiber, and it is necessary to increase the transition optical fiber or adapter, which increases the cost, complexity, construction difficulty and maintenance difficulty of the entire link; 2. The reduction of the cladding outer diameter and the coating outer diameter will increase the macro-bending and micro-bending loss; 3. The large size of the outer diameter (generally >200 μm) used to avoid macro-bending and micro-bending interference will reduce the fiber capacity in a single optical cable and the flexibility of the optical fiber itself. However, if the core diameter of the hollow core anti-resonant optical fiber is reduced to match the mode field diameter of the conventional single-mode optical fiber, the confinement loss will increase sharply and become the dominant loss mechanism.

[0004] Similar patents such as CN202010425225 use innovative structures to reduce fiber transmission loss by cutting fan-shaped tubes as the tube wall near the core in the microstructure cladding and adding a nested tube structure inside. CN202311478016 uses a microstructure unit with one or more layers of circular arcs to construct the cladding to confine the light beam in the core. Under the premise of ensuring low loss of the optical fiber, the size of the optical fiber is effectively reduced, making the hollow core fiber structure have good compatibility and being suitable for more widely applicable scenarios. The hollow core fiber includes an outer cladding and an inner cladding. The outer cladding is a hollow tubular structure, and the inner cladding is arranged inside the outer cladding. The inner cladding includes a plurality of rotationally symmetric structures, each rotationally symmetric structure includes at least one sheet structure, and each sheet structure is connected to the outer cladding at opposite ends. The loss uplift caused by mode interaction on the long-wavelength side of the light guide passband can be suppressed, and the low-loss passband of the optical fiber can be effectively widened.

[0005] Although the above patents propose fan-shaped, circular-arc-shaped or sheet-shaped structures and three-unit rotationally symmetric designs, the following problems exist: 1. The mode field diameter of the optical fiber to achieve low loss is about 20 μm (core diameter of about 30 μm); 2. The distance between the core boundary and the outer cladding is difficult to continue to increase; 3. Considering the single-mode purity and the feasibility of preparation, the number of radial anti-resonance layers is difficult to continue to increase; 4. Reducing the glass outer diameter and the coated outer diameter will increase the macro-bending and micro-bending loss of the optical fiber. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a small outer diameter hollow core fiber matching the mode field diameter of a conventional single-mode optical fiber for low loss and high quality interconnection.

[0007] The technical solution adopted by the present application is as follows:

[0008] A small outer diameter hollow core fiber matching the mode field diameter of a conventional single-mode optical fiber, comprising an outer cladding and an inner cladding, the inner cladding is composed of anti-resonance structure units, the anti-resonance structure units are arranged along the circumference of the inner wall of the outer cladding and connected to the inner wall of the outer cladding, and the central cavity covered by the inner cladding forms a core, characterized in that: the inner cladding includes three groups of anti-resonance structure units, the three groups of anti-resonance structure units are uniformly distributed along the circumference, an auxiliary inner cladding is arranged along the circumference of the inner wall of the outer cladding, the auxiliary inner cladding includes three auxiliary units, the auxiliary units are arranged along the circumference of the inner wall of the outer cladding and staggered with the anti-resonance structure units, and connected to the inner wall of the outer cladding, the anti-resonance structure units include four or more layers of anti-resonance tubes with different radii, including an outer anti-resonance tube and multiple inner anti-resonance tubes, the outer anti-resonance tube and the inner anti-resonance tube adjacent to the outer anti-resonance tube are circular arc-shaped, and the remaining inner anti-resonance tubes include circular arc-shaped anti-resonance tubes with different radii and / or circular anti-resonance tubes.

[0009] According to the technical scheme, when the rest of the inner anti-resonance tubes are all circular tubes with different radii, the circular anti-resonance tubes form a double-layer or multi-layer nested structure and are tangent to a point and tangent to the inner wall of the outer cladding.

[0010] According to the technical scheme, an inner anti-resonance tube adjacent to the outer anti-resonance tube is provided with a nested auxiliary unit on both sides of the double-layer or multi-layer nested structure.

[0011] According to the technical scheme, the nested auxiliary unit has a one-layer structure.

[0012] According to the technical scheme, the auxiliary unit and the nested auxiliary unit are anti-resonance tubes with a circular arc structure or a circular tube structure.

[0013] According to the technical scheme, 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 4±1 μm.

[0014] According to the technical scheme, the radial distance between the adjacent anti-resonance tubes of the anti-resonance structure unit is at least 0.5-0.62 times the diameter of the core, and the radial distance between each adjacent anti-resonance tube is not greater than 0.62 times the diameter of the core.

[0015] According to the technical scheme, the radial distance between the outer anti-resonance tube and the inner anti-resonance tube adjacent to the outer anti-resonance tube is not greater than 0.5 times the diameter of the core.

[0016] According to the technical scheme, the diameter of the core is in the range of 15±1 μm, and the corresponding mode field diameter is 10.5±0.7 μm.

[0017] According to the technical scheme, the distance between the core boundary and the outer cladding is 30-35 μm.

[0018] According to the technical scheme, the outer diameter of the outer cladding is 115-180 μm.

[0019] According to the technical scheme, the coated outer diameter of the optical fiber is controlled to be 230-300 μm.

[0020] According to the technical scheme, the circular arc 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 rest of the inner multi-layer anti-resonance tubes is preferably 190±10 degrees.

[0021] According to the technical scheme, the base 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.

[0022] According to the technical scheme, the core region and the cavity region in the other cladding are filled with gas.

[0023] According to the technical scheme, the gas is argon, nitrogen, helium, air or a mixture of multiple gases.

[0024] According to the technical scheme, 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 the wall thickness can be changed to enable the optical fiber to transmit optical signals of different wave bands with low loss.

[0025] According to the technical scheme, 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%.

[0026] According to the technical scheme, the coupling point loss is ≤0.4 dB when directly interconnected with a conventional single-mode optical fiber.

[0027] An application of the small-outer-diameter hollow-core optical fiber with a mode field diameter matching a conventional single-mode optical fiber as described above, characterized in that the hollow-core optical fiber is applied to the fields of communication, laser or sensing.

[0028] The present application has the following advantages:

[0029] 1. The present application increases the number of anti-resonance layers and the core-cladding distance by arranging three groups of anti-resonance structure units that do not contact each other and have a circular arc structure on the outer layer, and combines the auxiliary unit to ensure that the excess cavity area is filled and the distance between the outer circular arc anti-resonance tubes of each group of anti-resonance structure units is increased to improve the kilometer-level drawing stability. The above design can ensure high single-mode purity signal transmission with ultra-low loss while reducing the core diameter, and the optical fiber has excellent bending resistance. The mode field diameter of the low-hollow-core anti-resonance optical fiber of the present application can match the conventional G652 optical fiber, reducing the direct interconnection loss of the hollow-core anti-resonance optical fiber and the conventional single-mode optical fiber, thereby saving transition optical fibers or adapter devices.

[0030] 2. When the present application is fused or connected with a conventional single-mode solid-core optical fiber, the intermediate transition optical fiber or adapter device can be omitted, realizing low-loss and high-quality interconnection. At the same time, the unique macro-bend and micro-bend insensitivity of the small core can allow the optical fiber to have a smaller glass outer diameter and coating outer diameter, thereby increasing the fiber capacity in a single optical cable.

[0031] 3. The present application reduces the loss of a hollow-core anti-resonance optical fiber with a core diameter of 15 μm to below 0.15 dB / km at 1550 nm by increasing the radial distance of the core boundary-cladding, the number of anti-resonance layers of the anti-resonance structure unit, and combining the auxiliary unit to fill the excess cavity area, and allows a smaller glass and coating outer diameter.

[0032] 4、The present application can inhibit the fundamental mode energy from leaking along the gap by setting the distance between the outer arc-shaped anti-resonance tubes of each group of anti-resonance structure units as 4±1 μm, in combination with the auxiliary unit design. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0034] Figure 1 is a small outer diameter hollow core fiber structure schematic diagram provided by the embodiment 1 of the present application for matching the mode field diameter of the conventional single mode fiber.

[0035] Figure 2 is a local enlarged schematic diagram of the anti-resonance structure unit provided by the embodiment 1 of the present application.

[0036] Figure 3 is a small outer diameter hollow core fiber structure schematic diagram provided by the embodiment 2 of the present application for matching the mode field diameter of the conventional single mode fiber.

[0037] Figure 4 is a comparison diagram of the confinement loss of the five-unit three-layer anti-resonance tube, the four-unit three-layer anti-resonance tube and the gap tube provided by the embodiment 1 and the embodiment 2 of the present application.

[0038] Figure 5 is a loss curve of the embodiment 1 of the present application when the bending diameter is 6 cm.

[0039] Figure 6 is a small outer diameter hollow core fiber structure schematic diagram provided by the embodiment 3 of the present application for matching the mode field diameter of the conventional single mode fiber.

[0040] Figure 7 is a small outer diameter hollow core fiber structure schematic diagram provided by the embodiment 4 of the present application for matching the mode field diameter of the conventional single mode fiber.

[0041] Figure 8 is a small outer diameter hollow core fiber structure schematic diagram provided by the embodiment 5 of the present application for matching the mode field diameter of the conventional single mode fiber.

[0042] Note: the structure variation principles of the embodiments 3-5 based on the embodiment 1 are also applicable to the embodiment 2.

[0043] In the figure: 1 - outer cladding, 2 - core (the dotted line only serves to illustrate, and does not exist in the actual structure), 3 - auxiliary unit, 4 - outer anti-resonance tube, 5 - first inner anti-resonance tube, 6 - second inner anti-resonance tube, 7 - third inner anti-resonance tube, 8 - fourth inner anti-resonance tube, g01 - the minimum spacing between the outer anti-resonance tubes of each group of anti-resonance structure units, g02 - the spacing between the outer anti-resonance tube and the first inner anti-resonance tube, g03 - the spacing between the first inner anti-resonance tube and the second inner anti-resonance tube, g04 - the spacing between the second inner anti-resonance tube and the third inner anti-resonance tube, g05 - the spacing between the third inner anti-resonance tube and the fourth inner anti-resonance tube, g06 - the inner diameter of the fourth inner anti-resonance tube, g07 - the minimum spacing between the auxiliary unit and the outer anti-resonance tube, g08 - the inner diameter of the auxiliary unit, 9 - circular arc-shaped fourth inner anti-resonance tube, 10 - circular arc-shaped auxiliary unit, 11 - double-layer nested structure, 12 - three-layer nested structure, 13 - nested auxiliary unit. DETAILED DESCRIPTION

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. 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.

[0045] Embodiment 1:

[0046] As Figure 1 , 2As shown, the embodiment provides a small outer diameter hollow core fiber matching the mode field diameter of conventional single mode fiber, comprising an outer cladding 1 and an inner cladding, the inner cladding is composed of anti-resonant structure units, the anti-resonant structure units are arranged along the circumference of the inner wall of the outer cladding and are in contact with the inner wall of the outer cladding 1, the central cavity covered by the inner cladding forms a core 2, the inner cladding comprises three anti-resonant structure units, the three anti-resonant structure units are uniformly distributed along the circumference at intervals, the anti-resonant structure unit comprises four or more layers of multi-layer anti-resonant tubes with different radii, including an outer anti-resonant tube and an inner multi-layer anti-resonant tube, the outer anti-resonant tube and the inner anti-resonant tube adjacent to the outer anti-resonant tube are circular arc-shaped, and the remaining inner multi-layer anti-resonant tubes comprise circular arc-shaped anti-resonant tubes and / or circular tube anti-resonant tubes with different radii, that is, the remaining inner multi-layer anti-resonant tubes can all be circular arc-shaped anti-resonant tubes, or all be circular tube anti-resonant tubes, or be in the form of combination of circular arc-shaped anti-resonant tubes and circular tube anti-resonant tubes. In the embodiment, the anti-resonant structure unit comprises five layers of multi-layer anti-resonant tubes with different radii, including an outer circular arc-shaped anti-resonant tube 4, a first inner anti-resonant tube 5, a second inner anti-resonant tube 6, a third inner anti-resonant tube 7 and a fourth inner anti-resonant tube 8. The two end points of the circular arc-shaped anti-resonant tube are in contact with the inner wall of the outer cladding 1, and the circular tube anti-resonant tube is tangent to the inner wall of the outer cladding 1. The core region and other outer cladding inner cavity regions are filled with air.

[0047] In the embodiment 1 of the present application, the optical signal transmission is in the fiber core 2, the dashed line approximately represents the fiber core boundary, and the diameter is 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 radial leakage, and at the same time to ensure that each layer of the inner cladding (anti-resonance microstructure) does not adhere to each other to form a harmful node, three groups of anti-resonance structure units arranged in rotational symmetry 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 coated outer diameter 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 structure units adopts a circular arc structure, which fills the excess cavity area generated between the groups to avoid the leakage of the fiber core fundamental mode energy. The minimum distance g01 between the outer anti-resonance tubes 4 of the groups is preferably controlled to be 4.5±0.5 μm, which is a distance that can suppress the leakage of the fundamental mode energy along the gap and is stable, easy to control and not easy to adhere to form a node 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 arranged along the inner wall of the outer cladding in the circumferential direction, the auxiliary unit 3 comprises three circular tube structure auxiliary anti-resonance tubes, the auxiliary unit 3 is arranged in the circumferential direction of the inner wall of the outer cladding and is in contact with the inner wall of the outer cladding, and the auxiliary unit is a one-layer structure anti-resonance tube, which can ensure that the area cannot form a circular cavity with a diameter greater than 0.62 times the diameter of the fiber core, thereby avoiding the leakage of the fiber core fundamental mode energy.

[0048] As shown in Figure 2 In order to realize the preparation feasibility, the distance g01 corresponding to the optical fiber profile given in the embodiment 1 is 4.68 μm, g07 is 4.25 μm, and the corresponding g08 is 4.7 μm. Among them, g07 is preferably 4.5±0.5 μm, 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 fiber core boundary to the outer cladding 1 is increased, more than three anti-resonance tubes can be added to the channel of the radial leakage of the fiber core optical signal energy to form an anti-resonance barrier. In the embodiment 1, five anti-resonance tubes are arranged, and each anti-resonance tube is in contact with the inner wall of the outer cladding. Each anti-resonance tube produces two anti-resonance reflections (the air layer between the solid layers also has an anti-resonance reflection effect), and at this time the radial leakage of the fiber core energy will pass through 10 anti-resonance barriers. Similarly, in order to fill the excess cavity 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 a circular arc 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 distances g02, g03, g04, g05 and g06 between the anti-resonance tubes (4, 5, 6, 7, 8) in the same group should be 0.5-0.62 times the distance between the fiber cores, and g03 is preferably arranged.Figure 2 As shown in the table, in Example 1, g02, g03, g04, g05, g06 are set to 5, 8.05, 5, 5.35, 4.7 μm respectively. In the optical fiber preform corresponding to Example 1, the circular arc-shaped anti-resonance tubes 4-7 in this embodiment are obtained by cutting a circular mother tube, and the cutting angles are 209°, 195°, 192°, 191° respectively. It should be noted that the cutting angle of the outer circular arc-shaped anti-resonance tube 4 can be further increased, but g01 will be shortened, g01 < 3 μm will increase the risk of preparation, or it can be further reduced, but it will widen g01, g01 > 5 μm will increase the risk of core mode energy leakage. 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, and the same should be considered in combination with the preparation feasibility and the risk of core mode energy leakage. In Example 1, the layer wall thickness of all anti-resonance tubes is set to 1.15 μm, and the material is pure quartz glass. As shown in the table, Figure 4 As shown in the simulation results (the core diameter of all optical fiber structures is 15 μm), the confinement loss of Example 1 at 1550 nm is as low as below 0.01 dB / km, which is much lower than that of the five-unit three-layer and four-unit three-layer structures. And 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 gap between the five-unit and four-unit groups and the outer nested tube is 2.63 and 3.5 μm respectively, which is extremely unstable in actual preparation. In addition, in order to increase the air area available for segmentation in the microstructure cladding, the anti-resonance tube (anti-resonance layer) wall thickness of the five-unit three-layer and four-unit three-layer structures corresponds to the first-order guided light passband (the wall thickness is thinner by about 370-515 nm), and the structure has a very high duty cycle, which is extremely unstable in actual preparation. As shown in the table, Figure 5 As shown in the simulation results, the loss of Example 1 at 1550 nm is < 0.02 dB / km when the bending diameter is 6 cm. As shown in the structure parameters of Example 1, the high-order mode extinction ratio at 1550 nm is about 10 6 In Example 1, because the ratio of the core diameter 15 μm to the working wavelength 1550 nm is less than 10, the microbend is extremely insensitive, and the outer diameter of the outer cladding can be reduced to match the 125 ± 1 μm of the conventional single-mode optical fiber. Further, the coating outer diameter of the optical fiber can be reduced to match the 240 ± 5 μm of the conventional single-mode optical fiber, thereby improving the fiber capacity in a single optical cable.

[0049] The present embodiment also provides an application of a small outer diameter hollow core optical fiber with a mode field diameter matching a conventional single-mode optical fiber, which is applied to communication, laser, and sensing.

[0050] Example 2:

[0051] Compared with Example 1, Example 2 of the present embodiment reduces one layer of circular arc-shaped anti-resonance tubes along the radial direction, and the spacing between the corresponding adjacent anti-resonance tubes is also slightly adjusted.Figure 4 As shown, the loss of Example 2 at 1550 nm is <0.3 dB / km. Because there can be two layer spacings along the radial direction that are 0.5-0.62 times the core diameter, the structure shown in Example 2 cannot observe the existence of high-order modes in the core in the simulation calculation, and the single-mode performance is better than that of Example 1. Therefore, it is particularly suitable for short-distance data center interconnection applications with high requirements for single-mode performance.

[0052] Example 3:

[0053] As shown, Example 3 has a structure basically the same as that of Example 1, except that the circular tube structure of the auxiliary unit 3 and the fourth inner anti-resonant tube 8 are changed to a circular arc auxiliary unit 10 and a circular arc fourth inner anti-resonant tube 9, respectively. Figure 6 Example 4:

[0054] As shown, Example 4 has a structure basically the same as that of Example 1, except that the third inner anti-resonant tube 7 is arranged as a circular tube anti-resonant tube and is combined with the fourth inner anti-resonant tube 8 into a double-layer nested structure 11, and the two circular anti-resonant tubes are tangent to a point and tangent to the inner wall of the outer cladding.

[0055] Figure 7 Example 5:

[0056] As shown, Example 5 has a structure basically the same as that of Example 1, except that the inner-layer second and third anti-resonant tubes are arranged as circular tube anti-resonant tubes, and the inner-layer second, third, and fourth nested anti-resonant tubes 6, 7, and 8 are combined into a triple-layer nested structure 12, and the three circular tube anti-resonant tubes are tangent to a point and tangent to the inner wall of the outer cladding. At the same time, inside the first inner anti-resonant tube 5, on both sides of the triple-layer nested structure 12, and on the inner wall of the outer cladding 1, two nested auxiliary units 13 are additionally arranged, which are used to fill the excess cavity formed between the triple-layer nested structure 12 and the first inner anti-resonant tube 5 and prevent the core fundamental mode energy from leaking. The nested auxiliary unit 13 in Example 5 is a circular structure nested auxiliary anti-resonant tube, but it can also be a circular arc structure nested auxiliary anti-resonant tube.

[0057] It should be noted that the structural changes of Examples 3-5 based on Example 1 are also applicable to Example 2. Figure 8 It should be noted that based on the design principles, theoretical expectations, and simulation calculation results as shown in

[0058] , the optical performance of Examples 3-5 is similar to that of Example 1. The description of the structure and theory in Example 1 also applies to Examples 2-5.

[0059] Figure 4 5 It should be noted that based on the design principles, theoretical expectations, and simulation calculation results as shown in

[0060] ​​The embodiments described above are only part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

Claims

1. A small outer diameter hollow core fiber matched with a mode field diameter of a conventional single mode fiber, comprising an outer cladding and an inner cladding, the inner cladding is composed of anti-resonant structure units, the anti-resonant structure units are arranged along the circumference of the inner wall of the outer cladding and are in contact with the inner wall of the outer cladding, and a central cavity covered by the inner cladding forms a core, characterized in that: The inner cladding comprises three groups of anti-resonance structure units, which are uniformly distributed along the circumference, and an auxiliary inner cladding is arranged along the circumference of the inner wall of the outer cladding, the auxiliary inner cladding comprises three auxiliary units, the auxiliary units are arranged along the circumference of the inner wall of the outer cladding and are staggered with the anti-resonance structure units, and the auxiliary units are connected with the inner wall of the outer cladding, the anti-resonance structure unit comprises four or more anti-resonance tubes with different radii, and comprises an outer anti-resonance tube and a plurality of inner anti-resonance tubes, the outer anti-resonance tube and the inner anti-resonance tube adjacent to the outer anti-resonance tube are circular arc-shaped, and the remaining inner anti-resonance tubes comprise circular arc-shaped anti-resonance tubes with different radii and / or circular anti-resonance tubes. ​ 2. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter according to claim 1, characterized in that: When the remaining inner anti-resonance tubes are all circular tubes with different radii, the circular anti-resonance tubes form a double-layer or multi-layer nested structure, and are tangent to a point and tangent to the inner wall of the outer cladding.

3. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter according to claim 2, characterized in that: A nested auxiliary unit is arranged 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 fiber matching a regular single mode fiber in mode field diameter according to claim 3, characterized in that: The nested auxiliary unit has a one-layer structure.

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

6. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter according to claim 1 or 2, characterized in that: The distance between the outer anti-resonance tube of 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 the adjacent anti-resonance structure units are 4±1 μm.

7. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter according to claim 1 or 2, characterized in that: The radial distance between the adjacent anti-resonance tubes of the anti-resonance structure unit is at least 0.5-0.62 times the diameter of the core, and the radial distance between the adjacent anti-resonance tubes is not greater than 0.62 times the diameter of the core.

8. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter 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 not greater than 0.5 times the diameter of the core.

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

13. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter according to claim 1 or 2, characterized in that: The circular 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 tube is 190±10 degrees.

14. The small outer diameter hollow core fiber matching a mode field diameter of a conventional single mode fiber according to claim 3, characterized in that: The base 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 fiber matching a mode field diameter of a conventional single mode fiber according to claim 1 or 2, characterized in that: The core region and other inner cavity regions of the outer cladding are filled with gas.

16. The small outer diameter hollow core fiber matching a regular single mode fiber in mode field diameter 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 fiber matching a mode field diameter of a conventional single mode fiber of claim 3, wherein: 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 different waveband optical signals with low loss.

18. The small outer diameter hollow core fiber matching a mode field diameter of a conventional single mode fiber of claim 3, wherein: 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 fiber matching a mode field diameter of a conventional single mode fiber according to claim 1 or 2, characterized in that: When directly interconnected with a conventional single-mode optical fiber, the coupling point loss is ≤0.4 dB.

20. Use of a small outer diameter hollow core fiber matching the mode field diameter of a regular single mode fiber according to any one of claims 1 to 19, characterized in that: The hollow core optical fiber is applied to the fields of communication, laser or sensing.

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