Ultralow-loss hollow-core anti-resonance optical fiber with birefringence structure

Abstract

The invention relates to an ultralow-loss hollow-core anti-resonance optical fiber with a birefringence structure, which comprises 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 circumferential direction of the inner wall of the outer cladding and are connected with the inner wall of the outer cladding, the inner cladding comprises four anti-resonance structure units, and the anti-resonance structure units are arranged along the circumferential direction of the inner wall of the outer cladding and are connected with the inner wall of the outer cladding. The four anti-resonance structure units are evenly distributed at intervals in the circumferential direction and comprise two long-axis anti-resonance structure units and two short-axis anti-resonance structure units, the two long-axis anti-resonance structure units are symmetrically arranged on the two sides of the inner wall of the outer cladding layer, and the two short-axis anti-resonance structure units are symmetrically arranged on the other two sides of the inner wall of the outer cladding layer. A central cavity wrapped by an inner wrapping layer formed by the four anti-resonance structure units forms an elliptical fiber core with a long axis and a short axis. According to the invention, the transmission loss can be reduced while the high birefringence performance is maintained, the shape of each part of the microstructure cladding is regular, and the preparation is convenient.

Description

Technical Field

[0001] The invention relates to an ultra-low-loss hollow-core anti-resonant optical fiber with a birefringence structure, which can realize low-loss single-polarization fundamental mode transmission and belongs to the technical field of special optical fibers. Background Art

[0002] Polarization-maintaining optical fibers are widely used in various fields of the national economy, such as aerospace, aviation, navigation, industrial manufacturing technology, and communications. Existing polarization-maintaining optical fibers are solid-core optical fibers. By controlling the shape of the core or applying stress units to the cladding, polarization-maintaining solid-core optical fibers can achieve effective single-polarization fundamental mode transmission. They have been used for many years in fields such as fiber optic gyroscopes in aerospace. However, since the light field is transmitted in a solid core, when there is high or low temperature interference or strong radiation, the performance of the polarization-maintaining solid-core optical fiber will be significantly reduced, thereby reducing its application value. In addition, due to the fluctuations in fluid density generated during optical fiber drawing, the intrinsic Rayleigh scattering loss of the solid-core optical fiber has a limit that cannot be further reduced, and it also causes higher backscattering, which will damage its working conditions in actual application scenarios.

[0003] Hollow core antiresonant optical fiber can confine most of the light field in the air core through the antiresonant reflective optical waveguide for low-loss transmission, so it is extremely insensitive to external temperature, radiation, etc. The overlap between the core light field and the quartz part can be as low as 10 -5 (This is related to wavelength and core diameter.) Therefore, compared to another member of the hollow-core fiber family, hollow-core photonic bandgap fiber, hollow-core antiresonant fiber exhibits lower backscattered light intensity and lower transmission loss. The development of hollow-core antiresonant fiber has significantly surpassed the transmission loss of solid-core single-mode fiber in the near-infrared band. However, due to the low overlap between the fiber and the quartz, achieving birefringence in hollow-core antiresonant fiber presents significant challenges.

[0004] Existing patents, such as CN118795594A, CN119224919A, CN116840966A, and CN116699754A, achieve high birefringence at target wavelengths by varying the shape of individual or multiple antiresonant elements within the microstructured cladding, or the shape of the outer cladding and its internal boundary surfaces. It is generally agreed that current hollow-core fiber fabrication processes are unable to produce structures with elliptical antiresonant elements (or other non-arc or non-circular shapes) or irregularly shaped outer cladding and its internal boundary surfaces. Therefore, assessing fabrication feasibility is crucial before considering the optical performance of the fiber. CN117872524A and CN118068479A achieve high birefringence by varying the wall thickness of the antiresonant layer in two orthogonal directions through a four-unit circular arc structure. While fabrication feasibility is possible, the high loss makes further reduction difficult.

[0005] CN111474628A discloses a polarization-maintaining hollow-core antiresonant optical fiber. The microstructure region comprises three thin walls. High birefringence is introduced by varying the thickness of the first and second walls. The quasi-multiple symmetry of the first and second walls effectively amplifies the birefringence effect. While this patent demonstrates fabrication feasibility and considerable birefringence performance, the fiber still exhibits high attenuation and significant attenuation spectrum jitter, leading to significant instability in actual applications. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure in view of the deficiencies in the above-mentioned prior art, which can reduce transmission loss while maintaining high birefringence and is easy to prepare.

[0007] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: it includes an outer cladding and an inner cladding, the inner cladding is composed of antiresonance structural units, the antiresonance structural units are arranged along the circumference of the inner wall of the outer cladding and are connected to the inner wall of the outer cladding, and the central cavity covered by the inner cladding forms a fiber core, characterized in that the inner cladding includes four antiresonance structural units, the four antiresonance structural units are evenly spaced along the circumference, the four antiresonance structural units include two long-axis antiresonance structural units and two short-axis antiresonance structural units, the two long-axis antiresonance structural units are symmetrically arranged on both sides of the inner wall of the outer cladding, and the two short-axis antiresonance structural units are symmetrically arranged on the other two sides of the inner wall of the outer cladding, and the central cavity covered by the inner cladding formed by the four antiresonance structural units forms an elliptical fiber core with long and short axes.

[0008] According to the above scheme, the long-axis anti-resonance structure unit includes at least three layers of anti-resonance tubes with different radii, including an outer anti-resonance tube and an inner anti-resonance tube. The outer anti-resonance tube is an arc-shaped anti-resonance tube, and the inner anti-resonance tube includes arc-shaped anti-resonance tubes and / or circular anti-resonance tubes with different radii. The outer periphery of the arc-shaped outer anti-resonance tube has a long distance from the center of the fiber core, which is the long axis of the elliptical fiber core.

[0009] According to the above solution, each arc anti-resonance tube in the long-axis anti-resonance structure unit intersects with the inner wall of the outer cladding or the adjacent outer anti-resonance tube, each circular anti-resonance tube is tangent to each circular anti-resonance tube, or each circular anti-resonance tube is tangent to the inner wall of the outer cladding.

[0010] According to the above scheme, the short-axis anti-resonance structure unit includes at least three layers of anti-resonance tubes with different radii, including an outer anti-resonance tube and an inner anti-resonance tube. The outer anti-resonance tube is a circular anti-resonance tube, and the inner anti-resonance tube includes circular anti-resonance tubes with different radii. The outer periphery of the circular outer anti-resonance tube has a shorter distance from the center of the fiber core, which is the short axis of the elliptical fiber core.

[0011] According to the above solution, the inner and outer circular anti-resonance tubes in the short-axis anti-resonance structural unit are tangent to each other at one point and are tangent to the inner cavity wall of the outer cladding.

[0012] According to the above solution, the outer cladding and the inner wall are both circular, the two long-axis anti-resonance structural units have the same structure, and the two short-axis anti-resonance structural units have the same structure.

[0013] According to the above solution, the major axis of the elliptical fiber core is 30±2 μm, and the minor axis of the elliptical fiber core is 20±2 μm.

[0014] According to the above solution, a circumferential gap is maintained between the four anti-resonance structural units in the inner cladding, and the gap is 4.5±0.5 μm.

[0015] According to the above scheme, the short-axis anti-resonance structure unit includes three layers of circular anti-resonance tubes with different radii, including one circular outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The inner and outer circular anti-resonance tubes are tangent to each other at one point and to the inner cavity wall of the outer cladding. The long-axis anti-resonance structure unit includes three layers of arc-shaped anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube and two arc-shaped inner anti-resonance tubes with different radii. Each of the arc-shaped anti-resonance tubes intersects with the inner wall of the outer cladding.

[0016] According to the above scheme, the short-axis anti-resonance structure unit includes three layers of circular anti-resonance tubes with different radii, including one circular outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The inner and outer circular anti-resonance tubes are tangent to each other at one point and to the inner cavity wall of the outer cladding. The long-axis anti-resonance structure unit includes three layers of anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The arc-shaped outer anti-resonance tube intersects with the inner wall of the outer cladding, and the two circular inner anti-resonance tubes with different radii are tangent to each other at one point and to the inner cavity wall of the outer cladding.

[0017] According to the above scheme, the short-axis anti-resonance structure unit includes three layers of circular anti-resonance tubes with different radii, including one circular outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The inner and outer circular anti-resonance tubes are tangent to each other at one point and are tangent to the inner cavity wall of the outer cladding. The long-axis anti-resonance structure unit includes three layers of anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube, one arc-shaped inner anti-resonance tube, and one circular inner anti-resonance tube arranged in the arc-shaped inner anti-resonance tube. The inner and outer arc-shaped anti-resonance tubes intersect with the inner wall of the outer cladding, and the circular inner anti-resonance tube is tangent to the inner cavity wall of the outer cladding.

[0018] According to the above solution, auxiliary structural units are symmetrically arranged on both sides of the circular inner anti-resonance tube, and the auxiliary structural units are connected to the inner cavity wall of the outer cladding.

[0019] According to the above solution, the auxiliary structural unit includes an arc tube or a circular tube, the arc tube intersects with the inner wall of the outer cladding, and the circular tube is tangent to the inner wall of the outer cladding.

[0020] According to the above solution, the wall thickness of the arc-shaped outer anti-resonance tube of the long-axis anti-resonance structure unit is inconsistent with the wall thickness of the circular outer anti-resonance tube of the short-axis anti-resonance structure unit, and is different from the wall thickness of the inner anti-resonance tube of each anti-resonance structure unit.

[0021] According to the above solution, the arc angle of the circular anti-resonance tube is 120±5°.

[0022] According to the above solution, the outer cladding layer and the substrate material of the anti-resonance structure unit are both pure quartz glass.

[0023] According to the above solution, the core region and other hollow regions within the outer cladding are filled with gas.

[0024] According to the above scheme, the gas is argon, nitrogen, helium, air or a mixture of multiple gases.

[0025] According to the above solution, the diameter of the outer cladding is 200-250 μm; the outer cladding is covered with a coating layer, and the diameter of the coating layer is 320-410 μm.

[0026] According to the above solution, the limiting loss of the optical fiber is less than 0.1 dB / km.

[0027] According to the above scheme, the optical fiber has 8×10 -5 birefringence performance.

[0028] The beneficial effects of the present invention are: 1. The optical fiber microstructure is composed of four groups of nested anti-resonance units. The antiresonant elements with inconsistent wall thickness near the core in two orthogonal directions introduce a birefringence effect. In addition, in the direction where the wall thickness (the radial distance between the antiresonant structure unit and the outer cladding inner cavity wall) is thinner, an arc-shaped nested antiresonant structure is introduced as an antiresonant element near the core. While increasing the core diameter in this direction, it further divides the air region formed by it, the circular tubular nested structure in the other orthogonal direction, and the boundary of the outer cladding inner cavity wall, thereby preventing the risk of fundamental mode energy leaking along the gaps between each group of antiresonant units. Furthermore, each of the four groups of antiresonant units contains multiple layers and multiple antiresonant elements, which reduces the radial leakage of the core fundamental mode energy along the antiresonant units. The entire microstructured cladding surrounds the core into an elliptical core with major and minor axes. The light field in the minor axis has a high degree of overlap with the solid material of the microstructured cladding, which enhances the birefringence effect. The major axis portion effectively increases the core diameter, thereby significantly reducing the attenuation of the birefringence structure hollow-core antiresonant fiber while maintaining high birefringence. The limiting loss of the optical fiber is less than 0.1dB / km, and it has an 8×10 -5 The birefringence performance can be further increased by increasing the difference between the major and minor axes of the core to reach 1×10 -4 . birefringence performance. 2. The long-axis anti-resonance structure unit is provided with an auxiliary anti-resonance structure unit or an inner arc-shaped anti-resonance tube, which functions to fill the excess cavity area formed between the outermost layer and the inner cavity wall of the outer cladding due to the adoption of the arc-shaped structure, thereby reducing the energy leakage of the core. 3. Except for the structure on the outermost side that introduces the birefringence effect, the rest are anti-resonance elements. According to the corresponding light guiding theory, the low-loss working band of the optical fiber can be changed by modifying the thin-wall thickness. For the wall thickness of the outermost tubular structure corresponding to the short axis of the fiber core, the target wavelength falls on the short-wavelength band edge of the light guiding passband. For the wall thickness of the outermost arc structure corresponding to the long axis of the fiber core, the target wavelength falls on the long-wavelength band edge of the light guiding passband. 4. Since the microstructure cladding is composed of tubular and arc structures, and the outer cladding and its internal boundary are regular circles, there is no special-shaped structure, and each part of the optical fiber cross-section can be prepared by the stacking-drawing method, so the present invention has the characteristic of being easy to prepare. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the radial cross-sectional structure of an embodiment of the present invention.

[0030] Figure 2 It is the real part of the effective refractive index of the two polarization fundamental modes obtained by simulation in one embodiment of the present invention.

[0031] Figure 3 This is the limiting loss of the two polarization fundamental modes obtained by simulation according to one embodiment of the present invention.

[0032] Figure 4 This is a birefringence curve obtained by simulation according to an embodiment of the present invention.

[0033] Figure 5 It is a schematic diagram of the radial cross-sectional structure of the second embodiment of the present invention.

[0034] Figure 6 It is a schematic diagram of the radial cross-sectional structure of the third embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the embodiments.

[0036] The first embodiment of the present invention is Figures 1 to 4 As shown, Figure 1The horizontal and vertical directions are X and Y directions respectively. In this embodiment, the optical fiber structure includes an outer cladding 2 and an inner cladding. The inner cladding includes four anti-resonance structure units. The four anti-resonance structure units are evenly spaced along the circumference. The four anti-resonance structure units include two long-axis anti-resonance structure units and two short-axis anti-resonance structure units. The two long-axis anti-resonance structure units are symmetrically arranged on the left and right sides of the inner wall of the outer cladding, that is, on both sides of the inner wall of the outer cladding along the X direction. The two short-axis anti-resonance structure units are symmetrically arranged on the upper and lower sides of the inner wall of the outer cladding, that is, on both sides of the inner wall of the outer cladding along the Y direction. The short-axis anti-resonance structure unit includes three layers of different half-axis anti-resonance structure units. The circular anti-resonance tube has a diameter of 1 / 4, including a circular outer anti-resonance tube 7 and two circular inner anti-resonance tubes 8 and 9 with different radii, the inner and outer circular anti-resonance tubes are tangent to each other at one point and are tangent to the inner cavity wall of the outer cladding; the long-axis anti-resonance structure unit includes an arc-shaped outer anti-resonance tube 3 and two circular inner anti-resonance tubes 5 and 4 with different radii, the arc-shaped outer anti-resonance tube intersects with the inner wall of the outer cladding, the two inner circular anti-resonance tubes with different radii are tangent to each other at one point and are tangent to the inner cavity wall of the outer cladding, and auxiliary structure units 6 are symmetrically arranged on both sides of the inner circular anti-resonance tube. The auxiliary structure units are circular tubes, and the circular tubes are connected to the inner cavity wall of the outer cladding. The central cavity enclosed by the inner cladding formed by the four antiresonance structural units forms an equivalent elliptical fiber core 1 with a major and minor axis that is tangent to the four antiresonance structural units. The outer periphery of the circular arc-shaped outer antiresonance tube of the long-axis antiresonance structural unit is spaced relatively long from the center of the fiber core, which is the major axis of the elliptical fiber core. The outer periphery of the circular outer antiresonance tube of the short-axis antiresonance structural unit is spaced relatively short from the center of the fiber core, which is the minor axis of the elliptical fiber core. A circumferential gap of approximately 4.5 μm is maintained between the four antiresonance structural units in the inner cladding. The circular arc-shaped outer antiresonance tube 3 of the long-axis antiresonance structural unit and the circular outer antiresonance tube 7 of the short-axis antiresonance structural unit have different wall thicknesses, thereby destroying the phase accumulation of the fundamental mode in the two orthogonal solid layers adjacent to the fiber core, and ultimately causing a birefringence effect of the fundamental mode in the fiber core. Because the optical field-solid layer overlap is related to the fiber core diameter and wall thickness, the thickness of the arc-shaped outer antiresonance tube of the long-axis antiresonance structural unit is less than the antiresonance wall thickness of the target wavelength, and the thickness of the circular outer antiresonance tube of the short-axis antiresonance structural unit is greater than the antiresonance wall thickness of the target wavelength. Furthermore, because the birefringence effect exacerbates the transmission loss of the optical fiber, the introduction of the long axis can effectively increase the core diameter. Combined with multiple layers of antiresonance elements of the inner antiresonance tube added for the target wavelength, the optical fiber attenuation can be significantly reduced. The auxiliary structural unit 6 of the long-axis antiresonance structural unit is used to fill the large space area formed between the arc-shaped outer antiresonance tube 3 and the circular inner antiresonance tube to prevent the formation of a cavity that can cause energy coupling of the fiber core fundamental mode.The arc-shaped outer anti-resonance tube 3 not only changes the diameter of the fiber core along the X direction, but also further divides the air area between the circular outer anti-resonance tube 7 of the short-axis anti-resonance structural unit and the inner cavity of the outer cladding 2, thereby reducing the energy of the fiber core fundamental mode leaking along the gap between the microstructure units.

[0037] In this embodiment, the optical fiber structural parameters for the 1550nm band are as follows: the short-axis diameter of the elliptical core 1 is 20μm; the long-axis diameter is 30μm; the circular outer antiresonance tube 7 of the short-axis antiresonance structure unit has an outer diameter of 36μm and a wall thickness of 1.42μm; the full circle diameter of the long-axis first circular arc structure 3 is 71.23μm, the arc angle is 117°, the cutting angle is 243°, and the wall thickness is 0.94μm; the two circular inner antiresonance tubes 5 and 4 and the auxiliary structure unit 6 have outer diameters of 22.6μm, 8μm, and 8μm, respectively; the circular inner antiresonance tubes 8 and 9 have outer diameters of 26μm and 12.7μm, respectively, and the wall thickness is 1.15μm, designed for the second-order antiresonance at 1550nm. The substrate material of the outer cladding and the antiresonance structure unit is pure quartz glass. The core region and other cavity regions within the outer cladding are filled with gas. It should be noted that the above structural parameters are established based on the performance description of the first embodiment of the present invention, and the structural parameters can be adjusted based on different wavelengths and optical fiber performances.

[0038] Figure 2 The figure shows the real part of the effective refractive index of the two polarization states of the core fundamental mode obtained by simulation calculation based on the structural parameters of the above embodiment. Figure 3 The figure shows the limiting loss curve obtained by simulation based on the structural parameters of the above embodiment. The Y polarization fundamental mode loss at 1560nm can be less than 0.1dB / km, and the birefringence is 7×10 -5 . Figure 4 The figure shows the birefringence curve obtained by simulation calculation based on the structural parameters of the above embodiment. In the low-loss band, the maximum birefringence appears at 1520nm, 8×10 -5 At this time, the fundamental mode X and Y polarization-limited losses are 0.3 dB / km and 0.18 dB / km respectively.

[0039] The second embodiment of the present invention is Figure 5As shown, the main difference from the previous embodiment is that the long-axis anti-resonance structure unit includes three layers of anti-resonance tubes with different radii, including an arc-shaped outer anti-resonance tube, an arc-shaped inner anti-resonance tube 10, and a circular inner anti-resonance tube arranged inside the arc-shaped inner anti-resonance tube. The inner and outer arc-shaped anti-resonance tubes intersect with the inner wall of the outer cladding, and the circular inner anti-resonance tube is tangent to the inner cavity wall of the outer cladding. Auxiliary structure units 11 are symmetrically arranged on both sides of the circular inner anti-resonance tube inside the arc-shaped inner anti-resonance tube. The auxiliary structure units are circular tubes, and the auxiliary structure units are tangent to the inner cavity wall of the outer cladding. The diameter of the circular tube of the auxiliary structure unit is the same as the diameter of the circular inner anti-resonance tube. The rest of the structure is the same as the previous embodiment.

[0040] The third embodiment of the present invention is Figure 6 As shown, the main difference between it and the first embodiment is that the long-axis anti-resonance structural unit includes three layers of arc-shaped anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube and two arc-shaped inner anti-resonance tubes 10 and 12 with different radii, and each of the arc-shaped anti-resonance tubes intersects with the inner wall of the outer cladding.

[0041] It should be noted that the structural parameter design principles based on the first embodiment are also applicable to the second and third embodiments. Figure 2-4 The simulation results show that the second and third embodiments have optical performances similar to that of the first embodiment.

Claims

1. An ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure, comprising an outer cladding and an inner cladding, wherein the inner cladding is composed of antiresonant structural units, the antiresonant structural 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 fiber core, characterized in that The inner cladding includes four anti-resonance structural units, and the four anti-resonance structural units are evenly spaced along the circumferential direction. The four anti-resonance structural units include two long-axis anti-resonance structural units and two short-axis anti-resonance structural units. The two long-axis anti-resonance structural units are symmetrically arranged on both sides of the inner wall of the outer cladding, and the two short-axis anti-resonance structural units are symmetrically arranged on the other two sides of the inner wall of the outer cladding. The central cavity covered by the inner cladding formed by the four anti-resonance structural units forms an elliptical fiber core with long and short axes.

2. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1, characterized in that The long-axis anti-resonance structure unit includes at least three layers of anti-resonance tubes with different radii, including an outer anti-resonance tube and an inner anti-resonance tube. The outer anti-resonance tube is an arc-shaped outer anti-resonance tube, and the inner anti-resonance tube includes an arc-shaped inner anti-resonance tube with different radii and / or a circular inner anti-resonance tube. The outer periphery of the arc-shaped outer anti-resonance tube has a long distance from the center of the fiber core, which is the long axis of the elliptical fiber core.

3. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 2, characterized in that In the long-axis anti-resonance structure unit, each arc anti-resonance tube intersects with the inner wall of the outer cladding or the adjacent outer anti-resonance tube, each circular anti-resonance tube is tangent to each circular anti-resonance tube, or each circular anti-resonance tube is tangent to the inner wall of the outer cladding.

4. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 2, characterized in that The short-axis anti-resonance structure unit includes at least three layers of anti-resonance tubes with different radii, including an outer anti-resonance tube and an inner anti-resonance tube. The outer anti-resonance tube is a circular outer anti-resonance tube, and the inner anti-resonance tube includes circular inner anti-resonance tubes with different radii. The outer periphery of the circular outer anti-resonance tube has a shorter distance from the center of the fiber core, which is the short axis of the elliptical fiber core.

5. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 4, characterized in that In the short-axis anti-resonance structural unit, the inner and outer circular anti-resonance tubes are tangent to each other at one point and are tangent to the inner cavity wall of the outer cladding.

6. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The outer cladding and the inner wall are both circular, the two long-axis anti-resonance structural units have the same structure, and the two short-axis anti-resonance structural units have the same structure.

7. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The major axis of the elliptical fiber core is 30±2 μm, and the minor axis of the elliptical fiber core is 20±2 μm.

8. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that A circumferential gap is maintained between the four anti-resonance structural units in the inner cladding, and the gap is 4.5±0.5 μm.

9. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 4, characterized in that The short-axis anti-resonance structure unit includes three layers of circular anti-resonance tubes with different radii, including one circular outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The inner and outer circular anti-resonance tubes are tangent to each other at one point and to the inner cavity wall of the outer cladding. The long-axis anti-resonance structure unit includes three layers of arc-shaped anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube and two arc-shaped inner anti-resonance tubes with different radii. Each of the arc-shaped anti-resonance tubes intersects with the inner wall of the outer cladding.

10. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 4, characterized in that The short-axis anti-resonance structure unit includes three layers of circular anti-resonance tubes with different radii, including one circular outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The inner and outer circular anti-resonance tubes are tangent to each other at one point and to the inner cavity wall of the outer cladding. The long-axis anti-resonance structure unit includes three layers of anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The arc-shaped outer anti-resonance tube intersects with the inner wall of the outer cladding, and the two circular inner anti-resonance tubes with different radii are tangent to each other at one point and to the inner cavity wall of the outer cladding.

11. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 4, characterized in that The short-axis anti-resonance structure unit includes three layers of circular anti-resonance tubes with different radii, including one circular outer anti-resonance tube and two circular inner anti-resonance tubes with different radii. The inner and outer circular anti-resonance tubes are tangent to each other at one point and to the inner cavity wall of the outer cladding. The long-axis anti-resonance structure unit includes three layers of anti-resonance tubes with different radii, including one arc-shaped outer anti-resonance tube, one arc-shaped inner anti-resonance tube adjacent to the outer anti-resonance tube, and one circular inner anti-resonance tube arranged within the arc-shaped inner anti-resonance tube. The arc-shaped inner and outer anti-resonance tubes intersect with the inner wall of the outer cladding, and the circular inner anti-resonance tube is tangent to the inner cavity wall of the outer cladding.

12. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 10 or 11, characterized in that Auxiliary structural units are symmetrically arranged on both sides of the circular inner anti-resonance tube, and the auxiliary structural units are connected to the inner cavity wall of the outer cladding.

13. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 12, characterized in that The auxiliary structural unit includes an arc tube or a circular tube. The arc tube intersects with the inner cavity wall of the outer cladding layer, and the circular tube is tangent to the inner cavity wall of the outer cladding layer.

14. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 4, characterized in that The wall thickness of the arc-shaped outer anti-resonance tube of the long-axis anti-resonance structure unit is inconsistent with the wall thickness of the circular outer anti-resonance tube of the short-axis anti-resonance structure unit, and is different from the wall thickness of the inner anti-resonance tube of each anti-resonance structure unit.

15. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 2, characterized in that The arc angle of the circular anti-resonance tube is 120±5°.

16. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The substrate materials of the outer cladding and the anti-resonance structure unit are pure quartz glass, doped quartz glass, sulfide glass, fluoride glass or plastic.

17. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The core region and other hollow regions within the outer cladding are filled with gas.

18. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 17, characterized in that The gas is argon, nitrogen, helium, air or a mixture of multiple gases.

19. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The outer cladding has a diameter of 180-400 μm; the outer cladding is covered with a coating layer, and the coating layer has a diameter of 300-550 μm.

20. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The limiting loss of the optical fiber is less than 0.1 dB / km.

21. The ultra-low loss hollow-core antiresonant optical fiber with a birefringence structure according to claim 1 or 2, characterized in that The optical fiber has 8×10 -5 birefringence performance.

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