A low-loss hollow optical fiber and its applications

Abstract

This invention relates to a low-loss hollow-core optical fiber and its applications. The low-loss hollow-core optical fiber includes an outer cladding and an inner cladding. The inner cladding is composed of anti-resonant structural units, which are arranged circumferentially along the inner wall of the outer cladding and connected to the inner wall. The central cavity covered by the inner cladding forms the fiber core. The invention is characterized in that: each anti-resonant structural unit includes four or more circular anti-resonant tubes of different radii; the outer anti-resonant tube of the anti-resonant structural unit is tangent to the inner wall of the outer cladding; two adjacent circular anti-resonant tubes are sequentially tangent, with the tangency points alternating between the side furthest from the geometric center of the fiber core and the side closest to the geometric center of the fiber core. In the structure of this invention, the multiple layers of anti-resonant glass and the air region included in the inner cladding effectively confine the transmitted light within the fiber core for low-loss transmission; by setting four nested glass tubes, the number of reflective surfaces in the inner cladding is increased, reducing the loss of the hollow-core optical fiber.

Description

Technical Field

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

[0002] Since the invention of the first solid optical fiber, optical fiber technology has been widely applied in various fields, including communications, sensing, and medicine, after more than half a century of development. With the rapid development of society and the improvement of people's living standards, there is an urgent need for optical fibers with longer transmission distances, higher power, and larger capacity. However, the performance of traditional silica optical fibers has approached its theoretical limits, prompting people to explore more advanced optical fiber technologies to meet the ever-increasing demand for data transmission.

[0003] Hollow-core fiber, as a novel type of optical fiber, confines light waves within an air core, exhibiting intrinsic advantages such as low Rayleigh scattering, low nonlinearity, and tunable dispersion. It can theoretically achieve extremely low loss and provide a higher laser damage threshold, showing potential applications in high-power laser transmission, ultraviolet / mid-infrared light transmission, pulse compression, and optical soliton transmission. Furthermore, the air core possesses characteristics such as large mode area, single-mode operation, low nonlinearity, low dispersion, and low latency, potentially breaking the nonlinear Shannon limit of traditional optical fibers and providing a new transmission medium for next-generation high-capacity, long-distance optical communication systems.

[0004] The most common structure of hollow fiber is the multi-layer nested nodeless hollow fiber. Related patents are mostly concentrated on double-layer and triple-layer nested structures, such as patents CN111474627B, CN117388980A, and CN118688896A. However, there is relatively little research on hollow fiber with four or more nested structures currently available. At the same time, lower fiber attenuation can also be achieved by adding a glass anti-resonant layer in the inner cladding. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a low-loss hollow fiber and its application that can reduce the transmission loss of hollow fiber, which addresses the shortcomings of the prior art.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0007] A low-loss hollow-core optical fiber includes an outer cladding and an inner cladding. The inner cladding is composed of anti-resonant structural units, which are arranged circumferentially along the inner wall of the outer cladding and connected to the inner wall of the outer cladding. The central cavity covered by the inner cladding forms the fiber core. The anti-resonant structural unit includes four or more circular anti-resonant tubes of different radii. The outer anti-resonant tube of the anti-resonant structural unit is tangent to the inner wall of the outer cladding. Two adjacent circular anti-resonant tubes are tangent to each other in sequence, and the positions of each tangency point alternate from the outside to the inside, on the side away from the geometric center of the fiber core and on the side closer to the geometric center of the fiber core.

[0008] According to the above technical solution, the anti-resonance structure unit includes four layers of anti-resonance tubes with different radii, from the outside to the inside including an outer anti-resonance tube, a first inner anti-resonance tube, a second inner anti-resonance tube, and a third inner anti-resonance tube. The outer anti-resonance tube is tangent to the inner wall of the outer cladding; the first inner anti-resonance tube is tangent to the inner wall of the outer anti-resonance tube, with the tangency point on the side away from the geometric center of the fiber core; the second inner anti-resonance tube is tangent to the inner wall of the first inner anti-resonance tube, with the tangency point on the side closer to the geometric center of the fiber core; and the third inner anti-resonance tube is tangent to the inner wall of the second inner anti-resonance tube, with the tangency point on the side away from the geometric center of the fiber core.

[0009] According to the above technical solution, the line connecting the curvature centers of each anti-resonant tube coincides with the extension line connecting the curvature center of the external anti-resonant tube and the geometric center of the fiber core.

[0010] According to the above technical solution, at least one adjacent and tangent anti-resonant tube's curvature center line forms a deflection angle with the line connecting the fiber core's geometric center and the outer anti-resonant tube's curvature center.

[0011] According to the above technical solution, the deflection angle is greater than 0° and less than or equal to 90°.

[0012] According to the above technical solution, the ratio of the outer diameters of the outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, and the third inner anti-resonant tube is 1:0.75~0.9:0.55~0.75:0.3~0.55, respectively.

[0013] According to the above technical solution, the wall thickness of each internal anti-resonant tube is the same, ranging from 0.3 to 1.5 μm.

[0014] According to the above technical solution, the wall thickness of each inner anti-resonator is different, and the thickness of each anti-resonator increases from the outside to the inside. The wall thickness of the outer anti-resonator is 0.8 to 1.22 μm, the wall thickness of the first inner anti-resonator is 0.8 to 1.5 μm, the wall thickness of the second inner anti-resonator is 0.8 to 1.5 μm, and the wall thickness of the third inner anti-resonator is 1.22 to 1.5 μm.

[0015] According to the above technical solution, the inner cladding layer has 4 to 6 anti-resonance structural units.

[0016] According to the above technical solution, both the outer cladding and the inner wall are circular.

[0017] According to the above technical solution, the substrate materials of the outer cladding layer and the anti-resonance structural unit are both pure quartz glass.

[0018] According to the above technical solution, the core region and other inner cladding cavity regions are filled with gas.

[0019] According to the above technical solution, the gas is argon, nitrogen, helium, air, or a mixture of multiple gases.

[0020] According to the above technical solution, the LP01 mode loss of the optical fiber is less than 1dB / km.

[0021] An application of the low-loss hollow-core optical fiber as described above, characterized in that the low-loss hollow-core optical fiber is used in the fields of communication, laser, or sensing.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. In the structure of the present invention, the multi-layer anti-resonant nested glass layer and air region included in the inner cladding effectively confine the transmitted light in the fiber core for low-loss transmission; by setting four or more layers of nested glass tubes, the number of reflective surfaces in the inner cladding is increased, thereby reducing the loss of the hollow fiber.

[0024] 2. This structure increases the number of glass tubes, raising the number of glass reflective layers to at least nine, allowing light to return to the fiber core after multiple reflections. This enables low-loss transmission. The separation of the tangent points between the glass tubes minimizes geometric deformation caused by adhesion, while excessive geometric deformation significantly increases fiber loss.

[0025] 3. Since the glass tube wall of the hollow fiber itself acts as a Fabry-Perot resonator, different wall thicknesses can make it in an anti-resonance state at the corresponding wavelength, and the light is reflected back to the fiber core. When the anti-resonator tube is thinner, it can reflect light of a shorter wavelength, and when the anti-resonator tube is thicker, it can reflect light of a longer wavelength. This invention can achieve complementary anti-resonance effects of different wavelengths of light by setting anti-resonator tubes with progressively thicker thicknesses from the outside to the inside, thereby achieving a better low-attenuation bandwidth. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a radial cross-sectional view of a low-loss hollow optical fiber provided in Embodiment 1 of the present invention.

[0028] Figure 2 This is a partial enlarged view of an anti-resonant tube in Embodiment 1 of the present invention.

[0029] Figure 3 This is a graph showing the LP01 mode loss versus wavelength in the first embodiment of the present invention.

[0030] Figure 4 This is a radial cross-sectional diagram of a low-loss hollow optical fiber provided in Embodiment 2 of the present invention.

[0031] Figure 5 This is a radial cross-sectional diagram of a low-loss hollow optical fiber provided in Embodiment 3 of the present invention.

[0032] Figure 6 This is a radial cross-sectional diagram of a low-loss hollow optical fiber provided in Embodiment 4 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0034] Example 1:

[0035] The first embodiment of the invention is as follows: Figure 1 , 2As shown, the structure includes an outer cladding layer 1 and an inner cladding layer. The inner cladding layer is composed of four anti-resonant structural units, which are arranged circumferentially along the inner wall of the outer cladding layer and connected to it. The central cavity covered by the inner cladding layer forms a fiber core 10. Each anti-resonant structural unit comprises four circular anti-resonant tubes of different radii: an outer anti-resonant tube 2, a first inner anti-resonant tube 3, a second inner anti-resonant tube 4, and a third inner anti-resonant tube 5. The circular anti-resonant tubes consist of four circular anti-resonant tubes of different radii, with the outer anti-resonant tube having a diameter of d1, the first inner anti-resonant tube having a diameter of d2, the second inner anti-resonant tube having a diameter of d3, and the third inner anti-resonant tube having a diameter of d4. The wall thickness of the outer anti-resonant tube is h1, the first inner anti-resonant tube has a wall thickness of h2, the second inner anti-resonant tube has a wall thickness of h3, and the third inner anti-resonant tube has a wall thickness of h4. The line connecting the curvature centers of the first, second, third, and fourth inner anti-resonator tubes completely coincides with the extension of the line connecting the curvature center of the outer anti-resonator tube and the geometric center of the fiber core. The outer wall of the outer anti-resonator tube is tangent to the inner wall of the outer cladding; the outer wall of the first inner anti-resonator tube is tangent to the inner wall of the outer anti-resonator tube, with the tangency point located away from the geometric center of the fiber core; the outer wall of the second inner anti-resonator tube is tangent to the inner wall of the second nested tube, with the tangency point located near the geometric center of the fiber core; the third inner anti-resonator tube is tangent to the inner wall of the second inner anti-resonator tube, with the tangency point located away from the geometric center of the fiber core. The fiber core region and other internal spaces, including the outer anti-resonator tube cavity 6, the first inner anti-resonator tube cavity 7, the third nested tube glass cavity 8, and the fourth nested glass cavity 9, are filled with gas. The gas is argon, nitrogen, helium, air, or a mixture of multiple gases.

[0036] Specifically, the relevant parameters in this embodiment are as follows: the core diameter D is 31 μm, the outer diameter d1 of the outer anti-resonator is 54 μm, the outer diameter d2 of the first inner anti-resonator is 46 μm, the outer diameter d3 of the second inner anti-resonator is 38 μm, and the outer diameter d3 of the third inner anti-resonator is 28 μm; the inner diameter of the outer cladding (outer cladding cavity diameter) is 139 μm. The wall thickness h1 of the outer anti-resonator, the wall thickness h2 of the first inner anti-resonator, the wall thickness h3 of the second inner anti-resonator, and the wall thickness h4 of the third inner anti-resonator are all 1.22 μm.

[0037] This embodiment also provides an application of low-loss hollow fiber, which is used in communication, laser, or sensing fields.

[0038] This invention combines a reasonable and feasible nested structure with an optimized anti-resonant tube structure, resulting in the following combined technical effects: the nine-layer glass reflective layer provided by the four-layer anti-resonant tube can significantly reduce the attenuation of hollow-core optical fiber, such as... Figure 3 As shown, the lowest loss in the LP01 mode of this invention is 0.027 dB / km.

[0039] Example 2:

[0040] A second embodiment of the invention, for example Figure 4 As shown, it differs from the first embodiment in that the third inner anti-resonator tube is tangent to the inner wall of the second inner anti-resonator tube and deflects to one side. That is, the line L1 connecting the curvature center of the third inner anti-resonator tube and the curvature center of the second inner anti-resonator tube forms a deflection angle of 50° with the line L2 connecting the geometric center of the fiber core and the curvature center of the outer anti-resonator tube.

[0041] Example 3:

[0042] A third embodiment of the invention, for example Figure 5 As shown, the difference between it and the second embodiment is that the second inner anti-resonator tube is tangent to the inner wall of the first inner anti-resonator tube and deflects to one side. That is, the line L3 connecting the curvature center of the second inner anti-resonator tube and the curvature center of the first inner anti-resonator tube and the line L4 connecting the geometric center of the fiber core and the curvature center of the outer anti-resonator tube form a deflection angle of 45°.

[0043] Example 4:

[0044] Fourth embodiment of the invention, for example Figure 6 As shown, it differs from the third embodiment in that the first inner anti-resonant tube is tangent to the inner wall of the outer anti-resonant tube and deflects to one side. That is, the line L5 connecting the curvature center of the first inner anti-resonant tube and the curvature center of the outer anti-resonant tube and the line L6 connecting the geometric center of the fiber core and the curvature center of the outer anti-resonant tube form a deflection angle of 60°.

[0045] The wall thicknesses h1, h2, h3, and h4 of the outer anti-resonator, the first inner anti-resonator, and the second inner anti-resonator are different and increase from the outside to the inside, respectively: 0.8 μm, 1 μm, 1.22 μm, and 1.35 μm.

[0046] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A low-loss hollow-core optical fiber, comprising an outer cladding and an inner cladding, wherein the inner cladding is composed of anti-resonant structural units, the anti-resonant structural units being arranged circumferentially along 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 forming the fiber core, characterized in that: The anti-resonance structure unit includes four or more circular anti-resonance tubes with different radii. The outer anti-resonance tube of the anti-resonance structure unit is tangent to the inner wall of the outer cladding. Two adjacent circular anti-resonance tubes are tangent to each other in sequence, and the positions of each tangent point alternate from the outside to the inside, on the side away from the geometric center of the fiber core and on the side close to the geometric center of the fiber core.

2. The low-loss hollow-core optical fiber according to claim 1, characterized in that: The aforementioned anti-resonance structure unit includes four layers of anti-resonance tubes with different radii, from the outside to the inside: an outer anti-resonance tube, a first inner anti-resonance tube, a second inner anti-resonance tube, and a third inner anti-resonance tube. The outer anti-resonance tube is tangent to the inner wall of the outer cladding; the first inner anti-resonance tube is tangent to the inner wall of the outer anti-resonance tube, with the tangency point on the side away from the geometric center of the fiber core; the second inner anti-resonance tube is tangent to the inner wall of the first inner anti-resonance tube, with the tangency point on the side closer to the geometric center of the fiber core; and the third inner anti-resonance tube is tangent to the inner wall of the second inner anti-resonance tube, with the tangency point on the side away from the geometric center of the fiber core.

3. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: The line connecting the curvature centers of each anti-resonator coincides with the extension of the line connecting the curvature center of the external anti-resonator and the geometric center of the fiber core.

4. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: At least one adjacent and tangent anti-resonator has a deflection angle formed by the line connecting the curvature centers of the two anti-resonator tubes and the line connecting the geometric center of the fiber core and the curvature center of the outer anti-resonator tube.

5. The low-loss hollow-core optical fiber according to claim 4, characterized in that: The deflection angle is greater than 0° and less than or equal to 90°.

6. The low-loss hollow-core optical fiber according to claim 2, characterized in that: The ratios of the outer diameters of the outer anti-resonant tube, the first inner anti-resonant tube, the second inner anti-resonant tube, and the third inner anti-resonant tube are 1:0.75~0.9:0.55~0.75:0.3~0.55, respectively.

7. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: The wall thickness of each internal anti-resonant tube is the same, ranging from 0.3 to 1.5 μm.

8. The low-loss hollow-core optical fiber according to claim 6, characterized in that: The wall thickness of each inner anti-resonator is different, and the thickness of each anti-resonator increases from the outside to the inside. The wall thickness of the outer anti-resonator is 0.8 to 1.22 μm, the wall thickness of the first inner anti-resonator is 0.8 to 1.5 μm, the wall thickness of the second inner anti-resonator is 0.8 to 1.5 μm, and the wall thickness of the third inner anti-resonator is 1.22 to 1.5 μm.

9. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: The inner cladding has 4 to 6 anti-resonant structural units.

10. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: Both the outer cladding and the inner wall are circular.

11. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: The substrate materials for both the outer cladding layer and the anti-resonance structural unit are pure quartz glass.

12. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: The core region and other inner cladding cavity regions are filled with gas.

13. The low-loss hollow-core optical fiber according to claim 12, characterized in that: The gas is argon, nitrogen, helium, air, or a mixture of multiple gases.

14. The low-loss hollow-core optical fiber according to claim 1 or 2, characterized in that: The LP01 mode loss of the optical fiber is less than 1 dB / km.

15. An application of a low-loss hollow-core optical fiber as described in any one of claims 1 to 14, characterized in that, The low-loss hollow fiber is used in communication, laser, or sensing fields.

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