Hollow-core Anti-resonant optical fiber with high single-mode performance and low loss

Abstract

The present invention relates to a hollow-core anti-resonant optical fiber with a high single-mode performance and low loss. The hollow-core anti-resonant optical fiber comprises an outer cladding and an inner cladding, wherein the inner cladding consists of nested structural units, which are arranged in the circumferential direction of the inner wall of the outer cladding and are connected to the inner wall of the outer cladding, and a central cavity enclosed by the inner cladding forms a fiber core. The hollow-core anti-resonant optical fiber is characterized in that each nested structural unit comprises two nested glass tubes with different radii, namely, an outer nested glass tube and an inner nested glass tube, and at least one inner nested glass tube is deflected to one side relative to the outer nested glass tube where the inner nested glass tube is located, with a deflection angle of 5-55°. In the present invention, by means of the modification of a cladding structure, combined with the rational and fabricable shape of the nested structural units, an optimized combination of nested dimensions and the deflection of the inner nested glass tubes, the leakage loss of an LP11 mode is significantly improved, and the influence on the fundamental mode performance is relatively small, thereby finally effectively improving the single-mode performance of the optical fiber.

Description

A high single-mode, low-loss hollow antiresonant optical fiber Technical Field

[0001] This invention relates to the field of hollow-core optical fiber technology, specifically to a high single-mode, low-loss hollow-core anti-resonant optical fiber, belonging to the field of optical communication and transmission technology. Background Technology

[0002] Hollow-core antiresonant fiber possesses a unique microstructure design that confines transmitted light waves within an air core, making it crucial for applications in fields such as light-filled material interactions, nonlinear optics, gas detection, gas laser generation, and optofluidics. Due to its unique structure and light-guiding mechanism, it achieves ultra-low Rayleigh scattering, low nonlinear coefficients, and tunable dispersion, providing a higher laser damage threshold and potential applications in high-power laser transmission, ultraviolet / mid-infrared light transmission, pulse compression, and optical soliton transmission. The ultra-low loss, low dispersion, low nonlinearity, and near-light-speed propagation of the air core enable the development of hollow-core fiber communication transmission and communication devices, laying the foundation for the construction and development of next-generation ultra-high-capacity, low-latency, and high-speed optical communication systems.

[0003] Even though hollow-core optical fiber has unique and significant advantages in design and application, its inherent lack of higher-order mode cutoff means that higher-order modes cannot be effectively filtered out like those in solid-core single-mode fiber. This greatly limits its application in short-distance transmission scenarios. Recent research has shown that, through reasonable structural design, the leakage loss of higher-order modes can be improved to some extent, thus producing an effect similar to single-mode after a certain distance.

[0004] A commonly used method for filtering higher-order modes is to select a high-attenuation cladding mode and, through structural design, achieve a high phase match with the LP11 mode in the fiber core, thereby effectively improving the leakage loss of the LP11 mode. The key factors in this design method are the inherent attenuation of the cladding mode and its phase match with the LP11 mode. Generally, the higher the attenuation of the cladding mode and the greater the phase match with the LP11 mode, the greater the improvement in LP11 mode leakage loss and the better the single-mode performance.

[0005] US Patent 11733451B2 discloses a single-ring hollow anti-resonant fiber. This patent proposes utilizing a high-loss anti-resonant unit (ARE) mode with a high phase match between the core LP11 mode. The structure is very simple, relatively easy to draw, and can achieve an ultra-high higher-order mode suppression ratio. By maintaining a cladding tube to core size ratio of approximately 0.68, a high degree of single-mode bandwidth can be achieved, with LP11 mode attenuation reaching 10%. 2The attenuation is in the dB / m range. However, this structure is difficult to achieve ultra-low attenuation transmission. The lowest attenuation currently achieved is 4.3 dB / km (1080 nm) in the near-infrared band, and the attenuation is even higher in the communication band. It also has poor bending resistance, so it does not have much advantage in many applications in the near-infrared band.

[0006] Chinese patent CN110515152B discloses a single-nested tube nodeless hollow-core anti-resonant fiber (NANF) and a double-nested tube nodeless hollow-core anti-resonant fiber (DNANF). Both structures effectively reduce the transmission loss of the fundamental mode by increasing the number of anti-resonant layers. For NANF fiber, the lowest attenuation has reached 0.22 dB / km, while DNANF has broken the record for the lowest attenuation of traditional solid-core fiber, reaching 0.11 dB / km. However, while achieving ultra-low attenuation, both fibers also maintain a relatively low LP11 mode loss. When the NANF structure achieves optimal resonant leakage design for the LP11 mode, the theoretical LP11 attenuation is approximately 10. 2 ~10 3 The attenuation is in the dB / km range, and under actual fabrication and placement conditions, the highest current attenuation is 2.6 dB / m. The native attenuation of its cladding mode has decreased significantly with increasing structural layers, thus the attenuation of the LP11 mode cannot reach a sufficiently high level. This situation is even more severe in DNANF structures: firstly, the attenuation of the cladding mode in DNANF structures is further reduced; secondly, the cladding region of DNANF structures does not have enough space for the LP11 mode to achieve sufficient phase matching with the cladding mode, and the theoretical attenuation of the LP11 mode is already below 10 dB / km. 2 dB / km, which means that DNANF fiber cannot effectively filter out higher-order modes, seriously affecting signal transmission quality. Summary of the Invention

[0007] The problem to be solved by the present invention is to provide a high single-mode, low-loss hollow anti-resonant optical fiber that addresses the shortcomings of the prior art by improving the loss of higher-order modes through changes in the cladding structure, thereby achieving high-purity single-mode transmission.

[0008] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: it includes an outer cladding layer and an inner cladding layer. The inner cladding layer is composed of nested structural units. The nested structural units are arranged circumferentially along the inner wall of the outer cladding layer and are connected to the inner wall of the outer cladding layer. The central cavity covered by the inner cladding layer forms a fiber core. The nested structural unit includes two nested glass tubes with different radii, including an outer nested glass tube and an inner nested glass tube. At least one inner nested glass tube is deflected to one side relative to the outer nested glass tube it is in, with a deflection angle of 5~55°.

[0009] According to the above scheme, the inner nested glass tube is deflected to one side relative to the outer nested glass tube. That is, the line L2 connecting the curvature center of the inner nested glass tube and the curvature center of the outer nested glass tube forms a deflection angle with the extension line L1 connecting the curvature center of the outer nested glass tube and the geometric center of the fiber core.

[0010] According to the above scheme, the inner cladding layer includes 4 to 6 nested structural units.

[0011] According to the above scheme, the nested structural units are evenly distributed circumferentially along the inner wall of the outer cladding.

[0012] According to the above scheme, both the outer cladding and the inner wall are circular.

[0013] According to the above scheme, the nested glass tube includes circular nested glass tubes with different radii, each circular nested glass tube is tangent to the others, and the outer nested glass tube is tangent to the inner wall of the outer cladding layer.

[0014] According to the above scheme, the nested glass tubes include arc-shaped nested glass tubes and circular nested glass tubes with different radii, wherein each arc-shaped nested glass tube intersects with the inner wall of the outer cladding layer, or each circular nested glass tube is tangent to the inner wall of the outer cladding layer.

[0015] According to the above scheme, the nested glass tubes include circular arc nested glass tubes with different radii, and each circular arc nested glass tube intersects with the inner wall of the outer cladding layer.

[0016] According to the above scheme, the multiple or all inner nested glass tubes are deflected to the same side relative to the outer nested glass tubes, and the deflection angles are the same or substantially the same.

[0017] According to the above scheme, the inner nested glass tube is partially deflected to one side and partially deflected to the other side relative to the outer nested glass tube.

[0018] According to the above scheme, the outer nested glass tube is an arc-shaped nested glass tube, and the inner nested tube is a circular nested glass tube or an arc-shaped nested glass tube.

[0019] According to the above scheme, the deflection angle is 15~45°; further, the deflection angle is 25~40°; further, the deflection angle is 30~40°.

[0020] According to the above scheme, the base material of the outer cladding layer and the nested structural unit is pure quartz glass.

[0021] According to the above scheme, the wall thickness of the inner and outer nested glass tubes is 0.3 to 1.5 μm.

[0022] According to the above scheme, the ratio of the outer diameter of the outer nested glass tube to the outer diameter of the inner nested glass tube is 1:0.35~0.6.

[0023] According to the above scheme, the core region and other cavity 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 scheme, the fundamental mode loss of the optical fiber is 0.4~2dB / km; furthermore, the attenuation value is less than 0.5 dB / km.

[0026] According to the above scheme, the higher-order mode loss of the optical fiber is 4~10dB / km; furthermore, the attenuation value is higher than 6 dB / m.

[0027] The beneficial effects of this invention are as follows: 1. In the structure of this invention, the inner cladding includes multiple layers of anti-resonant quartz walls and an air layer, effectively confining the transmitted fundamental mode within the fiber core, thus reducing confinement loss. This invention, through changes in the cladding structure, combines a reasonable and fabricable nested structure unit shape, optimized nesting size combinations, and the deflection of the inner nested glass tube, significantly improving the leakage loss of the LP11 mode with minimal impact on fundamental mode performance, ultimately effectively enhancing the single-mode performance of the optical fiber. The key to this invention is that, when optimizing the ratio of the outer diameter of the outer nested glass tube to the inner nested glass tube to the optimal value, the inner nested glass tube is deflected to one side within the outer nested glass tube. This structure can improve the leakage efficiency of the LP11 mode, thereby achieving higher single-mode performance. 2. This invention designs phase matching between the higher-order modes in the fiber core and the modes in the inner air region, and designs to increase the cladding mode loss, enabling more efficient leakage of higher-order modes and further improving higher-order mode attenuation, resulting in excellent single-mode transmission performance. 3. The single-mode performance of this invention does not exhibit wavelength selectivity, achieving high single-mode transmission within the operating wavelength range. This invention provides a hollow-core optical fiber that balances attenuation and single-mode characteristics, providing a high-performance transmission medium for fields such as high-speed communication, high-power transmission, gas lasers, and gas detection. Attached Figure Description

[0028] Figure 1 is a radial cross-sectional structural diagram of the first embodiment of the present invention.

[0029] Figure 2 is a partial enlarged view of one of the nested tubes in Figure 1.

[0030] Figure 3 is a radial cross-sectional structural diagram of the second embodiment of the present invention.

[0031] Figure 4 is a graph showing the variation of LP11 mode loss with rotation angle in the first embodiment of the present invention.

[0032] Figure 5 is a graph showing the variation of LP11 mode loss with geometry in the first embodiment of the present invention.

[0033] Figure 6 is a graph showing the variation of fundamental mode loss with wavelength in the first embodiment of the present invention.

[0034] Figure 7 is a radial cross-sectional structural diagram of the third embodiment of the present invention.

[0035] Figure 8 is a radial cross-sectional structural diagram of the fourth embodiment of the present invention. Embodiments of the present invention

[0036] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0037] A common method for filtering higher-order modes in hollow-core optical fibers is to select a high-attenuation cladding mode and, through structural design, achieve a high phase match with the LP11 mode in the fiber core, thereby effectively improving the leakage loss of the LP11 mode. The LP11 mode attenuation achieved through this design method can be estimated using the following formula:

[0038]

[0039] in, The imaginary part of the propagation constant of the LP11 mode after resonant filtering is given, and its value is related to the final loss. Proportional. The difference between the imaginary parts of the native propagation constants of the cladding mode and the LP11 mode represents the loss difference between the two modes in the initial state. K is the coupling coefficient between the two modes, which can be considered a constant here. The difference between the real parts of the propagation constants of the two modes represents the degree of phase matching between the two modes. The smaller this value is, the higher the degree of phase matching.

[0040] The above formula shows that the attenuation of the designed LP11 mode depends on the native attenuation of the cladding mode and its phase matching degree with the LP11 mode. Generally, the higher the attenuation of the cladding mode and the higher the phase matching degree with the LP11 mode, the greater the improvement in leakage of the LP11 mode and the better the single-mode performance. By adjusting the phase matching method alone (as shown by the dotted line in Figure 4), the attenuation of the LP11 mode can only reach the level of the perfect match point, i.e., the circular marker in Figure 4. After reaching the perfect match condition, this limitation can be broken by rotating the cladding glass tube, further increasing the loss of the LP11 mode (as shown by the solid line in Figure 4). At the star marker in Figure 4, the attenuation of the LP11 mode can reach 11 dB / m.

[0041] The first embodiment of the present invention is shown in Figures 1 and 2, including an outer cladding layer 1 and an inner cladding layer. The inner cladding layer is composed of 5 nested structural units, which are arranged circumferentially along the inner wall of the outer cladding layer. Each nested structural unit includes two nested glass tubes with different radii, including an outer nested glass tube 2 and an inner nested glass tube 3, forming an anti-resonance unit. The nested glass tubes include two circular nested glass tubes with different radii, wherein the diameter of the outer nested glass tube is d1 and the diameter of the inner nested glass tube is d2. The outer nested glass tube is tangent to the inner wall of the outer cladding layer. The inner nested glass tube is tangent to the outer nested glass tube and deflects to one side relative to the point of tangency between the outer nested glass tube and the inner wall of the outer cladding layer. That is, the line L2 connecting the curvature center (center) of the inner nested glass tube and the curvature center (center) of the outer nested glass tube forms a deflection angle L1 with the extension line L1 connecting the curvature center of the outer nested glass tube and the geometric center of the fiber core. The deflection angle is 35°, and the deflection direction of all inner nested glass tubes is the same. The central cavity enclosed by the inner cladding forms the fiber core 6. The fiber core region and other internal spaces, including the inner nested glass tube cavity 5 and the outer nested glass tube cavity 4, are filled with gas. The gas is argon, nitrogen, helium, air, or a mixture of multiple gases. Specifically, the relevant parameters in this embodiment are: the fiber core diameter D is 32 μm, the outer diameter d1 of the outer nested glass tube is 31.6 μm, the outer diameter d2 of the inner nested glass tube is 14.5 μm, and the ratio of the inner and outer nested glass tube diameters is 0.46; the inner diameter of the outer cladding (outer cladding cavity diameter) is 95 μm. In this embodiment, the wall thickness of each nested glass tube is 1.1 μm. When the wall thickness of each nested glass tube is approximately 0.95 μm, the second resonant operating band is extended to 1310 nm. When using the first anti-resonant window as the communication operating band, the wall thickness of each nested glass tube is approximately 0.5 μm. It should be noted that the fundamental mode leakage loss of hollow-core antiresonant fiber increases as the ratio of the outer to inner diameter of the nested glass tube decreases. However, the leakage loss of the LP11 mode does not increase indefinitely with this ratio; instead, it reaches a certain peak and then decreases. This peak corresponds to the point where the resonance between the LP11 mode and the cladding mode is strongest. Therefore, the improvement in LP11 mode loss achieved by adjusting this ratio is limited. This invention combines a reasonable and fabricable nested structure unit shape, an optimized nesting size combination, and the deflection of the inner glass tube, resulting in the following combined technical effects: significantly improved LP11 mode leakage loss with minimal impact on fundamental mode performance, ultimately effectively improving the single-mode performance of the fiber. As shown in Figure 4, when the ratio of the outer to inner diameter of the nested glass tube is 0.46 and the rotation angle is 35°, the LP11 mode loss is higher than 11 dB / m.

[0042] The second embodiment of the present invention is shown in Figure 3. It differs from the first embodiment in that two of the inner nested glass tubes are deflected to one side relative to the outer nested glass tubes, while the other three are deflected to the other side. The other structures are the same as the first embodiment.

[0043] The third embodiment of the present invention is shown in Figure 7. It differs from the first embodiment in that the outer nested glass tube is an arc-shaped nested glass tube with a circumferential angle of 280°. The outer arc-shaped nested glass tube intersects the inner wall of the outer cladding. The inner nested glass tube is a circular nested glass tube, tangent to the inner wall of the outer cladding. The line L2 connecting the curvature center (center) of the inner nested glass tube and the curvature center (center) of the outer nested glass tube forms a deflection angle L1 with the extension of the line connecting the curvature center of the outer nested glass tube and the geometric center of the fiber core. This deflection angle is 35°, and all inner nested glass tubes deflect in the same direction. Other structural features are the same as in the first embodiment.

[0044] The fourth embodiment of the present invention is shown in Figure 8. It differs from the first embodiment in that both the inner and outer nested glass tubes are arc-shaped nested glass tubes, with a circumferential angle of approximately 280° for both. Each arc-shaped nested glass tube intersects with the inner wall of the outer cladding. The line L2 connecting the curvature center (center) of the inner nested glass tube and the curvature center (center) of the outer nested glass tube forms a deflection angle of 35° with the extension line L1 connecting the curvature center of the outer nested glass tube and the geometric center of the fiber core. The deflection direction of all inner nested glass tubes is consistent. Other structural features are the same as in the first embodiment.

Claims

1. A high single-mode, low-loss hollow-core anti-resonant optical fiber, comprising an outer cladding and an inner cladding, wherein the inner cladding is composed of nested structural units 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 forms the fiber core, characterized in that... The nested structure unit includes two layers of nested glass tubes with different radii, including an outer nested glass tube and an inner nested glass tube. At least one inner nested glass tube is deflected to one side relative to the outer nested glass tube it is in, with a deflection angle of 5 to 55°.

2. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1, characterized in that... The inner nested glass tube is deflected to one side relative to the outer nested glass tube. That is, the line L2 connecting the curvature center of the inner nested glass tube and the curvature center of the outer nested glass tube forms a deflection angle with the extension line L1 connecting the curvature center of the outer nested glass tube and the geometric center of the fiber core.

3. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The inner cladding layer comprises 4 to 6 nested structural units.

4. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 3, characterized in that... The nested structural units are evenly distributed circumferentially along the inner wall of the outer cladding layer.

5. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 3, characterized in that... Both the outer cladding and the inner wall are circular.

6. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The nested glass tubes include circular nested glass tubes of different radii, all of which are tangent to each other, and the outer nested glass tube is tangent to the inner wall of the outer cladding layer.

7. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The nested glass tubes include arc-shaped nested glass tubes and circular nested glass tubes with different radii, wherein each arc-shaped nested glass tube intersects with the inner wall of the outer cladding layer, or each circular nested glass tube is tangent to the inner wall of the outer cladding layer.

8. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The nested glass tubes include circular arc nested glass tubes with different radii, and each circular arc nested glass tube intersects with the inner wall of the outer cladding layer.

9. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The multiple or all inner nested glass tubes are deflected to the same side relative to the outer nested glass tubes, and the deflection angles are the same or substantially the same.

10. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The inner nested glass tube is partially deflected to one side and partially deflected to the other side relative to the outer nested glass tube.

11. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The outer nested glass tube is an arc-shaped nested glass tube, and the inner nested tube is a circular nested glass tube or an arc-shaped nested glass tube.

12. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The deflection angle is 15~45°.

13. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The deflection angle is 25~40°.

14. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1, 2, or 3, characterized in that... The deflection angle is 30~40°.

15. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The base material for both the outer cladding layer and the nested structural unit is pure quartz glass.

16. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The wall thickness of the inner and outer nested glass tubes is 0.3 to 1.5 μm.

17. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The ratio of the outer diameter of the outer nested glass tube to the outer diameter of the inner nested glass tube is 1:0.35~0.

6.

18. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 1 or 2, characterized in that... The core region and other cavities within the outer cladding are filled with gas.

19. The high single-mode, low-loss hollow anti-resonant optical fiber according to claim 18, characterized in that... The gas is argon, nitrogen, helium, air, or a mixture of multiple gases.

20. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The fundamental mode loss of the optical fiber is less than 0.5 dB / km.

21. The high single-mode, low-loss hollow antiresonant optical fiber according to claim 1 or 2, characterized in that... The higher-order mode loss of the optical fiber is higher than 6 dB / m.

Images