High-single-mode low-loss hollow-core anti-resonance optical fiber

Abstract

The invention relates to a high-single-mode low-loss hollow-core anti-resonance optical fiber which comprises an outer cladding and an inner cladding, the inner cladding is composed of nested structure units, the nested structure units are arranged in the circumferential direction of the inner wall of the outer cladding and are connected with the inner wall of the outer cladding, a fiber core is formed by a central cavity wrapped by the inner cladding, and the fiber core is connected with the inner cladding through the nested structure units. The nesting structure is characterized in that each nesting structure unit comprises two layers of nesting glass tubes with different radiuses, the nesting glass tubes comprise outer nesting glass tubes and inner nesting glass tubes, at least one inner nesting glass tube deflects towards one side relative to the outer nesting glass tube where the inner nesting glass tube is located, and the deflection included angle ranges from 5 degrees to 55 degrees. According to the invention, through the change of the cladding structure, the reasonable nested structure unit shape capable of being prepared, the optimized nested size combination and the deflection of the embedded glass tube, the leakage loss of the LP11 mode is obviously improved, the influence on the fundamental mode performance is small, and finally the single-mode performance of the optical fiber is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of hollow core optical fibers, in particular to a high single-mode low-loss hollow core anti-resonance optical fiber, belonging to the technical field of optical communication and transmission. Background Art

[0002] Hollow-core antiresonant optical fiber has a unique microstructure design that can confine the transmitted light wave in the air core, and has important applications in the fields of interaction between light and filling materials, nonlinear optics, gas detection, gas laser generation, optofluidic technology, etc.; due to its unique structure and light-guiding mechanism, it can obtain ultra-low Rayleigh scattering, low nonlinear coefficient, and adjustable dispersion characteristics, which can provide a higher laser damage threshold, making it potentially applicable in high-power laser transmission, ultraviolet / mid-infrared light transmission, pulse compression, and optical soliton transmission; the air core's ultra-low loss, low dispersion, low nonlinearity, and propagation speed close to the speed of light can realize the development of hollow-core optical fiber communication transmission and communication devices, laying the foundation for the construction and development of the next generation of ultra-large capacity, low-latency, and high-speed optical communication systems.

[0003] Even though hollow-core optical fiber has unique and huge advantages in design and application, the high-order modes of hollow-core optical fiber cannot be effectively filtered out like solid-core single-mode optical fiber because it does not naturally have high-order mode cutoff conditions. This will greatly limit its application scenarios in short-distance transmission. Research work in recent years has shown that reasonable structural design can improve the leakage loss of high-order mode modes to a certain extent, thereby producing an effect close to single-mode after a certain distance.

[0004] The commonly used method for filtering out high-order modes is to select a high-attenuation cladding mode and make it highly phase-matched with the LP11 mode in the fiber core through structural design, thereby effectively improving the leakage loss of the LP11 mode. The key factors in this design method are: the native attenuation of the cladding mode and its phase matching with the LP11 mode. Generally speaking, the higher the attenuation of the cladding mode and the higher the phase matching with the LP11 mode, the greater the improvement in the leakage of the LP11 mode and the better the single-mode property.

[0005] US Patent US11733451B2 discloses a single-ring hollow core antiresonant fiber. The patent proposes to use the high-loss antiresonant unit (ARE) mode to highly phase-match the core LP11 mode. The structure is very simple, the drawing difficulty is relatively low, and it can achieve an ultra-high high-order mode suppression ratio. When the cladding tube and core size ratio is about 0.68, a broadband high single-mode effect can be achieved, and the LP11 mode attenuation can reach 10 2However, this structure is difficult to achieve ultra-low attenuation transmission. Currently, the lowest attenuation in the near-infrared band is 4.3dB / km (1080nm), and the attenuation in the communication band is even higher. In addition, the bending resistance is poor, 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 antiresonant fiber (Nested Anti-Resonant Nodeless Fiber, NANF) and a double nested tube nodeless hollow core antiresonant fiber (Double Nested Anti-Resonant Nodeless Fiber, DNANF). These two structures effectively reduce the transmission loss of the fundamental mode by increasing the number of antiresonant layers. For NANF fiber, its minimum attenuation has reached 0.22dB / km, and DNANF has broken the minimum attenuation record of traditional solid core fiber, reaching 0.11dB / km. However, while achieving ultra-low attenuation, the above two optical fibers also keep the loss of the LP11 mode at a very low level. When the NANF structure realizes the optimal resonant leakage design of the LP11 mode, the theoretical LP11 attenuation is about 10 2 ~10 3 dB / km level, under actual manufacturing and placement conditions, the current maximum can reach 2.6dB / m. The native attenuation of its cladding mode has been greatly reduced with the increase in the number of structural layers, so the attenuation of the LP11 mode cannot reach a sufficiently high level. This situation is more serious in the DNANF structure: first, the attenuation of the cladding mode in the DNANF structure is further reduced; second, there is not enough space in the cladding area of ​​the DNANF structure to achieve sufficient phase matching between the LP11 mode and the cladding mode, and the theoretical attenuation of the LP11 mode is already less than 10 2 dB / km, which means that DNANF fiber cannot effectively filter out high-order modes, seriously affecting the 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-core anti-resonant optical fiber in view of the deficiencies in the above-mentioned prior art, and to improve the high-order mode loss and realize high-purity single-mode transmission by changing the cladding structure.

[0008] 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 nested structural units, the nested 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 nested structural units include two layers of nested glass tubes with different radii, including 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 it is located, and the deflection angle is 5 to 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 center of curvature of the inner nested glass tube and the center of curvature of the outer nested glass tube forms a deflection angle with the extended line L1 connecting the center of curvature 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 solution, the nested structural units are evenly spaced along the circumference of the inner wall of the outer cladding.

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

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

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

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

[0016] According to the above solution, the plurality or all of the 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 tubes are arc-shaped nested glass tubes, and the inner nested tubes are circular nested glass tubes or arc-shaped nested glass tubes.

[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 solution, the outer cladding layer and the base material of the nested structural unit are both 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 diameters of the outer nested glass tube and the inner nested glass tube is 1:0.35-0.6.

[0023] According to the above scheme, 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 fundamental mode loss of the optical fiber is 0.4-2dB / km; further, the attenuation value is lower than 0.5dB / km.

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

[0027] The beneficial effects of the present invention are as follows: 1. In the structure of the present invention, the inner cladding includes a multi-layer anti-resonant quartz wall and an air layer, and the transmitted fundamental mode is effectively confined in the core, and the limiting loss is reduced; the present invention significantly improves the leakage loss of the LP11 mode through the change of the cladding structure, and has a reasonable and manufacturable nested structural unit shape, an optimized nested size combination and a deflection of the inner nested glass tube, and has a small impact on the fundamental mode performance, and finally effectively improves the single-mode performance of the optical fiber. The key to the present invention is that when the ratio of the outer diameter of the outer nested glass tube to the inner nested glass tube is optimized to the best, the inner nested glass tube is deflected to one side in the outer nested glass tube, and the structure can improve the leakage efficiency of the LP11 mode, thereby obtaining higher single-mode performance. 2. The present invention designs the phase matching of the core high-order mode and the mode of the inner air region, and designs to increase the cladding mode loss, so that the high-order mode leaks more efficiently, further improves the attenuation of the high-order mode, and has excellent single-mode transmission performance; 3. The single-mode performance of the present invention does not have wavelength selectivity, and highly single-mode transmission can be achieved within the working wavelength. The present invention provides a hollow core optical fiber that takes into account both attenuation and single-mode characteristics, and provides a transmission medium with excellent performance for the fields of high-speed communication, high-power transmission, gas lasers, gas detection, etc. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 yes Figure 1 A magnified detail of one of the nested tubes.

[0030] Figure 3 It 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 It is a curve diagram showing the variation of LP11 mode loss with geometric dimensions in the first embodiment of the present invention.

[0033] Figure 6 This is a curve diagram of fundamental mode loss versus wavelength in the first embodiment of the present invention.

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

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

[0036] The present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings.

[0037] The commonly used high-order mode filtering method in hollow-core optical fiber is to select a high-attenuation cladding mode and make it highly phase-matched with the LP11 mode in the core through structural design, thereby effectively improving the leakage loss of the LP11 mode. The LP11 mode attenuation achieved by this design method can be estimated by the following formula:

[0038]

[0039] in, is the imaginary part of the propagation constant of the LP11 mode after resonant filtering, and its value is related to the final loss α′ 11 Directly proportional. is the difference between the imaginary parts of the native propagation constants of the cladding mode and the LP11 mode, representing the difference in loss between the two modes in the initial state. K is the coupling coefficient between the two modes, which can be regarded as a constant here. It is the difference between the real parts of the propagation constants of the two modes, representing the phase matching degree of the two modes. The smaller the value, the higher the phase matching degree.

[0040] The above formula shows that the designed LP11 mode attenuation depends on the original attenuation of the cladding mode and its phase matching with the LP11 mode. In general, the higher the attenuation of the cladding mode and the higher the phase matching with the LP11 mode, the greater the leakage improvement of the LP11 mode and the better the single-mode performance. Figure 4 The attenuation of the LP11 mode can only reach the level of the perfect matching point, that is, Figure 4 After reaching the perfect matching condition, this limitation can be overcome by rotating the cladding glass tube and further improving the loss of the LP11 mode (e.g. Figure 4 ). Figure 4 At the star mark point in the figure, the attenuation of LP11 mode can reach 11dB / m.

[0041] The first embodiment of the present invention is Figure 1 , 2As shown, it includes an outer cladding 1 and an inner cladding, the inner cladding is composed of 5 nested structural units, the nested structural units are arranged along the circumference of the inner wall of the outer cladding, the nested structural units include 2 layers of 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 2 circular nested glass tubes with different radii, wherein the diameter of the outer nested glass tube is d1, 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, the inner nested glass tube is tangent to the outer nested glass tube and deflected to one side relative to the tangent point between the outer nested glass tube and the inner cavity wall of the outer cladding, that is, the line L2 connecting the center of curvature (center of circle) of the inner nested glass tube and the center of curvature (center of circle) of the outer nested glass tube forms a deflection angle with the extended line L1 connecting the center of curvature of the outer nested glass tube and the geometric center of the fiber core, the deflection angle is 35°, and the deflection directions of all the inner nested glass tubes are consistent. The central cavity covered by the inner cladding forms a core 6, and the 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 of this embodiment are: the core diameter D is 32μm, the outer diameter d1 of the outer nested glass tube is 31.6μm, the outer diameter d2 of the inner nested glass tube is 14.5μm, and the ratio to the outer diameter of the outer nested glass tube is 0.46; the inner diameter of the outer cladding (the outer cladding cavity diameter) is 95μm. In this embodiment, the wall thickness of each nested glass tube is 1.1μm. When the wall thickness of each nested glass tube is about 0.95μm, the second resonant working band is extended to 1310nm. When the first anti-resonance window is used as the communication working band, the wall thickness of each nested glass tube is about 0.5μm. It should be noted that the fundamental mode leakage loss of the hollow-core antiresonant optical fiber increases with the decrease in the ratio of the outer diameter of the outer nested glass tube to the inner nested glass tube. However, the leakage loss of the LP11 mode does not continue to increase with the decrease in this ratio, but reaches a peak value and then decreases. This peak value corresponds to the strongest point of resonance between the LP11 mode and the cladding mode. Therefore, the improvement in the LP11 mode loss achieved by adjusting this ratio is limited. The present invention combines a reasonable and manufacturable nested structural unit shape, an optimized nested size combination, and the deflection of the inner nested glass tube, which comprehensively produces the following technical effects: significantly improving the leakage loss of the LP11 mode, with little effect on the fundamental mode performance, and ultimately effectively improving the single-mode performance of the optical fiber. Figure 4 As shown, when the ratio of the outer diameter of the outer nested glass tube to the inner nested glass tube is 0.46 and the rotation angle is 35°, the LP11 mode loss is higher than 11dB / m.

[0042] The second embodiment of the present invention is Figure 3As shown, the difference between the first embodiment and the second embodiment is that two of the inner nested glass tubes are deflected to one side relative to the outer nested glass tubes, and the other three are deflected to the other side. The other structures are the same as those of the first embodiment.

[0043] The third embodiment of the present invention is Figure 7 As shown, the difference between it and the first embodiment is that the outer nested glass tube is an arc nested glass tube, the circumferential angle of the arc is 280°, wherein the outer arc nested glass tube intersects with the inner wall of the outer cladding, the inner nested glass tube is a circular nested glass tube, the circular inner nested glass tube is tangent to the inner wall of the outer cladding, the line L2 connecting the center of curvature (center of circle) of the inner nested glass tube and the center of curvature (center of circle) of the outer nested glass tube, and the extended line L1 connecting the center of curvature of the outer nested glass tube and the geometric center of the fiber core form a deflection angle of 35°, and the deflection direction of all the inner nested glass tubes is consistent. The other structures are the same as those of the first embodiment.

[0044] The fourth embodiment of the present invention is Figure 8 As shown, the difference between it and the first embodiment is that the inner and outer nested glass tubes are both arc-shaped nested glass tubes, the circumferential angles of the arc-shaped inner and outer nested glass tubes are both about 280°, and the inner and outer arc-shaped nested glass tubes intersect with the inner wall of the outer cladding. The line L2 connecting the center of curvature (center of circle) of the inner nested glass tube and the center of curvature (center of circle) of the outer nested glass tube forms a deflection angle with the extended line L1 connecting the center of curvature of the outer nested glass tube and the geometric center of the fiber core, and the deflection angle is 35°, and the deflection directions of all the inner nested glass tubes are consistent. The other structures are the same as those of the first embodiment.

Claims

1. A high single-mode low-loss hollow-core antiresonant optical fiber, comprising an outer cladding and an inner cladding, wherein the inner cladding is composed of nested structural units, the nested 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 nested structural 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 where it is located, and the deflection angle is 5-55°.

2. The high single-mode low-loss hollow-core antiresonant 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 extended 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-core antiresonant 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-core antiresonant optical fiber according to claim 3, characterized in that The nested structural units are evenly spaced along the circumference of the inner wall of the outer cladding.

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

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

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

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

9. The high single-mode low-loss hollow-core 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-core antiresonant 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-core antiresonant optical fiber according to claim 1 or 2, characterized in that The outer nested glass tubes are arc-shaped nested glass tubes, and the inner nested glass tubes are circular nested glass tubes or arc-shaped nested glass tubes.

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

16. The high single-mode low-loss hollow-core 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-core antiresonant optical fiber according to claim 1 or 2, characterized in that The ratio of the outer diameters of the outer nested glass tube to the inner nested glass tube is 1:0.35-0.

6.

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

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

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

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