Hollow-core optical fiber and preparation method thereof

Abstract

The invention discloses a hollow-core optical fiber and a preparation method thereof, the hollow-core optical fiber comprises a coating layer, an inward concave negative curvature structure outer cladding layer, 12 or more anti-resonance units and an inflation fiber core, the coating layer is arranged outside the inward concave negative curvature structure outer cladding layer, the number of the anti-resonance units is 12 or more, and the inflation fiber core is arranged between the coating layer and the negative curvature structure outer cladding layer. The inflation fiber core is located at the central position of the hollow-core optical fiber, and the inflation fiber core is tangent to the outer wall of the anti-resonance unit on the periphery of the inflation fiber core. The hollow-core optical fiber has the advantages of low confinement loss, low nonlinear coefficient and flat dispersion; a plurality of nested structures can be better maintained, the wall thickness can be kept to meet the anti-resonance condition, the area of gaps between nested pipes is reduced, attenuation is reduced, meanwhile, the bending performance of the hollow-core optical fiber is optimized through reduction of substrate loss, the signal transmission efficiency is improved, and the anti-interference capability is enhanced; and the aluminum oxide transparent ceramic base tube which is more resistant to high temperature and corrosion is adopted, so that the optical performance of the hollow-core optical fiber is optimized.

Description

Technical Field

[0001] The invention belongs to the technical field of optical communication, and in particular relates to a hollow core optical fiber and a preparation method thereof. Background Art

[0002] With the rapid development of emerging technologies such as big data, cloud computing, and the Internet of Things, the performance requirements for optical communication systems are increasing. In order to overcome the limitations of traditional optical fibers in terms of capacity, transmission distance, and latency, hollow-core optical fibers have attracted much attention due to their unique structure and excellent performance. The structural design of hollow-core optical fibers has an important influence on their performance. How to optimize the arrangement, size, and shape of air holes to achieve lower losses is a hot topic and difficulty in current research.

[0003] The existing ultra-low loss anti-resonant hollow-core optical fiber generally adopts ≥5 tube structural units (5-fold symmetric structure), and the core mode field presents pentagons, hexagons or quasi-circular shapes. This structure is an ideal structure when making a two-layer nested tube structure. However, in order to further reduce the loss, it is necessary to increase the number of anti-resonant layers. When designing a three-layer anti-resonant layer structure, some problems will arise: since the air layer area is not enough to filter out the high-order mode, it is not easy to achieve good single-mode characteristics. Usually, the difference between the fundamental mode loss and the high-order mode loss is only about one order of magnitude, and the high-order mode is prone to crosstalk with the fundamental mode; in order to achieve a high high-order mode suppression ratio, the area of ​​a certain air layer has to be reduced, which may put the air layer in a resonant state, thereby increasing the limiting loss or bending loss. At the same time, due to the special structure of the hollow-core optical fiber, its bending performance is relatively poor, and it is easy to produce large losses when bending, affecting the transmission efficiency of light.

[0004] The Chinese invention patent, publication number CN115745391A, discloses an integrated hollow-core optical fiber preform, optical fiber and preparation method thereof, wherein the initial preform is obtained by drilling, and then the optical fiber with antiresonant ring structure is prepared by introducing gas into the hole during the drawing process for pressurization control. The focus is on simplifying complex profiles and designing thinner wall thickness to improve attenuation, but there is no further improvement in other parameter performance.

[0005] The Chinese invention patent, publication number CN117388980A, discloses an ultra-low attenuation single-mode hollow-core optical fiber and its preparation method. The radial cross-section of the inner cavity of the outer cladding is a regular quadrilateral or a quasi-regular quadrilateral, maintaining a 4-nested unit structure and maintaining a wall thickness that meets the anti-resonance condition. The quasi-quasi-quasi-inner cavity is formed by adding filling layers to the upper, lower, left and right edges of the circular base cavity. The focus is on reducing the crosstalk between the anti-resonance hollow-core optical fiber fundamental mode and the high-order mode to maintain the single-mode output characteristics, but no further research has been done on the improvement of attenuation and bending performance.

[0006] None of the above patents mentions research on the direction of reducing bending loss. Summary of the invention

[0007] In order to solve the technical problems existing in the prior art, the object of the present invention is to provide a hollow core optical fiber and a preparation method thereof.

[0008] In order to achieve the above purpose and the above technical effect, the technical solution adopted by the present invention is:

[0009] A hollow core optical fiber comprises a coating layer, an inwardly concave outer cladding with a negative curvature structure, an anti-resonance unit and an air-filled core, wherein the coating layer is arranged outside the inwardly concave outer cladding with a negative curvature structure, 12 or more anti-resonance units are arranged in total and are evenly arranged on the inner cavity wall of the inwardly concave outer cladding with a negative curvature structure, the air-filled core is located at the central position of the hollow core optical fiber, and the air-filled core is tangent to the outer wall of the anti-resonance unit on its periphery.

[0010] Furthermore, the outer cladding of the inwardly concave negative curvature structure is made of a highly transparent alumina ceramic base tube, and the real part of the refractive index is 1.2-1.8 μm.

[0011] Furthermore, the anti-resonance unit is formed by nesting a plurality of capillaries with different diameters in sequence from the inside to the outside.

[0012] Furthermore, each anti-resonance unit is composed of three capillaries of different diameters nested in sequence from the inside to the outside. The three capillaries of different diameters are recorded as the first capillary, the second capillary, and the third capillary from the outside to the inside. The inner wall of the first capillary is tangent to the outer wall of the second capillary, and the inner wall of the second capillary is tangent to the outer wall of the third capillary.

[0013] Furthermore, the diameter of the first capillary is 18-27 μm, the diameter of the second capillary is 13-17 μm, and the diameter of the third capillary is 8-12 μm.

[0014] Furthermore, the diameter of the first capillary is 25.03 μm, the diameter of the second capillary is 16.86 μm, and the diameter of the third capillary is 11.36 μm.

[0015] Furthermore, the diameter of the first capillary is 19.87 μm, the diameter of the second capillary is 13.39 μm, and the diameter of the third capillary is 9.02 μm.

[0016] Furthermore, the total diameter of the hollow-core optical fiber is 240-250 μm, the total diameter of the hollow-core optical fiber excluding the coating layer is 110-150 μm, and the diameter of the air-filled core is 33-45 μm.

[0017] The present invention also discloses a method for preparing a hollow core optical fiber, comprising the following steps:

[0018] S1: Drawing several capillaries with different diameters through the tube drawing platform;

[0019] S2: Capillaries of different diameters are made into anti-resonance units;

[0020] S3: All anti-resonance units are evenly glued to the inner wall of the concave area of ​​the outer sleeve, and the capillary and the outer sleeve are bonded together through a welding process. The assembled structure is vacuum treated so that the vacuum degree reaches 10 -6 mbar or even higher, which is convenient for subsequent filling with special gases with low refractive index;

[0021] S4: After welding is completed, stretching and drawing are carried out. During the drawing process, an inwardly concave negative curvature structure boundary is formed through the action of pressure difference and surface tension, thereby forming an anti-resonant nested structure surrounded by an inwardly concave negative curvature structure outer cladding; then filled with low refractive index gas to further reduce the transmission loss of light in the optical fiber.

[0022] Furthermore, the low refractive index gas is any one of compressed air, nitrogen, helium, and argon, or a combination of several of them.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The inwardly concave negative curvature structure disclosed in the present invention has 12 sides or more of the radial cross section of the inner cavity of the outer cladding layer having a negative curvature structure, and the hollow-core optical fiber made therefrom has the advantages of low limiting loss, low nonlinear coefficient, and flat dispersion;

[0025] 2) The present invention can better maintain the nested structure of multiple capillaries and keep the wall thickness to meet the anti-resonance condition, reduce the area of ​​the nested tubes, i.e. the gap between the capillaries, reduce attenuation, and at the same time, the reduction of substrate loss optimizes the bending performance of the hollow-core optical fiber, improves the signal transmission efficiency, and enhances the anti-interference ability;

[0026] 3) The inwardly concave negative curvature structure outer cladding disclosed in the present invention is made of a high-transparency alumina ceramic base tube that is more resistant to high temperature and corrosion, and the real part of the refractive index is 1.2-1.8μm, which is convenient for better control of the refractive index of the hollow-core optical fiber. At the same time, its good light transmittance can reduce the loss and significantly optimize the optical performance of the hollow-core optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0029] A brief summary of one or more aspects is given below to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceived aspects, and is neither intended to identify the key or critical elements of all aspects nor to define the scope of any or all aspects. Its only purpose is to give some concepts of one or more aspects in a simplified form as a prelude to a more detailed description that will be given later.

[0030] like Figure 1 As shown, the present invention discloses a hollow-core optical fiber, comprising a coating layer 1, an outer cladding 2 with a negative curvature structure that is concave inward, an anti-resonance unit 3 and an air-filled core 4, wherein the coating layer 1 is arranged outside the outer cladding 2 with a negative curvature structure that is concave inward, and the 12 sides and above of the radial cross-section of the inner cavity of the outer cladding are all negative curvature structures, and there are 12 or more anti-resonance units 3, which are evenly arranged on the inner cavity wall of the outer cladding 2 with a negative curvature structure that is concave inward, and the air-filled core 4 is located in the central position of the hollow-core optical fiber, and the air-filled core 4 is tangent to the outer wall of the anti-resonance unit 3 around it. The present invention can reduce optical fiber loss and bending loss by designing the outer cladding 2 with a negative curvature structure that is concave inward, and can solve the problem that the ordinary outer cladding has a circular boundary and a large loss.

[0031] In some embodiments, the total diameter of the hollow core optical fiber is 240-250 μm, the total diameter of the hollow core optical fiber excluding the coating layer 1 is 110-150 μm, and the diameter of the air-filled core 4 is 33-45 μm.

[0032] In some embodiments, the coating layer 1 is made of MgAl2O4, which is still stable at a high temperature of 1200°C. The purpose of designing the coating layer 1 is: the hollow-core optical fiber has a special structure, and the air-filled core 4 is an air core. By setting the coating layer 1, foreign matter can be prevented from entering the hollow-core optical fiber structure, thereby avoiding interference with the optical performance of the optical fiber.

[0033] In some embodiments, the anti-resonance unit is formed by nesting a plurality of capillaries of different diameters from the inside to the outside. Preferably, each anti-resonance unit 3 is formed by nesting three capillaries of different diameters in sequence, and the three capillaries of different diameters are sequentially recorded as the first capillary 5, the second capillary 6, and the third capillary 7 from the outside to the inside, and the inner and outer walls of the three capillaries are sequentially tangent, specifically, the inner wall of the first capillary 5 is tangent to the outer wall of the second capillary 6, and the inner wall of the second capillary 6 is tangent to the outer wall of the third capillary 7.

[0034] In some embodiments, the diameter of the first capillary 5 is 18-27 μm, the diameter of the second capillary 6 is 13-17 μm, and the diameter of the third capillary 7 is 8-12 μm.

[0035] In some embodiments, the capillary is made of quartz material.

[0036] In some embodiments, the outer sleeve is made of a highly transparent alumina ceramic base tube with a real part of the refractive index of 1.2-1.8 μm, which is used to form an outer cladding 2 with a negative curvature structure that is concave inward.

[0037] The present invention also discloses a method for preparing a hollow core optical fiber, comprising the following steps:

[0038] S1: Draw several capillaries of different diameters with the required specifications through the tube drawing platform, and wash various assembly materials or instruments including the capillaries with water. During the washing, insert M3 paper into the capillaries to remove the glass slag in the tubes through the water pressure to prevent breakage during extension;

[0039] S2: assembling the capillaries into anti-resonance units 3 by means of an assembly platform in a nested order from the inside to the outside, and manufacturing all the anti-resonance units 3 in the same manner;

[0040] S3: All anti-resonance units 3 are evenly glued to the inner wall of the concave area of ​​the outer sleeve to maintain the overall shape and integrity of the subsequently drawn optical fiber and the circular cross-sectional shape of the hollow-core optical fiber. The capillary and the outer sleeve are bonded together through a welding process, and the assembled structure is vacuum treated so that the vacuum degree reaches 10 -6 mbar or even higher, which is convenient for subsequent filling of special gases with low refractive index. After welding the tail tube, slowly cool it down to prevent the tube structure from cracking due to stress caused by excessive heating. Tail tube welding helps the hollow-core optical fiber intermediate to form a sealed structure to prevent external impurities such as water vapor and dust from entering. It should be noted that if the pressure divider has been installed, the tail tube does not need to be welded;

[0041] S4: After welding is completed, stretching and wire drawing are carried out. During the wire drawing process, an inwardly concave negative curvature structure boundary is formed through the action of pressure difference and surface tension, thereby forming an anti-resonance nested structure surrounded by an inwardly concave negative curvature structure outer cladding 2; then fill with a low refractive index gas to further reduce the transmission loss of light in the optical fiber. Preferably, the gas filled in this step is any one or a combination of several of compressed air, nitrogen, helium, and argon. The nodeless anti-resonance cavity constitutes the inner cladding. The diameter of the air-filled core 4 is controlled at 33-45μm, the minimum wall thickness of the anti-resonance nested structure is ≤1μm, and the wall thickness of the anti-resonance unit 3 formed by sequentially nesting capillaries of different diameters meets the anti-resonance reflection condition.

[0042] The hollow-core optical fiber structure prepared by the present invention has low transmission loss, can have low limiting loss in a large wavelength range in the 1.87-4μm band, a large mode field area, and near-zero flat dispersion with a dispersion coefficient between 0±0.45ps / (nm / km) in the 1.46-1.65μm wavelength range, meeting the needs of optical communication and optical fiber sensing. This hollow-core optical fiber structure can reduce the fundamental mode transmission loss to below 0.08dB / km, and maintain a difference of 2-3 orders of magnitude from the higher-order mode loss, thereby avoiding crosstalk between modes and achieving single-mode transmission.

[0043] Example 1

[0044] like Figure 1 As shown, a hollow-core optical fiber comprises a coating layer 1, an outer cladding 2 with a negative curvature structure recessed inwardly, an antiresonance unit 3 and an air-filled core 4, wherein the coating layer 1 is arranged outside the outer cladding 2 with a negative curvature structure recessed inwardly, 12 sides of the radial cross section of the inner cavity of the outer cladding are all negative curvature structures, there are 12 antiresonance units 3, which are evenly arranged on the inner cavity wall of the outer cladding 2 with a negative curvature structure recessed inwardly, the air-filled core 4 is located at the central position of the hollow-core optical fiber, and the air-filled core 4 is tangent to the outer wall of the antiresonance unit 3 around it, and by designing the outer cladding 2 with a negative curvature structure recessed inwardly, the optical fiber loss and bending loss can be reduced, and the problem that the ordinary outer cladding has a circular boundary and a large loss can be solved.

[0045] In this embodiment, the total diameter of the hollow core optical fiber is 245 μm, the total diameter of the hollow core optical fiber excluding the coating layer 1 is 110 μm, and the diameter of the air-filled core 4 is 36 μm.

[0046] The coating layer 1 is made of MgAl2O4, which is still stable at a high temperature of 1200°C. The purpose of designing the coating layer 1 is: the hollow-core optical fiber has a special structure, and the air-filled core 4 is an air core. By setting the coating layer 1, foreign substances can be prevented from entering the hollow-core optical fiber structure, thereby avoiding interference with the optical performance of the optical fiber.

[0047] Each anti-resonance unit 3 is composed of three capillaries of different diameters nested in sequence. The capillaries are made of quartz material. The three capillaries of different diameters are recorded as the first capillary 5, the second capillary 6, and the third capillary 7 from the outside to the inside. The inner and outer walls of the three capillaries are tangent to each other in sequence. The inner wall of the first capillary 5 is tangent to the outer wall of the second capillary 6, and the inner wall of the second capillary 6 is tangent to the outer wall of the third capillary 7. The diameter of the first capillary 5 is d1=19.87μm, the diameter of the second capillary 6 is d2=13.39μm, and the diameter of the third capillary 7 is d3=9.02μm.

[0048] The outer sleeve adopts a highly transparent alumina ceramic base tube with a thickness of 0.75 μm and a real part of the refractive index of 1.76 μm, which is used to form an inwardly concave negative curvature structure outer cladding 2 and satisfies d1 / D=0.552, where D is the diameter of the air-filled core 4.

[0049] A method for preparing a hollow core optical fiber comprises the following steps:

[0050] S1: drawing a first capillary 5, a second capillary 6, and a third capillary 7 of required specifications through a tube drawing platform, and washing the assembly materials including the first capillary 5, the second capillary 6, and the third capillary 7 with water, inserting M3 paper into the capillary during the washing, and removing glass slag in the tube by the action of water pressure to prevent breakage during extension;

[0051] S2: assembling a third capillary 7, a second capillary 6, and a first capillary 5 into an anti-resonance unit 3 by assembling the platform in a nested order from the inside to the outside. Similarly, 12 anti-resonance units 3 are manufactured in the same way;

[0052] S3: All anti-resonance units 3 are evenly glued to the inner wall of the concave area of ​​the outer sleeve to maintain the overall shape and integrity of the subsequently drawn optical fiber and the circular cross-sectional shape of the hollow-core optical fiber. The capillary and the outer sleeve are bonded together through a welding process, and the assembled structure is vacuum treated so that the vacuum degree reaches 10 -6 mbar, which is convenient for subsequent filling of special gases with low refractive index. After welding the tail tube, slowly cool it down to prevent the tube structure from cracking due to stress caused by excessive heating. Tail tube welding helps the hollow-core optical fiber intermediate to form a sealed structure to prevent the entry of external impurities such as water vapor and dust. If the pressure divider device has been installed, the tail tube does not need to be welded;

[0053] S4: After welding is completed, stretching and drawing are carried out. During the drawing process, the pressure difference and surface tension form an inwardly concave negative curvature structure boundary, thereby forming an anti-resonance nested structure surrounded by an inwardly concave negative curvature structure outer cladding 2; then fill with low refractive index nitrogen to further reduce the transmission loss of light in the optical fiber. The nodeless anti-resonance cavity constitutes the inner cladding. The diameter of the air-filled core 4 is controlled at 36μm, the minimum wall thickness of the anti-resonance nested structure is 1μm, and the wall thickness of the anti-resonance unit 3 formed by sequentially nesting capillaries of different diameters meets the anti-resonance reflection condition.

[0054] The hollow-core optical fiber structure prepared by this embodiment has low transmission loss, can have low limiting loss in a large wavelength range in the 1.87-4μm band, a large mode field area, and a near-zero flat dispersion with a dispersion coefficient of about 0.26ps / (nm / km) in the 1.46-1.65μm wavelength range. It also has good single-mode characteristics at 3μm, meeting the needs of optical communication and optical fiber sensing. The loss in the 1550-1610nm range is 0.182db / km, which is on par with the performance of the latest generation of glass core optical fibers. At the extreme bending radius of 0.25cm, the bending loss of the hollow-core optical fiber is measured to be 3.56×10 -3 dB@1550nm.

[0055] Example 2

[0056] like Figure 1 As shown, a hollow-core optical fiber comprises a coating layer 1, an outer cladding 2 with a negative curvature structure recessed inwardly, an antiresonance unit 3 and an air-filled core 4, wherein the coating layer 1 is arranged outside the outer cladding 2 with a negative curvature structure recessed inwardly, 12 sides of the radial cross section of the inner cavity of the outer cladding are all negative curvature structures, a total of 12 antiresonance units 3 are arranged, which are evenly arranged on the inner cavity wall of the outer cladding 2 with a negative curvature structure recessed inwardly, the air-filled core 4 is located at the central position of the hollow-core optical fiber, and the air-filled core 4 is tangent to the outer wall of the antiresonance unit 3 around it, and by designing the outer cladding 2 with a negative curvature structure recessed inwardly, the optical fiber loss and bending loss can be reduced, and the problem that the ordinary outer cladding has a circular boundary and a large loss can be solved.

[0057] In this embodiment, the total diameter of the hollow core optical fiber is 250 μm, the total diameter of the hollow core optical fiber excluding the coating layer 1 is 149 μm, and the diameter of the air-filled core 4 is 44 μm.

[0058] The coating layer 1 is made of MgAl2O4, which is still stable at a high temperature of 1200°C. The purpose of designing the coating layer 1 is: the hollow-core optical fiber has a special structure, and the air-filled core 4 is an air core. By setting the coating layer 1, foreign substances can be prevented from entering the hollow-core optical fiber structure, thereby avoiding interference with the optical performance of the optical fiber.

[0059] Each anti-resonance unit 3 is composed of three capillaries of different diameters nested in sequence. The capillaries are made of quartz material. The three capillaries of different diameters are recorded as the first capillary 5, the second capillary 6, and the third capillary 7 from the outside to the inside. The inner and outer walls of the three capillaries are tangent to each other in sequence. The inner wall of the first capillary 5 is tangent to the outer wall of the second capillary 6, and the inner wall of the second capillary 6 is tangent to the outer wall of the third capillary 7. The diameter of the first capillary 5 is d1=25.03μm, the diameter of the second capillary 6 is d2=16.86μm, and the diameter of the third capillary 7 is d3=11.36μm.

[0060] The outer sleeve adopts a high-transparency alumina ceramic base tube with a thickness of 0.4 μm and a real part of the refractive index of 1.757 μm, which is used to form an inwardly concave negative curvature structure outer cladding 2.

[0061] A method for preparing a hollow core optical fiber comprises the following steps:

[0062] S1: drawing a first capillary 5, a second capillary 6, and a third capillary 7 of required specifications through a tube drawing platform, and washing the assembly materials including the first capillary 5, the second capillary 6, and the third capillary 7 with water, inserting M3 paper into the capillary during the washing, and removing glass slag in the tube by the action of water pressure to prevent breakage during extension;

[0063] S2: assembling a third capillary 7, a second capillary 6, and a first capillary 5 into an anti-resonance unit 3 by assembling the platform in a nested order from the inside to the outside. Similarly, 12 anti-resonance units 3 are manufactured in the same way;

[0064] S3: All anti-resonance units 3 are evenly glued to the inner wall of the concave area of ​​the outer sleeve to maintain the overall shape and integrity of the subsequently drawn optical fiber and the circular cross-sectional shape of the hollow-core optical fiber. The capillary and the outer sleeve are bonded together through a welding process, and the assembled structure is vacuum treated so that the vacuum degree reaches 10 -6 mbar, which is convenient for subsequent filling of special gases with low refractive index. After welding the tail tube, slowly cool it down to prevent the tube structure from cracking due to stress caused by excessive heating. Tail tube welding helps the hollow-core optical fiber intermediate to form a sealed structure to prevent the entry of external impurities such as water vapor and dust. If the pressure divider device has been installed, the tail tube does not need to be welded;

[0065] S4: After welding is completed, stretching and wire drawing are carried out. During the wire drawing process, an inwardly concave negative curvature structure boundary is formed by the action of pressure difference and surface tension, thereby forming an anti-resonance nested structure surrounded by an inwardly concave negative curvature structure outer cladding 2; then fill with a low refractive index gas to further reduce the transmission loss of light in the optical fiber. Preferably, the gas is any one or a combination of several of compressed air, nitrogen, helium, and argon. Furthermore, a nodeless anti-resonance cavity constitutes the inner cladding. The diameter of the air-filled core 4 is controlled at 44μm, the minimum wall thickness of the anti-resonance nested structure is 1μm, and the wall thickness of the anti-resonance unit 3 formed by sequentially nesting capillaries of different diameters meets the anti-resonance reflection condition.

[0066] The hollow-core optical fiber structure prepared by this embodiment has low transmission loss, can have low limiting loss in a large wavelength range in the 1.87-4μm band, a large mode field area, and a near-zero flat dispersion with a dispersion coefficient of about 0.25ps / (nm / km) in the wavelength range of 1.46-1.65μm. It also has good single-mode characteristics at 3μm, meeting the needs of optical communication and optical fiber sensing. The loss in the range of 1550-1610nm is 0.178db / km, which is on par with the performance of the latest generation of glass core optical fibers. At the extreme bending radius of 0.25cm, the bending loss of the hollow-core optical fiber is measured to be 3.67×10 -3 dB@1550nm.

[0067] The rest is the same as in Example 1.

[0068] Parts or structures not specifically described in the present invention may adopt existing technologies or existing products and will not be described in detail here.

[0069] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A hollow core optical fiber, characterized in that: The hollow-core optical fiber comprises a coating layer, an outer cladding with a negative curvature structure that is recessed inwards, an antiresonance unit and an air-filled core. The coating layer is arranged outside the outer cladding with a negative curvature structure that is recessed inwards. There are 12 or more antiresonance units that are uniformly arranged on the inner cavity wall of the outer cladding with a negative curvature structure that is recessed inwards. The air-filled core is located at the center of the hollow-core optical fiber, and the air-filled core is tangent to the outer wall of the antiresonance unit around it.

2. A hollow core optical fiber according to claim 1, characterized in that: The inwardly concave negative curvature structure outer cladding is made of a highly transparent alumina ceramic base tube, and the real part of the refractive index is 1.2-1.8 μm.

3. The hollow core optical fiber according to claim 1, characterized in that: The anti-resonance unit is formed by nesting a plurality of capillaries with different diameters in sequence from the inside to the outside.

4. A hollow core optical fiber according to claim 3, characterized in that: Each anti-resonance unit is composed of three capillaries of different diameters nested in sequence from the inside to the outside. The three capillaries of different diameters are recorded as the first capillary, the second capillary, and the third capillary from the outside to the inside. The inner wall of the first capillary is tangent to the outer wall of the second capillary, and the inner wall of the second capillary is tangent to the outer wall of the third capillary.

5. A hollow core optical fiber according to claim 4, characterized in that: The diameter of the first capillary is 18-27 μm, the diameter of the second capillary is 13-17 μm, and the diameter of the third capillary is 8-12 μm.

6. A hollow core optical fiber according to claim 5, characterized in that: The diameter of the first capillary is 25.03 μm, the diameter of the second capillary is 16.86 μm, and the diameter of the third capillary is 11.36 μm.

7. The hollow core optical fiber according to claim 5, characterized in that: The diameter of the first capillary is 19.87 μm, the diameter of the second capillary is 13.39 μm, and the diameter of the third capillary is 9.02 μm.

8. The hollow core optical fiber according to claim 1, characterized in that: The total diameter of the hollow core optical fiber is 240-250 μm, the total diameter of the hollow core optical fiber excluding the coating layer is 110-150 μm, and the diameter of the air-filled core is 33-45 μm.

9. A method for preparing a hollow core optical fiber according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: Drawing several capillaries with different diameters through the tube drawing platform; S2: Capillaries of different diameters are made into anti-resonance units; S3: All anti-resonance units are evenly glued to the inner wall of the concave area of ​​the outer sleeve, and the capillary and the outer sleeve are bonded together through a welding process. The assembled structure is vacuum treated so that the vacuum degree reaches 10 -6 mbar or even higher, which is convenient for subsequent filling with special gases with low refractive index; S4: After welding is completed, stretching and drawing are carried out. During the drawing process, an inwardly concave negative curvature structure boundary is formed through the action of pressure difference and surface tension, thereby forming an anti-resonant nested structure surrounded by an inwardly concave negative curvature structure outer cladding; then filled with low refractive index gas to further reduce the transmission loss of light in the optical fiber.

10. The method for preparing a hollow core optical fiber according to claim 9, characterized in that: The low refractive index gas is any one of compressed air, nitrogen, helium and argon, or a combination of several of them.

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