Hollow-core fiber having azimuth mark and hollow-core fiber end face detection method

Abstract

A hollow-core fiber having an azimuth mark and a hollow-core fiber end face detection method. The fiber comprises a cladding hollow-core sleeve and a plurality of anti-resonant microstructure units arranged and adhered to the inner wall of the cladding hollow-core sleeve uniformly in the circumferential direction; a hollow area surrounded by the anti-resonant microstructure units is a fiber core; and there is at least one anti-resonant microstructure unit of which the azimuth is different from that of at least one of the other anti-resonant microstructure units. By using the azimuth mark, the anti-resonant microstructure units in the hollow-core fiber can be quickly distinguished while the complexity of optical fiber preparation is not improved and the optical fiber transmission performance is hardly affected, and the geometric uniformity of the anti-resonant microstructure units can be conveniently controlled on line.

Description

A hollow-core optical fiber with azimuth marking and hollow-core optical fiber end face detection method Technical Field

[0001] The present invention belongs to the field of optical communications, and more specifically, relates to an azimuthally marked hollow-core optical fiber and a hollow-core optical fiber end face detection method. Background Art

[0002] Hollow-core microstructured optical fiber has the characteristics of simple structure, hollow-core single-mode light guidance, and wide transmission spectrum. It has important applications in the fields of interaction between light and filling materials, nonlinear optics, gas detection, gas laser generation, optofluidic technology, etc.; large air hole core light guidance has 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 ultra-low loss, low dispersion, low nonlinearity, and propagation speed close to the speed of light of the air core 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] While hollow-core fibers offer significant advantages in design and application, their transmission loss has consistently been higher than that of traditional quartz fibers. Recent discoveries have shown that hollow-core fibers, based on the principle of antiresonance, can effectively reduce transmission loss with appropriate structural design, demonstrating their potential as ultra-long-haul communication fibers. Further reducing attenuation is a key issue in the fabrication of hollow-core microstructured fibers.

[0004] Although known hollow-core antiresonant fibers, especially those with nested structural elements, can significantly reduce optical fiber attenuation, the manufacturing process of hollow-core antiresonant fibers is fundamentally different from that of conventional solid-core fibers. The microscopic three-dimensional structure of hollow-core fibers is the basis of their light guidance. In order to form or maintain this specific microstructure, gas must be continuously introduced during the drawing process. Due to factors such as the inhomogeneity of the raw materials, deviations during the stacking of nested structural elements, and uneven thermal field distribution during the drawing process, the antiresonant structural elements of the drawn hollow-core antiresonant fibers will have different sizes, as shown in Figure 1. This geometric structural inhomogeneity will greatly affect the transmission loss of the hollow-core antiresonant fibers. Precisely because this manufacturing method is subversive compared to existing solid-core fibers, the conventional method of increasing the size of the fiber preform used for solid-core fibers cannot be used to improve geometric inhomogeneity.

[0005] Summary of the Invention

[0006] In response to the above defects or improvement needs of the prior art, the present invention provides an azimuthally marked hollow-core optical fiber and a hollow-core optical fiber end face detection method, the purpose of which is to adjust the azimuth angle of the anti-resonant microstructure unit having multiple layers of negative curvature layers, mark the optical fiber end face while ensuring the optical fiber transmission performance, and identify each anti-resonant microstructure unit, which can be used to detect the geometric uniformity of the optical fiber, thereby solving the technical problem that the anti-resonant units of the existing hollow-core optical fiber are difficult to distinguish from each other and the geometric uniformity cannot be detected.

[0007] To achieve the above objectives, according to one aspect of the present invention, there is provided an azimuthally marked hollow-core optical fiber, comprising a cladding hollow-core sleeve and a plurality of circumferentially uniformly arranged antiresonant microstructure units arranged and attached to the inner wall of the cladding hollow-core sleeve, wherein the hollow region surrounded by the antiresonant microstructure units serves as the fiber core;

[0008] The antiresonance microstructure unit has multiple layers of negative curvature, with the inner side being away from the fiber core and the outer side being close to the fiber core, and the angle formed by connecting the center of curvature of the outermost negative curvature layer, the geometric center of the optical fiber, and then the center of curvature of the innermost negative curvature layer is the azimuth angle;

[0009] The azimuth angle of at least one anti-resonance microstructure unit is different from the azimuth angle of at least one other anti-resonance microstructure unit.

[0010] Preferably, the azimuthally marked hollow-core optical fibers have azimuth angle differences of ≥1.5°.

[0011] Preferably, in the azimuthally marked hollow-core optical fiber, the azimuth angle of the marked anti-resonance microstructure unit is different from that of all other anti-resonance microstructure units.

[0012] Preferably, the azimuth angles of all other antiresonance microstructure units of the azimuthally marked hollow-core optical fiber are the same.

[0013] Preferably, in the hollow-core optical fiber with the azimuth angle mark, the azimuth angles of all other antiresonant microstructure units are 0°.

[0014] Preferably, in the hollow-core optical fiber with the azimuth angle mark, the azimuth angle of the marked anti-resonance microstructure unit is θ, and 1.5°≤θ≤45°.

[0015] Preferably, the antiresonant microstructure unit of the azimuthally marked hollow-core optical fiber comprises a double layer of tangentially nested capillaries, and the angle formed by the three points from the center of the inner capillary to the geometric center of the optical fiber and then to the center of the outer capillary is the azimuth angle of the antiresonant microstructure unit.

[0016] Preferably, in the hollow-core optical fiber with the azimuth angle mark, the capillary tangent points of the other antiresonance microstructure units are attached to the inner wall of the cladding hollow-core sleeve.

[0017] Preferably, the cladding hollow-core sleeve of the azimuthally marked hollow-core optical fiber is circular, and the outer contours of the plurality of anti-resonance microstructure units are the same.

[0018] According to another aspect of the present invention, there is provided a method for detecting the end face of a hollow-core optical fiber, comprising the following steps:

[0019] (1) Cutting the hollow-core optical fiber with azimuth marking at a preset position;

[0020] (2) imaging the truncated end face obtained in step (1) using transmitted light or reflected light to obtain an end face image of the hollow-core optical fiber at that position;

[0021] (3) for the end face image obtained in step (2), identifying the antiresonant microstructure unit according to its azimuth angle, and obtaining an image of each antiresonant microstructure unit;

[0022] (4) Extracting geometric parameters from the image of the anti-structure microstructure unit identified in step (3) to determine the geometric uniformity of the hollow-core optical fiber.

[0023] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0024] The present invention provides an azimuthally marked hollow-core optical fiber and a hollow-core optical fiber end face detection method. By adopting the azimuth mark, the anti-resonance microstructure units in the hollow-core optical fiber can be quickly identified without increasing the complexity of optical fiber preparation and almost without affecting the optical fiber transmission performance. This facilitates online control of the geometric uniformity of the anti-resonance microstructure units and is beneficial to reducing the transmission loss of the hollow-core optical fiber. At the same time, during the hollow-core optical fiber coupling process, different anti-resonance microstructure units are easily identified, thereby reducing the coupling loss of the hollow-core optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic structural diagram of a hollow-core optical fiber preform providing azimuth angle markings according to Example 1 of the present invention;

[0026] FIG2 is a schematic diagram of an unmarked hollow-core optical fiber, for comparison with Example 1;

[0027] 3 is a schematic diagram of pressure control during the drawing process of a hollow-core optical fiber preform providing azimuth angle markings according to Example 1 of the present invention;

[0028] FIG4 is a schematic diagram of pressure control during the drawing process of a hollow-core optical fiber preform with two azimuth marks provided in Example 2 of the present invention;

[0029] FIG5 is a schematic diagram of pressure control during the drawing process of a hollow-core optical fiber preform with azimuth markings provided in Example 3 of the present invention.

[0030] In all the drawings, the same figure marks are used to represent the same elements or structures, wherein: 1 is an antiresonant microstructure unit, 2 is a cladding hollow-core sleeve, 3 is a uniquely marked antiresonant microstructure unit used in Example 1, 4 and 5 are two adjacent marked antiresonant microstructure units used in Example 2, and 6, 7, and 8 are three adjacent marked antiresonant microstructure units used in Example 3. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0032] The azimuthally marked hollow-core optical fiber provided by the present invention comprises a cladding hollow-core sleeve and a plurality of circumferentially uniformly arranged antiresonant microstructure units arranged and attached to the inner wall of the cladding hollow-core sleeve. The hollow area surrounded by the antiresonant microstructure units is the fiber core. The cladding hollow-core sleeve is circular, and the outer contours of the plurality of antiresonant microstructure units are the same.

[0033] The number of anti-resonant microstructure units n≥3.

[0034] The antiresonance microstructure unit has multiple layers of negative curvature, with the inner side being away from the fiber core and the outer side being close to the fiber core. The azimuth angle is from the center of curvature of the outermost negative curvature layer to the geometric center of the optical fiber and then to the center of curvature of the innermost negative curvature layer.

[0035] There is at least one antiresonant microstructure unit whose azimuth angle is different from that of at least one other antiresonant microstructure unit. All antiresonant microstructure units can be identified by identifying the difference in azimuth angles: first identify the antiresonant microstructure unit with the difference, and then identify the other antiresonant microstructure units by their relative positions with the above-mentioned antiresonant microstructure unit with the difference. In order to easily identify the antiresonant microstructure unit, the difference in azimuth angle needs to be above 1.5°, so as to be clearly distinguished from the assembly error of the antiresonant microstructure unit. That is, the offset of the azimuth angle of the antiresonant microstructure unit is used as an indicator of the orientation of the hollow-core optical fiber, and the number of antiresonant microstructure units with offset azimuth angles is m, where m≥1.

[0036] The antiresonant microstructure unit that has an azimuth angle different from all other antiresonant microstructure units is easy to identify and is called a marked antiresonant microstructure unit.

[0037] The azimuth angle of the antiresonant microstructure unit affects the transmission performance of the hollow-core fiber to a certain extent, and is preferably ≤ 45°. When the azimuth angle of the antiresonant microstructure unit is 0°, the multiple layers of negative curvature are oriented directly toward the fiber core. Typically, two layers of negative curvature both face directly toward the fiber core, resulting in theoretically better transmission performance. Therefore, in the preferred embodiment, the azimuth angle of all antiresonant microstructure units, except for the marked antiresonant microstructure unit, is 0°.

[0038] It is relatively easy to implement by using a unique marking anti-resonance microstructure unit so that its azimuth angle is different from that of all other anti-resonance microstructure units, while the azimuth angles of all other anti-resonance microstructure units are the same. In this way, the marking anti-resonance microstructure unit is easier to identify, while the other anti-resonance microstructure units are identified by their relative position with the marking anti-resonance microstructure unit.

[0039] However, the azimuth angle differences of the antiresonant microstructure units also affect the transmission performance of the optical fiber. Excessive azimuth angle differences not only increase the transmission loss of the optical fiber, but also may distort the light propagation mode due to the significant asymmetry of the optical fiber cross section. Therefore, the azimuth angle of the antiresonant microstructure units is set to θ within a range of 1.5°≤θ≤45°, preferably 1.5°≤θ≤15°, to maintain the good transmission performance of the hollow-core fiber.

[0040] Preferably, the antiresonant microstructure unit comprises two layers of tangentially nested capillaries, and the azimuth angle of the antiresonant microstructure unit is from the center of the inner capillary to the geometric center of the optical fiber and then to the center of the outer capillary. Except for the marked antiresonant microstructure unit, the tangent points of the capillaries of the other antiresonant microstructure units are attached to the inner wall of the cladding hollow core sleeve, with an azimuth angle of 0°.

[0041] The method for preparing an azimuthally marked hollow-core optical fiber provided by the present invention comprises the following steps:

[0042] Step 1: Prepare the anti-resonant microstructure unit with a nested structure: draw the required capillary tube through the mother tube in a high-temperature drawing furnace; the capillary tube can be subjected to secondary processing according to design requirements, such as cutting, grinding, welding, etc., to form the anti-resonant microstructure unit with a nested structure.

[0043] Step 2, preform stacking: The nested anti-resonant microstructure units obtained in step 1 are stacked and assembled in a sleeve, wherein m nested anti-resonant microstructure units are selected to generate an azimuth offset during stacking, which is used as an identifier of the hollow-core optical fiber orientation, thereby forming an azimuthally marked hollow-core optical fiber preform.

[0044] Step 3: The hollow-core optical fiber preform with the azimuth angle mark in step 2 is directly drawn into a hollow-core optical fiber, or first drawn into an intermediate preform, which is then sleeved into a casing to draw into the hollow-core optical fiber. During the drawing process, the azimuth angle mark is used to quickly distinguish the correspondence between the antiresonant microstructure units in the optical fiber and the antiresonant microstructure units in the preform, thereby adjusting the size of the antiresonant microstructure units in the optical fiber by controlling the air pressure within the antiresonant microstructure units in the preform.

[0045] Furthermore, the antiresonant microstructure unit, sleeve and azimuth mark can be made of high-purity silicon dioxide, doped quartz (doped with one or more elements such as germanium, fluorine, chlorine, boron, aluminum, etc.), multi-component glass, plastic, etc.

[0046] Furthermore, the hollow-core optical fiber has a cladding diameter greater than or equal to 100 μm.

[0047] The hollow-core optical fiber end face detection method provided by the present invention comprises the following steps:

[0048] (1) Cutting the hollow-core optical fiber with azimuth marking at a preset position;

[0049] (2) imaging the truncated end face obtained in step (1) using transmitted light or reflected light to obtain an end face image of the hollow-core optical fiber at that position;

[0050] (3) for the end face image obtained in step (2), identifying the antiresonant microstructure unit according to its azimuth angle, and obtaining an image of each antiresonant microstructure unit;

[0051] (4) Extracting geometric parameters from the image of the anti-structure microstructure unit identified in step (3) to determine the geometric uniformity of the hollow-core optical fiber.

[0052] According to its geometric uniformity, the pressure of the gas introduced into each area of ​​each antiresonant microstructure unit and the sleeve during the drawing of the hollow-core optical fiber can be adjusted, thereby controlling the optical fiber drawing process, improving the geometric uniformity of the optical fiber, and making the hollow-core optical fiber have lower transmission loss and fusion loss.

[0053] The hollow-core optical fiber provided by the present invention has low transmission loss, with the lowest transmission loss being ≤30dB / km, and more preferably ≤1dB / km; and has low splicing loss, with the hollow-core optical fiber self-splice loss being ≤0.5dB.

[0054] The following are examples:

[0055] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0056] Example 1

[0057] The hollow-core optical fiber structure provided in this embodiment is shown in Figure 1, which includes a cladding hollow-core sleeve and five circumferentially evenly arranged anti-resonance microstructure units arranged and attached to the inner wall of the cladding hollow-core sleeve. The hollow area surrounded by the anti-resonance microstructure units is the fiber core; the cladding hollow-core sleeve is circular, and the outer contours of the multiple anti-resonance microstructure units are the same.

[0058] The antiresonant microstructure unit comprises two layers of tangentially nested capillaries. The angle formed by the three points, from the center of the inner capillary to the geometric center of the optical fiber and then to the center of the outer capillary, is the azimuth angle of the antiresonant microstructure unit. A unique marked antiresonant microstructure unit is used, and its azimuth angle is θ = 7.8°. The azimuth angles of all other antiresonant microstructure units are 0°, and the tangent points of the capillaries are attached to the inner wall of the cladding hollow core sleeve. The preparation method is as follows:

[0059] First, two sizes of capillaries are prepared from a mother tube. The large capillary has an outer diameter of 10.4 mm and a wall thickness of 0.32 mm, and the small capillary has an outer diameter of 6.2 mm and a wall thickness of 0.34 mm. The small capillary is inserted into the large capillary and then fixed by laser heating to form an antiresonant microstructure unit 1. A pure silica sleeve is then prepared with an outer diameter of 65 mm and an inner diameter of 55 mm. Five antiresonant microstructure units 1 are stacked in the sleeve 2 to form a hollow-core optical fiber preform as shown in Figure 1. The azimuth angle of one of the antiresonant microstructure units 3 is offset during the stacking process, θ being 7.8°, while the assembly error of the remaining azimuth angles is maintained at ≤1.5°, thus obtaining an azimuthally marked hollow-core optical fiber preform. The azimuthally marked hollow-core optical fiber preform can be directly drawn into a hollow-core optical fiber in a drawing furnace. However, during wire drawing, temperature fluctuations will cause the size of the anti-resonant microstructure unit to be different. As shown in Figure 2, the maximum deviation of the outer diameter of the anti-resonant microstructure unit is 25%. To this end, it is necessary to introduce gases of different pressures into the anti-resonant microstructure unit to make the size of the anti-resonant microstructure unit uniform. As shown in Figure 3, the azimuth mark is used to identify the size of the required air pressure in the anti-resonant microstructure unit. P1, P2, P3, P4, and P5 are the air pressures in the large capillary of the anti-resonant microstructure unit, and their values ​​are 15.3mbar, 15.5mbar, 15.5mbar, 15.8mbar, and 15.2mbar respectively. P6, P7, P8, P9, and P10 are the air pressures in the small capillary of the anti-resonant microstructure unit, and their values ​​are 64.3mbar, 64.4mbar, 64.9mbar, 64.7mbar, and 64.5mbar respectively. After being drawn into optical fiber, the maximum deviation in the outer diameter of the large capillary in the antiresonant microstructure unit is 2.9%, and the maximum deviation in the outer diameter of the small capillary in the antiresonant microstructure unit is 3.3%. Its attenuation at 1550nm is 0.58dB / km. When splicing this hollow-core fiber, the azimuth marker unit can be used to identify the capillary orientation, allowing for more precise splicing. The minimum splicing loss is 0.36dB.

[0060] Example 2

[0061] The hollow-core optical fiber structure provided in this embodiment is shown in Figure 4, which includes a cladding hollow-core sleeve and five circumferentially evenly arranged anti-resonance microstructure units arranged and attached to the inner wall of the cladding hollow-core sleeve. The hollow area surrounded by the anti-resonance microstructure units is the fiber core; the cladding hollow-core sleeve is circular, and the outer contours of the multiple anti-resonance microstructure units are the same.

[0062] The antiresonant microstructure unit comprises two layers of tangentially nested capillaries, with the azimuth angle of the antiresonant microstructure unit extending from the center of the inner capillary to the geometric center of the optical fiber and then to the center of the outer capillary. Two adjacent antiresonant microstructure units 4 and 5 are labeled, with azimuth angles θ of 11.2° and 9.4°, respectively. The azimuth angles of all other antiresonant microstructure units are 0°, and the tangent points of the capillaries are attached to the inner wall of the cladding hollow-core sleeve. The preparation method is as follows:

[0063] First, two sizes of capillaries are prepared through the mother tube. The outer diameter of the large capillary is 8.2mm and the wall thickness is 0.62mm. The outer diameter of the small capillary is 4.15mm and the wall thickness is 0.44mm. The small capillary is inserted into the large capillary and then fixed by laser heating to form an antiresonant microstructure unit 1. Then a pure silica sleeve is prepared with an outer diameter of 55mm and an inner diameter of 45mm. Five antiresonant microstructure units 1 are stacked in the sleeve 2 to form a hollow-core optical fiber preform as shown in Figure 4, wherein the azimuth angles of two antiresonant microstructure units (4 and 5) are offset during the stacking process, the azimuth angle θ of the antiresonant microstructure unit 4 is 11.2°, the azimuth angle θ of the antiresonant microstructure unit 5 is 9.4°, and the other azimuth angles are kept ≤1.5°, thereby obtaining an azimuthally marked hollow-core optical fiber preform. The hollow-core optical fiber preform with azimuth angle marking can be first drawn into an intermediate preform in a drawing furnace. The outer diameter of the intermediate preform is 7.5 mm, and then it is inserted into a sleeve with an outer diameter of 14.2 mm and an inner diameter of 8.1 mm for drawing. As in the previous embodiment, the size of the anti-resonance microstructure unit is made uniform by introducing gases of different pressures into the anti-resonance microstructure unit. As shown in Figure 4, the azimuth angle marking unit is used to identify the size of the required air pressure in the anti-resonance microstructure unit. P1, P2, P3, P4, and P5 are the air pressures in the large capillary in the anti-resonance microstructure unit, and their values ​​are 29.9 mbar, 29.8 mbar, 30.2 mbar, 30.3 mbar, and 30.4 mbar, respectively. P6, P7, P8, P9, and P10 represent the air pressure in the small capillaries within the antiresonant microstructure unit, with values ​​of 112.5 mbar, 112.1 mbar, 113.2 mbar, 112.7 mbar, and 113.2 mbar, respectively. After being drawn into optical fiber, the maximum deviation in the outer diameter of the large capillary within the antiresonant microstructure unit is 2.7%, and the maximum deviation in the outer diameter of the small capillary within the antiresonant microstructure unit is 2.8%. Its attenuation at 1550 nm is 0.46 dB / km. When splicing this hollow-core fiber, the azimuth marker unit can be used to identify the capillary orientation, enabling more precise splicing. The minimum splice loss is 0.25 dB.

[0064] Example 3

[0065] The hollow-core optical fiber structure provided in this embodiment is shown in Figure 5, which includes a cladding hollow-core sleeve and five circumferentially evenly arranged anti-resonance microstructure units arranged and attached to the inner wall of the cladding hollow-core sleeve. The hollow area surrounded by the anti-resonance microstructure units is the fiber core; the cladding hollow-core sleeve is circular, and the outer contours of the multiple anti-resonance microstructure units are the same.

[0066] The antiresonance microstructure unit comprises two layers of tangentially nested capillaries, wherein the angle formed by the three points from the center of the inner capillary to the geometric center of the optical fiber and then to the center of the outer capillary is the azimuth angle of the antiresonance microstructure unit. Three adjacent antiresonance microstructure units 6, 7, and 8 are used, and their azimuth angles θ are 6.4°, 7.2°, and 7.8°, respectively. The azimuth angles of all other antiresonance microstructure units are 0°, and the tangent points of the capillaries are attached to the inner wall of the cladding hollow core sleeve. The preparation method is as follows:

[0067] As shown in FIG5 , two sizes of capillaries are first prepared through a mother tube. The outer diameter of the large capillary is 6.6 mm and the wall thickness is 0.37 mm. The outer diameter of the small capillary is 2.8 mm and the wall thickness is 0.24 mm. The small capillary is inserted into the large capillary and then fixed by laser heating to form an antiresonant microstructure unit 1. A pure silica sleeve is then prepared with an outer diameter of 27 mm and an inner diameter of 21 mm. Five antiresonant microstructure units 1 are stacked in the sleeve 2 to form a hollow-core optical fiber preform as shown in FIG5 , wherein the azimuth angles of the three antiresonant microstructure units (6, 7 and 8) are shifted during the stacking process. The azimuth angle θ of the antiresonant microstructure unit 6 is 6.4°, the azimuth angle θ of the antiresonant microstructure unit 7 is 7.2°, the azimuth angle θ of the antiresonant microstructure unit 8 is 7.8°, and the remaining azimuth angles are kept ≤1.5°, thereby obtaining an azimuthally marked hollow-core optical fiber preform. The hollow-core optical fiber preform with azimuth angle marking can be first drawn into an intermediate preform in a drawing furnace. The outer diameter of the intermediate preform is 10.5 mm, and then it is inserted into a sleeve with an outer diameter of 18.2 mm and an inner diameter of 11.0 mm for drawing. As in the previous embodiment, the size of the anti-resonance microstructure unit is made uniform by introducing gases of different pressures into the anti-resonance microstructure unit. As shown in Figure 5, the azimuth angle marking unit is used to identify the size of the required air pressure in the anti-resonance microstructure unit. P1, P2, P3, P4, and P5 are the air pressures in the large capillary in the anti-resonance microstructure unit, and their values ​​are 46.2 mbar, 46.9 mbar, 47.6 mbar, 46.3 mbar, and 46.5 mbar, respectively. P6, P7, P8, P9, and P10 represent the air pressures in the small and large capillaries within the antiresonant microstructure unit, with values ​​of 156.3 mbar, 157.4 mbar, 159.4 mbar, 158.5 mbar, and 157.9 mbar, respectively. After being drawn into optical fiber, the maximum deviation in the outer diameter of the large capillary within the antiresonant microstructure unit is 3.1%, and the maximum deviation in the outer diameter of the small capillary within the antiresonant microstructure unit is 3.4%. Its attenuation at 1550 nm is 0.43 dB / km. When splicing this hollow-core fiber, the azimuth marker unit can be used to identify the capillary orientation, enabling more precise splicing. The minimum splice loss is 0.27 dB.

[0068] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An azimuthally marked hollow-core optical fiber, characterized in that: It comprises a cladding hollow core sleeve and a plurality of circumferentially uniformly arranged anti-resonance microstructure units arranged and attached to the inner wall of the cladding hollow core sleeve, wherein the hollow area surrounded by the anti-resonance microstructure units is the fiber core; The anti-resonance microstructure unit has multiple layers of negative curvature, with the inner side being away from the fiber core and the outer side being close to the fiber core, and the angle formed by connecting the curvature center of the outermost negative curvature layer, the optical fiber geometric center, and then the curvature center of the innermost negative curvature layer is the azimuth angle; The azimuth angle of at least one anti-resonance micro-structure unit is different from the azimuth angle of at least one other anti-resonance micro-structure unit.

2. The azimuthally marked hollow-core optical fiber according to claim 1, characterized in that: The difference between the azimuths was ≥ 1.5°.

3. The azimuthally marked hollow-core optical fiber according to claim 1 or 2, characterized in that: The marked anti-resonance microstructure unit has a different azimuth angle from all other anti-resonance microstructure units.

4. The azimuthally marked hollow-core optical fiber according to claim 3, characterized in that: The azimuth angles of all other anti-resonance microstructure units are the same.

5. The azimuthally marked hollow-core optical fiber according to claim 4, characterized in that: The azimuth angles of all other anti-resonance microstructure units are 0°.

6. The azimuthally marked hollow-core optical fiber according to claim 3, characterized in that: The azimuth angle of the marked anti-resonance microstructure unit is θ, and 1.5°≤θ≤45°.

7. The azimuthally marked hollow-core optical fiber according to claim 3, characterized in that: The antiresonance microstructure unit comprises two layers of tangentially nested capillaries, and the angle formed by the three points from the center of the inner capillary to the geometric center of the optical fiber and then to the center of the outer capillary is the azimuth angle of the antiresonance microstructure unit.

8. The azimuthally marked hollow-core optical fiber according to claim 7, characterized in that: The capillary tangents of the other anti-resonance microstructure units are attached to the inner wall of the cladding hollow core sleeve.

9. The azimuthally marked hollow core optical fiber according to claim 1, characterized in that: The cladding hollow core sleeve is circular, and the outer contours of the plurality of anti-resonance microstructure units are the same.

10. The hollow-core optical fiber end face detection method according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) Cutting the hollow-core optical fiber marked with an azimuth angle at a preset position; (2) imaging the truncated end face obtained in step (1) using transmitted light or reflected light to obtain an end face image of the hollow-core optical fiber at that position; (3) for the end surface image obtained in step (2), identifying the antiresonant microstructure unit according to its azimuth angle, and obtaining an image of each antiresonant microstructure unit; (4) Extracting geometric parameters from the image of the anti-structure microstructure unit identified in step (3) to determine the geometric uniformity of the hollow-core optical fiber.

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