A hollow fiber optic connector and its fabrication method

Abstract

This application relates to a hollow-core fiber optic connector and its fabrication method. A structural component is formed by low-temperature etching on the end face of the hollow-core fiber. The refractive index of the structural component is greater than that of the hollow-core fiber, ensuring effective modulation of the optical wave phase and avoiding thermal effects under high power with low loss. The nanopillars distributed in the structural component array exhibit radially varying diameters, constructing a metasurface lens on the end face of the hollow-core fiber. This metasurface lens possesses radial phase variation, achieving wavefront shaping. This allows the large mode field beam of the hollow-core fiber to be effectively reduced and matched to the mode field of the solid-core fiber, significantly reducing insertion loss. Simultaneously, the structural component is directly integrated into the end face of the hollow-core fiber, eliminating the need for an additional lens, simplifying the fiber optic connector structure, supporting on-site installation, and allowing for repeated insertion and removal, improving coupling efficiency and stability, and solving the high-loss problem caused by mode field mismatch. Furthermore, the entire process is performed at low temperatures, preventing hollow core collapse and making it suitable for mass production automation.

Description

Technical Field

[0001] This application relates to the field of optical fiber communication and optical fiber devices, and in particular to a hollow optical fiber connector and its fabrication method. Background Technology

[0002] In recent years, with the development of high-power laser transmission, low-latency communication, and mid-infrared spectroscopy applications, hollow-core fiber (HCF) has attracted widespread attention due to its advantages such as low nonlinearity, low dispersion, and high damage threshold. However, the mode field diameter (MFD) of HCF is typically greater than 20µm, while the MFD of standard single-mode fiber (SMF) is about 10.4µm. Directly connecting the two will result in an insertion loss greater than 1.5dB. In addition, since traditional connectors are fixed with epoxy resin, the adhesive layer absorbs heat and carbonizes during high-power applications, leading to end-face burnout.

[0003] In practical applications, the solid core method used and the problems are as follows: (1) Using mode field matching fiber, this method requires fusion splicing or particle exchange, which is extremely complex and there is a risk of collapse failure in the mode field transition region; (2) Blocking the end face of hollow fiber cannot improve the mode field mismatch problem. It is only suitable for inter-HCF connection and has the problem of increasing return loss. (3) When using epoxy resin to fix the end face of hollow fiber, the epoxy resin will carbonize during high power transmission, releasing gas / dust that contaminates the end face of hollow fiber. Summary of the Invention

[0004] This application provides a hollow fiber optic connector and its manufacturing method to solve the technical problem of high insertion loss in the connection of hollow and solid optical fibers in related technologies.

[0005] In a first aspect, a hollow fiber optic connector is provided, comprising: The connector ferrule has a coaxial solid fiber and a hollow fiber inside its inner hole; A structural component located between solid and hollow optical fibers and connected to the end face of the hollow optical fiber. The refractive index of the structural component is greater than that of the hollow fiber; the structural component includes a nanopillar array; the diameter of the nanopillars (400) of the nanopillar array is configured to vary radially so that the phase of the optical path varies radially.

[0006] Preferably, the material of the structural component is any one of TiO2, Ta2O5 and Si3N4.

[0007] Preferably, the axial length of the nanopillar satisfies the following formula: H≈λ / (n1 1); where n1 is the refractive index of the structural component; λ is the operating wavelength of the hollow fiber; and H is the axial length of the nanopillar.

[0008] Preferably, the nanopillars in the nanopillar array are arranged in multiple concentric ring arrays; the nanopillars in a ring array are evenly spaced and have the same diameter. In the radial direction, in two adjacent annular arrays, the diameter of the nanopillars in one annular array is different from the diameter of the nanopillars in the other annular array.

[0009] Preferably, the diameter of the multiple annular array of nanopillars gradually increases or decreases in the radial direction.

[0010] Preferably, the annular array is a circular array or a regular polygon array; the regular polygon array includes an equilateral triangle array, a regular quadrilateral array, a regular hexagonal array, or a regular octagonal array.

[0011] Preferably, the spacing between the centers of any two adjacent nanopillars is equal and less than the operating wavelength of the hollow fiber.

[0012] Preferably, the axial length, diameter, and spacing of the nanopillars are configured to provide a phase delay range of 0 to 2π at the operating wavelength of the hollow fiber, and to form a target equivalent focal length for reducing the mode field diameter of the hollow fiber.

[0013] Preferably, the hollow fiber optic connector further includes a quartz capillary and a metal tailstock: One end of the quartz capillary is located in the inner hole of the connector ferrule and is sleeved on the hollow optical fiber; the end face of the quartz capillary near the solid optical fiber is flush with the end face of the hollow optical fiber. The metal tail sleeve is fitted on the outside of the connector ferrule. The end of the quartz capillary away from the solid fiber extends into the metal tail sleeve. The hollow fiber passes through the metal tail sleeve, and the metal tail sleeve is encapsulated with glue.

[0014] Secondly, a method for manufacturing a hollow fiber optic connector is provided, comprising: After the hollow fiber is cut, it is inserted into the hollow fiber connector for fixation, and then the end face is polished. A femtosecond laser is used to etch the end face of the polished hollow fiber to form a nanopillar array; the axial length, diameter, and spacing of the nanopillars in the nanopillar array, as well as the array configuration, meet the preset parameters. The nanopillar array is cleaned using a focused ion beam, followed by ultrasonic cleaning and nitrogen drying to form the structural component; the processing temperature of the above steps is lower than the preset temperature. Insert the hollow fiber with structural components into the connector ferrule.

[0015] The beneficial effects of the technical solution provided in this application include: This application provides a hollow fiber optic connector and its fabrication method. In order to focus and couple a divergent large-mode-field beam into a small-mode-field fiber, a lens effect is required. Traditional lenses rely on thickness changes to generate optical path difference, while structural components rely on phase abrupt changes. The high refractive index of the structural component, i.e., the refractive index of the structural component is greater than that of the hollow fiber, ensures the effective modulation capability of the structural component for the phase of the light wave, and the low loss avoids the thermal effect under high power.

[0016] By varying the radial diameter of the nanopillars, a metasurface lens is constructed on the end face of the hollow fiber. This metasurface lens exhibits radial phase variation, which is used to achieve wavefront shaping. This allows the large mode field beam of the hollow fiber to be effectively reduced and matched to the mode field of the solid fiber, significantly reducing insertion loss. Simultaneously, the structural components are directly integrated into the end face, eliminating the need for additional lenses, simplifying the fiber optic connector structure, supporting on-site installation, and allowing for repeated insertion and removal, making it more convenient to use, improving coupling efficiency and stability, and solving the high loss problem caused by mode field mismatch. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the internal structure of a hollow fiber optic connector provided in an embodiment of this application; Figure 2 A schematic diagram illustrating a portion of the nanopillar array provided for an embodiment of this application; Figure 3 A schematic diagram illustrating the three-dimensional structural distribution of the entire nanopillar array provided for embodiments of this application; Figure 4 This is a schematic diagram of the simulation results of the mode field overlap integral provided in the embodiments of this application.

[0019] In the diagram: 1. Connector ferrule; 2. Solid fiber; 3. Hollow fiber; 4. Structural component; 400 nanopillar; 5. Quartz capillary; 6. Metal tailstock; 7. Epoxy adhesive isolation area. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] To understand the technical solution of this application, the following explanation is provided first: This application addresses a solution for connecting hollow-core and solid-core optical fibers. Because the hollow-core fiber end face is sealed, it cannot improve the mode field mismatch problem, making it only suitable for interlocking HCFs and increasing return loss. The root cause of insertion loss is that the mode field diameter (MFD) of hollow-core optical fibers is typically greater than 20µm, while the MFD of standard solid-core single-mode fiber (SMF) is approximately 10.4µm. Directly connecting the two will result in an insertion loss greater than 1.5dB. Furthermore, considering the cumbersome operation of on-site fusion splicing, this application eliminates the lens between the hollow-core and solid-core optical fibers, forming a structure on the end face of the hollow-core fiber that reduces the mode field diameter.

[0022] In addition, regarding adhesive connections, during high-power transmission, the epoxy adhesive carbonizes, releasing gases / dust that contaminate the hollow fiber end face. To address this, connections should be made directly away from the fiber's mating area to avoid the heat impact of optical transmission.

[0023] The following is a detailed explanation of how this application solves the above problems: Firstly, reference Figure 1 A hollow fiber optic connector is provided, comprising: The connector ferrule 1 has a coaxial solid optical fiber 2 and a hollow optical fiber 3 inside its inner hole; Structural component 4 is located between solid fiber 2 and hollow fiber 3 and is connected to the end face of hollow fiber 3; in fact, structural component 4 can be connected to either solid fiber 2 or hollow fiber 3. For convenience, the following description will use connection to hollow fiber 3 as an example. The refractive index of structural component 4 is greater than that of hollow fiber; structural component 4 includes a nanopillar array; the diameter of the nanopillars 400 of the nanopillar array is configured to vary radially so that the phase of the optical path varies radially.

[0024] The high refractive index of structural component 4, which is greater than that of hollow fiber 2, ensures the effective modulation capability of structural component 4 for the phase of optical waves, and the low loss avoids the thermal effect under high power.

[0025] To focus and couple a diverging large-mode-field beam into a small-mode-field fiber, a lens effect is required. Traditional lenses rely on thickness variations to create optical path difference, while structural component 4 relies on phase abrupt changes. The nanopillar 400 has a radially varying diameter, creating a metasurface lens on the end face of the hollow fiber 3. This metasurface lens exhibits radial phase changes, which are used to achieve wavefront shaping. This allows the large-mode-field beam from the hollow fiber 3 to be effectively reduced and matched to the mode field of the solid fiber 2, significantly reducing insertion loss. Simultaneously, structural component 4 is directly integrated into the end face, eliminating the need for an additional lens, simplifying the fiber optic connector structure, supporting on-site installation, and allowing for repeated insertion and removal, making it more convenient to use, improving coupling efficiency and stability, and solving the high-loss problem caused by mode field mismatch.

[0026] In some embodiments, the material of structural component 4 is any one of TiO2, Ta2O5, and Si3N4. These materials exhibit high refractive index and low absorption loss characteristics in the communication band. The high refractive index ensures effective modulation capability of the optical wave phase, while the low loss avoids thermal effects under high power. This not only meets the refractive index contrast requirements of the nanopillar array but also ensures the optical performance stability of the connector during long-term operation.

[0027] In some embodiments, to further define the specific parameters of the nanopillar array of structure 4, the specific considerations are explained below: The design logic of metasurface lenses is reverse design, that is, first determine the desired light effect, and then work backward to deduce the structural parameters.

[0028] A. Formula for determining phase distribution of optical targets To focus and couple a diverging large-mode-field beam into a small-mode-field fiber, a lens effect is required. Traditional lenses generate optical path difference through thickness variations, while metasurfaces rely on phase abrupt changes.

[0029] The phase distribution formula is: φ(r) = πr² / (λf); r refers to the radial distance, that is, the distance from any point on the end face of the structural component to the center of the optical axis; f is the equivalent focal length.

[0030] At the core of the 4th end face of the structural component, r=0: the phase delay is the minimum or maximum.

[0031] At the edge of the 4th end face of the structural component, r=r: the phase delay is at its maximum or minimum.

[0032] All points with the same r form a ring, and the nanopillars 400 at these points have the same geometric dimensions, i.e., diameter, thus achieving a rotationally symmetric lens effect.

[0033] As can be seen from the above, the phase distribution formula, i.e., the distribution of the radial secondary phase, is related to the equivalent focal length, which is directly determined by the size of the nanopillar.

[0034] B. The geometric parameters of the 400 nanopillars determine the local phase value for effective refractive index control; that is, the geometric parameters include diameter, axial length, spacing distance, and array method.

[0035] The axial length is usually fixed, and its function is to ensure that the maximum phase difference can reach 2π. If the height is insufficient, the phase coverage will not reach 2π, and the lens efficiency will be low.

[0036] The 400° spacing between any two adjacent nanopillars is usually fixed to ensure that the subwavelength condition is met and to avoid generating higher-order diffraction light.

[0037] The diameter is a variable; at different radii r, nanopillars with different diameters 400 are designed. For example, the larger the diameter, the higher the effective refractive index and the greater the phase retardation.

[0038] C. The refractive index of the material determines the modulation capability. When the refractive index of the nanopillar 400 is significantly higher than that of the surrounding medium, light passing through the nanopillar 400 will produce a noticeable phase lag. This is a fundamental premise; without the contrast in refractive index, no matter how the diameter is adjusted, the phase change will be very weak, and a lens cannot be formed.

[0039] Therefore, based on the above explanation, a positive interpretation is provided, for reference only. Figures 2-3 The binding parameters of the nanopillars 400 need to be specifically defined, as follows: The first parameter, the axial length of the nanopillar 400, satisfies the following formula: H≈λ / (n1 1); where n1 is the refractive index of structural component 4; λ is the operating wavelength of hollow fiber 3; and H is the axial length of nanopillar 400. Based on the principle of optical path difference, the axial length ensures a maximum 2π phase difference between light passing through the nanopillar and light passing through the air gap. This allows the metasurface to cover the complete 0 to 2π phase range, thereby achieving efficient wavefront modulation. Insufficient height would result in incomplete phase coverage and reduced diffraction efficiency; this specific axial length design maximizes phase modulation efficiency, ensures optimal mode field shaping, and reduces energy waste and stray light generation.

[0040] The second parameter is that the multiple nanopillars 400 in the nanopillar array are distributed in multiple concentric ring arrays; the nanopillars 400 in a ring array are evenly spaced and have the same diameter. In the radial direction, in two adjacent annular arrays, the diameter of the nanopillars 400 in one annular array differs from the diameter of the nanopillars 400 in the other annular array. (See reference...) Figure 3 As shown. Regarding Figure 2 A circular array of regular hexagons, and only a portion of the circular array is shown. Figure 3 All the circular arrays were displayed, and presented in a three-dimensional format; from Figure 2 and Figure 3 As can be seen, there is a 400 nanopillar in the core of the innermost ring array.

[0041] This discretized design conforms to the principle of metasurface phase quantization, facilitating micro- and nano-fabrication. The concentric structure ensures the rotational symmetry of the optical system, avoiding astigmatism. By changing the diameter in a stepped manner, a continuous phase distribution is approximately achieved, reducing fabrication complexity while maintaining good focusing performance, resulting in a more uniform and stable light field distribution within connector ferrule 1.

[0042] The third parameter is that, in the radial direction, the diameter of the multiple annular array of nanopillars 400 gradually increases or decreases.

[0043] The gradual increase or decrease in diameter corresponds to a smooth transition in phase delay. This gradient structure can more accurately fit the secondary phase distribution of the target and reduce diffraction noise caused by abrupt phase changes. The smooth phase change helps to form a high-quality Gaussian beam focus, further improving the mode field overlap integral between the hollow fiber 3 and the solid fiber 2, thereby improving the quality of the coupled beam and the signal-to-noise ratio of the signal transmission while ensuring low loss.

[0044] The fourth parameter specifies whether the circular array is a circular array or a regular polygon array; regular polygon arrays include regular triangle arrays, regular quadrilateral arrays, regular hexagonal arrays, or regular octagonal arrays.

[0045] The lattice structure of nanopillar 400 was defined. The close-packed structure with regular hexagonal shapes allows for more nanopillars to be filled within a unit area, improving space utilization and smoothness. Different array configurations affect the isotropy of the equivalent medium; selecting a suitable regular polygon array helps reduce grating lobe effects, ensuring consistent metasurface performance under different polarization states and enhancing the robustness of the connector to the polarization state of the input light.

[0046] The fifth parameter is that the spacing between the centers of any two adjacent nanopillars 400 is equal and less than the operating wavelength of the hollow fiber 3.

[0047] The spacing between the diffraction lines is equal and less than the operating wavelength, satisfying the subwavelength condition. This feature suppresses the generation of higher-order diffraction orders, ensuring that optical energy is mainly concentrated in the zero-order transmission direction. If the period is too large, grating diffraction effects will occur, leading to energy loss. This design makes the metasurface behave as an equivalent homogeneous medium, achieving efficient beam shaping, avoiding stray light interference with the transmission of solid fiber 2, and ensuring the efficiency and purity of the optical path.

[0048] Furthermore, this application provides a specific parameter description for structural component 4, which satisfies the above conditions: Operating wavelength λ = 1550 nm; Nanopillar material: Si3N4, refractive index n1=2.00; The substrate material, namely the three end faces of the hollow fiber, is SiO2 with a refractive index of n2=1.47. Phase distribution: φ(r) = πr² / (λf), r∈[0,15µm]; r∈[0,15µm] This corresponds to the mode field radius region of hollow fiber. Beyond this range, the light intensity is very weak, and there is no need to design nanopillars 400. H≈λ / (n1 1) = 1200nm; Phase discrete order: 8 levels, i.e., 3-bit; fabrication error < ±5nm; The spacing between any two adjacent nanopillars 400 is P = 1050 nm; or P = 700 nm, and the diameter of the nanopillar 400 is d = 385 nm; Reflectivity: R<0.1%, no coating, relying on the anti-reflective properties of the metasurface itself.

[0049] This allows the axial length, diameter, and spacing of the nanopillars 400 to be configured to provide a phase delay range of 0 to 2π at the operating wavelength of the hollow fiber 3, and to form a target equivalent focal length f≈125µm for reducing the mode field diameter of the hollow fiber 3. The mode field of the hollow fiber 3 is reduced, and the integral overlap with the mode field of the solid fiber is >92%.

[0050] The reduction factor of the three-mode field diameter in hollow-core optical fibers is not unique and can be adjusted according to actual specifications. Similarly, the mating gap between HCFs and SMFs is not unique and can be adjusted according to actual specifications. For optical signal transmission between HCFs, the connector structure remains unchanged; only the axial length, spacing, and diameter of the nanopillars on the metasurface need to be adjusted.

[0051] In some embodiments, to address the issue of epoxy resin carbonization and gas / dust contamination of the hollow fiber end face during high-power transmission, which can occur with adhesive bonding, structural component 4 is used. Therefore, epoxy resin bonding is not employed here, and the following setup is implemented instead: The hollow fiber optic connector also includes a quartz capillary tube 5 and a metal tail shank 6. One end of the quartz capillary 5 is located in the inner hole of the connector ferrule 1 and is sleeved on the hollow fiber 3; the end face of the quartz capillary 5 near the solid fiber 2 is flush with the end face of the hollow fiber 3. The metal tail shank 6 is fitted on the outside of the connector ferrule 1. The end of the quartz capillary tube 5 away from the solid fiber 2 extends into the metal tail shank 6. The hollow fiber 3 passes through the metal tail shank 6, and the metal tail shank 6 is encapsulated with glue.

[0052] Because the quartz capillary tube 5 protects the hollow fiber 3, and the metal tailstock 6 is fixed with the adhesive away from the optical path, this adhesive-free optical path design avoids the risk of adhesive carbonization and burning of the end face under high-power laser conditions. The quartz capillary tube 5 being flush with the end face ensures mechanical support stability. This structure achieves a completely adhesive-free and weld-free optical path area, significantly increasing the connector's power handling capacity, making it suitable for high-power laser transmission scenarios, while also facilitating on-site installation and maintenance, enhancing its engineering practicality.

[0053] In addition, the connector core 1 and the quartz capillary tube 5 are fitted with a clearance, and there is a gap g=5µm between the HCF and SMF. Physical contact between the end faces is achieved through precision grinding. The entire optical path is free of glue, lenses, and fusion. Fixing is achieved solely by pressing the metal tail shank 6. The epoxy adhesive isolation zone 7 is located inside the metal tail shank 6, so that the epoxy adhesive is only located at the tail of the tail shank, away from the optical path, to avoid heat absorption and carbonization.

[0054] In summary, the structural component 4 formed by direct etching of the end face of the hollow fiber 3 achieves mode field expansion and completes low-loss, high-return-loss connection under completely glue-free, fusion-free, and lens-free conditions.

[0055] Secondly, a method for manufacturing a hollow fiber optic connector is provided, comprising: After pre-processing the hollow fiber 3 and cutting it, insert it into the hollow fiber connector for fixation and perform end face grinding. The end face of the polished hollow fiber 3 is etched using a femtosecond laser to form a nanopillar array; the axial length, diameter, and spacing of the nanopillars 400 in the nanopillar array, as well as the array configuration, meet the preset parameters; the preset parameters are the geometric parameters of the nanopillars 400 of the structural component 4 described above; this step is specifically as follows: the nanopillar array is directly written using a femtosecond laser at 800nm, 100fs, and 1kHz, with a writing field size of 30µm×30µm, a single pulse energy of 25nJ, and a scanning speed of 50µm / s; The nanopillar array was cleaned using a focused ion beam with a sidewall roughness Ra < 3 nm, followed by ultrasonic cleaning and nitrogen drying to form structural component 4; the ultrasonic cleaning was then placed in a solution of acetone and isopropanol. The processing temperature in the above steps is lower than the preset temperature. If the preset temperature is less than 80℃, it falls under the category of cold processing. Insert the hollow fiber 3 with structural component 4 into the connector ferrule 1; After local heating of the metal tailstock 6, it is pressed and fixed. Actively align with SMF on a standard alignment instrument, monitor insertion loss, and mark the relative angle after meeting the requirement of ≤0.3dB; assemble the SC shell to complete the finished product.

[0056] The above steps employ femtosecond laser etching and focused ion beam cleaning, with the processing temperature below a preset temperature. This cold processing avoids the risk of microstructure collapse in hollow fiber 3 due to high temperatures. Femtosecond laser etching achieves high-precision nanopillar 400 forming, while focused ion beam cleaning removes the recast layer, ensuring optical surface quality. This method ensures reliable fabrication of metasurface structures on the fragile end face of hollow fiber, enabling automated mass production. It is suitable for mass automation, with lower overall design costs and higher reliability, while ensuring high device yield and consistent optical performance.

[0057] The hollow fiber optic connectors described above can be extended to FC, LC, MPO, and other types, simply by changing the dimensions of the ferrule and surrounding structural components. The "hollow fiber" described above is not limited to the five-ring, two-nested configuration; any ring combination can be used, as long as it is a hollow anti-resonant fiber. For example, a five-ring, three-nested configuration is also possible. In addition, this application provides a simulation diagram of an actual hollow fiber optic connector connection, demonstrating evidence of the beneficial effects of the structure presented in this application; see also Figure 4 As shown, the mode field of HCF fiber, taking 20 micrometers as an example, is reduced by 1.9 times after passing through structural component 4, to 10.53 micrometers, and then efficiently coupled with standard single-mode fiber. The mode field diameter of standard single-mode fiber is 10.4 micrometers, and the insertion loss is ≤0.3dB.

[0058] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0059] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A hollow core optical fiber connector, characterized by, It includes: The connector ferrule (1) has a coaxial solid optical fiber (2) and hollow optical fiber (3) in its inner hole. Structural component (4) is located between solid fiber (2) and hollow fiber (3) and is connected to the end face of hollow fiber (3); The refractive index of the structural component (4) is greater than that of the hollow fiber (3); the structural component (4) includes a nanopillar array; the diameter of the nanopillars (400) of the nanopillar array is configured to vary radially so that the phase of the optical path varies radially.

2. The hollow fiber optic connector as described in claim 1, characterized in that: The material of the structural component (4) is any one of TiO2, Ta2O5 and Si3N4.

3. The hollow fiber optic connector as described in claim 1, characterized in that: The axial length of the nanopillar (400) satisfies the following formula: H ~ λ / (n1 1); wherein n1 is the refractive index of the structure (4); λ is the operating wavelength of the hollow core fiber (3) and H is the axial length of the nanopillar (400).

4. The hollow fiber optic connector as described in claim 1, characterized in that: The nanopillars (400) in the nanopillar array are arranged in a concentric ring array; the nanopillars (400) in a ring array are evenly spaced and have the same diameter; In the radial direction, in two adjacent annular arrays, the diameter of the nanopillars (400) in one annular array is different from the diameter of the nanopillars (400) in the other annular array.

5. The hollow fiber optic connector as described in claim 4, characterized in that: In the radial direction, the diameter of the multiple annular array of nanopillars (400) gradually increases or decreases.

6. The hollow fiber optic connector as described in claim 4, characterized in that: The ring array is a circular array or a regular polygon array; the regular polygon array includes an equilateral triangle array, a regular quadrilateral array, a regular hexagonal array, or a regular octagonal array.

7. The hollow fiber optic connector as described in claim 5, characterized in that: The spacing between the centers of any two adjacent nanopillars (400) is equal and less than the operating wavelength of the hollow fiber (3).

8. The hollow fiber optic connector as described in claim 7, characterized in that: The axial length, diameter, and spacing of the nanopillars (400) are configured to provide a phase delay range of 0 to 2π at the operating wavelength of the hollow fiber (3) and to form a target equivalent focal length for reducing the mode field diameter of the hollow fiber (3).

9. The hollow fiber optic connector as described in claim 1, characterized in that: The hollow fiber optic connector also includes a quartz capillary (5) and a metal tailstock (6): One end of the quartz capillary (5) is located in the inner hole of the connector ferrule (1) and is sleeved on the hollow fiber (3); the end face of the quartz capillary (5) near the solid fiber (2) is flush with the end face of the hollow fiber (3). The metal tail (6) is sleeved on the outside of the connector core (1), the end of the quartz capillary (5) away from the solid optical fiber (2) extends into the metal tail (6), the hollow optical fiber (3) passes through the metal tail (6), and the metal tail (6) is encapsulated with glue.

10. A method of making a hollow optical fiber connector as claimed in claim 1, wherein, It includes: After the hollow fiber (3) is cut, it is inserted into the hollow fiber connector for fixation and the end face is polished. The end face of the polished hollow fiber (3) is etched using a femtosecond laser to form a nanopillar array; the axial length, diameter and spacing of the nanopillars (400) of the nanopillar array, as well as the array method, meet the preset parameters. The nanopillar array is cleaned using a focused ion beam, followed by ultrasonic cleaning and nitrogen drying to form a structural component (4); wherein the processing temperature of the above steps is lower than the preset temperature; Insert the hollow fiber (3) with structural component (4) into the connector ferrule (1).

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