Single-lens coupling assembly, single-lens mode field conversion device and manufacturing method therefor

Abstract

Disclosed in the present invention are a single-lens coupling assembly (300), a single-lens mode field conversion device and a manufacturing method therefor. The single-lens coupling assembly (300) comprises a solid-core single-mode optical fiber (1) having a first mode field diameter; a hollow-core optical fiber (2) having a second mode field diameter; a sleeve (3), which has a hollow tubular cavity that runs through both ends, wherein one end of the solid-core single-mode optical fiber (1) and one end of the hollow-core optical fiber (2) respectively extend into the hollow tubular cavity via two open ends of the sleeve (3); and a lens (4), which is located in the sleeve (3) between the solid-core single-mode optical fiber (1) and the hollow-core optical fiber (2) and is used for implementing the conversion of the mode field diameters between the solid-core single-mode optical fiber (1) and the hollow-core optical fiber (2). In the present invention, the conversion of different mode fields between the solid-core single-mode optical fiber (1) and the hollow-core optical fiber (2) is implemented by means of a single lens (4), such that a reliable and stable connection between the solid-core single-mode optical fiber (1) and the hollow-core optical fiber (2) is achieved.

Description

Single-lens coupling assembly, single-lens mode field conversion device and manufacturing method thereof Technical Field

[0001] The present invention belongs to the technical field of optical fiber communications, and in particular relates to a single-lens coupling component, a single-lens mode field conversion device and a manufacturing method thereof. Background Art

[0002] Hollow-core antiresonant optical fiber (hereinafter referred to as hollow-core optical fiber) realizes hollow-core light guidance through the antiresonant reflection optical waveguide mechanism. It has the advantages of low latency, low dispersion, low nonlinearity, high damage threshold, broadband light guidance, low thermal sensitivity, and radiation resistance. Therefore, it has great application prospects in optical communications, high-power laser transmission, ultrafast optics, nonlinear optics, optical fiber sensing and other fields, and is very suitable for harsh environments such as aerospace radiation.

[0003] To enhance the compatibility of hollow-core fibers with traditional fiber-optic device systems, or between optical fibers and optical waveguides, achieving low insertion loss, high return loss, and highly stable connections between different optical fibers is a core issue that needs to be addressed. However, significant structural and mode field differences between the two often make efficient and reliable coupling difficult. Fiber mode field conversion devices can alter the mode field characteristics of transmitted light, thereby breaking through the coupling bottleneck between hollow-core fibers and traditional single-mode fibers, enabling efficient integration of fiber-optic photonic devices and opening up new possibilities for their development and application. The development of fiber mode field conversion devices is necessary to meet the impending large-scale application demands of hollow-core fibers in high-speed, high-capacity optical communications, high-power laser transmission, fiber-optic sensing, and special-scenario optical transmission.

[0004] There are three main technical bottlenecks in developing hollow-core fiber mode field diameter conversion devices to achieve efficient connection between hollow-core fibers and traditional solid-core single-mode fibers widely used in existing optical transmission systems. First, the mode field diameter of traditional solid-core single-mode fibers at a transmission wavelength of 1310nm is approximately 9.2μm, while the mode field diameter of hollow-core fibers is generally 20-40μm. The mode field sizes of the two are seriously mismatched, resulting in high coupling losses. In addition, the mode field mismatch at the coupling interface between the two may also excite higher-order modes in the hollow-core fiber, affecting the quality of the transmitted beam. Therefore, matching the mode field characteristics of the two optical fibers is one of the key technical bottlenecks that need to be solved. Second, there is an air structure in the core of the hollow-core fiber. The air-glass interface at the coupling interface between the traditional solid-core single-mode fiber and the hollow-core fiber will also produce strong Fresnel reflection, thereby increasing insertion loss and causing back reflection. Therefore, the effective suppression of Fresnel reflection at the interface is the second technical bottleneck that needs to be solved. Thirdly, for hollow-core optical fibers with internal microstructures, since the optical fiber itself relies on the internal microstructure to achieve low-loss light transmission, ensuring the integrity of the internal microstructure of the optical fiber during coupling is also a key technical bottleneck that needs to be solved.

[0005] In the prior art, optical fiber coupling often involves fixing an optical waveguide module on an optical fiber to achieve conversion of the optical fiber's mode field diameter. However, the optical waveguide module is relatively small, making size control difficult and not easy to process. Furthermore, in order to increase return loss, the end of the optical waveguide module needs to have a certain tilt angle, which further increases the difficulty of processing and makes coupling even more difficult. Summary of the Invention

[0006] The present invention aims to solve one of the technical problems in the related art to at least some extent.

[0007] To this end, one embodiment of the present invention proposes a single-lens coupling assembly. This single lens achieves the conversion of different mode fields between a single-mode fiber and a hollow-core fiber, thereby achieving a reliable and stable connection between the two fibers. Furthermore, the internal structure of the mode field conversion device is designed based on the characteristics of hollow-core fiber and the requirements for low insertion loss and high return loss.

[0008] One of the objectives of the present invention is to provide a single-lens coupling assembly, comprising a solid-core single-mode optical fiber having a first mode field diameter; a hollow-core optical fiber having a second mode field diameter; a sleeve having a hollow lumen with two through-holes, with one end of the solid-core single-mode optical fiber and one end of the hollow-core optical fiber respectively extending into the hollow lumen from openings at both ends of the sleeve; and a lens located in the sleeve between the solid-core single-mode optical fiber and the hollow-core optical fiber, for achieving conversion of the mode field diameter between the solid-core single-mode optical fiber and the hollow-core optical fiber.

[0009] As a preferred solution, the end faces of the lens facing the optical fibers at both ends are both curved structures.

[0010] As a preferred solution, the first end of the solid-core single-mode optical fiber is a solid-core bare optical fiber segment without a coating layer, and the solid-core bare optical fiber segment is arranged in the hollow tube cavity of the solid-core pin to form a solid-core optical fiber component. The first end of the hollow-core optical fiber is a hollow-core bare optical fiber segment without a coating layer, and the end of the hollow-core bare optical fiber segment is arranged in the hollow tube cavity of the hollow-core pin to form a hollow-core optical fiber component.

[0011] As a preferred embodiment, the sleeve is a hollow cylindrical structure, and the sleeve includes a first sub-kit and a second sub-kit, the ends of the first sub-kit and the second sub-kit are butt-jointed and coaxially arranged, wherein the first end of the lens extends into the lumen of the first sub-kit, and the second end of the lens extends into the lumen of the second sub-kit.

[0012] As a preferred solution, a chamfered surface is formed on the end of the solid core optical fiber component facing the lens, and the chamfered surface is not perpendicular to the axial direction of the solid core pin.

[0013] As a preferred solution, an anti-reflection film is provided on the beveled surface, and an anti-reflection film is provided on the arc surface structure on the side of the lens opposite to the solid core optical fiber component.

[0014] A second object of the present invention is to provide a single-lens mode field conversion device, comprising a single-lens coupling assembly as described in any one of the above items.

[0015] As a preferred solution, it also includes a solid core end fixing component and a hollow core end fixing component, the solid core end fixing component includes a solid core end outer shell, the hollow core end fixing component includes a hollow core end outer shell, the butt ends of the solid core end outer shell and the hollow core end outer shell are connected to form a shell structure, and a cavity for accommodating a single lens coupling component is provided in the shell structure, the solid core end fixing sleeve fixes the solid core single-mode optical fiber to the end of the solid core end outer shell, and the hollow core end fixing sleeve fixes the hollow core optical fiber to the end of the hollow core end outer shell.

[0016] As a preferred solution, the opposite ends of the solid end outer shell and the hollow end outer shell are both provided with a compression joint that cooperates with the fixing sleeve.

[0017] As a preferred solution, at least one annular sealing connection groove is provided on the outer cylindrical surface of the crimping head.

[0018] As a preferred solution, the solid end fixing assembly also includes a flange and a retaining ring. The flange is a cylindrical structure, and a cavity for accommodating the solid core optical fiber component is formed along the axial direction of the flange. A limiting boss is provided on the outer wall near the first end of the flange, and a groove for installing the retaining ring is provided on the outer wall near the second end of the flange. The flange is fixedly connected to the solid core optical fiber component, and the first end of the flange cooperates with the retaining boss in the tube cavity of the solid end outer shell through the limiting boss to limit the position of the flange relative to the solid end outer shell along the first axial direction, and the second end of the flange cooperates with the groove and the retaining ring to limit the position of the flange relative to the solid end outer shell along the second axial direction, wherein the first axial direction and the second axial direction are opposite.

[0019] The third object of the present invention is to propose a method for manufacturing a single-lens mode field conversion device, comprising the following steps: inserting a bare fiber segment without a coating layer at the end of a solid-core single-mode optical fiber into a solid-core pin cavity and fixing it to form a solid-core optical fiber component; inserting a bare fiber segment without a coating layer at the end of a hollow-core optical fiber into a hollow-core pin cavity and fixing it to form a hollow-core optical fiber component; inserting a lens into the tube cavity of a sleeve and fixing it, inserting the obtained solid-core optical fiber component and hollow-core optical fiber component from the opposite end ports of the sleeve respectively, and bonding and fixing the positions of the solid-core optical fiber component and the hollow-core optical fiber component after light-through debugging to form a single-lens coupling assembly; fixing the butt ends of a solid-core end fixing assembly that is inserted through the outside of the solid-core end of the single-lens coupling assembly and a hollow-core end fixing assembly that is inserted through the outside of the hollow-core end of the single-lens coupling assembly; fixing the solid-core single-mode optical fiber on the solid-core end fixing assembly through a solid-core end fixing sleeve, and fixing the hollow-core optical fiber on the hollow-core end fixing assembly through a hollow-core end fixing sleeve.

[0020] As a preferred solution, the sleeve includes a first sub-assembly and a second sub-assembly. The first end of the lens is first inserted into the lumen of the first sub-assembly and bonded and fixed. The second end of the lens is then inserted into the lumen of the second sub-assembly and bonded and fixed. The solid-core optical fiber component and the hollow-core optical fiber component are then respectively inserted through the opposite end ports of the sleeve. After light-through debugging, the positions of the solid-core optical fiber component and the hollow-core optical fiber component are bonded and fixed when the coupling loss is minimized to form a single-lens coupling assembly.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: First, this solution optimizes the structure of the fiber coupling assembly through structural improvements. The provision of a dedicated lens facilitates batch processing of the lens, reducing the manufacturing difficulty of the fiber coupling assembly to a certain extent. Furthermore, after the structural improvements, a single dedicated lens is used to achieve mode field conversion between two optical fibers with different mode field diameters, reducing the insertion loss of the hollow-core fiber. Return loss is improved through fiber bevel processing and coating. Since Fresnel reflection occurs when light enters the interface between two media with different refractive indices, this solution suppresses Fresnel reflection by coating the end faces of the solid-core single-mode fiber and the lens with an anti-reflection coating. By providing a solid-core ferrule at the end of the solid-core single-mode fiber and a hollow-core ferrule at the end of the hollow-core fiber, the fiber ends are reinforced and the position of the fibers can be adjusted during subsequent commissioning. A solid-end fixing assembly and a hollow-core fixing assembly are provided on the exterior of the two mode field diameter fibers to form an outer shell, thereby securing and effectively protecting the internal structure.

[0022] Secondly, this solution optimizes the manufacturing process of the single-lens mode field conversion device. By coordinating with the specific structure of the above-mentioned single-lens mode field conversion device and strictly implementing the manufacturing process, it can avoid contamination of the internal components of the conversion device. At the same time, it reduces the processing difficulty to a certain extent and improves the coupling effect of the manufactured product. The two ends of the lens are respectively extended and fixed by two sub-kits. This solution uses a specific pin structure to introduce the solid core optical fiber component and the single-mode optical fiber component from the two ends of the sleeve, which is convenient for light-through debugging to adjust the optical fiber position, realize the precise coupling of the two mode field diameter optical fibers, and thus achieve a reliable and stable connection effect between the two mode field diameter optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] FIG1 is an overall structural appearance diagram of a single-lens mode field conversion device according to the present invention; FIG2 is a cross-sectional view of the overall structural appearance diagram of a single-lens mode field conversion device according to the present invention; FIG3 is an appearance structural diagram of a single-lens coupling assembly according to the present invention; FIG4 is a cross-sectional view of a single-lens coupling assembly according to the present invention; FIG5 is a partial enlarged view of the connection between a solid-core end shell and a hollow-core end shell according to the present invention; FIG6 is a partial enlarged view of the connection between a solid-core ferrule optical fiber component and a solid-core end shell according to the present invention; FIG7 is a partial enlarged view of the connection between a hollow-core ferrule optical fiber component and a hollow-core end shell according to the present invention; FIG8 is a schematic diagram of the connection between a solid-core single-mode optical fiber and a solid-core ferrule according to the present invention; FIG9 is a schematic diagram of the connection between a hollow-core optical fiber and a hollow-core ferrule according to the present invention; FIG10 is a schematic diagram of the connection between a lens according to the present invention and a first subassembly; FIG11 is a schematic diagram of the connection between a lens according to the present invention and a second subassembly; FIG12 is a schematic diagram of the working principle of mode field conversion of a single-lens mode field conversion device according to the present invention; FIG13 is a schematic diagram of the structure of a single-lens mode field conversion device according to a specific embodiment of the present invention; FIG14 is a simulation diagram of a specific embodiment of the present invention: solid-core single-mode optical fiber-hollow-core optical fiber; FIG15 is a simulation diagram of a specific embodiment of the present invention: hollow-core fiber-solid-core single-mode fiber; markings in the figure: 1, solid-core single-mode fiber, 11, solid-core single-mode fiber I, 12, solid-core single-mode fiber II, 2, hollow-core fiber, 3, sleeve, 31, first sub-assembly, 311, cavity I, 32, second sub-assembly, 321, cavity II, 4, lens, 41, lens I, 42, lens II, 5, solid-core pin, 51, tapered insertion hole, 52, beveled surface, 6, hollow-core pin, 7, solid-core end outer shell, 8, hollow-core end outer shell, 9, solid-core end fixing sleeve, 10, hollow-core end fixing sleeve, 13, flange, 131, limiting boss, 132, groove, 14, retaining ring, 10 0. Solid-core optical fiber component, 111. Crimping joint, 112. Annular groove, 200. Hollow-core optical fiber component, 300. Single lens coupling assembly, 400. Solid-core end fixing assembly, 500. Hollow-core end fixing assembly, 600. Light beam transmission, 101. Solid-core optical fiber outer jacket layer, 102. Solid-core bare optical fiber segment, 103. Solid-core optical fiber coating layer, 104. Solid-core optical fiber protective layer, 105. Solid-core optical fiber reinforcement element, 201. Hollow-core optical fiber outer jacket layer, 202. Hollow-core bare optical fiber segment, 203. Hollow-core optical fiber coating layer, 204. Hollow-core optical fiber reinforcement element, A. Glue area. DETAILED DESCRIPTION

[0025] The present invention is described in detail below by way of exemplary embodiments. However, it should be understood that elements, structures, and features in one embodiment may also be beneficially combined in other embodiments without further description.

[0026] It should be noted that: unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons having ordinary skills in the field to which the invention belongs. The words "one", "an" or "the" and the like used in the patent application specification and claims of the present invention do not express a quantitative limitation, but rather indicate the presence of at least one. Words such as "include" or "comprise" indicate that the elements or objects appearing before "include" or "comprises" include the elements or objects listed after "include" or "comprises" and their equivalents, but do not exclude other elements or objects with the same function.

[0027] As shown in the figure, a preferred embodiment of the present scheme provides a single-lens coupling assembly, including a solid-core single-mode optical fiber 1, a hollow-core optical fiber 2, a sleeve 3 and a lens 4, wherein the mode field diameters of the solid-core single-mode optical fiber 1 and the hollow-core optical fiber 2 are different, wherein the solid-core single-mode optical fiber 1 has a first mode field diameter, the hollow-core optical fiber 2 has a second mode field diameter, and the mode field diameter of the hollow-core optical fiber 2 is larger than the mode field diameter of the solid-core single-mode optical fiber 1, the sleeve 3 is a glass tube with a hollow cavity, the lens 4 is arranged in the hollow cavity of the sleeve 3, the first end portions of the solid-core single-mode optical fiber 1 and the hollow-core optical fiber 2 respectively extend into the inner cavity of the sleeve 3 from the openings at both ends, and the solid-core single-mode optical fiber 1 and the hollow-core optical fiber 2 are relatively arranged at both ends of the lens 4; the lens 4 is a separately arranged component, which is convenient for batch and separate processing, and the two ends of the lens 4 corresponding to the solid-core single-mode optical fiber 1 and the hollow-core optical fiber 2 are arc-shaped convex structures.

[0028] This solution specifically includes the following two scenarios, depending on the direction of light beam transmission: the first end of the lens 4 near the small-mode-field solid-core single-mode fiber 1 is used to expand and collimate the light emitted from the solid-core single-mode fiber 1, and the second end of the lens 4 near the large-mode-field hollow-core fiber 2 is used to focus the collimated light to a spot mode field size that matches the large-mode-field hollow-core fiber 2. Alternatively, the second end of the lens 4 near the large-mode-field hollow-core fiber 2 is used to expand and collimate the light emitted from the hollow-core fiber 2, and the first end of the lens 4 near the small-mode-field solid-core single-mode fiber 2 is used to focus the collimated light to a spot mode field size that matches the small-mode-field solid-core single-mode fiber 1.

[0029] In this solution, in order to facilitate the installation of the lens 4, the sleeve 3 is divided into two parts along a cross section perpendicular to its axial direction, namely a first sub-assembly 31 and a second sub-assembly 32, wherein the first curved convex end of the lens 4 is arranged in the cavity 1 311 of the first sub-assembly 31, and the second curved convex end of the lens 4 is arranged in the cavity 2 321 of the second sub-assembly 32. The shape and inner diameter of cavity 1 311 and cavity 2 321 are the same. The purpose of such setting is to take into account that: if the sleeve 3 is set to be integrally formed, the lens 4 needs to be inserted into its cavity from a side port of the sleeve 3 and enter the position near the middle section of the sleeve 3. Since the cylindrical surface of the lens 4 is coated with glue for bonding, the glue will adhere to the inner wall of the sleeve 3 when the lens 4 is installed, which will cause pollution to the inner wall of the sleeve 3. Since the sleeve 3 in this solution is predetermined to be broken into two parts, when the lens is installed, only one end of the lens 4 needs to be inserted into the hollow cavity of the first sub-assembly 31 and fixed with glue, and the other end of the lens 4 needs to be inserted into the hollow cavity of the second sub-assembly 32 and fixed with glue. This will avoid pollution of the inner wall of the sleeve 3.

[0030] In a typical embodiment of the present invention, the solid-core ferrule 5 is a hollow cylindrical glass tube with a tapered insertion hole 51 at the end of the solid-core ferrule 5. The tapered insertion hole 51 facilitates the insertion of the end of the solid-core single-mode fiber 1 into the ferrule cavity and also serves to accommodate adhesive, further securing the connection between the fiber and the ferrule. The end of the solid-core ferrule 5 facing the lens 4 forms a chamfered surface 52 at an 8° angle to the axial direction, and is coated with an anti-reflection coating. The hollow-core ferrule 6 is a cylindrical glass tube with flush end faces at both ends. The provision of the solid-core ferrule 5 and the hollow-core ferrule 6 not only reinforces the fiber end but also facilitates a series of fiber position adjustments during the subsequent manufacturing and commissioning of the conversion device.

[0031] This solution, taking a solid-core single-mode fiber 1 and a hollow-core fiber 2 as examples, involves inserting a bare solid fiber segment 102 of the solid-core single-mode fiber 1 without a coating 101 into a solid-core ferrule 5 and securing it with adhesive. The end faces of the solid-core single-mode fiber 1 and solid-core ferrule 5 are then polished and coated with an anti-reflection coating, thereby forming a solid-core fiber component 100. A bare hollow-core fiber segment 202 of the hollow-core fiber 2 without a coating 201 is passed through a hollow-core ferrule 6. The end of the hollow-core fiber 2 extending beyond the hollow-core ferrule 6 is then cut flat with a fiber cleaver. The end face of the hollow-core fiber 2 is then pulled back into the cavity of the hollow-core ferrule 6. The bare hollow-core fiber segment of the hollow-core fiber 2 and the hollow-core ferrule 6 are then secured with adhesive, thereby forming a hollow-core fiber component 200. The solid-core fiber component 100 and the hollow-core fiber component 200 extend from opposite ends of the ferrule 3 into the interior of the ferrule 3, achieving mode field conversion and matching between the two optical fibers.

[0032] In this embodiment, since Fresnel reflection occurs when light enters the interface between two media with different refractive indices, this solution suppresses Fresnel reflection by coating the end faces of the small-mode-field solid-core single-mode fiber 1 and the lens 4 with an anti-reflection coating. The principle behind the anti-reflection coating is that the two reflected beams from the upper and lower surfaces of the film undergo destructive interference. Therefore, the optical path difference between the two reflected beams should be an odd multiple of half a wavelength, and the optical thickness of the film (the product of the actual thickness and the material's refractive index) must be an odd multiple of a quarter wavelength.

[0033] In this solution, in order to further improve the return loss, the end face of the small mode field solid core single mode optical fiber 1 component is polished into an 8° bevel surface 52, which can make a part of the reflected light reflect to the cladding at a certain angle, thereby reducing more reflected light in the fiber core returning to the light source and increasing the return loss.

[0034] As shown in the figure, the present solution also provides a single-lens mode field conversion device, including the above-mentioned single-lens coupling assembly 300, wherein a solid core end fixing assembly 400 is provided on the periphery of the solid core end of the single-lens coupling assembly 300, and a hollow core end fixing assembly 500 is provided on the periphery of the hollow core end of the single-lens coupling assembly 300, and the solid core end fixing assembly 400 and the hollow core end fixing assembly 500 are connected by threads, and a solid core end fixing sleeve 9 is provided on the outside of the connection between the solid core end fixing assembly 400 and the solid core optical fiber component 100, and the solid core end fixing sleeve 9 is used to fix and press the solid core single-mode optical fiber 1 on the crimping end of the solid core end fixing assembly 400, and a hollow core end fixing sleeve 10 is provided on the outside of the connection between the hollow core end fixing assembly 500 and the hollow core optical fiber component 100, and is used to fix and press the hollow core optical fiber 2 on the crimping end of the hollow core end fixing assembly 500.

[0035] In a typical embodiment of the present invention, the solid end fixing assembly 400 includes a solid end outer shell 7, and the hollow end fixing assembly 500 includes a hollow end outer shell 8. The solid end outer shell 7 and the hollow end outer shell 8 are both rotating cylindrical structures with hollow cavities arranged along their respective central axes. The relatively arranged connecting ends of the solid end outer shell 7 and the hollow end outer shell 8 are correspondingly provided with internal threaded portions and external threaded portions, so that the opposite ends of the solid end outer shell 7 and the hollow end outer shell 8 can be fixedly connected by threads. After the solid end outer shell 7 and the hollow end outer shell 8 are threadedly connected, a complete shell structure is formed, and a accommodating cavity for accommodating the single lens coupling assembly 300 is formed in the shell structure.

[0036] In a preferred embodiment of the present scheme, a pressing joint 111 is provided at the opposite end of the solid end outer shell 7 and the hollow end outer shell 8, and at least one annular groove 112 along the axial direction is formed on the pressing joint 111. The function of providing the annular groove 112 is to cooperate with the solid end fixing sleeve 9 and the hollow end fixing sleeve 10. For example, if the fixing sleeve adopts a shrinkage crimping method, the fixing sleeve will be fastened to the position of the annular groove 112 after deformation and tightening. The annular groove 112 can increase the relative friction between the fixing sleeve and the pressing joint 111 along the axial direction and enhance the sealing effect. If the fixing sleeve is fixed by gluing, the annular groove 112 can be used to accommodate glue, thereby increasing the firmness of the bonding and enhancing the sealing effect.

[0037] In the present invention, the solid-core end fixing sleeve 9 and the hollow-core end fixing sleeve 10 have the same or similar structures, both being annular sleeves comprising a large-diameter end and a small-diameter end. The large-diameter end of the solid-core end fixing sleeve 9 is used to press and secure, or bond, the outer jacket layer 103 of the solid-core single-mode optical fiber 1, which has been stripped from its end, to the crimping joint 111 of the solid-core end outer shell 11, while the small-diameter end of the solid-core end fixing sleeve 9 is used to connect to the solid-core single-mode optical fiber 1. The hollow-core end fixing sleeve 10 presses and secures, or bonds, the outer jacket layer 203 of the hollow-core optical fiber 2 to the crimping joint 111 of the hollow-core end outer shell 12.

[0038] In a typical embodiment of the present invention, the solid end fixing assembly 400 further includes a flange 13 and a retaining ring 14 for fixing the position of the flange 13, wherein the main body of the flange 13 is a hollow cylindrical structure, the tail end of the solid pin 5 is fixed to the inner wall of the flange 13 by glue, and the head end of the solid pin 5 extends into the interior of the sleeve 3 and corresponds to the lens 4. A limiting boss 131 is provided on the outer wall near the first end of the flange 13, and a stopper 102 is formed at the connection between the accommodating cavity of the solid core end outer shell 11 and the crimping head 101. The stopper 102 can cooperate with the limiting boss 131 to limit the relative position between the solid core optical fiber component 100 and the solid core end outer shell 11 along the first axial direction of the A axis, and a groove 132 for installing the retaining ring 14 is provided on the outer wall near the second end of the flange 13. After the retaining ring 14 is installed, it is located at the outer end portion of the crimping head 111 of the solid core end outer shell 11, so that the relative position between the solid core optical fiber component 100 and the solid core end outer shell 11 along the second axial direction of the A axis is limited by the retaining ring 14. The direction of the second axial direction is opposite. Specifically, the distance between the retaining ring 14 and the limiting boss 131 is equal to the axial length of the crimping joint 111 of the solid core end outer shell 11 it accommodates, so that the axial position of the solid core optical fiber component 100 relative to the solid core end outer shell 11 can be limited from both ends. It should be pointed out that after the retaining ring 14 is installed, it is basically flush with the outer cylindrical surface of the crimping joint 101 of the solid core end outer shell 11, thereby facilitating the installation of the solid core end fixing sleeve 9. Since the solid core end fixing component 7 and the hollow core end fixing component 8 are threadedly connected, the limiting cooperation of the limiting boss 131 and the retaining ring 14 can realize the limitation of the relative position of the single lens coupling component 300 and the overall shell along the axial direction.

[0039] In this embodiment, the solid-core single-mode optical fiber 1 comprises, from the outside in, a solid-core optical fiber outer jacket 101, a solid-core optical fiber reinforcement element 105, a solid-core optical fiber protective layer 104, a solid-core optical fiber coating 103, and a solid-core optical fiber bare fiber segment 102. The solid-core optical fiber bare fiber segment 102 comprises a cladding and a core. The hollow-core optical fiber 2 comprises, from the outside in, a hollow-core optical fiber outer jacket 201, a hollow-core optical fiber reinforcement element 204, a hollow-core optical fiber coating 203, and a hollow-core optical fiber bare fiber segment 202.

[0040] The method for manufacturing a single-lens mode field conversion device of the present invention comprises the following steps: inserting an uncoated solid-core bare fiber segment 102 of a solid-core single-mode optical fiber 1 into the cavity of a solid-core ferrule 5 and fixing it to form a solid-core optical fiber component 100; inserting an uncoated hollow-core bare fiber segment 202 of a hollow-core optical fiber 2 into the cavity of a hollow-core ferrule 6 and fixing it to form a hollow-core optical fiber component 200; in this step, the solid-core optical fiber coating 103 outside the optical fiber cladding of the first end of the solid-core single-mode optical fiber 1 is removed, and the solid-core bare fiber segment 102 of the solid-core single-mode optical fiber 1 with the stripped solid-core optical fiber coating 103 is inserted into the hollow lumen of the solid-core ferrule 5 and fixed with glue; the end face of the combination of the solid-core single-mode optical fiber 1 and the solid-core ferrule 5 is polished to form a beveled surface 52 with an acute angle of 8° with the axial direction of the solid-core ferrule 5; and an anti-reflection coating is applied to the arc-shaped convex surface of the beveled surface 52 opposite to the lens 4 to form the solid-core optical fiber component 100.

[0041] In this step, the hollow-core fiber coating 203 outside the fiber cladding in the hollow-core fiber 200 is partially removed, and the hollow-core bare fiber segment 202 of the hollow-core fiber 2 with the hollow-core fiber coating 203 stripped off is passed through the hollow tube cavity of the hollow-core pin 6. The end of the hollow-core bare fiber segment 202 of the hollow-core fiber 2 that has passed through one end is cut flat using a fiber optic cutter, and the hollow-core bare fiber segment 202 is pulled back into the hollow tube cavity of the hollow-core pin 6 and fixed with glue to form the hollow-core fiber component 200.

[0042] It should be pointed out that, in this solution, the outer layer of the solid core optical fiber outer sheath layer 101 that has been stripped is only separated from the solid core bare optical fiber segment 102, while the stripped solid core optical fiber outer sheath layer 101 and the rear end unstripped solid core optical fiber outer sheath layer 101 are still connected together, and the outer layer of the hollow core outer sheath layer 201 that has been stripped is only separated from the hollow core bare optical fiber segment 202, while the stripped hollow core optical fiber outer sheath layer 201 and the rear end unstripped hollow core optical fiber outer sheath layer 201 are still connected together.

[0043] The lens 4 is inserted into the lumen of the sleeve 3 and fixed, and the solid core optical fiber component 100 and the hollow core optical fiber component 200 are respectively inserted from the opposite end ports of the sleeve 3. After light-through debugging, the positions of the solid core optical fiber component 100 and the hollow core optical fiber component 200 are bonded and fixed to form a single lens coupling assembly 300.

[0044] In this step, the lens 4 is inserted into the body of the sleeve 3 and fixed, and the solid-core fiber component 100 and the hollow-core fiber component 200 are inserted into the predetermined theoretical design positions in the sleeve 3. After online optical debugging, the axial and radial positions of the solid-core fiber component 100 and the hollow-core fiber component 200 are fine-tuned. When the coupling loss is minimized, the positions of the solid-core fiber component 100 and the hollow-core fiber component 200 are fixed to form a single-lens coupling assembly 300. Because the ends of the solid-core fiber component 100 and the hollow-core fiber component 200 are both set in the glass pin component, during the optical debugging process, while the optical fiber is reinforced, it is very convenient to accurately adjust the position to achieve a high-efficiency coupling effect.

[0045] In this step, preferably, the sleeve 3 includes a first subassembly 31 and a second subassembly 32. The first end of the lens 4 is first inserted into the lumen of the first subassembly 31 and bonded and fixed. The second end of the lens 4 is then inserted into the lumen of the second subassembly 32 and bonded and fixed. The solid-core optical fiber component 100 and the hollow-core optical fiber component 200 are then respectively inserted through the opposite end ports of the sleeve 3. After optical debugging, the solid-core optical fiber component 100 and the hollow-core optical fiber component 200 are bonded and fixed at their positions when the coupling loss is minimized, thereby forming a single-lens coupling assembly 300. In this way, when installing the lens 4, only one end of the lens 4 needs to be inserted into the hollow cavity of the first subassembly 31 and fixed with adhesive, and the other end of the lens 4 needs to be inserted into the hollow cavity of the second subassembly 32 and fixed with adhesive. This will effectively avoid contamination of the inner wall of the sleeve 3.

[0046] The solid core end fixing assembly 400, which is inserted through the solid core end of the single-lens coupling assembly 300, and the hollow core end fixing assembly 500, which is inserted through the hollow core end of the single-lens coupling assembly 300, are fixedly connected at their butt ends. In this step, the solid core optical fiber component 100 of the single-lens coupling assembly 300 obtained in the above step is fixedly connected to the flange 13 by gluing. Then, the solid core end outer shell 7 is mounted on the outer surface of one end of the flange 13 of the single-lens coupling assembly 300, and a retaining ring 14 is used to block and limit the axial relative sliding between the flange 13 and the solid core end outer shell 7. Specifically, the retaining ring 14 abuts against the end of the solid core end outer shell 7. The hollow core end outer shell 8 is mounted on the hollow core end of the single-lens coupling assembly 300, and the solid core end outer shell 7 and the hollow core end outer shell 8 are screwed together.

[0047] The solid core fiber outer jacket layer 101 stripped from the solid core single-mode optical fiber 1 is fixed to the solid core end fixture 400 via the solid core end fixing sleeve 9, and the hollow core fiber outer jacket layer 201 stripped from the hollow core optical fiber 2 is fixed to the hollow core end fixing assembly 500 via the hollow core end fixing sleeve 10. In this step, specifically, the large-diameter end of the solid core end fixing sleeve 9 fixes the stripped outer jacket and aramid fiber of the solid core single-mode optical fiber 1 between the solid core end fixing sleeve 9 and the crimping joint 111 of the solid core end outer shell 7 by crimping or bonding. At the same time, the stripped outer jacket and aramid fiber of the hollow core optical fiber 2 are fixed between the hollow core end fixing sleeve 10 and the crimping joint 111 of the hollow core end outer shell 8 by crimping or bonding. It should be noted that the solid core end fixing sleeve 9 and the solid core end outer shell 7 are pre-installed on the solid core optical fiber component 100, while the hollow core end fixing sleeve 10 and the hollow core end outer shell 8 are pre-installed on the hollow core optical fiber component 200.

[0048] The following is explained in conjunction with a specific embodiment: This specific embodiment adopts the above-mentioned manufacturing method. This embodiment is specifically a solid core single-mode fiber-hollow core fiber-solid core single-mode fiber transmission optical path, including two optical paths of solid core single-mode fiber Ⅰ11-hollow core fiber 2 and hollow core fiber 2-solid core single-mode fiber Ⅱ12. Both optical paths are mode-field coupled through the above-mentioned structure, wherein the mode field of the solid core single-mode fiber 11-hollow core fiber 2 is converted from a small mode field diameter to a large mode field diameter, thereby realizing the coupling of the solid core single-mode fiber 11-hollow core fiber 2 through lens Ⅰ41, and the mode field of the hollow core fiber 2-solid core single-mode fiber Ⅱ12 is converted from a large mode field diameter to a small mode field diameter, as shown in Figures 13-15.

[0049] In this embodiment, the distance between solid-core single-mode fiber I11 and the first end of lens I41 is L1 (1.4-1.5 mm), the distance between the second end of lens I41 and the first end of hollow-core fiber 2 is L2 (3.6-3.7 mm), the distance between the second end of hollow-core fiber 2 and the first end of lens II42 is L3 (3.7-3.8 mm), and the distance between the second end of lens II42 and the adjacent end of solid-core single-mode fiber II12 is L4 (1.4-1.5 mm). Specifically, in this embodiment, the mode field diameters of solid-core single-mode fiber I11 and solid-core single-mode fiber 12 are equal, both being 9.2 μm (@1310 nm transmission wavelength); the mode field diameter of hollow-core fiber 2 is 20 μm (@1310 nm transmission wavelength).

[0050] In this embodiment, with lens I 41 as the zero point, the radial deviation value of the solid-core single-mode optical fiber I 11 on the left side of lens I 41 is 0.066 mm, and the radial deviation value of the hollow-core optical fiber 2 on the right side of lens I 41 is 0.155 mm, while there is no radial deviation of the optical path components from the hollow-core optical fiber 2 through lens II 42 to the solid-core single-mode optical fiber II 12.

[0051] Lenses I and II in this scheme share the same parameters: material: N-SF11; lens curvature: 1.15mm radius on one end; lens length: 4.85mm on the other. The 1.15mm convex surfaces of the two lenses (lenses I and II) are oriented toward solid-core single-mode fiber I11 and solid-core single-mode fiber II12, respectively. The 2.52mm convex surfaces of the two lenses are oriented toward hollow-core fiber 2.

[0052] In the above embodiment, through theoretical simulation, the coupling loss from solid-core single-mode fiber Ⅰ11 to hollow-core fiber 2 is 0.17dB, the coupling loss from hollow-core fiber 2 to solid-core single-mode fiber Ⅱ12 is 0.23dB, and the return loss exceeds 45dB, which meets the use requirements.

[0053] This solution also provides a comparative example. The parameters of the solid-core single-mode fiber and hollow-core fiber used in this comparative example are the same as those in the above embodiment. The difference is that this comparative example does not include the single-lens mode field conversion device of this solution. Instead, the solid-core single-mode fiber 1 and the hollow-core fiber 2 are directly connected using conventional fusion splicing methods in the existing technology. The mode field diameter of the solid-core single-mode fiber 1 is 9.2μm (at a transmission wavelength of 1310nm); the mode field diameter of the hollow-core fiber 2 is 20μm (at a transmission wavelength of 1310nm). In this comparative example, the coupling loss is greater than 2.4dB, and the return loss is approximately 15dB.

[0054] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A single lens coupling assembly, characterized in that: include a solid core single-mode optical fiber having a first mode field diameter; a hollow core optical fiber having a second mode field diameter; The sleeve has a hollow lumen with two ends extending therethrough, and one end of the solid-core single-mode optical fiber and one end of the hollow-core optical fiber extend into the hollow lumen from openings at both ends of the sleeve respectively; The lens is located in the sleeve between the solid-core single-mode optical fiber and the hollow-core optical fiber and is used to achieve the conversion of the mode field diameter between the solid-core single-mode optical fiber and the hollow-core optical fiber.

2. The single lens coupling assembly according to claim 1, wherein: The end faces of the lens facing the optical fibers at both ends are both arc-shaped structures.

3. The single lens coupling assembly according to claim 2, wherein: The first end of the solid-core single-mode optical fiber is a solid-core bare optical fiber segment without a coating layer, and the solid-core bare optical fiber segment is arranged in the hollow tube cavity of the solid-core pin to form a solid-core optical fiber component. The first end of the hollow-core optical fiber is a hollow-core bare optical fiber segment without a coating layer, and the hollow-core bare optical fiber segment is arranged in the hollow tube cavity of the hollow-core pin to form a hollow-core optical fiber component.

4. The single lens coupling assembly according to claim 2, wherein: The sleeve is a hollow cylindrical structure and includes a first sub-assembly and a second sub-assembly. The ends of the first sub-assembly and the second sub-assembly are butt-jointed and coaxially arranged, wherein the first end of the lens extends into the lumen of the first sub-assembly and the second end of the lens extends into the lumen of the second sub-assembly.

5. The single lens coupling assembly according to claim 3, wherein: An oblique cut surface is formed on the end of the solid core optical fiber component facing the lens, and the oblique cut surface is not perpendicular to the axial direction of the solid core pin.

6. The single lens coupling assembly according to claim 5, characterized in that: An anti-reflection film is provided on the beveled surface, and an anti-reflection film is provided on the arc surface structure on the side opposite to the solid core optical fiber component of the lens.

7. A single-lens mode field conversion device, characterized in that: A single lens coupling assembly comprising any one of claims 1-6.

8. The single-lens mode field conversion device according to claim 7, characterized in that: It also includes a solid core end fixing component and a hollow core end fixing component, the solid core end fixing component includes a solid core end outer shell, the hollow core end fixing component includes a hollow core end outer shell, the butt ends of the solid core end outer shell and the hollow core end outer shell are connected to form a shell structure, and a cavity for accommodating a single lens coupling component is provided in the shell structure, the solid core end fixing sleeve fixes the solid core single-mode optical fiber to the end of the solid core end outer shell, and the hollow core end fixing sleeve fixes the hollow core optical fiber to the end of the hollow core end outer shell.

9. The single-lens mode field conversion device according to claim 8, characterized in that: The opposite ends of the solid end outer shell and the hollow end outer shell are both provided with a press joint matched with the fixing sleeve.

10. The single-lens mode field conversion device according to claim 9, characterized in that: At least one annular sealing connection groove is provided on the outer cylindrical surface of the crimping head.

11. The single-lens mode field conversion device according to claim 8, characterized in that: The solid end fixing assembly also includes a flange and a retaining ring. The flange is a cylindrical structure, and a cavity for accommodating the solid core optical fiber component is formed along the axial direction of the flange. A limiting boss is provided on the outer wall near the first end of the flange, and a groove for installing the retaining ring is provided on the outer wall near the second end of the flange. The flange is fixedly connected to the solid core optical fiber component, and the first end of the flange cooperates with the retaining boss in the tube cavity of the solid end outer shell through the limiting boss to limit the position of the flange relative to the solid end outer shell along the first axial direction. The second end of the flange cooperates with the groove and the retaining ring to limit the position of the flange relative to the solid end outer shell along the second axial direction, wherein the first axial direction and the second axial direction are opposite.

12. A method for manufacturing a single-lens mode field conversion device, characterized in that: The steps include: Inserting the bare fiber section without coating layer at the end of solid core single mode optical fiber into the solid core pin cavity and fixing it to form a solid core optical fiber component; inserting the bare fiber section without coating layer at the end of hollow core optical fiber into the hollow core pin cavity and fixing it to form a hollow core optical fiber component; Inserting the lens into the lumen of the sleeve and fixing it, inserting the obtained solid-core optical fiber component and hollow-core optical fiber component through the opposite end ports of the sleeve respectively, and bonding and fixing the positions of the solid-core optical fiber component and the hollow-core optical fiber component after optical debugging to form a single-lens coupling assembly; The solid end fixing component provided on the outside of the solid end of the single lens coupling component and the butt end of the hollow end fixing component provided on the outside of the hollow end of the single lens coupling component are fixedly connected; The solid core single mode optical fiber is fixed on the solid core end fixing assembly through the solid core end fixing sleeve, and the hollow core optical fiber is fixed on the hollow core end fixing assembly through the hollow core end fixing sleeve.

13. The method for manufacturing a single-lens mode field conversion device according to claim 12, wherein: The sleeve includes a first sub-assembly and a second sub-assembly. First, the first end of the lens is inserted into the tube cavity of the first sub-assembly and bonded and fixed. Then, the second end of the lens is inserted into the tube cavity of the second sub-assembly and bonded and fixed. Then, the solid core optical fiber component and the hollow core optical fiber component are respectively inserted into the opposite end ports of the sleeve. After light testing, the positions of the solid core optical fiber component and the hollow core optical fiber component are bonded and fixed when the coupling loss is minimized to form a single lens coupling assembly.

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