Conversion core member, double-lens mode field conversion device and manufacturing method therefor

Abstract

Disclosed in the present invention are a conversion core member (9), a double-lens mode field conversion device and a manufacturing method therefor. The conversion core member (9) comprises a solid-core optical fiber part (1), a hollow-core optical fiber part (2) and a calibration sleeve (3), wherein the solid-core optical fiber part (1) comprises a solid-core-end lens (12) and a solid-core single-mode optical fiber (11) having a first mode field diameter, and the solid-core end lens (12) is located at the tail end of the solid-core optical fiber part (1); the hollow-core optical fiber part (2) comprises a hollow-core-end lens (22) and a hollow-core optical fiber (21) having a second mode field diameter; the calibration sleeve (3) has a hollow cavity I (31) in the axial direction thereof; the solid-core optical fiber part (1) and the hollow-core optical fiber part (2) respectively extend into the cavity I (31) of the calibration sleeve (3) via two open ends of the cavity I (31); and the solid-core-end lens (12) and the hollow-core-end lens (22) are arranged opposite each other. In the device, the conversion of different mode field diameters between the single-mode optical fiber and the hollow-core optical fiber (21) is implemented by means of two lenses, such that a reliable and stable connection between the single-mode optical fiber and the hollow-core optical fiber (21) is achieved.

Description

A conversion core, a dual-lens mode field conversion device and a manufacturing method thereof Technical Field

[0001] The present invention belongs to the technical field of optical signal transmission, and in particular relates to a conversion core component, a dual-lens mode field conversion component 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] Developing hollow-core fiber mode field diameter conversion devices to achieve efficient connections between hollow-core fibers and traditional solid-core single-mode fibers widely used in existing optical transmission systems presents three key technical bottlenecks. First, the mode field diameter of traditional solid-core single-mode fibers at a transmission wavelength of 1310 nm is approximately 9.2 μm, while the mode field diameter of hollow-core fibers is typically 20-40 μm. This significant mismatch in mode field size leads to high coupling losses. Furthermore, the mode field mismatch at the coupling interface can 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 fibers is one of the key technical bottlenecks that needs to be addressed. Second, the air-glass interface at the fiber coupling interface also produces strong Fresnel reflections, which increase insertion loss and cause back reflections. Therefore, improving return loss is a second technical bottleneck that needs to be addressed. Third, for hollow-core fibers with internal microstructures, since the fibers themselves rely on these internal microstructures for low-loss light transmission, ensuring the integrity of the internal microstructure during coupling is also a key technical bottleneck that needs to be addressed. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and provide a conversion core component, a dual-lens mode field conversion device and a manufacturing method thereof. The device uses two lenses to realize the conversion of different mode field diameters between single-mode optical fiber and hollow-core optical fiber, thereby achieving a reliable and stable connection between single-mode optical fiber and hollow-core optical fiber.

[0006] To achieve the above-mentioned objectives, one of the objectives of the present invention is to provide a conversion core component, including a solid core optical fiber component, a hollow core optical fiber component and a calibration sleeve, wherein the solid core optical fiber component includes a solid core end lens and a solid core single-mode optical fiber with a first mode field diameter, and the solid core end lens is located at the terminal end of the solid core optical fiber component; the hollow core optical fiber component includes a hollow core end lens and a hollow core optical fiber with a second mode field diameter, and the hollow core end lens is located at the terminal end of the hollow core optical fiber component; the calibration sleeve has a hollow cavity I along its axial direction, the solid core optical fiber component and the hollow core optical fiber component extend into the two ends of the calibration sleeve cavity I respectively, and the solid core end lens and the hollow core end lens are arranged opposite to each other.

[0007] As a preferred embodiment, the solid-core optical fiber component further comprises a solid-core end sleeve, which has a cavity II with openings at both ends along its axial direction, the solid-core single-mode optical fiber extends into the cavity II of the solid-core end sleeve at one end, and the solid-core end lens is arranged at the other end of the cavity II of the solid-core end sleeve and extends outward; the hollow-core optical fiber component further comprises a hollow-core end sleeve, which has a cavity III with openings at both ends along its axial direction, the hollow-core optical fiber extends into the cavity III of the hollow-core end sleeve at one end, and the hollow-core end lens is arranged at the other end of the cavity III of the hollow-core end sleeve and extends outward.

[0008] As a preferred embodiment, the solid-core end lens and the hollow-core end lens adopt a C lens, and the C lens has two ends, one end of which is a convex spherical surface and the other end is a plane. The solid-core end lens includes a first spherical end and a first plane end, and the first spherical end is arranged toward the solid-core single-mode optical fiber. The hollow-core end lens includes a second spherical end and a second plane end, and the second spherical end is arranged toward the hollow-core optical fiber, and the first plane end and the second plane end are arranged correspondingly.

[0009] As a preferred embodiment, the first planar end of the solid end lens extends out of the solid end sleeve, and the first planar end is a beveled surface, and the first planar end is not perpendicular to the axis of the solid end lens; the second planar end of the hollow end lens extends out of the hollow end sleeve, and the second planar end is a beveled surface, and the second planar end is not perpendicular to the axis of the hollow end lens; the first planar end and the second planar end are arranged opposite to and parallel to each other.

[0010] As a preferred embodiment, 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 of the solid-core single-mode optical fiber is disposed in the hollow lumen of the solid-core end ferrule to form a solid-core ferrule assembly, and the solid-core ferrule assembly is inserted into and fixed in the solid-core end ferrule through one end of the solid-core end ferrule; 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 disposed in the hollow lumen of the hollow-core end ferrule to form a hollow-core ferrule assembly, and the hollow-core ferrule assembly is inserted into and fixed in the hollow-core end ferrule through one end of the hollow-core end ferrule.

[0011] As a preferred solution, an oblique surface is formed on one end of the solid pin assembly facing the solid end lens, and the oblique surface of the solid pin assembly is not perpendicular to the axis of the solid pin assembly.

[0012] As a preferred solution, the chamfered surface of the solid pin assembly and the first spherical end of the solid end lens are both coated with an anti-reflection film.

[0013] A second object of the present invention is to provide a dual-lens mode field conversion device, comprising a conversion core component as described in any one of the above items.

[0014] As a preferred solution, it also includes a shell, which is arranged outside the conversion core component and includes a hollow core end shell body and a solid core end shell body. The butt ends of the solid core end shell body and the hollow core end shell body are fixedly connected, the solid core end fixing sleeve fixes the solid core single-mode optical fiber to the end of the solid core end shell body, and the hollow core end fixing sleeve fixes the hollow core optical fiber to the end of the hollow core end shell body.

[0015] As a preferred embodiment, a flange is further included, wherein an adjustable gap is formed between one end of the flange and the end of the solid end sleeve, wherein the adjustable gap is used to accommodate the bonding layer, the flange has an inner tube cavity along the central axis, and one end of the flange is correspondingly connected to the end of the solid end sleeve.

[0016] As a preferred embodiment, the inner tube cavity of the flange includes cavity IV and cavity V that are interconnected. The cavity IV and cavity V are coaxially arranged, and the cross-sectional diameter of cavity IV is larger than the cross-sectional diameter of cavity V. The two ends of the solid core pin assembly are respectively located in the cavity IV and the solid core end sleeve and fixed, and the cavity V is used to pass the solid core single-mode optical fiber.

[0017] As a preferred embodiment, an annular protrusion is provided on the outer cylindrical surface near the first end of the flange, and the column head part of the annular protrusion near the first end side of the flange is inserted into the cavity I of the calibration sleeve, and the annular protrusion abuts against one end of the calibration sleeve; a groove for installing a retaining ring is provided on the outer wall of the flange near its second end, and the first end of the flange cooperates with the retaining platform in the tube cavity of the solid end outer shell through the annular protrusion to limit the position of the flange relative to the solid end outer shell along the first direction, and the second end of the flange cooperates with the end of the solid end outer shell and the retaining ring to limit the position of the flange relative to the solid end outer shell along the second direction, wherein the first direction and the second direction are opposite.

[0018] A third object of the present invention is to provide a method for manufacturing a dual-lens mode field converter, comprising the following steps:

[0019] Step 1: Assemble a solid end lens and a solid end sleeve to form a solid end lens component, assemble a solid core single-mode optical fiber and a solid end ferrule to form a solid core ferrule component, and extend the solid core ferrule component from the end opposite to the solid end lens into cavity II of the solid end sleeve to obtain a solid core optical fiber component;

[0020] Assembling a hollow-core end lens and a hollow-core end sleeve to form a hollow-core end lens component, assembling a hollow-core optical fiber and a hollow-core end ferrule to form a hollow-core ferrule component, and extending the hollow-core ferrule component from the end opposite to the hollow-core end lens into cavity III of the hollow-core end sleeve to obtain a hollow-core optical fiber component;

[0021] Step 2: inserting the solid core optical fiber component and the hollow core optical fiber component into the calibration sleeve from both ends thereof and fixing them to obtain a conversion core component;

[0022] Step 3: Place the solid end of the conversion core in the solid end outer shell, insert the hollow end of the conversion core into the hollow end outer shell, and then connect the solid end outer shell and the hollow end outer shell at opposite ends;

[0023] Step 4: fix the solid core fiber outer sheath layer of the solid core single mode optical fiber to the solid core end outer shell through the solid core end fixing sleeve, and fix the hollow core fiber outer sheath layer of the hollow core optical fiber to the hollow core end outer shell through the hollow core end fixing sleeve.

[0024] As a preferred embodiment, in step 1, the method for manufacturing the solid core ferrule assembly includes the following steps: after removing the coating from the terminal end of the solid core single-mode optical fiber, the end of the solid core single-mode optical fiber with the coating removed is inserted into the hollow lumen thereof by the first end of the solid core end ferrule and fixed, and the first end of the solid core end ferrule is inserted into the inner lumen of the flange and fixed.

[0025] As a preferred solution, in step 4, after the solid end outer shell and the hollow end outer shell are connected together, a retaining ring is set in the groove of the flange to limit the outer shell relative to the conversion core in the axial direction.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] First, the present invention improves the structure and is designed according to the characteristics of hollow-core optical fibers and the requirements of low insertion loss and high return loss. Two different C lenses are used to realize the conversion of different mode field diameters between single-mode optical fibers and hollow-core optical fibers, thereby realizing a reliable and stable connection between single-mode optical fibers and hollow-core optical fibers. In this solution, the solid-core end lens and the solid-core single-mode optical fiber are combined into a solid-core optical fiber component through a solid-core end sleeve, and the hollow-core end lens and the hollow-core optical fiber are combined into a hollow-core optical fiber component through a hollow-core end sleeve. During the installation and adjustment process, the hollow-core optical fiber component and the solid-core optical fiber component are introduced into the calibration sleeve, thereby being used for alignment between the solid-core hollow-core optical fiber component and the solid-core optical fiber component. In this way, by respectively providing lenses on the solid-core optical fiber component and the hollow-core optical fiber component, the conversion of different mode field diameters between the single-mode optical fiber and the hollow-core optical fiber can be realized, thereby realizing a reliable and stable connection between the single-mode optical fiber and the hollow-core optical fiber. The two lenses have opposing flat end faces with beveled surfaces at a certain angle to their respective axial directions. These beveled surfaces are also coated with an anti-reflection film to reduce the impact of the Fresnel effect. This design aims to improve return loss through the aforementioned means.

[0028] Secondly, this solution optimizes the manufacturing process of the conversion device. By combining it with the specific structure of the above-mentioned dual-lens mode field conversion device, it refines the various steps of the manufacturing process. First, the solid-core end sleeve and the solid-core end lens are combined into a solid-core end lens component, and the solid-core single-mode optical fiber and the solid-core ferrule are combined into a solid-core ferrule assembly. Then, the solid-core end lens component and the solid-core ferrule assembly are debugged and installed to form a solid-core optical fiber component. Then, the hollow-core end sleeve and the hollow-core end lens are combined into a hollow-core end lens component, and the hollow-core optical fiber and the hollow-core ferrule are combined into a hollow-core ferrule assembly. Then, the hollow-core end lens component and the hollow-core ferrule assembly are debugged and installed to form a hollow-core optical fiber component. In this way, during the final adjustment, only the axial distance and radial offset value of the hollow-core optical fiber component and the solid-core optical fiber component in the calibration sleeve need to be adjusted. The above-mentioned step-by-step adjustment method reduces the difficulty of debugging and installation during the manufacturing process to a certain extent, and improves the optical fiber coupling effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] FIG1 is a structural diagram of the appearance of a dual-lens mode field conversion device according to the present invention;

[0031] FIG2 is a cross-sectional view of a dual-lens mode field conversion device according to the present invention;

[0032] FIG3 is a cross-sectional view of a conversion core member of the present invention;

[0033] FIG4 is a structural diagram of a solid end lens component of the present invention;

[0034] FIG5 is a structural diagram of a solid pin component of the present invention;

[0035] FIG6 is a structural diagram of a solid core optical fiber component of the present invention;

[0036] FIG7 is a structural diagram of an embodiment of a flange in the present invention;

[0037] FIG8 is a schematic diagram of the connection between the flange and the calibration sleeve of the present invention;

[0038] FIG9 is a schematic diagram showing the connection between the annular protrusion and the groove of the flange of the present invention;

[0039] FIG10 is a structural diagram of a hollow end lens component of the present invention;

[0040] FIG11 is a structural diagram of a hollow pin component of the present invention;

[0041] FIG12 is a structural diagram of a hollow-core optical fiber component of the present invention;

[0042] FIG13 is a structural diagram of a specific embodiment of the present invention;

[0043] FIG14 is a simulation diagram of a specific embodiment of the present invention: solid core single mode fiber I-hollow core fiber;

[0044] FIG15 is a simulation diagram of a specific embodiment of the present invention: hollow core fiber-solid core single mode fiber II;

[0045] Markings in the figure: 1. Solid core optical fiber component, 11. Solid core single-mode optical fiber, 111. Solid core single-mode optical fiber I, 112. Solid core single-mode optical fiber II, 113. Solid core bare optical fiber segment, 114. Solid core optical fiber outer jacket layer, 115. Solid core optical fiber coating layer, 116. Solid core optical fiber reinforcement element, 117. Solid core optical fiber inner protective layer, 12. Solid core end lens, 121. Solid core end lens I, 122. Solid core end lens II, 1201. First spherical end, 1202. First flat end, 13. Solid core end sleeve, 131. Cavity II, 14. Solid core end pin, 141. Beveled surface, 15. Flange, 151. Annular protrusion, 152. Groove, 153. Inner tube cavity, 154. Cavity IV, 155. Cavity V, 156. Column head part, 16. Adjustable gap , 2. Hollow-core optical fiber components, 21. Hollow-core optical fiber, 211. Hollow-core optical fiber bare fiber segment, 212. Hollow-core optical fiber outer jacket layer, 213. Hollow-core optical fiber coating layer, 214. Hollow-core optical fiber strengthening element, 22. Hollow-core end lens, 221. Hollow-core end lens I, 222. Hollow-core end lens II, 2201. Second spherical end, 2202. Second plane end, 23. Hollow-core end sleeve, 231. Cavity III, 24. Hollow-core end pin, 3. Calibration sleeve, 31. Cavity I, 4. Solid-core end outer shell, 41. Stop, 5. Hollow-core end outer shell, 6. Solid-core end fixing sleeve, 7. Hollow-core end fixing sleeve, 8. Retaining ring, 9. Conversion core, 100. Solid-core pin assembly, 200. Hollow-core pin assembly, A. Bonding point, B. Crimping or bonding point, D. Center axis. DETAILED DESCRIPTION

[0046] 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.

[0047] 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.

[0048] As shown in the figure, a typical embodiment of the present invention provides a conversion core component, including a calibration sleeve 3, which is a cylindrical structure and has a cavity Ⅰ31 with two ends extending through it in the axial direction. The solid core fiber component 1 and the hollow core fiber component 2 respectively extend into the cavity Ⅰ31 of the calibration sleeve 3 from the openings at both ends. The solid core fiber component 1 includes a solid core single-mode fiber 11 and a solid core end lens 12. The solid core single-mode fiber 11 has a first mode field diameter. The hollow core fiber component 2 includes a hollow core fiber 21 and a hollow core end lens 22. The hollow core fiber 21 has a second mode field diameter. The solid core fiber component 1 and the hollow core fiber component 2 respectively extend into the cavity of the calibration sleeve 3 from the two ends. The solid core end lens 12 and the hollow core end lens 22 are arranged opposite to each other. By using two lenses, the conversion of different mode field diameters between the solid core single-mode fiber 11 and the hollow core fiber 21 is achieved, thereby achieving a reliable and stable connection between the solid core single-mode fiber 11 and the hollow core fiber 21.

[0049] This solution achieves mode field matching of the two optical fibers through a dual-lens structure, wherein the solid-core end lens 12 near the small-mode-field solid-core single-mode fiber 11 is used to expand and collimate the light emitted from the small-mode-field solid-core single-mode fiber 11, and the hollow-core end lens 22 near the large-mode-field hollow-core fiber 21 is used to focus the collimated light to a light spot mode field size close to that of the large-mode-field hollow-core fiber 21. Alternatively, in this solution, the hollow-core end lens 22 near the large-mode-field hollow-core fiber 21 is used to expand and collimate the light emitted from the large-mode-field hollow-core fiber 21, and the solid-core end lens 12 near the small-mode-field solid-core single-mode fiber 11 is used to focus the collimated light to a light spot mode field size close to that of the small-mode-field solid-core single-mode fiber 21.

[0050] In this solution, to facilitate the reinforcement of the optical fiber ends and a series of subsequent debugging processes, the ends of the solid-core single-mode optical fiber 11 and the hollow-core optical fiber 21 are respectively provided with a ferrule structure. The specific implementation method is as follows: the solid core optical fiber coating 115 outside the optical fiber cladding is removed from the first end of the solid-core single-mode optical fiber 11. The solid core bare optical fiber segment 113 of the solid-core single-mode optical fiber 11 without the solid core optical fiber coating 115 includes a core and a cladding. The solid core bare optical fiber segment 113 is disposed in the hollow lumen of the solid-core end ferrule 14 to form a solid core ferrule assembly 100. The axis of the solid core ferrule assembly 100 refers to its central axis D along the axial direction. The end of the solid core ferrule assembly 100 is formed with a beveled surface 141 that is not perpendicular to the central axis D of the solid core ferrule assembly 100. The purpose of this design is to improve return loss. The hollow core fiber 21 is removed from the first end of the hollow core fiber 21 by removing the hollow core fiber coating 213 outside the fiber cladding, and the hollow core bare fiber segment 211 with the hollow core fiber coating 213 removed is set in the capillary hollow cavity of the hollow core end pin 24 to form the hollow core pin assembly 200.

[0051] In the present invention, to further achieve the connection between the optical fiber and the lens and facilitate a series of subsequent debugging, the solid core optical fiber component 1 is further provided with a solid core end sleeve 13, wherein the solid core end sleeve 13 is a hollow cylindrical structure with a cavity I 31 extending through both ends. The solid core ferrule assembly 100 extends into the first end of the cavity of the solid core end sleeve 13, and the solid core end lens 12 is disposed at the second end of the cavity of the solid core end sleeve 13. The solid core ferrule assembly 100 is placed near the focal plane of the solid core end lens 13, and the axial distance between the solid core ferrule assembly 100 and the solid core end lens 13 is finely adjusted near the focal plane. When the output light of the solid core end lens 13 is collimated, the positions of the solid core ferrule assembly 100 and the solid core end lens 12 in the solid core end sleeve 13 are fixed by adhesive, and the size of the collimated light spot at this time is recorded to obtain the solid core optical fiber component 1. On the other hand, the hollow-core optical fiber component 2 is further provided with a hollow-core end sleeve 23. The hollow-core end sleeve 23 is a cylindrical structure with a through cavity III 231 along its axis. The hollow-core ferrule component 200 extends into the first end of the cavity of the hollow-core end sleeve 23, and the hollow-core end lens 22 is disposed at the second end of the cavity of the hollow-core end sleeve 23. The axial distance between the hollow-core ferrule assembly 200 and the hollow-core end lens 22 is adjusted according to the theoretical design value. By adjusting the axial distance between the hollow-core ferrule assembly 200 and the hollow-core end lens 22 and the lateral offset distance within the hollow-core end sleeve 23, the position of the hollow-core ferrule assembly 200 is found when the output collimated light spot is closest to the collimated light spot on the solid core side, which is the optimal coupling state. The hollow-core optical fiber component 2 is thus obtained by fixing the hollow-core optical fiber end ferrule assembly 200 and the hollow-core end lens 22.

[0052] In a preferred embodiment of the present scheme, the solid core end lens 12 adopts a C lens, and the two ends of the C lens are spherical and flat respectively. The solid core end lens 12 includes a first spherical end 1201 and a first flat end 1202. The first spherical end 1201 is arranged toward the solid core single-mode optical fiber 11, and the first flat end 1202 of the solid core end lens 12 extends out of the solid core end sleeve 13, and the first flat end 1202 is a beveled surface. The first flat end 1202 forms an angle of 8° with the axial direction of the solid core end lens 12; the hollow core end lens 22 adopts a C lens, and the hollow core end lens 22 includes a second spherical end 2201 and a second flat end 2202. The second spherical end 2202 is arranged toward the hollow core optical fiber 21, and the first flat end 1202 and the second flat end 2202 are arranged correspondingly. The curvature radius of the first spherical end 1201 is smaller than the curvature radius of the second spherical end 2201. The second planar end 2202 of the hollow end lens 22 extends outward from the hollow end sleeve 23, and the second planar end 2202 is a beveled surface, and the second planar end 2202 forms an 8° angle with the axial direction of the hollow end lens 22; the first planar end 1202 and the second planar end 2202 are arranged opposite and parallel to each other. In this solution, the first planar end 1202 and the second planar end 2202 are both beveled surfaces with an 8° angle, the main function of which is to eliminate the Fresnel effect existing therein, and the ultimate goal is to improve the return loss. Specifically, this solution can process bevels with different inclination angles of 1-14° according to different return loss standards, and at the same time, coat them with an anti-reflection film to make the transmittance higher than 99.9%.

[0053] Since Fresnel reflection occurs when light is incident on 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 optical fiber 11 and the solid-core end lens 12 with an anti-reflection film. The principle behind the design of the anti-reflection film is that the two reflected light beams on the upper and lower surfaces of the film undergo destructive interference. Therefore, the optical path difference between the two reflected lights should be an odd multiple of half a wavelength, and the optical thickness of the film layer [the product of the actual thickness and the refractive index of the material] must be an odd multiple of a quarter wavelength. Fresnel reflection occurs at every material interface, and each time the reflected light reaches another interface, a portion of it will undergo additional Fresnel reflection.

[0054] Another embodiment of the present invention provides a dual-lens mode field converter device, comprising the conversion core 9 of the above embodiment and a housing disposed outside the conversion core 9. The housing is used to protect the conversion core from external contamination and provide a certain degree of mechanical strength protection for the internal connection structure, thereby preventing mechanical damage to the internal conversion core 9. The housing includes a solid core end housing body 4 and a hollow core end housing body 5, which are threadedly connected. As shown in FIG2 , the solid core end fixing sleeve 6 fixes the solid core fiber outer jacket layer 114 of the solid core single-mode optical fiber 11 to the end of the solid core end housing body 4 by crimping or bonding, and the hollow core end fixing sleeve 7 fixes the hollow core fiber outer jacket layer 212 of the hollow core optical fiber 21 to the end of the hollow core end housing body 5 by crimping or bonding.

[0055] In a typical embodiment of the present invention, the solid end fixing sleeve 6 and the hollow end fixing sleeve 7 are both annular sleeve structures, including a large diameter end and a small diameter end, wherein the large diameter end of the solid end fixing sleeve 6 is connected to the compression joint at the end of the solid end outer shell 4, and the small diameter end of the solid end fixing sleeve 6 is in contact with the outer sheath layer 114 of the solid core optical fiber, and the large diameter end of the hollow end fixing sleeve 7 is connected to the compression joint at the end of the hollow end outer shell 5, and the small diameter end of the hollow end fixing sleeve 7 is in contact with the outer sheath layer 212 of the hollow core optical fiber. It should be noted that Yes, the solid end fixing sleeve 6 and the hollow end fixing sleeve 7 can be crimped. Specifically, the solid end fixing sleeve 6 and the hollow end fixing sleeve 7 are made of elastic material. The contraction force of the elastic material is used to fasten and crimp the optical fibers at both ends to the solid end fixing sleeve 6 and the hollow end fixing sleeve 7, respectively. Alternatively, a bonding method can be used. Specifically, the outer skins of the optical fibers at both ends are bonded to the small-diameter end of the fixing sleeve by glue, and the crimping joints of the solid end outer shell 4 and the hollow end outer shell 5 are bonded to the large-diameter end of the fixing sleeve by glue.

[0056] In this embodiment, in order to achieve a better fixing effect, at least one annular groove is provided on the outer cylindrical surface of the crimping joint of the solid end outer shell body 4 and the hollow end outer shell body 5. Preferably, the annular groove of this scheme is set to two along the axial direction of the crimping joint. With such a design, when the solid end fixing sleeve 6 and the hollow end fixing sleeve 7 are crimped by shrinkage, the fixing sleeve will be fastened to the position of the annular groove after deformation and tightening. The annular groove can increase the relative friction between the fixing sleeve and the crimping joint, thereby strengthening the connection strength and improving the sealing effect of the connection. If the solid end fixing sleeve 6 and the hollow end fixing sleeve 7 are fixed by gluing, the annular groove is used to accommodate glue, thereby increasing the bonding strength and improving the sealing effect of the connection.

[0057] This solution also includes a flange 15 and a retaining ring 8, which are used to achieve a fixed connection between the outer shell and the conversion core 9. The specific method is as follows: the main structure of the flange 15 is a hollow cylindrical structure, and an annular protrusion 151 and a groove 152 are respectively provided near the two end portions of the flange 15, wherein one end of the flange 15 with the annular protrusion 151 is connected to the solid end sleeve 13, and the central axis of the flange 15 is parallel to or coincides with the central axis of the solid end sleeve 13, the flange 15 has an inner tube cavity 153 along the central axis, and one end of the flange 15 is bonded to the end of the solid end sleeve 13. Specifically, an adjustable gap 16 is formed between the flange 15 and the solid end sleeve 13. The adjustable gap 16 is used to accommodate the adhesive layer, so that the spacing between the two components can be adjusted during the installation process after the adhesive layer solidifies. The adjustable gap 16 is provided to adjust the axial spacing between the solid core pin assembly 100 and the solid core end lens 12. A column head portion 156 is formed between the annular protrusion 151 of the flange 15 and the end portion. The column head portion 156 is used to insert a portion of the end of the flange 15 into the cavity of the calibration sleeve 3. During installation, the flange 15 and the solid core pin component 100 need to be fixed together with an adhesive in advance, and then connected to the solid end sleeve 13 to form the solid core optical fiber component 1. Then the solid core optical fiber component 1 is inserted into the calibration sleeve 3 as a whole. At this time, after the annular protrusion 151 is in contact with one end of the calibration sleeve 3, the retaining ring 8 is buckled into the groove 152 at the other end of the flange 15. In this way, the axial limitation of the solid core optical fiber component 1 and the solid core end outer shell 4 is achieved through the annular protrusion 151 and the groove 152 on both sides. The first end of the flange 15 is blocked and limited by the annular protrusion 151 and the stopper 41 in the tube cavity of the solid core end outer shell 4, limiting the position of the flange 15 relative to the solid core end outer shell 4 along the first direction. The second end of the flange 15 is blocked and limited by the groove 152 and the retaining ring 8, limiting the position of the flange 15 relative to the solid core end outer shell 4 along the second direction, wherein the first direction and the second direction are opposite.

[0058] In this embodiment, the inner tube cavity 153 of the flange 15 includes a cavity IV 154 and a cavity V 155 that are interconnected and coaxially arranged, wherein the cross-sectional diameter of cavity IV 154 is larger than the cross-sectional diameter of cavity V 155. Cavity IV 154 is used to accommodate one end of the solid core pin assembly 100 and bond it to fix it, and the cavity V 155 is used to pass the solid core single-mode optical fiber 11.

[0059] In this embodiment, the solid-core single-mode optical fiber 11 comprises, from the outside in, a solid-core outer jacket 114, a solid-core reinforcing element 116, a solid-core inner protective layer 117, a solid-core coating 115, and a bare solid-core fiber segment 113. The bare solid-core fiber segment 113 comprises a cladding and a core. The hollow-core optical fiber 21 comprises, from the outside in, a hollow-core outer jacket 212, a hollow-core reinforcing element 214, a hollow-core coating 213, and a bare hollow-core fiber segment 211.

[0060] In this embodiment, since the solid-core optical fiber component 1, the calibration sleeve 3 and the hollow-core optical fiber component 2 are fixed by bonding, and the solid-core end outer shell 4 and the hollow-core end outer shell 5 are fixed by threads, the connection and cooperation between the retaining ring 8 and the flange 15 can achieve the fixation of the relative position of the entire outer shell and the internal conversion core 9 in the axial direction.

[0061] The present invention also provides another embodiment, a method for manufacturing a dual-lens mode field converter, the specific steps of which are as follows:

[0062] Step 1: Assemble the solid end lens 12 and the solid end sleeve 13 to form a solid end lens component, assemble the solid core single-mode optical fiber 11 and the solid core end ferrule 14 to form a solid core ferrule component 100, and extend the solid core ferrule component 100 from the end opposite to the solid end lens 12 into the cavity II 131 of the solid end sleeve 13, and debug it to obtain the solid core optical fiber component 1.

[0063] In this solution, the solid core pin assembly 100 is manufactured by the following steps: removing the coating layer from the end portion of the solid core single-mode optical fiber 11 to form a solid core optical fiber bare fiber segment 113; inserting the solid core optical fiber bare fiber segment 113 with the coating layer removed into the hollow tube cavity thereof through the first end of the solid core end pin 14 and bonding it to fix it; and inserting the first end of the solid core end pin 14 into the cavity IV 154 of the flange 15 and bonding it to fix it.

[0064] The debugging process for this step is as follows: light is injected from one end of solid-core single-mode fiber 11, coupled through solid-core end lens 12, and then transmitted to a beam quality analysis device for online monitoring. Specifically, the end face of solid-core ferrule assembly 100 is placed at the focal plane of solid-core end lens 12. The axial distance between solid-core ferrule assembly 100 and solid-core end lens 12 is fine-tuned nearby. When the output light is collimated, the positions of solid-core ferrule assembly 100 and solid-core end lens 12 within solid-core end sleeve 13 are fixed, and the collimated light spot size at this point is recorded.

[0065] Step 2: Assemble the hollow-core end lens 22 and the hollow-core end sleeve 23 to form a hollow-core end lens component, and assemble the hollow-core optical fiber 21 and the hollow-core end ferrule 24 to form a hollow-core ferrule component 200. Insert the hollow-core ferrule component 200 from the end opposite the hollow-core end lens 22 into the cavity of the hollow-core end sleeve 23, and perform debugging to obtain the hollow-core optical fiber component 2;

[0066] In this step, the debugging process is as follows: first, connect the hollow-core fiber 2 to the light source, couple it through the hollow-core end lens 22, and then connect it to the beam quality analysis equipment for online monitoring. Specifically, the axial distance between the end face of the hollow-core ferrule assembly 200 and the hollow-core end lens 22 is adjusted according to the theoretical design value. By adjusting the axial distance between the hollow-core ferrule assembly 200 and the hollow-core end lens 22, as well as the lateral offset (radial offset) of the hollow-core ferrule assembly 200 and the hollow-core end lens 22 within the hollow-core end sleeve 23, the position of the hollow-core ferrule assembly 200 is found when the output collimated light spot is closest to the collimated light spot on the other side, which is the optimal coupling state. The position of the hollow-core ferrule assembly 200 and the hollow-core end lens 22 is then fixed.

[0067] In this solution, in order to protect the internal microstructure of the hollow-core fiber 21, the microstructure inside the hollow-core fiber 21 allows light to be confined to the hollow-core fiber 21 and transmitted with low loss. Therefore, the internal microstructure cannot be damaged, and the glue cannot be absorbed to affect light transmission. The fixing method of the traditional solid-core single-mode optical fiber 11 and the solid-core end pin 14 is different from that of the solid-core pin assembly in the following ways:

[0068] In the traditional method, the bare fiber segment 113 of the solid-core optical fiber is inserted into the solid-core end ferrule 14. The solid-core single-mode optical fiber 11 is first fixed with glue and the end face of the solid-core ferrule assembly 100 is polished. However, these steps in the traditional method can easily damage the end face structure of the hollow-core optical fiber 21 and cause the glue to be absorbed into the capillaries inside the hollow-core optical fiber 21.

[0069] In this solution, during actual operation, a portion of the hollow-core fiber coating 213 near the end face of the hollow-core fiber 21 is first removed to form a hollow-core fiber bare fiber segment 211. The hollow-core fiber bare fiber segment 211 is then inserted into the central cavity of the hollow-core end ferrule 24 to form the hollow-core ferrule assembly 200. A fiber cleaver is then used to cleave the end face of the hollow-core fiber bare fiber segment 211. The hollow-core fiber 21 is then pulled back into the cavity of the hollow-core end ferrule 24, with the end face of the hollow-core fiber bare fiber segment 211 slightly recessed within the end face of the hollow-core end ferrule 24. The end of the hollow-core fiber 21 is then carefully secured within the cavity of the hollow-core end ferrule 24 using glue. This design effectively avoids damage to the end face of the hollow-core fiber 21 and prevents glue from being drawn into the capillary tubes within the hollow-core fiber 21.

[0070] Step 3: insert the solid core optical fiber component 1 obtained in step 1 and the hollow core optical fiber component 2 obtained in step 2 into the calibration sleeve 3 from both ends thereof, and after debugging, fix the solid core optical fiber component 1 and the hollow core optical fiber component 2 in the calibration sleeve 3 to obtain a conversion core component 9;

[0071] In this solution, a calibration sleeve 3 is used to adjust and secure the position of the solid-core fiber component 1 and the hollow-core fiber component 2, forming a single unit. Note that the opposing chamfered surfaces of the two lenses protrude slightly from the two sleeve end faces. This design facilitates alignment of the two chamfered surfaces during adjustment, thereby reducing the additional loss caused by misalignment.

[0072] Step 4: Place the solid end of the conversion core 9 in the solid end outer shell 4, insert the hollow end of the conversion core 9 into the hollow end outer shell 5, and then screw the threaded ends of the solid end outer shell 4 and the hollow end outer shell 5 together.

[0073] In this solution, after the threaded ends of the solid end outer shell 4 and the hollow end outer shell 5 are screwed together, the retaining ring 8 is set in the groove 152 of the flange 15 to limit the outer shell relative to the conversion core 9 in the axial direction.

[0074] Step 5: Fix the solid core fiber outer sheath layer 114 of the solid core single-mode optical fiber 1 on the solid core end outer shell 4 through the solid core end fixing sleeve 6, and fix the hollow core fiber outer sheath layer 212 of the hollow core optical fiber 2 on the hollow core end outer shell 5 through the hollow core end fixing sleeve 7.

[0075] Specifically, the solid core fiber outer sheath layer 114 of the solid core single-mode optical fiber 11 is fixed between the solid core end fixing sleeve 6 and the solid core end outer shell 4, and the hollow core fiber outer sheath layer 212 of the hollow core optical fiber 21 is fixed between the hollow core end fixing sleeve 7 and the hollow core end outer shell 5.

[0076] The following is described with reference to specific embodiments:

[0077] Figures 13-15 illustrate a specific embodiment of a designed dual-lens structure, enabling a low-insertion-loss, high-return-loss optical transmission link consisting of solid-core single-mode fiber I 111, hollow-core fiber 21, and solid-core single-mode fiber II 112. The mode field diameters of solid-core single-mode fibers I, II 111, and 112, and hollow-core fiber 21, are 9.2 μm and 20 μm, respectively (at a transmission wavelength of 1310 nm). This solution includes two optical paths, in which the solid-core single-mode fiber I 111-hollow-core fiber 21 and the hollow-core fiber 21-solid-core single-mode fiber II 112 both use the dual-lens mode field converter of the above structure. The data of the dual-lens coupling system designed in this embodiment are shown in the following table, where the basic parameters of the solid-core end lenses I, II 121, and 122 are: material N-SF11, radius of curvature 1.15 mm, and length 2.35 mm; the basic parameters of the hollow-core end lenses I, II 221, and 222 are: material N-SF11, radius of curvature 2.52 mm, and length 2.5 mm. The transmittance of the anti-reflection film on the beveled surface in this embodiment is greater than 99.9%. As shown in Table 1, the distance from the solid core single-mode optical fiber I111 to the solid core end lens I121 is L1; the distance from the solid core end lens I121 to the hollow core end lens I221 is L2; ​​the distance from the hollow core end lens I221 to the first end of the hollow core optical fiber 21 is L3, and the distance from the second end of the hollow core optical fiber 21 to the hollow core end lens II222 is L4; the distance between the hollow core end lens II222 and the solid core end lens II122 is L5, and the distance between the solid core end lens II122 and the solid core single-mode optical fiber II112 is L6.

[0078] Table 1 Axial distance data between components

[0079]

[0080] Table 2 Transverse offset data between components

[0081]

[0082] The lateral offset distance values ​​(radial offset distance values) of each element in Table 2 are obtained with the position of the solid-core single-mode optical fiber 11 as the origin.

[0083] The above theoretical simulation shows that after the end face of the single-mode optical fiber is beveled, in this embodiment, the beveled surfaces of the solid-core end lens I, the hollow-core end lens I, the hollow-core end lens II, and the solid-core end lens II all form an angle of 8° with the axial direction of each lens.

[0084] In this solution, the coupling loss from the solid-core single-mode fiber I 111 to the hollow-core fiber 21 is ≤0.3 dB, the coupling loss from the hollow-core fiber 21 to the solid-core single-mode fiber II 112 is ≤0.3 dB, and the return loss exceeds 45 dB.

[0085] The solid-core single-mode fiber 1 and hollow-core fiber 2 were directly connected using conventional fusion splicing methods. The difference was that the fiber structure in this fusion splicing method did not include the dual-lens mode field conversion device of this solution. The mode field diameter of the solid-core single-mode fiber 1 was 9.2μm (at a transmission wavelength of 1310nm); the mode field diameter of the hollow-core fiber 2 was 20μm (at a transmission wavelength of 1310nm). The coupling loss of the fiber structure after direct fusion splicing was greater than 2.4dB, and the return loss was approximately 15dB.

[0086] 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 conversion core, characterized in that: It includes a solid core optical fiber component, a hollow core optical fiber component and a calibration sleeve, wherein the solid core optical fiber component includes a solid core end lens and a solid core single-mode optical fiber with a first mode field diameter, and the solid core end lens is located at the terminal end of the solid core optical fiber component; the hollow core optical fiber component includes a hollow core end lens and a hollow core optical fiber with a second mode field diameter, and the hollow core end lens is located at the terminal end of the hollow core optical fiber component; the calibration sleeve has a hollow cavity I along its axial direction, the solid core optical fiber component and the hollow core optical fiber component extend into the calibration sleeve cavity I respectively from two ends, and the solid core end lens and the hollow core end lens are arranged opposite to each other.

2. The conversion core according to claim 1, characterized in that: The solid core optical fiber component further includes a solid core end sleeve, the solid core end sleeve having a cavity II with two ends open along its axial direction, the solid core single-mode optical fiber extends into the cavity II of the solid core end sleeve at one end, and the solid core end lens is arranged at the other end of the cavity II of the solid core end sleeve and extends outward; The hollow-core optical fiber component also includes a hollow-core end sleeve, which has a cavity III with two ends open along its axial direction. The hollow-core optical fiber extends into the cavity III of the hollow-core end sleeve from one end, and the hollow-core end lens is arranged at the other end of the cavity III of the hollow-core end sleeve and extends outward.

3. A conversion core according to claim 1 or 2, characterized in that: The solid-core end lens and the hollow-core end lens adopt C lenses, and the C lens has two ends, one end of which is a convex spherical surface and the other end is a plane. The solid-core end lens includes a first spherical end and a first plane end, and the first spherical end is set toward the solid-core single-mode optical fiber. The hollow-core end lens includes a second spherical end and a second plane end, and the second spherical end is set toward the hollow-core optical fiber. The first plane end and the second plane end are set correspondingly.

4. The conversion core according to claim 3, characterized in that: The first plane end of the solid end lens extends out of the solid end sleeve, and the first plane end is an oblique cut surface, and the first plane end is not perpendicular to the axis of the solid end lens; The second plane end of the hollow end lens extends out of the hollow end sleeve, and the second plane end is a beveled surface, and the second plane end is not perpendicular to the axis of the hollow end lens; The first plane end and the second plane end are arranged opposite to and in parallel.

5. The conversion core according to claim 2, characterized in that: The first end of the solid-core single-mode optical fiber is a solid-core bare optical fiber segment without a coating layer. The solid-core bare optical fiber segment of the solid-core single-mode optical fiber is disposed in the hollow lumen of the solid-core end ferrule to form a solid-core ferrule assembly. The solid-core ferrule assembly is inserted into and fixed in the solid-core end ferrule through one end of the solid-core end ferrule. The first end of the hollow-core optical fiber is a hollow-core bare optical fiber segment without a coating layer. The hollow-core bare optical fiber segment is disposed in the hollow lumen of the hollow-core end ferrule to form a hollow-core ferrule assembly. The hollow-core ferrule assembly is inserted into and fixed in the hollow-core end ferrule through one end of the hollow-core end ferrule.

6. The conversion core according to any one of claim 5, characterized in that: An oblique surface is formed on one end of the solid pin assembly facing the solid end lens, and the oblique surface of the solid pin assembly is not perpendicular to the axis of the solid pin assembly.

7. The conversion core according to claim 6, characterized in that: The chamfered surface of the solid pin assembly and the first spherical end of the solid end lens are both coated with an anti-reflection film.

8. A dual-lens mode field conversion device, characterized in that: A conversion core comprising any one of claims 1-7.

9. The dual-lens mode field conversion device according to claim 8, characterized in that: It also includes a shell, which is arranged outside the conversion core component and includes a hollow core end shell body and a solid core end shell body. The butt ends of the solid core end shell body and the hollow core end shell body are fixedly connected. The solid core end fixing sleeve fixes the solid core single-mode optical fiber to the end of the solid core end shell body, and the hollow core end fixing sleeve fixes the hollow core optical fiber to the end of the hollow core end shell body.

10. The dual-lens mode field conversion device according to claim 9, characterized in that: It also includes a flange, an adjustable gap is formed between one end of the flange and the end of the solid end sleeve, the adjustable gap is used to accommodate the bonding layer, the flange has an inner tube cavity along the central axis, and one end of the flange is correspondingly connected to the end of the solid end sleeve.

11. The conversion core according to claim 10, characterized in that: The inner tube cavity of the flange includes cavity IV and cavity V that are interconnected. The cavity IV and cavity V are coaxially arranged. The cross-sectional diameter of cavity IV is larger than the cross-sectional diameter of cavity V. The two ends of the solid core pin assembly are respectively located in the cavity IV and the solid core end sleeve and fixed. The cavity V is used to pass the solid core single-mode optical fiber.

12. The conversion core according to claim 10, characterized in that: An annular protrusion is provided on the outer cylindrical surface near the first end of the flange, and the column head part of the annular protrusion near the first end side of the flange is inserted into the cavity I of the calibration sleeve, and the annular protrusion abuts against one end of the calibration sleeve; a groove for installing a retaining ring is provided on the outer wall of the flange near its second end, and the first end of the flange cooperates with the retaining platform in the tube cavity of the solid end outer shell through the annular protrusion to limit the position of the flange relative to the solid end outer shell along the first direction, and the second end of the flange cooperates with the end of the solid end outer shell and the retaining ring to limit the position of the flange relative to the solid end outer shell along the second direction, wherein the first direction and the second direction are opposite.

13. A method for manufacturing a dual-lens mode field converter, characterized in that: The steps include: Step 1: Assemble a solid end lens and a solid end sleeve to form a solid end lens component, assemble a solid core single-mode optical fiber and a solid end ferrule to form a solid core ferrule component, and extend the solid core ferrule component from the end opposite to the solid end lens into cavity II of the solid end sleeve to obtain a solid core optical fiber component; Assembling a hollow-core end lens and a hollow-core end sleeve to form a hollow-core end lens component, assembling a hollow-core optical fiber and a hollow-core end ferrule to form a hollow-core ferrule component, and extending the hollow-core ferrule component from the end opposite to the hollow-core end lens into cavity III of the hollow-core end sleeve to obtain a hollow-core optical fiber component; Step 2: inserting the solid core optical fiber component and the hollow core optical fiber component into the calibration sleeve from both ends thereof and fixing them to obtain a conversion core component; Step 3: Place the solid end of the conversion core in the solid end outer shell, insert the hollow end of the conversion core into the hollow end outer shell, and then connect the solid end outer shell and the hollow end outer shell at opposite ends; Step 4: fix the solid core fiber outer sheath layer of the solid core single mode optical fiber to the solid core end outer shell through the solid core end fixing sleeve, and fix the hollow core fiber outer sheath layer of the hollow core optical fiber to the hollow core end outer shell through the hollow core end fixing sleeve.

14. The method for manufacturing a dual-lens mode field converter according to claim 13, wherein: In step 1, the method for manufacturing the solid core pin assembly includes the following steps: after removing the coating layer from the terminal end of the solid core single-mode optical fiber, the end of the solid core single-mode optical fiber with the coating layer removed is inserted into the hollow tube cavity thereof by the first end of the solid core end pin and fixed, and the first end of the solid core end pin is inserted into the inner tube cavity of the flange and fixed.

15. The method for manufacturing a dual-lens mode field converter according to claim 14, wherein: In the fourth step, after the solid end outer shell and the hollow end outer shell are connected together, a retaining ring is arranged in the groove of the flange to limit the outer shell relative to the conversion core in the axial direction.

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