A solid-core and hollow-core optical fiber conversion device

Abstract

This invention discloses a solid-core and hollow-core fiber conversion device, comprising: a dual-spherical lens, a glass tube, a single-mode solid-core fiber pigtail, and a hollow-core fiber pigtail; the dual-spherical lens includes a first end spherical surface and a second end spherical surface, wherein the curvature of the first end spherical surface is less than the curvature of the second end spherical surface; the first end spherical surface of the dual-spherical lens is close to the single-mode solid-core fiber pigtail, and the second end spherical surface of the dual-spherical lens is close to the hollow-core fiber pigtail. Using this structure, the size of the light spot converged by the first end spherical surface is the same as the size of the light spot emitted by the hollow-core fiber pigtail, enabling the conversion of light between hollow-core and solid-core fibers. It also solves the problems of ultra-high loss and extremely low return loss caused by fusion splicing of solid-core and hollow-core fibers, and features a simple and compact structure, low cost, and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a solid-core and hollow-core optical fiber conversion device. Background Technology

[0002] Hollow-core optical fiber, as a disruptive optical communication technology, has made breakthrough progress in transmission performance in recent years, with its loss reduced to 0.1 dB / km, breaking through the physical limits of traditional solid-core optical fiber. The transmission speed of optical signals in hollow-core optical fiber is increased by about 47%, and the latency is reduced by more than 30%. Air guiding reduces nonlinear effects by 3-4 orders of magnitude, supports a 10-fold increase in fiber input power, and enables repeaterless transmission distances exceeding 800 kilometers. However, the large-scale commercialization of hollow-core optical fiber still faces multiple challenges, including technology, cost, and supply chain coordination. The biggest challenge is that because the core of hollow-core optical fiber is air, it is susceptible to water and contaminants, making it impossible to directly make connectors to achieve rapid interconnection between optical fibers.

[0003] One current method involves using solid-core optical fibers as connectors. Simply connecting the ends of hollow-core fibers to a solid-core fiber connector achieves fiber optic interconnection. This requires signal conversion between solid and hollow fibers. Currently, the known method is to use fusion splicing to achieve this conversion, but the insertion loss is at least 3dB (half the power is lost), and the return loss is also unsatisfactory at around 15dB (because the solid fiber end face is flattened and fused to the hollow fiber core, the flat end face produces specular reflection). Summary of the Invention

[0004] Therefore, it is necessary to provide a solid-core and hollow-core fiber conversion device, which realizes the conversion of optical signals between solid-core and hollow-core fibers by adopting an optical structure design that couples solid-core and hollow-core fibers with double spherical lenses. It has the characteristics of small structure, simple process, low cost and good performance.

[0005] This invention provides a solid-core and hollow-core optical fiber conversion device, comprising: a double spherical lens, a glass tube, a single-mode solid-core optical fiber pigtail, and a hollow-core optical fiber pigtail;

[0006] The double spherical lens includes a first spherical end and a second spherical end, wherein the curvature of the first spherical end is less than the curvature of the second spherical end;

[0007] The first spherical surface of the bispherical lens is close to the single-mode solid fiber pigtail, and the second spherical surface of the bispherical lens is close to the hollow fiber pigtail.

[0008] The first spherical end of the double spherical lens is focused with the single-mode solid fiber pigtail.

[0009] The second spherical end of the double spherical lens is focused with the hollow fiber pigtail;

[0010] The glass tube is a component that connects the double spherical lens, the single-mode solid fiber pigtail, and the hollow fiber pigtail and supports the entire device. The inner diameter of the glass tube can accommodate the double spherical lens, the single-mode solid fiber pigtail, and the hollow fiber pigtail.

[0011] The light emitted from the single-mode solid fiber pigtail passes through the double spherical lens and enters the hollow fiber pigtail.

[0012] Specifically, the double spherical lens is made of N-SF11 glass.

[0013] Specifically, the glass tubes are available in one-section, two-section, or three-section designs of different lengths.

[0014] Specifically, the end face of the single-mode solid fiber pigtail closest to the double spherical lens is the first end face.

[0015] Specifically, the first end face is an inclined plane.

[0016] Specifically, obtaining the optimal tilt angle of the first end face includes:

[0017] S1, Obtain the historical tilt angle set A = {A1, ..., A1} of the first end face. i , ..., A m}, where A i It is the set of historical tilt angles of the first end face corresponding to the numerical aperture of the i-th solid fiber, and A i ={A i1 , ..., A ij , ..., A in}, A ij It is A i The historical tilt angle of the j-th first end face is given, where i ranges from 1 to m, m is the number of historical tilt angle groups of the first end face corresponding to the numerical aperture of the solid fiber, and m ≥ 2; j ranges from 1 to n, where n is the A i The number of historical tilt angles of the first end face, where n≥2;

[0018] S2, obtain the initial fiber loss information set B = {B1, ..., B1} corresponding to A. i , ..., B m}, B i ={B i1 , ..., B ij , ..., B in}, B ij = (B 1 ij B 2 ij ), B 1 ij It is A ij The corresponding initial return loss, B2 ij It is A ij The corresponding initial insertion loss;

[0019] S3, based on B, obtain the target tilt angle of the first end face.

[0020] Specifically, step S3 also includes the following steps:

[0021] S31, Based on B, obtain the initial fiber loss priority set F = {F1, ..., F2} corresponding to B. i , ..., F m}, F i ={F i1 , ..., F ij , ..., F in}, F ij It is B ij The corresponding initial fiber loss priority, where F ij Meets the following conditions:

[0022] F ij =W 1 ×(B 1 ij -B 1 0) / B 1 0+W 2 ×(B 2 ij -B 2 0) / B 2 0, B 1 0 is the preset return loss threshold, B 2 0 is the preset insertion loss threshold, W 1 It is the weight of return loss, W 2 It is the weight of the insertion loss;

[0023] S32, from F i In the middle, select F i The maximum tilt angle range H of the corresponding first end face i ;

[0024] S33, all H i By performing intersection processing, the final tilt angle range H of the first end face is obtained. 0 ;

[0025] S34, Get H 0 The average maximum value of all initial fiber loss priorities corresponding to each historical tilt angle is used as the optimal tilt angle.

[0026] Specifically, the first end face is coated with an anti-reflective film.

[0027] Specifically, the end face of the hollow fiber pigtail closest to the double spherical lens is the second end face.

[0028] Specifically, the second end face is a plane.

[0029] Implementing the embodiments of the present invention will have the following beneficial effects:

[0030] A solid-core and hollow-core fiber optic conversion device according to the present invention includes: a bispherical lens, a glass tube, a single-mode solid-core fiber pigtail, and a hollow-core fiber pigtail; the bispherical lens includes a first end spherical surface and a second end spherical surface, wherein the curvature of the first end spherical surface is less than the curvature of the second end spherical surface; the first end spherical surface of the bispherical lens is close to the single-mode solid-core fiber pigtail, and the second end spherical surface of the bispherical lens is close to the hollow-core fiber pigtail; the first end spherical surface of the bispherical lens is focused with the single-mode solid-core fiber pigtail; the second end spherical surface of the bispherical lens is focused with the hollow-core fiber pigtail; the single-mode... Light emitted from a solid fiber pigtail passes through the double spherical lens and enters the hollow fiber pigtail. The light emitted from the single-mode solid fiber pigtail is focused into parallel light by the first end face and then transmitted to the double spherical lens for coupling. By setting the size of the parallel light spot focused by the first end face of the double spherical lens to be the same as the size of the light spot emitted by the hollow fiber pigtail, the light from the hollow fiber and the solid fiber can be interconverted. This also solves the problems of ultra-high loss and extremely low return loss caused by fusion splicing of solid and hollow fibers. It features a simple and compact structure, low cost, and excellent performance. By setting the first end face, return loss can be improved and return energy reduced while ensuring a certain insertion loss, thus avoiding device damage caused by high return energy. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of a single-segment solid-core and hollow-core optical fiber conversion device in one embodiment.

[0033] Figure 2 This is a schematic diagram of a two-section solid-core and hollow-core optical fiber interchange device in one embodiment.

[0034] Figure 3 This is a schematic diagram of a three-segment solid-core and hollow-core optical fiber interchange device in one embodiment.

[0035] Figure 4 This is a flowchart illustrating the acquisition of the tilt angle of a solid optical fiber in one embodiment.

[0036] Reference numerals in the attached diagram: 1. Double spherical lens; 2. Glass tube; 3. Single-mode solid fiber pigtail; 4. Hollow fiber pigtail. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0039] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0041] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0042] Example 1

[0043] like Figure 1 As shown, this embodiment provides a solid-core and hollow-core fiber conversion device, including: a double spherical lens 1, a glass tube 2, a single-mode solid-core fiber pigtail 3, and a hollow-core fiber pigtail 4;

[0044] The double spherical lens 1 includes a first spherical end and a second spherical end, wherein the curvature of the first spherical end is less than the curvature of the second spherical end;

[0045] The first spherical surface of the bispherical lens 1 is close to the single-mode solid fiber pigtail 3, and the second spherical surface of the bispherical lens 1 is close to the hollow fiber pigtail 4.

[0046] The first spherical end of the double spherical lens 1 is focused with the single-mode solid fiber pigtail 3;

[0047] The second spherical surface of the double spherical lens 1 is focused with the hollow fiber pigtail 4;

[0048] The glass tube 2 is a component that connects the bispherical lens 1, the single-mode solid fiber pigtail 3, and the hollow fiber pigtail 4 and supports the entire device. The inner diameter of the glass tube 2 can accommodate the bispherical lens 1, the single-mode solid fiber pigtail 3, and the hollow fiber pigtail 4.

[0049] The light emitted by the single-mode solid fiber pigtail 3 passes through the double spherical lens 1 and enters the hollow fiber pigtail 4.

[0050] Specifically, the double spherical lens 1 is made of N-SF11 glass, but it can also be made of any other glass material.

[0051] Preferably, the double spherical lens 1 is used to converge and collimate the light beam. It is mainly used to converge and collimate the light beam. In this invention, it is mainly used to converge the light emitted from one focal length into parallel light through the first spherical surface of the double spherical lens and transmit it inside the lens. After the parallel light passes through the second spherical surface, it converges to the other focal length.

[0052] Combination Figures 1 to 3 The glass tube 2 can be divided into one-section, two-section, or three-section glass tubes of different lengths, which can be respectively fitted onto the double spherical lens, single-mode solid fiber pigtail, and hollow fiber pigtail, using end-face bonding.

[0053] Specifically, the single-mode solid fiber pigtail 3 includes a single-mode fiber and a glass capillary tube for inserting the single-mode fiber, which can realize the function of fixing the single-mode fiber. The fiber end face is generally formed by grinding and then coating with an anti-reflection film.

[0054] Furthermore, the end face of the single-mode solid fiber pigtail 3 near the double spherical lens 1 is the first end face.

[0055] Furthermore, the first end face is an inclined surface.

[0056] In one specific embodiment, the tilt angle θ1 of the first end face meets the following condition:

[0057] Where NA is the numerical aperture of the solid fiber.

[0058] like Figure 4 As shown, it also includes the following steps:

[0059] S1, Obtain the historical tilt angle set A = {A1, ..., A1} of the first end face. i , ..., Am}, where A i It is the set of historical tilt angles of the first end face corresponding to the numerical aperture of the i-th solid fiber, and A i ={A i1 , ..., A ij , ..., A in}, A ij It is A i The historical tilt angle of the j-th first end face is given, where i ranges from 1 to m, m is the number of historical tilt angle groups of the first end face corresponding to the numerical aperture of the solid fiber, and m ≥ 2; j ranges from 1 to n, where n is the A i The number of historical tilt angles of the first end face, where n≥2.

[0060] Furthermore, A i1 To A in The historical tilt angles are sorted in ascending order and the difference between adjacent historical tilt angles is 1 degree.

[0061] Furthermore, A i1 It meets the condition of θ1.

[0062] S2, obtain the initial fiber loss information set B = {B1, ..., B1} corresponding to A. i , ..., B m}, B i ={B i1 , ..., B ij , ..., B in}, B ij = (B 1 ij B 2 ij ), B 1 ij It is A ij The corresponding initial return loss, B 2 ij It is A ij The corresponding initial insertion loss.

[0063] S3, based on B, obtain the target tilt angle of the first end face.

[0064] Specifically, step S3 also includes the following steps:

[0065] S31, Based on B, obtain the initial fiber loss priority set F = {F1, ..., F2} corresponding to B. i , ..., F m}, F i ={F i1 , ..., F ij , ..., F in}, F ij It is Bij The corresponding initial fiber loss priority, where F ij Meets the following conditions:

[0066] F ij =W 1 ×(B 1 ij -B 1 0) / B 1 0+W 2 ×(B 2 ij -B 2 0) / B 2 0, B 1 0 is the preset return loss threshold, B 2 0 is the preset insertion loss threshold, W 1 It is the weight of return loss, W 2 It is the weight of the insertion loss.

[0067] Preferred, B 1 0 = 60dB.

[0068] Preferred, B 2 0 = 0.25dB.

[0069] Preferred, W 1 =W 2 And W 1 +W 2 =1.

[0070] S32, from F i In the middle, select F i The maximum tilt angle range H of the corresponding first end face i To further understand: Select F i The maximum variance value of the corresponding sliding window is used as the range of the maximum tilt angle of the first end face, F. i The corresponding sliding window is F i The maximum value is the center point, and a sliding window is generated with a length of r / 2 adjacent initial fiber loss priorities.

[0071] S33, all H i By performing intersection processing, the final tilt angle range H of the first end face is obtained. 0 .

[0072] S34, Get H 0 The average maximum value of all initial fiber loss priorities corresponding to each historical tilt angle is used, and the historical tilt angle corresponding to the average maximum value is taken as the optimal tilt angle.

[0073] Preferably, the optimal tilt angle of the first end face obtained in steps S1-S3 is 8 degrees, which can improve the return loss and avoid device damage caused by high return energy. That is, the optimal tilt angle of the first end face is 8 degrees, which improves the return loss (>60dB) and ensures the optimal insertion loss (<0.25dB).

[0074] Furthermore, an antireflective coating is deposited on the surface of the first end face.

[0075] Specifically, the hollow fiber pigtail 4 includes an optical fiber and a glass capillary tube for optical fiber insertion.

[0076] Furthermore, the end face of the hollow fiber pigtail 4 near the double spherical lens 1 is the second end face.

[0077] Furthermore, the second end face is a plane.

[0078] Preferably, the light beams emitted by the single-mode solid fiber pigtail 3 and the hollow fiber pigtail 4 are both Gaussian beams or Gaussian-like beams.

[0079] Furthermore, when a parallel beam is focused at the principal focal point by a convex lens, the spot size can theoretically reach the diffraction limit under ideal conditions, and vice versa. When a beam is emitted from the principal focal point of a convex lens and becomes a collimated beam after passing through the lens, the spot size ω of the collimated beam satisfies the following condition:

[0080] ω=4λR / πd(n-1), where λ is the wavelength of light, R is the radius of curvature of the lens, π is pi, d is the diameter of the fiber mode field, and n is the refractive index of the lens.

[0081] In one specific embodiment, parameters are preset: the single-mode solid fiber pigtail 3, the hollow fiber pigtail 4, the preset collimated beam spot size, and the lens refractive index.

[0082] Specifically, the mode field diameter of the single-mode solid fiber pigtail 3 ranges from 9.2µm to 10.5µm.

[0083] Specifically, the mode field diameter of the hollow fiber pigtail 4 ranges from 19µm to 40µm.

[0084] Furthermore, the preset collimated beam spot size ranges from 126µm to 378µm.

[0085] Furthermore, the refractive index of the double spherical lens 1 is n=1.74474.

[0086] Furthermore, the range of the radii of curvature of the first and second spherical surfaces is calculated based on the collimated beam spot size ω meeting the following conditions: the radius of curvature ROC1 of the first spherical surface of the double spherical lens 1 ranges from 0.5mm to 1.5mm, and the radius of curvature ROC2 of the second spherical surface of the double spherical lens 1 ranges from 0.9mm to 2.71mm. This satisfies the condition that regardless of which end of the optical fiber emits light, after passing through the lens spherical surface, its spot size reaches the preset collimated beam spot size, thereby realizing the mutual conversion function; as shown in the table below:

[0087]

[0088] In one specific embodiment, based on the data in the table, it can be known that: preferably, the radius of curvature of the first end sphere is R0.9mm, and the radius of curvature of the second end sphere is R1.63mm.

[0089] In another specific embodiment, the following steps are also included:

[0090] S100, Obtain the initial radius of curvature information D={D1, ..., D2} of the first end sphere. x , ..., D p}, D x It is the x-th initial radius of curvature of the first end sphere, where x ranges from 1 to p, and p is the number of initial radii of curvature of the first end sphere;

[0091] S200, Obtain the initial radius of curvature information G={G1, ..., G2} of the second end sphere. y , ..., G q}, G y It is the y-th initial radius of curvature of the second end sphere, where y ranges from 1 to q, and q is the number of initial radii of curvature of the second end sphere;

[0092] S300, D x Input the preset collimated beam spot size model to obtain D. x The corresponding mid-curvature radius information L of the second end sphere x ={L x1 , ..., L xg , ..., L xz}, L xg It is D x The corresponding g-th intermediate radius of curvature of the second end sphere, where g ranges from 1 to z, and z is the number of intermediate radii of curvature of the second end sphere;

[0093] S400, L x Match with G and select L. x The critical radius of curvature of the second spherical surface intersecting with G ranges from K. x;

[0094] S500, obtain K x The corresponding critical fiber loss priority set KF x You can refer to steps S1-S3 to obtain the priority of critical fiber loss.

[0095] S600, based on all KF x The maximum critical fiber loss priority is selected; and the initial radius of curvature of the first end sphere and the initial radius of curvature of the second end sphere corresponding to the maximum critical fiber loss priority are determined; thus, the optimal radius of curvature of the first end sphere and the optimal radius of curvature of the second end sphere are obtained.

[0096] This embodiment provides a solid-core and hollow-core fiber optic conversion device, including: a bispherical lens, a glass tube, a single-mode solid-core fiber optic pigtail, and a hollow-core fiber optic pigtail; the bispherical lens includes a first end spherical surface and a second end spherical surface, wherein the curvature of the first end spherical surface is less than the curvature of the second end spherical surface; the first end spherical surface of the bispherical lens is close to the single-mode solid-core fiber optic pigtail, and the second end spherical surface of the bispherical lens is close to the hollow-core fiber optic pigtail; the first end spherical surface of the bispherical lens is focused with the single-mode solid-core fiber optic pigtail; the second end spherical surface of the bispherical lens is focused with the hollow-core fiber optic pigtail; the single... Light emitted from the solid-core fiber pigtail passes through the double-spherical lens and enters the hollow-core fiber pigtail. Light emitted from the solid-core fiber pigtail is focused into parallel light by the first end face and transmitted to the double-spherical lens for coupling. By setting the size of the parallel light spot focused by the first end face of the double-spherical lens to be the same as the size of the light spot emitted by the hollow-core fiber pigtail, the light from the hollow-core and solid-core fibers can be interconverted. This also solves the problems of ultra-high loss and extremely low return loss caused by fusion splicing of solid-core and hollow-core fibers. It features a simple and compact structure, low cost, and excellent performance. By setting the first end face, return loss can be improved and return energy reduced while ensuring a certain insertion loss, thus avoiding device damage caused by high return energy.

[0097] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0098] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A solid-core and hollow-core optical fiber conversion device, characterized in that, include: Double spherical lens (1), glass tube (2), single-mode solid fiber pigtail (3) and hollow fiber pigtail (4). The double spherical lens (1) includes a first end spherical surface and a second end spherical surface, wherein the curvature of the first end spherical surface is less than the curvature of the second end spherical surface; The first spherical surface of the double spherical lens (1) is close to the single-mode solid fiber pigtail (3), and the second spherical surface of the double spherical lens (1) is close to the hollow fiber pigtail (4). The first spherical end of the double spherical lens (1) is focused with the single-mode solid fiber pigtail (3); The second spherical surface of the double spherical lens (1) is focused with the hollow fiber pigtail (4); The glass tube (2) is a component that connects the double spherical lens (1), the single-mode solid fiber pigtail (3) and the hollow fiber pigtail (4) and supports the entire device. The inner diameter of the glass tube (2) can be inserted into the double spherical lens (1), the single-mode solid fiber pigtail (3) and the hollow fiber pigtail (4). The light emitted by the single-mode solid fiber pigtail (3) passes through the double spherical lens (1) and enters the hollow fiber pigtail (4). The end face of the single-mode solid fiber pigtail (3) near the double spherical lens (1) is the first end face, which is an inclined surface. The optimal tilt angle of the first end face is obtained by: S1, Obtain the historical tilt angle set A = {A1, ..., A1} of the first end face. i , ..., A m }, where A i It is the set of historical tilt angles of the first end face corresponding to the numerical aperture of the i-th solid fiber, and A i ={A i1 , ..., A ij , ..., A in }, A ij It is A i The historical tilt angle of the j-th first end face is given, where i ranges from 1 to m, m is the number of historical tilt angle groups of the first end face corresponding to the numerical aperture of the solid fiber, and m ≥ 2; j ranges from 1 to n, where n is the numerical aperture of the optical fiber. i The number of historical tilt angles of the first end face, where n≥2; S2, obtain the initial fiber loss information set B = {B1, ..., B1} corresponding to A. i , ..., B m }, B i ={B i1 , ..., B ij , ..., B in }, B ij = (B 1 ij B 2 ij ), B 1 ij It is A ij The corresponding initial return loss, B 2 ij It is A ij The corresponding initial insertion loss; S3, based on B, obtain the target tilt angle of the first end face. Step S3 also includes the following steps: S31, Based on B, obtain the initial fiber loss priority set F = {F1, ..., F2} corresponding to B. i , ..., F m }, F i ={F i1 , ..., F ij , ..., F in }, F ij It is B ij The corresponding initial fiber loss priority, where F ij The following conditions must be met: F ij =W 1 ×(B 1 ij -B 1 0) / B 1 0+W 2 ×(B 2 ij -B 2 0) / B 2 0, B 1 0 is the preset return loss threshold, B 2 0 is the preset insertion loss threshold, W 1 It is the weight of return loss, W 2 It is the weight of the insertion loss; S32, from F i In the middle, select F i The maximum tilt angle range H of the corresponding first end face i ; S33, all H i By performing intersection processing, the final tilt angle range H of the first end face is obtained. 0 ; S34, Get H 0 The average maximum value of all initial fiber loss priorities corresponding to each historical tilt angle is used, and the historical tilt angle corresponding to the average maximum value is taken as the optimal tilt angle.

2. The solid-core and hollow-core optical fiber conversion device according to claim 1, characterized in that, The material of the double spherical lens (1) is N-SF11.

3. The solid-core and hollow-core optical fiber conversion device according to claim 1, characterized in that, The glass tube (2) is divided into one-section, two-section or three-section types of different lengths.

4. The solid-core and hollow-core optical fiber conversion device according to claim 1, characterized in that, The first end face is coated with an anti-reflective film.

5. The solid-core and hollow-core optical fiber conversion device according to claim 1, characterized in that, The end face of the hollow fiber pigtail (4) near the double spherical lens (1) is the second end face.

6. The solid-core and hollow-core optical fiber conversion device according to claim 5, characterized in that, The second end face is a plane.

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