Hollow core optical fiber and method of fusion splicing a hollow core optical fiber

Abstract

The application discloses an air-core optical fiber and a fusion method of the air-core optical fiber. The air-core optical fiber comprises an air core for transmitting an optical signal and a cladding for confining the optical signal in the air core for transmission. A material with a first refractive index is used in a first region of the cladding, and a material with a second refractive index is used in a second region of the cladding. The first refractive index is greater than the second refractive index.

Description

Technical Field

[0001] This invention relates to the field of communication network technology, and in particular to a hollow optical fiber and a fusion splicing method for hollow optical fibers. Background Technology

[0002] Currently, hollow-core optical fibers have a flexible structure and can achieve special performance that traditional optical fibers cannot achieve in optical transmission scenarios. These include low latency, flat dispersion, low nonlinearity, and the ability to achieve single-mode transmission across the entire wavelength range. However, during the splicing of hollow-core and solid-core optical fibers, the reflection at the end face of the solid-core fiber introduces strong signal reflection and loss. Summary of the Invention

[0003] In view of this, embodiments of the present invention aim to provide a hollow optical fiber and a fusion splicing method for hollow optical fibers.

[0004] The technical solution of this invention is implemented as follows:

[0005] At least one embodiment of the present invention provides a hollow optical fiber, comprising:

[0006] Air core, used to transmit optical signals;

[0007] Cladding is used to enclose optical signals within an air core for transmission;

[0008] The first region of the cladding layer uses a material with a first refractive index, and the second region of the cladding layer uses a material with a second refractive index; the first refractive index is greater than the second refractive index.

[0009] Furthermore, according to at least one embodiment of the present invention, the cladding layer includes:

[0010] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0011] The first region is formed on the walls of the N air holes in the inner cladding;

[0012] The second region is formed by the walls of the MN air holes in the inner cladding and the entire area of ​​the outer cladding;

[0013] The positions of the N air holes are different from the positions of the MN air holes; M and N are both positive integers, and M is greater than N.

[0014] Furthermore, according to at least one embodiment of the present invention, the cladding layer includes:

[0015] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0016] The first region is formed on the walls of the M air holes in the inner cladding;

[0017] The second region is formed over the entire area of ​​the outer cladding layer;

[0018] Where M is a positive integer;

[0019] Furthermore, according to at least one embodiment of the present invention, the cladding layer includes:

[0020] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0021] The first region is formed on the walls of the M air holes in the inner cladding and on the inner side of the outer cladding;

[0022] The second region is formed in the outer cladding layer in areas other than the inner region;

[0023] Where M is a positive integer.

[0024] Furthermore, according to at least one embodiment of the present invention,

[0025] The third region of the cladding uses a material with a third refractive index; the second refractive index is greater than or equal to the third refractive index.

[0026] Furthermore, according to at least one embodiment of the present invention, the cladding layer includes:

[0027] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0028] The first region is formed on the walls of the N air holes in the inner cladding;

[0029] The second region is formed on the walls of the MN air holes in the inner cladding and on the inner side of the outer cladding;

[0030] The third region is formed in the outer cladding layer in regions other than the inner region.

[0031] The positions of the N air holes are different from the positions of the MN air holes; M and N are both positive integers, and M is greater than N.

[0032] Furthermore, according to at least one embodiment of the present invention, the cladding layer includes:

[0033] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0034] The first region is formed on the walls of the M air holes in the inner cladding;

[0035] The second region is formed in the inner region of the outer cladding layer;

[0036] The third region is formed in the outer cladding layer in regions other than the inner region.

[0037] Where M is a positive integer.

[0038] Furthermore, according to at least one embodiment of the present invention, the cladding layer includes:

[0039] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0040] The first region is formed on the walls of the M air holes in the inner cladding and on the inner side of the outer cladding;

[0041] The second region and the third region are formed in the outer cladding layer in areas other than the inner region;

[0042] Where M is a positive integer.

[0043] At least one embodiment of the present invention provides a fusion splicing method for hollow optical fibers, the hollow optical fibers comprising an air core and a cladding, the air core being used to transmit optical signals, the cladding being used to enclose the optical signals within the air core for transmission, a material with a first refractive index being used in a first region of the cladding, and a material with a second refractive index being used in a second region of the cladding, wherein the first refractive index is greater than the second refractive index, the method comprising:

[0044] Hollow-core optical fibers are fused and / or tapered to form a specific region within the hollow-core optical fiber; the specific region includes a tapered hollow core portion and a solid core portion without air holes; in the solid core portion without air holes, a first region of the cladding forms a first structure, and a second region of the cladding forms a second structure;

[0045] A cutting point is determined in the solid core portion without air holes in the specific region, and cutting is performed at the cutting point to obtain two hollow optical fibers with the first structure and the second structure.

[0046] The first structure of any one of the two hollow fiber segments is aligned with the core of the solid fiber, and the second structure is aligned with the cladding of the solid fiber, and then fusion spliced.

[0047] This invention provides a hollow-core optical fiber and a fusion splicing method for hollow-core optical fibers. The hollow-core optical fiber includes: an air core for transmitting optical signals; and a cladding for enclosing the optical signals within the air core for transmission. A first region of the cladding uses a material with a first refractive index, and a second region of the cladding uses a material with a second refractive index; the first refractive index is greater than the second refractive index. The hollow-core optical fiber is fused and / or tapered to form a specific region within the fiber. This specific region includes a tapered hollow portion and a solid core portion without air holes. In the solid core portion without air holes, a first structure is formed in the first region of the cladding, and a second structure is formed in the second region of the cladding. A cleaving point is determined in the specific region, and the fiber is cleaved at the cleaving point to obtain two segments of hollow-core optical fiber with the first and second structures. The first structure of any one segment of the hollow-core optical fiber is aligned with the core of the solid optical fiber, and the second structure is aligned with the cladding of the solid optical fiber, and then fusion spliced. By employing the technical solution of this invention, during the fusion splicing of the hollow-core optical fiber and the solid-core optical fiber, the hollow-core optical fiber is first fused and / or tapered to form a first structure without air holes in a first region of the cladding of the hollow-core optical fiber, and a second structure without air holes in a second region of the cladding. The refractive index of the first structure material is greater than that of the second structure material, achieving a structure similar to the solid-core optical fiber where the core refractive index is greater than that of the cladding. The first structure and the core of the solid-core optical fiber are aligned, and the second structure and the cladding of the solid-core optical fiber are aligned before fusion splicing. In this way, the optical signal transmitted in the hollow-core optical fiber can be transmitted to the solid-core optical fiber, avoiding the introduction of strong signal reflection and loss. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of hollow optical fiber in related technologies;

[0049] Figure 2 This is a schematic diagram of fusion splicing hollow-core and solid-core optical fibers in related technologies. Figure 1 ;

[0050] Figure 3 This is a schematic diagram of fusion splicing hollow-core and solid-core optical fibers in related technologies. Figure 2 ;

[0051] Figure 4 This is a schematic diagram of fusion splicing hollow-core and solid-core optical fibers in related technologies. Figure 3 ;

[0052] Figure 5 This is a schematic diagram illustrating how a tapered fiber can be used to achieve mode matching between single-mode and multimode optical fibers, thereby enabling low insertion loss fusion splicing in related technologies.

[0053] Figure 6This is a schematic diagram of the composition structure of the hollow-core optical fiber according to an embodiment of the present invention;

[0054] Figure 7 This is a schematic diagram of the first and second regions in an embodiment of the present invention. Figure 1 ;

[0055] Figure 8 This is a schematic diagram of the first and second regions in an embodiment of the present invention. Figure 2 ;

[0056] Figure 9 This is a schematic diagram of the first and second regions in an embodiment of the present invention. Figure 3 ;

[0057] Figure 10 This is a schematic diagram of the first, second, and third regions of an embodiment of the present invention. Figure 1 ;

[0058] Figure 11 This is a schematic diagram of the first, second, and third regions of an embodiment of the present invention. Figure 2 ;

[0059] Figure 12 This is a schematic diagram of the first, second, and third regions of an embodiment of the present invention. Figure 3 ;

[0060] Figure 13 This is a schematic diagram illustrating the implementation process of the fusion splicing method for hollow optical fibers according to an embodiment of the present invention;

[0061] Figure 14 This is a schematic diagram of splicing hollow optical fiber and solid optical fiber according to an embodiment of the present invention. Detailed Implementation

[0062] Before introducing the technical solutions of the embodiments of the present invention, the relevant technologies will be explained first.

[0063] Among related technologies, hollow-core optical fiber has a flexible structure and can achieve special performance that traditional optical fibers cannot achieve for optical transmission scenarios. For example, it has low latency, flat dispersion, low nonlinear coefficient, and can achieve single-mode transmission across the entire wavelength range.

[0064] Figure 1 This is a schematic diagram of the structure of hollow optical fiber in related technologies. For example... Figure 1 As shown, in the traditional structure of hollow optical fiber, the core is an air core, while the cladding uses a porous honeycomb structure, a multi-air-hole microstructure, or a refractive index ring change, a reflective film, etc., to confine the light in the air core.

[0065] Figure 2 This is a schematic diagram illustrating the fusion splicing of hollow-core and solid-core optical fibers in related technologies, such as... Figure 2As shown, firstly, the hollow-core fiber and the solid-core fiber are cut to have flat end faces; then, the hollow-core fiber and the solid-core fiber are spliced ​​by means of thermal fusion splicing, cold splicing, and jacket fixing.

[0066] Patent application number 20195031915.1, entitled "A Connector and Method for Optical Fiber Fusion Splicing," discloses a connector and method for optical fiber fusion splicing, specifically revealing the following technical features: The connector includes an optical fiber end cap and a transition ring, enabling fusion splicing of different types of optical fibers, particularly solid-core and hollow-core optical fibers used for high-power laser transmission. The connector employs optical fiber end cap technology to expand the laser beam, reducing the power density at the output end face. A transition ring is then introduced at the laser output end face of the end cap, and an anti-reflection coating is applied to the laser output end face of the end cap. Finally, the transition ring is fused to the hollow-core optical fiber. Figure 3 As shown.

[0067] Patent application number 201980065378.0, entitled "Optical Waveguide Adapter Assembly," discloses an optical waveguide adapter assembly and specifically outlines the following technical features: the assembly includes a solid optical waveguide, a hollow optical waveguide, and an optical mode field adapter. A first end of the optical mode field adapter is coupled to the coupling end of the solid optical waveguide to provide optical coupling between the waveguide core of the solid optical waveguide and the waveguide core of the optical mode field adapter. A second end of the optical mode field adapter is coupled to the coupling end of the hollow optical waveguide to provide optical coupling between the waveguide core of the hollow optical waveguide and the waveguide core of the optical mode field adapter. Figure 4 As shown.

[0068] Figure 5 This is a schematic diagram illustrating how tapered fiber optic cables achieve mode matching between single-mode and multimode fibers to enable low insertion loss fusion splicing in related technologies. Figure 5 As shown, by rationally designing the tapering parameters of single-mode and multimode optical fibers, the mode field of the single-mode fiber can be well matched with that of the multimode fiber, thus enabling the excitation of the fundamental mode in the multimode fiber.

[0069] However, the following technical defects exist in the fusion splicing process of hollow-core optical fiber and solid-core optical fiber:

[0070] First, the reflective nature of solid fiber end faces introduces significant signal transmission and loss. Second, weak splices or gaps expose the hollow fiber, allowing contaminants to enter and cause substantial loss. Third, using traditional arc discharge splicing methods to fuse air-core photonic bandgap fibers with ordinary single-mode fibers inevitably leads to the collapse of the air holes in the air-core photonic bandgap fiber, resulting in significant coupling loss.

[0071] Based on this, in this embodiment of the invention, a novel hollow optical fiber is provided, comprising: an air core for transmitting optical signals; and a cladding for enclosing the optical signals within the air core for transmission; wherein a material with a first refractive index is used in a first region of the cladding, and a material with a second refractive index is used in a second region of the cladding; the first refractive index is greater than the second refractive index.

[0072] Figure 6 This is a schematic diagram of the composition structure of the hollow-core optical fiber according to an embodiment of the present invention, as shown below. Figure 6 As shown, hollow optical fiber includes:

[0073] Air core 61, used for transmitting optical signals;

[0074] Cladding 62 is used to enclose the optical signal in an air core for transmission;

[0075] The first region of the cladding 62 uses a material with a first refractive index, and the second region of the cladding 62 uses a material with a second refractive index; the first refractive index is greater than the second refractive index.

[0076] It is understood that a material with a third refractive index may also be used in the third region of the cladding 62; the second refractive index is greater than or equal to the third refractive index.

[0077] It is understood that the structure of the hollow optical fiber can be honeycomb, anti-resonance, resonant ring, etc., and there are no restrictions on this in the embodiments of the present invention.

[0078] In one implementation, the cladding layer 62 may include:

[0079] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-porous structure; the outer cladding layer has a solid structure.

[0080] in,

[0081] The first region is formed on the wall of a portion of the air holes in the inner cladding; the second region is formed on the wall of another portion of the air holes in the inner cladding and the entire area of ​​the outer cladding.

[0082] or,

[0083] The first region is formed on the walls of all the air pores in the inner cladding; the second region is formed over the entire area of ​​the outer cladding.

[0084] or,

[0085] A first region is formed by the walls of all the air pores in the inner cladding and a portion of the outer cladding; a second region is formed by another portion of the outer cladding.

[0086] In another implementation, the cladding layer 62 may include:

[0087] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-porous structure; the outer cladding layer has a solid structure.

[0088] in,

[0089] The first region is formed on the wall of a portion of the air holes in the inner cladding; the second region is formed on the wall of another portion of the air holes in the inner cladding and on a portion of the outer cladding; the third region is formed on another portion of the outer cladding.

[0090] or,

[0091] The first region is formed on the walls of all the air pores in the inner cladding; the second region is formed on a portion of the outer cladding; and the third region is formed on another portion of the outer cladding.

[0092] or,

[0093] A first region is formed on the walls of all the air pores in the inner cladding and a portion of the outer cladding; a second region and the third region are formed in another portion of the outer cladding.

[0094] The specific structure of the cladding 62 will be described in detail below.

[0095] In one embodiment, the cladding layer 62 includes:

[0096] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0097] The first region is formed on the walls of the N air holes in the inner cladding;

[0098] The second region is formed by the walls of the MN air holes in the inner cladding and the entire area of ​​the outer cladding;

[0099] The positions of the N air holes are different from the positions of the MN air holes; M and N are both positive integers, and M is greater than N.

[0100] Figure 7 This is a schematic diagram of the first and second regions, as shown below. Figure 7As shown, the first region is formed by the walls of some of the air holes in the inner cladding, and the second region is formed by the walls of another portion of the air holes in the inner cladding and the entire area of ​​the outer cladding. The walls of the air holes in the first and second regions are made of materials with different refractive indices; specifically, the refractive index of the material used for the walls of the air holes in the first region is higher than that of the material used for the walls of the air holes in the second region, and the refractive index of the material used for the walls of the air holes in the first region is higher than that of the material used for the outer cladding in the second region.

[0101] In one embodiment, the cladding layer 62 includes:

[0102] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0103] The first region is formed on the walls of the M air holes in the inner cladding; the second region is formed over the entire area of ​​the outer cladding.

[0104] Where M is a positive integer.

[0105] Figure 8 This is a schematic diagram of the first and second regions, as shown below. Figure 8 As shown, the first region is formed by the walls of all the air holes in the inner cladding, and the second region is formed by the entire area of ​​the outer cladding. The walls of the air holes in the first region and the outer cladding in the second region are made of materials with different refractive indices, and the refractive index of the material used for the walls of the air holes in the first region is higher than that of the material used for the outer cladding in the second region.

[0106] In one embodiment, the cladding layer 62 includes:

[0107] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0108] The first region is formed on the walls of the M air holes in the inner cladding and on the inner side of the outer cladding; the second region is formed in the other regions of the outer cladding besides the inner side.

[0109] Where M is a positive integer.

[0110] Figure 9 This is a schematic diagram of the first and second regions, as shown below. Figure 9As shown, the first region is formed by the walls of all the air holes in the inner cladding and the inner region of the outer cladding, and the second region is formed by the other regions of the outer cladding except for the inner region. The walls of the air holes in the first region and the outer cladding in the second region are made of materials with different refractive indices, and the refractive index of the material used in the first region is higher than that of the material used in the second region.

[0111] In one embodiment, the cladding layer 62 includes:

[0112] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0113] The first region is formed on the walls of the N air holes in the inner cladding;

[0114] The second region is formed on the walls of the MN air holes in the inner cladding and on the inner side of the outer cladding;

[0115] The third region is formed in the outer cladding layer in regions other than the inner region.

[0116] The positions of the N air holes are different from the positions of the MN air holes; M and N are both positive integers, and M is greater than N.

[0117] Figure 10 This is a schematic diagram of the first, second, and third regions, as shown below. Figure 10 As shown, the first region is formed by the pore walls of a portion of the air holes in the inner cladding, the second region is formed by the pore walls of another portion of the air holes in the inner cladding and the inner region of the outer cladding, and the third region is formed by the other regions in the outer cladding excluding the inner region. The refractive index of the material used in the first region is greater than that of the material used in the second region, and the refractive index of the material used in the second region is greater than or equal to that of the material used in the third region.

[0118] In one embodiment, the cladding layer 62 includes:

[0119] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0120] The first region is formed on the walls of the M air holes in the inner cladding;

[0121] The second region is formed in the inner region of the outer cladding layer;

[0122] The third region is formed in the outer cladding layer in regions other than the inner region.

[0123] Where M is a positive integer.

[0124] Figure 11 This is a schematic diagram of the first, second, and third regions, as shown below. Figure 11 As shown, the first region is formed by the walls of all the air pores in the inner cladding, the second region is formed by the inner region of the outer cladding, and the third region is formed by the other regions in the outer cladding except for the inner region. The refractive index of the material used in the first region is greater than that of the material used in the second region, and the refractive index of the material used in the second region is greater than or equal to that of the material used in the third region.

[0125] In one embodiment, the cladding layer 62 includes:

[0126] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0127] The first region is formed on the walls of the M air holes in the inner cladding and on the inner side of the outer cladding;

[0128] The second region and the third region are formed in the outer cladding layer in areas other than the inner region;

[0129] Where M is a positive integer.

[0130] Figure 12 This is a schematic diagram of the first, second, and third regions, as shown below. Figure 12 As shown, the first region is formed by the walls of all the air pores in the inner cladding and the inner region of the outer cladding. The second and third regions are formed by the other regions of the outer cladding, excluding the inner region. The refractive index of the material used in the first region is greater than that of the material used in the second region, and the refractive index of the material used in the second region is greater than or equal to that of the material used in the third region.

[0131] The hollow-core optical fiber proposed in this embodiment of the invention has the following specific structural features:

[0132] (1) Within a certain range of the cladding, a first region is formed using a material with a high refractive index.

[0133] (2) The first region may be formed by the hole walls of some of the air holes in the inner cladding, or by the hole walls of all the air holes in the inner cladding, or by the hole walls of all the air holes in the inner cladding and a portion of the solid cladding in the outer cladding.

[0134] Figure 13 This is a schematic diagram illustrating the implementation process of the fusion splicing method for hollow optical fibers according to an embodiment of the present invention, as shown below. Figure 13 As shown, the method includes steps 1301 to 1303:

[0135] Step 1301: The hollow fiber is fused and / or tapered to form a specific region in the hollow fiber; the specific region includes a tapered hollow portion and a solid portion without air holes; in the solid portion without air holes, a first region of the cladding of the hollow fiber forms a first structure, and a second region of the cladding forms a second structure.

[0136] Step 1302: Determine the cutting point in the solid core portion without air holes in the specific region, and cut at the cutting point to obtain two hollow optical fibers with the first structure and the second structure.

[0137] Step 1303: Align the first structure of any one of the two hollow fiber segments with the core of the solid fiber, and align the second structure with the cladding of the solid fiber, and then perform fusion splicing.

[0138] Understandably, when splicing with solid fiber, the hollow fiber is first fused and / or tapered in the middle. Since some of the air hole walls or cladding inside the hollow fiber are made of high-refractive-index material, after fusion and / or tapering, the hollow core and air hole portions are completely fused, naturally forming a high-refractive-index optical mode conversion structure similar to that of solid fiber. Then, it is cut in the fused and / or tapered area to form a solid end face, which is then fused with solid fiber using a standard fusion splicing method. This method can effectively achieve splicing with solid fiber. Figure 14 As shown.

[0139] If it is necessary to perform fusion splicing between ordinary hollow-core optical fibers and solid-core optical fibers, the hollow-core optical fiber provided in this embodiment of the invention can be used as an adapter. That is, one end of the hollow-core optical fiber provided in this embodiment of the invention is fused to an ordinary hollow-core optical fiber, and the other end of the hollow-core optical fiber provided in this embodiment of the invention is fused to a solid-core optical fiber using the fusion splicing method provided in this embodiment of the invention. Since ordinary hollow-core optical fibers and the hollow-core optical fiber provided in this embodiment of the invention have similar spatial structures, the fusion splicing difficulty is low and the loss is relatively small. This method can effectively improve the fusion quality and reduce fusion loss and reflection.

[0140] The hollow optical fiber includes:

[0141] Air core, used to transmit optical signals;

[0142] Cladding is used to enclose optical signals in an air core for transmission;

[0143] The first region of the cladding layer uses a material with a first refractive index, and the second region of the cladding layer uses a material with a second refractive index; the first refractive index is greater than the second refractive index.

[0144] It is understood that a material with a third refractive index may also be used in the third region of the cladding; the second refractive index is greater than or equal to the third refractive index.

[0145] It is understood that the structure of hollow optical fiber can be honeycomb, anti-resonance, resonant ring, etc., and there are no restrictions on this in the embodiments of the present invention.

[0146] In one embodiment, the cladding layer includes:

[0147] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0148] The first region is formed on the walls of the N air holes in the inner cladding;

[0149] The second region is formed by the walls of the MN air holes in the inner cladding and the entire area of ​​the outer cladding;

[0150] The positions of the N air holes are different from the positions of the MN air holes; M and N are both positive integers, and M is greater than N.

[0151] In one embodiment, the cladding layer includes:

[0152] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0153] The first region is formed on the walls of the M air holes in the inner cladding; the second region is formed over the entire area of ​​the outer cladding.

[0154] Where M is a positive integer.

[0155] In one embodiment, the cladding layer includes:

[0156] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0157] The first region is formed on the walls of the M air holes in the inner cladding and on the inner side of the outer cladding; the second region is formed in the other regions of the outer cladding besides the inner side.

[0158] Where M is a positive integer.

[0159] In one embodiment, the cladding layer includes:

[0160] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0161] The first region is formed on the walls of the N air holes in the inner cladding;

[0162] The second region is formed on the walls of the MN air holes in the inner cladding and on the inner side of the outer cladding;

[0163] The third region is formed in the outer cladding layer in regions other than the inner region.

[0164] The positions of the N air holes are different from the positions of the MN air holes; M and N are both positive integers, and M is greater than N.

[0165] In one embodiment, the cladding layer includes:

[0166] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0167] The first region is formed on the walls of the M air holes in the inner cladding;

[0168] The second region is formed in the inner region of the outer cladding layer;

[0169] The third region is formed in the outer cladding layer in regions other than the inner region.

[0170] Where M is a positive integer.

[0171] In one embodiment, the cladding layer includes:

[0172] The inner cladding layer and the outer cladding layer; the inner cladding layer has a multi-pore structure and consists of M air pores; the outer cladding layer has a solid structure.

[0173] The first region is formed on the walls of the M air holes in the inner cladding and on the inner side of the outer cladding;

[0174] The second region and the third region are formed in the outer cladding layer in areas other than the inner region;

[0175] Where M is a positive integer.

[0176] In this embodiment of the invention, fusion splicing hollow-core optical fibers and solid-core optical fibers has the following advantages:

[0177] (1) Within a certain range of the cladding, a first region is formed using a high-refractive-index material. Thus, during the process of fusion splicing and / or tapering the hollow fiber, a first structure is formed in the first region of the cladding, and a second structure without air holes is formed in the second region of the cladding, so that after the hollow fiber and the solid fiber are fused together, the optical signal transmitted in the hollow fiber can be transmitted to the solid fiber.

[0178] (2) It can avoid the problem of strong signal transmission and loss caused by the reflection of the end face of solid optical fiber in related technologies.

Claims

1. A hollow core optical fiber, characterized by, The air core optical fiber comprises: an air core for transmitting an optical signal; a cladding for confining the optical signal in the air core for transmission; the cladding comprises an inner cladding and an outer cladding; the inner cladding has a multi-hole structure and is composed of M air holes; the outer cladding has a solid structure; wherein a material with a first refractive index is used in a first region of the cladding, and a material with a second refractive index is used in a second region of the cladding; the first refractive index is greater than the second refractive index; the cladding is formed in the following way: the hole walls of N air holes of the inner cladding form the first region; the hole walls of M-N air holes of the inner cladding and the entire region of the outer cladding form the second region; or, the hole walls of M air holes of the inner cladding form the first region; the entire region of the outer cladding forms the second region; or, the hole walls of M air holes of the inner cladding and the inner region of the outer cladding form the first region; the regions of the outer cladding other than the inner region form the second region; or, the hole walls of N air holes of the inner cladding form the first region; the hole walls of M-N air holes of the inner cladding and the inner region of the outer cladding form the second region; the regions of the outer cladding other than the inner region form a third region of the cladding; or, the hole walls of M air holes of the inner cladding form the first region; the inner region of the outer cladding forms the second region; the regions of the outer cladding other than the inner region form a third region; or, the hole walls of M air holes of the inner cladding and the inner region of the outer cladding form the first region; the regions of the outer cladding other than the inner region form the second region and the third region; wherein the positions of the N air holes are different from the positions of the M-N air holes; M and N are both positive integers, and M is greater than N.

2. The air core optical fiber according to claim 1, wherein in the case that the third region is formed in the outer cladding, the third region uses a material with a third refractive index; the second refractive index is greater than or equal to the third refractive index.

3. The hollow core fiber according to claim 1, characterized in that, The structure of the air core optical fiber comprises one of a honeycomb structure, an anti-resonant structure, and a resonant ring.

4. A method of fusion splicing an air-core optical fiber, characterized by, The air core optical fiber comprises an air core for transmitting an optical signal and a cladding for confining the optical signal in the air core for transmission; a material with a first refractive index is used in a first region of the cladding, and a material with a second refractive index is used in a second region of the cladding; the first refractive index is greater than the second refractive index; the method comprises: fusing and / or tapering the air core optical fiber to form a specific region in the air core optical fiber; the specific region comprises a tapered air core part and a solid core part without air holes; in the solid core part without air holes, the first region of the cladding forms a first structure, and the second region of the cladding forms a second structure; The solid core part of the specific region without air holes determines a cutting point, and cutting is performed at the cutting point to obtain two segments of hollow core optical fiber with the first structure and the second structure; The first structure of any one of the two segments of hollow core optical fiber is aligned with the core of the solid core optical fiber, and the second structure is aligned with the cladding of the solid core optical fiber, and fusion splicing is performed; The cladding comprises an inner cladding and an outer cladding; the inner cladding is a multi-air hole structure and is composed of M air holes; the outer cladding is a solid structure; The cladding is formed in the following manner: The first region is formed on the hole walls of N air holes of the inner cladding; The second region is formed on the hole walls of M-N air holes of the inner cladding and the entire region of the outer cladding; Or, The first region is formed on the hole walls of M air holes of the inner cladding; The second region is formed on the entire region of the outer cladding; Or, The first region is formed on the hole walls of M air holes of the inner cladding and the inner region of the outer cladding; The second region is formed on the other region of the outer cladding except the inner region; Or, The first region is formed on the hole walls of N air holes of the inner cladding; The second region is formed on the hole walls of M-N air holes of the inner cladding and the inner region of the outer cladding; The third region of the cladding is formed on the other region of the outer cladding except the inner region; Or, The first region is formed on the hole walls of M air holes of the inner cladding; The second region is formed on the inner region of the outer cladding; The third region is formed on the other region of the outer cladding except the inner region; Or, The first region is formed on the hole walls of M air holes of the inner cladding and the inner region of the outer cladding; The second region and the third region are formed on the other region of the outer cladding except the inner region; The positions of the N air holes are different from the positions of the M-N air holes; M and N are positive integers, and M is greater than N.

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