Composite hollow core optical fiber and applications thereof

Abstract

The application belongs to the technical field of optical fibers, and discloses a composite hollow-core optical fiber and application thereof. The composite hollow-core optical fiber comprises, from outside to inside, an outer cladding layer, an inner cladding layer and a core; the inner cladding layer is composed of an outer-layer kagome lattice structure, an inner-layer kagome lattice structure and a nested tube structure; the outer-layer kagome lattice structure is composed of a plurality of regular hexagonal air holes and a plurality of regular triangular air holes; the inner-layer kagome lattice structure is composed of a plurality of air holes with negative curvature and a plurality of regular triangular air holes; the nested tube structure comprises a plurality of unit nested tube structures, each unit nested tube structure is composed of a first tubular structure and a second tubular structure, the radius of the first tubular structure is greater than the radius of the second tubular structure, and the inner side of the first tubular structure is tangent to the outer side of the second tubular structure. The application can reduce the transmission loss of the hollow-core optical fiber, and is particularly suitable for VCSEL communication.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fibers, and more particularly relates to a composite hollow-core optical fiber and application thereof. BACKGROUND

[0002] Hollow-core optical fiber is an important research direction of fiber optics. With its specific microstructure design, the light field can be confined in the air core, reducing the overlap of the light field and the quartz region. Compared with traditional solid-core optical fibers, hollow-core optical fibers overcome intrinsic losses such as material and scattering, and can theoretically achieve ultra-low loss optical transmission. In addition, they also have the advantages of low delay, low dispersion, low nonlinearity, high optical damage threshold, anti-interference, and high flexibility of filling liquid or gas, and have broad application prospects in high-power pulsed laser transmission, ultrafast optics, and nonlinear optics.

[0003] Although hollow-core optical fibers have developed rapidly, most of the current research on hollow-core optical fibers is focused on the wavelength band greater than 1000 nm, and the research on the wavelength band less than 1000 nm is relatively less, and the existing research has relatively large transmission loss in the wavelength band less than 1000 nm.

[0004] VCSEL (Vertical-Cavity Surface-Emitting Laser) has low production cost and is the main light source for short-distance transmission in modern data centers and supercomputing systems, and its wavelength is 850 nm. The transmission loss of 850 nm wavelength light in a solid-core optical fiber is very large, because Rayleigh scattering is very large at 850 nm. Rayleigh scattering is mainly caused by the distribution of silicon atoms and oxygen atoms. The solid-core optical fiber is limited by the distribution of silicon atoms and oxygen atoms in the glass material, and has requirements for the transmission wavelength, and cannot meet the low-loss transmission of 850 nm wavelength light.

[0005] The existing research on hollow-core optical fibers has relatively large transmission loss in the wavelength band less than 1000 nm, so it is also difficult to achieve low-loss transmission of 850 nm wavelength light, and is not suitable for VCSEL communication.

[0006] How to reduce the transmission loss of the hollow-core optical fiber and make it suitable for VCSEL communication is a technical problem that needs to be solved in the field. SUMMARY

[0007] The present application provides a composite hollow-core optical fiber and application thereof, which solves the problem of large transmission loss of the hollow-core optical fiber in the prior art and the difficulty in applying it to VCSEL communication.

[0008] The present application provides a composite hollow-core optical fiber, comprising: from the outside to the inside, an outer cladding, an inner cladding and a core;

[0009] The inner cladding is composed of an outer layer kagome lattice structure, an inner layer kagome lattice structure and a nested tube structure;

[0010] The outer layer kagome lattice structure is composed of a plurality of regular hexagonal air holes and a plurality of regular triangular air holes;

[0011] The inner layer kagome lattice structure is composed of a plurality of air holes with negative curvature and a plurality of regular triangular air holes;

[0012] The nested tube structure includes a plurality of unit nested tube structures, each of which is composed of a first tubular structure and a second tubular structure, the radius of the first tubular structure is greater than the radius of the second tubular structure, and the inner side of the first tubular structure is tangent to the outer side of the second tubular structure.

[0013] Preferably, the inner layer kagome lattice structure is composed of a plurality of first negative curvature structures, a plurality of second negative curvature structures and a plurality of regular triangular air holes; the first negative curvature structure and the second negative curvature structure are both evolved from a regular hexagonal air hole, the first negative curvature structure is an air hole in which two sides of a regular hexagon are evolved into a circular arc, and the second negative curvature structure is an air hole in which three sides of a regular hexagon are evolved into a circular arc.

[0014] Preferably, the outer contour of the outer cladding is circular, and the inner contour of the outer cladding is a regular hexagon;

[0015] The outer layer kagome lattice structure forms a regular hexagon, and in the outer layer kagome lattice structure, regular hexagonal air holes and regular triangular air holes are arranged in sequence, and two regular triangular air holes are arranged between two adjacent regular hexagonal air holes;

[0016] In the inner layer kagome lattice structure, a plurality of first negative curvature structures are arranged at the corner positions of the regular hexagons formed by the outer layer kagome lattice structure, a plurality of second negative curvature structures are arranged between two first negative curvature structures, and regular triangular air holes are arranged in the remaining area of the inner layer kagome lattice structure.

[0017] Preferably, the nested tube structure is supported and connected by the inner layer kagome lattice structure, and the outer side of the first tubular structure is tangent to the outer side of the second negative curvature structure.

[0018] Preferably, the nested tube structure is composed of six unit nested tube structures that do not contact each other, and the centers of the first tubular structure and the second tubular structure are both on the diagonal of the regular hexagon as the inner contour of the outer cladding.

[0019] Preferably, the filling medium of the outer cladding is silica glass; the inner cladding is made of silica glass; and the medium of the core is air.

[0020] Preferably, all the air holes in the outer layer kagome lattice structure, the inner layer kagome lattice structure, and the first tubular structure and the second tubular structure have the same wall thickness, and the wall thickness is in the range of 0.55 μm to 0.65 μm.

[0021] The length of the side of the regular hexagonal air hole in the outer layer kagome lattice structure is in the range of 7.7 μm to 8.7 μm.

[0022] The distance between two adjacent unit nested tube structures is in the range of 2.05 μm to 3.05 μm.

[0023] The radius of the first tubular structure is in the range of 11.95 μm to 12.95 μm, and the maximum distance between the inner diameter of the first tubular structure and the outer diameter of the second tubular structure is in the range of 2.94 μm to 3.84 μm.

[0024] Preferably, the diameter of the circumscribed circle of the outer cladding is in the range of 170 μm to 250 μm.

[0025] The length of the side of the regular hexagonal air hole in the outer cladding is in the range of 76.81 μm to 77.81 μm.

[0026] The radius of the core is in the range of 14.5 μm to 15.5 μm.

[0027] Preferably, the loss of the composite hollow core fiber is less than 0.4 dB / km when the wavelength range of the transmitted light is 800 nm to 890 nm.

[0028] In another aspect, the application provides a use of the composite hollow core fiber as described above, which is applied to VCSEL communication.

[0029] One or more technical solutions provided in the application have at least the following technical effects or advantages:

[0030] The composite hollow-core optical fiber provided by this invention comprises an outer cladding, an inner cladding, and a core, from the outside in. The inner cladding consists of an outer kagome lattice structure, an inner kagome lattice structure, and a nested tube structure. The outer kagome lattice structure comprises multiple hexagonal air holes and multiple equilateral triangular air holes. The inner kagome lattice structure comprises multiple air holes with negative curvature and multiple equilateral triangular air holes. The nested tube structure comprises multiple unit nested tube structures. Each unit nested tube structure consists of a first tubular structure and a second tubular structure. The radius of the first tubular structure is larger than the radius of the second tubular structure, and the inner side of the first tubular structure is tangent to the outer side of the second tubular structure. This invention utilizes a combination of kagome lattices and nested tubes to design hollow-core optical fibers. The kagome lattice can perform secondary confinement of the light precession leaking from the nested tubes, thereby reducing transmission loss. The outer kagome lattice consists of hexagonal and triangular air holes of a certain thickness, while the inner kagome lattice consists of specially shaped air holes and triangular air holes. These specially shaped air holes evolve from hexagonal air holes, with some edges of the hexagons becoming arcs, resulting in a negative curvature structure. This design further confines the transmitted light, thereby further reducing loss. The kagome lattice in this invention is generally composed of hexagons (including evolved hexagonal structures) and triangular shapes, ensuring structural stability and ease of fabrication. This invention also optimizes the design for specific transmission wavelengths below 1000nm. The composite hollow-core fiber provided by this invention exhibits a loss of less than 0.4dB / km at 800nm ​​to 890nm and a loss of 0.3dB / km at a transmission wavelength of 850nm, making it particularly suitable for VCSEL communication. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the cross-sectional structure of a composite hollow optical fiber provided in Embodiment 1 of the present invention;

[0032] Figure 2 This is a partially enlarged structural schematic diagram of the cross-section of a composite hollow optical fiber provided in Embodiment 1 of the present invention;

[0033] Figure 3 This is a distribution diagram of electric field modes in a composite hollow optical fiber provided in Embodiment 1 of the present invention;

[0034] Figure 4 This is a graph showing the variation of various losses of a composite hollow optical fiber with transmission wavelength, provided in Embodiment 1 of the present invention.

[0035] Figure 5 This is a graph showing the variation of total loss of a composite hollow optical fiber with the bending radius of the fiber, as provided in Embodiment 1 of the present invention.

[0036] Figure 6 A graph of the effective refractive index of a composite hollow core fiber provided for embodiment 1 as a function of wavelength. DETAILED DESCRIPTION

[0037] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings of the specification and specific embodiments.

[0038] Embodiment 1:

[0039] Embodiment 1 provides a composite hollow core fiber, referring to Figure 1 , comprising: from the outside to the inside, an outer cladding 8, an inner cladding and a core 5; the inner cladding is composed of an outer layer kagome lattice structure, an inner layer kagome lattice structure and a nested tube structure; the outer layer kagome lattice structure is composed of a plurality of regular hexagonal air holes 1 and a plurality of regular triangular air holes 6; the inner layer kagome lattice structure is composed of a plurality of air holes with negative curvature and a plurality of regular triangular air holes 6; the nested tube structure includes a plurality of unit nested tube structures, each of the unit nested tube structures is composed of a first tubular structure 4 and a second tubular structure 3, the radius of the first tubular structure 4 is greater than the radius of the second tubular structure 3, and the inner side of the first tubular structure 4 is tangent to the outer side of the second tubular structure 3.

[0040] The present application adopts the structure of combining kagome lattice and nested tube, and can effectively reduce the loss based on the anti-resonance principle. The inner cladding includes two layers of kagome lattice and one layer of nested tube structure, the kagome lattice as the outer layer is composed of regular hexagonal air holes 1 with a certain thickness and regular triangular air holes 6, and the kagome lattice as the inner layer is composed of special-shaped air holes and regular triangular air holes 6, the special-shaped air holes are evolved from the regular hexagonal air holes 1, and part of the edges of the regular hexagonal air holes 1 are evolved into circular arc shape, i.e. have negative curvature structure, this design can further limit the transmission light, thereby further reducing the loss.

[0041] The design of the inner layer kagome lattice structure in the present application can also be understood as follows: first, the inner layer kagome lattice structure is designed to be composed of regular hexagonal air holes 1 with a certain thickness and regular triangular air holes 6, and then part of the edges of the regular hexagonal air holes 1 close to the core 5 are designed to be circular arc shape, to obtain air holes with negative curvature.

[0042] The inner layer kagome lattice structure is composed of a plurality of first negative curvature structures 2, a plurality of second negative curvature structures 7, and a plurality of positive triangular air holes 6; the first negative curvature structure 2 and the second negative curvature structure 7 are both evolved from a positive hexagonal air hole 1, the first negative curvature structure 2 is an air hole in which two edges of the positive hexagonal air hole 1 are evolved into circular arcs, and the second negative curvature structure 7 is an air hole in which three edges of the positive hexagonal air hole 1 are evolved into circular arcs. That is, the inner layer kagome lattice structure includes two kinds of negative curvature structures, one of which is a structure in which three edges of a positive hexagon are evolved into circular arcs, and the other of which is a structure in which two edges of a positive hexagon are evolved into circular arcs.

[0043] Referring to Figure 1 、 Figure 2 , the air hole with negative curvature is evolved from a positive hexagonal air hole 1. Specifically, taking the geometric center of the positive hexagonal air hole 1 as the circle point, taking the edge length of the positive hexagonal air hole 1 as the radius, and taking one of the vertices of the positive hexagonal air hole 1 as the starting point, after rotating an angle (for example, 120°), two edges of the positive hexagon are evolved into circular arcs to form the first negative curvature structure 2. Taking the geometric center of the positive hexagonal air hole 1 as the circle point, taking the edge length of the positive hexagonal air hole 1 as the radius, and taking one of the vertices of the positive hexagonal air hole 1 as the starting point, after rotating an angle α (for example, 180°), three edges of the positive hexagon are evolved into circular arcs to form the second negative curvature structure 7.

[0044] The outer contour of the outer cladding layer 8 is circular, and the inner contour of the outer cladding layer 8 is hexagonal. That is, the outer cladding layer 8 is a columnar structure with a circular outer contour and a hexagonal inner contour, and it wraps the inner cladding layer and the core 5.

[0045] The outer layer kagome lattice structure forms a hexagon, and in the outer layer kagome lattice structure, the positive hexagonal air holes 1 and the positive triangular air holes 6 are arranged in sequence, and two positive triangular air holes 6 are arranged between two adjacent positive hexagonal air holes 1.

[0046] In the inner layer kagome lattice structure, a plurality of the first negative curvature structures 2 are arranged at the apex positions of the hexagons formed by the outer layer kagome lattice structure, a plurality of the second negative curvature structures 7 are arranged between two first negative curvature structures 2, and the remaining area of the inner layer kagome lattice structure is arranged with positive triangular air holes 6.

[0047] That is, the inner cladding layer is a kagome lattice composed of regular hexagonal air holes 1, regular triangular air holes 6, the first negative curvature structure 2, and the second negative curvature structure 7 with a certain thickness, and a nested tube structure composed of the first tubular structure 4 and the second tubular structure 3 with a certain thickness. Taking the inner layer kagome lattice structure as an example, the kagome lattice is composed of two layers, the outer layer is composed of regular hexagonal air holes 1 and regular triangular air holes 6 arranged in turn, and two regular triangular air holes 6 are arranged in the gap (which can be understood as the upper and lower gap regions) between two adjacent regular hexagonal air holes 1; the inner layer is composed of regular triangular air holes 6, the first negative curvature structure 2, and the second negative curvature structure 7, six first negative curvature structures 2 are arranged at the positions of the six top corners of the large regular hexagon formed by the outer layer, and the second negative curvature structure 7 is arranged in the middle of two first negative curvature structures 2, and the rest is a regular triangular air hole 6, one regular triangular air hole 6 is arranged in the gap between two adjacent negative curvature structures away from the core 5 (including the gap between the first negative curvature structure 2 and the second negative curvature structure 7, and the gap between two second negative curvature structures 7), which can be understood as that one side of the regular triangular air hole 6 in the inner layer kagome lattice structure coincides with the side length of the air hole in the outer layer kagome lattice structure, and no regular triangular air hole 6 is arranged in the gap between two adjacent negative curvature structures close to the core 5.

[0048] The second tubular structure 3 is nested in the first tubular structure 4, and the second tubular structure 3 is close to the outer cladding layer 8, and the first tubular structure 4 and the second tubular structure 3 are tangent. For example, the nested tube structure is composed of six mutually non-contacting unit nested tube structures, and the centers of the first tubular structure 4 and the second tubular structure 3 are on the diagonal of the regular hexagon as the inner contour of the outer cladding layer 8. The nested tube structure is supported and connected by the inner layer kagome lattice structure, and the outer side of the first tubular structure 4 is tangent to the outer side of the second negative curvature structure 7.

[0049] The outer cladding layer 8 is filled with silica glass, that is, the outer cladding layer 8 is a silica glass matrix. The inner cladding layer is made of silica glass, and the refractive index n of the silica glass is 1.4565 to 1.4504.

[0050] The core 5 is a circular region composed of the outer sides of a plurality of first tubular structures 4, and the core 5 is located in the center region of the composite hollow optical fiber. The medium of the core 5 is air, which is used for transmitting light, and the refractive index of air is 1.

[0051] The parameter design of the composite hollow core optical fiber provided by the application is described below.

[0052] Referring to Figure 1 All air holes (including the regular hexagonal air hole 1, the regular triangular air hole 6, the first negative curvature structure 2, and the second negative curvature structure 7) in the outer layer kagome lattice structure and the inner layer kagome lattice structure, and the first tubular structure 4 and the second tubular structure 3 have the same wall thickness t, and the wall thickness t ranges from 0.55 μm to 0.65 μm. That is, the thickness of all silica glass walls in the composite hollow core optical fiber is consistent.

[0053] Specifically, the wall thickness t is calculated by the following formula:

[0054]

[0055] In the formula, λ is the center wavelength of the transmitted light, n is the refractive index of the silica glass, and m is a positive integer.

[0056] In the application, the value of m is 2, the value of λ ranges from 800 nm to 890 nm, and the range of t is 0.55 μm to 0.65 μm.

[0057] The length of the side of the regular hexagonal air hole 1 in the outer layer kagome lattice structure ranges from 7.7 μm to 8.7 μm. Correspondingly, the length of the side of the regular triangular air hole 6 in the outer layer kagome lattice structure and the length of the side of the regular triangular air hole 6 in the inner layer kagome lattice structure are both h.

[0058] The distance g between two adjacent unit nested tube structures ranges from 2.05 μm to 3.05 μm.

[0059] The radius b of the first tubular structure 4 ranges from 11.95 μm to 12.95 μm, and the maximum distance d between the inner diameter of the first tubular structure 4 and the outer diameter of the second tubular structure 3 ranges from 2.94 μm to 3.84 μm.

[0060] The diameter of the circumscribed circle of the outer cladding 8 is 170 μm to 250 μm.

[0061] The length of the side 2c of the regular hexagon as the inner profile of the outer cladding 8 ranges from 76.81 μm to 77.81 μm. It can also be understood that the kagome lattice forms a large regular hexagon, that is, the inner cladding is a regular hexagon with a side length of 76.81 μm to 77.81 μm.

[0062] The radius a of the core 5 ranges from 14.5 μm to 15.5 μm.

[0063] The composite hollow core optical fiber provided by the application has good tuning characteristics, and further optimization of the structural parameters of the optical fiber can further reduce the loss.

[0064] The performance of the composite hollow core optical fiber provided by the application is described below.

[0065] The distribution of the electric field mode in the composite hollow core optical fiber provided by the application is shown in the two-dimensional and three-dimensional diagrams of the distribution of the electric field mode in the core, and it can be seen that the composite hollow core optical fiber can well confine light in the core. Figure 3

[0066] The total loss (the sum of the confinement loss and the surface scattering loss), the confinement loss, and the surface scattering loss of the composite hollow core optical fiber provided by the application vary with the transmission wavelength, as shown in the graph Figure 4 It can be seen that the composite hollow core optical fiber has very low loss. Specifically, when the wavelength range of the transmitted light is 800nm to 890nm, the total loss of the composite hollow core optical fiber is less than 0.4dB / km, and the lowest total loss of 0.26dB / km is achieved at 860nm, and when the transmission wavelength is 850nm, the total loss is as low as 0.3dB / km. That is, the composite hollow core optical fiber provided by the application can realize low-loss transmission of light at a wavelength of 850nm.

[0067] The total loss of the composite hollow core optical fiber provided by the application varies with the fiber bending radius, as shown in the graph Figure 5 When the bending radius is greater than 9cm, the transmission loss change rate is basically stable, and it can be seen that the composite hollow core optical fiber has good bending resistance.

[0068] The effective refractive index of the composite hollow core optical fiber provided by the application varies with the wavelength, as shown in the graph Figure 6 It can be seen that the effective transmission of the fundamental mode in the composite hollow core optical fiber decreases as the transmission wavelength increases, and the effective refractive index of the light in the core is close to the refractive index of air, which is 1.

[0069] It can be seen that the composite hollow core optical fiber provided by Example 1 has low transmission loss and good bending resistance in the wavelength range of 800nm to 890nm, and can realize low-loss transmission.

[0070] In addition, since the composite hollow core optical fiber provided by Example 1 is a kind of hollow core optical fiber, the principle of anti-resonance is used to confine light in the core, so that the direct contact of light with the optical fiber material can be greatly reduced, and the optical fiber is not easy to be burned out, that is, the damage threshold is high.

[0071] ​In summary, the composite hollow core fiber provided by the embodiment 1 has low loss transmission, wide spectral bandwidth (800nm to 890nm), small bending loss, high damage threshold and the like.

[0072] Embodiment 2:

[0073] The embodiment 2 provides an application of the composite hollow core fiber as described in the embodiment 1, and the composite hollow core fiber is applied to VCSEL communication.

[0074] Compared with the solid core fiber, the core of the composite hollow core fiber provided by the present application is air, which can avoid the interaction of signal light with silicon atoms and oxygen atoms. And the present application is aimed at a wavelength band less than 1000nm, especially a specific transmission wavelength of 850nm. By specially designing the inner cladding of the hollow core fiber and optimizing the fiber parameters, the loss of the fiber is reduced.

[0075] Based on the description of the embodiment 1, it can be known that the composite hollow core fiber provided by the present application has a loss of 0.3dB / km at a transmission wavelength of 850nm.

[0076] In summary, the composite hollow core fiber provided by the present application can be combined with the VCSEL light source to realize low loss transmission. The present application can realize low loss transmission of light with a wavelength of 850nm, which has very important significance.

[0077] Finally, it should be explained that the above specific embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A composite hollow core optical fiber, characterized by, The composite hollow core fiber comprises: an outer cladding, an inner cladding and a core from outside to inside; the inner cladding is composed of an outer layer kagome lattice structure, an inner layer kagome lattice structure and a nested tube structure; the outer layer kagome lattice structure is composed of a plurality of regular hexagonal air holes and a plurality of regular triangular air holes; the inner layer kagome lattice structure is composed of a plurality of air holes with negative curvature and a plurality of regular triangular air holes; the nested tube structure comprises a plurality of unit nested tube structures, each of which is composed of a first tubular structure and a second tubular structure, the radius of the first tubular structure is greater than the radius of the second tubular structure, and the inner side of the first tubular structure is tangent to the outer side of the second tubular structure; wherein the inner layer kagome lattice structure is composed of a plurality of first negative curvature structures, a plurality of second negative curvature structures and a plurality of regular triangular air holes; the first negative curvature structure and the second negative curvature structure are both evolved from a regular hexagonal air hole, and the side length of the regular hexagonal air hole as the evolution basis is equal to the side length of the regular hexagonal air hole in the outer layer kagome lattice structure; taking the geometric center of the regular hexagonal air hole as the circle point, taking the side length of the regular hexagonal air hole as the radius, and taking one of the vertices of the regular hexagonal air hole as the starting point, after rotating the angle, two sides of the regular hexagonal air hole are evolved into circular arcs to form the first negative curvature structure; taking the geometric center of the regular hexagonal air hole as the circle point, taking the side length of the regular hexagonal air hole as the radius, and taking one of the vertices of the regular hexagonal air hole as the starting point, after rotating the angle, three sides of the regular hexagonal air hole are evolved into circular arcs to form the second negative curvature structure; the outer layer kagome lattice structure forms a regular hexagon; in the inner layer kagome lattice structure, a plurality of the first negative curvature structures are arranged at the apex positions of the regular hexagon formed by the outer layer kagome lattice structure, a plurality of the second negative curvature structures are arranged between two of the first negative curvature structures, and regular triangular air holes are arranged in the remaining area of the inner layer kagome lattice structure; the application range of the composite hollow core fiber is less than 1000 nm; when the wavelength range of the transmitted light is 800 nm to 890 nm, the loss of the composite hollow core fiber is less than 0.4 dB / km.

2. The composite hollow core optical fiber of claim 1, wherein, the outer side profile of the outer cladding is circular, and the inner side profile of the outer cladding is a regular hexagon; in the outer layer kagome lattice structure, the regular hexagonal air holes and the regular triangular air holes are arranged in sequence, and two regular triangular air holes are arranged between two adjacent regular hexagonal air holes.

3. The composite hollow core optical fiber of claim 1, wherein, the nested tube structure is supported and connected by the inner layer kagome lattice structure, and the outer side of the first tubular structure is tangent to the outer side of the second negative curvature structure.

4. The composite hollow core optical fiber of claim 2, wherein, the nested tube structure is composed of six unit nested tube structures that do not contact each other, and the centers of the first tubular structure and the second tubular structure are on the diagonal of the regular hexagon as the inner side profile of the outer cladding.

5. The composite hollow core optical fiber of claim 1, wherein, The filling medium of the outer cladding is silica glass; the inner cladding is prepared by using silica glass; and the medium of the core is air.

6. The composite hollow core optical fiber of claim 1, wherein, All the air holes in the outer layer kagome lattice structure, the inner layer kagome lattice structure, and the first tubular structure and the second tubular structure have the same wall thickness, and the wall thickness ranges from 0.55 μm to 0.65 μm; The length of the side of the regular hexagonal air hole in the outer layer kagome lattice structure ranges from 7.7 μm to 8.7 μm; The distance between two adjacent unit nested tube structures ranges from 2.05 μm to 3.05 μm; The radius of the first tubular structure ranges from 11.95 μm to 12.95 μm, and the maximum distance between the inner diameter of the first tubular structure and the outer diameter of the second tubular structure ranges from 2.94 μm to 3.84 μm.

7. The composite hollow core optical fiber of claim 2, wherein, The diameter of the circumscribed circle of the outer cladding ranges from 170 μm to 250 μm; The length of the side of the regular hexagon as the inner profile of the outer cladding ranges from 76.81 μm to 77.81 μm; The radius of the core ranges from 14.5 μm to 15.5 μm.

8. Use of a composite hollow optical fiber as claimed in any one of claims 1 to 7, characterized in that, The composite hollow core fiber is applied to VCSEL communication.

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