Topological photonic crystal fiber based on double vortex lines

Abstract

The invention discloses a topological photonic crystal fiber. The topological photonic crystal fiber comprises a plurality of primitive cells periodically arrayed in the Z direction; each primitive cell is of a multi-layer honeycomb lattice structure and is provided with an upper layer assembly, a first middle layer assembly, a lower layer assembly and a second middle layer assembly which are stacked from top to bottom. The upper-layer assembly and the lower-layer assembly respectively comprise a plurality of aperiodic upper-layer and lower-layer structure units; the second intermediate layer assembly and the first intermediate layer assembly have the same structure and each comprise a plurality of periodic intermediate layer structure units; the primitive cells are further configured to form double vortex centers in an X-Y plane, and the vortex centers are connected in the Z direction to form double vortex lines. According to the invention, a central state with spin attribute and propagation track binding can be realized in a complete band gap of the topological photonic crystal fiber, and low-loss and robust transmission of electromagnetic waves along the center of the device can be realized without applying an external magnetic field.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic wave transmission, and particularly relates to a topological photonic crystal optical fiber based on a double-vortex line. BACKGROUND

[0002] A photonic crystal is an artificial optical structure with a periodic refractive index distribution. When the photonic wavelength is comparable to the lattice constant, the periodic distribution can form a band structure for photons, similar to an electronic band structure. At present, based on the passband or bandgap of the photonic crystal, various new phenomena such as the super-prism effect and negative refraction have been realized, and various new functional devices such as the super-high quality factor cavity and the photonic crystal optical fiber have also been realized.

[0003] As one of the important applications of photonic crystals, the photonic crystal optical fiber is different from the traditional optical fiber (composed of a high refractive index core and a cladding) and guides light by using the defect mode in the cladding bandgap. The cladding cross-section of the photonic crystal optical fiber is designed as a two-dimensional photonic crystal structure. This light guiding mechanism can realize low propagation loss and support wideband single-mode transmission. However, due to process factors, it is still challenging to further reduce the bending loss and backscattering loss in the transmission process.

[0004] The topologically protected boundary state in topological physics can realize defect-immune directional transmission, which provides a potential way to solve the limitations of the above-mentioned photonic crystal optical fiber. It has been found that the topological properties of photonic band structures are related to their symmetry. Using photonic crystal and metamaterial platforms, various important topological physical phenomena have been observed, thereby forming a new research field-topological photonics. Typical examples include photonic quantum Hall effect, topological insulator, topological semimetal, topological laser, and high-order topological structure.

[0005] As a potential application scheme for future communication technology, the topological photonic crystal optical fiber can simultaneously realize low propagation loss, mode adjustability, and backscattering immune transmission characteristics. However, due to the body-edge correspondence principle, topological behavior usually exists in lower-dimensional boundaries, such as one-dimensional hinge states and two-dimensional surface states in three-dimensional structures. This characteristic indicates that ideal robust fiber transmission may need to be associated with higher-dimensional systems. Although acoustic models have confirmed that scalar acoustic waves can propagate in defects, it has not yet been realized to achieve topological photonic crystal optical fiber transmission in the vector electromagnetic wave system, which is of great interest, due to the technical challenges in simultaneously generating complete bandgaps in three-dimensional photonic crystals and compatible photonic spin symmetry.

[0006] Therefore, there are still technical challenges in realizing optical devices that combine the principles of topological physics to enable defect-immune transmission of electromagnetic waves in the fiber core. SUMMARY

[0007] Therefore, the application provides a photonic crystal fiber device based on double-vortex lines, which can realize a center state with spin attribute and propagation orbit binding in a complete band gap of a topological photonic crystal fiber and has a defect immune transmission capability.

[0008] The technical scheme of the application is as follows:

[0009] The application discloses a topological photonic crystal fiber, which comprises a plurality of unit cells arranged periodically along a Z direction; the unit cell is a multilayer honeycomb lattice structure, and has an upper layer assembly, a first intermediate layer assembly, a lower layer assembly and a second intermediate layer assembly arranged in a top-down manner, wherein the upper layer assembly and the lower layer assembly have a pi phase difference delay; the upper layer assembly and the lower layer assembly respectively comprise a plurality of non-periodic upper layer structure units and lower layer structure units; the first intermediate layer assembly comprises a plurality of periodic intermediate layer structure units, and the second intermediate layer assembly has the same structure as the first intermediate layer assembly; the unit cell is further configured to form double-vortex centers in an X-Y plane by introducing a rotation parameter in the upper layer structure units and the lower layer structure units and the pi phase difference delay between the upper layer assembly and the lower layer assembly, and the vortex centers are connected in the Z direction to form double-vortex lines.

[0010] As an optional solution, the upper layer structure unit comprises a structure body and metal pattern layers arranged on upper and lower surfaces of the structure body; the metal pattern layers on the upper and lower surfaces satisfy C 6Z rotational symmetry and are mirror symmetric about the Y-axis direction; a projection of the structure body in the X-Y plane is a regular hexagon with a side length of a, and a first through hole penetrating in the Z direction is arranged at the center of the regular hexagon, the first through hole is connected with the metal pattern layers, and a hole wall of the first through hole has a metal plating layer with the same material as the metal pattern layers; the lower layer structure unit and the upper layer structure unit have the same structure, and the only difference is that the hole diameters of the first through holes are different; the hole diameter r u of the upper layer structure unit is a function of (r, θ), and the hole diameter r l of the lower layer structure unit is a function of (r, θ+pi), wherein r is the position of the center point of the upper layer structure unit, θ is an included angle between a connecting line of the center point of the upper layer structure unit and the center point of the upper layer assembly and the X-axis, 0 < θ < 2pi, and the θ is the rotation parameter.

[0011] As an optional solution, the hole diameter function relationship of the upper layer structure unit is:

[0012] r u = r0+ δrcos(2K·r+ θ), (1)

[0013] The hole diameter function relationship of the lower layer structure unit is:

[0014] r l= r0+ δr cos(2K·r+ θ+ π), (2)

[0015] In the formula, r0 and δr are constants related to the aperture, wherein r0 is a preset aperture reference value, and δr determines the range of aperture variation; K is a Brillouin zone constant related to the size of the structural unit,

[0016] As an alternative, the projection of the metal pattern layer on the X-Y plane is configured as a windmill pattern formed by cutting a composite pattern at the vertices of the regular hexagon; the composite pattern is composed of three rectangles whose center points of the short sides coincide at the vertices of the regular hexagon, adjacent rectangles coincide at the opposite vertices with a rotation of 120°, and adjacent composite patterns at the vertices coincide with a rotation of 60° relative to the center of the regular hexagon.

[0017] As an alternative, the structural body is further provided with a second through hole penetrating in the Z direction at each vertex of the regular hexagon.

[0018] As an alternative, the projection of the intermediate layer structural unit on the X-Y plane is a regular hexagon with a side length of a, and a third through hole penetrating in the Z direction is provided at the center and each vertex of the regular hexagon; the diameter of the third through hole is d, which is less than or equal to the short side length W of the rectangle in the composite pattern; the height of the intermediate layer structural unit is less than the height of the first structural unit.

[0019] As an alternative, the dielectric constant of the structural body is 2.5-3, and Teflon material or perfluoroalkoxy resin is selected; the material of the metal pattern layer is any one of copper foil, gold, silver, iron, and tin; the dielectric constant of the intermediate layer structural unit is close to air, and any one of XPMI, PMI, and PU foam is selected.

[0020] As an alternative, the number of periods of the primitive cell in the Z direction periodic array is greater than or equal to 10; the diameter of the primitive cell is greater than 15 cm.

[0021] As an alternative, the size of the topological photonic crystal fiber device is overall scaled up or scaled down, and the defect immune transmission property remains unchanged.

[0022] Further, the second aspect of the present application discloses an optical device comprising the topological photonic crystal fiber of the first aspect of the present application and any one of the alternative schemes thereof.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The topological photonic crystal fiber provided by the application realizes a one-dimensional rotation parameter in three-dimensional space, that is, a transmission mechanism of guiding electromagnetic waves based on double-vortex lines is realized in a high-dimensional system.

[0025] (2) The topological photonic crystal fiber provided by the application realizes a pair of center states with spin properties in a complete band gap, that is, robust electromagnetic wave transmission along the positive direction of the Z axis (corresponding to the "spin" upward state) and along the negative direction of the Z axis (corresponding to the "spin" downward state) can be realized.

[0026] (3) The topological photonic crystal fiber provided by the application is different from existing magneto-optical transport materials, and does not need to apply an external magnetic field, so that the device is more convenient in experimental implementation and operation.

[0027] (4) The topological photonic crystal fiber provided by the application can be uniformly scaled (enlarged or reduced), and the robust electromagnetic wave transmission characteristics are maintained during the process, and only the working frequency band is changed. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a photo of the topological photonic crystal fiber, wherein: (a) the overall picture of the device; (b) the top view of each layer component in one unit cell.

[0029] Figure 2 It is a schematic diagram of the structural unit of the unit cell, wherein the left side is the overall structural unit; and the right side is the top view of the structural unit of the upper layer component, the middle layer component and the lower layer component from top to bottom.

[0030] Figure 3 It is a schematic diagram of the center state, wherein: (a) the projected band diagram along the Z direction, wherein the deep purple points at the top and bottom of the diagram represent edge states distributed at the edge of the device, and the red and blue connecting lines in the middle of the diagram represent the center states transmitted along the positive direction of the Z axis (spin upward) and the negative direction of the Z axis (spin downward) respectively; (b) the field distribution diagrams of the center states transmitted along the positive direction of the Z axis and the negative direction of the Z axis at k z =0.1(π / h) are shown on the left and right respectively, and are marked as i|u>+|l> and |u>+i|l> respectively, and the field distribution multiplied by i represents the imaginary part of the field distribution. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be clearly and completely described below in conjunction with specific embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present application.

[0032] In the description of the present application, if terms indicating orientation or positional relationship such as "upper", "lower", "inner", "outer", "top", "bottom" and the like appear, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the present application in that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, but can include other elements not clearly listed or inherent to the products or devices.

[0033] The present application provides a kind of topological photonic crystal fiber, one-dimensional double vortex line is combined into three-dimensional double layer topological photonic crystal, can be realized in complete band gap with the spin attribute and propagation orbit binding center state.The fiber is modulated by introducing rotation parameter in three-dimensional space (specifically represented as the modulation of the radius of metal hole in the upper sublattice and the lower sublattice) to double-layer sublattice structure with π phase delay, to realize double-vortex center;Then the unit cell is arrayed along the Z direction, and a topological photonic crystal fiber structure based on double-vortex line is formed.

[0034] It is worth mentioning that the present application does not need to introduce external magnetic field, by introducing an additional parameter dimension in three-dimensional geometry to form vortex, so that under microwave conditions, a pair of spin center states can be observed along the center of the topological photonic crystal fiber robust transmission, that is, the center state with spin attribute is excited and maintained in the complete band gap of the photonic crystal. The center state can guide electromagnetic wave to transmit along the center axis of the fiber with low loss, and has anti-interference ability to structural defects. In addition, the fiber structure design is easy to prepare, and the transmission performance is stable and reliable. The device can be scaled (enlarged or reduced) as a whole, while maintaining its robust transmission characteristics, the working frequency band is adjusted accordingly, so as to meet the transmission needs of electromagnetic waves of different frequency bands.

[0035] In conjunction with Figure 1 The embodiment of the present application provides a kind of topological photonic crystal fiber based on double-vortex line (hereinafter referred to as "the fiber"), which is a unit cell periodic array in Z direction, and the unit cell is a multi-layer honeycomb lattice, which is specifically composed of a plurality of structure units arranged on X-Y plane.

[0036] As Figure 1As shown in (a), since rotational parameters are introduced in the upper and lower components to form vortex centers, and the upper and lower rotational parameters have a phase difference of π, there are double vortex centers, forming double vortex lines in the Z direction.

[0037] like Figure 1 As shown in (b), the unit cell includes, from top to bottom, an upper component 1, an intermediate component 2, a lower component 3 and an intermediate component 4 stacked sequentially. The intermediate component 2 and the intermediate component 4 have the same structure, and there is a π phase difference delay between the upper component and the lower component.

[0038] The upper component 1 and lower component 3 each include multiple aperiodic upper and lower structural units, respectively, while the middle component 2 includes multiple periodically arranged middle structural units. Therefore, each component in the unit cell, viewed in the XY plane, can be considered as a multi-layered honeycomb lattice composed of multiple structural unit components.

[0039] like Figure 2 The structural unit components shown are, from top to bottom, an upper structural unit, a middle structural unit, a lower structural unit, and another middle structural unit. The structural unit is projected onto the XY plane as a regular hexagon with side length *a* and a height of *h* in the Z direction. It should be noted that although the hexagonal corners of the regular hexagonal structure in this invention are perforated, it is still referred to as a regular hexagon overall.

[0040] The upper structural unit, projected onto the XY plane, is a regular hexagon with holes drilled at its center and hexagonal corners, and has a height of t. Specifically, the upper structural unit includes a regular hexagonal structural body 11 and copper foil layers 12 formed on the upper and lower surfaces of the structural body. The structural body 11 has a through hole at its center, which can be called a central hole 13, with a radius of r. u At each of the six vertices of the structural body 11, a corner hole 14 with a diameter of d is cut out with the corner point as the center, mainly for the convenience of experimental measurement. The wall of the central hole 13 is plated with copper, and the rotation parameter is introduced to form the vortex center by adjusting the size of the central hole. The copper foil 12 on the upper and lower surfaces can be regarded as a windmill pattern formed by removing a composite graphic from each of the six corner points of a regular hexagon. The composite graphic is composed of a rectangle (length l, width w) whose center points of the three short sides coincide at the corner points of the hexagon. Adjacent rectangles coincide with each other by rotating 120° relative to their corner points, and adjacent composite graphics at the corner points coincide with each other by rotating 60° relative to the center point of the regular hexagon.

[0041] It should be noted that the copper foil layers 12 located on the upper and lower surfaces of the upper structural unit 1 need to satisfy C 6Z Its rotational symmetry, and mirror symmetry about the Y-axis, serves to break the inversion symmetry, forming a structure that only supports E. ZThe polarized planar waveguide structure. The copper foil layer 12 is connected with the hole wall of the central hole 13 and has the same material, so that the electromagnetic wave is not conducted at the material.

[0042] The radius r of the central hole 13 in the upper structure unit u The central point position r of the upper structure unit (i.e. the displacement of the central point of the upper assembly to the central point of the hexagon where the upper structure unit is located, referred to as "displacement vector r") and the angle θ between the line connecting the central point of the upper structure unit to the central point of the upper assembly and the X-axis (referred to as "angle θ" or "rotation parameter θ") are related. It can be understood that the central point of a structure in the present application refers to the projection point of the central point in the X-Y plane, so that the relative position relationship of all central points is discussed in the same plane.

[0043] As Figure 1 (b) The red arrow shown in indicates a function of (r, θ), and the specific function relationship is:

[0044] r u = r0+ δrcos(2K·r+ θ), (1)

[0045] In the formula, r0 and δr are constants related to the hole diameter, wherein r0 is a preset hole diameter reference value, and δr determines the range of hole diameter change, i.e. r0- δr≤r u ≤r0+ δr; K is a Brillouin zone constant related to the size of the structure unit, θ is the angle between r and the X-axis direction, and the value range is 0 to 2π; a is the side length of the hexagon.

[0046] For the lower structure unit, the plated copper hole radius r l is a function of (r, θ+π), and the specific relationship is:

[0047] r l = r0+ δrcos(2K·r+ θ+π), (2);

[0048] It can be understood that the difference between the upper structure unit and the lower structure unit in the same structure unit is only the size of the plated copper central hole, which is specifically manifested in the function relationship of the hole diameter, which is different by π.

[0049] It is worth noting that the present application takes the rotation parameter (i.e. angle θ) as an additional dimension, and since the hole diameter of the central hole in the upper and lower structure units varies with the angle of the position, the hole diameter of the central hole in the upper and lower structure units in each structure unit is different, the structure unit is non-periodic in the X-Y plane, the angle θ is between 0 and 2π (including the end values), and therefore the unit cell is not periodic in the X-Y plane. The introduced angle θ forms a vortex center at the center of the unit cell, and since the upper assembly and the lower assembly have a phase delay of π (which is manifested as the difference in the hole diameter function in the upper and lower structure units), there are two vortex centers in the unit cell, as shown in Figure 1 (a) The red and blue arrows in (a) are obtained by arraying the unit cell in the Z direction, that is, a double vortex line is obtained. The electromagnetic wave is locally transmitted in the center of the double vortex line.

[0050] The intermediate layer structure unit is projected as a regular hexagon in the X-Y plane after the center and the hexagonal hole with a diameter of d are removed, and the height is (h-2t) / 2, that is, the diameters of the central hole and the corner hole are both d. The intermediate layer structure unit is a connecting layer between the upper structure unit and the lower structure unit, and is used to separate the copper foil on the bottom surface of the upper structure unit and the top surface of the lower structure unit, and the height is less than the height of the upper structure unit and the lower structure unit. The circular hole in the intermediate layer structure unit is mainly considered for convenience of experimental measurement, and the device performance will not be changed without the hole. It should be noted that if the hole is removed, the diameter of the central hole should not exceed the short side length w of the rectangle in the composite pattern.

[0051] It should be noted that the unit cell is a multi-layer honeycomb lattice structure, and a certain number of structure units are required to form the unit cell and form a vortex center. Generally, the more the number of structure units in the X-Y plane, the more localized the electromagnetic wave in the plane. Therefore, the diameter of the unit cell needs to be greater than 15 cm. In addition, the topological photonic crystal fiber also needs a certain period in the Z direction to form periodicity, so that the central state can propagate in the center. Therefore, the period of the topological acoustic fiber device is greater than 10.

[0052] In the material selection, Teflon material can be selected as the material of the upper assembly and the lower assembly in the embodiment, and the dielectric constant is 2.75. The central hole of the upper structure unit and the lower structure unit is plated with copper, and the upper and lower surfaces are windmill-shaped copper foils, and the thickness of the copper is 0.035 nm.

[0053] In other embodiments, the material of the upper assembly and the lower assembly can also be selected from other materials with a dielectric constant of 2.5-3, such as perfluoroalkoxy resin. The hole wall material of the central hole is consistent with the windmill pattern material of the upper and lower surfaces, and it only needs to be an electrically conductive material, in addition to copper, it can also be selected from metal conductive materials such as gold, silver, iron, tin, etc.

[0054] The material of the middle layer assembly can be a lightweight material with a dielectric constant close to that of air (typically 1.05-1.07), such as XPMI, PMI or PU type foam.

[0055] In terms of manufacturing process, the upper layer assembly and the lower layer assembly can be manufactured by CAD software and printed circuit board technology. The middle layer material can be manufactured by CAD software and then punched into foam. Finally, they can be assembled together by edge bonding and the like.

[0056] Based on the above description, in one specific embodiment, the height of the structural unit is h = 0.8 cm; the side length of the hexagon is a = 0.3 cm; the width of the rectangle in the composite pattern is w = 0.24 cm; the length of the rectangle in the composite pattern is l = 0.35 cm; the aperture constant r0 = 0.12 cm; and the aperture constant δr = 0.03 cm. The height of the upper layer and lower layer structural units is t = 0.3 cm; the height of the middle layer structural unit is 0.1 cm; the width of the rectangle in the composite pattern is w = 0.24 cm; the length of the rectangle in the composite pattern is l = 0.35 cm; the aperture constant r0 = 0.12 cm; and the aperture constant δr = 0.03 cm. The diameter of the device in the X-Y plane (the diameter of the primitive cell) is 15 cm, and the height is 18.4 cm.

[0057] In each structural unit, the aperture of the central hole in the upper layer structural unit and the lower layer structural unit is related to the position and angle, which can be calculated by respectively bringing the displacement vector r and the angle θ into formula (1) or formula (2).

[0058] It should be noted that the above parameters are the optimal parameters selected, and in actual application, the parameters can be varied within a range of 5% based on the above. The size parameters are related to the transmission frequency range of the device.

[0059] In other embodiments, the topological photonic crystal fiber can be scaled up or down as a whole based on the parameters given in the above embodiments, and the defect immune transmission property of the device remains unchanged, and the working frequency changes accordingly.

[0060] Figure 3 (a) shows the projection band of the topological photonic crystal fiber in the Z direction, where the dark purple points at the top and bottom represent the edge state, i.e. the electromagnetic wave at this frequency is distributed on the edge of the device for transmission, and the red and blue connected points in the middle of the figure represent the center state for positive transmission (spin up) and negative transmission (spin down) along the Z axis, respectively.

[0061] Figure 3 (b) is the center state for positive transmission and negative transmission along the Z axis, respectively, in the k zThe field distribution diagrams of the upper and lower layer assembly cross sections when =0.1(π / h) are marked as |i|u>+|l> and |u>+i|l> respectively, and the field distribution multiplied by i represents the imaginary part of the field distribution. It can be seen that the field distributions are concentrated in the middle of the device, and the imaginary parts of the positive upper layer assembly field distribution and the negative lower layer field distribution are taken respectively, and the central state is in k z The field distributions at the two points of =0.1(π / h) are consistent, which represents that they are a pair of spin states.

[0062] It can be seen that the electromagnetic wave frequency range of the topological photonic crystal fiber with vortex line as the central axis and transmitted in the Z direction is 12.25-12.75GHz, which is also the complete band gap range in the photonic crystal fiber.

[0063] As can be seen, the application provides a kind of topological photonic crystal fiber based on double vortex line, by introducing rotation parameter θ in upper layer assembly and lower layer assembly, the size of copper-plated aperture is modulated, and double vortex is formed with π phase delay in modulation function, without additional magnetic field, electromagnetic wave transmission along the center double vortex line of the device can be realized. In addition, the geometric size of the topological photonic crystal fiber can be scaled up or down, and the core transmission characteristics remain unchanged. The application has immunity to structural defects, has the advantages of low transmission loss and effective suppression of backscattering, and the device is easy to prepare and has stable properties.

[0064] Finally, it needs to be pointed out that although the embodiments of the application are described above in combination with the drawings, the application is not limited to the above specific embodiments and application fields, and the above specific embodiments are only illustrative and guiding, but not limiting. Those skilled in the art can make many forms under the guidance of this specification without departing from the scope protected by the claims of the application, which are all within the protection of the application.

Claims

1. A topological photonic crystal fiber based on a double vortex, characterized in that, It includes multiple unit cells arranged in a periodic array along the Z direction; each unit cell is a multilayer honeycomb lattice structure with an upper component, a first intermediate layer component, a lower component, and a second intermediate layer component stacked from top to bottom, wherein there is a π phase difference delay between the upper component and the lower component; the upper component and the lower component each include multiple aperiodic upper structural units and lower structural units; the first intermediate layer component includes multiple periodic intermediate layer structural units, and the second intermediate component has the same structure as the first intermediate component; The unit cell is also configured to form a double vortex center in the XY plane by introducing rotational parameters in the upper and lower structural units and a π phase difference delay between the upper and lower components, and the vortex centers are connected in the Z direction to form a double vortex line.

2. The topological photonic crystal fiber as described in claim 1, characterized in that, The upper structural unit includes a structural body and metal pattern layers arranged on the upper and lower surfaces of the structural body; the metal pattern layers on the upper and lower surfaces satisfy C 6Z It exhibits rotational symmetry and mirror symmetry about the Y-axis; the projection of the structure body onto the XY plane is a regular hexagon with side length a, and the center of the regular hexagon has a first through hole extending along the Z-direction, the first through hole being connected to the metal pattern layer and its hole wall having a metal plating layer of the same material as the metal pattern layer. The lower structural unit and the upper structural unit have the same structure, the only difference being the size of the first through hole. The aperture r of the upper structural unit u The aperture r of the lower structural unit is a function of (r, θ). l Let r be a function of (r, θ+π), where r is the position of the center point of the upper structural unit, θ is the angle between the line connecting the center point of the upper structural unit to the center point of the upper component and the X-axis, 0 < θ < 2π, and θ is the rotation parameter.

3. The topological photonic crystal fiber as described in claim 2, characterized in that, The aperture function relationship of the upper structural unit is as follows: r u =r0+δrcos(2K·r+θ),(1) The aperture function relationship of the lower structural unit is as follows: r l =r0+δrcos(2K·r+θ+π),(2) In the formula, r0 and δr are constants related to the aperture, where r0 is a preset aperture reference value, and δr determines the range of aperture variation; K is a Brillouin zone constant related to the structural unit size.

4. The topological photonic crystal fiber as described in claim 2, characterized in that, The projection of the metal pattern layer on the XY plane is constructed as follows: a windmill pattern is formed by removing a composite graphic from each of the six corner points of a regular hexagon; the composite graphic is composed of a rectangle whose center points of the three short sides coincide at the corner points of the hexagon, adjacent rectangles are rotated 120° to coincide with each other, and adjacent composite graphics at the hexagonal points are rotated 60° to coincide with each other relative to the center point of the regular hexagon.

5. The topological photonic crystal fiber as described in claim 4, characterized in that, The structure body also has a second through hole at each corner of the regular hexagon, extending along the Z direction.

6. The topological photonic crystal fiber as described in claim 5, characterized in that, The projection of the intermediate layer structural unit onto the XY plane is a regular hexagon with side length a, and a third through hole is provided at the center and each corner of the regular hexagon, extending along the Z direction; the diameter of the third through hole is d, which is less than or equal to the short side length W of the rectangle in the composite graphic; the height of the intermediate layer structural unit is less than the height of the first structural unit.

7. The topological photonic crystal fiber as described in claim 2, characterized in that, The dielectric constant of the main body of the structure is 2.5 to 3, and it is made of Teflon or perfluoroalkoxy resin; the material of the metal pattern layer is any one of copper foil, gold, silver, iron, and tin; the dielectric constant of the intermediate layer structural unit is close to that of air, and it is made of any one of XPMI, PMI, and PU foam.

8. The topological photonic crystal fiber according to any one of claims 1 to 7, characterized in that, The number of periods of the unit cell in the Z-axis periodic array is greater than or equal to 10; the diameter of the unit cell is greater than 15 cm.

9. The topological photonic crystal fiber according to any one of claims 1 to 7, characterized in that, The defect-immune transmission properties of the aforementioned topological photonic crystal fiber device remain unchanged after the overall size is scaled up or scaled down proportionally.

10. An optical device, characterized in that, Including the topological photonic crystal fiber based on double vortex lines as described in any one of claims 1 to 9.

Images