Dual-mode orbital angular momentum focusing basic unit array and metasurface preparation method

Abstract

The present invention discloses a dual-mode orbital angular momentum focusing basic unit array and a super surface preparation method, wherein the basic unit array comprises 2 n (2 n ‑1) anisotropic unit structures and 2 n The present invention constructs a polarization-controlled dual-mode orbital angular momentum focusing basic unit array by arranging a plurality of anisotropic unit structures and a small number of isotropic unit structures, and then the basic unit array can be used to construct a metasurface in the future. In addition, the use of a basic unit array to form a metasurface can converge the OAM beam.

Description

Technical Field

[0001] The present invention relates to the field of electronic material communication technology, and in particular to a dual-mode orbital angular momentum focusing basic unit array and a supersurface preparation method. Background Art

[0002] With the rapid iteration and evolution of science and technology, the channel capacity in the field of communication technology has reached its limit. Due to the current limitations of spectrum and polarization resources, further improvements in transmission rates will encounter many challenges. Today's wireless communication field is developing along the trend of low profile, small size, and multi-function. How to seek to establish a powerful communication system with strong anti-interference ability, fast and stable communication rate, and more reasonable use of limited spectrum resources is imminent. Therefore, new wireless transmission technologies with electromagnetic wave angular momentum characteristics have become a research hotspot. By utilizing the orthogonal characteristics of different modes of orbital angular momentum, a larger channel capacity can be achieved, and vortex electromagnetic waves have the characteristics of high spectrum utilization and anti-interference in communication, and have been widely used in radio, optics, and quantum communications.

[0003] Similar to spin orbital angular momentum, orbital angular momentum (OAM) is also one of the basic physical quantities of electromagnetic waves. In classical electromagnetic theory, angular momentum is divided into spin angular momentum and orbital angular momentum. Linear polarization, circular polarization, and elliptical polarization generated by electron spin belong to spin angular momentum, while those associated with spatial distribution belong to orbital angular momentum, which is a representative feature of vortex waves, and orbital angular momentum modes carrying different topological charges are orthogonal to each other.

[0004] There are usually the following solutions for generating orbital angular momentum, such as spiral phase plates, array antennas, q-plates, and spiral grating fibers. Most of the above solutions require high-precision processing and manufacturing processes, and are large in size, greatly increasing the complexity of the system, and are usually difficult to be reasonably used in practice.

[0005] In recent years, metasurfaces have attracted extensive attention from researchers at home and abroad. Devices constructed by metasurfaces have the advantages of low profile, small size, light weight, and easy manufacturing, so they are widely used. The generation of vortex beams carrying OAM at microwave and millimeter wave frequencies has once become a research hotspot. Unlike electromagnetic metamaterials, metasurfaces can be used as the two-dimensional equivalent of metamaterials, that is, two-dimensional planar material structures. By designing unit structures with different shapes and arrangements, the amplitude, phase, polarization and propagation characteristics of electromagnetic waves can be effectively controlled. However, the existing metasurfaces prepared based on basic units have the problem of single function and obvious divergence of the generated OAM beams. Therefore, how to improve the basic units that make up the metasurface has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a dual-mode orbital angular momentum focusing basic unit array and a metasurface preparation method to achieve dual-mode polarization control.

[0007] To achieve the above object, the present invention provides a dual-mode orbital angular momentum focusing basic unit array, the basic unit array comprising 2 n (2 n -1) anisotropic unit structure and 2 n isotropic unit structure; the basic unit array is 2 n ×2 n An array structure of, where n is the number of bits;

[0008] The anisotropic unit structure comprises: a bottom ground layer, a dielectric substrate layer and a top pattern layer arranged in sequence from bottom to top; the top pattern layer of the anisotropic unit structure is an axisymmetric H-shaped structure;

[0009] The isotropic unit structure comprises: a bottom ground layer, a dielectric substrate layer and a top pattern layer which are arranged in sequence from bottom to top; the top pattern layer of the isotropic unit structure is a square structure.

[0010] Optionally, the H-type structural parameters in different anisotropic unit structures are different.

[0011] Optionally, the bottom ground layer and the top pattern layer in the anisotropic unit structure and the bottom ground layer and the top pattern layer in the isotropic unit structure are both made of metal materials, and the dielectric substrate layer in the anisotropic unit structure and the dielectric substrate layer in the isotropic unit structure are both made of materials with a dielectric constant of 2.65.

[0012] Optionally, the bottom ground layer and the dielectric substrate layer in the anisotropic unit structure have the same periodic size, and the bottom ground layer and the dielectric substrate layer in the isotropic unit structure have the same periodic size.

[0013] The present invention also provides a method for preparing a dual-mode orbital angular momentum focusing metasurface, the method comprising:

[0014] Based on orbital angular momentum OAM n (2 n -1) phase requirements of anisotropic unit structures, and determining the optimal parameters corresponding to various bit states of each anisotropic unit structure in two polarization directions by optimization, where n is the number of bits;

[0015] According to 2 n (2 n-1) The optimal parameters corresponding to various bit states of the anisotropic unit structure in two polarization directions are constructed 2 n (2 n -1) said anisotropic unit structure;

[0016] Based on orbital angular momentum OAM n The phase requirements of an isotropic unit structure are determined by optimization to determine the optimal parameters corresponding to the isotropic unit structure;

[0017] According to 2 n The optimal parameters corresponding to the isotropic unit structure are constructed 2 n Isotropic unit cell structure;

[0018] Based on 2 n (2 n -1) the anisotropic unit structure and 2 n The isotropic unit structures are used to construct the basic unit array;

[0019] Based on the Helmholtz equation of free space, the compensation phase of each basic unit array of the converging vortex beam is derived;

[0020] In MATLAB, an OAM focusing metasurface carrying different topological charges is constructed based on the compensated phase of each basic unit array.

[0021] Optionally, the orbital angular momentum OAM is based on 2 n (2 n -1) phase requirements of anisotropic unit structures, and determining the optimal parameters corresponding to various bit states of each anisotropic unit structure in two polarization directions by optimization, specifically including:

[0022] In the three-dimensional electromagnetic field simulation software CST, roughly simulating each of the anisotropic unit structures in two polarization directions to obtain a first rough phase value;

[0023] Performing fine adjustment based on the first rough phase value until a first precise phase value is reached;

[0024] The size parameter corresponding to the first precise phase value is used as the optimal parameter of the anisotropic unit structure.

[0025] Optionally, the orbital angular momentum OAM is based on 2 n The phase requirements of an isotropic unit structure are determined by optimization to determine the optimal parameters corresponding to the isotropic unit structure, including:

[0026] In the three-dimensional electromagnetic field simulation software CST, each of the isotropic unit structures is roughly simulated to obtain a second rough phase value;

[0027] Performing fine adjustment based on the second rough phase value until a second precise phase value is reached;

[0028] The size parameter corresponding to the second precise phase value is used as the optimal parameter of each of the isotropic unit structures.

[0029] Optionally, the fine adjustment is performed based on the first rough phase value until a first precise phase value is reached, and the specific formula is:

[0030]

[0031] Among them, φ ith is the first rough phase value, is the first accurate phase value.

[0032] Optionally, the compensation phase of each basic unit array of the converging vortex beam is derived from the Helmholtz equation based on free space, and the specific formula is:

[0033]

[0034] in, represents the compensation phase of each basic unit array of the convergent vortex beam, λ represents the wavelength in free space, L represents the topological charge of OAM, F represents the focal length, and x, y represent the position coordinates corresponding to the coding array respectively.

[0035] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0036] The present invention discloses a dual-mode orbital angular momentum focusing basic unit array and a super surface preparation method, wherein the basic unit array comprises 2 n (2 n -1) anisotropic unit structure and 2 n isotropic unit structure; the basic unit array is 2 n ×2 n, n is the number of bits; the anisotropic unit structure includes: a bottom ground layer, a dielectric substrate layer and a top pattern layer arranged in sequence from bottom to top; the top pattern layer is an axisymmetric H-shaped structure; the isotropic unit structure includes: a bottom ground layer, a dielectric substrate layer and a top pattern layer arranged in sequence from bottom to top; the top pattern layer is a square structure. The present invention constructs a polarization-controlled dual-mode orbital angular momentum focusing basic unit array by arranging multiple anisotropic unit structures and a small number of isotropic unit structures, and then the basic unit array can be used to construct a metasurface in the future. In addition, the use of a basic unit array to form a metasurface can converge the OAM beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 A schematic diagram of a basic unit array constituting an orbital angular momentum focusing metasurface of the present invention;

[0039] Figure 2 Schematic diagram of the anisotropic unit structure of the present invention;

[0040] Figure 3 It is a schematic diagram of the isotropic unit structure of the present invention;

[0041] Figure 4 This is a schematic diagram of a dual-mode OAM converging metasurface calculated by MATLAB in the present invention;

[0042] Figure 5 The input phase, output phase and compensation phase distribution diagram of the dual-mode OAM focusing metasurface calculated in MATLAB in the present invention;

[0043] Figure 6 It is a two-dimensional far-field scattering diagram obtained by CST software simulation in the present invention;

[0044] Figure 7 This is a schematic diagram of the amplitude results of OAM generated by CST software simulation in the present invention;

[0045] Figure 8 A schematic diagram of the phase result corresponding to the dual-mode OAM focusing metasurface controlled by polarization of the present invention;

[0046] Fig. 9 The three-dimensional far-field scattering diagram of the dual-mode OAM focusing metasurface controlled by polarization of the present invention;

[0047] Explanation of symbols:

[0048] 1- anisotropic unit structure, 2- isotropic unit structure, 3- bottom ground layer, 4- dielectric substrate layer, 5- top pattern layer. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] The purpose of the present invention is to provide a dual-mode orbital angular momentum focusing basic unit array and a metasurface preparation method to achieve dual-mode polarization control.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Example 1

[0053] The present invention provides a dual-mode orbital angular momentum focusing basic unit array, the basic unit array comprising 2 n (2 n -1) Anisotropic unit structures 1 and 2 n isotropic unit structure 2; the basic unit array is 2 n ×2 n , wherein n is the number of bits. The anisotropic unit structure 1 comprises: a bottom ground layer 3, a dielectric substrate layer 4 and a top pattern layer 5 arranged in sequence from bottom to top; the top pattern layer 5 is an axisymmetric H-type structure; the isotropic unit structure 2 comprises: a bottom ground layer 3, a dielectric substrate layer 4 and a top pattern layer 5 arranged in sequence from bottom to top; the top pattern layer 5 is a square structure. The H-type structural parameters in different anisotropic unit structures 1 of the present invention are different. The bottom ground layer 3 and the top pattern layer 5 in the anisotropic unit structure 1 and the bottom ground layer 3 and the top pattern layer 5 in the isotropic unit structure 2 are all made of metal materials, the bottom ground layer 3 and the dielectric substrate layer 4 in the anisotropic unit structure 1 have the same periodic size, the bottom ground layer 3 and the dielectric substrate layer 4 in the isotropic unit structure 2 have the same periodic size, and the dielectric substrate layer in the isotropic unit structure 2 and the dielectric substrate layer in the anisotropic unit structure 1 are both made of low-loss materials with a dielectric constant of 2.65.

[0054] The present invention takes n as 3 as an example for analysis. Figure 1 As shown, the basic unit array with reflective dual-function characteristics includes 56 anisotropic unit structures 1 and 8 isotropic unit structures 2; the basic unit array is an 8×8 array structure, and the 8 isotropic unit structures 2 are arranged on the diagonal of the array structure. The 64 basic unit structures of the present invention can achieve a phase difference of 360°, and the phase gradient between adjacent basic unit structures satisfies the relationship of 360° / 2n or -360° / 2n. For the basic unit array of 3-bit anisotropic coding, a total of 64 basic unit structures are required, of which 8 are isotropic unit structures 2 and the other 56 are anisotropic unit structures 1. Half of the total number of anisotropic unit structures 1 can be obtained by rotating the other half along its center point by 90°, which greatly reduces its simulation complexity.

[0055] Figure 2 Figure (a) is a top view of the anisotropic unit structure. Figure 2 Figure (b) is the main view of the anisotropic unit structure. Figure 2 As shown, the anisotropic unit structure 1 includes: a bottom ground layer 3, a dielectric substrate layer 4 and a top pattern layer 5 arranged in sequence from bottom to top; the top pattern layer 5 is an axisymmetric H-type structure; the bottom ground layer 3 and the dielectric substrate layer 4 have the same periodic size p; the bottom ground layer 3 and the top pattern layer 5 are made of a metal material with a high reflectivity, generally copper, and the dielectric substrate layer is made of a low-loss material with a dielectric constant of 2.65. It should be pointed out that the changes in parameters h1 and h2 are more sensitive to y-polarized waves, and the changes in parameters w1 and w2 are more sensitive to x-polarized waves, that is, the unit size parameters corresponding to various bit states in the two polarization directions can be determined by optimization, and the size of each parameter in each of the anisotropic unit structures 1 is in the range of 0 to 6 mm. In addition, the division of the bit state of the coding unit of the present invention depends on the phase difference between the reflective anisotropic unit structure 1 or the isotropic unit structure 2. For example, for a basic cell array of 1-bit coding, the phase difference between two adjacent anisotropic cell structures 1 or isotropic cell structures 2 is 180°, for a basic cell array of 2-bit coding, the phase difference between two adjacent anisotropic cell structures 1 or isotropic cell structures 2 is 90°, for a basic cell array of 3-bit coding, the phase difference between two adjacent anisotropic cell structures 1 or isotropic cell structures 2 is 45°, and for a basic cell array of 4-bit coding, the phase difference between two adjacent anisotropic cell structures 1 or isotropic cell structures 2 is 22.5°.

[0056] Due to the non-central symmetry of the anisotropic unit structure 1, there is a difference between the two reflection phases under x and y polarization. Therefore, the dielectric substrate layer of the anisotropic unit structure 1 designed by the present invention uses F4B, with a dielectric constant of 2.65, a loss of 0.001, a thickness d of only 0.6 mm, a thickness d of 0.032 times the working wavelength, and a period p = 6 mm. The bottom ground layer 3 and the H-shaped metal structure use a conductivity of 5.96×10 7 Sm -1 The copper patch is made of, and the thickness t is usually set to 0.018mm.

[0057] Figure 3 Figure (a) is a top view of the isotropic unit structure 2. Figure 3 Figure (b) is a front view of the isotropic unit structure 2, as shown in Figure 3 As shown, the isotropic unit structure 2 includes: a bottom ground layer 3, a dielectric substrate layer 4 and a top pattern layer 5 arranged in sequence from bottom to top; the top pattern layer 5 is a square structure. The dielectric substrate layer of the isotropic unit structure 2 in this embodiment is F4B, with a dielectric constant of 2.65, a loss of 0.001, a thickness d of only 0.6 mm, a thickness d of 0.032 times the working wavelength, and a period p = 6 mm. The bottom ground layer 3 and the H-shaped metal structure adopt a conductivity of 5.96×10 7 Sm -1 The copper patch is made of, and the thickness t is usually set to 0.018mm.

[0058] Example 2

[0059] The present invention discloses a method for preparing a dual-mode orbital angular momentum focusing metasurface, the method comprising:

[0060] Step S1: Based on orbital angular momentum OAM pair 2 n (2 n -1) phase requirements of anisotropic unit structures, and determining the optimal parameters corresponding to various bit states of each anisotropic unit structure in two polarization directions by optimization, wherein n is the number of bits.

[0061] Step S1 specifically includes:

[0062] Step S11: In the three-dimensional electromagnetic field simulation software CST, roughly simulate each of the anisotropic unit structures in two polarization directions to obtain a first rough phase value.

[0063] Step S12: fine-tune based on the first rough phase value until a first precise phase value is reached. The specific formula is:

[0064]

[0065] Among them, φ ith is the first rough phase value, is the first accurate phase value.

[0066] when When it is 0, the corresponding state is "000". When it is 45°, the corresponding state is "001". When it is 90°, the corresponding state is "010", and so on. When it is 315°, the corresponding state is "111".

[0067] For the 1-bit coded basic unit array, there are 2 corresponding coding states under x or y polarization, so the entire interval is divided into 2 intervals with equal spacing. For the 2-bit coded basic unit array, there are 4 corresponding coding states under x or y polarization, so the entire interval is divided into 4 intervals with equal spacing. For the 3-bit coded basic unit array, there are 8 corresponding coding states under x or y polarization, so the entire interval is divided into 8 intervals with equal spacing. For the 4-bit coded basic unit array, there are 16 corresponding coding states under x or y polarization, so the entire interval is divided into 16 intervals with equal spacing. And so on.

[0068] Step S13: Using the size parameters corresponding to the first precise phase value as the optimal parameters of the anisotropic unit structure. In this embodiment, the size parameters corresponding to the first precise phase value include parameters w1, w2, h1 and h2, such as Figure 2 shown.

[0069] Step S2: According to 2 n (2 n -1) The optimal parameters corresponding to various bit states of the anisotropic unit structure in two polarization directions are constructed 2 n (2 n -1) the anisotropic unit structure. In this embodiment, the optimal parameters of the anisotropic unit structures are different.

[0070] Step S3: Based on orbital angular momentum OAM pair 2 n The phase requirements of an isotropic unit structure are determined by optimization to determine the optimal parameters corresponding to the isotropic unit structure, including:

[0071] Step S31: In the three-dimensional electromagnetic field simulation software CST, roughly simulate each of the isotropic unit structures to obtain a second rough phase value.

[0072] Step S32: fine-tuning based on the second rough phase value until a second precise phase value is reached.

[0073] Step S33: taking the size parameters corresponding to the second precise phase value as the optimal parameters of each of the isotropic unit structures; the size parameters corresponding to the second precise phase value include parameters x and y, and x is equal to y, specifically: Figure 3 shown.

[0074] like Figure 3 As shown, the isotropic unit structure includes: a bottom ground layer, a dielectric substrate layer and a top pattern layer arranged in sequence from bottom to top; the top pattern layer is a square metal structure; the bottom ground layer and the dielectric substrate layer have the same period size p; the bottom ground layer and the top pattern layer are composed of a metal material with a high reflectivity, generally copper, and the dielectric substrate layer is composed of a low-loss material with a dielectric constant of 2.65.

[0075] Step S4: According to 2 n The optimal parameters corresponding to the isotropic unit structure are constructed 2 n An isotropic unit cell structure.

[0076] Step S5: Based on 2 n (2 n -1) the anisotropic unit structure and 2 n The isotropic unit structures are used to construct a basic unit array.

[0077] Step S6: Derivation of the compensation phase of each basic unit array of the convergent vortex beam based on the Helmholtz equation of free space The specific formula is:

[0078]

[0079] Among them, λ represents the wavelength in free space, L represents the topological charge of OAM, which can be any integer, F represents the focal length, that is, the distance from the point source to the center point of the metasurface unit, and x and y represent the position coordinates corresponding to the coding array. In addition, is the input phase, and L·arctan(y / x) is the output phase.

[0080] In practice, in order to ensure the generation effect of near-field orbital angular momentum vortex waves, a point source is usually used as the excitation source of the metasurface unit. Therefore, the distance from the point source to the center point of the metasurface unit is F = k*D; k is the proportional factor and can be 0.6 to 1, usually taking the median value of 0.8, and D is the physical length of a single side of the basic unit array, and its value is 246 mm.

[0081] Step S7: In MATLAB, an OAM converging metasurface carrying different topological charges is constructed based on the compensation phase of each of the basic unit arrays, such as Figure 4As shown. The present invention designs a dual-mode OAM focusing metasurface with topological charges of 1 and 2 and controlled by polarization, and uses the concept of units to weaken the coupling between each basic unit array. The overall size of the OAM focusing metasurface is about 16 times the working wavelength, and the distance between the spherical wave source and the metasurface can be set to 10 to 16 times the working wavelength, usually taking an intermediate value.

[0082] The present invention can set the excitation source as a horn or a waveguide, and utilize the anisotropic unit structure and the isotropic unit structure to construct a dual-mode orbital angular momentum basic unit array in the CST simulation software. It should be pointed out that manually constructing the required array takes a lot of time and effort, and cannot guarantee zero error. Therefore, MATLAB-CST joint simulation modeling can be used to ensure the accuracy of modeling.

[0083] The present invention designs an OAM convergence metasurface antenna that can carry topological charges 1 and 2 at the same time. The antenna has high gain (21.7dBi in mode 1 at 16GH and 20.8dBi in mode 2) and small divergence angle (6.5° in mode 1 at 16GH and 10.6° in mode 2). Modes 1 and 2 correspond to the topological charges carried by the dual-function OAM antenna. It should be pointed out that the structure has a simple manufacturing process and low material cost, making it possible to mass-produce and standardize it, thus realizing an ultra-thin, efficient, and simple-structured OAM convergence metasurface.

[0084] Example 3

[0085] In this embodiment, the anisotropic unit structure is mainly divided into three layers, a bottom ground layer, a dielectric substrate layer and a top pattern layer; wherein the period length and width of the bottom metal layer and the dielectric substrate layer are both 6 mm, and the thickness of the dielectric substrate layer is only 0.6 mm, which is 0.032 times the working wavelength; the bottom ground layer and the top pattern layer are both made of a conductive material with a conductivity of 5.96×10 7 Sm -1 The dielectric substrate layer is composed of metal copper with a dielectric constant of 2.65 and a loss of 0.001. The overall size of the structure is 246mm×246mm (13.12λ0×13.12λ0).

[0086] Step 1: According to the basic principles of geometric optics, electromagnetic waves will reflect and refract at the interface of two materials. Therefore, we can first design an anisotropic unit structure based on the phase response of the metasurface to different polarizations of electromagnetic waves, and then model and simulate the anisotropic unit structure in CST and optimize it. Figure 2The w1, w2, h1, and h2 in the equation are optimization variables. It should be noted that the changes in the parameters h1 and h2 are more sensitive to the y-polarized wave, and the changes in w1 and w2 are more sensitive to the x-polarized wave. The anisotropic unit structure size parameters corresponding to various bit states in the two polarization directions can be determined by optimizing the corresponding parameters. Figure 2 The four parameters corresponding to the above formula can be used to obtain 56 anisotropic unit structures corresponding to 3-bit anisotropy. Then, 8 isotropic unit structures need to be obtained. After all the unit structures are obtained, they are quantized and encoded by formula (1). The vortex phase distribution diagram is obtained in MATLAB by formula (2). Figure 5 As shown, Figure 5 Figures (a), (b) and (c) are schematic diagrams of the input phase, output phase and compensation phase distribution of the OAM focusing metasurface when the incident electromagnetic wave is along the x-polarization, and the topological charge it carries is positive 1st order; Figure 5 Figures (d), (e) and (f) are schematic diagrams of the input phase, output phase and compensation phase distribution of the OAM focusing metasurface when the electromagnetic wave is incident along the y polarization, and the topological charge it carries is positive 2nd order. For example, the unit phase values ​​corresponding to the 000-001 coding state correspond to 0° and 45° in the x and y polarization directions, respectively. The anisotropic unit structure size parameters can be queried from Table 1. For the reflective basic unit array, since the bottom of its unit structure is fully covered by metal and uses a low-loss dielectric substrate, its reflection amplitude is close to 1, so only its phase information needs to be paid attention to during design.

[0087] Table 1 Anisotropic unit structure size parameters (unit: mm)

[0088]

[0089]

[0090] Step 2: According to the relevant theories of electromagnetic waves, the phase requirements of dual-function OAM can be realized. The vortex phase distribution in the x and y polarization directions can be independently controlled to realize dual-mode OA controlled by polarization. M Converging metasurface. For this case, the central operating frequency is 16 GHz, and the feed source can be a waveguide or a horn, and the distance is set to 246 mm between the feed phase center and the center of the metasurface. Then, according to the basic principle of generating OAM vortex beams and the phase compensation formula required for spherical waves to be equivalent to plane waves, the required vortex phase distribution diagram is obtained by coding and drawing in MATLAB.

[0091] Step 3: According to the vortex phase distribution diagram obtained by MATLAB in step 2, a polarization-controlled dual-mode OAM focusing metasurface is constructed. The present invention uses MATLAB-CST for joint simulation modeling, and the established model is as follows: Figure 4 The working frequency of the designed metasurface is 16 GHz. In order to reduce the complexity of the simulation, a suitable waveguide can be selected as the feed source. The waveguide is 13.12 times the working wavelength away from the center of the metasurface, and the actual distance is 246 mm. The electric field amplitude and phase are then obtained by CST analysis. The two-dimensional and three-dimensional far-field scattering diagrams and phase distribution diagrams are shown in Figure 1. Figures 6 to 9 shown. Figure 6 This is the two-dimensional far-field scattering diagram obtained by CST software simulation in the present invention. Figure 6 Figures (a) and (b) in the figure respectively represent the two-dimensional far-field scattering diagrams of the OAM converging metasurface carrying topological charges 1 and 2 drawn in the yoz plane. Figure 6 It can be seen that when the topological charge is 1, the divergence angle d is about 6.5, and when the topological charge is 1, the divergence angle d is about 10.6; Figure 7 This is a schematic diagram of the amplitude results of OAM generated by CST software simulation in the present invention, Figure 7 Figures (a) and (b) in the figure respectively show the amplitude results of the xoy plane at a position of 246 mm away from the Z axis of the OAM converging metasurface carrying topological charges 1 and 2; Figure 8 This is a schematic diagram of the phase result corresponding to the OAM focusing metasurface of the present invention. Figure 8 Figures (a) and (b) in the figure respectively show the phase results corresponding to the OAM converging metasurfaces carrying topological charges 1 and 2; Fig. 9 This is the three-dimensional far-field scattering diagram of the dual-mode OAM focusing metasurface controlled by polarization in the present invention. Fig. 9 Figures (a) and (b) in the figure represent the three-dimensional far-field scattering diagrams of the OAM converging metasurface carrying topological charges 1 and 2, respectively. Fig. 9 As shown in FIG. 1 , it is well verified that the designed orbital angular momentum antenna has a high gain (21.4 dBi in mode 1 and 20.3 dBi in mode 2 at 16 GH); Figure 6 As shown in FIG. 1 , it is well verified that the designed orbital angular momentum antenna has a small divergence angle (6.5° for mode 1 and 10.6° for mode 2 at 16 GH); Figure 6-Figure 9 As shown in the figure, mode 1 and mode 2 correspond to the topological charges carried by the dual-mode OAM converging metasurface regulated by polarization, and the theoretical prediction and simulation results are in good agreement.

[0092] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0093] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A dual-mode orbital angular momentum focusing basic unit array, characterized in that: The basic unit array includes 2 n (2 n -1) anisotropic unit structure and 2 n isotropic unit structure; the basic unit array is 2 n ×2 n An array structure of, where n is the number of bits; The anisotropic unit structure comprises: a bottom ground layer, a dielectric substrate layer and a top pattern layer arranged in sequence from bottom to top; the top pattern layer of the anisotropic unit structure is an axisymmetric H-shaped structure; The isotropic unit structure comprises: a bottom ground layer, a dielectric substrate layer and a top pattern layer which are arranged in sequence from bottom to top; the top pattern layer of the isotropic unit structure is a square structure.

2. The dual-mode orbital angular momentum focusing basic unit array according to claim 1, characterized in that: The H-type structural parameters in different anisotropic unit structures are different.

3. The dual-mode orbital angular momentum focusing basic unit array according to claim 1, characterized in that: The bottom ground layer and the top pattern layer in the anisotropic unit structure and the bottom ground layer and the top pattern layer in the isotropic unit structure are both made of metal materials, and the dielectric substrate layer in the anisotropic unit structure and the dielectric substrate layer in the isotropic unit structure are both made of materials with a dielectric constant of 2.

65.

4. The dual-mode orbital angular momentum focusing basic unit array according to claim 1, characterized in that: The bottom ground layer and the dielectric substrate layer in the anisotropic unit structure have the same periodic size, and the bottom ground layer and the dielectric substrate layer in the isotropic unit structure have the same periodic size.

5. A method for preparing a dual-mode orbital angular momentum focusing metasurface, characterized in that: The super surface preparation method comprises: Based on orbital angular momentum OAM n (2 n -1) phase requirements of anisotropic unit structures, and determining the optimal parameters corresponding to various bit states of each anisotropic unit structure in two polarization directions by optimization, where n is the number of bits; According to 2 n (2 n -1) The optimal parameters corresponding to various bit states of the anisotropic unit structure in two polarization directions are constructed 2 n (2 n -1) said anisotropic unit structure; Based on orbital angular momentum OAM n The phase requirements of an isotropic unit structure are determined by optimization to determine the optimal parameters corresponding to the isotropic unit structure; According to 2 n The optimal parameters corresponding to the isotropic unit structure are constructed 2 n Isotropic unit cell structure; Based on 2 n (2 n -1) the anisotropic unit structure and 2 n The isotropic unit structures are used to construct the basic unit array according to any one of claims 1 to 4; Based on the Helmholtz equation of free space, the compensation phase of each basic unit array of the converging vortex beam is derived; In MATLAB, an OAM focusing metasurface carrying different topological charges is constructed based on the compensated phase of each basic unit array.

6. The method for preparing a dual-mode orbital angular momentum focusing metasurface according to claim 5, characterized in that: The orbital angular momentum OAM is based on n (2 n -1) phase requirements of anisotropic unit structures, and determining the optimal parameters corresponding to various bit states of each anisotropic unit structure in two polarization directions by optimization, specifically including: In the three-dimensional electromagnetic field simulation software CST, roughly simulating each of the anisotropic unit structures in two polarization directions to obtain a first rough phase value; Performing fine adjustment based on the first rough phase value until a first precise phase value is reached; The size parameter corresponding to the first precise phase value is used as the optimal parameter of the anisotropic unit structure.

7. The method for preparing a dual-mode orbital angular momentum focusing metasurface according to claim 5, characterized in that: The orbital angular momentum OAM is based on n The phase requirements of an isotropic unit structure are determined by optimization to determine the optimal parameters corresponding to the isotropic unit structure, including: In the three-dimensional electromagnetic field simulation software CST, each of the isotropic unit structures is roughly simulated to obtain a second rough phase value; Performing fine adjustment based on the second rough phase value until a second precise phase value is reached; The size parameter corresponding to the second precise phase value is used as the optimal parameter of each of the isotropic unit structures.

8. The method for preparing a dual-mode orbital angular momentum focusing metasurface according to claim 6, characterized in that: The fine adjustment is performed based on the first rough phase value until the first precise phase value is reached. The specific formula is: Among them, φ ith is the first rough phase value, is the first accurate phase value.

9. The method for preparing a dual-mode orbital angular momentum focusing metasurface according to claim 6, characterized in that: The compensation phase of each basic unit array of the converging vortex beam is derived from the Helmholtz equation based on free space. The specific formula is: in, represents the compensation phase of each basic unit array of the convergent vortex beam, λ represents the wavelength in free space, L represents the topological charge of OAM, F represents the focal length, and x, y represent the position coordinates corresponding to the coding array respectively.

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