阅读说明：本技术 基于非均匀透射宽带pb超表面的设计方法 (Design method based on non-uniform transmission broadband PB super surface ) 是由 贾冰 张屾 于 2020-06-04 设计创作，主要内容包括：本发明提供一种基于非均匀透射宽带PB超表面的设计方法,该方法可以用于设计宽带涡旋光产生器,包括如下步骤：理论推导了当两个线极化间相位差满足|φ<Sub>x</Sub>-φ<Sub>y</Sub>|＝π且透射幅度满足|T<Sub>x</Sub>|＝|T<Sub>y</Sub>|＝1时,可以实现PB单元的高效透射,建立了宽带PB超表面工作方程为<Image he="135" wi="635" file="DDA0002525037950000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>其中f<Sub>i</Sub>为f<Sub>1</Sub>到f<Sub>2</Sub>频率范围内的任一频率,<Image he="80" wi="132" file="DDA0002525037950000012.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image><Image he="78" wi="75" file="DDA0002525037950000013.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>表征左旋圆极化波激励时右旋圆极化波的透射相位,也就是说超表面具有一致的相位变化率；与相关技术相比,本发明首先基于该单元设计的涡旋光产生器具有带宽大、圆极化纯度高、效率高等优良性能,为宽带涡旋光产生器的研制提供了新的研究思路。(The invention provides a design method based on a non-uniform transmission broadband PB super surface, which can be used for designing a broadband vortex light generator and comprises the following steps: theory deduces that when the phase difference between two linear polarizations satisfies | phi x ‑φ y Pi and transmission amplitude satisfying T x |＝|T y When 1, the high-efficiency transmission of the PB unit can be realized, and the broadband PB super-surface working equation is established as Wherein f is i Is f 1 To f 2 Any one of a range of frequencies is used, characterised by the transmission phase of right-hand circularly polarised waves when excited by left-hand circularly polarised waves, i.e. the metasurfaces have a uniform phaseThe rate of change of phase of; compared with the related art, the vortex light generator designed based on the unit has the excellent performances of large bandwidth, high circular polarization purity, high efficiency and the like, and provides a new research idea for the development of the broadband vortex light generator.)

1. A design method based on a non-uniform transmission broadband PB super surface is characterized in that the method can be used for designing a broadband vortex light generator and comprises the following steps:

s1, theory deduces that when the phase difference between two linear polarizations satisfies | phi_x-φ_yPi and transmission amplitude satisfying T_x|＝|T_yWhen 1, the high-efficiency transmission of the PB unit can be realized, and the broadband PB super-surface working equation is established asWherein f is_iIs f₁To f₂Any one of a range of frequencies is used,representing the transmission phase of the right-hand circularly polarized wave when the left-hand circularly polarized wave is excited, namely the super surface has consistent phase change rate;

s2, providing a method for regulating and controlling amplitude and phase of transmitted waves by adopting a non-uniform thickness structure, wherein the transmission amplitude of the non-uniform thickness structure in a pass band changes more stably, and a non-uniform thickness system has larger bandwidth₁＝4mm，h₂6mm and h₁4mm, and the transmission phase in the range of 8.5-10.5GHzThe transmissivity reaches more than 0.8;

s3, analyzing a phase distribution equation of the surface of the vortex light generator based on the broadband non-uniform PB transmission unit, and designing and preparing a broadband transmission vortex light generator;

s4, a near-field and far-field experimental test method of the broadband transmission vortex light generator is provided, a clear vortex arm can be seen in the near-field effect of the vortex light generator, and the normal radiation depth is better than-15 dB;

s5, establishing an efficiency evaluation method of the vortex light generator, wherein the efficiency of the center frequency of the designed vortex light generator reaches 72% and exceeds 65% in the range of 8.5-10.5 GHz.

2. The method as claimed in claim 1, wherein the broadband nonuniform PB transmission unit comprises four layers of the same unit, each layer of unit comprises a dielectric layer and a metal resonance structure attached thereon, and the dielectric layer has a thickness h₁＝0.2mm，_rThe metal resonance structure is an orthogonal cross structure which is an anisotropic structure and has good polarization isolation, and the metal resonance structure is used for regulating and controlling dielectric constant parameters in different polarization states, namely an F4B substrate with 2.65 and tan being 0.005.

3. The design method based on the nonuniform transmission broadband PB super surface as claimed in claim 2, wherein the broadband nonuniform PB transmission unit has good polarization isolation, so that the transmission phase can be optimized by fixing one arm in a cross structure, adjusting the length of the other arm, and taking the two length distributions as the lengths of the two arms when the length of one arm is changed to satisfy the phase difference of ± 180 °, that is, achieving | φ °_x-φ_yHigh efficiency condition of | ═ pi.

4. The non-uniform transmission broadband PB super surface based design method according to claim 3, wherein the broadband transmission vortex light generator uses an Archimedes spiral antenna with an opening radius of only 15mm as a feed source.

5. The design method based on the non-uniform transmission broadband PB super surface as claimed in claim 4, wherein the manufactured broadband transmission vortex light generator is composed of 14 x 14 broadband non-uniform PB transmission units, a 182 x 182mm square array is formed, four layers of identical super surfaces are fixed by paperboards according to the intervals of 4mm, 6mm and 4mm when the units are designed, the broadband transmission vortex light generator is assembled by placing the Archimedes spiral antenna at the focus of the super surfaces, and the Archimedes spiral antenna is fixed and supported by foam with the thickness of 80 mm.

Technical Field

The invention relates to the technical field of communication, in particular to a design method based on a non-uniform transmission broadband PB (Pancharatnam-Berry) super surface.

Background

Incident waves and transmitted waves of a transmission system are separated in a physical space, so that adverse factors such as feed source shielding, mutual interference of reflected waves and the incident waves and the like in a reflection system are avoided, the method is more convenient and more practical in practical application, but the transmission system is a dual-port channel, the transmitted waves and the reflected waves need to be concerned about, so that the transmission type super-structure surface is more complex in design, and the important problem that how to realize the high-efficiency transmission type super-structure surface needs to be solved urgently is solved.

Vortex rotation refers to a type of light beam carrying

The wave front travels spirally in the propagation direction and the central light intensity is zero during transmission. By virtue of their unique electromagnetic properties, researchers have attracted their attention for their potential applications in the fields of optics, atomic physics, and communications. Because the vortex light beams with different topological charge numbers are mutually orthogonal, each vortex light beam with different topological charge numbers can be used as an independent signal channel to transmit signals, and theoretically, the vortex light beams have innumerable orthogonal orbital angular momentum, so that huge potential is provided for greatly improving optical communication capacity, a foundation is provided for realizing free space optical communication of orbital angular momentum multiplexing, and meanwhile, the application of vortex optical rotation in information coding also ensures that the confidentiality of coded information is stronger and the transmission process is safer; when the orbital angular momentum of the light beam is used for capturing the particles, the requirement on the refractive index of the particles in the traditional method is made up, the damage to the particles is reduced, and a solid foundation is laid for the application of the orbital angular momentum in the optical tweezers technology. The transmission vortex light is affected by the bandwidth and efficiency of the transmission system, so that the practical application of the transmission vortex light is severely restricted, and how to realize a broadband efficient transmission vortex light generator becomes an important subject for scientists.

Therefore, there is a need to provide a new design method based on non-uniform transmission broadband PB super surface to solve the above problems.

Disclosure of Invention

The invention aims to overcome the defects of the technology, establish a high-efficiency working theory of a multi-layer geometric transmission system with non-uniform thickness for the first time and realize the broadband and high efficiency of the transmission geometric super-structure surface.

The invention provides a design method based on a non-uniform transmission broadband PB super surface, which can be used for designing a broadband vortex light generator and comprises the following steps:

s1, theory deduces that when the phase difference between two linear polarizations satisfies | phi_x-φ_yPi and transmission amplitude satisfying T_x|＝|T_yWhen 1, the high-efficiency transmission of the PB unit can be realized, and the broadband PB super-surface working equation is established as

Wherein f is_iIs f₁To f₂Any one of a range of frequencies is used,representing the transmission phase of the right-hand circularly polarized wave when the left-hand circularly polarized wave is excited, namely the super surface has consistent phase change rate;

s2, providing a method for regulating and controlling amplitude and phase of transmitted waves by adopting a non-uniform thickness structure, wherein the transmission amplitude of the non-uniform thickness structure in a pass band changes more stably, and a non-uniform thickness system has larger bandwidth₁＝4mm，h₂6mm and h₁4mm, and the transmission phase in the range of 8.5-10.5GHzThe transmissivity reaches more than 0.8;

s3, analyzing a phase distribution equation of the surface of the vortex light generator based on the broadband non-uniform PB transmission unit, and designing and preparing a broadband transmission vortex light generator;

s4, a near-field and far-field experimental test method of the broadband transmission vortex light generator is provided, a clear vortex arm can be seen in the near-field effect of the vortex light generator, and the normal radiation depth is better than-15 dB;

s5, establishing an efficiency evaluation method of the vortex light generator, wherein the efficiency of the center frequency of the designed vortex light generator reaches 72% and exceeds 65% in the range of 8.5-10.5 GHz.

Preferably, the broadband nonuniform PB transmission unit is composed of four layers of same units, each layer of unit is composed of a dielectric layer and a metal resonance structure attached to the dielectric layer, and the dielectric layer is of thickness h₁＝0.2mm，_rThe metal resonance structure is an orthogonal cross structure which is an anisotropic structure and has good polarization isolation, and the metal resonance structure is used for regulating and controlling dielectric constant parameters in different polarization states, namely an F4B substrate with 2.65 and tan being 0.005.

Preferably, since the broadband nonuniform PB transmission unit has good polarization isolation, the transmission phase can be optimized by fixing one arm in a cross structure, adjusting the length of the other arm, and taking the two length distributions as the lengths of the two arms when the length of one arm is changed to meet the phase difference of +/-180 degrees, namely, realizing that phi is_x-φ_yHigh efficiency condition of | ═ pi.

Preferably, the broadband transmissive vortex light generator adopts an Archimedes spiral antenna with an opening radius of only 15mm as a feed source.

Preferably, the manufactured broadband transmission vortex light generator is composed of 14 × 14 broadband non-uniform PB transmission units, a square array of 182mm × 182mm is formed, four layers of identical super surfaces are fixed by using paperboards according to the intervals of 4mm, 6mm and 4mm when the units are designed, the broadband transmission vortex light generator is assembled by placing an Archimedes spiral antenna at the focus of the super surfaces, and the Archimedes spiral antenna is fixed and supported by foam with the thickness of 80 mm.

Compared with the prior art, the invention firstly deduces the high-efficiency realization condition of the transmission PB unit in a broadband range from theory based on the Jones matrix; the thought of regulating and controlling the transmission super-surface amplitude and the bandwidth by adopting the thickness factor is put forward for the first time, and the designed four-layer transmission geometric unit with non-uniform thickness obviously inhibits the fluctuation of the transmission amplitude of a multilayer structure, improves the efficiency of the transmission unit, and has the transmission rate of more than 0.8 within the range of 8.5-10.5 GHz. A transmissive vortex light generator was then developed based on this cell under excitation by an archimedes spiral antenna. Experiment results show that the efficiency of the device reaches 72.1% at most, and the working bandwidth reaches 21%.

The vortex light generator based on the unit design has the excellent performances of large bandwidth, high circular polarization purity, high efficiency and the like, and provides a new research idea for the development of the broadband vortex light generator.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts, wherein:

FIG. 1 is a PB super-surface structure schematic diagram of a design method based on a non-uniform transmission broadband PB super-surface. Wherein FIG. 1(a) is a schematic diagram of the structure before rotation; wherein FIG. 1(b) is a schematic diagram of the rotated structure;

FIG. 2 is (a) a front view and (b) a side view of a topological structure of an orthogonal cross unit in the design method based on the nonuniform transmission broadband PB super surface;

FIG. 3 is a schematic diagram of the cell characteristics in the design method based on the nonuniform transmission broadband PB super surface, wherein FIG. 3(a) is a schematic diagram of polarization isolation analysis; FIG. 3(b) is a schematic diagram of the amplitude of the transmitted wave under the condition of normal incidence of the x-polarized wave and the y-polarized wave; FIG. 3(c) is a schematic diagram of the phases of the transmitted waves under the condition of normal incidence of the x-polarized wave and the y-polarized wave; FIG. 3(d) is a schematic diagram showing the transmission coefficient and the transmission phase at a rotation angle θ of the unit when a circularly polarized wave is incident;

FIG. 4 is a schematic diagram of phase distribution on a transmission ultrastructural surface in the design method based on the non-uniform transmission broadband PB ultrasurface; wherein FIG. 4(a) is a schematic diagram of a phase distribution of a focusing surface, FIG. 4(b) is a schematic diagram of a phase distribution of a spiral phase plate and FIG. 4(c) is a schematic diagram of a phase distribution of a vortex light generator;

FIG. 5 is a schematic diagram of a processed sample and an experimental device in the design method based on the nonuniform transmission broadband PB super surface; wherein FIG. 5(a) is a schematic diagram of a near field testing method and FIG. 5(b) is a diagram of a processed sample of a microstructured surface;

FIG. 6 is a schematic diagram of a near field test result in the design method based on the nonuniform transmission broadband PB super surface; wherein FIG. 6(a) is an amplitude diagram, FIG. 6(b) is a real field diagram of an electric field and FIG. 6(c) is a phase distribution;

FIG. 7 is a schematic diagram of three-dimensional far-field distribution obtained by FDTD simulation in a design method based on a non-uniform transmission broadband PB super surface; wherein FIG. 7(a) is an overall view, FIG. 7(b) is a diagram of a right-handed component and FIG. 7(c) is a diagram of a left-handed component;

FIG. 8 is a two-dimensional far-field distribution diagram obtained by simulation and testing in the design method based on the non-uniform transmission broadband PB super surface; wherein FIG. 8(a) is 8.5GHz, (b) is 9GHz, (c) is 9.5GHz, (d) is 10GHz, (e) is 10.5GHz and (f) is 11 GHz.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

To solve the above technical problem, please refer to fig. 1 to 8; the invention provides a design method based on a non-uniform transmission broadband PB super surface, which can be used for designing a broadband vortex light generator and comprises the following steps:

s1, theory deduces that when the phase difference between two linear polarizations satisfies | phi_x-φ_yPi and transmission amplitude satisfying T_x|＝|T_yWhen 1, the high-efficiency transmission of the PB unit can be realized, and the broadband PB super-surface working equation is established asWherein f is_iIs f₁To f₂Any one of a range of frequencies is used,representing the transmission phase of the right-hand circularly polarized wave when the left-hand circularly polarized wave is excited, namely the super surface has consistent phase change rate;

s2, providing a method for regulating and controlling amplitude and phase of transmitted waves by adopting a non-uniform thickness structure, wherein the transmission amplitude of the non-uniform thickness structure in a pass band changes more stably, and a non-uniform thickness system has larger bandwidth₁＝4mm，h₂6mm and h₁4mm, and the transmission phase in the range of 8.5-10.5GHzThe transmissivity reaches more than 0.8;

s3, analyzing a phase distribution equation of the surface of the vortex light generator based on the broadband non-uniform PB transmission unit, and designing and preparing a broadband transmission vortex light generator;

s4, a near-field and far-field experimental test method of the broadband transmission vortex light generator is provided, a clear vortex arm can be seen in the near-field effect of the vortex light generator, and the normal radiation depth is better than-15 dB;

s5, establishing an efficiency evaluation method of the vortex light generator, wherein the efficiency of the center frequency of the designed vortex light generator reaches 72% and exceeds 65% in the range of 8.5-10.5 GHz.

Efficient working mechanism of transmissive PB nanostructured surface: the transmission PB super surface is also called a geometric transmission super surface, and refers to a technology for realizing transmission phase change quantitatively by rotating an artificial medium unit. As shown in FIG. 1, the periodically arranged transmissive meta-surfaces are assumed to be placed in the xoy plane, which has mirror symmetry properties in the x and y axes.

For transmissive cells, where the right hand circularly polarized wave is incident in the-z direction, the electric field of the incident wave can be expressed as

The transmitted wave is

Wherein E₀Is the amplitude of the electric field, T_xAnd T_yThe transmission coefficient amplitude, phi, of the x-polarization and y-polarization components of the transmitted wave, respectively_xPhi and phi_yThe phase shift of the two perpendicular components in the x and y directions of the transmitted wave relative to the incident wave, respectively. When the cell rotates counterclockwise by an angle θ, the incident wave electric field can be expressed in a rotating coordinate system

The transmitted wave is

Because the incident wave is circularly polarized wave, the phase shift phi generated by the transmitted wave in the u direction after rotation_uPhase shift phi generated in the x direction from the transmitted wave when not rotating_xAre equal, i.e. phi_x＝φ_uIn the same way, phi_y＝φ_v. Transmission coefficient amplitude T of u polarization component of transmission wave after same rotation_uTransmission coefficient amplitude T of x-polarized component of transmitted wave without rotation_xAre equal, i.e. T_x＝T_uIn the same way as T_y＝T_vThe transmitted wave in the xyz coordinate system can then be expressed as

The transmitted wave can be obviously found to contain a left-handed componentAnd the right-hand component

Two parts

When T is_x＝T_yT and | phi_x-φ_yWhen | ═ pi, formulae (6) and (7) can be written as

At this time, only the left-handed circularly polarized wave having the opposite polarization to the incident wave is present in the transmitted wave, and the phase change amount of the transmitted wave is-2 θ, that is, 2 times the rotation angle. To make the transmitted wave a pure circularly polarized wave, | phi_x-φ_yThe value of | should be as close to π as possible; to improve the transmission efficiency, T is as close to 1 as possible.

For broadband operation, the transmissive PB super-surface is at f₁To f₂Within a frequency range

Wherein f is_iIs f₁To f₂Any one of a range of frequencies is used,

transmission of right-hand circularly polarized waves during characterization of excitation of left-hand circularly polarized wavesThe phase, that is to say the super-surface, has a uniform rate of change of phase.

Design of non-uniform PB transmission cell: based on the theoretical analysis, a transmission PB super-structural unit is designed and optimized, a structural schematic diagram is shown in FIG. 2, and the structural size parameters are p ═ 13mm, t ═ 0.5mm, and b₁＝3.6mm，b₂＝9.4mm，h₁＝4mm，h ₂6 mm. The broadband nonuniform PB transmission unit is composed of four layers of same units, each layer of unit is composed of a dielectric layer and a metal resonance structure attached to the dielectric layer, and the dielectric layer is of a thickness h₁＝0.2mm，_rThe metal resonance structure is an orthogonal cross structure which is an anisotropic structure and has good polarization isolation, and the metal resonance structure is used for regulating and controlling dielectric constant parameters in different polarization states, namely an F4B substrate with 2.65 and tan being 0.005.

The structure is optimized by simulation, so that the structure has the maximum bandwidth when the transmission coefficient is greater than 0.8, and the obtained structure size parameters are shown in figure 2. Relative to the reported transmission units, the unit of the application introduces the freedom of thickness regulation and control by adjusting h₂The parameters achieve a maximization of the transmission bandwidth. First, the polarization isolation of the cell is studied, namely, whether changing the size of one arm in the cross-shaped orthogonal structure only affects the transmission phase of the incident wave along the polarization direction, but does not affect the transmission phase of the incident wave along the orthogonal polarization direction is discussed through simulation.

FIG. 3(a) shows the change of the length b of the branch in the x-direction at a center frequency of 10GHz₁The influence on the transmission phase of the y-polarized wave can be seen as the arbitrary length b₁The influence of the change on the transmission phase of the y-polarized wave is small and can be approximately ignored; similarly, length b of the y-polarization direction arm₂The change in the transmission phase of the x-polarized wave is also negligible, so the cell can be said to be polarization independent.

Since the broadband non-uniform PB transmission unit has good polarization isolation, the transmission phase can be optimized by fixing one arm in a cross structure, adjusting the length of the other arm, and changing the length of one arm to meet the condition that the phase difference is +/-180 DEG when the two lengths are changedThe distribution being taken as the length of the two arms, i.e. ∠ t is achieved_x-∠t_yHigh efficiency condition of + -pi.

After optimization, when b₁3.6mm and b₂The difference between the corresponding transmission phases is 180 ° at 9.4mm and the parallelism of the two phase curves is best, so the parameter b for each of the two arms defining the cross is determined₁3.6mm and b₂Fig. 3(b) shows the transmission phases of x-polarized wave and y-polarized wave at normal incidence, and fig. 3(c) shows the transmission coefficients at the same conditions, as seen from the graph, in the range of 8.5 to 10.5GHzAnd T_x>0.8，T_y>0.8, a higher transmittance is ensured, i.e., the efficient and broadband conditions of equation (8-10) are verified. FIG. 3(d) shows the transmission phase and transmission amplitude distribution at different rotation angles, and it can be seen that the right-hand circularly polarized wave t is transmitted in the frequency band of 8.5-10.5GHz_RL>0.8, the cross polarization conversion of high transmittance is realized, and at the same time, when the rotation angle of the unit is theta, the variation of the transmission phase corresponding to the central frequency is-2 theta, which is consistent with the result of theoretical derivation, as shown in fig. 3(d), so that the transmission phase when the circularly polarized wave is incident can be accurately controlled by rotating the unit.

Design of broadband transmissive vortex light generator: the broadband transmission vortex light generator adopts an Archimedes spiral antenna with the aperture radius of only 15mm as a feed source,

the antenna has two advantages: the aperture of the antenna is small, so that the shielding effect of a feed source is greatly reduced, and the miniaturization of a vortex light generator system is convenient to realize; the Archimedes spiral antenna has a simple structure, is easy to process, reduces the cost, and can stably radiate circularly polarized waves in the frequency band of 8-15 GHz. The two advantages can well meet the electromagnetic radiation requirement of the feed source part of the vortex light generator. The radiation field of the archimedean spiral antenna is a spherical wave, and in order to generate a vortex wave front, a focusing phase and a vortex phase distribution need to be combined. When the antenna is located at the focus, the emitted spherical wave is first converted into a plane wave, and then the vortex sheet converts the plane wave into a vortex beam. The calculation method of the focusing phase distribution comprises the following steps:

wherein

Is the propagation constant, F₀Is the focal length of the focusing surface, which in this design is set to F₀＝80mm，

For reference phase, is selected asm and n represent the number of units in the x and y directions, and the number of units on the surface of the nanostructure can be freely selected, and m is 14. The phase distribution of the vortex plate can be calculated as:

where l is the OAM mode number of the vortex optical phase singularity, also called the topological charge number. Taking l as an example, 1, the number of working modes of vortex rotation is designed. Thus, the sum of the phases required for each transmission cell in the vortex light generator is obtained:

the rotation angle of each superunit obtained by the transmission PB theory is as follows:

FIG. 4 shows the focusing surface, vortex plate and total phase distribution during the design calculation.

Next, a vortex superstructure surface with a center frequency of 10GHz was fabricated using standard Printed Circuit Board (PCB) technology, as shown in FIG. 5 (b). The manufactured broadband transmission vortex light generator is composed of 14 multiplied by 14 units, a square array of 182mm multiplied by 182mm is formed, four layers of identical super-structure surfaces are fixed by paper boards according to the intervals of 4mm, 6mm and 4mm when the broadband non-uniform PB transmission unit is designed, and the broadband transmission vortex light generator is assembled by placing the processed Archimedes spiral antenna at the focus of the super-surface. The archimedes spiral antenna is fixed and supported by foam having a thickness of 80 mm.

Near-far field experiment of broadband transmissive vortex light generator: first, the near field performance of the vortex light generator was evaluated. The vortex light generator system is fixed on a near-field test platform, a waveguide probe of an X-wave band (8-12GHz) is adopted to perform plane scanning on a xoy plane on the transmission side of the surface of the super structure to measure the near-field electric field of the transmission wave, and a test schematic diagram is shown in fig. 5 (a). The Archimedes spiral antenna and the waveguide probe are respectively connected to two ports of a vector network analyzer Agilent AV3672B for real-time data recording so as to obtain the amplitude and phase information of an electric field. The computer controls a stepping motor to drive the waveguide probe to scan at a position of 0.2m in front of the surface of the super structure at a stepping interval of 2mm, and the scanning area is set to be 200mm multiplied by 200 mm. According to the electric field data (containing amplitude and phase information) acquired by the vector network, an amplitude, a real part and a phase diagram of the electric field on the xoy plane are calculated and extracted through an MATLAB program. As shown in FIG. 6, the amplitude, real part and phase distribution of the electric field tested in the range of 8.5-11GHz under right-handed circular polarized wave excitation. The first row of fig. 6 shows the amplitude of the test electric field, the second row shows the real part information of the electric field, and the third row shows the phase distribution. It is clear from the figure that the vortex light generator performs well in the operating band, mainly in: firstly, the amplitude of the vortex light generator is distributed in a hollow ring shape, the energy at the center of the surface of the super structure is zero, the point is a phase singularity in theoretical analysis, and the high efficiency of the vortex light generator is indirectly verified; secondly, the transmission field has obvious vortex arms from the real part field, and the number of modes l of the transmission field can be determined to be 1 from the number of the vortex arms, which is consistent with the design of the invention; third, within the operating band, experimentally tested phase data showed that the phase change contained a full 360 ° around the center of the metamaterial surface, which is in perfect agreement with the vortex optical properties analyzed theoretically. It is evident from the figure that at a centre frequency of 10GHz, the vortex light generator performs best, and no other scattering modes are present at this frequency point, and a clean vortex beam can be found.

The far field radiation characteristics of the transmissive vortex light generator were next evaluated. FIG. 7 shows the three-dimensional far-field distribution of the total, left-hand and right-hand components of the transmitted wave obtained by FDTD simulation in the frequency range of 8.5-11GHz under the excitation of the right-hand circularly polarized wave. As can be seen from the figure, in the transmitted wave, the cross-polarization component (i.e., left-hand circularly polarized component) is dominant and the same-polarization component (i.e., right-hand circularly polarized component) is very low, which is consistent with the phase theory result of the transmissive cell PB. Meanwhile, the three-dimensional far-field characteristic of the transmitted wave shows that the center of the radiation beam is in a hollow ring shape, the radiation energy in the normal direction is very small, and the gain at the zero depth is lower than-22 dB, which shows that a phase singularity is arranged at the center, and the phase singularity is not in line with the vortex light near-field characteristic. Based on the far field test platform in the microwave darkroom, the far field characteristics were tested on the xoz plane of the vortex light generator. In the experimental test, the vortex light generator system is fixed on a far-field test turntable, and the radiation fields of the vortex light generator system are tested by using left-hand circularly polarized and right-hand circularly polarized horn antennas respectively, and the far-field test method is shown in fig. 5 (d). The simulated and tested two-dimensional radiation distribution at the xoz plane in the 8.5-11GHz range is shown in fig. 8, and it can be clearly seen that there is an amplitude zero depth at the beam center, which corresponds to the results of the phase singularity in the three-dimensional far field calculated by the simulation. It is clear that the test results agree well with the simulation results, with a gain measured in the normal direction at least 10dB lower than the main beam. Particularly, the zero depth of the normal radiation amplitude of the test and the simulation in the normal direction at the central frequency of 10GHz respectively reaches-15 dB and-17 dB. In the range of 8.5-11GHz, the normal radiation levels are better than-10 dB from the two-dimensional far-field pattern (fig. 8), but the effect becomes worse beyond 10.5GHz, which is mainly determined by the cell characteristics no longer satisfying the high efficiency condition.

Efficiency calculation for broadband transmissive vortex light generator: finally, the efficiency of the vortex light generator in the broadband range is verified. When right-handed circularly polarized waves emitted by the feed source pass through the vortex light generator, transmission energy is converted into five parts: respectively transmission right-hand circularly polarized wave | T_RRL, transmission left-hand circularly polarized wave | T_LRI, reflection right-handed circularly polarized wave | R_RRI, reflecting left-handed circularly polarized wave | R_LRWhile the nanostructured surface will have a partial absorption of the incident wave energy A, in which a left-handed circularly polarized wave | T is transmitted_LRI is the vortex light signal converted by the required super-structured surface, because the absorption of the super-structured surface is fixed, the other three beams will affect the efficiency of the vortex light generator. Therefore, the left-handed circularly polarized wave | T will be transmitted_LRThe ratio of | to incident wave energy is defined as the efficiency of the vortex light generator and can be calculated as:

the four modes are integrated, according to the calculation of the formula, the efficiency of the vortex light generator at the central frequency of 10GHz is the highest, the simulation and test results are 73.5% and 72.1% respectively, meanwhile, within the range of 8.5-10.5GHz, the efficiency of the sample can exceed 65%, and the advantage that the designed vortex light generator is efficient within the broadband range is further verified. Along with the deviation of the working frequency from the central frequency, other three scattering modes can be continuously enhanced, and the mutual superposition of different scattering modes can influence the purity of vortex rotation, thereby reducing the working efficiency of the vortex rotation.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.