CN214153215U

CN214153215U - Full-polarization reflection type plane super lens based on graphene phase gradient super surface

Info

Publication number: CN214153215U
Application number: CN202120326372.9U
Authority: CN
Inventors: 丁佩; 王沛; 许军伟; 田喜敏; 曾凡光
Original assignee: Zhengzhou University of Aeronautics
Current assignee: Zhengzhou University of Aeronautics
Priority date: 2021-02-04
Filing date: 2021-02-04
Publication date: 2021-09-07
Anticipated expiration: 2031-02-04

Abstract

The utility model discloses a fully polarized reflection type flat super-lens based on a graphene phase gradient metasurface. The super-lens structure includes a metal base layer, a dielectric layer and a graphene structure arranged with a graphene ring array from bottom to top. layer, as well as an ion gel layer and a metal electrode overlaid on the graphene structure layer for the unified regulation of graphene ring Fermi energy. The utility model realizes the spatial distribution of a specific phase by periodically arranging graphene rings with different inner and outer diameters in the graphene structure layer, regulates the propagation direction of the reflected wave, and makes the reflected wave converge, and the plane superlens has no effect on the polarization state of the incident wave. Sensitive, electromagnetic waves of any polarization are effective, and the focusing effect can be dynamically tuned.

Description

Full-polarization reflection type plane super lens based on graphene phase gradient super surface

Technical Field

The utility model relates to a novel artifical electromagnetic material and electromagnetic wave regulation and control technical field especially relate to a hyperpolarization reflection-type plane super lens based on graphite alkene phase gradient super surface.

Background

In recent years, researches on artificial electromagnetic materials and structures represented by metamaterials and metamaterials have attracted extensive attention in academic circles. By designing different metamaterials and super-surface structures, people can flexibly control the intensity, phase, polarization mode, propagation mode and the like of electromagnetic waves in the frequency range from microwave to visible light, and the metamaterial-based super-surface structure is used for manufacturing various electromagnetic waves or optical devices.

The super surface is a two-dimensional form of a metamaterial and is formed by sub-wavelength artificial electromagnetic structures according to a certain arrangement mode. Compared with a metamaterial, the super surface has the characteristics of simple structure, easiness in manufacturing, convenience in integration and the like, and has huge application potential. Phase gradient metasurfaces are a class of metasurfaces that cause abrupt changes in the phase of an incident wave. The traditional electromagnetic wave or optical element realizes the phase regulation by utilizing the accumulation effect of the optical path of the electromagnetic wave (light) in the medium transmission process, and the phase gradient super surface can realize the phase mutation in the transmission distance of the sub-wavelength scale. By designing the phase gradient super surface, different phase abrupt changes can be introduced at different positions of the interface to obtain specific phase space distribution, so as to control the propagation direction of the reflected wave or the transmitted wave. The phase gradient super-surface breaks through the traditional reflection and refraction laws, can realize abnormal reflection and refraction, is used for constructing various novel electromagnetic wave regulation and control devices, and has wide application prospects in the fields of stealth, communication, holographic imaging, planar lenses and the like.

From the viewpoint of the mechanism of generation of the electromagnetic phase, the electromagnetic super surface can be classified into a resonance phase super surface using the resonance response of the microstructure and a geometric phase super surface using the anisotropic response of the microstructure. The phase mutation of the former comes from structural resonance and consists of units with different structural sizes, such as a V-shaped metal microstructure provided by the F.Capasso subject group of Harvard university at the earliest and a gradually-changed H-shaped metal microstructure provided by the peri subject group of redun university at the earliest, and the phase shift of the reflected wave can cover the range of 0-2 pi under the excitation of the linear polarized wave by changing the partial structural sizes of the units; the geometric phase super-surface is composed of the same artificial microstructures with different rotation angles, such as metal rods or metal slits which are sequentially arranged and have different rotation angles, and is used for phase control of circularly polarized waves.

Polarization or polarization is one of the most important physical characteristics of electromagnetic waves, and due to the dependency of electromagnetic response on the structure of an electromagnetic resonance unit, most of the existing super-surface structures have anisotropic structural characteristics, and only generate specific electromagnetic response under the irradiation of specifically polarized electromagnetic waves, so that a functional device constructed based on a super-surface generally has polarization sensitivity, cannot realize the same phase modulation effect on different polarized waves, and limits the application range of a phase gradient super-surface device.

Electromagnetic super-surfaces are generally composed of metal microstructures, and in order to overcome the loss of metal in high frequency band, dielectric super-surfaces based on materials such as high dielectric ceramics, silicon, titanium dioxide and the like are developed in recent years. The electromagnetic properties of a super-surface, whether metallic or dielectric, are difficult to change once fabrication is complete. In order to expand the working bandwidth of the super-surface and improve the performance of the super-surface device, researchers further explore the integration of active devices or functional materials with the traditional super-surface, change the electromagnetic parameters of the super-surface by means of the changes of environmental temperature, force, light, electricity, magnetic fields and the like, and develop a tunable or reconfigurable super-surface capable of dynamically controlling electromagnetic waves. The programmable super surface provided by the research group of the iron force of the treg of the southeast university realizes a plurality of new functions by using the loaded variable capacitance diode to regulate and control the electromagnetic resonance of different units, and provides a new idea for the design of the phase gradient super surface. However, the drastic miniaturization of dimensions in the terahertz to infrared and visible frequency ranges makes it difficult to load the cells with active devices to control the phase.

Graphene is an ideal material to achieve tunable or reconfigurable super-surfaces. Unlike traditional materials-metal, dielectric medium-which construct the super surface, the conductivity of graphene can be flexibly regulated by controlling the graphene fermi energy (carrier concentration) through bias voltage, electric field, magnetic field, chemical doping or photo-induced doping. Due to the high carrier mobility, the graphene is an excellent plasma material, and strong local surface plasmon resonance is supported in the terahertz to mid-infrared band. The graphene shows an attractive application prospect in the aspect of constructing high-performance tunable terahertz and infrared super-surface devices.

SUMMERY OF THE UTILITY MODEL

The utility model provides a work is at super surface of full polarization reflection-type graphite alkene phase gradient of terahertz frequency range, no matter the plane super lens that founds based on this super surface is linear polarization or circular polarization, homoenergetic effective work to solve present most super surface function device can only be applied to specific polarization electromagnetic wave, and the difficult harmonious problem of performance.

In order to achieve the above purpose, the utility model adopts the following technical scheme:

the full-polarization reflection type planar super lens based on the graphene phase gradient super surface comprises a metal substrate layer, a dielectric layer, a graphene structure layer, an ion gel layer and a metal electrode from bottom to top; the graphene structure layer is formed by graphene ring arrays with different inner and outer diameter sizes, so that different phase mutations are introduced at different positions of the super-surface interface to obtain specific phase space distribution, and the propagation direction of reflected waves or transmitted waves is controlled.

Preferably, the inner diameter and the outer diameter of the arranged annular graphene sheets are different, and when the inner diameter is not zero, the graphene sheets are annular patches, and when the inner diameter is zero, the graphene sheets are graphene disc-shaped patches.

Preferably, the graphene patch structure is arranged with rotational symmetry to achieve insensitivity to incident wave polarization.

Preferably, an ion gel layer and a metal electrode are arranged on the graphene structure layer, and the fermi energy of the graphene ring is regulated and controlled by constructing an ion gel top gate configuration (ion-gel top gate configuration).

Preferably, the thickness of the ionic gel layer arranged on the graphene structure layer is about 100 nm.

Preferably, the thickness of the dielectric layer is about one quarter of the wavelength of the incident electromagnetic wave propagating in the medium.

Preferably, the functional device is a graphene planar superlens.

Preferably, when the graphene rings with different geometric dimensions are arranged and meet the axisymmetric distribution, line focusing is realized, and when the arrangement meets the point symmetric distribution, point focusing is realized.

Compared with the prior art, the utility model discloses possess following advantage:

the utility model discloses, through the different graphite alkene ring of external diameter in graphite alkene structural layer periodic arrangement, can realize the super surface function device of multiple phase gradient. The planar super lens constructed on the basis of the phase gradient super surface is insensitive to the polarization state of incident waves, electromagnetic waves polarized at will are effective, and dynamic tuning of focusing performance can be realized due to the flexible and adjustable electromagnetic characteristic of graphene.

Drawings

Fig. 1- (a) is a schematic diagram of a graphene super-surface structure according to an embodiment of the present invention;

fig. 1- (b) is a schematic structural unit diagram of a graphene super-surface according to an embodiment of the present invention;

FIG. 2- (a) is a graph showing the correspondence between reflection phases of the units of the super-surface structure shown in FIG. 1- (b) and the geometric dimensions of the inner diameter and the outer diameter of the graphene ring;

FIG. 2- (b) is a graph of the reflectance of the super-surface structure unit shown in FIG. 1- (b) versus the geometrical dimensions of the inner diameter and the outer diameter of the graphene ring;

FIG. 3- (a) is a schematic diagram of a fully-polarized planar superlens structure capable of achieving line focusing based on a graphene ring super-surface;

fig. 3- (b) is a row of graphene rings aligned along the x-axis direction shown in fig. 3- (a);

FIG. 4 is a schematic diagram of the arrangement of graphene rings in a fully-polarized planar superlens structure for point focusing;

FIG. 5 shows the frequency f₀When the linear polarization wave and the circular polarization wave which are 2THz are vertically incident to the planar super lens structure shown in the figure 3- (a), the electric field convergence effect diagram of the reflected linear polarization wave and the circular polarization wave in the x-z plane is shown;

FIG. 6 is a frequency f₀When a 2THz linearly polarized wave is incident and graphene ring fermi energy is different in sequence, the electric field intensity amplitude of a reflected wave is distributed along the z axis in the y-z plane (x is 0);

in the figure: the device comprises a metal substrate layer 1, a dielectric layer 2, a graphene structure layer 3, an ion gel layer 4 and a metal electrode 5.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments.

Referring to fig. 1-6, the fully-polarized reflection type planar superlens based on a graphene phase gradient super-surface comprises, from bottom to top, a metal substrate layer 1, a dielectric layer 2, a graphene structure layer 3, and an ionic gel layer 4 and a metal electrode 5 (shown in fig. 1) for regulating and controlling graphene fermi energy; the metal substrate 1 is a reflective layer, and the material for making the metal substrate may include, but is not limited to, gold, silver, and copper, but the present invention is not limited thereto; the dielectric layer 2 should not absorb the terahertz wave and the mid-and-far infrared light strongly, the thickness of the dielectric layer 2 is about one quarter of the propagation wavelength of the incident electromagnetic wave in the dielectric, and in this embodiment, the dielectric layer 2 is made of silicon dioxide.

The graphene structure layer 3 is formed by graphene ring arrays with different inner and outer diameter sizes, different phase mutation is introduced at different positions of a super-surface interface to obtain specific phase space distribution, so that the propagation direction of reflected waves or transmitted waves is controlled, the geometric parameters of the graphene rings, namely the inner diameter and the outer diameter, are changed in the process, or the Fermi level of the graphene rings is controlled, the electromagnetic wave phase can be regulated, and the effective control on the propagation direction of reflected electromagnetic waves is realized.

The inner diameter and the outer diameter of the arranged annular graphene sheets are different, when the inner diameter is not zero, the annular graphene sheets are represented as annular patches, and when the inner diameter is zero, the graphene disc-shaped patches are represented.

The graphene patch structure has rotational symmetry so as to realize insensitivity to incident wave polarization, and the modulation effect on reflection phases is the same no matter linear polarization or circular polarization, so that full polarization work can be realized.

An ionic gel layer 4 and a metal electrode 5 are arranged on the graphene structure layer 3, and unified regulation and control of the Fermi level (conductivity) of the graphene ring can be realized by constructing an ionic gel top gate configuration and applying an external voltage. The thickness of an ionic gel (ion-gel) layer arranged on the graphene structure layer 3 is 100nm, the ionic gel has high capacitance, and the Fermi level of graphene can be changed in a large range under a small gate voltage by using the ionic gel.

The functional device is a graphene plane superlens.

When the graphene rings with different geometric dimensions are arranged and meet the axisymmetric distribution, the line focusing is realized, and when the arrangement meets the point symmetric distribution, the point focusing is realized.

As shown in fig. 1, taking the phase gradient super-surface operating in the terahertz waveband as an example, the distance between the geometric centers of two adjacent graphene rings, that is, the graphene super-surface structure unit period p, is 20 μm; in order to strengthen the plasma resonance of the graphene ring, the thickness value of the metal substrate layer 1, which is the dielectric layer 2, from the graphene layer is about one fourth of the medium wavelength of the dielectric, the utility model discloses SiO₂The layer thickness t is 20 μm; the value ranges of the outer diameter a and the inner diameter b of the graphene ring are respectively 3-9 mu m and 0-8 mu m, and the frequency f of the vertically downward incident terahertz linearly polarized wave₀Fermi energy E of graphene ═ 2THz_f＝0.6eV。

The corresponding relation between the phase and the reflection coefficient of the reflection wave of the graphene ring super-surface structure unit and the geometric dimension of the inner diameter and the outer diameter of the graphene ring is obtained by utilizing finite element electromagnetic field simulation software Commol Multiphysics simulation calculation and is shown in figure 2. As can be seen from the figure, the reflection phase change can cover the range of 0-2 pi by changing the geometric dimension of the graphene ring.

The fully polarized reflection type plane super lens is constructed based on the super surface structure of the graphene ring.

The fully-polarized reflection type convergent planar superlens structure based on the graphene ring super-surface is shown in fig. 3. Due to the fact that the inner diameter and the outer diameter of the graphene ring are different, reflection phases contributed by the super-surface structure units are also different, and the graphene ring super-surface structure unit array with specific geometric dimensions can generate specific phase gradient spatial distribution on an interface so as to change the propagation direction of reflected waves and enable the reflected waves to converge at a specific spatial position.

In fig. 3, the graphene ring structures in one row aligned in the y direction are the same, and the graphene ring structures in one row aligned in the x direction are mirror-symmetric with respect to the y-z plane (x is 0), as shown in fig. 3- (b). The planar superlens with the graphene ring arrangement shown in fig. 3 can converge incident linear polarized waves and circularly polarized waves on a straight line parallel to the y axis in the y-z plane (line focusing). If the super-surface structure units of the graphene ring are arranged in a rotationally symmetric manner with respect to the z-axis, as shown in fig. 4, the reflected waves can converge at one point (point focusing) on the z-axis, so that the graphene ring can be reasonably arranged according to actual requirements.

The planar superlens is designed in advance, and the focal length is set to 700 um. In order to realize line focusing, in the x-axis direction of the super surface, the phase space distribution should satisfy the formula (1):

in the formula, F represents a focal length, x represents an x coordinate of the geometric center position of the graphene super-surface structure unit, and lambda₀Representing the wavelength in vacuum.

The distribution of the reflection phases of the super-surface structure units sequentially arranged along the x-axis direction of the planar super-lens is shown in the insert diagram in fig. 2- (a).

Furthermore, the functional device is a reflection-type plane super lens, and can realize the linear focusing of reflected linear polarized waves and circularly polarized waves.

Further, the graphene super-surface structure units are arranged on an x-y plane, and the phase space distribution meets the formula (2):

wherein F represents focal length, (x, y) represents position coordinate of geometric center of graphene super-surface structure unit, and lambda₀Representing the wavelength in vacuum.

Furthermore, the functional device is a reflection-type plane super lens, and can realize point focusing of reflected linear polarized waves and circular polarized waves.

Further, according to the correspondence relationship between the graphene ring geometric dimension and the reflection phase/amplitude given in fig. 2, the graphene ring geometric dimensions satisfying the reflection phase distribution at different spatial positions are determined, and the graphene ring super-surface structure units having specific inner and outer diameter dimensions are arranged at corresponding positions along the x-axis direction. As shown in fig. 3- (b), the super surface of a row of graphene rings arranged along the x-axis direction includes 2n (n ≧ 20) units, and the center x is 0, and the n rings on the right side and the n rings on the left side are in one-to-one symmetry.

Fig. 5 is a diagram illustrating the focusing effect of reflected waves in the x-z plane when x (y) polarized waves and right (left) circularly polarized waves with a frequency of 2THz are perpendicularly incident on the graphene ring planar superlens structure shown in fig. 3. The reflected linearly and circularly polarized waves converge near 600um z, slightly less than 700um designed focal length F, due to the limited Number of structural elements and the small Fresnel Number of the superlens.

Fig. 6 shows that when a linearly polarized wave with a frequency of 2THz is incident and the fermi energy of the graphene layer is different, the electric field intensity amplitude of the reflected wave is distributed along the z-axis direction in the y-z plane (x is 0), and when the fermi energy of the graphene ring is increased from 0.3eV to 0.9eV, the z-axis coordinate corresponding to the peak position of the electric field intensity curve gradually decreases, which means that the focal position approaches the lens plane, the focal length of the superlens decreases, and the light intensity at the focal position gradually increases, thereby realizing dynamic tuning of the focusing effect of the superlens.

The utility model provides a super surperficial preparation of phase gradient based on graphite alkene ring can adopt following method preparation:

(1) and preparing single-layer graphene on the surface of the copper foil by using a chemical vapor deposition method.

(2) Transfer of graphene to pre-prepared SiO using wet transfer techniques₂On a metal substrate.

(3) And etching a pattern of the graphene ring array on the surface of the graphene single layer by adopting an electron beam lithography and oxygen plasma etching technology.

(4) And preparing an ionic gel thin layer with the thickness of 100nm on the surface of the graphene structure layer 3 by using a spin coating method.

(5) And preparing a metal electrode 5 on the surface layer of the gel by adopting an electron beam lithography and electron beam evaporation process, and constructing an ion gel top grid structure capable of regulating and controlling graphene Fermi energy.

The above, only be the concrete implementation of the preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and any person skilled in the art is in the technical scope of the present invention, according to the technical solution of the present invention and the utility model, the concept of which is equivalent to replace or change, should be covered within the protection scope of the present invention.

Claims

1. based on the fully polarized reflection type plane superlens of graphene phase gradient metasurface, it is characterized in that, phase gradient metasurface comprises metal base layer (1), dielectric layer (2), graphene structure layer ( 3), an ion gel layer (4) and a metal electrode (5); the graphene structure layer (3) is composed of graphene ring arrays with different inner and outer diameters.

2. the fully polarized reflection type plane superlens based on the graphene phase gradient metasurface according to claim 1, is characterized in that, the annular graphene sheet of arrangement has different inner and outer diameters, and when the inner diameter is not zero, the performance It is a ring-shaped patch, and when the inner diameter is zero, it appears as a graphene disc-shaped patch.

3 . The fully polarized reflective planar metalens based on the graphene phase gradient metasurface according to claim 1 , wherein the arranged graphene patch structures have rotational symmetry. 4 .

4. the totally polarized reflection type plane superlens based on graphene phase gradient metasurface according to claim 3, is characterized in that, described graphene structure layer (3) is provided with ion gel layer (4) and Metal electrode (5), which modulates the Fermi energy of graphene rings by constructing an ionogel top-gate structure.

5. the fully polarized reflection type plane superlens based on graphene phase gradient metasurface according to claim 1, is characterized in that, the ion gel layer (4) thickness that is set on described graphene structure layer (3) is 100nm.

6. the fully polarized reflection type planar superlens based on graphene phase gradient metasurface according to claim 1, is characterized in that, the thickness of described dielectric layer (2) is the quarter of incident electromagnetic wave propagation wavelength in medium one.

7 . The fully polarized reflective planar metalens based on graphene phase gradient metasurface according to claim 1 , wherein the functional device is a graphene planar metalens. 8 .

8. a kind of fully polarized reflection type plane superlens based on graphene phase gradient metasurface according to claim 1, it is characterized in that, when the graphene ring arrangement of different geometric sizes satisfies axisymmetric distribution, realizes line focusing, When the arrangement satisfies the point-symmetric distribution, point focusing is achieved.