Asymmetric electromagnetic wave separator based on binary ultrastructural surface
阅读说明：本技术 基于二元超构表面的不对称电磁波分离器 (Asymmetric electromagnetic wave separator based on binary ultrastructural surface ) 是由 徐亚东 伏洋洋 高雷 于 2020-07-06 设计创作，主要内容包括：本发明揭示了一种基于二元超构表面的不对称电磁波分离器,所述分离器包括相对设置的第一超构光栅和第二超构光栅,第一超构光栅和第二超构光栅之间具有气隙,第一超构光栅包括若干交替设置的第一结构单元和第二结构单元,第二超构光栅包括若干交替设置的第三结构单元和第四结构单元,第一结构单元和第二结构单元的高度h和宽度a<Sub>1</Sub>均相等,相位差为π,第三结构单元和第四结构单元的高度h和宽度a<Sub>2</Sub>均相等,相位差为π,且第一超构光栅的周期长度p<Sub>1</Sub>与第二超构光栅的周期长度p<Sub>2</Sub>满足p<Sub>2</Sub>＝2p<Sub>1</Sub>。本发明具有很好的不对称电磁波分裂的效果,并且分离器构简单易于制备,通过调节周期可以控制光束的分裂角,通过改变空气间隙的大小调节不对称传输的效率。(The invention discloses an asymmetric electromagnetic wave separator based on a binary ultrastructural surface, which comprises a first ultrastructural grating and a second ultrastructural grating which are oppositely arranged, wherein an air gap is arranged between the first ultrastructural grating and the second ultrastructural grating, the first ultrastructural grating comprises a plurality of first structure units and a plurality of second structure units which are alternately arranged, the second ultrastructural grating comprises a plurality of third structure units and a plurality of fourth structure units which are alternately arranged, and the heights h and the widths a of the first structure units and the second structure units 1 Equal phase difference of pi, height h and width a of the third structural unit and the fourth structural unit 2 Are equal, the phase difference is pi, and the period length p of the first super-structured grating 1 And the period length p of the second super-structure grating 2 Satisfies p 2 ＝2p 1 . The invention has good asymmetric electromagnetic wave splitting effect, simple separator structure and easy preparation, and can be controlled by adjusting the periodThe splitting angle of the light beam adjusts the efficiency of the asymmetric transmission by changing the size of the air gap.)
1. An asymmetric electromagnetic wave separator based on a binary super-structure surface is characterized in that the separator comprises a first super-structure grating and a second super-structure grating which are oppositely arranged, an air gap is arranged between the first super-structure grating and the second super-structure grating, the first super-structure grating comprises a plurality of first structure units and second structure units which are alternately arranged, each first structure unit comprises a metal matrix and a first dielectric material filled in the metal matrix,the second structural unit comprises a metal matrix and a second dielectric material filled in the metal matrix, the second super-structured grating comprises a plurality of third structural units and fourth structural units which are alternately arranged, the third structural units comprise two groups of first structural units, the fourth structural units comprise two groups of second structural units, and the heights h and the widths a of the first structural units and the second structural units1Equal phase difference of pi, height h and width a of the third structural unit and the fourth structural unit2Are equal, the phase difference is pi, and the period length p of the first super-structured grating1And the period length p of the second super-structure grating2Satisfies p2＝2p1。
2. The binary unstructured surface based asymmetric electromagnetic wave separator according to claim 1, wherein the separator satisfies:
p1＝2a1＜λ，p2＝2a2＞λ，θs＝arcsin(λ/p2)；
where λ is the wavelength of the incident electromagnetic wave, θsIs the angle of splitting of the electromagnetic wave.
3. The binary unstructured surface based asymmetric electromagnetic wave separator as recited in claim 2, wherein the first and second dielectric materials are different materials, and the first and second dielectric materials are both filled to a thickness h.
4. The binary unstructured surface based asymmetric electromagnetic wave separator as recited in claim 3, wherein the metal matrix material is Ag, the first dielectric material is air, and the second dielectric material has a dielectric constant and magnetic permeability of 2.
5. The binary unstructured surface based asymmetric electromagnetic wave separator according to claim 4, wherein the air gap thickness Δ satisfies Δ ≧ 0.5 λ.
6. According toThe binary unstructured surface based asymmetric electromagnetic wave separator of claim 3, wherein the first and second unstructured gratings satisfy: Δ ═ 0.5 λ, h ═ 0.5 λ,
7. The binary unstructured surface based asymmetric electromagnetic wave separator as claimed in claim 2, wherein the first and second dielectric materials are the same material, and the first and second dielectric materials have respective filling thicknesses d1And d2And d is1＜d2。
8. The binary unstructured surface based asymmetric electromagnetic wave separator according to claim 7, wherein the air gap thickness Δ satisfies Δ ≧ λ.
9. The binary metamaterial surface based asymmetric electromagnetic wave separator as claimed in claim 8, wherein the first and second metamorphic gratings satisfy: Δ ═ λ, h ═ 0.75 λ, preferably, λ 650nm, d1＝133nm，d2＝406.5nm。
Technical Field
The invention belongs to the technical field of electromagnetic wave propagation, and particularly relates to an asymmetric electromagnetic wave separator based on a binary ultrastructural surface.
Background
Free and efficient control of electromagnetic wave transmission is a problem that researchers are always concerned about, and the appearance of the metamaterial provides a new idea and a material basis for achieving the purpose. Two-dimensional artificial gradual change micro-nano structures (ultra-structure surfaces) gradually having ultra-thin structures and excellent electromagnetic wave regulation and control performance attract wide attention of people. Optical nanostructured surfaces have been used to achieve a wide variety of applications, including optical stealth, holographic imaging, coherent perfect absorbers, and the photon spin hall effect, among others. But the ultra-thin super-structure surface has certain limitation due to the characteristic of the structure of the ultra-thin super-structure surface, so that a non-ultra-thin gradually-changed super-structure surface (i.e. a super-structure grating) with the 2 pi mutation phase covering is provided. Perfect wavefront control, perfect abnormal transflectance and the like can be realized by inhibiting diffraction of a certain order through a reasonably designed super-structured grating.
Asymmetric electromagnetic transmission has been widely explored as one of the most important applications, enabling one-way wave propagation. But still has the disadvantages of complex overall structure, high preparation difficulty, low conversion efficiency and the like. To obtain a smooth wavefront, the surface of the superstructure is required to provide local and continuous phase shifts over its span, which is typically discretized and implemented by a large number of unit cells to achieve high resolution. Thus, these optical meta-surfaces for asymmetric transmission are typically composed of multiple cells, which not only increases the complexity of the design, but also more cells in the meta-surface can bring more absorption due to multiple reflection effects, which may degrade the performance of the asymmetric transmission.
Therefore, in view of the above technical problems, there is a need to provide an asymmetric electromagnetic wave separator based on a binary metamaterial surface.
Disclosure of Invention
The invention aims to provide an asymmetric electromagnetic wave separator based on a binary metamaterial surface.
In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:
an asymmetric electromagnetic wave separator based on a binary meta-structure surface comprises a first meta-structure grating and a second meta-structure grating which are oppositely arranged, an air gap is arranged between the first meta-structure grating and the second meta-structure grating, and the first meta-structure grating comprises a plurality of alternately arranged gratingsThe first structural unit comprises a metal matrix and a first dielectric material filled in the metal matrix, the second structural unit comprises a metal matrix and a second dielectric material filled in the metal matrix, the second super-structured grating comprises a plurality of third structural units and fourth structural units which are alternately arranged, the third structural units comprise two groups of first structural units, the fourth structural units comprise two groups of second structural units, and the heights h and the widths a of the first structural units and the second structural units1Equal phase difference of pi, height h and width a of the third structural unit and the fourth structural unit2Are equal, the phase difference is pi, and the period length p of the first super-structured grating1And the period length p of the second super-structure grating2Satisfies p2＝2p1。
In one embodiment, the separator satisfies:
p1＝2a1＜λ，p2＝2a2＞λ，θs＝arcsin(λ/p2)；
where λ is the wavelength of the incident electromagnetic wave, θsIs the angle of splitting of the electromagnetic wave.
In an embodiment, the first dielectric material and the second dielectric material are different materials, and the filling thickness of the first dielectric material and the filling thickness of the second dielectric material are both h.
In one embodiment, the metal matrix material is Ag, the first dielectric material is air, and the second dielectric material has a dielectric constant and a magnetic permeability of 2.
In one embodiment, the air gap thickness Δ satisfies Δ ≧ 0.5 λ.
In one embodiment, the first and second super-structured gratings satisfy: Δ ═ 0.5 λ, h ═ 0.5 λ,
In one embodiment, the first dielectric material and the second dielectric material are the same material, and the filling thicknesses of the first dielectric material and the second dielectric material are d1And d2And is andd1＜d2。
in one embodiment, the air gap thickness Δ satisfies Δ ≧ λ.
In one embodiment, the first and second super-structured gratings satisfy: Δ ═ λ, h ═ 0.75 λ,preferably, λ 650nm, d1＝133nm，d2＝406.5nm。
Compared with the prior art, the invention has the following advantages:
the asymmetrical electromagnetic wave separator based on the binary super-structure surface has good asymmetrical electromagnetic wave splitting effect under the conditions of impedance matching and impedance mismatching, the separator is simple and easy to prepare, the splitting angle of a light beam can be controlled by adjusting the period, and the asymmetrical transmission efficiency is adjusted by changing the size of the air gap.
The high-efficiency asymmetric electromagnetic wave separator has potential application in imaging systems, sensing systems and the like, and is small in size and easy to prepare, so that more possibilities are provided for integration and miniaturization of optical devices.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1a is a schematic structural diagram of a first grating (MG-1) in the present invention;
FIG. 1b is a schematic diagram of the structure of a second grating (MG-2) according to the present invention;
FIG. 1c is a schematic structural diagram of an asymmetric electromagnetic wave separator according to the present invention, which is composed of a first grating (MG-1) and a second grating (MG-2);
in fig. 2, (a) and (b) are magnetic field patterns of the electromagnetic wave incident from above and below the double-layer metamaterial grating having Δ ═ 0 in the present invention, respectively, and (c) and (d) are magnetic field patterns of the electromagnetic wave incident from above and below the double-layer metamaterial grating having Δ ═ 0.5 λ in the present invention, respectively;
FIG. 3a is a schematic diagram of a single cell structure in an embodiment of the present invention;
FIG. 3b is a graph of medium depth d and phase and transmittance for a single cell structure in accordance with an embodiment of the present invention;
FIGS. 3c and 3d are schematic structural diagrams of the first grating (MG-1) and the second grating (MG-2), respectively, according to an embodiment of the present invention;
in fig. 4, (a) and (b) are respectively the magnetic field patterns when the electromagnetic wave is incident from the first grating (MG-1) and the second grating (MG-2) in an embodiment of the present invention, (c) and (d) are respectively the magnetic field patterns when the incident electromagnetic wave is incident from above and below the double-layer metamaterial grating with Δ ═ 0 in an embodiment of the present invention, and (e) and (f) are respectively the magnetic field patterns when the incident electromagnetic wave is incident from above and below the double-layer metamaterial grating with Δ ═ λ in an embodiment of the present invention;
FIG. 5 is a graph of air gap Δ and transmittance and reflectance at incidence from above a two-layer super-structured grating in accordance with an embodiment of the present invention;
in fig. 6, left and right are magnetic field patterns of electromagnetic waves incident from above and below the double-layer super-structured grating having Δ 580nm, respectively.
Detailed Description
The present invention will be described in detail below with reference to embodiments shown in the drawings. The embodiments are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to the embodiments are included in the scope of the present invention.
The invention discloses an asymmetric electromagnetic wave separator based on a binary super-structure surface, which comprises a first super-structure grating and a second super-structure grating which are oppositely arranged, wherein an air gap is arranged between the first super-structure grating and the second super-structure grating, and the first super-structure grating comprises a plurality of first structure units and a plurality of second structure units which are alternately arrangedTwo structural units, the first structural unit includes the metal matrix and fills the first dielectric material in the metal matrix, the second structural unit includes the metal matrix and fills the second dielectric material in the metal matrix, the second super structure grating includes a plurality of third structural units and fourth structural units that set up in turn, the third structural unit includes two sets of first structural units, the fourth structural unit includes two sets of second structural units, the height h and the width a of first structural unit and second structural unit1Equal phase difference of pi, height h and width a of the third structural unit and the fourth structural unit2Are equal, the phase difference is pi, and the period length p of the first super-structured grating1And the period length p of the second super-structure grating2Satisfies p2＝2p1。
The invention designs a double-layer super-structure grating (MGs for short), and a super cell of each layer of super-structure grating only comprises two unit structures. It was found that the asymmetric transmission phenomenon of the electromagnetic wave, which is expressed as beam splitting and total reflection when the electromagnetic wave is incident to the double-layer MGs from the forward direction or the reverse direction, respectively, can be achieved using such double-layer MGs. Asymmetric beam splitting is achieved in a dual layer MGs with an appropriate air gap, which can be turned into symmetric beam splitting by closing the air gap, and the relationship between the size of the air gap and the transmission efficiency is obtained. Numerical results indicate that in the designed dual-layer binary MGs, both impedance-matched and impedance-mismatched materials can achieve efficient asymmetric and symmetric beam splitting. The invention provides a simplified solution, which can flexibly control the wave propagation and has great application prospect in optical devices such as communication transmission, imaging systems and the like.
To clearly illustrate the idea of the present invention and the concept of the double-layer super-structured grating, first, the wave scattering of two different single-layer super-structured gratings, namely the first super-structured grating and the second super-structured grating in the present invention, are studied, and fig. 1a and 1b are shown.
Referring to fig. 1c, the first super-structured grating 10(MG-1) includes a plurality of first structure units 11 and
The asymmetric electromagnetic wave separator of the invention satisfies the following conditions:
p1＝2a1＜λ，p2＝2a2＞λ；
where λ is the wavelength of the incident electromagnetic wave.
Referring to fig. 1c, an air gap is formed between the first and second meta-gratings 10(MG-1, MG-2) and has a thickness Δ. For the period length p normally incident with electromagnetic waves1＝2a1< λ of the first super-structured grating 10(MG-1), the transmitted and reflected waves will follow the formula:
wherein n is the diffraction order of MG-1, G1＝2π/p1Is the reciprocal lattice vector of MG-1, due to G1＞k0，k0When an incident electromagnetic wave is normally incident, the diffracted wave of non-zero order is an evanescent wave, so that only transmission and reflection of order n-0 exist. MG-1 is designed to have a two-unit structure, since the number of multiple transmissions is relatively uniform, the incident wave is totally reflected back, resulting in surface waves being bound at the transmission surface. MG-2 is designed based on the binary unit structure of MG-1, each unit is connected in a periodic structureThe structure being repeated once, i.e. p2＝2p1. When electromagnetic wave is normally incident on p2＝2a2At MG-2 > λ, the transmitted and reflected waves follow the formula:
wherein n is the diffraction order of MG-2, G2＝2π/p2Is the reciprocal lattice vector of the second grating, and G2＜k0，k0Diffraction orders of 2 pi/λ, n ± 1 and
As shown in FIG. 1c, when a TM electromagnetic wave is incident from below, the beam first splits at MG-2 and reaches MG-1 through an air gap, and diffracts according to the diffraction law of MG-1. When using TM electromagnetic waves incident from above, coupling between MG-1 and MG-2 is avoided as long as the air gap is large enough, so most of the light will be reflected back and only a small part of the beam will be cleaved. The modulation of the asymmetric beam splitting can be performed by adjusting the size of the air gap delta.
Specifically, when the incident wavelength λ is 650nm, for MG-1, the height h is 0.5 λ, the perioda1＝
When a gaussian light beam having a wavelength of 650nm is incident on the double-layer MGs having Δ ═ 0, as shown in fig. 2 (a) and (b), it is found that the light beam is efficiently split whether the incident light is incident from above or below the double-layer MGs. When a gaussian beam having a wavelength of 650nm is incident on the double-layered MGs having Δ ═ 0.5 λ, as shown in fig. 2 (c), when the incident light is incident on the double-layered MGs from above, the incident light beam is almost completely reflected by MG-1, and an extremely low zero-order transmitted wave impinges on MG-2, resulting in very weak beam splitting. As in fig. 2 (d), when the incident light is incident from below the double-layer MGs, the light beam is split and the refraction angle is 45 °. Therefore, the feasibility of the theory is verified, and the double-layer MGs are proved to have a good asymmetric splitting effect on the light beams.
In another aspect of the present invention, when the filling material is a material having impedance mismatch, a schematic diagram of a cell structure is shown in fig. 3a, air grooves are made on a metal substrate, and dielectric materials (impedance mismatch dielectric materials) having different depths are filled into the air grooves so that a phase difference of 0-2 pi exists. Height h of single unit structure is 0.75 lambda, width
When the wavelength of the incident electromagnetic wave is 650nm, MG of a single layer is first verified. As shown in fig. 4 (a) and (b), when the incident light is incident on MG-1, it can be seen that substantially all reflection is achieved, when the incident light is incident on MG-2, the light beam is split into two beams and the emergent angle is about 45 °, and weak transmission and reflection of other diffraction orders also exist, which indicates that the designed structure is reasonable.
Further expanding the research into the double-layered MGs structure, as shown in fig. 4 (c) and (d), when the air gap Δ is 0, a good splitting effect can be seen for the light beam regardless of whether the incident wave is incident on the double-layered MGs from above or from below. When the air gap is expanded to Δ ═ λ, as in fig. 4 (e), when the incident wave is incident from above the double-layer MGs, the light beam is perfectly reflected back, as in fig. 4 (f), and the incident wave is incident from below the double-layer MGs, the light beam can pass through the double-layer MGs smoothly and be cleaved. Based on these phenomena, the double-layer MGs designed by the present invention still have good effect on impedance mismatched materials.
It should be understood that asymmetric transmission and splitting can be achieved with an air gap of 0.5 λ in the impedance matching material, and that the air gap needs to be increased to be larger when impedance mismatched materials are used.
According to the graph of the air gap, the transmittance and the reflectance shown in fig. 5 obtained by numerical simulation, it can be found that the reflectance is increased with the increase of the air gap Δ, and finally the reflectance is smoothed after reaching 0.8, and the transmittance is gradually reduced and finally reaches zero. The reflectivity is up to 0.8 due to unavoidable absorption by the metallic material, so that a controllable asymmetric transmission can be achieved by controlling the air gap Δ. As the air gap Δ increases, the reflectivity fluctuates significantly, and it can be found whether there is some reflection at the air gap Δ from below the double layer MGs. An optimum point Δ 580nm can be found where the reflection tends to zero. When the incident wave is incident from above the double-layer MGs as in the left diagram of fig. 6, the light beam is perfectly reflected back, whereas when the incident wave is incident from below the double-layer MGs as in the right diagram of fig. 6, the light beam can pass through the double-layer MGs smoothly and be cleaved and the reflection is very weak. The effect of the air gap on the efficiency of the asymmetric transmission is thus demonstrated.
According to the technical scheme, the invention has the following beneficial effects:
the asymmetrical electromagnetic wave separator based on the binary super-structure surface has good asymmetrical electromagnetic wave splitting effect under the conditions of impedance matching and impedance mismatching, the separator is simple and easy to prepare, the splitting angle of a light beam can be controlled by adjusting the period, and the asymmetrical transmission efficiency is adjusted by changing the size of the air gap.
The high-efficiency asymmetric electromagnetic wave separator has potential application in imaging systems, sensing systems and the like, and is small in size and easy to prepare, so that more possibilities are provided for integration and miniaturization of optical devices.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
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