CN212905552U - Asymmetric electromagnetic wave separator based on binary ultrastructural surface - Google Patents
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Abstract
本实用新型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a1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a2均相等，相位差为π，且第一超构光栅的周期长度p1与第二超构光栅的周期长度p2满足p2＝2p1。本实用新型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 utility model discloses an asymmetric electromagnetic wave separator based on a binary meta-surface, the separator comprises a first meta-grating and a second meta-grating arranged oppositely, the first meta-grating and the second meta-grating There is an air gap between the gratings, the first super-structure grating includes a plurality of alternately arranged first structural units and a second structural unit, the second super-structured grating includes a plurality of alternately arranged third structural units and fourth structural units, the first structure The height h and width a 1 of the unit and the second structural unit are equal, the phase difference is π, the height h and width a 2 of the third structural unit and the fourth structural unit are equal, the phase difference is π, and the first superstructure The period length p 1 of the grating and the period length p 2 of the second meta-grating satisfy p 2 =2p 1 . The utility model has a good effect of splitting asymmetric electromagnetic waves, and the splitter has a simple structure and is easy to prepare, the splitting angle of the beam can be controlled by adjusting the period, and the efficiency of asymmetric transmission can be adjusted by changing the size of the air gap.
Description
Technical Field
The utility model belongs to the technical field of the electromagnetic wave propagates, concretely relates to asymmetric electromagnetic wave separator based on 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.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to provide an asymmetric electromagnetic wave separator based on binary superstructure surface.
In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:
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 a plurality of second structure units which are alternately arranged, each first structure unit comprises a metal matrix and a first medium material filled in the metal matrix, each second structure unit comprises a metal matrix and a second medium material filled in the metal matrix, each second super-structure grating comprises a plurality of third structure units and a plurality of fourth structure units which are alternately arranged, each third structure unit comprises two groups of first structure units, each fourth structure unit comprises two groups of second structure units, and the height h and the width a of each first structure unit and each second structure unit are respectively equal to the height h and the width a of each first structure unit and the width a of each second structure 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。
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,
preferably λ 650 nm.
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 d is1＜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 utility model has the advantages of it is following:
the utility model discloses asymmetric electromagnetic wave separator based on binary super structure surface all has the effect of fine asymmetric electromagnetic wave splitting under impedance match and the unmatched condition of impedance to the separator constructs simple easily preparation, can control the split angle of light beam through the regulation cycle, adjusts asymmetric transmission's efficiency through the size that changes air gap.
The utility model discloses high-efficient asymmetric electromagnetic wave separator has potential application in imaging system, sensing system etc. and small easily preparation provides more possibilities for its integration and miniaturization at optical device.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be 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 structural diagram of a second grating (MG-2) according to the present invention;
FIG. 1c is a schematic structural diagram of an asymmetric electromagnetic wave separator of 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 the magnetic field patterns when the electromagnetic wave is incident from above and below the double-layer super-structured grating with Δ ═ 0 according to the present invention, respectively, (c) and (d) are the magnetic field patterns when the electromagnetic wave is incident from above and below the double-layer super-structured grating with Δ ═ 0.5 λ according to the present invention, respectively;
FIG. 3a is a schematic diagram of a single cell structure according to an embodiment of the present invention;
FIG. 3b is a graph of medium depth d and phase and transmittance for a single cell structure according to an embodiment of the present invention;
fig. 3c and fig. 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 the magnetic field patterns when the electromagnetic wave is incident from the first grating (MG-1) and the second grating (MG-2), respectively, in an embodiment of the present invention, (c) and (d) are the magnetic field patterns when the incident electromagnetic wave is incident from above and below the double-layer super-structured grating with Δ ═ 0, respectively, in an embodiment of the present invention, (e) and (f) are the magnetic field patterns when the incident electromagnetic wave is incident from above and below the double-layer super-structured grating with Δ ═ λ, respectively, in an embodiment of the present invention;
FIG. 5 is a graph of air gap Δ and transmittance and reflectance for incident light from above a double layered super-structured grating in 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. However, the present invention is not limited to the embodiments, and the structural, method, or functional changes made by those skilled in the art according to the embodiments are all included in the scope of the present invention.
The utility model discloses an asymmetric electromagnetic wave separator based on binary super structure surface, the separator is including relative first super structure grating and the super structure grating of second that sets up, the air gap has between first super structure grating and the super structure grating of second, first super structure grating includes a plurality of first constitutional unit and the second constitutional unit that set up in turn, first constitutional unit includes metal matrix and fills the first dielectric material in metal matrix, the second constitutional unit includes metal matrix and fills the second dielectric material in metal matrix, the super structure grating of second includes a plurality of third constitutional unit and the fourth constitutional unit that set up in turn, the third constitutional unit includes two sets of first constitutional unit, the fourth constitutional unit includes two sets of second constitutional unit, the height h and the width a of first constitutional unit and second constitutional 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 utility model discloses a double-deck super structure grating (MGs for short), every layer super structure grating's supercell all only contains 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 utility model provides a solution of simplifying can control the propagation of wave in a flexible way, makes it communication transmission, has very big application prospect among optical devices such as imaging system.
In order to clearly illustrate the idea and concept of the double-layer super-structure grating of the present invention, the wave scattering of two different single-layer super-structure gratings is first studied, and the two single-layer super-structure gratings are the first super-structure grating and the second super-structure grating of the present invention, which are shown in fig. 1a and fig. 1b, respectively.
Referring to fig. 1c, the first super-structured grating 10(MG-1) includes a plurality of first structural units 11 and second structural units 12 alternately arranged, the first structural units 11 include a metal matrix 111 and a first dielectric material 112 filled in the metal matrix, the second structural units include a metal matrix 121 and a second dielectric material 122 filled in the metal matrix, the second super-structured grating 20(MG-2) includes a plurality of third structural units 21 and fourth structural units 22 alternately arranged, the third structural units 21 include two groups of first structural units 11, the fourth structural units 22 include two groups of second structural units 12, and the heights h and widths a of the first structural units 11 and the second structural units 12 are equal to each other1Are all equal, the phase difference is pi, the height h and the width a of the third structural unit 21 and the fourth structural unit 222Are 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 utility model provides an asymmetric electromagnetic wave separator satisfies:
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 binary unit structure of MG-1, and each unit structure is repeated once in a periodic structure, 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 n 0 are present. Generally, one-way propagation with n ═ 1 is better than the round-trip repeat propagation with n ═ 0. So that beam splitting of different orders with n ═ 1 can be realized for normal incidence electromagnetic waves, the splitting angle theta of the beamsIs formed by the period p2Determined, splitting angle thetas＝arcsin(λ/p2). According to the above-mentioned p1< lambda and p2The splitting angle theta of the light beam can be found when lambda is larger thansAnd may be between 30 deg. and 90 deg.. Therefore, it is considered that MG-1 and MG-2 are combined, and splitting of an asymmetric electromagnetic wave is realized by changing the air gap Δ therebetween.
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 period
a1＝p 12, for MG-2, height h is 0.5 λ, period
a2＝p2And/2, filling by using an ideal impedance matching material, wherein the metal base material is Ag, the first dielectric material is air, and the second dielectric material is an ideal material with the dielectric constant and the magnetic permeability of 2.
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 with mismatched impedance, the schematic diagram of the unit structure is shown in fig. 3a, the air groove is made on the metal substrate, and the dielectric materials with different depths (dielectric materials with mismatched impedance) are filled into the air groove so that there is a phase difference of 0-2 pi. Height h of single unit structure is 0.75 lambda, width
The width of the air slot is 180nm and the depth of the dielectric material is d. Wavelength lambda of incident electromagnetic waveWidth λ 650nm, dielectric constant of metallic silver emDielectric material with dielectric constant of 4, dielectric depth d, phase and transmission as shown in fig. 3b, d is selected to cover 2 pi phase difference1＝133nm、d2MG-1 and MG-2 were designed at 406.5nm, respectively, as in fig. 3c and 3 d.
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 can be obtained the utility model discloses a double-deck MGs still has fine effect to impedance unmatched material.
It should be understood that the present invention can realize asymmetric transmission and splitting in the impedance matching material with an air gap of 0.5 λ, and the air gap needs to be increased to be larger when the impedance unmatched material is 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 provided by the utility model, the utility model discloses following beneficial effect has:
the utility model discloses asymmetric electromagnetic wave separator based on binary super structure surface all has the effect of fine asymmetric electromagnetic wave splitting under impedance match and the unmatched condition of impedance to the separator constructs simple easily preparation, can control the split angle of light beam through the regulation cycle, adjusts asymmetric transmission's efficiency through the size that changes air gap.
The utility model discloses high-efficient asymmetric electromagnetic wave separator has potential application in imaging system, sensing system etc. and small easily preparation provides more possibilities for its integration and miniaturization at optical device.
It is obvious to a person skilled in the art that the invention is not restricted to details of the above-described exemplary embodiments, but that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. 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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