Performance Design Of Optically Transparent Chiral Metamirrors

Recently,metamaterials have attracted extensive attention because of their powerful ability to control electromagnetic waves.As two-dimensional counterparts,metasurfaces are composed of subwavelength units according to certain rules.Through appropriate design of the shape and the material of each unit,metasurfaces can select and manipulate electromagnetic wave’s frequency,phase and polarization.At the same time,they can realize some unique electromagnetic responses which are hard for natural materials to achieve.So they are widely used in perfect imaging,photovoltaic power generation,biosensor and other fields.Among these applications,the ability to control polarization is more prominent.As one kind of metasurface,chiral metamirror can reflect the specific circular polarization wave and absorb other incident waves at resonance frequency,which provides additional freedom for the design of electromagnetic and optical devices.We carry out a study on the performance design of chiral metamirrors.On the basis of metamirror’s coupled modes theory,we have designed two kinds of broadband chiral metamirrors with optical transparency and a gradient chiral metamirror with abnormal reflection.The specific work is summarized as follows:1.Introduce the basic theory of metasurface design,summarize the principle of absorbing electromagnetic waves and the design methods of general metasurfaces,including the realization of impedance matching,coupled mode theory and matrix analysis method,which lay the foundation for the design,simulation and inversion of metasurfaces in the following chapters.2.Establish models of the coupled mode theory,treat the incident wave and the reflected wave of the metamirror as two coherent waves that incident in opposite directions simultaneously.The key parameters affecting the bandwidth performance of the chiral metamirror are clarified3.By using the coupled mode theory,a broadband chiral metamirror based on asymmetric split-ring is designed.The bandwidth of the metamirror is about 7 times of the copper based metamirror’s bandwidth.Additionally,it has good optical transparency.Theoretical simulation and experimental tests verify that it has good performance,and has some potential applications in the integration of electromagnetic and optical devices.Based on ITO metamirror,the feasible method of realizing higher circular dichroism is proposed.By introducing the structure of nano-silver film with different sheet resistance values,a double-layer chiral metamirror is constructed.While retaining the advantages of high optical transmittance and broadband,the circular dichroism of this metamirror can be improved significantly and it makes the specific circular polarized wave which incidents on the metamirror reflect to a great extent.At the same time,the double-layer chiral metamirror also shows the characteristics of insensitive to incident angle.4.A kind of chiral metamirror with abnormal reflection is designed.The metamirror is based on asymmetric split-ring resonators.By rotating the fixed angle in sequence,RCP wave can be reflected abnormally at the resonant frequency.The metamirror can absorb LCP wave and reflect RCP wave at an angle of-32.3°,avoiding the interference caused by the coincidence of the incident wave and the reflected wave.It has some practical significance.The above work shows the design and optimization of some kinds of chiral broadband metamirrors,and analyzes the internal reasons for the unique electromagnetic response of these metamirrors.