Tunable Linear Polarization Conversion In Chiral Metamaterials

Metamaterials with artificial subwavelength elements can achieve unusual electromagnetic properties that are inaccessible in naturally occurring materials.In recent years,manipulating polarization of electromagnetic waves has attracted considerable attention based on metamaterials.Chiral and anisotroptic metamaterials can realize cross-polarization conversion due to the cross coupling between the magnetic and electric responses,which is of great significance to the integration development of polarization devices.On the other hand,the study of tunable properties also possesses considerable flexibility in terms of structure design in metamaterial,which promises important applications such as optical switches,modulators and filters.The main contents of this work are two kinds of metamaterials,which are based on the theory of polarization conversion,and the polarization conversion and tunable characteristics are analyzed and studied by means of numerical simulation.The main work is as follows:?1?Design and make use of the combination of type I and type L structure to form quasi-three-dimensional chiral metamaterial structure,realize asymmetric transmission of linearly polarized terahertz wave and numerically study its geometrical parameters on the properties of metamaterials in order to achieve linear polarization conversion coefficient of the optimized double-layer IL structure.In this work,we design an optically controlled terahertz metamaterial,which is composed of a double I-I structure and semiconductor silicon.The asymmetric transmission coefficient and the circularly polarized asymmetric transmission coefficient of the terahertz line are nearly zero without pump.With illumination,the asymmetric transmission coefficient and the circularly polarized asymmetric transmission coefficients of the terahertz wave exceed 50%and 30%,respectively.?2?Based on the phase transition characteristics,we proposed the tunable switch in the terahertz band,in which the VO₂ phase transition is utilized to dynamically manipulate the polarization conversion.At different temperatures,the linear cross polarization transmittance can be switched from the"on"to the"off"state.As a result,it has the characteristics of the temperature switch.The influence of the geometrical parameters of the metamaterial on the linear polarization conversion is studied.The phase transition of VO₂can perfectly control the polarization conversion efficiency over a wide range of parameters,thus obtaining a good temperature switching effect.