Research On Graphene-based Electrically Controllable Terahertz Polarization Modulation Devices

Terahertz polarization modulation technology is widely used in many fields such as imaging,detection and communication.However,there is still a lack of effective methods to realize electrically controllable terahertz polarization control via traditional materials.Graphene is widely used in various electrical adjustable devices due to its adjustable properties.This article focuses on graphene-based terahertz polarization electrically controllable technology.The research content and results are as follows:A graphene-based electrically controllable terahertz polarizer is proposed,which is composed of a periodic array of asymmetric cross metal-dielectric-graphene sandwich structures and is located on a dielectric substrate supported by a thick metal film.By properly designing structural parameters and Fermi level of graphene,absorption with orthogonal directions can be obtained,corresponding to two polarizers with orthogonal polarization directions.Numerical simulation results show that the structure can realize the orthogonal conversion of the polarization direction at a specific frequency by electronically adjusting the Fermi level.At the operating frequency of 25.215 THz,the polarization extinction ratio of the polarizer in both states reaches above 25 d B.Electrically controllable conversion of terahertz half-wave plate and quarter-wave plate is realized based on graphene.The structure consists of a periodic array of rectangular metal-dielectric-graphene sandwich structures on a dielectric substrate supported by a thick metal film.Graphene and cross metal are used to provide magnetic plasmon resonance to obtain tunable phase delays of 90° and 180°,corresponding to quarter-wave plate and half-wave plate,respectively.Numerical simulation results show that the structure can realize the conversion between two wave-plate states at a specific frequency by adjusting the Fermi level.Both states exhibit high energy conversion efficiency,83% and 90% respectively at 15.96 THz,and the polarization conversion ratio is close to 1.