Terahertz Polarization Converters Based On Novel Metasurface

Polarization is an important feature of terahertz waves,and traditional terahertz wave polarization conversion devices are large in size and have serious dispersion.Metasurface is an artificially constructed ultra-thin two-dimensional array plane,which is conducive to the miniaturization and integration of terahertz systems.Therefore,the use of metasurfaces to control the polarization of terahertz waves can successfully get over the flaws of traditional polarization converters.In this paper,the goal of terahertz wave polarization control is to construct a reconfigurable metasurface through vanadium dioxide and graphene to realize dynamic control of terahertz wave polarization.Here are the three parts:1.The basic theory of terahertz wave polarization control on metasurfaces has been studied,and the design and optimization methods of polarization control devices based on metasurfaces have been studied;the characteristics of vanadium dioxide and graphene have been studied,and the supersurface based on vanadium dioxide and graphene has been studied.Method for constructing surface terahertz functional devices.2.Based on the metal-vanadium dioxide composite metasurface,a broadband,high-efficiency,and functionally switchable half-wave plate and quarter-wave plate is designed.When the linearly polarized terahertz wave is incident perpendicularly,by adjusting the temperature of vanadium dioxide,the polarization direction of the terahertz wave in the frequency range of 0.66-1.40THz can be rotated by 90°,or can be converted into a circularly polarized wave.The bandwidth is 71.8%.In addition,the polarization converter also exhibits good performance when it is incident obliquely within a certain angle range.3.Based on the metal-graphene composite metasurface,a broadband tunable terahertz half-wave plate and quarter-wave plate are designed.When the graphene Fermi energy level is 0eV,the device is in the range of 0.68-1.36THz.With half-wave plate function,the polarization conversion rate is greater than 90%.After simulation verification,the half-wave plate can also achieve better results when the oblique incidence angle is less than 30 °.When adjusting the Fermi level of graphene to 0.5eV,the device has a quarter-wave plate function and the ellipticity is 0.99 in the range of 0.75-1.32THz.In addition,when the Fermi level changes from 0-1eV,continuous adjustment of the polarization conversion rate can be realized,and the adjustable range of the polarization conversion rate is 90%-20%.The dynamic control method of terahertz wave polarization proposed in this paper has important reference value for the design of active control device of terahertz wave.