Reach On Terahertz Wave Polarization Dynamic Control Devices Based On Vanadium Dioxide Metasurface

Terahertz（THz）waves have the characteristics of low energy,high penetration,broadband and fingerprint spectrum,and have broad application prospects in security inspection,imaging,sensing,communication,biomedicine and other fields.Polarization conversion is essential in many terahertz wave applications,and it is also one of the research hotspots in the field of terahertz.Traditional polarization converters have the disadvantages of low conversion efficiency,large volum,and narrow bandwidth,and the emergence of metasurfaces provides important ideas to solve these shortcomings.By changing its structure or dynamic reconstruction,the equivalent electromagnetic parameters can be freely designed,so as to realize the dynamic regulation of electromagnetic waves.Vanadium dioxide（VO₂）is a phase change material,which can change from insulating to metallic under external stimulation,which is of great significance for constructing reconfigurable metasurfaces to achieve dynamic regulation of terahertz waves.Paper main work content is as follows:（1）Theoretical research on polarization regulators.Firstly,the research status of terahertz metasurface and metasurface polarization regulators at home and abroad is analyzed.Then,polarization classification,metasurface correlation theory,and metasurface polarization regulator structure design methods are studied.Finally,the phase transition mechanism and preparation method of vanadium dioxide were studied.（2）A terahertz asymmetric reflective polarization device based on VO₂composite metasurface was designed.The device is composed of metal aluminum substrate,polyimide（PI）dielectric layer,VO₂ and aluminum（Al）composite metasurface.The unit cell has two concentric oblique-split-ring-resonators（OSRRs）connected by patterned VO₂.When VO₂is in the insulated state,the polarization conversion rate（PCR）in the range of 0.56～1.21THz is higher than 90%;Circular polarization conversion of lines is also possible at 0.48THz and 1.31 THz.When VO₂ is in the metallic state,the PCR value is higher than 90%in the range of 0.58～0.78 THz.Linear circular polarization conversion is possible at 0.52 THz and 0.91 THz.（3）A polarization converter using VO₂ to achieve transmission reflection polarization switchable is designed.Each unit cell consists of a metal metasurface layer,a polyimide dielectric layer,and a metal grating layer inlaid with vanadium dioxide.When VO₂ is insulated,the conversion from common polarization to cross-polarization is realized in the range of 0.74～1.76 THz.When VO₂ is in a metallic state,the linear polarization wave can be converted into a left-handed circular polarization wave in the range of 0.91～0.96 THz,and the mutual conversion between y-polarized wave and x-polarized wave can be realized between 1.25～1.87 THz.The two polarization converters designed in this paper can dynamically regulate the polarization state of terahertz waves by thermal excitation,which has potential application value in the field of terahertz communication and imaging.