Polarization insensitive tunable terahertz coding metasurface based on vanadium dioxide

Abstract

Coding metasurface has attracted much attention due to its flexible design of coding sequences and powerful control ability of light beams. However, the traditional coding metasurfaces with pin-diode switches between two metallic patches are usually used in the microwave band. Few studies have been carried out in the terahertz (THz) region with tunable metastructures. In order to realize the dynamic modulation of terahertz metasurface, in this paper we use the phase change material vanadium dioxide (VO2) to activate modulation coding metasurface in the terahertz band. We designed a VO2 embedded hybrid structure with metallic patches as the metasurface unit, which can produce a 180- degree phase change near 0.69 THz during the phase transition of VO2 from an insulating state to the metallic state. Meanwhile, we have constructed a metasurface array with the above designed tunable VO2 components and non-tunable metallic units to realize the dynamic switching of the far-field beam at that frequency. Our simulated results indicate that when the VO2 conductivity increases from 200 to 200000 S/m, the far-field reflected beams of the metasurface array can change from the separation of about 41° apart to close together. Notably, this coding metasurface will remain the reflectivity higher than 0.76 at the working frequency and exhibit polarization insensitive feature to the incident light. The active coding metasurface we designed provides a new idea for flexible beam control and has broad application prospects in terahertz functional devices.