A simple structured and homo-frequency point mode switchable THz full-space metasurface based on temperature-controlled vanadium dioxide

Abstract

Terahertz (THz) full-space metasurfaces have attracted great attention in the field of modern communication systems due to their inherent advantages in electromagnetic (EM) wave manipulation. However, nearly all the reported full-space metasurfaces are realized by multilayer dielectric cascade structures. Furthermore, for mode switchable metasurfaces, reflection and transmission modes are always switched at different frequency points, which limits their application prospects. In this paper, we propose a full-space THz metasurface that can switch between reflection and transmission modes at the same frequency point only by controlling a single substrate layer of vanadium dioxide. The reflection and transmission properties can be independently controlled by rotating the optimized meta-atoms on the metasurface independently. To demonstrate its application potential for multifunctional devices, full-space focusing vortex beam generator and near-field imaging are practiced. A mode switchable focusing vortex beam generator using right circularly polarized (RCP) light at 1.312 THz is designed. The mode purity of the vortex beam under both the transmission and reflection directions is above 85 %. Then a full-space near-field imaging of letters “UPC” at 200 μm from the reference plane is achieved both in the reflection and transmission direction. The transmission and reflection modes can be switched simply by regulating the temperature of the vanadium dioxide substrate through a thermistor. Our suggested design concept of homo-frequency points and simple structure is more conducive to future practical engineering applications of metasurface and provides a worthwhile direction for future research of full-space functional devices.