Lightweight switchable bifunctional metasurface based on VO2: High-efficiency absorption and ultra-wideband circular polarization conversion

Switchable multi-function metasurfaces have received much attention due to their excellent performance of manipulating electromagnetic waves. In this paper, we present a novel design that can realize a high-efficiency absorber and an ultra-wideband circular polarization converter based on an anisotropic metasurface through the phase transition of vanadium dioxide (VO2). At room temperature, the metasurface acts an ultra-wideband circular polarization converter with the VO2 film maintains an insulating state, the theoretical analysis and numerical simulation show that the polarization conversion ratio reaches more than 90% in an ultra-wide band (6.3–15.0 THz) and even reaches almost 100% at two peaks, the relative bandwidth is 82%. When the temperature increases to 68 ℃, the metasurface becomes a high-efficiency absorber with VO2 film in metallic state. Numerical calculations show that the absorber has over 90% high-efficiency absorption of X-linearly polarized wave in the 10.8–13.2 THz frequency range and over 90% high-efficiency absorption of left-handed circular polarization wave in the 10.8–14.4 THz frequency range, both are angle insensitivity for small incident angles from 0° to 20°. The physical mechanisms of the two functions based on our structure are discussed. Our novel design has potential significance in future terahertz medical imaging, non-destructive detectors, polarization converters, and THz communication system.