Independently tunable bifunctional terahertz metasurface based on double-layer graphene

Abstract

Artificial metasurfaces are one of the most promising candidates for realizing flexibly tunable devices. Here we propose a tunable bifunctional metasurface (TBM), which incorporates two layers of independently controllable hollow-patterned graphene that contribute to wideband linear polarization conversion mode and dual-band absorption mode, respectively. When working in linear polarization conversion mode, it can achieve the polarization conversion ratio (PCR) of over 96.1% and the relative bandwidth of about 42.2% in 3.98–6.11 THz; when operating in dual-band absorption mode, the absorptivity can reach 97.1% and 99.9% at 3.55 THz and 4.98 THz, respectively. The working mechanisms are elucidated through the eigenmode decomposition, transmission line model, surface current and field distributions. In addition, the influences of the chemical potential and relaxation time of graphene, main geometric parameters of the TBM, and incident angle of terahertz waves are discussed, implying that the TBM has excellent tunability and tolerance, and may provide a scheme for designing terahertz devices such as isolators, modulators and rotators.