Study on a bifunctional switchable metasurface with perfect absorption and polarization conversion based on VO2 and graphene in THz region

A switchable metamaterial device with dual function (SMDDF) based on vanadium dioxide (VO2) and graphene is designed in this paper, where VO2 is a phase change material and it can transition from the insulating state to the metallic state when it is stimulated by external conditions such as heat, electricity or light. In addition, graphene is a 2D active material and its conductivity can be well controlled by adjusting its bias voltage dependent chemical potential, which makes it have the advantage of easy integration. When VO2 is in the metallic state and the chemical potential of graphene is set as 0.65 eV, the proposed SMDDF can behave as a single band absorber with the peak absorbance higher than 99.9 % at 1.8768 THz. However, when VO2 is in the insulated state, and the chemical potential of the graphene pattern layer (GPL) is set as 0 eV, the proposed SMDDF will behave as a broadband linear polarization converter. It can convert the incident linearly polarized EM waves into the cross-polarized reflected waves within the frequency range of 2.12–3.58 THz, and the polarization conversion ratio (PCR) is >90 % with the relative bandwidth (WRB) up to 51.23 %. Research results prove that the overall performances of the proposed bifunctional metamaterial device is superior to some of those reported in the literatures. Therefore, the research results of this paper may provide guidance for designing switchable multi-function terahertz devices using VO2 and graphene in variable areas of practical applications.