Switchable Triple-Mode Terahertz Polarization Control Based on a Hybrid Graphene-VO2 Metasurface

We propose a gold-graphene-vanadium dioxide (VO2) hybrid metasurface capable of reversibly switching among three operational modes in the terahertz regime. The device achieves flexible polarization control by combining the insulator-to-metal phase transition of VO2 with the electrical tunability of graphene. Simulation results reveal three distinct behaviors depending on the biasing conditions of the materials. With graphene held at a chemical potential of 0 eV and VO2 in the insulating state, the metasurface acts as a linear-to-linear polarization converter. The polarization conversion ratio (PCR) exceeds 0.9 over the frequency range from 5.5 to 8.6 THz. When the graphene chemical potential is raised to 0.9 eV while VO2 remains insulating, the metasurface switches to linear-to-circular conversion. Notably, the handedness of the outgoing wave depends on the polarization of the incoming signal. Over the 6.45–8.36 THz band, the axial ratio (AR) remains below 3 dB. A third functional state emerges when VO2 switches to its metallic phase. In this state, the device simply operates as a broadband co-polarized reflector, covering the terahertz communication band from 0.1 to 10 THz. This switchable, multifunctional behavior should prove useful for terahertz communications, polarization imaging, and sensing applications.