LAUSR

In recent years, the integration of active materials into a metasurface to achieve tunable devices has attracted much attention. Here, we design an Au-VO2 hybrid metasurface, which can switch between quarter-wave plate and half-wave plate due to the phase transition of VO2. At 298 K, the proposed structure acts as a quarter-wave plate in the 0.87-1.2 THz band, achieving the mutual conversion between linear polarization and circular polarization. Raising the temperature to 358 K, it works as a broadband half-wave plate in the range of 0.65-1.45 THz, with the reflective chirality preservation of circular polarization and the cross-polarization conversion of linear polarization. In the above cases, the response efficiencies are both above 90%. The switchable multifunction results from the tunable geometric phase of the metasurface, where the elaborately designed Au and VO2 blocks separately bring the phase of π/2. Furthermore, the electric field and current density distributions are employed to explain the physical mechanisms leading to the different functions. Such an active broadband metasurface is expected to find applications in tunable and multifunction devices manipulating the polarization and phase of terahertz waves.