Broadband switchable terahertz half-/quarter-wave plate based on VO2-metal hybrid metasurface with over/underdamped transition

Dynamically switchable half-/quarter-wave plates have recently been the focus in the terahertz regime. Conventional design strategies lead to multilayer metamaterials or narrowband metasurfaces. Here we propose a novel design strategy and a VO₂-metal hybrid metasurface for achieving broadband dynamically switchable half-/quarter-wave plate (HWP/QWP) based on the transition from the overdamped to the underdamped resonance. Simulation results show that, by varying the VO₂ conductivity by three orders of magnitude, the proposed metasurface's function can be switched between an HWP with polarization conversion ratio larger than 96% and a QWP with ellipticity close to -1 over the broad working band of 0.8-1.2 THz. We expect that the proposed design strategy will advance the engineering of metasurfaces for dynamically switchable functionalities beyond the terahertz regime.