Switchable VO 2 -metasurface for terahertz polarization converter and absorber

The integration of metasurfaces with functional materials has attracted significant attention for the development of active terahertz (THz) devices. In this study, we demonstrate a switchable THz metasurface incorporating vanadium dioxide (VO 2 ) phase-change material, capable of dynamically switching between three distinct operational modes: half-wave plate (HWP), quarter-wave plate (QWP), and broadband absorber. Specifically, when both VO 2 layers are in the insulating phase (IP) state, the proposed structure functions as an efficient HWP, achieving a polarization conversion ratio (PCR) exceeding 72% across a broad frequency range of 1.39-2.52 THz. When the middle VO 2 layer transitions from IP to the metallic phase (MP) state, the device switches to a QWP mode, achieving an exceptional polarization elliptical ratio (PER) of 0.98 within the frequency range of 1.20-2.20 THz. Furthermore, when both VO 2 layers are in the MP state, the metasurface functions as a broadband absorber, maintaining absorption efficiency above 68% over an ultra-wide bandwidth spanning 0.60-2.46 THz. Notably, the designed metasurface exhibits significant overlapping bandwidth characteristics within its operational frequency range. This work presents a highly effective strategy for developing reconfigurable THz devices, highlighting their significant potential for practical applications.