Terahertz ultra-broadband perfect absorption and absorption-to-transparency switching based on Brewster metasurfaces

In this paper, we propose a non-resonant tilted anisotropic Brewster metasurface to investigate its ultra-broadband absorption characteristics in the terahertz (THz) band. It consists of periodically tilted vanadium dioxide (VO₂) films arranged in a silicon dioxide substrate. Based on the anomalous Brewster effect, the metasurface can exhibit perfect broadband absorption characteristics when VO₂ is in the metallic phase. Through VO₂ phase transition to the insulating phase, the metasurface can present perfect broadband transmission characteristics, achieving a THz perfect broadband absorption/transmission switch. The effect of the structural parameters of the Brewster metasurface on its absorption performance is analyzed. Its broadband high absorption performance can not only almost cover the conventional full THz band, but also be extended to higher frequencies to achieve ultra-broadband high absorption ranging from 2 to 22.5 THz. Moreover, a gradient Brewster metasurface is designed to exhibit dynamical controllability toward THz waves with nearly omnidirectional wavefronts. The proposed metasurfaces have great potential for applications in THz stealth and THz switching devices.