Difunctional terahertz metasurface with switchable polarization conversion and absorption by VO2 and photosensitive silicon

Abstract

In this study, a terahertz (THz) switchable multifunctional metasurface is proposed to realize polarization conversion and absorption. When vanadium dioxide (VO₂) is in the dielectric state, the structure demonstrates polarization conversion with double broadband transmission. The transmittance of the double broadband is greater than 80% in the frequency ranges of 2.05–2.38 THz and 3.38–3.68 THz, and the polarization conversion rate (PCR) is greater than 90%. Excellent asymmetric transmission (AT) properties are exhibited by polarization conversion. The transmittance of the double broadband can be modulated dynamically by the pump light by controlling the conductivity of the photosensitive silicon (PS). When VO₂ is in the metallic state, the metasurface is switched to be a bidirectional THz absorber for TE and TM wave incidence, and the maximum absorptance of the absorber can reach more than 95%. Furthermore, the absorption is insensitive to the angle of incidence, and the absorption frequency and intensity can be dynamically tuned by changing the polarization angle. By changing the conductivity of the PS, the intensity and frequency of the absorption can also be adjusted. Using the metasurface, we achieved a dynamic multiplexing imaging function for linearly polarized waves. The metasurface showed a new vision for multifunctional THz devices and exhibited a wide application prospect in the field of THz imaging.