VO₂-based reconfigurable metamaterial enabling switchable single-dual-band asymmetric transmission at terahertz...

To address the challenge of dynamically controlling the operating bands of terahertz wave polarization conversion, we propose a tunable terahertz metamaterial device capable of switching its asymmetric transmission between single-band and dual-band modes. The device consists of a top layer of gold and vanadium dioxide, separated from the bottom layer by a polyimide spacer layer. The bottom layer is a mirror-symmetric and 90°-rotated configuration of the top structure. Leveraging vanadium dioxide's phase transition property from an insulating to a metallic state upon heating enables the tunability of incident terahertz waves. In the metallic state, the structure exhibits pronounced single-band asymmetric transmission, with a transmission coefficient T_yx reaching 0.85 at 1.54 THz, while T_xy remains at 0.06. In the insulating state, dual-band asymmetric transmission is observed, with peak T_yx values of 0.786 at 1.45 THz and 0.783 at 2.0 THz, and corresponding T_xy values of 0.06 and 0.07, respectively. Analysis of the structural surface currents reveals that the structure excites asymmetric dipole current resonance, which enables cross-coupling between the incident electric field and induced magnetic field, resulting in asymmetric transmission. The introduction of the coupled-mode theory abstracts the metamaterial as a coupled dual-resonator system, thereby providing further insights into the physical mechanism of dual-band polarization conversion. This tunable asymmetric transmission device presents a promising approach for expanding the applications of filters and tunable optoelectronic devices.