Ultrabroadband vanadium-dioxide-based metamaterial absorber based on two resonance modes at a terahertz frequency

Abstract

A terahertz (THz) ultrabroadband metamaterial absorber consisting of a periodically patterned vanadium dioxide (VO2) array, loss-free dielectric layer, and a continuous gold film is designed. Its resonance features can be dynamically tuned by applying different temperatures to the VO2 to promote phase transformation. When the VO2 is in the metallic state, the designed metamaterial has an absorption bandwidth of 6.08 THz with an absorptivity more than 90%, from 3.84 THz to 9.92 THz. The broadband absorption is attributed to the combination of two absorption peaks localized at 4.73 THz and 9.05 THz that are based on the localized resonance mode and surface lattice resonance mode. Taking advantage of the temperature phase transition of  VO2, the designed absorber can be switched between ultrabroadband absorption and near-total reflection. Its maximum modulation depth can reach 99%, and it achieves an excellent modulation effect with a bandwidth of about 6 THz. The physical mechanism of the ultrabroadband absorption is discussed through an analysis of the near-field distribution and the current density distribution of the absorption peaks. The effect of structural parameters on the absorption are also investigated. The designed metamaterial absorber could have application potential in THz imaging, THz communications and smart devices.