Switchable bi-functional metamaterial based on vanadium dioxide for broadband absorption and broadband polarization in terahertz band

A switchable bi-functional optical metamaterial for broadband absorption and broadband cross-polarization conversion is proposed in the terahertz band based on the phase transition of vanadium dioxide (VO2). When VO2 is in the metal phase, the designed metamaterial has the function of a broadband absorber. This absorber consists of a VO2 top structure, a polyimide layer, and VO2 film. Calculated results show that the absorptance of the absorber is higher than 90% in the 3.33-5.62 THz range. Because of its symmetry, the absorber is insensitive to polarization and maintains high absorptance in incident angles from 0 degrees to 60 degrees. When VO2 is in the insulator phase, the designed metamaterial has the function of a broadband cross-polarization converter. This polarization converter comprises two gap gold square rings, a polyimide layer, and a gold substrate. The calculated results show that more than 90% cross-polarization conversion can be achieved at the vertical incidence of x and y polarization in the 2.54-4.55 THz range. Nearly 100% cross-polarization conversion can be achieved at 2.62, 3.29, and 4.33 THz. The designed metamaterial has a wide potential application prospect in fields including stealth technology, solar electromagnetism, and radar communication.