Broadband terahertz holography using isotropic VO2 metasurfaces

Vanadium dioxide (VO₂) exhibits exceptional phase transition characteristics that enable dynamic manipulation of electromagnetic wave. In this study, a novel design of bilayer isotropic metasurface is introduced. It leverages insulating-to-metallic phase transition of VO₂ to enable broadband holography for terahertz wave. For the metallic VO₂, the upper VO₂ antennas reflect incident terahertz wave and generate hologram. For the insulating VO₂, incident wave is reflected by the lower gold antennas and the same hologram is generated with frequency doubling. Working frequencies of the designed holograms are 1.2 THz for metallic VO₂ and 1.9 THz for insulating VO₂. Due to the broadband performance under each state, the proposed metasurface can achieve holography within 1.0-2.1 THz. It is noteworthy that the generated holograms under two states of VO₂ remain entirely independent, and another metasurface that achieves frequency-multiplexed holograms is presented. Our design may have possible applications in holographic display and information encryption.