Reconfigurable three multi-mode terahertz metasurface.

We designed a three reconfigurable multi-mode terahertz metasurface based on a concentric elliptical ring structure. The proposed unit cell is a concentric elliptical ring composed of copper, vanadium oxide and photosensitive silicon from the inside ring to the outside ring. The conductivity of photosensitive silicon and vanadium oxide can be adjusted by changing the external operating temperature and pump light intensity. The same unit cell can reconstruct three kinds of states with different properties, and they have completely different transmission characteristics in various terahertz bands. By encoding the arrangement, through changing external stimulus and operating frequencies, the reconfigurable terahertz metasurface can achieve multiple functions including terahertz focusing with adjustable focal length, vortex beam with different topological charge, and near-field imaging with different patterns. It provides what we believe to be a new idea for the field of information security and the design of multifunctional and multifrequency terahertz devices.