Reconfigurable three-channel terahertz reflective metasurface.

A reconfigurable three-channel terahertz reflective metasurface based on vanadium dioxide, photosensitive silicon, gold, and silica is proposed. The unit of the metasurface adopts a six-layer sandwich structure, which is mainly designed by the composite resonator on the top layer and the back-to-back double E-shaped structure in the middle layer. Based on the geometric phase principle, through rotating the design pattern in plane, the unit in the range of 360° realizes the 3 bit quantization of the compensation phase of the metasurface's cross reflection. By adjusting the external temperature and illumination conditions, the states of two phase change materials are changed, and the encoded metasurface realizes the reflection of incident circularly polarized electromagnetic waves in three channels. Based on the convolution theorem, complex addition theorem, focusing theorem, and Gerchberg-Saxton algorithm, the phase distribution relationship of the coded metasurface is calculated. The complex wavefront control of terahertz reflected beam, such as vortex, offset focusing, and holographic imaging, can be realized simultaneously on the same metasurface. The metasurface proposed in this paper is simple in structure and reconfigurable in function, which can provide a reference for the design of efficient, lightweight, low cost, and multi-functional terahertz devices.