Terahertz Wave Tunable Metalens Based on Phase Change Material Coded Metasurface

Based on phase change material and Pancharatnam-Berry phase principle, a tunable coded metasurface is designed to realize terahertz wave metalens. When the vanadium dioxide phase change material is reversibly converted from metal state to medium state, the lens can achieve the tunable function of reflection focusing and transmission focusing. The unique feature of our tunable metalens is that when the vanadium dioxide material is in the medium state, the silicon cuboid column plays the main role. We can rotate the silicon column structure to obtain the geometric phase coding unit. When the phase change material is in the metallic state, the vanadium dioxide metal rod structure plays the main role and rotates the element structure to obtain the reflective geometric phase coding element. In order to control the focus position of the transmission-reflection tunable metalens, we further designed non-central focusing and bifocal focusing metalens.