Ultra-broadband high-efficiency circular polarization conversion and terahertz wavefront manipulation based on an all-metallic reflective metasurface

In this paper, an all-metal metasurface (MS), which can achieve high-efficient reflective circular-polarization conversion and multifunctional terahertz (THz) wavefront manipulation in an ultra-broadband frequency range, is proposed and investigated theoretically. The proposed all-metal MS consists of the periodic array of a gold vertical-split-ring (VSR) structure adhered on gold substrate. Numerical simulation results indicate that the proposed MS structure can convert the incident circular-polarization (CP) wave into its orthogonal component after reflection with a conversion coefficient over 95% from 0.8 to 1.65 THz (relative bandwidth of 68.3%). The full 2π phase shift of the proposed MS in this frequency range can be obtained by changing the rotation angle of the VSR structure along the wave propagation direction. As proof of concept for the multifunctional wavefront manipulation, anomalous reflection, reflective planar focusing, and vortex beam generation are numerically demonstrated based on the Pancharatnam-Berry (PB) phase principle. Our work can provide an effective method of enhancing the performance of reflective-type all-metal MS and show endless potential in wavefront manipulation and communication applications in THz and even optical region.