Broadband metasurface based on metallic stereo split-ring structure for full-space terahertz beam deflection and focusing effect

In this paper, we proposed an all-metal metasurface that enables circular polarization (CP) conversion and wavefront manipulation of the both transmitted and reflected terahertz (THz) waves over a wide frequency range. The proposed metasurface consists of a periodic array of the metallic stereo split-ring (MSSR) structure adhered on an ultrathin dielectric substrate made of benzocyclobutene (BCB). Numerical simulations show that the incident CP waves through the proposed MSSR can be converted into their orthogonal components in the full-space in a broadband range, with transmission conversion coefficients exceeding 40 % and reflection conversion coefficients exceeding 50 % between 0.8 and 1.1 THz (relative bandwidth of 31.6 %). Based on the geometric phase principle, 2π-phase full coverage can be realized by changing the rotation angle of the MSSR structure in the operating frequency range. Specifically, to demonstrate the multifunctional wavefront manipulation, we numerically simulated the anomalous deflection of THz beams and the full-space planar focusing functionality, respectively. Our research provides a valuable reference for the study of multifunctional components that possess full-space amplitude and phase modulation capabilities. This work holds particular significance in the field of device research in the THz region.