Extremely Simplified Binary-Phase Metasurfaces for Circularly Polarized Terahertz Waves Manipulation

Phase and wavefront manipulations of circularly polarized waves is one of the important topics in electromagnetic metasurfaces. The main methods currently used are to construct multi-valued phase gradients using Pancharatnam-Berry phase, chiral phase, or hybrid phase. However, such schemes require massive parameter calculations and selections. Here, we propose a new scheme for circular polarization multiplexed wavefront manipulation based on binary-phase metasurfaces demonstrated in the terahertz band. Using only two rectangular resonators with different sizes and their four derived meta-atoms obtained by introducing geometric phase, we have demonstrated two silicon metasurfaces with functions of dual-channel longitudinally separated focusing for circularly polarized beams and vector beam generation using the principle of phase-type Fresnel zone plates. Both simulation and experimental results show that the metasurfaces have strong performance of wavefront control for orthogonal circularly polarized terahertz waves at the design frequency of 0.7 THz. This simplified method for circularly polarized electromagnetic wave manipulation can also be extended to other bands, as well as for additional applications such as beam splitting, holography, and other wavefront design.