Terahertz generations of transmissive deflection, focusing, and orbital angular momentum with polarization conversion

By coding meta-atom with discrete phase, electromagnetic wavefront can be flexibly manipulated with the pre-designed coding sequence. In this work, transmissive metasurfaces are proposed to achieve wavefront reconfiguration with polarization conversion for terahertz wave. Based on composite structures of metallic resonators and polyimides, the designed meta-atoms are capable of polarization conversion and 360° phase modulation by changing notch angle and rotation angle of resonators at 2.0 THz. Then, three types of metasurfaces are designed. Firstly, transmissive wavefront of gradient metasurface is reconstructed through periodic alignment of eight meta-atoms along x axis. This metasurface realizes anomalous transmission and transforms x-polarized incidence to y-polarized wave. Secondly, two focusing lenses are implemented, and they realize single-focusing and dual-focusing under x-polarized incidence. Finally, two vortex beam generators are proposed with orbital angular momentum modes of l = 1 and l = 2 in channel of cross polarization. Our designs may be applied in the fields of terahertz communication, focusing, and encryption.