Free Manipulation of Terahertz Wave Based on the Transmission Type Geometric Phase Coding Metasurface

In order to realize the free manipulation of terahertz beams, a multi-layer C-type unit structure is proposed to realize the phase control of the transmissionterahertz waves from 0 to 2 pi at the target frequency based on the Pancharatnam-Berry geometric phase theory. Based on the generalized Snell's law, 2-bit and 3-bit coding metasurfaces are constructed. The scattering angle of the transmissive terahertz beam can be controlled with the incidence of circular polarization wave. By using the Fourier convolution operation in the digital signal processing theory, the four-bit encoding convolution operation is performed on the coding metasurfaces of different periodic sequences to obtain a new coding sequence and realize the free adjustment of the transmission angle of the terahertz wave. The multi-layer C-encoded metasurface unit structure is used to perform rotary encoding to realize the 1st and 2nd order vortex phase plates and generate different orders of terahertz wave vortex beams.