Controls of transmitted electromagnetic waves for diverse functionalities using polarization-selective dual-band 2bit coding metasurface

We present a polarization-selective transmission-type 2 bit coding metasurface (MS) to achieve dual-band performance, in which the operating frequency band is adjustable between the lower (K-u-band) and higher (K-band) bands by changing the polarization of the linearly polarized incident wave. Three coding MS devices are designed by using specific coding sequences of the proposed coding meta-atoms. Firstly, two coding MSs are presented for vortex beam generation that carries orbital angular momentum with different topological charges in the two operating bands. Secondly, a coding MS is proposed to anomalously refract the cross-polarized field with different deflection angles in the two frequency bands. Finally, the proposed scheme is extended to design a coding MS that focuses the transmitted fields at two frequencies by changing the polarization of the incident wave. Furthermore, the proposed designs are valid to perform the same functions for waves propagating along both the '+z' and '-z' directions in the same frequency bands but with orthogonal polarizations of incident waves. The sign of the topological charge can be altered by changing the direction of propagation from '+z' to '-z'. To demonstrate the easiness of implementations, experiments of the fabricated samples are performed for the vortex beam generation and focusing. We believe that the proposed method may find potential applications in the future optical devices for multi-spectrum and multi-function operations.