Fully-control of OAM vortex beam and realization of retro and negative reflection at oblique incidence using dual-band 2-bit coding metasurface.

Abstract

This paper addresses a reflection-type dual-band 2-bit coding metasurface (CM) design to achieve the dual-band functionalities in two different operating bands, independently. We are particularly interested to control linearly-polarized incident waves by encoding the propagation / dynamic phase in order to realize and fully control the orbital angular momentum (OAM) vortex beam (VB) for dual-band, independently. In this regard, we perform digital addition operations to combine the coding sequences of traditional OAM and phase-gradient to construct the proposed CM. The proposed CM generates and steers the OAM-VB with different topological charges in both lower and higher bands, independently. Similarly, the proposed CM is further extended for OAM-VB shaping by combining the coding sequences of traditional OAM and splitting phase unit-cells, and, we discuss two different scenarios. Firstly, OAM-VB splitting is performed to achieve different topological charges in both lower and higher bands, independently. Secondly, quad-beam shaping is realized to verify the proposed concept of this paper. Finally yet importantly, we also examine that the reflected beam directions can be further independently controlled to achieve anomalous, negative and retro-reflection at two different operating bands. The proposed concept will open up possibilities of multi-functional meta-devices and will be useful in many applications such as optical spanners, quantum optics, spatial mode multiplexing for telecommunications, and astronomy etc.