Full space terahertz quasi-non-diffraction vortex beam generation based on a metasurface

Abstract

The divergence of orbital angular momentum (OAM) plays a crucial role in practical terahertz OAM applications. However, most of the existing research focuses on half-space configurations, which significantly limit the utilization of space and are not aligned with the future development of wireless communication. In this paper, we present the modeling and design of two broadband high-efficiency janus transmit-reflect metasurfaces (JTRMS). These metasurfaces enable the generation of quasi-non-diffracting terahertz beams carrying OAM in the forward transmission space (FTS), forward reflection space (FRS), and backward transmission space (BTS). The key difference lies in the polarization characteristics: TRMS1 produces a left-handed circularly polarized (LHCP) quasi-non-diffracting beam in both the FTS and FRS, while generating a right-handed circularly polarized (RHCP) beam in the BTS. On the other hand, TRMS2 generates a LHCP beam in the FTS and BTS, while producing a RHCP beam in the FRS. This design allows for flexible control of the polarization of the outgoing waves in different spaces. The proposed design strategy and the high-performance janus transmit-reflect metasurfaces hold promising application prospects in future communication systems that require large capacity and support multi-directional communication scenarios.