Broadband transparent terahertz vortex beam generator based on thermally tunable geometric metasurface

Abstract

Metasurfaces have been successfully employed for realization of orbital angular momentum (OAM) waves, however, current available vortex beam generators suffer from low efficiency and limited bandwidth. In this study, we propose a transparent geometric metasurface composed of InSb cylindroid to generate vortex beams in terahertz region. The operating frequency can achieve broadband coverage from 1.8 THz to 4.5 THz, with a fractional bandwidth of 85.7%, by changing the temperature of the InSb cylindroid from 220K to 340K. Based on geometric phase principle, the full 2π phase shift can be obtained at the operating frequency by rotating the cylindroid. Vortex beam generators with topological charges of +1 and −2 are designed over a broadband range by employing the InSb cylindroid with different temperature. The results indicate that the generated vortex beams have high mode purity at different frequencies. The proposed vortex beam generators can reconstruct the operating frequency by directly changing the external temperature without altering the size of device, which show tremendous potential in wireless communication system. • A reconfigurable InSb metasurface is proposed to generate vortex beams in terahertz region. • The operating frequency of InSb metasurface can be reconstructed by changing the external temperature. • Generated vortex beams have high mode purity over a broadband.