Vortex beam generator based on single-layer porous metasurface

Based on the geometric phase theory, a broadband terahertz wave vortex beam generator based on a transmissive plasmonic metasurface is proposed. The metasurface is composed of rectangular holes on a gold film. By deriving the relationship between the unit rotation angle and azimuth angle, arranging the rectangular holes can generate vortex beams with different topological charges. In this paper, three vortex phase plates with different topological charges are designed. The performance of metasurface vortex beam generators under normal incidence of circularly polarized beams is analyzed and discussed. In the bandwidth range of 2 THz–3 THz, the transmission efficiency can reach about 24%. The designed device is close to the transmission limit of a single-layer transmissive metasurface.