Numerical investigations of generation and switching of perfect vortex beams based on Ge2Sb2Te5 metasurface

Vortex beams are a special kind of beams that have significant applications in many fields due to their ability to carry orbital angular momentum (OAM). Metasurfaces have obtained increasing attention due to their extremely small size and excellent wavefront modulation ability. Despite significant progress, most existing metasurfaces lack the ability for dynamic modulation. In this paper, we propose a tunable perfect vortex beam (PVB) generator for the mid-infrared band. Pre-designed metasurfaces can generate PVBs with topological charges (TCs) of +4, +1 and -2 in the far field. Numerical simulations demonstrate that the generation and switching of PVBs in the superposition field could be achieved by controlling the phase states of Ge2Sb2Te5 (GST) at different spatial locations. This study provides a simple and feasible scheme based on the unique properties of phase-change materials, which can achieve the generation and dynamic control of composite vortex beams in the mid-infrared band.