Broadband Generation of Fractional Perfect Optical Vortices via Plasmonic Metasurface

A fractional perfect optical vortex (FPOV) represents a class of structured light characterized by phase singularities carrying fractional orbital angular momentum (OAM). It manifests a notched annular intensity distribution, and notably, the size of this distribution remains independent of the topological charge. Conventional methods for generating FPOVs involve a series of cascaded bulk components, leading to optical aberrations due to alignment errors and impeding their integration into highly integrated devices. In this work, an experimental demonstration is presented of the broadband generation of FPOVs in the visible spectrum utilizing a monolithic plasmonic metasurface with phase-only modulation. The metasurface allows for flexible control of various parameters of the FPOVs, including their topological charge, beam radius, ellipticity factor, orientation, and the number of opening gaps. Furthermore, as a proof-of-concept, an FPOV pair is utilized to encode a double-digit hexadecimal number, showcasing the potential of a metasurface array for optical information encryption. This research establishes a highly integrated platform for FPOV generation, with implications for advancing their applications in optical information security.