Generation of Perfect Vortex Beams by Dielectric Geometric Metasurface for Visible Light

Abstract

AbstractA perfect vortex beam (PVB) is a propagating optical field carrying orbital angular momentum (OAM) with a radial intensity profile that is independent of topological charge. PVBs can be generated through the Fourier transform of a Bessel–Gaussian beam, which typically requires a well‐aligned optical setup consisting of a spiral phase plate, an axion, and a lens. Here, based on a single‐layer dielectric metasurface, the broadband generation of PVBs across the entire visible spectrum is demonstrated. The metasurface is composed of TiO2 nanopillars acting as deep‐subwavelength half‐waveplates, and able to provide the desired geometric phase profile to an incident circularly polarized light for the generation of PVBs. Through rigorous optimization of the nanopillars’ structural parameters, the authors experimentally generate vortex beams carrying OAM with different topological charges that exhibit constant radial intensity profiles, verifying their “perfect” characteristics. Furthermore, it is also demonstrated that the ellipticity and diameter of a PVB can be simultaneously controlled by adjusting the structural parameters of the metasurface, which further increases the flexibility in their design. These results open a new route towards creating ultra‐compact, flat, multifunctional nanophotonic platforms for efficient generation of structured light beams.