Two-dimensional optical nanovortices at visible light

Abstract

This work demonstrates optical vortices of visible light confined to tens of nanometers. Confinement to such dimensions is considered beyond standard optical capabilities. The significant down-scaling is achieved by engineering a short-wavelength platform, consisting of high-index dielectrics and metals that support hybrid photonic-plasmonic modes of very short wavelength propagating in two dimensions. Additional confinement is achieved using super-oscillations between two guided modes in carefully designed waveguides. The authors utilize phase-resolved near-field measurements to demonstrate optical vortices with topological charge as high as five that are still smaller than the size of a diffraction-limited spot of the illuminating light. The size of the vortices may allow for future orbital-angular-momentum based light-matter interactions with quantum systems.