Sharp focusing of vector optical vortices using a metalens

Using an FDTD-simulation, we numerically show that a spiral metalens with topological charge m = 1, numerical aperture 1, and a focal length equal to the incident wavelength produces a tight near-surface focal spot shaped as a circle for incident TE-waves or a doughnut for TM-waves. It is also demonstrated numerically and theoretically that in the intensity pattern of the resulting focal spot there are local (symmetric and asymmetric) regions, which can be located both at its center or on the periphery, where the energy flux has the opposite direction. For example, the reverse energy flux is found to occur at m = 1 and left-handed circular polarization or at m = 2 and right-handed circular polarization. This effect can be used for moving a microparticle in the opposite direction to the beam propagation.