Backward Energy Flux in Sharp Focus of Beams with Linear and Circular Polarization

Using the FDTD-aided numerical simulation, we show that uniform linearly or circularly polarized light passing through the described optical metasurface and then tightly focused with a binary zone plate generates an on-axis near-focus energy backflow comparable in magnitude with the incident energy. Notably, the magnitude of the reverse energy flow is shown to be the same when focusing a circularly polarized optical vortex with topological charge m = 2 and a light beam with the second-order polarization singularity.