Dynamics of photonic toroidal vortices mediated by orbital angular momenta.

Abstract

The dynamics of fluidic vortex rings have long captivated researchers because of their complex behavior despite simple structure. Photonic toroidal vortices constitute a family of three-dimensional, spacetime nonseparable structured light fields carrying transverse orbital angular momentum (OAM). However, as solutions to the dispersive Maxwells' equations, these wave packets do not survive nondispersive propagation, and their dynamics remain elusive. In this article, the dynamics of photonic toroidal vortices under various dispersion regimes, mediated by transverse and longitudinal OAM, are investigated through simulations and experiments. The results reveal that the motion of a toroidal vortex is strongly affected by longitudinal OAM. The swirling flow destabilizes the toroidal structure under dispersion and induces topological transformations of vortex lines, characterized by annihilation and subsequent reformation in vacuum. The renascent toroidal vortex exhibits robust propagation in vacuum while maintaining its structure. These findings are supported by experimental validation and highlight the potential of photonic toroidal vortices as controllable channels for directional energy and information transfer.