Propagation Dynamics of Photonic Toroidal Vortices Mediated by Orbital Angular Momenta

TL;DR

This paper investigates the complex propagation behavior of photonic toroidal vortices carrying orbital angular momentum, revealing how dispersion and angular momentum influence their stability and topological transformations, with experimental validation.

Contribution

It provides the first detailed analysis of how longitudinal and transverse orbital angular momentum affect the dynamics and stability of photonic toroidal vortices under dispersion.

Findings

Longitudinal orbital angular momentum destabilizes vortices under dispersion.

Vortices undergo topological transformations including annihilation and reformation.

Photonic toroidal vortices can propagate robustly in vacuum after reformation.

Abstract

The dynamics of vortex rings in fluids have long captivated researchers due to the intriguing complexity of their behavior, despite the apparent simplicity of their structure. In optics, photonic toroidal vortices constitute a novel class of three-dimensional, space-time nonseparable structured light fields that carry transverse orbital angular momentum. However, as solutions to the dispersive form of Maxwell's equations, these wavepackets do not survive upon nondispersive propagation, and their dynamics remain elusive. In this article, the dynamics of photonic toroidal vortices under various dispersion regimes, mediated by both transverse and longitudinal orbital angular momentum, are investigated through simulations and experiments. The results reveal that the motion of a toroidal vortex is strongly affected by the presence of longitudinal orbital angular momentum. The swirling flow destabilizes the toroidal structure under dispersion conditions and induces topological transformations in the vortex line characterized by its annihilation and subsequent reformation in vacuum. Remarkably, the renascent toroidal vortex exhibits robust propagation in vacuum while maintaining its toroidal 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.