Space–time multimode helical light bullets in ring-core fibers

This article demonstrates that ring-core fibers support the propagation of light bullets, i.e., space–time multimode solitons, regardless of the group velocity dispersion regime. These space–time wavepackets rigidly rotate in both space and time during propagation due to the dynamic equilibrium between space- and time-group velocity dispersion and the Kerr effect. The presented analytical solutions can propagate over hundreds of nonlinear lengths without significant space–time distortion, despite suffering from modulational instabilities. Finally, it is numerically shown that helical solitons, which are solutions of the scalar two-dimensional nonlinear Schrödinger equation, remain robust even when higher-order effects are taken into account. In particular, simulations reveal that spin-orbit coupling does not alter the propagation of light bullets provided they possess a moderately high total angular momentum.