Continuously tunable terahertz spatiotemporal vortex generator enabled by magneto-optical effects

Abstract

Spatiotemporal optical vortices (STOVs), characterized by transverse orbital angular momentum perpendicular to the pulse propagation direction, have shown great potential in a wide range of applications. While various methods have been developed to stably generate STOVs, schemes enabling actively tunable and independently controllable spatiotemporal vortex characteristics remain scarce. This study proposes and theoretically validates a general scheme for tuning terahertz spatiotemporal optical vortices by deliberately breaking the time-reversal symmetry of the system. The scheme can be implemented either by controlling material losses or by introducing magneto-optical (MO) effects, and this work focuses on the MO route. Using a magneto-dielectric misaligned nanograting as the platform, we induce tunable intrinsic topological singularities in the frequency–momentum space. By tuning the strength and orientation of the external magnetic field to modify the symmetry breaking of the resonant mode coupling matrix, we achieve active control over the central frequency and wave vector of the topological singularities, and reconstruct and generate terahertz spatiotemporal optical vortices wave packets at different frequencies within a finite and fixed wave vector range. In addition, this approach also provides an effective strategy to compensate for singularity shifts and wave packet distortions induced by material losses, offering a new pathway toward actively tunable spatiotemporal vortex devices in the terahertz regime.