Multiplication of polaritonic vortices via sublinear dispersion

Optical vortices promise enhanced optical and quantum information processing via the orbital angular momentum multiplexing. Nanophotonics opens the possibility of realizing subwavelength optical vortices through coupling optical beams into subwavelength surface polaritons in the near-field, although the topological charge is always fixed. We report dispersion-driven topological charge multiplication by leveraging the strong sublinear dispersion of low-loss surface phonon polaritons on silicon carbide membranes, capable of switching the topological charges within a small ∼3% frequency range in the mid-infrared frequency range. This offers the possibility of all-optical ultrafast switching of optical vortices at mid-infrared frequencies.