Multiplication of the orbital angular momentum of phonon polaritons via sublinear dispersion

TL;DR

This paper demonstrates a method to multiply the orbital angular momentum of phonon polaritons by exploiting their sublinear dispersion, enabling on-chip topological charge control within a narrow frequency range.

Contribution

It introduces dispersion-driven topological charge multiplication for phonon polaritons, allowing dynamic control of optical vortices on-chip without structural modifications.

Findings

Topological charge can be switched within 3% frequency range.

Sublinear dispersion enables charge multiplication.

Near-field imaging confirms topological order manipulation.

Abstract

Optical vortices (OVs) promise to greatly enhance optical information capacity via orbital angular momentum (OAM) multiplexing. The need for on-chip integration of OAM technologies has prompted research into subwavelength-confined polaritonic OVs. However, the topological order imprinted by the structure used for the transduction from free-space beams to surface polaritons is inherently fixed after fabrication. Here, we overcome this limitation via dispersion-driven topological charge multiplication. We switch the OV topological charge within a small $\sim 3 \%$ frequency range by leveraging the strong sublinear dispersion of low-loss surface phonon polaritons (SPhP) on silicon carbide membranes. Applying the Huygens principle we quantitatively evaluate the topological order of the experimental OVs detected by near-field imaging. We further explore the deuterogenic effect, which predicts the coexistence of multiple topological charges in higher-order polaritonic OVs. Our work demonstrates a viable method to manipulate the topological charge of polaritonic OVs, paving the way for the exploration of novel OAM-enabled light-matter interactions at mid-infrared frequencies.