Asymmetric topological pumping in nonparaxial photonics

TL;DR

This paper uncovers an unexpected asymmetric topological pumping phenomenon in nonparaxial photonic waveguides, challenging the traditional quantum-optical analogy and opening new avenues for topological photonics research.

Contribution

It demonstrates both theoretically and experimentally that nonparaxial effects lead to asymmetric topological pumping, a phenomenon not predicted by the paraxial approximation.

Findings

Asymmetric topological pumping observed in experiments.

Reverse pumping process is forbidden, unlike in paraxial systems.

Nonparaxiality enables new topological phenomena in photonics.

Abstract

Topological photonics was initially inspired by the quantum-optical analogy between the Schr\"odinger equation for an electron wavefunction and the paraxial equation for a light beam. Here, we reveal an unexpected phenomenon in topological pumping observed in arrays of nonparaxial optical waveguides where the quantum-optical analogy becomes invalid. We predict theoretically and demonstrate experimentally an asymmetric topological pumping when the injected field transfers from one side of the waveguide array to the other side whereas the reverse process is unexpectedly forbidden. Our finding could open an avenue for exploring topological photonics that enables nontrivial topological phenomena and designs in photonics driven by nonparaxiality.