Asymmetric topological pumping in nonparaxial photonics

Qingqing Cheng,Tao Chen,Yiming Pan,Yongguan Ke,Yuri S Kivshar,Ye Yu,Huaiqiang Wang,Chaohong Lee

doi:10.1038/s41467-021-27773-9

Abstract

Topological photonics was initially inspired by the quantum-optical analogy between the Schrödinger 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.

Highlights

Topological photonics was initially inspired by the quantum-optical analogy between the Schrödinger equation for an electron wavefunction and the paraxial equation for a light beam
Seminal studies in topological photonics include quantum simulations of topological edge states[8,9,10,11,12,13,14] and topological pumping[15,16,17,18,19,20,21]. Similarities of those concepts are based primarily on a direct correspondence between the dynamics of the electron wavefunction governed by the Schrödinger equation and the propagation of a light beam described by the paraxial Helmholtz equation
Our experimental results are nicely consistent with both simulations and analysis from the exact Helmholtz wave equation. We believe these findings may open an avenue to topological photonics, and may provide further insights for the study of topological phases and dynamics triggered by nonparaxiality of light

Summary

Introduction

Topological photonics was initially inspired by the quantum-optical analogy between the Schrödinger equation for an electron wavefunction and the paraxial equation for a light beam. We demonstrate experimentally a remarkable effect of asymmetric topological pumping when the injected field transfers from one side of the waveguide array to the other side, whereas the reverse process becomes forbidden.

Results

Conclusion