Probing topological protection using a designer surface plasmon structure

Abstract

Topological photonic states, inspired by robust chiral edge states in topological insulators, have recently been demonstrated in a few photonic systems, including an array of coupled on-chip ring resonators at communication wavelengths. However, the intrinsic difference between electrons and photons determines that the ‘topological protection' in time-reversal-invariant photonic systems does not share the same robustness as its counterpart in electronic topological insulators. Here in a designer surface plasmon platform consisting of tunable metallic sub-wavelength structures, we construct photonic topological edge states and probe their robustness against a variety of defect classes, including some common time-reversal-invariant photonic defects that can break the topological protection, but do not exist in electronic topological insulators. This is also an experimental realization of anomalous Floquet topological edge states, whose topological phase cannot be predicted by the usual Chern number topological invariants.

Anomalous Floquet-Anderson Insulator as a Nonadiabatic Quantized Charge Pump

“…This situation stands in sharp contrast to that of static two-dimensional systems, where the existence of chiral edge states is intimately tied to the topological structure of the system's bulk bands, as captured by their Chern numbers [34]. A system exhibiting this anomalous behavior was recently realized using microwave photonic networks [35,36].…”

Guiding, bending, and splitting of coupled defect surface modes in a surface-wave photonic crystal

“…Compared with conventional waveguides of spoof surface plasmons [10][11][12][13][14][15][16][17][18][19][20][21][22] which generally suffer from scattering and crosstalk when packed densely, this coupled-defect surface waveguide (CDSW) is achieved through weak coupling between otherwise tightly localized surface defect cavities, which allows shaping the flow of surface waves almost as will 30 with minimal crosstalk.…”

“…On the other hand, electromagnetic modes supported on periodically textured metal surfaces, which are commonly termed as spoof (or designer) surface plasmons [10][11][12][13][14][15][16][17][18][19][20][21][22] , possess spatial scales typically much smaller than the wavelength. In particular, some structured metal surfaces exhibit a complete photonic bandgap where no surface guided modes are permitted [23][24][25][26] .…”

Exceptional points in a non-Hermitian topological pump

“…Yet in settings such as topological photonics, non-Hermitian effectsin the form of gain and/or loss-are easily introduced, and may be both substantial and unavoidable in practical implementations. 9 Broadly speaking, non-Hermiticity poses two problems for standard theories.…”