Unidirectional light transport in dynamically modulated waveguides

One-way edge states at the surface of photonic topological insulators are of significant interest for communications and nonlinear and quantum optics. Moreover, when reciprocity is broken in a photonic topological insulator, these states provide protection against disorder, which is of particular importance for slow-light applications. Achieving such a one-way edge state, however, requires the construction of a two-dimensional structure. Here, we show how unidiriectional Floquet bands can arise in purely one-dimensional, adiabatically modulated dynamic systems, in contrast with the higher dimensionality needed in topological insulators. We also show that, using realistic experimental parameters, the concept can be implemented using both a coupled-resonator optical waveguide and a photonic-crystal waveguide. Furthermore, we illustrate the associated protection against disorder and find it to be of a different nature when compared to Floquet topological insulators.