Floquet Topological Phases in One-Dimensional Nonlinear Photonic Crystals.

We report on a theoretical analysis of the Floquet topological crystalline phases in driven one-dimensional photonic crystals mediated by second-order optical nonlinearity. We define the photonic Berry connection and photonic polarization in such systems using different methods and prove their equivalence. We present two examples of topological phase transitions in which two Floquet bands cross and open new gaps under the driving field. Finally, we analyze the physical consequences of each topological phase transition by examining edge states and filling anomalies. Our study presents routes toward the realization of robust reconfigurable photonic cavities with topologically protected light confinement.