Fig. 1

Floquet bands and gaps in a periodically driven nonlinear photonic crystal. a Schematic of a nonlinear photonic crystal (PhC) placed in a monochromatic driving field E^d at frequency Ω. b Due to the periodic drive, static bands of the PhC (solid lines) create copies of themselves—Floquet bands (dashed lines)—by shifting up or down in the spectrum. c Two of the Floquet bands |1, m = 0〉 and |2, m = −1〉 cross at ±k₁. Their coupling term V₂₁ opens a new gap E_g—Floquet gap—and its size is linearly proportional to the magnitude of their coupling strength |V₂₁| under weak drive