Wide edge state supercontinuum in a Floquet–Lieb topological photonic insulator

Abstract

Conventional topological photonic insulators typically have narrow nontrivial band gaps truncated by broad dispersive bulk bands, resulting in limited edge mode transmission bandwidths that can be exploited for potential applications. Here, we demonstrate a Floquet–Lieb topological photonic insulator with all flat bands that can support continuous edge mode transmission across multiple Floquet–Brillouin zones. This supercontinuum of edge states results from the coexistence and orthogonality of the localized flat-band modes and the edge states, allowing for continuous excitation of the latter without scattering into the bulk modes. Moreover, we show that these flat bands are perfectly immune to random variations in the on-site potential, regardless of how large the perturbations are, thus ensuring complete robustness of the edge modes to this type of disorder. We realized Floquet–Lieb insulators using 2D microring resonator lattices with perfect nearest-neighbor couplings. Transmission measurements and direct imaging of the scattered light distributions showed an edge mode supercontinuum spanning more than three microring free spectral ranges. The proposed Floquet–Lieb insulator can potentially be used to realize topological photonic devices with wide bandwidths and super robustness for applications in integrated quantum photonics and programmable photonic circuits.