Robust Unidirectional Edge States in the Continuum in non-Topological Floquet Photonic Crystals

Abstract

Robust unidirectional edge propagation is conventionally attributed to topological protection. Whether edge states in the continuum (EICs) can exhibit such robustness in non-topological systems remains an open question. Here we demonstrate robust unidirectional EICs in Floquet photonic crystals (PhCs) composed of a honeycomb lattice of helical waveguides, where both time-reversal and spatial inversion symmetries are broken. Within a topologically trivial parameter regime of this system, where the Chern, valley Chern, and winding numbers all vanish, the EIC robustness is decoupled from topology. Instead, the robustness originates from a z-periodic Floquet artificial gauge field geometrically locked to the helical lattice. Numerical simulations show that the EIC survives 120 bent edges, 6% on-site potential noise, and 27% hopping phase noise. This work establishes a paradigm for robust light propagation in non topological systems and broadens the physical basis for unidirectional EICs.