Observation of topological edge states in photonic bilayer SSH lattice

We present experimental observations of topological edge states in photonic bilayer Su–Schrieffer–Heeger (SSH) lattices. Using the femtosecond laser direct writing technology, we establish two distinct types of nontrivial bilayer SSH lattices with varying interlayer couplings, allowing us to observe two different types of topological edge states. Interestingly, we find that these topological edge states can either remain within the bandgap or transition into gapless bound states in the continuum without hybridization under different interlayer couplings. Our work illustrates a scheme to investigate topology and bound states in the continuum physics in artificial systems, potentially opening up many possibilities in topology-driven photonic devices.