Long-Range Evanescent Coupling through Photonic Molecules

Abstract Photonic molecules support the excitation of higher-order states, which could become a key solution for long-range coupling in photonics. In this work we demonstrate the resonant excitation of photonic molecular states that evanescently couple to single-mode waveguides. We implement the experiments on femtosecond laser written photonic structures and demonstrate an efficient resonant excitation of higher-orbital states, optimized at specific wavelengths and propagation distances. We suggest the use of long photonic molecules as long-distance photonic links, and reveal strong coupling for very distant waveguides separated by 127 μm. We apply this concept to a trivial one-dimensional lattice and demonstrate the excitation of topological edge states emerging due to the third-order next-nearest-neighbor interactions. Our findings demonstrate effective long-range evanescent coupling which could be a concrete solution for fiber-based photonic chips, topological physics emerging from long-range interactions, or fundamental studies of initially uncoupled systems.