Long-range evanescent coupling through photonic molecules

TL;DR

This paper demonstrates long-range evanescent coupling in photonic molecules, enabling efficient excitation of higher-order states and topological edge states, with potential applications in photonic chips and topological physics.

Contribution

It introduces a method for resonant excitation of photonic molecular states with long-distance coupling, including the first demonstration of topological edge states from third-order interactions.

Findings

Strong coupling over 127 μm distance between waveguides

Efficient resonant excitation of higher-orbital states

Observation of topological edge states from long-range interactions

Abstract

Photonic molecules support the excitation of higher-order states, which are otherwise hard to access at individual waveguides. In this work, we demonstrate the resonant excitation of photonic molecular states which 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 demonstrate strong coupling for very distant waveguides separated by 127 {\mu}m. We apply this concept to a one-dimensional lattice and demonstrate the excitation of topological edge states emerging due to the third-order next-neighbour 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.