Spectral finger-prints of photonic molecules

Clusters of circular resonators with coupled whispering gallery modes (WGMs) have interesting spectral and optical transport properties. We employ the finite-difference time-domain method to numerically study these properties. Using evanescent couplers, we show that various configurations of cavities display distinct spectral features (mode splitting) in the vicinity of their WGMs resonances. These features can be considered as spectral finger-prints of different clusters of cavities. We observed some of these spectral finger-prints experimentally using sorted polystyrene microspheres with uniform WGM resonances. The results can be used for understanding mechanisms of light transport in such complex optical networks and for developing spectral filters, delay lines, sensors, microspectrometers, and spectral markers.