Symmetric photonic molecules formed from coupled microspheres

Coherent coupling of optical resonances in spherical microcavities results in the formation of so called photonic molecules. The name originates from the analogy to chemical molecules. The coupled optical modes are similar to the atomic orbitals of a chemical molecule. In this work, we studied the resonance spectrum of the symmetric photonic molecules. Furthermore, symmetric directional emission of light from the photonic molecules is experimentally shown. The photonic molecules are illuminated in the vertical direction with a defocused laser beam. The emission is attributed to photonic nanojets generated in the structure. Spectral analysis exhibit whispering gallery mode resonances of coupled and uncoupled modes. A benzene molecule-like structure consisting of a 7-microspheres cyclic photonic molecule shows a field emission pattern similar to the spatial distribution of the orbitals of the benzene molecule.