Spectroscopy of coherently coupled whispering gallery modes in supermonodispersive bispheres

Coherent coupling between whispering gallery modes (WGMs) is studied in almost identical (size deviation ≪0.03%) polystyrene bispheres with average sizes varying from 2.9 to 6 µm. In a special geometrical configuration peculiar kite shapes are observed in the spectral images of such photonic molecules. The origin of these kites is explained due to coupling of multiple pairs of azimuthal modes. Using various geometries of the experiments we quantified the dependence of coupling constant on the sizes of spheres for maximally coupled fundamental modes located in the equatorial planes of spheres on the substrate. The results show the feasibility of achieving a coherent WGM-based optical transport in microsphere resonator circuits.