Spectroscopy of coherently coupled whispering-gallery modes in size-matched bispheres assembled on a substrate

Abstract

Coupling between whispering-gallery modes is studied using imaging spectroscopy in pairs of size-selected (size deviation of <0.03%) spheres in a touching position. In a special geometrical configuration, peculiar shapes resembling kites are observed in the spectral images of bispheres by coupling of multiple pairs of azimuthal modes. The maximal WGM coupling is observed in the equatorial plane of spheres determined by the substrate. The WGM coupling constant is quantified for spheres from 2.9 to 6 microm for such modes.