We observe coherent resonant coupling of optical whispering-gallery modes in fluorescence from dye doped polymer bispheres with diameters ranging from 2 to 5μm. By monitoring the frequencies of fluorescence peaks of individual spheres, we sort out two spheres with appropriate size matching and bring them into contact. Wave optics calculation also gives good agreement with the experiment. By taking into account harmonic coupling of the whispering-gallery modes, the obtained features of normal mode splitting are well explained by the tight-binding photon picture.
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