Observation of intersphere coupling of optical whispering gallery modes

Summary form only given.Confinement of photons in a dielectric microsphere is attracting current interest from a fundamental as well as an application point of view. According to the Lorenz-Mie theory, microspheres with diameters of a few microns show very narrow optical resonance modes, which are known as optical whispering gallery modes (WGMs). A very high quality factor (Q value) has been observed in various materials. If we can form three-dimensional or two-dimensional arrayed structures with spheres of identical size, we can obtain modes with the characteristics of extremely slow group velocity. Such modes can be regarded as photonic band modes resulting from the tight-binding coupling of WGMs. To realize the idea of tight-binding photonic modes, precise control of sphere size is crucial. As the first step, we need to study the mode coupling between two attached spheres. In this report, we present evidence of mode splitting of WGM in bisphere geometry. From the fluorescence resonances of an individual dye-doped polymer sphere with a diameter of /spl sim/5 /spl mu/m, we can determine the size within 0.2% error and thus can form the resonant bispheres.