Fundamentals and applications of microsphere resonator circuits

Microsphere resonator circuits have emerged as a technology allowing integration of cavities in all three spatial dimensions (3D) in chip-scale structures. This presentation is devoted to fabrication, optical properties and applications of mesoscale structures formed by microspheres. The ldquomesophotonicsrdquo properties of such structures stem from two properties of individual dielectric microspheres with dimensions comparable to the wavelength of light: (i) high quality factors of whispering gallery modes (WGMs) and (ii) subwavelength dimensions of the focused spots termed ldquophotonic nanojetsrdquo. Traditionally, the resonant optical transport properties of such structures have been described by a tight binding approximation for photonic atoms. Recently we showed that the WGM-based transport in 2D and 3D systems with disorder can be understood on the basis of analogy with a percolation theory. Along with these resonant coupling effects very interesting properties of periodical focusing of light were observed in long chains of spheres. These properties were explained due to formation of nanojet-induced modes with small propagation losses. At the device level, these studies stimulate developing designs where coupled cavities are applied to developing narrow spectral filters, delay lines, arrayed-resonator light emitting devices, tight focusing micro-probes, sensors, and compact spectrometers.