Integrated Circuits of Coupled Mircospheres for Optoelectronics Applications

The paper is devoted to theoretical modeling, fabrication, and advanced spectroscopic characterization of circuits of microspheres with high quality whispering gallery modes (WGMs). The discussion of results is based on three mechanisms of optical coupling between spherical cavities: (i) resonant coupling between WGMs in identical cavities, (ii) Fano resonance between a discrete energy state (true WGM excited in the source sphere) and a continuum of quasi-WGM states with distorted noncircular shape which can be induced in the receiving cavity, and (iii) photonic nanojet mechanism. For the case of identical cavities we present numerical modeling results demonstrating a good impedance matching, and a tunable nanosecond delay for propagating pulses. We experimentally studied optical coupling in size-mismatched bispheres with controllable inter-cavity separations, and showed the validity of mechanism based on Fano resonance. Finally, we observed photonic nanojets in extremely long chains of fluorescent microspheres with propagation losses less than 1 dB per sphere