Tunable Fano interference effect in coupled-microsphere resonator-induced transparency

Abstract

We investigated interference effect between two whispering gallery modes in a system of ultrahigh-Q silica microspheres in which the resonance frequencies of spheres were precisely controlled through thermal tuning. A symmetric transmission peak of coupled—resonator—induced transparency reshaped into a sharp asymmetric spectrum similar to Fano effect in atomic system as the resonance frequency of the second sphere was detuned. The resonance modes showed frequency shifts as a function of the coupling strength between the two spheres, indicating that two whispering gallery modes were configurationally mixed. The observations were compared with calculations and discussed using double-spiral structures in the phase space in the transmitted field.