Dynamic control of Fano resonances in a coupled dual microring resonator system

We propose a coupled optical microresonator system that can be used as a new and flexible platform to form asymmetric Fano-like resonances and dynamically control their line shapes and frequencies. The coupled microresonator system was formed using two microring resonators coupled via a 3 × 3 coupler. The upper microring resonator is the add-drop type, whereas the lower one is the all-pass type, providing the (semi-) continuum and discrete states, respectively. We simulated the behavior of the coupled system using the finite-difference time-domain method and observed asymmetric Fano line shapes in the transmission spectra. We demonstrated that the line shapes and frequencies of Fano resonances can be controlled by dynamically varying the refractive index of a small region of the upper or lower microring resonators. We also introduced a small gap in the upper microring resonator to control the continuum state more efficiently. The proposed coupled microresonator concept is simple, easy to fabricate and sufficiently flexible to be engineered for different applications.