Spectral engineering with coupled microcavities: active control of resonant mode-splitting.

Optical mode-splitting is an efficient tool to shape and fine-tune the spectral response of resonant nanophotonic devices. The active control of mode-splitting, however, is either small or accompanied by undesired resonance-shifts, often much larger than the resonance splitting. We report a control mechanism that enables reconfigurable and widely tunable mode splitting while efficiently mitigating undesired resonance shifts. This is achieved by actively controlling the excitation of counter-traveling modes in coupled resonators. The transition from a large splitting (80 GHz) to a single-notch resonance is demonstrated using low-power microheaters (35 mW). We show that the spurious resonance shift in our device is only limited by thermal crosstalk, and resonance-shift-free splitting control may be achieved.