Coupled loss-gain microresonators with Fano resonance for high-sensitivity refractometric sensing

Abstract

The strong photon limiting ability of the resonant cavity makes it a critical general-purpose device. The silicon-based photonic resonant cavity is the most potential high-efficiency, low-cost on-chip solution. The organic combination of mature microelectronic technology and broadband optoelectronic technology in the micro-nano category makes this arrangement a bright future. Fano resonance with the sharp symmetry-broken line shapes occurs when a discrete quantum state interferes with a continuum band of states. Here, we analyze two directly coupled microresonators (a low- Q passive resonator and a high-Q active resonator) using the temporal coupled-mode theory (CMT). High-sensitivity refractometric sensing based on Fano resonance with directly coupled active and passive optical microresonators is investigated theoretically. It is shown that the line shape and amplitude of power transmission spectra is determined by the judgment coefficient and the pump gain of high-Q microresonator. Through modulating the loss rate, pump gain, and the detuning frequency of both cavities, the refractive index sensitivity can be enhanced six order than two directly coupled loss-loss microresonators. As the system response to the slight change of external parameter benefits from the critical behavior, ultrahigh-sensitivity refractometric sensing could be realizable due to the mechanism achieving a large slope with a relatively high extinction ratio. Our scheme is valuable for various applications of refractometric sensing in the future.