High-sensitivity refractometric sensing with an indirectly coupled active and passive microresonator-waveguide system

Abstract

We investigate high-sensitivity refractometric sensing with indirectly coupled active and passive optical microresonators mediated by drop-filter waveguides. It is shown that the line shape and amplitude of power reflection and transmission spectra are relevant with both phase delay and gain of microresonators, and high-sensitivity refractometric sensing may be realizable with three enhancement mechanisms, i.e., phase delay-induced sharp Fano spectra, gain-induced narrow-linewidth Lorentzian spectra, and exceptional points (EPs). Between the former two enhancement mechanisms, the competitive relationship, which is determined by the interplay of phase delay and gain, exists. The system could be tuned into the vicinity of the EP by choosing appropriate phase delay and gain. As the system response to the slight change of external parameter is evidently benefiting from the critical behavior, ultrahigh-sensitivity refractometric sensing could be realizable due to the dynamical amplification effect.