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.

中文翻译：

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间接耦合有源和无源微谐振器-波导系统的高灵敏度折光检测

我们研究了由滴滤波导间接耦合的主动和被动光学微谐振器的高灵敏度折射仪传感。结果表明，功率反射和透射谱的线形和幅度与微谐振器的相位延迟和增益都相关，并且可以通过三种增强机制来实现高灵敏度折光检测，即相位延迟引起的尖锐Fano光谱，增益引起的窄线宽洛伦兹谱和例外点（EPs）。在前两种增强机制之间，存在竞争关系，竞争关系由相位延迟和增益的相互作用决定。通过选择适当的相位延迟和增益，可以将系统调谐到EP的附近。