Interferometric cavity ringdown technique for ultrahigh Q-factor microresonators

Microresonators (MRs) are key components in integrated optics. As a result, the estimation of their energy storage capacity as measured by quality factor (Q) is crucial. However, MRs with high/ultrahigh Q, wall-surface roughness dominates intrinsic Q and generates coupling between counter-propagating modes. This splits usual sharp single resonance makes use classical methods to assess difficult. Here, we theoretically show that an interferometric excitation can be exploited cavity ringdown (CRD) method measure ultimate MR. In fact, under suitable conditions, resonant doublet merges into Lorentzian, time dynamics MR assumes behavior single-mode resonator unaffected backscattering. allows us obtain typical exponential decay charging discharging MR, thus, estimate its measuring photon lifetime.