  Modulated optical cavities have been proposed and demonstrated for
applications in communications, laser frequency stabilization,
microwave-to-optical conversion and frequency comb generation. However, most
studies are restricted to the adiabatic regime, where either the maximum
excursion of the modulation or the modulation frequency itself is below the
linewidth of the cavity. Here, using a fiber ring resonator with an embedded
electro-optic phase modulator, we investigate the nonadiabatic regime. By
strongly driving the modulator at frequencies that are significantly smaller
than the free-spectral range of the ring resonator, but well beyond the
linewidth of the resonator, we experimentally observe counterintuitive behavior
predicted in a recent theoretical study by Minkov et al. [APL Photonics 2,
076101 (2017)], such as the complete suppression of drop-port transmission even
when the input laser wavelength is on resonance with the optical cavity. This
can be understood as dynamical isolation of the cavity from the input light. We
also show qualitative differences in the steady-state responses of the system
between the adiabatic and nonadiabatic limits. Our experiments probe a seldom
explored regime of operation that is promising for applications in integrated
photonic systems with current state-of-the-art technology.
