We present a simple method to determine simultaneously the main characteristics of passive or active high-Q optical resonators. The method is based on cavity ringdown spectroscopy, where the probe wavelength is rapidly swept across the resonance. It has already been shown that this technique allows the loaded cavity lifetime of passive resonators to be obtained. We show that we can also infer the coupling regime for passive resonators and the resonant gain for active resonators. The method is tested on ${\mathrm{Er}}^{3+}$ doped fiber resonators and also applied to determine the intrinsic and external Q-factors of an $\mathrm{Mg}{\mathrm{F}}_2$ whispering gallery mode resonator.

We demonstrate experimentally coupled active-resonator-induced transparency in a fiber system. We show that the use of ${\mathrm{Er}}^{3+}$-doped fibers can compensate for the optical losses leading to a high transparency of the system. Using a Mach-Zehnder fiber interferometer, we measure the dispersion properties of our coupled active resonators under different pumping rates. We show that the active feature of the system allows us to engineer the different orders of its artificial dispersion. This experimental demonstration shows the potential of active coupled resonators for dispersion tailoring and slow-light applications.

We numerically demonstrate the feasibility of constructing an all-optical pulse restorer by using a microresonator structure with Kerr nonlinearity. We obtain a clear nonlinear power transfer curve capable of improving the signal-to-noise ratio and reducing the bit error rate for digital signals. Since we take advantage of field enhancement at resonance, this integrated reshaper could be much smaller than other gates based on nonlinear fibers or waveguides.

We propose a simple way to design a fully integrated and passive all-optical pulse reshaper in the aim of reamplifying and reshaping (2R) regeneration of optical digital signals. The device could be achieved from a coupled microresonator structure with Kerr nonlinearity. By using time-domain simulation, we show that we can obtain a clear nonlinear power transfer that is capable of improving signal-to-noise ratio and reducing bit error rate for digital signals. The reshaping performances are estimated by calculating Q-factor enhancement. Since we take benefit from field enhancement at resonance, this integrated reshaper could be much smaller than other gates based on nonlinear fibers or waveguides.