Measurement of the Nonlinear Loss and Effective Free Carrier Lifetime in Silicon Microring Resonators

A methodology is presented to characterize the nonlinear absorption loss coefficient and the effective free carrier lifetime in silicon ring resonators at high intra-ring optical power density. The proposed methodology uses a continuous-wave pump-probe measurement to capture distortion-free transmission spectra in the regime of nonlinear absorption. The measured nonlinear loss coefficient using this method is 30–40% higher than that obtained with a single high-power continuous-wave laser. The pump-probe measurement also reveals that the optical loss sharply increases beyond ∼11.6 mW in the bus waveguide for the ring design with the highest quality-factor, most likely due to the saturation of trap states by electrons and holes generated by two-photon absorption.