Coherent backscattering in optical microring resonators

The effects of backscattering induced by waveguide sidewall roughness in integrated ring resonators (RRs) are experimentally observed. We demonstrate that coherent backscattering, originated by multiple round trips in the RR, increases with the square of the effective group index of the cavity and can dramatically affect the behavior of integrated RRs even at moderate quality factors of 10^4. From our results backscattering emerges as one of the most severe limiting factors on the performance of RRs fabricated with state-of-the-art silicon-on-insulator nanowaveguides.