Fundamental suppression of backscattering in silicon microrings

In this paper we theoretically prove and experimentally demonstrate a novel approach to eliminate the effects of backscattering in silicon ring resonators. Not only the resonance-splitting can be completely suppressed, but also the unwanted light reflected to the in port and directed to the add port can be dramatically reduced. Ring resonators have become one of the most intensively used integrated optical components for various applications. However, in high-index-contrast platforms like silicon photonics, sidewall roughness induced backscattering imposes limits on the performance of ring resonators. It frequently induces resonance-splitting in through and drop ports. At the same time, there will be unwanted light directed to the add port and reflected to the in port. We show that, by putting an intentional tunable reflector inside the ring to compete with the stochastic backscattering, the ring can work under a normal condition. All resonances can be tuned to be non-split with an improved extinction ratio and there will be significantly less light coming out from the in and the add ports.