Using Backscattering and Backcoupling in Silicon Ring Resonators as a New Degree of Design Freedom

Abstract Silicon optical ring resonators are potentially valuable for many applications. Due to the limited design freedom (coupling coefficient and roundtrip length), the functionality and performance cannot always be fully explored and optimized. In addition, high‐contrast silicon ring resonators suffer from parasitic coupling between their clockwise and counterclockwise modes as well as parasitic coupling from the input to both circulating modes, which degrades or even distorts the response. Herein, an overview is given to harness these effects as additional design parameters to overcome the detrimental effects and realize novel functionalities in silicon ring resonators. Through simulations and experimental characterization, it is shown how the manipulation of backreflection and backcoupling enables various novel functions, including tunable Fano resonances with maximum slope rate over 700 dB nm −1 , tunable electromagnetically induced transparency, which slows light down over 1100 ps, a single‐mode silicon ring resonator with a free spectral range over 150 nm and tuning efficiency over 11 times higher compared to that of conventional silicon ring resonators, fundamental suppression of inevitable backscattering, spectral tuning, single sideband filtering, and ultrahigh Q /large finesse resonances.