Monolithically Integrated High- Rings for Narrow Linewidth Widely Tunable Lasers

We theoretically analyze the use of fully integrated high-Q ring cavities (intrinsic Q ~ 1 million) with widely tunable semiconductor lasers to realize narrow linewidth lasers. Different configurations are studied, including cases where the high-Q cavity is external to the laser cavity and provides filtered optical feedback to the laser cavity and cases where the high-Q cavity is an integral part of the laser cavity. We show that the current heterogeneous silicon platform should allow subkilohertz instantaneous linewidths, and we outline the advantages and disadvantages of different high-Q cavity placements.