High-Q silicon microring resonators with optimized spot-size converters

In this paper, an optimized design method for the on-chip microring resonator (MRR) that integrates spot-size converters (SSCs) has been proposed and demonstrated. The tapered SSCs were specially designed based on Bezier free-form curves to improve the quality factor Q of the MRRs and reduce their minimum bend radius. Two SSCs with lengths of 25 and 15 μm were designed and employed to construct two MRRs. The two MRRs were subsequently manufactured and experimentally measured. The loaded quality factors of the two MRRs were measured to be 4.34 × 10<sup>5</sup> and 3.24 × 10<sup>5</sup>, respectively. In comparison to a typical MRR with integrated 50 μm long linear tapered SSCs with the same footprint, the proposed method resulted in a 2.3 and 1.7 times increase in Q, as well as a reduction in effective radii from 55 to 25 μm and 15 μm, respectively. This work effectively promotes the improvement of performance and miniaturization of MRRs with integrated SSCs.