High‐Efficiency O‐Band Bright Soliton Microcomb on the CMOS‐Compatible 300‐nm‐Thick Silicon Nitride Platform

Silicon nitride (Si 3 N 4 ) has become an ideal platform for microcomb generation, yet achieving high‐performance microcombs via CMOS‐compatible processes remains challenging. Bright soliton microcombs operating in the anomalous dispersion regime typically require thick‐film Si 3 N 4 , posing significant fabrication challenges. Additionally, while offering broad bandwidth, they suffer from low conversion efficiency. In contrast, dark pulse microcombs generated in normal‐dispersion microresonators can relieve the need for thick‐film Si 3 N 4 and offer high conversion efficiency, but they are constrained by limited bandwidth and uneven spectra. In this work, we overcome these limitations and achieve high‐performance O‐band microcombs on the CMOS‐compatible 300‐nm‐thick Si 3 N 4 platform by incorporating dispersion‐engineered concentric‐coupled‐ring microresonators with laser self‐injection locking. Our approach enables deterministic generation of an O‐band bright soliton microcomb with a high pump‐to‐comb conversion efficiency of 41.64%. Simultaneously, the laser frequency noise is suppressed by 23 dB, narrowing the instantaneous linewidth from 406 kHz to 1.7 kHz. By tailoring the coupling gap between the rings, we further demonstrate a broadband near‐zero‐dispersion microcomb spanning 76 nm. This foundry‐compatible scheme delivers efficient, broadband O‐band microcombs, addressing the growing demand for higher data communication capacity in emerging applications such as co‐packaged optics and optical I/O.