Boosting SiN Ring Resonator Linewidth Lower Than 10 fm Through Optical Bistability

Ring resonator features are of paramount importance in various optical systems. In this context, the enhancement of linewidth, and in turn the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i>-factor, stands as the pivotal achievement. However, a distinctive trait of ring resonators lies in the delicate balance between the linewidth and resonance depth; an improvement in the linewidth may entail a compromise in the resonance extinction ratio. In this context, here a silicon nitride ring resonator is presented, boosting a record-breaking linewidth for a single-mode ring resonator lower than 10 fm (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i>-factor > 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup>), alongside an extinction ratio of 5 dB. This significant improvement of linewidth is experimentally demonstrated by harnessing the optical bistability effect through the combination of low optical losses (in dB/m) and the Kerr effect, suppressing the detrimental impact of self-heating-induced dissipation. This breakthrough holds several advantages, primarily in the realm of selectivity and signal-to-noise ratio, thereby paving the way for its utilization for data storage as well as numerous sensing applications.