All-optical noise quenching of an integrated frequency comb

Integrated frequency combs promise transformation of lab-based metrology into disruptive real-world applications, particularly with octave-spanning microcombs enabling self-referenced optical synthesis and clock implementations. However, the integrated resonators that support microcombs suffer from thermal fluctuations, limiting microcomb use outside laboratories due to the need for bulky feedback systems. Kerr-induced synchronization (KIS) offers a solution by eliminating this electronic servo control through all-optical locking. Here, we show how KIS profoundly alters the noise characteristics of soliton microcombs and enables a small device footprint to be compatible with low-noise operation. The phase locking between the dissipative Kerr soliton (DKS) and the injected reference reduces the tooth-to-tooth pump noise propagation—enabling easier carrier-envelope offset stabilization and uniform spectral performance—while also damping the impact of intracavity fluctuations on the DKS, such as thermo-refractive noise (TRN). Our theoretical and experimental results show that KIS modifies the comb noise elastic-tape model, maintaining comb tooth linewidths comparable to the pump lasers’, unlike single-pumped systems where linewidths increase by orders of magnitude from the comb center to its edges. Additionally, KIS quenches intrinsic noise sources at the soliton decay rate, regardless of laser coherence or microring thermo-refractive correlations. Using these findings, we demonstrate an octave-spanning microcomb operating below TRN limits, using both free-running lasers and lasers correlated via comb self-referencing, with performance limited only by laser frequency noise.