Ultralow-Power Photonic Chip-Based Soliton Frequency Combs

The generation of dissipative Kerr solitons in optical microresonators allow compact high repetition rate frequency combs. A particularly promising platform is photonic integrated Si3N4 microresonators. Yet to date, soliton formation in Si3N4 microresonators requires high input power thus additional optical amplifiers, which limit integration and practical use. Here, we demonstrate ultralow-power soliton formation in 1-THz-FSR Si3N4 microresonators of $\mathbf{Q_{0}} > \mathbf{6.2}$ million with $ input power, and in 88-GHz-FSR microresonators of $\mathbf{Q}_{0} > \pmb{8.2}$ million with a record low 48.6 mW input power. Our results show the technological readiness of Si 3 N 4 waveguides for future all-on-chip nonlinear photonic devices with ultra-low operating power.