Direct red-detuned soliton generation via lower-power auxiliary laser assistance

Abstract

Integrated soliton microcombs have emerged as a promising solution for applications in precision metrology, high-speed optical communications, and integrated photonics. In practical deployment of soliton microcombs, it is a challenge to generate stable solitons due to power-dependent resonance shifts caused by thermo-optic and Kerr effects. In this Letter, a direct red-detuned soliton generation method is proposed through backward tuning of the pump laser from the red-detuned side under lower-power auxiliary laser assistance. The auxiliary laser modifies intracavity Kerr dynamics, enabling the system to directly enter the soliton regime without encountering unstable power transitions. This method avoids the chaotic-to-soliton transitional state that typically occurs during forward tuning from the blue-detuned to the red-detuned side. Experimental results using silicon nitride microresonators show that backward tuning requires less than half the auxiliary laser power compared to forward tuning methods. Soliton is generated with the auxiliary laser power 1.46 dB lower than the pump laser under both lasers coupled into the same resonance mode. Note that the reduced auxiliary laser power in this method suppresses backscattering effects from the auxiliary-laser-generated comb, thereby preserves soliton spectral integrity. The proposed method provides a stable and power-efficient route to soliton generation for practical deployment of the soliton microcombs in compact and scalable photonic applications.