Harnessing thermo-optic dynamics for frequency-agile soliton microcombs
Dissipative Kerr soliton microcombs enable compact and scalable frequency comb sources for precision metrology, spectroscopy, communications and coherent LiDAR, where broad and reliable frequency tuning is essential. Thermo-optic response can support thermal locking during soliton operation, enabling resonance tracking and thereby extending the tuning range, albeit modestly. However, it also induces pronounced thermal instability during soliton initiation, hindering reliable access to this extended operating regime and limiting practical deployment in applications requiring frequency agility. Here we show that strong mode coupling reshapes the effective detuning trajectory governing soliton formation, establishing a distinct operating regime in which thermo-optic response is significantly reinforced and constructively harnessed. In this regime, soliton formation proceeds without the thermal instability inherent to conventional operation, enabling robust soliton generation in material platforms previously limited by strong thermal effects. Importantly, the enhanced thermo-optic response strengthens thermal locking during soliton operation, enabling more effective resonance tracking and substantially extending the tuning range. Leveraging this regime in AlGaAs-on-insulator multimode microresonators, we demonstrate soliton generation with a tuning range approaching 100 GHz at a pump power of 32 mW. The same mechanism further enables frequency-agile operation through direct pump-frequency tuning without auxiliary stabilization, allowing massively parallel chirped comb generation with more than 90 channels exhibiting frequency excursions exceeding 10 GHz. These results establish a general operating principle for transforming thermo-optic effects from a limiting factor into an active resource, enabling robust and frequency-agile integrated soliton microcombs.