Thermally controlled dual-mode Si3 N4 microresonators for generation of octave-spanning Kerr solitons

Octave-spanning soliton frequency combs generated by microresonators present a compact and low-noise tool for high-resolution time and distance measurements through self-referencing. While these soliton combs have been observed on various photonic platforms, their practical deployment is often hindered by complex control mechanisms, resulting in a low yield of useful devices. To address these challenges, we have optimized a dual-mode soliton scheme by incorporating heaters directly onto Si3N4 microresonators. The thermal control, achieved by adjusting the electrical power supplied to the heaters, effectively tunes the mode separation to a favorable level (∼100 pm for a 1 THz resonator), facilitating efficient thermal compensation and improving the yield of functional dual-mode resonators. Kerr solitons can be deterministically generated by simply reducing the heater voltage via either slow sweeping or fast pulse tuning with the pump wavelength and power fixed. Additionally, bidirectional voltage scanning enables a smooth transition from multisoliton to single-soliton states, optimizing both the bandwidth and comb power. The integrated heater allows for fine-tuning of both the repetition rate and carrier-envelope offset frequency of the soliton comb with slopes of -21.18 MHz/mW and +0.35 GHz/mW, respectively. We have successfully generated octave-spanning solitons across multiple resonators with different repetition rates (∼1 THz and ∼390 GHz). Additionally, a systematic dual-mode design strategy is explored for future optimization. These improvements mark a significant advancement toward cost-effective and practical Kerr frequency combs for applications such as optical clocks and frequency synthesizers.