Balancing thermal effects for soliton stabilization in Kerr-microresonator optical frequency combs

Kerr-microresonators are compact, chip-scale platforms for optical frequency combs, which are lasers with many discrete and equally spaced frequencies. Unlike traditional optical frequency combs created from mode-locked lasers, Kerr-microresonator combs (microcombs) can be mass-produced on silicon wafers and allow for integration with other on-chip devices. These microresonators support solitons, a low-noise optical pulse that maintains its intensity profile and velocity indefinitely. Soliton microcombs, in contrast to the chaotic combs also supported in the microresonator, have phase-locked optical frequencies and a stable pulse train. However, soliton combs have lower intracavity powers than their chaotic precursors, and thermal instabilities caused by the abrupt change in intensity lead to short soliton lifetimes. In this work, we reduce thermal effects using a technique that allows us to sweep the wavelength of the pump light at high speeds. An intensity modulator creates sidebands on a laser, and the sideband frequency is swept faster than the thermalization time of the resonator, to reduce heating. Using a Mach-Zehnder interferometer, we characterize sideband frequency sweep rates of up to 20 MHz/ns, which is 2000 times beyond cavity-based laser tuning rates. We observe increased lifetime of the soliton state for faster sweep speeds. This is a crucial step for future designs of low-cost, compact and portable frequency combs for many different applications beyond research.