Kerr Microresonator Soliton Frequency Combs at Cryogenic Temperatures
Gregory T. Moille, Xiyuan Lu, Ashutosh S. Rao, Qing Li, Daron A. Westly, Leonardo Ranzani, Scott B. Papp, Mohammad Soltani, Kartik A. Srinivasan
We present measurements of silicon nitride nonlinear microresonators and frequency comb generation at cryogenic temperatures as low as 7 K. A resulting two orders of magnitude reduction in the thermo-refractive coefficient relative to room-temperature enables single bright Kerr soliton states to become straightforward to directly access through adiabatic frequency tuning of the pump laser while remaining in thermal equilibrium. Our experimental results supported with our theoretical modeling show that single Kerr bright solitons are easily accessible at temperatures below 60K for the microresonator device under study. We further demonstrate that the cryogenic temperature only impacts the thermo-refractive coecient and that the other parameters critical to the generation of solitons, such as quality factor, dispersion, and e ective nonlinearity, are unaltered. Finally, we discuss the potential improvement in thermo-refractive noise resulting from cryogenic operation. The results of this study opens up new directions in advancing chip scale frequency comb optical clocks and metrology at cryogenic temperatures.