Effect of Thermal Tuning and Mode Coupling on Soliton Microcombs in ALN Microresonators

Optical resonator-based Kerr frequency combs allow an ultra-precise time and frequency measurements for a wide range of applications including ranging, biosensing, high-capacity communications, and quantum information technology. Kerr solitons are coherent frequency combs that are crucial for frequency synthesizer and chronometric instruments. The behavior of the soliton is determined by multiple factors while the key challenge for stable operation is to maintain thermal equilibrium in the resonator. In this work, owing to the stabilizing thermal effect caused by a neighboring auxiliary mode (TE
₁₀
), we demonstrate the generation of octave-spanning (1100-2380 nm) single-soliton within a wide laser detuning range (up to 16 GHz) by pumping the TE
₀₀
mode. The influence of temperature on the microcombs behavior is also explored. Firstly, diverse two-solitons are achieved by adjusting the temperature. Secondly, the soliton access possibility is reduced when further increasing the temperature due to the avoided mode crossing between the pump mode (TE
₀₀
) and another adjacent fundamental transverse-magnetic mode. At the same time, the spectral bandwidth of the microcomb that originates from TM
₀₀
modes is significantly enhanced. Finally, we show that the carrier offset frequency, which is evaluated to be ∼30-40 GHz, increases as the temperature is increased.