Tuning Kerr-Soliton Frequency Combs to Atomic Resonances

Frequency combs based on nonlinear optical phenomena in integrated photonics are a versatile light source that can explore new applications, including frequency metrology, optical communications, and sensing. We demonstrate robust frequency-control strategies for near-infrared, octave-bandwidth soliton frequency combs created with nanofabricated silicon nitride ring resonators. Group-velocity-dispersion engineering allows operation with a 1064-nm pump laser and generation of dual-dispersive-wave frequency combs linking wavelengths approximately between 767 and 1556 nm. To tune the mode frequencies of the comb, which are spaced by 1 THz, we design a photonic chip containing 75 ring resonators with systematically varied dimensions and we use a thermo-optic tuning range of 50 degrees C. This single-chip frequency-comb source provides access to every wavelength, including those critical for near-infrared atomic spectroscopy of rubidium, potassium, and cesium. To make this possible, solitons are generated consistently from device to device across a single chip with use of rapid pump-frequency sweeps that are provided by an optical modulator.