Fully integrated ultra-low power Kerr comb generation

Optical frequency combs are broadband sources that offer mutually coherent, equidistant spectral lines with unprecedented precision in frequency and timing for an array of applications1. Frequency combs generated in microresonators through the Kerr nonlinearity require a single-frequency pump laser and have the potential to provide highly compact, scalable and power-efficient devices2,3. Here we demonstrate a device—a laser-integrated Kerr frequency comb generator—that fulfils this potential through use of extremely low-loss silicon nitride waveguides that form both the microresonator and an integrated laser cavity. Our device generates low-noise soliton-mode-locked combs with a repetition rate of 194 gigahertz at wavelengths near 1,550 nanometres using only 98 milliwatts of electrical pump power. The dual-cavity configuration that we use combines the laser and microresonator, demonstrating the flexibility afforded by close integration of these components, and together with the ultra low power consumption should enable production of highly portable and robust frequency and timing references, sensors and signal sources. This chip-based integration of microresonators and lasers should also provide tools with which to investigate the dynamics of comb and soliton generation.