All-optical multiplication of ultrastable lasers using Kerr microcomb chip

Ultrastable lasers (USLs), characterized by exceptional phase coherence and frequency stability, are indispensable for various fields including fundamental physics, timekeeping, spectroscopy, metrology, quantum computing, and astronomy. However, conventional USLs are costly and bulky, limiting their availability to specialized laboratories. Here, we introduce a new concept for the multiplication of USLs using a microcavity Kerr frequency comb on-chip. We demonstrate that the Kerr microcomb can be all-optically locked to both the optical reference and microwave reference, allowing the microcomb teeth to inherit the spectral purity of the frequency standards and become an array of USLs. In our experiment, 100 Kerr microcomb teeth achieve integral linewidth significantly below 1 Hz and fractional frequency instability on the order of over 1-second average time, making them 100 state-of-the-art USLs. Our method holds potential to proliferate the use of ultrastable lasers in a wide range of applications.