Optical-Comb-Based Frequency Stability Transfer Across the Spectrum With a Multichannel FPGA

Abstract

Using the optical comb as a transfer oscillator is an effective approach to convert the spectral properties of ultrastable lasers to other wavelength domains. We describe a digital locking system that enables this process to be replicated for several lasers at a time, supporting the simultaneous and independent lock of up to six lasers to a single, high-performance reference oscillator. The locks are robust, easily reconfigured, and contribute a short-term instability lower than $3\times 10^{-{18}}$ at 1 s, even when the comb is operated in the broad-linewidth regime and with no need for lasers prestabilization. With this system, we transfer the coherence of the ultrastable clock laser of a Yb optical lattice clock at 1156 nm to various lasers in the 1550 nm region, including the one used for frequency dissemination with long-distance fibers, with less than $1\times 10^{-17}$ instability at 1 s. The digital implementation enables a modular approach with enhanced control over operational parameters, minimizing setup complexity and hardware-related undesired effects. It also allows for immediate reconfiguration and seamless upgrades, being suitable for applications requiring multiple ultrastable lasers at different wavelengths, such as local or distributed optical clock ensembles, coherent spectroscopy, and quantum simulation.