Progress on a Compact Ultra-stable Laser System for Photonic Microwave Generation

SummaryThe technique for low noise photonic microwave generation [1–5] based on ultra-stable cavity [6–8] and optical frequency comb is being used in a growing number of fields. The optical frequency generated from stable laser locked to high-finesse cavities can be converted into microwave signal with high fidelity. In addition to continuously pushing the relative frequency stability of the ultra-stable laser system used in laboratory to new limit, various field operation scenarios need the cavity-stabilized laser to be compact and portable. In particular, the focus of our lab is that this ultra-stable microwave conversion scheme can serve as local oscillators of the fountain clocks to improve stability and compactness. In this paper, we present the experimental characterization of a compact ultra-stable laser system for photonic microwave generation and efforts to improve its robustness. As the core component, a commercial ULE cavity with length of 25 mm and truncated cubic geometry, which is rigidly fixed to provide effective isolation from vibration disturbances. The thermal noise limit stability of the cavity is predicted at 5E-15.