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We demonstrate the use of a fiber-based femtosecond laser locked onto anultra-stable optical cavity to generate a low-noise microwave reference signal.Comparison with both a liquid Helium cryogenic sapphire oscillator (CSO) and aTi:Sapphire-based optical frequency comb system exhibit a stability about$3\times10^{-15}$ between 1 s and 10 s. The microwave signal from the fibersystem is used to perform Ramsey spectroscopy in a state-of-the-art Cesiumfountain clock. The resulting clock system is compared to the CSO and exhibitsa stability of $3.5\times10^{-14}\tau^{-1/2}$. Our continuously operatedfiber-based system therefore demonstrates its potential to replace the CSO foratomic clocks with high stability in both the optical and microwave domain,most particularly for operational primary frequency standards.

Ultra-low noise microwave generation with fiber-based optical frequency comb and application to atomic fountain clock