Sub-100 attoseconds stability optics-to-microwave synchronization

We use two fiber-based femtosecond frequency combs and a low-noise carrier suppression phase detection system to characterize the optical to microwave synchronization achievable with such frequency divider systems. By applying specific noise reduction strategies, a residual phase noise as low as -120 dBc/Hz at 1 Hz offset frequency from a 11.55 GHz carrier is measured. The fractional frequency instability from a single optical-to-microwave frequency divider is 1.1x10(-16) at 1 s averaging down to below 2x10(-19) after only 1000 s. The corresponding rms time deviation is lower than 100 attoseconds up to 1000 s averaging duration. (C) 2010 American Institute of Physics. [doi:10.1063/1.3431299]