The continuous, precise time and frequency synchronization system was built on an 80 km single urban fiber link, between Tsinghua University and the National Institute of Metrology. Through precise time and frequency synchronization, the frequency dissemination stability of 7×10^-15/s and 5×10^-19/d was obtained; with active transfer delaycompensation at the transmitting site, the time synchronization inaccuracy was < 50 ps. For the current fiber based frequency dissemination schemes, the disseminated frequencysignal can only be recovered at specific location. A multiple-access RF dissemination scheme was proposed and demonstrated. Using this method, the stable disseminatedfrequency signal can be recovered at an arbitrary node along theentire fiber pathway, which provides a solution for the time-frequency synchronization network in the future.

time and frequencysynchronization  /  fiber dissemination  /  atomic clock comparison  /  stability