Stable distribution of low jitter frequency standards over optical fiber networks

In this paper, the authors used the optical fiber as the transfer medium. In the first set of experiments, a microwave frequency standard was placed on the pulse repetition rate (comb spacing) of a mode-locked fiber laser. The authors then compared this method of encoding with simple modulation of a continuous wave laser and have found a marked improvement with the pulsed case. This improvement is due to reduction in the average power on the photodetectors necessary for a given SNR of the detected RF harmonic. By proper dispersion control, the shortest pulse can be delivered to the photodetector which in turn produces the highest SNR with the lowest average power. This result is now limited by the noise floor of the microwave measurement system.