The detailed origin of phase jitter in fiber-optic communication systems was firstly reviewed. An overview of
distribution of received phase jitter was presented. By contrasting the phase difference of sample pulses, variance of
phase noise of an DPSK system in dispersion-managed finite fiber spans was calculated and simulated by Matlab, and
the Gaussian shaped possibility density function (p.d.f.) was obtained. The performance of signal was analyzed by
estimating BER, which was calculated from the p.d.f.. By adding ASE noise of different power into the signal at each
EDFA, we found that the suppression of ASE noise contributing considerably to the improvement of signal performance.