simulations verify that when DPSK demodulation is conducted
better transmission performances can be achieved and the optimal FSR value obtained by adjusting the relative delay of the two arms of the Delay Line Interferometer(DLI) for optimizing the Free Spectrum Range(FSR) so as to make it greater than the transmission bit rate
than those by the conventional 1 bit delay.Besides
the DPSK system after FSR optimization is improved in both OSNR sensitivity and dispersion tolerance.However
its suppression effect on PMD is not obviously enhanced.