A theoretical study of the effect of zero-crossing points within the dispersion map upon a longhaul RZ-DPSK system.

A theoretical study focusing on the effect of zero-crossing points in the dispersion map for the long-haul return-to-zero differential phase shift keying (RZ-DPSK) transmission system had been conducted. Difference of the transmission performance was characterized with regard to number of zero-crossing points within the dispersion map. It was observed that increasing the number of zero-crossing points in the dispersion map combined with the self phase modulation (SPM) caused the performance degradation near the system zero dispersion wavelength.

Numerical study of the performance improvement of the APSK transmission system using zero-nulling method.

We have studied the transmission performance of amplitude and phase shift keying (APSK) format theoretically. As there is a trade-off between the performance of amplitude shift keying (ASK) and phase shift keying (PSK) through the extinction ratio of the ASK format, zero-nulling method to improve the performance of the PSK format had been proposed. A demerit of the zero-nulling method is a reduction of the total capacity.