Improvement of dispersion tolerance using phase-Modulated NRZ signals in 40-gb/s transmission systems

Compared with the conventional nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero, and chirped RZ signals by numerical simulation, a higher dispersion tolerance in the presence of fiber nonlinearities and amplifier noise has been obtained in this letter by using the phase-modulated NRZ signals. This scheme aims to improve resistance to residual dispersion by an adapted phase modulation at the transmitter.