Comparison of NRZ- and RZ-modulation format for 40-Gb/s TDM standard-fiber systems

Nonreturn-to-zero (NRZ) and return-to-zero (RZ) signal transmission in dispersion-managed high-speed time-division multiplexed (TDM) systems operating at 1.55 μm over the already installed standard-fiber network are compared by numerical simulations. It is shown that for upgrading the existing network to 40 Gb/s, the RZ-modulation format is superior compared to conventional NRZ-modulation. Standard fiber transmission distances of about 1200 km and 400 km are shown to be feasible within the RZ- and NRZ-format, respectively.