Ultralong-haul transmission of 40-Gb/s RZ-DPSK in a 10/40 G hybrid system over 2500 km of NZ-DSF

We report on dense wavelength-division-multiplexing transmission of 40-Gb/s return-to-zero differential phase-shift keying at distances of 2500 km over conventional nonzero dispersion-shifted fibers with large system margins and small transmission penalties in a hybrid system comprising of interleaved 10and 40-Gb/s data rates. We use all-Raman amplifiers with 100-km amplifier spacing and compare the transmission performance of the hybrid system to that of a system carrying only 40-Gb/s traffic.