Comparison of return-to-zero differential phase-shift keying and ON-OFF keying in longhaul dispersion managed transmission

Performance of return-to-zero (RZ) differential phase-shift keying (DPSK) in ultralong-haul dense wavelength-division-multiplexing (WDM) dispersion managed transmission is studied experimentally and compared with conventional ON-OFF keying (OOK) in a 10-Gb/s system. We show that, while OOK out-performs phase-shift keying in a low spectral efficiency WDM system, the performance of DPSK is comparable to OOK at 10-Gb/s transmission with a spectral efficiency of 0.2. Furthermore, RZ DPSK is advantageous in a high spectral efficiency (e.g., >0.4) system and our numerical simulation results show superior performance of DPSK at 10 Gb/s with 25-GHz channel separation.