Abstract
We investigate the performance of wavelength shift keying (WSK) technique and repeated unequal channel spacing (RUS) scheme and compare them considering a repeaterless optical wavelength-division-multiplexed (WDM) transmission system in the context of four-wave mixing (FWM) effect. The WSK-WDM system outperforms the RUS-WDM system within particular signal levels and enables higher allowable input power, lower power penalty, and higher transmission distance for a given bit error rate at the expense of increased bandwidth. The comparative performance provides important design considerations for a long-haul optical WDM system.