Wavelength division multiplexing in long-haul transmission systems

Wavelength division multiplexing shows great promise for the next generation of long-haul undersea cable transmission systems. WDM techniques will allow for greater transmission capacity and network flexibility compared to the present single-channel optical amplifier systems. The transmission of many WDM channels over transoceanic distances can be limited by a variety of phenomena, including the finite bandwidth of the erbium-doped fiber amplifier repeaters, the nonlinear interactions between channels, and the noise accumulation along the chain of amplifiers. Significant progress has been made over the past few years in understanding the nature of these impairments for long-distance transmission. This paper describes techniques used to transmit many WDM channels over transoceanic distances using the nonreturn-to-zero format and other nonsoliton methods. Data is presented for several WDM experiments including the transmission of 100 Gb/s (20 channels of 5 Gb/s) over 9100 km.