OPTIMIZATION OF WAVELENGTH SPACING IN A WDM TRANSMISSION-SYSTEM IN THE PRESENCE OF FIBER NONLINEARITIES

The paper studies the transmission limitation of wavelength division multiplexing (WDM) optical fibre systems using inline optical amplifiers imposed by fibre nonlinearities in the presence of optical amplifier noise and fibre dispersion. Two main nonlinear effects, namely four-wave mixing (FWM) and stimulated Raman scattering (SRS), are considered, with the emphasis on the FWM effect. Detailed analysis is carried out to evaluate the transmission distance limitation as a function of various system parameters such as wavelength channel spacing, number of channels and amplifier spacing. It is found that to maximise the transmission distance, a compromise needs to be made between conflicting requirements of channel spacing when considering the FWM and SRS effects, respectively. Various techniques to reduce the FWM impairments are also discussed.