Optimization of Interchannel Separation in WDM Transmission Systems in the presence of Fibre Nonlinearities

Wavelength division multiplexing (WDM) can give two benefits at the same time: enhancement of transmission capacity and increase in flexibility in optical network design. It is possible to build long distance transparent optical transmission links without electrical regenerators with the help of erbium-doped fiber amplifiers (EDFAs). In such systems, fibre nonlinearities are likely to impose a transmission limit due to increased total interaction length. Most of the work so far has been concentrated on the study of the limitation of input power per channel imposed by fibre nonlinearities. There are a number of optical nonlinear effects in optical fibers, such as stimulated Raman scattering (SRS), stimulated brillouin scattering (SBS), carrier induced phase modulation and four wave mixing (FWM). Out of these SRS and FWM are the dominant effects. The maximum possible transmission distance has been reported to be dependent on various system parameters like number of channels, channel spacing, the allowable power per channel, the amplifier spacing etc. In this paper an algorithm has been suggested for the optimization of interchannel separation considering the combined effect of SRS and FWM in the presence of amplifier spontaneous noise (ASE).