Fiber Non-linearities : Threat to the Performance Analysis of Optical Fiber System

Focus on development of broadband optical communication systems is incredible since it offers combination of wide bandwidth and low losses unmatched by any other transmission medium. One of the most important changes in fiber-optic communication systems brought about by EDFAs is the expansion of regenerator spacing up to transoceanic distances. However, a new problem has arisen, that is, the accumulation of fiber nonlinearities along the links with the increase in optical power levels. In optical communication systems, the input signal to the fiber is usually a composite optical signal modulated with information bit streams. When all the input signal frequencies interact due to fiber nonlinearities, the output bit stream may behave in a complicated way giving adverse effects on system performance. In wavelength-division-multiplexing (WDM) systems, inter-channel interference due to fiber nonlinearities may limit the system performance significantly While the other two conventional limiting factors in designing optical communication systems, namely, fiber loss and dispersion, are relatively well understood, and can be easily overcome by optical amplifiers and dispersion compensation, but,fiber nonlinearities have not been fully analyzed and understood despite a rich collection of literature dealing with fiber nonlinearities . Therefore, it is crucial to understand fiber nonlinearities and their effects on fiber-optic communication systems. The main motivation of this work was to study theoretical and simulation studies of broad band optical communication systems due to fiber nonlinearities. Here, we investigate power effects on simulation of optical communication systems with self phase modulation (SPM) and cross phase modulation(XPM). by using the parametric run feature in OptSim .By increasing the power, SPM grows and depletes the signal, and the measured power actually decreases with the increasing of the transmitted power. The eye diagram highlights the conversion due to the SPM and XPM. Specifically the eye opening decreases with increasing transmitted power. Keywords—Eye diagram, Optsim , SPM, XPM, Kerr effect