Mitigation of nonlinearities in fiber optic DWDM system

Abstract

To meet the growing internet data traffic, transmission capacity of fibers has to be increased. For that Dense Wavelength Division Multiplexing (DWDM) technique has been used nowadays. However, there is a nonlinear distortion which degrades the transmitted signal and hence decreases the overall system performance. The nonlinearities that arise in WDM systems are Cross Phase Modulation (XPM), Stimulated Raman Scattering (SRS) and Four Wave Mixing (FWM). Also it is found that these nonlinearities depend upon input power, dispersion and channel spacing. In this paper two methods have been proposed to eliminate FWM and SRS effect. Firstly, the fiber optic link has been analyzed by increasing the input power. From the analysis it is found that the FWM effect get increased by increasing the input power. But the transmission power should be optimum to transmit the information in long haul fiber optic link. The FWM effect is reduced by placing the Circular Polarizers alternatively in each transmitter before passing through the fiber link. Another method which has been proposed to eliminate SRS is optimum allocation of input power. The unwanted power tilt due to SRS effect is reduced by allocating the transmitted power randomly. The simulation studies are carried out using OPTSIM and OPTISYSTEM software. The simulations have been carried out for multichannel systems with equal spacing. It is found that the optimum power level allocation also improved the system performance.