Effect of XPM and FWM on the performance of M-ary WSK-DWDM transmission system

Abstract

Optical dense wavelength division multiplexing (DWDM) systems using low dispersion fibers and erbium-doped fiber amplifier (EDFA) are very attractive to meet up the growing demand for broadband information distribution networks. High data rates as well as long spans between amplifiers in a chain require high optical power per channel to satisfY the signal to noise ratio (SNR) requirements. For DWDM systems with long repeater-less spans, the simultaneous requirements of high launched power and low dispersion fibers lead to the generation of new waves by four-wave mixing (FWM) which limits the allowable power input to the fiber and these limits the transmission distance. In this thesis work, performance analysis is carried out for a DWDM system with M-ary walength shift keying (M-WSK) modulation considering the effect ofXl'M & FWM in a SMF. A direct detection receiver model is developed which is based on Mach-Zehnder Interferometer (MZI) and Maximum Likelihood (ML) detection. Analysis is carried out to fmd the expression for the signal photo current, shot noise due to signal and FWM power and beat noise components resulting out of beating of signal and FWM during photo detection process. Analysis is extended to find the expression for the bit error rate (BER) of M-WSK direct detection receiver in presence of Xl'M & FWM. Further, forward error correction coding like convolution -coding is applied to mitigate the effect ofXPM& FWM. Performance results are evaluated in terms of BER for different fiber length, input power and number of DWDM channels. Numerical results show that there is a significant reduction in the effect of FWMat higher order M-WSK system compared to binary. Significant amount of coding gain as well as increase in allowable input power are obtained due to rate-l/2 convolution coding compared to the system without coding. The results of this thesis will find application in design of a DWDM system in presence ofFWM.