Impact of cross - phase modulation on fiber - optic communication system in presence of first - and second order group velocity dispersion

Abstract

With the increasing demands on the capacity of WDM systems, cross-phase modulation (XPM) has become the most significant nonlinear effect and limits the system performance. On the other hand, group velocity dispersion (GVD) is one of the linear effects in the optical fiber that also restricts bit rates. As a result, the combined effects of GVD and XPM may cause further deterioration of transmission performance in a WDM system. In this research work, an analytical model for a WDM system is developed incorporating the combined effects of XPM, first- and second order GVD. The crosstalk expression for the affected channel is derived in terms of system parameters for standard single mode fiber (SSMF), dispersion shifted fiber (DSF) and large effective area fiber (LEAF). The spectral characteristics are strongly dependent on the channel spacing and GVD of the fiber i.e. the crosstalk effect is more at narrow channel spacing and lower GVD. It is found that at 10 GHz modulation frequency and 0.8nm channel spacing for 100 km distance DSF suffers XPM crosstalk penalty 23 dB and 16 dB more than SSMF for first order GVD and second order GVD respectively. The crosstalk effect due second order GVD is found insignificant in presence of first order GVD in single span system, but at high bit rate and long haul first order GVD compensated system, the effect of second order GVD become significant and play a critical role in limiting the system performance. Simulation results show that system suffers maximum penalty due to XPM effect at zero dispersion coefficient and XPM interference is linearly dependent on optical power of the injected signals in a very large range of system parameters. It is also found that system bit error rate and eye opening penalty is high at higher value of GVD. Among the 3-types of fiber, SSMF contributes least amount of XPM crosstalk for the same amount of pumps and probe power. Thus the findings of this thesis can predict accurate amount of crosstalk due to XPM and may be useful to design a WDM optical communication system.