638 International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) Volume No.3 Issue No.5, pp : 638-642 1 May 2014 IJSET@2014 Page 638 Impact of Cross Phase Modulation in Long Haul DWDM Fiber Optic Communication and its Suppression 1 T. Sabapathi, 2 H. Muneera Begum Department of Electronics and Communication Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamilnadu, India 1 sabapathi@mepcoeng.ac.in, 2 muneeralal@gmail.com Abstract- The explosive growth of the Internet urges the quantum leap in the transmission capacity of the optical fiber network. In long-haul DWDM systems, Cross-phase modulation is the dominant nonlinearity that impairs the system’s performance. Cross-phase modulation (XPM) will turn to intensity modulation by fiber dispersion and will cause the pulse’s distortion. Hence, there is a need to suppress cross phase modulation in order to increase transmission capacity. Optical Phase Conjugation is one of the methods to reduce impairments due to cross phase modulation. Besides intensity modulation, DQPSK modulation is carried out to increase bit rate. The technique presented is the simplest and produces good results for high power laser source. This paper analyses the effect of cross phase modulation in DWDM system and it is experimentally analyzed using OPTSIM (Optical Communication Simulator). Keywords- DQPSK (Differential Quadrature Phase Shift Keying), Cross Phase Modulation (XPM), DWDM, Optical Phase Conjugator (OPC), Kerr Non linearity. I. INTRODUCTION Due to the explosive growth of communication in recent years, network operators are having tremendous difficulty accommodating the increasing traffic. As demand on multimedia services including voice, data and video continue to grow, it is necessary to achieve a mature service with a high percentage of consumer use, lower and constant access charge, full time connectivity to service providers and higher bandwidth. But major restrictions in the transmission medium are the chromatic dispersion (CD) and Kerr nonlinearities[i] like self phase modulation cross-phase modulation (XPM) and stimulated scattering and their distribution over the propagation direction, which degrade the performance of wavelength division multiplexing (WDM) optical transmission systems. In general, the nonlinear effect XPM is caused by the modulation of the nonlinear refractive index by the total optical power in the fiber. In the presence of CD this would result in the modulation of the optical phase and the intensity of various signals would be affected. The performance degradation caused by XPM on intensity modulation–direct detection (IM-DD) WDM systems have been investigated through computer simulations and experiments. The extent of the intensity fluctuations caused by XPM as a function of channel separation [ii] and has the dependence of XPM- induced intensity modulation on the fiber length and channel separation has been investigated experimentally in single segment fiber links. II. CROSS PHASE MODULATION In future long-span, high-channel-count wavelength division- multiplexed (WDM) systems, cross-phase modulation (XPM) will be one of the most severe obstacles towards error free transmission. In a dispersive fiber, the dominant fiber nonlinearity that causes crosstalk is cross- phase modulation (XPM). XPM can cause several undesirable effects that could be obstacles to high speed telecommunication optical fibers. Cross Phase modulation is one of the inter channel interference caused by intensity dependence of refractive index. When the light signal carrying information passes through the optical fiber, due to imperfections in the fiber during manufacture or change in composition of fiber materials affects the optical communication. The effects may be of either linear or nonlinear. In WDM systems, the intensity dependent nonlinear effects are enhanced since the combined signal from all the channels can be quite intense, even when individual channels are operated at moderate powers. Thus the intensity dependent phase shift and consequent chirping induced by Self Phase Modulation (SPM) alone is enhanced because of the intensities of the signals in the other channels. Consider a WDM system with two channels (1) he nonlinear polarization is given by P NL (r,t)=ε 0 χ (3) ( 3 = ε 0 χ (3) ( + 2E 1 E 2 ) E 1 + Remaining Terms (2) The first term is due to SPM [iii] whereas the effect of the second term is called cross phase modulation (XPM) and