The integration of optical networks is a potential solution for the increasing capacity and mobility. The bandwidth hungry applications like Video-on-Demand [VoD], Games on Demand [GoD], 3G/4G Mobile services are putting burden on the fiber-optic trunk lines for the transmission rate of Peta bits per second. The increasing user's data traffic increases number of wavelengths which necessitates Dense Wavelength Division Multiplexing (DWDM), a cost effective method to increase the capacity of existing fibers without replacement. Nonlinearities arises as a limiting factor as light intensity inside a fiber is getting increased. Among various nonlinearities Stimulated Raman Scattering (SRS), Four Wave Mixing (FWM) and Stimulated Brillouin Scattering (SBS) in DWDM are dealt in this paper. The effect of dispersion and wavelength spacing on FWM are analyzed. This research aims at optimizing the dispersion, channel spacing and spectral width values for minimizing the FWM, thereby increasing the overall capacity of fiber optic trunk line. The growing importance of high-speed communication is creating a demand for ever faster information transfer rates, particularly in fiber-optic communication systems. Dense Wavelength Division Multiplexing (DWDM) can both significantly enhance transmission capacity and provide more flexibility in optical networks design. © International Science Press.