Optical fiber technologies have revolutionized telecommunication. The need for extensive transmission capability has spurred the production of fiber optics. This study aims to include a definition of XPM and FWM and how they influence the optical signal transmitted through nonlinear dispersive fibers. Consequently, Nonlinear fiber optics plays a significant role in implementing high-capacity optical networks. In this work, we evaluate the effect of XPM and FWM in fiber optics based on OptiSystem simulation results in this paper. We found the Nonlinear optics deals with the behavior of laser, Nonlinear effects in the optical fiber occurring due to nonlinear refractive index are Cross-Phase Modulation (XPM) and Four-Wave Mixing (FWM). In summary, Nonlinear effects are essential for in-venting lasers, amplifiers, switching, multiplexing devices, and demultiplexers.