The noise in optical fiber communication systems is caused by a variety of factors, including optical amplifier noise, dispersion-induced noise, thermal noise, shot noise, interference noise, Raman scattering noise, and polarization-related noise. The physics of noise in optical communication links is of great interest in the design of fiber optic communication systems. We examine the importance of the FON term as well as the dependence of NLIN on modulation format with respect to li k-length and number of spans. Dispersion-Induced Noise: Dispersion is a phenomenon in optical fibers where different wavelengths of light travel.