Nonlinear effects are the impairments in optical signal caused by interaction of power levels of various signals in fiber. Non-linear interactions between the signal and the silica fiber transmission medium begin to appear as optical signal powers are increased to achieve longer span lengths at high bit rates. Consequently, non-linear fiber behavior has emerged as an important consideration both in high capacity systems and in long unregenerated routes.
A variety of parameters influence the severity of these non-linear effects, including line code (modulation format), transmission rate, fiber dispersion characteristics, the effective area and non-linear refractive index of the fiber, the number and spacing of channels in multiple channel systems, overall unregenerated system length, as well as signal intensity and source line-width.
