Non scattering losses in optical fibers

Non-scattering losses occurs in optical fibers due to nonlinear effects. The transfer of optical power from one mode to another mode or same mode either in forward direction or backward direction at different frequency is termed as nonlinear scattering. There exist two types of nonlinear scattering. They are Stimulated Brillouin Scattering (SBS) and Stimulated Raman Scattering (SRS).  SBS occurs in systems which operate above 3 mW. SBS becomes very significant when interaction length is long and line width of signal is narrow. SBS can be minimized by broadening the line width. This is achieved by the usage of RF modulation on the laser injection current, by employing an external phase modulator or a self pulsating laser. High frequency optical photons are generated in Stimulated Raman scattering. SRS is a cause of concern in WDM systems. Stimulated Raman Scattering increases exponentially with increase in power. SRS can occur in both forward and backward direction.