ABSTRACT
This chapter provides an overview of the main features of fiber optical amplifiers based on stimulated Raman scattering, stimulated Brillouin scattering, and four-wave mixing effects. In an early stage, the ultimate capacity limits of optic-optic communication systems were determined by the spectral bandwidth of the signal source and of the fundamental fiber parameters: loss and dispersion. Several means of obtaining optical amplification had been suggested since the 1970s, including direct use of the transmission fiber as gain medium through nonlinear effects, semiconductor amplifiers, or doping optical waveguides with an active material that could provide gain. The dominant noise light in fiber Raman amplification is due to the amplified spontaneously Raman scattered light. In fact, a part of the pump energy is spontaneously converted into Stokes radiation extending over the entire bandwidth of the Raman gain spectrum and is amplified together with the signal.
