ABSTRACT
Several means of obtaining optical amplification have been suggested since the 1970s, including the direct use of transmission fiber as a gain medium through nonlinear effects, semiconductor amplifiers, or doping optical waveguides with an active material (rare-earth ions) that could provide gain. This entry discusses the general concepts of optical amplifiers, and details semiconductor optical amplifiers, rare-earth-doped fiber amplifiers, fiber Raman amplifiers, fiber Brillouin amplifiers, and fiber parametric amplifiers.
