ABSTRACT
From the first demonstrations of optical communication systems, a primary drive in the research activity has been directed towards constant increase in system capacity. Over the past 25 years, it has been an alternating activity to overcome the fundamental fiber limitations of either attenuation or dispersion, and on the basis of the limiting term of the transmission link, systems have been denoted as either loss limited or dispersion limited. The technological challenge was to develop a practical way of obtaining the needed gain, that is, to develop relatively simple and flexible optical amplifiers, which would be superior to the electrical regenerators. Ideally, an optical amplifier would amplify the signal by adding, in phase, a well-defined number of photons to each incident photon. Raman amplification is currently a very active field of research. The fiber-Raman amplifier works through the nonlinear process of stimulated Raman scattering (SRS) occurring in the fiber itself.
