Amplification in optical fibers by rare earth doping

An overview of the fundamental physical process responsible for optical amplification in Raman fiber amplifiers and in rare earth doped (thulium-doped and erbium-doped) fiber amplifiers, is discussed. We formulate basic equations governing optical amplification for each of the two types of amplifiers and define the important parameters used for performance characterization of these amplifiers. This paper outlines the method used in doped fiber amplifiers.