Theory Of Operation Of Three- And Four-Level Fiber Amplifiers And Sources

We review theoretical models of fiber amplifiers, resonant fiber lasers and superfluorescent fiber lasers made of a single mode laser fiber, for example a silica fiber doped with a rare earth laser ion. The quantities which are investigated are the optical gain, the threshold and conversion efficiency in fiber sources, and the spectral narrowing in superfluorescent sources. These models take into account the nature of the laser transition (i.e. 3- or 4-level), the potential presence of pump ESA, and the guided nature of the pump and signal waves interacting along the fiber. The emphasis is placed on the development of simple, closed-form expressions for these quantities.