Theoretical balance model of the ytterbium-doped fiber amplifier.

• Proposes the theoretical model of the ytterbium fiber amplifier based on the conservation laws. • Physical limits of this approach applicability are shown. • Presents a comparison of the proposed model and the models of a fiber amplifier. Based on conservation laws, kinetic equations for changes in ion populations in different energy states are written down, as well as equations how optical radiation intensity (and power) is changing in the optical fiber core is sequentially derived. Physical limitations of the given approach are also considered. A comparison of the results of a numerical analysis of the formation of luminescence in the ytterbium-doped optical fiber (with different representations of the probability of "survival" of spontaneous emission photons) with experimental data is presented. [ABSTRACT FROM AUTHOR]