Light pulse amplification in a single-mode fiber waveguide containing resonant impurities

Light pulse amplification in a fiber amplifier is analyzed using a two-level model of resonant impurity atoms in a preinverted state. A steady-state ultrashort pulse propagating in such an amplifier is predicted. The dispersion broadening of this pulse is compensated by a nonlinear compression due to self-interaction, whereas an increase in the amplitude is compensated by linear losses. The dependence of the total energy of a transient pulse on the fiber wavelength is determined and a study is made of the role of the spatial inhomogeneity of the population inversion of the impurity atoms. Quasicoherent amplification is discussed.