Supraluminal velocity of a pulse envelope maximum in amplifying optical fiber

Frequency-modulated Gaussian pulse propagation in an amplifying fiber is described within the framework of a linear model with an allowance for the second-order dispersion effects. It is demonstrated that the presence of an imaginary part in the group velocity dispersion parameter of the single-mode optical fiber with luminous gain leads to the possibility of the pulse envelope at a supraluminal velocity.