Modulation instability of optical radiation in single-mode amplifying fibres

The conditions for the appearance of the modulation instability of a wave packet in a medium with the imaginary components of the propagation constant and dispersion parameters are studied. The possibility of existence of modulation instability in the region of normal material dispersion, the bistable nature and the dependence of the dynamics of its development on the ratio of the imaginary and real components of dispersion parameters are revealed.