Compression of a Gaussian pulse in two-mode periodic optical waveguides with a complex refractive index

Using a FM Gaussian pulse travelling in a two-mode periodic optical fibre a s an example, it is shown that dispersion parameters caused by the complexi ty of the refractive index substantially affect the pulse dynamics. In part icular, the imaginary part of the effective dispersion enables one to compr ess a pulse in an amplifying medium without its initial frequency modulatio n.