INFLUENCE OF RESONANT ABSORPTION ON THE PROPAGATION OF FEMTOSECOND PULSES IN AN ER-DOPED OPTICAL-FIBER

By making numerical simulations the influence of resonant absorption i n Er-doped fibres on the propagation characteristics of femtosecond pu lses has been examined. It is shown that when the fibre background dis persion is relatively small compared to the dispersion caused by absor ption, the pulses propagating in an unpumped Er-doped fibre can be eit her compressed or broadened, depending on whether the spectrum of the launched pulse is on the longer or shorter wavelength side of the abso rption center. The phase distortion due to absorption has a more sever e impact on the temporal profile of a propagating pulse than the corre sponding amplitude attenuation. A switching of the sign of the actual fibre dispersion on one side of the absorption center occurs and this can lead to a change of pulse propagation characteristics from a solit on regime to a non-solitonic regime.