Spectral Shift and Distortion due to Self-Phase Modulation of Picosecond Pulses in 1.5-microns Optical Amplifiers.

Picosecond pulses are observed to exhibit large frequency shifts (-50 GHz) and spectral distortion on propagation through semiconductor laser optical amplifiers. The spectral changes are shown to result from self-phase modulation occurring due to the carrier- induced index changes that invariably accompany gain saturation. An analytic model for pulse amplication is presented by including the self-phase modulation effects. Its predictions are in good agreement with the experimental results.