Carrier-induced group-velocity dispersion and pulse compression in semiconductor laser amplifiers

The effect of gain dispersion on pulse amplification in semiconductor laser amplifiers is investigated theoretically. A novel phenomenon, referred to as carrier-induced group-velocity dispersion, is shown to influence considerably the amplified pulse. Chirped input pulses are predicted to be compressed in the presence of carrier-induced dispersion even when the amplifier operates far below saturation. The dependence of the compression factor on device parameters such as the pulse width, the amplifier gain, and the linewidth enhancement factor are studied using a simple analytic model. The results are important for optical communication systems as they imply that semiconductor laser amplifiers can be used to compensate simultaneously for the effects of both fibre loss and fibre dispersion when used as in-line amplifiers.