Self-slowdown and -advancement of fs pulses in a quantum-dot semiconductor optical amplifier

We demonstrate changes in the propagation time of 180 femtosecond pulses in a quantum-dot semiconductor optical amplifier as function of pulse input power and bias current. The results interpreted as a result of pulse reshaping by gain saturation but are also analogous to coherent population oscillations.

Relative pulse delays (i.e. pulse time delay to pulse FWHM ratio) up to 40% and relative advancements up to 15% are observed when the amplifier is biased at zero current and at currents well above transparency, respectively. Under gain conditions, no pulsedistortion is seen while a considerable pulse distortion occurs at zero bias.