Laser dynamics in self-pulsating quantum dot systems

We have studied self-pulsation in InGaAs quantum dot lasers with an emission wavelength in the 1 μm band. The use of saturable absorption to produce internal optical feedback in semiconductor lasers is well established and leads to the phenomenon of self-pulsation. The characteristics of this self-sustaining oscillation in the optical intensity are determined by the optical characteristics of the amplifying and absorbing media. These experiments therefore provide a direct measure of the intrinsic dynamics of the dot laser system free of any external parasitics. At room temperature, pulsation is observed up to a drive current of ${\text{1.5\hspace{0.05em}I}}_{\mathrm{th}}$ with a maximum pulsation frequency of 700 MHz. The self-pulsation is strongly temperature dependent, and cannot be maintained below a temperature of 150 K. Studies of the optical gain and carrier lifetime within the lasers indicate that the dynamic characteristics are controlled by the interaction of the quantum dots with the two-dimensional wetting layer surrounding them. The relatively low pulsation frequency results from the strong saturation of the gain with increasing injection at room temperature, while the thermal switch-off of pulsation is due to changes in the absorber recovery time.