Modelling of self-sustained pulsations in nonuniformly pumped semiconductor lasers

A numerical model of the carrier and photon densities in the active region of a nonuniformly pumped semiconductor laser is described. This model has been applied to the case of 2-contact, split-electrode ridge-waveguide InGaAsP-InP lasers, in order to simulate the self-sustained pulsations that have been observed in these devices. The resulting simulations show two different types of self-sustained pulsations: oscillations due to repetitive Q-switching, and a self-perpetuating modulation of a continuously lasing output. The driving force in both cases is the saturation of the absorption in the laser cavity: it is not necessary to introduce additional mechanisms such as mode competition or instability in order to simulate these two types of behaviour. The authors have characterised the output power, frequency and pulse shape for a series of devices that exemplify these two types of self-pulsing operation, and compared the results to experimental observations in the literature