Transient analysis of optical bistability in inhomogeneously pumped lasers

Inhomogeneously pumped devices such as SLEDS and multisegment lasers are known to exhibit absorptive bistability. A new model of the transient behaviour of the optical output during switching is presented for this class of device for the case of both optical and electrical triggering. The model includes the wavelength dependence of the stimulated gain and the spontaneous emission characteristics of the active material. This is particularly necessary because the gain curves are different in the pumped and passive segments. The variation of the photon flux along the length of the laser is also taken into account. Results are obtained for GaAs/GaAlAs devices. Optically induced switching is demonstrated for different wavelengths of the injected light, and the effect of triggering the device by optical injection into either the pumped or the passive segment is examined. The switch-on time is found to be dependent on the electrical or optical overdrive provided by the triggering pulse. Large transient changes in the wavelength are seen during switching, and under some conditions the device can switch off, immediately after switching on, due to strong stimulated recombination in the regions of gain. The recovery time from this can be several nanoseconds. It is seen that self-sustained pulsations can be induced in these devices by optically triggering the device with light at the peak superluminescing wavelength injected into the front facet.