Bistability and pulsations in semiconductor lasers with inhomogeneous current injection

Bistability and pulsation at microwave frequencies are observed in CW GaAs semiconductor lasers with inhomogeneous current injection. Inhomogeneous current injection is achieved with a segmented contact structure. Crucial to the understanding of the characteristics of this device is the discovery of a negative differential electrical resistance across the contacts of the absorbing section. Depending on the electrical bias condition, this negative differential resistance leads to bistability or light-jumps and self pulsations. A simple model based on conventional rate equations with a linear gain dependence on carrier density explains the observed behavior and suggests a new mechanism in inhomogeneously pumped diode lasers for light-jumps and pulsations which does not depend on the condition for the usually proposed repetitively -switching. Investigation of the switching dynamics of this bistable optoelectronic device reveals a delay time which is critically dependent on the trigger pulse amplitude and typically on the order of a few nanoseconds with power-delay products of 100 pJ. The observed critical slowing down and its origin is discussed. We also report on the characteristic of this laser coupled to an external optical cavity and we demonstrate successfully that this bistable laser can be used as a self coupled stylus for optical disk readout with an excellent signal to noise ratio.