Control of excitable pulses in an optically injected semiconductor laser

Excitability is a property of many nonlinear dynamical systems which is defined by the response of the system to external perturbations. A system is said to be excitable if a small perturbation leads to a linear response (which depends on the perturbation itself) while a large enough perturbation, above a certain threshold, leads to a response which does not depend on the perturbation. This precise property is key to the operation of many biological systems and in particular to the information processing capabilities of ensambles of neural cells: in such a system information is encoded in the temporal pattern of the pulses and not in their precise shape or amplitude. From this point of view, the realization and the control of excitable systems based on semiconductor lasers (fast, robust and versatile elements of many present and future key technologies) may bring to optical telecommunications systems functionalities typical of neural cells such as thresholding and signal restoration. In spite of many theoretical [1] or experimental [2,3] investigations devoted to the excitable character of lasers with injected signal, no experimental demonstration for the control of excitable pulses in injected semiconductor lasers has been reported yet. In the present contribution, we show that excitable pulses can be triggered by applying suitable perturbations in either the bias current of the device or in the injected beam parameters.