stephane barland - Institut de Physique de Nice - Keywords: nonlinear dynamics, delay, optics

stephane barland - Institut de Physique de Nice - Keywords: nonlinear dynamics, delay, optics

Contribution title: A regenerative memory based on a laser with delayed retroaction


The temporal evolution of complex systems (of any nature) is in general determined by their surroundings and by their immediate history. However, in some cases, a distant past may have a strong impact on the present evolution. Well known examples include the echo phenomenon during online conversations or the hot-cold shower temperature. In the echo case, the speaker and the listener perceive each other's messages but with some delay. Sometimes, the speaker also perceives his own message, fed back to him after some delay. In both situations, this delay leads to very complex conversation dynamics, each speaker interrupting the other, repeating his own messages or getting generally confused. In the "hot-cold" shower problem, a large delay between the user's action on the hot water tap and an actual change of incoming water temperature is often a source of very large and most unpleasant temperature fluctuations, to the point that a comfortable stationary regime may be very difficult to achieve. The above situations are particular examples of a very large class of systems which can be described as "delayed dynamical systems".

In this contribution, we study a specific example of "delayed dynamical system" based on a semiconductor laser. In the particular configuration we design, the laser mimics the response of a biological neuron in response to external perturbations: for weak stimuli, nothing happens but for sufficiently large stimuli, a spike is generated and the characteristics of this spike do not depend on the details of the stimulus. We demonstrate that, when submitted to a delayed feedback (ie, the spike is fed back into the laser after some time), this device can store information in spike timing patterns, provided light spikes do not interact too much with each other.