Lag Syncronization in Delay-Coupled Semiconductor Lasers

In this paper, the authors present an overview of the instabilities exhibited by delay-synchronized semiconductor lasers, the characteristics of the ensuing lag-synchronization regimes, and the relevance that these studies might have in other delay-coupled systems in nature. The authors also describe recent experimental results that address the question of how the leader-laggard dynamics emerges. According to these results, leader-laggard alternance emerges through a quasiperiodic state, a regime that is known to occur in delay-coupled semiconductor lasers. Finally, the paper discusses methods to control the lag time. In particular, it shows how the directionality of the coupling between two mutually injected lasers determines which one is leading the dynamics, even in the case of equal frequencies. It also reviews coupling architectures that lead to zero-lag synchronization, and introduce recent results showing that applying a common noise to the injection current of the lasers leads also to a zero lag.