Dynamical entrainment of unidirectionally coupled single mode diode lasers

We numerically study the entrainment of two unidirectional coupled single-mode semiconductor lasers in a master-slave configuration. The emitter laser is an external-cavity laser subject to optical feedback that operates in a chaotic regime while the receiver has no optical feedback and consequently operates under CW when it is uncoupled (open loop scheme). We compare the performance of this scheme with the close loop one in which both emitter and receiver are subjected to optical feedback and operate in a chaotic state. We compute the degree of entrainment or synchronization of the two lasers as a function of the detuning, the emitter-receiver coupling constant and the feedback rate of the receiver. We find that the close loop scheme has, in general, a larger region of synchronization when compared with the open loop. We also study the possibility of message encoding and decoding in the both open and close loops and their robustness against parameters mismatch. Finally we compute the time it takes the system to recover the synchronization or entrainment state when the coupling between the two subsystems is lost. We find that this time is much larger in the close loop than in the open one.