Synchronization Properties of a Cascaded System Consisting of Two External-Cavity Semiconductor Lasers Mutually Coupled via an Intermediate Laser

The properties of chaos synchronization in a cascaded mutual coupling semiconductor laser system consisting of two external-cavity semiconductor lasers (ECSLs) and an intermediate semiconductor laser in between are systematically investigated. We theoretically analyze the general conditions for the synchronization between the ECSLs and those for the global synchronization among all semiconductor lasers (SLs), and numerically investigate their distribution characteristics in the different operation parameter spaces, under the condition of that the ECSLs suffer identical feedback. The simulation results demonstrate that both stable isochronal chaos synchronization (ICS) and leader/laggard chaos synchronization (LLCS) can be achieved between the ECSLs in a large operation range, and they are independent of the feedback delay. This property can be adopted to achieve long-range chaos synchronization between two ECSLs. Also, the stable ICS and LLCS between ECSLs show prominent mismatch robustness and detuning tolerance when they suffer properly strong injections from the intermediate laser. On the other hand, when the mutual coupling parameters and the feedback parameters satisfy some certain relationships, a global isochronal chaos synchronization or hybrid chaos synchronization among all SLs can be achieved, and the global chaos synchronization affords message transmissions between any two SLs, which is beneficial for the implementation of chaos communication networks.