Dual synchronization of chaos in one-way coupled microchip lasers

We experimentally demonstrate the dual synchronization of chaos in two pairs of Nd:YVO₄ microchip lasers in a one-way coupling configuration over one transmission channel. Dual synchronization is achieved when the optical frequency is matched between the corresponding pairs of lasers by using injection locking. We investigate the influence of optical injection from the two master lasers to one slave laser, and found that the dual synchronization is observed when the injection locking is achieved between either of the master lasers and the slave laser. Under the condition of the injection locking between both of the master lasers and the slave laser, the injection locking is alternately achieved and the accuracy of dual synchronization is degraded. We also confirm these results by numerical calculation.