Enhanced chaos synchronization and communication in cascade-coupled semiconductor ring lasers

• Chaos synchronization between two semiconductor ring lasers (SRLs) is studied.
• Self-, cross-feedback, global and mode-selective injection are compared.
• Cascaded synchronization is realized among three SRLs.
• Enhanced chaotic communication in the cascade-coupled SRL system is achieved.

We numerically investigate the properties of chaos synchronization in a master–slave configuration consisting of a master semiconductor ring laser (SRL) with self-feedback or cross-feedback and a solitary SRL (slave). Different coupling schemes related to global injection and mode-selective injection are proposed and explored in our simulations. The numerical results demonstrate that among the studied coupling motifs the synchronization performance between the modes of the two chaotic SRLs is better when global injection scheme is employed. Furthermore, enhanced chaos synchronization and communication in three cascade-coupled SRLs via global injection are reported, where the time delay signature cannot be identified from the outputs of the three SRLs due to the proper selection of cross-feedback parameters of the master SRL.