Improving intergroup synchronization in a ring topology structure of semiconductor lasers by asymmetric coupling

We numerically demonstrate the enhancement of intergroup synchronization in a ring topology structure consisting of four semiconductor lasers (SLs) by asymmetric coupling. The lasers are divided into two groups, each of which consists of two non-adjacent lasers with the same optical frequency. We study the intergroup synchronization performance of symmetric coupling and asymmetric coupling. The results indicate that the synchronization coefficient (SC) of intergroup synchronization has a saturation value which displays a plateau ranging only from 0.8 to 0.9 in symmetric coupling ring structure. Through asymmetric coupling, the SC of intergroup synchronization above 0.9 can be obtained, and its maximum value can be enhanced up to 0.98 as coupling strength increases. Besides, the intragroup isochronal identical synchronization is kept. Our results also indicate that the enhancement of the intergroup synchronization is physically attributed to the injection-locking effects caused by asymmetric coupling between groups.