Tailoring laser coupling for efficient synchronization

Synchronization of semiconductor lasers is often hindered by their frequency differences and strong amplitude–phase coupling. Previous schemes for laser synchronization are mostly based on homogeneous coupling among the lasers, i.e., the coupling of one laser to other lasers is identical for every laser. We propose to overcome intrinsic disorder in lasing frequencies with tailored disorder in coupling strengths. In particular, the coupling strength between any pair of lasers scales with their frequency difference. We realize this approach experimentally with three single-mode vertical cavity surface emitting lasers (VCSELs) and use a spatial light modulator to control the coupling between the lasers. The critical coupling threshold for frequency locking of three VCSELs is significantly lower than that with uniform all-to-all coupling, and stable phase locking is observed over a wider range of coupling strength. Our method provides an efficient and scalable route toward large-scale synchronization of semiconductor lasers.