Tailoring complex coupling for efficient synchronization of semiconductor lasers

A grand challenge for laser synchronization is the intrinsic frequency disorder. We build an experimental platform for programming the complex coupling coefficients of semiconductor lasers to promote frequency and phase locking. The coupling amplitude between every pair of lasers in an array is tuned to scale with their frequency difference. Coupling phases are scanned to meet the phase matching conditions for constructive interference of coupled fields. The minimum coupling budget for global synchronization is significantly reduced, as shown experimentally for three vertical-cavity surface-emitting lasers with intrinsic frequency detuning. The customized coupling offers an efficient approach to stable synchronization of semiconductor laser arrays for coherent beam combining.