Coherence tuning in optically coupled phased vertical cavity laser arrays

Vertical-cavity surface-emitting laser arrays can be designed to operate in a coherently coupled mode, however, high yield has been challenging in past efforts. We discuss microcavity laser arrays that are designed to be optically coupled but with independent bias current injection into each array element. We demonstrate that these arrays can be electronically tuned to coherently coupled operation and at bias conditions not previously realized. Control of injection bias conditions to individual array elements allows resonance tuning of each element with the result that the phase relation and coherence of the array can be engineered. This control enables increased output power in either in-phase or out-of-phase coherent operation from a single array, and ensures coherent operation from nearly all arrays. This ability to tune into coherence will enhance the performance of phased vertical cavity laser arrays as well as improve their fabrication yield.