Coupling mechanism of gain-guided integrated semiconductor laser arrays

It is shown that a gain-guided laser array couples via propagating fields rather than the evanescent mode coupling typically responsible for directional coupling in passive (directional couplers) and active (laser array) devices. We show that these phase-locked modes exhibit an interference pattern, in the junction plane, which arises from the curvature of the phase fronts of optical fields of the interacting lasers. The experimental results are interpreted with the aid of a simple theoretical model, and the effect of the observed mode pattern on the coupling of gain-guided lasers is discussed.