Complex coupling coefficient in laterally coupled microcavity laser diode arrays

The complex component of the coupling coefficient κ = κ r + i κ i, used to describe the coupling between adjacent semiconductor microcavity laser diodes, is studied. The complex component κ i represents the gain or loss difference between the coherent in-phase and out-of-phase array supermodes obtained from two laterally coupled lasers. Steady-state analysis reveals that the threshold of the preferred coherent supermode is lower than that of an individual laser mode in proportion to κ i. We show that the complex component κ i can be experimentally extracted from a simple output power vs current measurement. Furthermore, the change in the lasing threshold at the onset of optical coupling perturbs the differential resistance of the coupled lasers. Therefore, an electrical signature of optical coupling can be detected in the diode array series resistance.