| Evanescent optical coupling between elements in vertical cavity surface emitting laser (VCSEL) arrays is interesting for applications in areas such as optical communications, image processing, and electronic beam-steering. Past work in coherently coupled VCSEL arrays has resulted in out-of-phase arrays or more desirable in-phase arrays, which suffer from complex fabrication processes. This work examines two types of evanescently coupled VCSEL arrays: photonic crystal (PhC) and implant-defined arrays. Both array types exhibit electronic beam-steering due to a variable phase difference between neighboring lasers. This phase difference is tunable with changes in the differential current injection between lasers. This work uses antenna array theory and coherence theory to discover that coherence is maximized around purely in-phase and out-of-phase operation conditions. Additionally, this work studies the modes of PhC VCSELs and develops a coupling theory which predicts the frequency splitting between lasers. Because implant-defined arrays do not include optical loss between lasers, these arrays tend to operate in-phase with minimal processing complexity. Thus, devices are studied and developed which operate in-phase and allow for electronic beam-steering, both of which are useful for potential applications. |
