In-phase antiguided bottom-emitting vertical cavity laser arrays

Introduction: Two-dimensional (2D)-phased vertical cavity surface-emitting laser (VCSEL) arrays offer unique advantages for scaling up single-mode power for high-brightness applications such as fibre laser pumps. They tend, however, to operate in the undesirable out-of-phase mode, which has an on-axis null in the far field [1]. In-phase VCSEL arrays with an on-axis maximum in the far field have been obtained primarily with antiguided, top-emitting designs [2–5]. These structures, however, face difficult challenges in thermal management and current injection uniformity, especially for larger arrays. These difficulties can be substantially mitigated with a bottom-emitting design, as commonly used for high-power incoherent 2D VCSEL arrays. The key design advantages include significantly reducing thermal resistance from the active region to the heatsink and direct current injection into the array elements. Previous bottom-emitting coherent arrays have employed reflectivity modulation and/or mesa etching, which led to an out-of-phase operation [1, 6, 7]. We report a bottom-emitting VCSEL array with an antiguided index profile created by a simple, self-aligned process to demonstrate in-phase, continuous-wave (CW) emission, which represents a critical step towards coherent, high-brightness arrays.