Two-dimensional coherently coupled vertical cavity laser arrays

Two-dimensional coherently coupled vertical cavity surface emitting laser (VCSEL) arrays have long been pursued for narrow divergence and high brightness applications. We discuss both top and bottom-emitting coherent VCSEL arrays that can operate in the in-phase mode. The key to their operation is strongly coupled leaky-mode operation, which can be achieved using ion implantation to define a periodically arrayed gain regions, and a 2D photonic crystal hole pattern etched into the top facet to control the lateral modes [1, 2]. The brightness of VCSEL arrays typically suffer from either incoherence between elements [3] or an out-of-phase far field profile [4], either of which can arise from periphery current injection. Bottom-emitting arrays can circumvent these difficulties by allowing direct current injection into all laser elements. Previous pulsed coherent bottom emitting arrays have employed reflectivity modulation to select the supermode, which necessarily leads to out-of-phase emission [5]. Here we report a simple self-aligned process to demonstrate inphase continuous wave (CW) emission in both top and bottom emitting coherently coupled VCSEL arrays. We also show for top emitting coherently coupled arrays that the phase can be varied by differential current injection over a full range of p which enables beam steering at modulation speeds up to 100 MHz [6].