Phase tuning in coherently coupled VCSEL array

Two potential applications of coherently coupled vertical cavity surface emitting laser (VCSEL) phased arrays include beam-steering [1,2] and high-brightness sources [3]. While a major difficulty for high brightness VCSEL arrays has been that typical evanescent coupling designs lead to the undesired out-of-phase supermode [4], we have shown reliable in-phase operation using ion-implantation and photonic crystal confinement, which requires a relatively simple fabrication process [5]. Common to both beam-steering and high power applications is the need to carefully control the phase difference between neighboring elements of the optically coupled array. We report measurement of the relative phase in coherently-coupled in-phase VCSEL arrays and show that the phase can be varied by differential current injection over a full range of π, requiring 200 μA, which is several orders of magnitude lower than phase tuning by similar methods in slab-coupled lasers [6].