Advances in coherent 2-dimensional vertical cavity laser arrays

Coupled 2-dimensional (2D) arrays of vertical cavity surface emitting lasers (VCSELs) have been pursued for more than two decades. Recently, we have found that VCSEL arrays defined by introducing an etched photonic crystal (PhC) into the top facet or with multiple implantation apertures demonstrate coherently coupled in-phase operation. We show that proton implantation may also be used to define individual elements in the coupled array. This approach adds no fabrication complexity to that of a conventional implant VCSEL. Because the implant provides electrical confinement without adding optical loss, the lasers tend to lock in-phase, which is the preferred mode of operation. We have also found that variable phase between the array pixels is possible and influences the coherence and far field pattern, where the latter can enable beam steering applications. Changing the current injection to one laser in the array causes the coherence and relative phase between the emission of the two lasers to change. The change in relative phase between defects results in a change in the far field angle of the peak emission. Because the relative phase variation is retained when the array current is pulsed, electronic (rather than thermal) effects create the induced refractive index changes which lead to phase shifting. By combining proton-implanted coherent arrays and separately controlling the injection into a 3-element array, up to 7° maximum beam steering into 2-dimensions has been achieved.