Supermodes with angular momentum from coherent VCSEL arrays-emergence and stability

Abstract

The VCSEL, combining a nonlinear medium with a two dimensional optical resonator, can be a source of complex optical field patterns - which can be employed both for sophisticated signaling in future free space optical interconnection schemes as well as for probing the internal laser nonlinearities. Coherently coupled VCSELs enhance further these notions. We present experimentally and theoretically the evolution of supermodes with angular momentum - composed of multiple optical vortices. The nonlinearity of the laser oscillators is the source both for generation of the optical vortex, for the interlaser coupling and for the stability/instability of the patterns. Exploring these issues assisted us in generating a source with novel emission as well as gaining understanding on the internal laser parameters. We examined the unique near-field (NF), far-field (FF) and spectral intensity patterns emerging from coherent arrays of bottom emitting proton implanted, medium area VCSELs (10-20 /spl mu/m in diameter each). Each VCSEL was emitting an optical field vortex characterized by two "charges" - the topological charge (either +1 or -1 with the respective angular momentum), and the relative phase (within the array). The rich variety of complex supermodes compared to arrays of "regular" beams stemmed from this dual charge. Starting from a pair of lasers, two supermodes were found: 1. Anti-phase locked vortices with the same charge and 2. In-phase locked vortices with opposite charges.