Grating-based surface-emitting tapered unstable resonator lasers simulations and experiments

We have fabricated and characterized tapered unstable resonator lasers with two slightly different resonator geometries, one with a linear taper and o ne with a nonlinear taper, to investigate the effect of resonator geometry on the performance characteristics. Special attention has been paid to the modal behavior and its dependence on drive current. We investigate the moda l behavior by monitoring the focused spot produced by an integrated focusin g grating coupler. To aid in the design of the lasers and the analysis of t he measurement results, we implemented numerical simulations based on the b eam-propagation method and obtained good agreement between measurements and simulations. We find that the threshold current, the efficiency and the op tical field stability, including filamentation threshold, are significantly improved by adjusting the shape of the current injection region to the div erging field profile in the tapered section. Improvements in threshold curr ent and efficiency are attributed to a more efficient use of the injected c arriers, while improvement in optical field stability is attributed to redu ced carrier induced phase front distortion. We conclude that a relatively s mall modification of the resonator geometry can lead to large improvements in laser performance.