Waveguide optimization of blue laser diodes

This work discusses the optimization of the ridge waveguide design of blue laser diodes with respect to minimal threshold current density and a high kink level for the fundamental mode. Additional conditions are given by the process technique and heat conduction from the active layer to the substrate. This study utilizes waveguide simulations which include two-dimensional plane-wave expansions of the scalar TE field and straightforward matrix diagonalization using complex refractive indices. Gain in the active layers and absorption losses are considered. These relatively simple simulations predict correctly the shapes of the fundamental and higher order lateral mode near fields. These simulations also predict lower losses for higher order lateral modes as compared to the fundamental mode with increasing ridge height (equivalent to an increasing etch depth), because higher order lateral modes have more degrees of freedom to omit the lossy p-waveguide. This is consistent with the experimental observation of an increasing tendency of kink formation for deeper etched ridge waveguides.