Effect of lateral index step on the performance of high-power broad-area 970-nm diode lasers based a large-optical-cavity waveguide structure

High brightness broad area lasers with high polarization purity are highly efficient light sources for high brightness fiber coupled and direct semiconductor lasers. Effect of lateral index step on the performance of high-power broad-area 970-nm diode lasers based a large-optical-cavity waveguide structure was studied and presented here. The index step of the 80-mu m wide ridge is found a key parameter to control the output power, lateral far-field angle, beam waist and polarization purity. The threshold current decreases with the increase of the etching depth while the slope efficiency increases. When gain guide lateral waveguide by very shallow etching was used, the beam waist expands to a size of more than 200 mu m, which was attributed to anti-guiding effect and current spreading. When large index step is introduced by deep etching, enhanced filamentation was observed, which is attributed to an enhanced confinement of the higher order modes. What's more, the strain introduced by the etching of the ridge can deteriorate the polarization purity. The study in this paper shows that the lateral index step should be optimized to fabricate high brightness high efficiency broad area lasers with high polarization purity.