High-brightness tapered diode lasers generally work in the fundamental transverse mode. Still, under the condition of high power, the beam quality is often deteriorated by the influence of higher-order modes. At the junction of the device ridge waveguide and the conical amplifier, there is a great difference in the refractive index step △n, which is the key area for producing high-order modes and influencing each other. In this paper, the physical process of high-order side mode excitation in a large optical cavity InGaAs/AlGaAs conical LD was studied. The mode changes of the propagation interface were simulated by the eigenmode expansion method (EME). The effects of various separation distances of the beam spoilers were compared and verified by experiments. The results show that through the practical design of the separation distance of beam spoilers at the mode propagation interface, the tapered LD can maintain the high beam quality of M2=1.9 at 3.2 W.
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-μm 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 μm, 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.
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