No abstract

Design and technology developments targeted at increasing both power conversion efficiency and optical output power of GaAs-based diode lasers are under intense study worldwide, driven by the demands of commercial laser systems. The conversion efficiency at the operation point is known to be limited by electrical and optical losses in the p-side waveguide. In this paper an 'extreme, double asymmetric' design to mitigate the impact of the p-side waveguide is studied and compared with a more conventional design. An increase of the efficiency at the highest power is demonstrated, but it is less than expected from simulations.

No abstract

High power 9xx-nm broad-area lasers with improved beam quality are required for many applications, but the physical limitations remain unclear, especially the relative importance of free-carrier and self-heating effects. Experimental data are, therefore, presented on a series of diagnostic lasers where the lateral carrier profile at the edges of the electrical contacts has been modified via implantation in order to assess its influence on beam quality. We show that carrier accumulation at the edges of the (90-µm wide) contacts can be eliminated and that as a consequence, near and far field are narrowed and the rate of increase of beam parameter product (BPP) with self-heating reduces by 35%. Overall, the suppression of lateral carrier accumulation allows BPP < 2 mm × mrad to be maintained to 7-W optical output, corresponding to a peak linear brightness of 3.5 W/mm × mrad, comparable with the highest reported values for 90-µm stripe devices.Index Terms-Broad area laser, deep implantation, lateral carrier profile, proton bombardment, slow axis beam quality.

Broad area lasers with novel extreme double asymmetric structure (EDAS) vertical designs featuring increased optical confinement in the quantum well, Γ, are shown to have improved temperature stability without compromising series resistance, internal efficiency or losses. Specifically, we present here vertical design considerations for the improved continuous wave (CW) performance of devices operating at 940 nm, based on systematically increasing Γ from 0.26% to 1.1%, and discuss the impact on power saturation mechanisms. The results indicate that key power saturation mechanisms at high temperatures originate in high threshold carrier densities, which arise in the quantum well at low Γ. The characteristic temperatures, T 0 and T 1 , are determined under short pulse conditions and are used to clarify the thermal contribution to power limiting mechanisms. Although increased Γ reduces thermal power saturation, it is accompanied by increased optical absorption losses in the active region, which has a significant impact on the differential external quantum efficiency, h diff . To quantify the impact of internal optical losses contributed by the quantum well, a resonator length-dependent simulation of h diff is performed and compared to the experiment, which also allows the estimation of experimental values for the light absorption cross sections of electrons and holes inside the quantum well. Overall, the analysis enables vertical designs to be developed, for devices with maximized power conversion efficiency at high CW optical power and high temperatures, in a trade-off between absorption in the well and power saturation. The best balance to date is achieved in devices using EDAS designs with G = 0.54%, which deliver efficiencies of 50% at 14 W optical output power at an elevated junction temperature of 105 °C.