Epitaxial design progress for high power, efficiency, and brightness in 970 nm broad area lasers

GaAs based high power broad area lasers are the most efficient source of optical energy and are used in many industrial applications. Despite considerable improvement in power and efficiency in recent years, further improvement is needed due to the high demand from industry. We review here progress in vertical epitaxial layer design, showing how higher performance is enabled by migrating from asymmetric large optical cavity (ASLOC) designs to the newly developed extreme-triple-asymmetric (ETAS) vertical structure. Building on earlier studies at 940 nm, we focus on gain-guided lasers that have operating wavelength 970 nm, have 90 μm stripe width and 4 mm resonator length. We can emphasize the positive impact of epitaxial layer design, without need for advanced lateral structures. We show how design improvement increases conversion efficiency ηE at 12 W output power from 56% to 66%, whilst peak (saturation) power increases from Popt = 14 to 19 W in continuous wave (CW) mode for p-down single emitters on CuW carriers (thermal resistance 3 K/W). Progress in epitaxial design also leads to smaller lateral beam parameter product (BP Plat) at higher bias, leading to lateral brightness Popt/BPPlat < 3 W/mm × mrad. Specifically, in these most recent ETAS structures, by design BPPlat increases more slowly with self-heating, and this leads directly to lower BPPlat at high bias. We will also review options for further increased performance, include efforts to understand and improve BPPlat, which is also limited by a non-thermal ground level BPP0 (here ∼ 1 mm × mrad).