Improving the power and efficiency of 9xx-nm 1 broad-area laser diodes has a great help in reducing the cost 2 of laser systems and expanding applications. This letter presents 3 an optimized epitaxial structure with high power and conversion 4 efficiency. Laser diodes with 230 µm emitter width and 5 mm 5 cavity length deliver continuous-wave output power up to 48.5 W 6 at 48 A, 30 • C, the highest power reported for 9xx-nm single 7 emitter lasers so far. The slope efficiency is as high as 1.23 W/A 8 due to a low internal optical loss of 0.31 cm −1 and a high internal 9 efficiency of 96%. The maximum power conversion efficiency 10 reaches 72.6% at 15.3 W and 67.3% at the operating power of 11 30 W under a heatsink temperature of 25 • C. Life test results 12 show no failure in 1000 hours for 55 laser diodes. 13 Index Terms-Semiconductor laser, laser diode, high power, 14 high efficiency, 915 nm. 15 I. INTRODUCTION 16 H IGH power 9xx-nm laser diodes (LDs) are widely used 17 as pump sources for fiber lasers and light sources for 18 direct-diode systems in various industrial applications [1], [2], 19 [3], [4]. 915 nm pump LDs are the major choice for fiber 20 lasers because of their broad absorption band for Yb-doped 21 fibers [1], which has a big advantage for working conditions 22 in a large temperature range. A high-performance laser system 23 with an output power of 1-10 kW needs a large quantity 24 (100 to 1000) of pump LDs. The cost of these systems relies 25 dramatically on the LDs, which gives a stringent requirement 26 for the performance, quality, and reliability of the LD chips 27 [5], [6]. LDs with more than 30 W output power com-28 bined with power conversion efficiency (PCE) above 65% 29 can provide a cost-effective high-power laser module. The 30 output power is mainly limited by the catastrophic optical

One of the persistent obstacles for high-power laser diodes (LDs) has been the catastrophic optical mirror damage (COMD), which limits the operating power level and lifetime of commercial high-power LDs. The output facet of LD reaches a critical temperature resulting in COMD, which is an irreversible device failure. Here, we fabricate multi-section LDs by tailoring the waveguide structure along the cavity that separates the output facet from the heat-generating lasing region. In this method, the LD waveguide is divided into electrically isolated laser and window sections along the cavity. The laser section is pumped at a high current to achieve high output power, and the window is biased at a low current with negligible heat generation. This design restricts the thermal impact of the laser section on the facet, and the window section allows lossless transport of the laser to the output facet. The lasers were operated continuous-wave up to the maximum achievable power. While standard LDs show COMD failures, the multi-section waveguide LDs are COMD-free. Our technique and results provide a pathway for high-reliability LDs, which would find diverse applications in semiconductor lasers.

We report on studying tunnel junctions and an optical cavity structure for developing epitaxially-stacked high-efficiency 905 nm high-power laser diodes. The GaAs tunnel junctions were explored via simulation and experiments to realize a high peak current density of 7.7×10 4 A/cm 2 and a low specific resistance of 1.5×10 -5 Ωcm 2 with a high n-doping concentration of 6×10 19 cm -3 . Employing a low-loss epitaxial structure design, single-, double-, and triple-cavity structure laser diodes demonstrated power scaling by epitaxial stacking. Triplecavity laser diodes have a low optical loss (0.42 cm -1 ) and generate a peak power of 83 W with a short cavity length of 750 µm at a limited current of 30 A.