High CW wallplug efficiency 1.5 micron-emitting diode lasers

High-power, long-wavelength InP-based diode lasers emitting around 1.5 µm are needed for pumping solid-state lasers, direct-diode imaging applications, and eye-safe free-space optical communications. Optical systems significantly benefit from diode lasers with high wallplug efficiency (WPE), high brightness and reduced temperature sensitivity. Early work on 1.5 µm-emitting low-power (≤ 20 mW) lasers for fiber-optical optical communications has demonstrated WPE values as high as 35% [1]. Currently, commercially available, broad-area diode lasers emitting around 1.5 µm have maximum WPE values around 20% at high (∼ 1–2 W) CW power levels. Thus, 80% of the applied electrical power is lost as heat. With a WPE value around 20%, a bar stack designed to produce 100 W of optical power requires approximately a 500 W power supply; thus, generates 400 W of waste heat. Increasing the maximum WPE from 20% to 50% results in a 2.5 times reduction in required electrical power. This benefit, in addition to the power savings associated with laser cooling, would translate into a significant reduction in weight and cost for diode-pumped fiber lasers and hand-held military target-surveillance and distance-acquisition systems. We have taken a systematic approach for analyzing the power-loss mechanisms in diode lasers emitting in the 1.50–1.55 µm range, and then optimized the devices for high CW WPE values. As a result, we have achieved 50% wallplug efficiency at room temperature, under CW operating conditions, for lasers emitting at 1.53 µm [2].