Lateral brightness improvement of high-power semiconductor laser diode

Abstract

High power diode lasers are widely used as the pump sources for fiber lasers and solid-state lasers, or the light sources for direct diode laser systems. The lateral brightness of diode lasers is the key parameter for the optical system with fiber coupling. The lateral brightness of a typical broad area diode laser is limited by the far-field booming rather than optical power at high operation current. In this paper, the far-field booming theory will be analyzed based on experimental observation of carrier density distribution and temperature profile along lateral direction. The temperature nonuniformity and the resulting thermal lens effect are supposed to be the dominate factor. We develop a novel high brightness laser diode structure with properly designed contact metal layer to modify the thermal conductivity profile. The thermal simulation indicate that the thermal lens effect is suppressed and the lateral far-field angle is reduced. Laser diodes with 230 μm emitter width and optimized structure are fabricated and the optical properties is investigated. The lateral far-field angle is reduced at current over 40A The optical power with same lateral brightness is increased up to 20%. This structure gives a promising high brightness solution for high power laser diode with power over 35 W. Chips with longer cavity length obtain higher power up to 51W.