Improved beam quality for high power tapered laser diodes with LMG (Low Modal Gain) epitaxial layer structures

In high-power, high-brightness laser diodes, beam filamentation is one of the main physical effects that limit the device performance. Due to the interaction between the optical power and the carrier density in the active region of broad area devices, spatial hole-burning leads to an inhomogenous optical index that causes the degradation of die optical beam profile. We show, that epitaxial layer structures with low optical confinement are much more insensitive to beam filamentation because of their reduced differential gain. Experimentally we find, that the beam quality of tapered laser ocillators can be improved by an order of magnitude, when epitaxial layer structures with reduced modal gain are used for the device fabrication. 2 mm long tapered devices with a 200 mu m wide output facet show near diffraction limited farfield profile up to output powers of more than 2 W cw.