10-W reliable 90-μm-wide broad area lasers with internal grating stabilization

Broad area (BA) diode lasers with narrow, temperature-stable spectral lines are required for pumping narrow spectral lines in solid state lasers and for dense spectral multiplexing in direct applications. Two device technologies in particular have reached a high performance level, based on development work at the Ferdinand-Braun-Institut (FBH). Firstly, etched surface gratings can be used to form the rear facet reflector, in distributed Bragg-reflector (DBR) format. Secondly, gratings can be buried within the semiconductor using etch and overgrowth technology, to form distributed feedback (DFB) lasers. In this case, the rear facet has a high reflectivity coating, and the DFB operates effectively as the low reflectivity out-coupler. For both technologies, BA diode lasers with 90-100μm stripes operating at 975nm deliver peak continuous wave (CW) powers of over 12W within a spectral width of < 1nm (with 95% power content). Recently, reliable operation has been confirmed for CW powers of 10W, and power conversion efficiency of up to 63% has been demonstrated. However, the two technologies have different strengths. For example, DBR-BA lasers have low sensitivity to external feedback and are insensitive to the onset of spectral side-modes. In contrast, DFB-BA lasers achieve the highest reported power conversion efficiencies. A comparison of the relative merits of the two technologies for different high power laser applications is presented.