Buried DFB gratings floating in AlGaAs with low oxygen contamination enable high power and efficiency DFB lasers

Abstract

We report a novel design and fabrication technique for buried overgrown DFB gratings floating in AlGaAs. In-situ etching enables low oxygen contamination and results in > 60% efficient and 10W reliable high power DFB lasers.Introduction: Diode lasers with monolithically integrated Bragg gratings for internal wavelength stabilization are of growing importance for applications such as pumping narrow absorption bands in gain media of solid state lasers, fiber lasers and amplifiers. In this field, broad area (BA) lasers with distributed feedback (DFB) gratings are promising candidates. Buried DFB gratings can be understood as large area optical nanostructures, and they must be compatible with the high current densities that flow through BA lasers. Therefore they must fulfill several specific requirements. Firstly, they have to provide sufficient optical feedback for wavelength stabilization. Secondly, the DFB grating should not obstruct the carrier transport and thirdly, the grating should not increase the internal optical loss. Finally, crystal defects have to be avoided for good reliability. It is particularly important to eliminate oxygen contamination, as this is a rapid carrier trap [1], especially in AlGaAs-based designs. We present an optimized design and grating fabrication technology and analyze the oxygen contamination, coupling coefficient, optical loss and series resistance of DFB gratings in an epitaxy structure for high power lasers [2]. We show that oxygen contamination can be largely eliminated, enabling DFB-BA lasers using this design to achieve peak power conversion efficiency > 60% and reliable optical output power > 10W.