Nonlinear Dynamics in Semiconductor Lasers - Abstract

Helal, Mohamad Anas

Beam quality degradation processes in high brightness tapered lasers

Authors: M.A. Helal, S.N. Kaunga-Nyirenda, S. Bull and E.C. Larkins High-power laser diodes with excellent beam quality are attractive for high-brightness laser systems due to their compactness, efficiency and low cost. As the applications of high-brightness laser diodes increase, even more stringent demands are being placed on their beam quality performance in real systems and at high operating powers. Recently, large optical cavity (LOC) DBR tapered lasers with high power conversion efficiency, low beam divergence and improved beam quality have become strong candidates for these systems. Nevertheless, their beam quality still degrades at high output power - resulting in power loss to higher order lateral modes. Recent experimental studies also suggest that their performance and reliability are affected by external optical feedback. In this work, we investigate the processes responsible for beam quality degradation at high operating powers and the impact of external cavity feedback. The DBR-ridge waveguide (DBR-RW) filter section acts as a spatial mode filter to remove the higher order lateral modes. Focusing on the DBR-RW section, we investigate the impact of width, etch depth and injection current on the performance of the DBR-RW filter and show that optical pumping and absorption bleaching play a key role in the lateral beam quality degradation. We also report on the self-consistent simulation of a tapered laser diode with optical feedback from reflections off the end of an uncoated fibre. Particular attention is given to light coupled back to the higher order vertical modes of the LOC waveguide and how propagation of these modes contributes to further absorption bleaching.