Far-field widening of high-power laser diodes
High-power broad-area laser diodes often exhibit an undesired widening of the lateral far-field with increasing current, which is commonly attributed to self-heating. The non-uniform temperature profile inside the waveguide leads to a lateral refractive index gradient (thermal lens) that enhances the built-in index guiding of laser modes. We studied this complex interaction of electronic, thermal, and optical processes using self-consistent numerical simulation. In good agreement with measurements, our calculations quantitatively link the widening of the far field to a rising order of lateral lasing modes which are supported by the thermal lens. But a relevant part of this widening also occurs without any heating, which is attributed to a non-uniform gain distribution. However, some features of the measured far-field cannot be reproduced in our simulation, e.g., the strong asymmetry. Does anybody know about more advanced models for this far-field widening ?  J. Piprek and Z. M. Li, Appl. Phys. Lett. 102, 221110 (2013).