Evaluation of design concepts for feedback-resistant 9xx-nm high-power laser diodes

In this work, we compare four different design concepts for external-cavity laser diodes (ECDL) with respect to the maximum achievable output power before the onset of catastrophic optical damage (COD). A multiphysics model of the ECDL with a self-consistent description of the electrical, optical and thermal properties of the device is used to evaluate the COD level. The feedback-induced failure is provoked by shifting the fast axis collimation (FAC) lens along the fast axis (smile error) resulting in an absorption of the feedback radiation within the highly p-doped and contact metal layers. The investigated design concepts include three local modifications at the front facet of the laser diode chip itself which are supposed to suppress injected current, optical absorption and leakage current from the quantum well. Within the considered parameter space these approaches lead to an increase of the COD level by 8%, 27% and 27% respectively, however at the cost of drawbacks like slightly reduced efficiency or beam quality along the fast axis. By combining all three approaches the output power can be increased by 37%. The fourth approach uses an additional lens within the external resonator to make it bi-telecentric and allows for a feedback field without image reversal. This approach completely removes the sensitivity of the setup regarding a vertical misalignment of the FAC lens. The drawback in this case is the increase of the resonator size by approximately a factor of 20.