In this work, we present DBR-TPL with an additional internal DBR-grating at the output side of the tapered amplifiersection in comparison with DBR-TPL with standard facet coating of different reflectivities.
Our DBR-TPLs are based on an epitaxial structure with a large and asymmetric waveguide to realize a small vertical far field for optimal coupling into SHG-crystals. All DBR-TPL consist of a 2 mm long ridge waveguide section, which contains a 1 mm long passive DBR-grating section at the end for longitudinal mode filtering. The amplifier-section is 4 mm long and forms a taper with a full angle of 6°.
The influence of the front mirror reflectivity on laser performance including reliability is investigated. The DBR-TPL emit up to 9 W of optical output power in continuous wave operation at 25°C in a longitudinal single mode at 1064 nm and yet the spectral width remains below 20 pm. In favor of a high radiance the power content in the central lobe at a total optical output power of 8 W is greater than 75% for almost all devices. Aging tests revealed significant differences in the lifetime of the devices depending on their front facet reflectivity or length of the front DBR-grating, respectively.