Distributed Bragg reflector tapered diode lasers (DBR-TPL) emitting at 1064 nm are highly efficient and narrowband light sources which e.g. can be used for the treatment of eye diseases including the two main causes of blindness worldwide (i.e diabetic retinopathy and age-related macular degeneration) by laser coagulation via second harmonic generation (SHG) to the green spectral region.
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.