Microreflectance inspection of diode laser front facets

We report on specular reflectivity measurements at the position of the waveguide at front facets of commercial diode laser arrays. Since the waveguide thickness is such semiconductor structures amounts about 1 micrometers an even better spatial resolution of the probe light spot is required. For this purpose, a micro-reflectance setup was designed and implemented. For re-locating the optically active region, e.g. after stepped-up operation time, we employ the photosensitivity of the active region by using the photocurrent induced by the probe beam for auto- alignment of the setup. We show for coated InGaAlAs/GaAs- single chip devices that during long-term operation the diode laser front facet reflectivity at the position of an emitter is almost constant with a slight tendency (about 0.002 at 633 nm) to increase. The results are explained in the framework of defect-induced refractive index changes within the semiconductor material close to the interface between waveguide and facet coating.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.