Effect of facet coatings on laser diode characteristics

Abstract

The cleaved facets of semiconductor diode lasers act like mirror. Mirror coatings are applied to change the reflectivity and passivate the surfaces. Design of antireflection coating is optimized for single layer of Al₂O₃and high reflection coating is optimized for stacks of Al₂O₃and Si Bragg reflector. Electron beam evaporation has been used to deposit uniform Al₂O₃/Si film under high vacuum with pressure 10^-6mbar and temperature 150-160°C. The optimization of experimental parameters for the dummy GaAs substrate has been discussed. Using these parameters laser facets were coated and changes in the L-I characteristics have been measured and investigated step by step. The output light power versus current characteristics of coated laser diode is compared with that of uncoated one for its characterization under pulsed conditions and have shown that the facet reflectivity has played a major role in determining threshold current density of semiconductor laser.