Amplification and front facet reflectivity of broad area lasers

The effect of front-facet reflectivity on the amplification performance of Broad Area Laser (BAL) diodes in a double-pass configurationis studied experimentally. A method to measure the front facet reflectivities of laser diodes is generalized to BALs. The method is based on fitting a model, with front facet reflectivity as a parameter, to the threshold current vs. external feedback of the diode. Reflectivities of three BAL diodes are measured, and their amplification abilities have been assessed. The tested diodes had amplification factors of 0, 1, and 10 and front facet reflectivities of 12.7 +/-1%, 4.6 +/-0.4%, and 1.2 +/-0.2% respectively. It is concluded that a front facet modal reflectivity of less than 4.6% is necessary for a BAL to function as an amplifier.