Abstract

High-brightness semiconductor lasers operating near 0.98µm are of considerable interest for applications such as free-space communications, Er-doped fiber pumping and frequency doubling. The spatial coherence of such devices, however, is often limited at high output power due to the onset of filamentation in the active region resulting from the linewidth enhancement factor or α parameter. The α parameter has been previously measured in strained-layer InGaAs quantum well lasers with narrow stripe widths at specific or limited ranges of carrier density, [1,2] where the modal gain and refractive index depend critically on the lateral waveguiding structure. We present an alternative method for measurement of gain and refractive index in semiconductor lasers which employs a far-field filtering technique and broad area Fabry-Perot lasers, in this way, we are able to obtain modal optical properties characteristic of the transverse epitaxial structure alone, free of effects associated with the details of lateral carrier and optical mode confinement.

© 1996 Optical Society of America