An Overgrowth-Free Design for InGaAlAs Spot-Size-Converted Ridge Waveguide Lasers

A great deal of work has been done over the past several years toward the development of lasers with integrated spot-size converters, for better coupling directly to flat cleaved fiber or better alignment tolerance in lensed systems. Many of the techniques, such as butt-coupling or lateral-taper-vertical-shift, require etch-and-regrowth over the active region and as such are not applicable directly to Al-containing lasers. In this letter, we demonstrate a simple method to achieve narrow (15deg times 15deg) far fields in Al-containing devices with a moderate degradation of dc, dynamic and thermal characteristics. At room temperature, uncoated 300-mum-long devices have thresholds of about 18 mA and slope efficiencies of about 0.24 W/A, with 27% power coupled directly into flat cleaved fiber compared to ~10% for a conventional (>30deg far field) device. Comparison between calculated and measured far fields versus ridge width and number of quantum wells gives design curve information for optimizing far field performance.