Narrow Stripe Broad Area Lasers With High Order Distributed Feedback Surface Gratings

GaAs-based narrow-stripe broad-area lasers with integrated surface gratings are shown to operate with high power and efficiency, low beam parameter product (BPP), and narrow spectra. These distributed feedback lasers are constructed using a surface-etched, 80th-order grating, leading to spectral width <formula formulatype="inline"><tex Notation="TeX">$\Delta\lambda_{95\%}<0.7~{\rm nm}$</tex></formula> (95% power) and wavelength <formula formulatype="inline"><tex Notation="TeX">${\sim}{\rm970}~{\rm nm}$</tex></formula>. Optical output powers <formula formulatype="inline"><tex Notation="TeX">$({>}{\rm 6}~{\rm W})$</tex></formula> and power conversion efficiencies <formula formulatype="inline"><tex Notation="TeX">$({>}{50\%})$</tex></formula> comparable with devices without grating are enabled by a small coupling coefficient, <formula formulatype="inline"><tex Notation="TeX">$\kappa{\rm L}{\sim}{0.3}$</tex></formula>, consistent with coupled mode theory calculations. The lasers were constructed with a stripe width of 30 <formula formulatype="inline"><tex Notation="TeX">$\mu{\rm m}$</tex></formula>, enabling BPP <formula formulatype="inline"> <tex Notation="TeX">${<}{\rm 1.8}~{\rm mm}$</tex></formula> mrad up to 6-W output power, improved over devices without gratings, that show BPP <formula formulatype="inline"><tex Notation="TeX">${>}{\rm 2.2}~{\rm mm}$</tex></formula> mrad. We attribute the improvement to spatial filtering of higher order lateral modes by the narrow surface grating. Such devices are attractive sources for use in spectral beam combination systems for material processing.