Low-divergence laser structures for cost-effective fiber coupling applications

We report on the design of lasers using waveguide engineering to achieve lo w-divergence emission with high butt-coupling efficiency to single-mode (SM F) and multimode fiber (MMF), A tolerant design principle is introduced for achieving low-divergence normal to the junction using a single epitaxial g rowth step. The design method is compatible with a wide range of material s ystems and is demonstrated using a 980-nm laser structure. The full-width h alf-maximum of the beam is reduced from more than 32 degrees to 21 degrees. Direct butt-coupling losses are improved from -10 dB to near -3 dB for rid ge waveguide to SMF coupling, while broad area devices coupled to MMF showe d coupling efficiencies of >75%.