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

We report on the design of lasers using waveguide engineering to achieve low-divergence emission with high butt-coupling efficiency to single-mode (SMF) and multimode fiber (MMF). A tolerant design principle is introduced for achieving low-divergence normal to the junction using a single epitaxial growth step. The design method is compatible with a wide range of material systems and is demonstrated using a 980-nm laser structure. The full-width half-maximum of the beam is reduced from more than 32° to 21°. Direct butt-coupling losses are improved from -10 dB to near -3 dB for ridge waveguide to SMF coupling, while broad area devices coupled to MMF showed coupling efficiencies of >75%.