Ball lenses Spherical ball lenses are commonly used for laser collimating and focusing, laser-to-fiber coupling, fiber-to-fiber coupling, and fiber-to-detector coupling. Larger spheres are easier to handle and ease the sensitivity of translational alignment. However, smaller spheres fit into smaller packages. The addition of a broadband MgF2 antireflection coating results in a highly efficient lens due to the high refractive index of the glass. Coupling efficiency is generally >90% due to the simplicity of these lenses.