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. Coupling efficiency is generally >90%  due to the simplicity of these lenses. For this spherical ball lenses we can make them from all of the glass material.