Fabrication and modeling of multimode fiber lenses

We report on the fabrication, modeling, and experimental verification of the emission of fiber lenses fabricated on multimode fibers in different media. Concave fiber lenses with a radius of 150 μm were fabricated onto a multimode silica fiber (100 μm core) by grinding and polishing against a ruby sphere template. In our theoretical model we assume that the fiber guides light from a Lambertian light source and that the emission cone is governed solely by the range of permitted emission angles. We investigate concave and convex lenses at 532 nm with different radii and in a variety of surrounding media from air (n(0)=1.00) to sapphire (n(0)=1.77). It was found that noticeable focusing or defocusing effects of a silica fiber lens in ethanol (n(0)=1.36) and dimethyl sulfoxide (DMSO) (n(0)=1.48) are only observed when the fiber lens radius was less than the fiber diameter.