Laser beam shaping using a single-mode fiber abrupt taper

A new beam-shaping device was realized by an abrupt taper with a length of ~700 μm and a waist of ~40 μm. The insertion loss of the device is less than 3%. The diameter of the flat beam top can be up to ~900 μm with a small intensity variation (4%) and a small half-divergence angle (2.5°). The conversion efficiency of the new device from a Gaussian-shaped to a flat-top profile is comparable with that of a long-period-gratings-based device, while keeping the fabrication cost low. The new device requires only a fusion splicer and standard SMF-28 fiber, eliminating the need for photolithographic procedures. The new device also has no obvious incident light polarization dependence.