Micro-lens machining on optical fibers by direct laser ablation

Beam shaping at the output of optical fibers is required in a variety of applications including optical sensors, telecommunication devices and medical applications. We present a laser micro-machining technique for the fabrication of micro-lenses directly upon the end face of silica fibers using a F-2-laser processing station. Ablation is performed in a mask projection arrangement with 25 x demagnification. A mask with an occluded circular beam shape is imaged perpendicular to the fiber axis. The fiber is rotated axially while the laser cuts through the fiber, yielding a spherically shaped tip with radius defined by the mask dimensions. Strong 157 nm absorption by the silica glass facilitates precise structuring without micro-crack formation. The quality of the fiber-lenses is characterized by AFM, SEM and by analysing the beam profile at the fiber output.