Sergii Yakunin and Johannes Heitz of Johannes Kepler University Linz (Linz, Austria) have developed a new way of microgrinding the tips of optical fibers to produce spherical tips with a 1 µm radius of curvature (smaller than any now commercially available), as well as axicons. Such microlensed fibers are well suited for handling high amounts of laser light flux for purposes ranging from photochemical etching to laser ablation.
In the grinding process (which is much simpler than techniques such as ion milling), the fiber is not rotated; instead, the fixed fiber is moved around inside a conical polishing surface. The conical polishing surface is made by pressing a series of metal pins with increasing cone angles into a polishing sheet. The fiber itself is etched to a conical shape before polishing. A homemade atomic-force-microscope (AFM) setup, along with additional software for tip-trajectory control, is used to manipulate the fiber in three translational dimensions. Both AFM and visual-microscope topography measurements showed a very accurate spherical tip shape. Microlenses with radii of 1 and 3 µm were created; the 3-µm-radius lens focused red (633 nm) light to a 340 nm focal spot that remained submicrometer in diameter up to a defocus of 6 µm. Contact Yakunin at [email protected].