Fiber tips for scanning near-field optical microscopy fabricated by normal and reverse etching

Optical fiber tips, used as probes for scanning near-field optical microscopy, are produced by chemical etching in fluorohydric acid, followed by vacuum deposition of an aluminium coating. Fabrication technique is presented for two different configurations. The effects of several etching parameters on the tip quality are discussed: acid concentration, solvent type, etching temperature, and etching speed are considered. In particular, a solution is proposed to obtain tips with large cone angles, resulting in optical transmission as high as 10−3 measured through a metallized tip.