Comparison of mechanically drawn and protection layer chemically etched optical fiber tips

Scanning near-field optical microscope tips are produced by mechanically drawing and by chemical etching of standard single mode fibers. The geometrical shapes and taper angles are compared. By mechanical drawing with a commercial micropipette puller, smooth tapers with point diameters below 50 nm are obtained. The final taper cone angle does not exceed 14° for small point sizes. The total length of the taper with decreasing core diameter ranges from 500 to 2000 μm. Strong variations of the cone angle can be observed depending on the chosen pulling conditions. Therefore the variations of the fiber diameter at different distances from the tip are measured for characterizing the shapes as a function of the pulling force. Chemical etching in 40% aqueous hydrofluoric acid covered with an organic solvent protection layer results in tips of conical shape in an autostopping process. The cone angle can be varied from 8° to 41° by the adequate choice of the organic solvent under static etching conditions. Tips with smooth surfaces and point diameters below 40 nm are realized.