COMPARISON OF MECHANICALLY DRAWN AND PROTECTION LAYER CHEMICALLY ETCHED OPTICAL-FIBER TIPS

Scanning near-field optical microscope tips are produced by mechanical ly drawing and by chemical etching of standard single mode fibers. The geometrical shapes and taper angles are compared. By mechanical drawi ng with a commercial micropipette puller, smooth tapers with point dia meters below 50 nm are obtained. The final taper cone angle does not e xceed 14 degrees for small point sizes. The total length of the taper with decreasing core diameter ranges from 500 to 2000 mu m. Strong var iations of the cone angle can be observed depending on the chosen pull ing conditions. Therefore the variations of the fiber diameter at diff erent distances from the tip are measured for characterizing the shape s as a function of the pulling force. Chemical etching in 40% aqueous hydrofluoric acid covered with an organic solvent protection layer res ults in tips of conical shape in an autostopping process. The cone ang le can be varied from 8 degrees to 41 degrees by the adequate choice o f the organic solvent under static etching conditions. Tips with smoot h surfaces and point diameters below 40 nm are realized.