Formation of glass fiber tips for scanning near-field optical microscopy by sealed- and open-tube etching

A method, sealed-tube etching, for fabricating glass fiber tips used in scanning near-field optical microscopy is reported. Two glass tips are formed simultaneously inside the acrylate jacket of an optical fiber that is sealed at the bottom end with plastic prior to etching in hydrofluoric acid. The qualities of the tips generated from this and conventional tube etching methods are compared in terms of their taper length, surface smoothness, as well as time evolution of the tip shapes. Etching mechanisms are proposed for this method, which provides more insight into the conventional tube etching method than previously considered.