High-quality near-field optical probes by tube etching

Abstract

A method called tube etching for the fabrication of near-field optical probes is presented. Tip formation occurs inside a cylindrical cavity formed by the polymer coating of an optical fiber which is not stripped away prior to etching in hydrofluoric acid. The influence of temperature, etchant concentration, and fiber type on the tip quality is studied. A tip formation mechanism for the given geometry is proposed. The procedure overcomes drawbacks of the conventional etching techniques while still producing large cone angles: (i) tips with reproducible shapes are formed in a high yield, (ii) the surface roughness on the taper is drastically reduced, and (iii) the tip quality is insensitive to vibrations and temperature fluctuations during the etching process. After aluminum coating, optical probes with well-defined apertures are obtained. Due to the smooth glass surface the aluminum coating is virtually free of pinholes.