Hydrofluoric acid-free etching of glass

Fraunhofer IZM develops a hydrofluoric acid-free etching process to manufacture reliable and robust glass fiber optic components and glass integrated optics.

The hydrofluoric (HF) acid-free etching based on molten salts permits to etch glass materials without surface microcracks. Such microcracks occur usually when the surface of the HF-etched glass is heated. This makes HF-etched glass highly susceptible to surface damage.

A molten salt etching station has been designed and built to etch glass with defined etch and process parameters. The etching attack of the molten salt is similar to the wet etching that uses a mixture of etchants to remove the glass material.
Several tests have been successfully conducted using fused silica optical fibers and borosilicate glass substrates, showing stable and uniform etched zones.

Etched glass fibers are used to develop optical components such as:

  • Radial firing tips with wedge shape for minimally-invasive laser therapy
  • Couplers for datacom, telecom, and OCT
  • Evanescent sensors for biomedicine and chemical analytics
Hydrofluoric acid-free etching of glass
© Fraunhofer IZM
Optical fibre (SMF-28, Ø125µm) etched with molten salt. Etch rate of 0.25 µm/min.