A simple method for metal re-coating of optical fibre Bragg gratings

This study presents a simple method for metal re-coating of silica optical fibre Bragg gratings. No vacuum techniques or any high-temperature methods such as dip or melt coating techniques are required. Optical fibres with metallic coatings such as aluminium, copper, tin and gold are commercially readily available. These coatings are usually applied in connection with the fibre drawing process, and these coating techniques cannot be used for coating existing fibres. Bragg-gratings are often written into the optical fibre after the original coating has been removed and therefore the fibre needs to be re-coated subsequent to the writing process in order to protect the fibre. Since no company providing metallic re-coating services was located, the coating process had to be developed. Researchers developing for instance high-temperature fibre optical Bragg-grating sensors will need a simple and cheap method for metal coating of fibres. The coating method presented in this work is developed with emphasis to further embedding the coated fibres into solid metal using, for example, vacuum brazing techniques. The method is based on electroplating, and therefore, the fibres can be coated with any metal or metal alloy applicable by this technique.