Abstract

Refractive index sensing based on etched fibre Bragg gratings (FBG) provides a simple and versatile technique for measuring the refractive index of variety of liquids with a high degree of precision[1, 2]. If the host of the sensor is a silica based fibre, the gratings are typically etched with hydrofluoric (HF) acid of varying concentration depending on the precision required in the final etch quality. An important parameter when seeking a high degree of precision of the sensor is the overlap between the evanescent field and the measurand. This overlap is specified by the final fibre diameter, and thus being able to determine the diameter with high precision, ideally in-situ during the etching process, is very desirable so the process can be stopped at the preferred target diameter.

© 2015 IEEE