The exploitation of thin film coatings for fibre sensors for the application of chemical sensing

Abstract

We report on the use of thin film coatings, both single and multi-layered, deposited on the flat side of a lapped, D-shaped fibre to enhance the sensitivity of two kinds of surface plasmon resonance based optical fibre sensors. The first kind involves the use of a tilted Bragg grating inscribed within the fibre core, prior to fibre coating, while the second relies on a surface relief grating photoinscribed after the fibre has been coated. Some of the devices operate in air with high coupling efficiency in excess of 40dB and an estimated index sensitivity of Δλ/Δn = 90nm from 1 to 1.15 index range showing potential for gas sensing. Other sensors produced index sensitivities (Δλ/Δn) ranging from 6790nm to 12500nm in the aqueous index regime. The materials used for these fibre optical devices are germanium, silica, silver, gold and palladium.