Sensitivity enhancement of a surface plasmon resonance based fibre optic refractive index sensor utilizing an additional layer of oxides

We have experimentally demonstrated the capability of metal and different oxide combinations to be used in surface plasmon resonance (SPR) based fibre-optic refractive index sensor by using wavelength interrogation technique. The analysis of the sensor response is carried out using multilayered structure and geometrical optics. The configuration contains copper as a SPR active metallic layer covered by one of the three oxide layers TiO2, SiO2, and SnO2. The thickness of the copper layer is optimized to achieve the most pronounced dip at the resonance condition. The maximum sensitivity is obtained for TiO2 film. Further, increase in the thickness of the TiO2 layer increases the sensitivity of the sensor. The trend of sensitivity obtained by experimental results match qualitatively with the theoretical results obtained using the N-layer model and the ray approach. The additional advantages of oxide layer, apart from sensitivity enhancement, are protection of metallic layer from oxidation, tunability of the resonance wavelength region, biocompatibility and capability of gas sensing.