Optical fibre sensors sensitized by phenyl-modified porous silica prepared by sol-gel

Porous silica and phenyl-modified porous silica were prepared by sol-gel method as cladding for optical fibres and tested for the chemical detection of aromatic and alkane vapours. The refractive indices and optical attenuation of the layers have been determined from the measured angular distributions of the output optical power. For this purpose, a model based on geometrical optics has been developed. The interaction of the porous layers with benzene, toluene, xylene and hexane has been investigated by measuring the changes of the output optical power induced by the effect of vapours of the hydrocarbons in air. On the basis of these measurements, the porosity of the layer, and the partition coefficients of the hydrocarbons have been estimated. The measured decrease of the optical power for the aromatic hydrocarbons and the increase of the output power for the aliphatic hydrocarbon have been explained on the basis of the developed model. Higher sensitivity for aromatic hydrocarbons has been found for the porous silica modified by phenyl moieties used as cladding for fiber-optic chemical sensor. (C) 1999 Elsevier Science S.A. All rights reserved.