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

Porous silica and phenyl-modified porous silica were prepared by sol-gel me thod as cladding for optical fibres and tested for the chemical detection o f aromatic and alkane vapours. The refractive indices and optical attenuati on of the layers have been determined from the measured angular distributio ns of the output optical power. For this purpose, a model based on geometri cal optics has been developed. The interaction of the porous layers with be nzene, toluene, xylene and hexane has been investigated by measuring the ch anges of the output optical power induced by the effect of vapours of the h ydrocarbons in air. On the basis of these measurements, the porosity of the layer, and the partition coefficients of the hydrocarbons have been estima ted. The measured decrease of the optical power for the aromatic hydrocarbo ns 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 phen yl moieties used as cladding for fiber-optic chemical sensor. (C) 1999 Else vier Science S.A. All rights reserved.