Optical fibre sensor coated with porous silica layers for gas and chemical vapour detection

Fibre optic sensors have been conceived in new technologies for detecting very small amounts of chemical, gaseous and biological species. Recently, new polymer-clad silica (PCS) fibres coated with thin porous silica layers have been developed. These porous layers have been prepared by the sol-gel method using the dip-coating technique. In this work, this new material has been investigated for detecting gases and vapours. By choosing a fixed incident angle, variation of light power transmitted through the fibre is detected as the vapour or gas to be detected is sorbed in the porous silica layer. Good sensitivity and reversibility have been obtained for this system. Moreover, both the response rime and the desorption time have been found less than 2 min. Chlorinated hydrocarbons such as trichloroethylene, carbon tetrachloride, chloroform, dichloromethane and alkanes such as propane, butane and hexane can be detected with detection limits of 0.6, 1.5, 1.7, 4, 25, 10 and 5% respectively. (C) 1997 Elsevier Science S.A.