OPTICAL-FIBER SENSOR COATED WITH POROUS SILICA LAYERS FOR GAS AND CHEMICAL-VAPOR DETECTION

Fibre optic sensors have been conceived in new technologies for detect ing very small amounts of chemical, gaseous and biological species. Re cently, new polymer-clad silica (PCS) fibres coated with thin porous s ilica layers have been developed. These porous layers have been prepar ed by the sol-gel method using the dip-coating technique. In this work , this new material has been investigated for detecting gases and vapo urs. By choosing a fixed incident angle, variation of light power tran smitted through the fibre is detected as the vapour or gas to be detec ted is sorbed in the porous silica layer. Good sensitivity and reversi bility have been obtained for this system. Moreover, both the response rime and the desorption time have been found less than 2 min. Chlorin ated hydrocarbons such as trichloroethylene, carbon tetrachloride, chl oroform, dichloromethane and alkanes such as propane, butane and hexan e can be detected with detection limits of 0.6, 1.5, 1.7, 4, 25, 10 an d 5% respectively. (C) 1997 Elsevier Science S.A.