Investigation of fiber-optic evanescent-wave sensors for detection of liquid hydrocarbons

Abstract

Several approaches for fiber-optic evanescent-wave detection of small amounts of liquid hydrocarbons are investigated in the paper. These approaches use polydimethylsiloxane-coated silica (PCS) fibres and detect changes of the fiber attenuation induced by the penetration of hydrocarbons into the fiber coating. The detection ability of bent PCS fibres both in the spectral region from 400 to 600 nm and near-infrared region from 900 to 1700 nm is studied by using available commercial or laboratory spectroscopic techniques. Straight sensing fibres coated with a thin high-refractive index layer and selective excitation of the fibres at 670 nm are investigated as well. A novel approach employing straight fibres coated with a thin siloxane coating and an output mode filter is described as a promising technique for increasing the detection sensitivity of fiber-optic evanescent-wave sensors to petrol fuels.