Sol-gel fiber-optic absorbance sensor for groundwater contaminants

An evanescent wave fiber optic sensor for the detection of groundwater contaminants is developed. A 62.5 μm fiber core, 15 mm in length, was chemically etched and coated with 20 μm porous silica medium using sol-gel dip-coating method. This lower-refractive index medium causes the light beam to be transmitted by total reflection and the resulting evanescent wave produces a net flow of energy across the reflecting surface in the surrounding medium where it interacts with the surrounding environment. The power intensity of the solgel modified fiber is measured in the 1540 to 1600 nm spectral range. Various amounts of pure hexane and ethanol were used to examine the response of the sensor. A remarkable influence of the absorption of the evanescent waves in the sol-gel modified fiber for hexane and ethanol was observed.