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 sol-gel 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.