Faseroptischer Sensor

In a fibre-optic sensor, comprising an optical fiber with a sensitive coating, the coating consists of a polysiloxane (I), obtained by hydrolysis of a di- or poly-unsaturated 3-(3'-dialkoxyalkylsilyl)- propylamino- or -propylthio)-propionic ester of formula (II); in which R = a linear or branched organic group derived from a compound R''' with not less than 2 double bonds and 5-50 carbon (C) atoms; R' = 1-4 C alkyl; R'' = 1-4 C alkyl, cyclohexyl, phenyl or aryl; X = sulphur (S) or imino (NH). USE - Sensors of this type are useful for monitoring pollutants in the workplace and the environment, regulating industrial processes or identifying substances in medicine. They are useful for detecting e.g. carbon dioxide (CO2) and hydrocarbons, e.g. heptane or xylenes including hydrocarbons in water. ADVANTAGE - Sensors of this type usually depend on changes in the optical properties, e.g. refractive index, of the coating . If the refractive index of the coating is lower than that of the optical fiber, an evanescent field develops and optical changes are easily detected. Until now, sensitive layers have been based on polymers, but these often have a refractive index of over 1.5 and are difficult to process by fiber drawing. Coatings based on (I) have a refractive index less than 1.6 and fiber drawing is possible.