Gas sensor based on an integrated optical interferometer

An integrated optical sensor for the detection of gases like CO2 and SO2 is described. The working principle is as follows: The gas to be measured is absorbed by a sensitive film, which changes its refractive index with gas absorption. The sensitive film is deposited onto an integrated optical interferometer. As the intensity distribution of waveguide modes is not totally confined to the waveguide, interferometer phase changes with the refractive index of the film. Tests have been made with interferometers of the Fabry-Perot-Type. Interferometer phase is measured continuously using the serrodyne detection scheme. As sensitive films organically modified silicates are used. These glassy films are prepared by the sol-gel-technique, which allows the incorporation of functional organic groups within a network of siloxane bonds. The ability of selective gas absorption of these materials is determined by chosing appropriate functional groups. Films sensitive towards e. g. CO2 and SO2 have bee n fabricated and tested under different gas atmospheres.