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4 December 1998 Integrated optical devices with liquid crystal overlays for the sensing of volatile organic compounds
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We report the application of nematic liquid crystals for the optical sensing of organic solvents using two different evanescent field probes. Liquid crystals with different nematic ranges are used as sensitive coating materials on integrated optical reflection grating couplers and on integrated optical Mach-Zehnder interferometers as well. A non-linear behavior was observed when the liquid crystal coated IO transducers were exposed to various concentrations of toluene, meta-xylene and para-xylene. The calibration over a wide range pointed out a phase transition of the liquid crystal due to the penetration by the analyte. The birefringend liquid crystal and an isotropic polymer coating are compared by their responses to the xylene isomeres. The data indicate that the liquid crystal's response is mainly given by a decrease of the order parameter S. Furthermore, we take advantage from the non-linearity and the clearing point in order to improve the performance of the sensor system.
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Bernd Drapp, D. Pauluth, Albrecht Brandenburg, and Guenter Gauglitz "Integrated optical devices with liquid crystal overlays for the sensing of volatile organic compounds", Proc. SPIE 3491, 1998 International Conference on Applications of Photonic Technology III: Closing the Gap between Theory, Development, and Applications, (4 December 1998);

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