Abstract:
Protection of public and military personnel from chemicaland biological warfare agents is an urgent and growing national security need.Along with this idea, we have developed a novel class of fiber optic chemical sensors,for detection of toxic and biological materials. The design of these fiberoptic sensors is based on a cladding modification approach. The originalpassive cladding of the fiber, in a small section, was removed and the fibercore was coated with a chemical sensitive material. Any change in the optical properties of the modified cladding material, due to the presence of a specific chemical vapor,changes the transmission properties of the fiber and result in modal power redistributionin multimode fibers. Both total intensity and modal power distribution (MPD) measurementswere used to detect the output power change through the sensing fibers. The MPDtechnique measures the power changes in the far field pattern, i.e. spatialintensity modulation in two dimensions. Conducting polymers, such aspolyaniline and polypyrrole, have been reported to undergo a reversible changein conductivity upon exposure to chemical vapors. It is found that theconductivity change is accompanied by optical property change in the material.Therefore, polyaniline and polypyrrole were selected as the modified claddingmaterial for the detection of hydrochloride (HCl), ammonia (NH3), hydrazine (H4N2),and dimethyl-methl-phosphonate (DMMP) {a nerve agent, sarin stimulant}, respectively.Several sensors were prepared and successfully tested. The results showed dramaticimprovement in the sensor sensitivity, when the MPD method was applied. In thispaper, an overview on the developed class of fiber optic sensors is presented and supported with successful achieved results.
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