Abstract: The paper examines the fabrication and properties of silica optical fibers suitable for the development of evanescent- wave fiber-optic sensors. Attention is given to factors increasing the fraction of power transmitted in the evanescent wave. The effects of the refractive-index profile and fiber bending in the evanescent-wave area and their relation to the sensor sensitivity are investigated. A simple thermometer is developed on the basis of these effects. Approaches for the modification of optical properties in the evanescent-wave area are examined. In this part, porous layers prepared by the sol-gel method based on the silicon and titanium alkoxides and standard polysiloxane polymer coatings are described. The sol-gel derived layers are investigated from the point of view of preparing an optical core with a porous part. The possibilities of controlling the refractive index, as well as absorption coefficient of the coatings by immobilizing pH indicators and Cu$+2$PLU$/-phthalocyanine are shown together with examples of using evanescent-wave sensing structures for the detection of organophosphorous compounds and pH measurements.!13
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