Commercial optical fibers were produced with a polymeric coating to protect and mechanical strength was provided to the optical waveguide that is made out of silica. In current practice, most fiber manufactures use a dual-layer coating technique. The primary coating was rubbery and served as a cushion to protect the glass fiber from mechanical loads. The second stiffer coating layer protected the fiber from abrasions and environmental exposure. Both layers were typically urethane- or acrylate-based but could contain photo initiators and additives, whose exact composition is a trade secret of the manufacturers. For this work, fibers we employed were single-mode optical fibers manufactured by Corning, type Corning SMF-28, core diameter: 8.3 µm, cladding diameter; 125 µm, coating diameter; and 245 µm, coating-cladding concentricity <12 µm. The coatings were applied sequentially in liquid form and are cured by exposure to ultraviolet light. We demonstrated that coatings on commercially available fibers could be used for chemical sensing [16 (link)]. Here, we investigated methods with which different sensing elements can be realized on the same optical fiber which has multiple sections with different chemistries.
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