Development of organically modified polysiloxanes for coating optical fibers and their sensitivity to gases and solvents

Materials for coating silica optical fibers which are UV-curable and consist of a siloxane chain modified with reactive groups are prepared by the sol-gel method. The value of the refractive index of these organically modified polysiloxanes (ORMOCERs) is controlled by chemical modification of input alkoxysilane precursors in the range 1.48 to 1.56. Several sensing structures based on silica optical fibers silica core coated with a thin porous Si-O-Ti sol-gel layer and with a composite optical core have been fabricated and characterized by measuring their attenuation. The sensitivity of the ORMOCERs coatings to solbents an to CO2 dissolved in water has been determined in immersion experiments. A new absorption band around 320 nm arising from interaction of the ORMOCERs with SO2 has been observerd, which causes the sensitivity of the ORMOCER layer to gaseous SO2.