Plastic optical fibers as gas sensors

Abstract

This thesis is mainly about polyethylene glycol (PEG) coated simple optical fibers and their use as gas sensors. In this study, a simple plastic optical fiber is coated with gamma-isocyanatopropyltriethoxysilane end-capped polyetylene glycol (PEG) and experiments with different chemical compunds are performed to check how the refractive index of the coated cladding layer changes in accordance with the conditions imposed. An intrinsic, intensity-based evanescent wave gas sensor is constructed and responses of plastic optical fiber (POF) gas sensor to toluene, xylene, methanol and acetone vapors are observed. POF gas sensor gives a different response pattern for each vapor. POF gives the highest response to methanol due to a decrease in the refractive index of the PEG film. This effect reveals itself as an increase in the output voltage intensity for the case of methanol. For acetone, the POF gas sensor response pattern reveals the fact that there occurs a slight decrease in the refractive index of the coated region of the cladding and this causes a minor growth in output voltage and then, a sharp increase in the refractive index takes place and generates a strong downward movement in output voltage intensity. For toluene and xylene there follows a similar pattern to each other. A decrease in output voltage occurs due to an increase in the refractive index of PEG thin film.