Fiber Bragg distributed chemical sensor

A distributed chemical sensor is developed by coating multiple Bragg gratings in a single glass fiber with chemical responsive coatings. The composition of the coating is tuned to the target chemicals to be measured and the optical response of the coated grating is optimized by changing the coating thickness. Specific recoaters were used to apply the responsive coatings reproducibly onto the glass fibers. The coating compositions can be based on UV curing or solvent based systems. In this paper we show the development and application of a distributed gas sensor for CO₂, H₂S and H₂O that can be used for down-hole monitoring in the oil and gas industry. We have developed a toolbox for the design and modeling of the responsive polymer coatings, and the performance of the actual sensors corresponded well with the predicted behavior.