Intrinsic Fiber Optic Chemical Sensor Based On Two-Stage Fluorescence Coupling.

This paper proposes a new generic technique for fiber optic chemical sensing, discusses experiments which demonstrate the technique, and briefly treats possible extensions and applications. Our results indicate a more than 100-fold increase in the coupling of energy from a chemically sensitive coating to guided models in the fiber core, when compared with other intrinsic sensor designs. Previous reports of distributed sensors making use of chemically sensitive dyes in optical fiber claddings describe sensors which depend on the direct coupling of light between the cladding and guided modes in the fiber core. This approach, particularly when used for distributed fluorescence sensors, is limited in sensitivity since coupling takes place through the evanescent field "tails" of the fiber's core-modes which extend only a short distance into the fiber cladding.