A Novel Approach to Evaluate the Sensitivities of the Optical Fiber Evanescent Field Sensors

Abstract

Optical fiber evanescent field sensors(OFEFS) are playing more and more important roles in detecting chemical, bacilli, toxin, and environmental pollutants for their high efficiency, good accuracy, low cost, and convenience (Maria et al., 2007; Wolfbeis, 2006; Angela et al., 2007). In general, these sensors exploit the interactions between evanescent field of the sensing fibers and the surrounding analyte under investigation. Concentrations of analyte can be related to the power attenuation caused by these interactions, and the more energy interacted with the analyte, the higher the sensitivities of the sensors. In order to expose the evanescent filed of the fiber to the analyte, the fiber cladding is often removed and the fiber core is surrounded by the detecting material. To make clear the operation principle of the evanescent field interacting with the analyte and to estimate the sensitivity according to this principle are extremely important to the sensor’s designers. This field has attracted a lot of research groups extraordinarily and been widely discussed both based on geometric optics and optical waveguide theory (Yu et al., 2006; Messica et al.,1996; Gupta & Singh, 1994; Guo & Albin, 2006). However a big difference between the theoretical and experimental values is often observed especially when the sensor’s absorbency is low (Payne & Hale, 1993; Wu et al., 2007; Deng, et al., 2006).