The outstanding influence of end-face-TIR on enhancing signal intensity of fiber-optic EW fluorescence sensor

Abstract

A fiber-optic evanescent wave (EW) fluorescence sensor is often selected for its excellent performance, to detect the surface-specific event that takes place within a wavelength thickness of the immediate surface layer of the fiber core outside. In this paper, we describe a specific fiber-optic EW fluorescence sensor with a naturally built-in high signal to noise ratio, including a novel sensing architecture. It includes two identical, low hydroxyl content, large core, multimode plastic-clad silica fibers that are set perpendicular to one another, with a fiber for delivering incident exciting light and the other for receiving fluorescent light. An assay on the fiber-optic fluorescence sensor capable of simultaneously enhancing fluorescent signal and eliminating stray excitation light was examined. Such a capability can be achieved by reshaping a fluorescent sample fluid droplet and regulating the distance between the light exit of incident fiber and the bare core segment of receiving fiber. The prime significance of this work lies in its revelation of the outstanding influence of end-face total internal reflection (end-face-TIR) on enhancing signal intensity of fiber-optic EW fluorescence sensor, which reroutes the trajectories of the end-face-TIR capable rays and causes some of them to be detectable at the receiving end.