Corrugated Fiber Grating for Detection of Lead Ions in Water

Optical fiber fluorescence sensors are widely used for chemical sensing. Intrinsic fluorescence sensors such as evanescent-wave sensors can be used for surface sensing while extrinsic sensors are used for bulk sensing. In intrinsic/extrinsic fluorescence sensors, typically the side-wall/end-face of a single/multimode fiber is used. In this paper, we introduce a novel intrinsic optical fiber fluorescence sensor which uses the side-wall of a large-core multimode fiber to collect the fluorescence from the bulk of samples. The method is to use a corrugated fiber grating, fabricated by a CO₂ laser, to couple radiating modes to the core modes. Using the sidewall of a fiber helps to fabricate a multitarget or a distributed sensor. We also report the sensing of Lead ions with concentration as low as few ppb in water using a fluorescence turn-on polymer as a chemical probe.