Acidity measurements based on a hetero-core structured fiber optic sensor

A noble sensing technique using a hetero-core structured fiber optic sensor is described based on evanescent wave interaction for the purpose of acidity measurements. The hetero-core sensing element reported in this work have been fabricated only by cleaving and fusion splicing. Since the sensor has no need to eliminate the cladding of the fiber to expose the core, this technique offers the advantages in terms of the fabrication complexity which the conventional fiber optic sensors have been confronted with. Acidity measurements have been demonstrated through the experiments using Chromoxane Cyanine R (CCR) indicator solved in solutions. Two acid solutions of HNO3 and H2SO4 are examined for the acidities ranged between 0.066-0.66 and 0.0895-0.716 M, respectively. The sensor response exhibited remarkable increases of absorption with increasing acidity at the wavelength of around 520 nm. The sensitivities of 11.5 and 14.2 dB/M have been obtained for HNO3 and H2SO4 solutions, respectively. (C) 2003 Elsevier B.V. All rights reserved.