In the present study, we report the design and development of a cost-effective, simple, sensitive LED - based fiber optic sensor for detecting trace amounts of chloride ions in water. A multimode plastic clad silica (PCS) fiber with the cladding removed and long period grating (LPG) written on its middle region acts as the sensing element. Exposure of the sensing region to water samples containing spectroscopic reagents for the detection of chloride ions causes evanescent wave absorption, which increases with increase in concentration. The limit of detection of the sensor is found to be a few parts per billion and the operational range covers more than five orders of magnitude.
Macrobending in optical fibers causes reduction in the amplitude of the light signal that passes through them. But in this manuscript we present details of using such a macrobend single mode optical fiber in the Mach-Zehnder interferometer configuration to measure displacement or force.
Permanently microbent fibers are potential candidates for chemical sensing 1. They behave more or less like an unclad optical fiber in many respects and the basic mechanism involved in chemical sensing application is the evanescent wave absorption. In this manuscript we propose its usage for refractive index measurement of solutions. The sensing configuration employed here is the dark field detection configuration which essentially involves the detection of cladding modes generated in and near the microbent region.
The design and fabrication of a fiber optic pH sensor working on the basis of evanescent wave absorption is presented. A pH sensitive dye is immobilized on the uncladed portion of the optic fiber by sol-gel route. The sensitivity of the device is found to increase when multiple sol-gel coatings are used as the cladding in the sensing region. The sensor response and its dynamic range are reported for two pH indicator dyes, viz. bromocresol purple and bromocresol green.