Tapered plastic multimode fiber sensor for salinity detection

Abstract

A simple tapered plastic multimode (PMM) fiber optic sensor is proposed and demonstrated for continuous monitoring of salinity based on different concentration of sodium chloride (NaCl) in de-ionized water. The working mechanism of such device is based on the observed increment in the transmission of the sensor that is immersed in sodium chloride solution of higher concentration which also reflects an increase in its refractive index. The tapered PMM fiber is fabricated using heat-pulling method to achieve a waist diameter and a length of 0.187 mm and 5 mm, respectively. As the solution concentration varies from 0% to 12%, the output voltage of the sensor increases linearly from 0.109 mV to 1.142 mV with a sensitivity of 0.0024 mV/% and a linearity of more than 98%. The main advantages of this sensor are the feasibility of using PMM fiber which makes the sensor tougher, easier to fabricate and handle.