Sensitivity enhanced interferometric optical sensor of taper-in-taper structure for heavy metal ions detection

Abstract

Heavy metal pollution in water resource is a serious issue that related to the ecosystem and the health status of human beings. Although there existed many detection methods, it is still difficult to create a device with ultrahigh sensitivity to detect heavy metal ions in situations with low concentrations. This paper proposed a taper-in-taper (T-I-T) interferometric fiber sensor of enhanced sensitivity and decorated with polyelectrolyte layers for Cu2+ detection. The T-I-T structure was created on the single-mode fiber via twice arc discharges. The maximum refractive index (RI) sensitivity of T-I-T fiber sensor is as high as 4170 nm/RIU, meanwhile, when apply in heavy metal ions detection, the sensitivity can reach 10.4 nm/ mM when the Cu2+ concentration is 0.1-1 mM. Furthermore, there is a low temperature cross sensitivity of only 0.12 nm/°C. The proposed T-I-T fiber sensor has the potential to be applied in water resource environmental monitoring due to its benefits of high sensitivity, compact structure, and excellent stability.