Hydrothermally grown ZnO nanorods based optical fiber sensor for salinity detection

• Highly sensitive reflection based no-core optical fiber probe is developed for salinity measurement. • Well arrayed ZnO nanorods have been grown over silica fiber surface by hydrothermal route. • Band gap modification and evanescent wave absorption are responsible for sensing mechanism. • Proposed sensor shows excellent sensing characteristics and can be used in chemical and biological fields. This work reports an intensity-modulated and reflection based NCF salinity sensor using ZnO nanorods as outer layer coating. As the accurate measurement of salt concentration is highly essential to monitor and control the negative effects of saline present in aqueous resources. The sensing principle is based on change in refractive index (RI) of ZnO layer being in contact with various saline solution leading to different EWA. This absorption of evanescent field by external medium is responsible for change in intensity of light detected at the output end. The ZnO nanorods deposited fiber sensor exhibits good sensitivity as well as excellent reproducibility, repeatability and durability. Proposed sensor contains simple, low cost, and reliable probe to detect the ambient RI changes utilizing a laser source, and resultant output power was modulated as saline concentration is varied. The highest average sensitivity of 0.574 dB/% is obtained in the salinity range of 0–25 % with a good stability and fast response time at room temperature.