ZnO nanostructure-enhanced tapered polymer optical fiber sensors for pH detection

This study presents an experimental investigation of tapered polymer optical fiber (POF) sensors enhanced with zinc oxide (ZnO) nanostructures for improved pH detection. Both ZnO-coated and uncoated POFs were fabricated and characterized to evaluate the effects of surface modification and probe length on sensing performance. The sensors were exposed to pH solutions ranging from 2 to 8, and their optical responses were assessed through variations in refractive index, output power, and voltage. Results indicate that ZnO-coated POFs exhibit enhanced sensitivity compared to uncoated fibers, with the 4 cm coated sensor achieving the highest sensitivity of 0.0464 V/pH and a linearity of 98.30%. The ZnO coating improved the evanescent field interaction by altering the refractive index profile, resulting in greater responsiveness to pH-induced optical changes. These findings highlight the potential of ZnO-coated tapered POFs for high-performance, low-cost pH sensing in biomedical and environmental applications.