Long-Period Fiber Grating Wide-Range pH Sensor Based on Polyvinyl Alcohol/Polyacrylic Acid Hydrogel Coating

A wide-range pH sensor based on a coated long-period fiber grating is proposed. The pH responsive PVA/PAA hydrogel coating on the surface of the long period grating (LPG) swells/ deswells in response to change the local pH. The experimental results demonstrate a wide range for the PVA/PAA coated sensor in acid solution (from pH range 1.916 to 7.252). Moreover the sensor also shows a high repeatability and stability.