Multiplexable Fiber pH Sensors Enabled by Intrinsic Fabry-Peìrot Interferometer Array

Abstract

This work presents multiplexable fiber optical sensors to perform multiple-point pH measurements. Using a femtosecond laser direct writing approach, array of intrinsic Fabry-Peìrot interferometer (IFPI) sensors were inscribed in standard single-mode fibers. A sol-gel dip coating process was used to deposit Palladium-doped Titanium Dioxide (Pd-TiO2) sensory film on IFPI sensors to perform pH measurement, while an uncoated sensor was used to measure temperature of aquatic solutions to remove influence of temperature fluctuation on pH measurements. Pd nanoparticles in sensory films acts as catalyst to convert hydrogen ion in aquatic solutions Pd hydride, which produce strains to IFPI sensors. White light interferometry demodulation algorithm was applied to resolve strain exerted to IFPI sensors induced by pH value changes in aquatic solution. The sensor exhibits reversible and reproducible response in aquatic solution with pH value from 1.0 to 7.0 at the room temperature. The response time of the pH sensors was approximately 7 s for all measurements performed. The sensor technology demonstrated in this paper has a potential to perform multi-point pH and temperature measurements using a single fiber.