Miniature pH sensor based on thin-core fiber Mach-Zehnder interferometer

A miniature pH sensor by using a tapered thin-core optical fiber based Mach-Zehnder interferometer coated with a pH sensitive film is demonstrated. Polyvinyl alcohol (PVA) and polyacrylic acid (PAA) were used to form a membrane structure on the taper by laminating self-assembly technique. By measuring wavelength change of the interference pattern or optical intensity, we achieved high sensitivity pH value measurement up to 2.06 nm/pH unit. The proposed sensor has small size, simple structure, good stability and a relatively short response time less than 52 s.