Simple Absorption Optical Fiber pH Sensor Based on Doped Sol−Gel Cladding Material

An organically doped sol−gel optical fiber pH sensor based on silica-entrapped α-naphtholphthalein, is described. The absorption-based device, pumped with a red He−Ne laser, exhibits a dynamic range of 100% change between pH 4 and 11. The design and setup are simple and low cost, and the recladded optical fiber probe is easily replaceable.