Abstract

A new Bromothymol blue (BTB) thin film coated optical fiber pH sensor has been proposed in this paper. The BTB thin film is prepared by depositing a thin layer of a solution containing Tetraethyl orthosilicate(TEOS)and BTB pH indicator in presence of surfactants, namely Cetyl tri-methyl ammonium bromide(C₁₉H₄₂BrN, CTAB) by sol-gel technology on unclad multimode fiber (MMF) surface. The number of layer and deposition length of the thin film has been varied and the power transmission versus pH variation has studied. The concentration of the surfactant has been increased to understand the effect of increasing porosity in the sol-gel matrix to achieve improved pH sensitivity. A sensitivity of 79.96 nW/pH is obtained by 20 layer thin-film coated sensor in the pH range from 3 to 12.

© 2016 Optical Society of America