Fiber optic pH sensor using TiO2-SiO2 composite layer with a temperature cross-sensitivity feature

An intensity-modulated fiber optic pH sensor is fabricated and demonstrated in the present work. Three pH indicators, bromothymol blue, cresol red and chlorophenol red along with titania-silica composite are used as pH sensitive layers. The sensing principle is based on evanescent field absorption and then transmitted power loss of light guided within the fiber. The sensor parameters were studied by changing the volume ratio of the composite layer, and a maximum sensitivity of 1.76 mu W/pH is obtained for 1:3 (TiO2:SiO2) composite layer with excellent linear response for pH value from 2 to 11. The TiO2 content induces strong interaction between guided light and outer medium and the concentration of SiO2 was increased to improve porosity in the sol-gel matrix to achieve enhanced sensitivity. A straight forward way has been introduced to utilize the temperature cross-sensitivity feature of the optical fiber pH sensor with high temperature sensitivity. In addition to its high sensitivity, the proposed sensor has additional characteristics of fast time response and good stability which are very useful in biomedical, environmental, food processing and industrial applications.