Fabrication and characterization of down-tapered optical fiber pH sensor using sol-gel method

In the present paper the fabrication and characterization of down-tapered optical fiber based pH sensor have been reported. The sensing probe is formed by fusing single mode fibers (SMF) to make it down-tapered which is spliced with multi-mode fiber (MMF). The sensing region is immobilized with sol-gel prepared by mixture of tetraethyl orthosilicate with three different pH indicators on to cladding of middle SMF. The proposed sensor utilizes intensity interrogation method and operates in low and high pH values. The maximum sensitivity of 0.49 dBm/pH is obtained with a good linear response for wide range of pH value varied from 4 to 13. In addition to high sensitivity, this sensor has additional advantages of good stability, fast response time and capable of using in remote sensing.