U-bend optical fiber pH sensor using multiple sol-gel coating over TiO2

A wide range and highly sensitive U shaped optical fiber pH sensor utilizing titanium dioxide (TiO2) layer with multiple sol-gel coating has been fabricated and demonstrated in this paper. TiO2 layer is deposited over uncladded U-shaped fiber to enhance the evanescent field in the pH sensing film. The wide range sensing film is prepared by using three different indicators of various pH ranges. The higher sensitivity of 0.68 dBm/pH was obtained for double layer of sol-gel at 1550 nm with a good linear response. The sensor is also demonstrated for stability, durability and fast response time.