Optical fiber; Sensor; pH; Side polished half block; Sol–gel; Sensitivity
Fabrication and characterization of side-polished single mode optical fiber pH sensor utilizing evanescent field absorption spectroscopy and dye doped sol–gel immobilization technology are presented. The sensor is prepared by fixing the fiber in a groove made on one of the surfaces of a fused silica block. To make the surface sensitive to pH it is polished up to the core of the fiber and a film containing a mixture of three pH sensitive dyes is coated on it using sol–gel technology. The influence of the radius of curvature of the groove on the sensitivity of the sensor is studied. The decrease in the radius of curvature of the groove increases the sensitivity. This occurs due to the increase in the evanescent field and hence its interaction with the pH sensitive dyes entrapped in the film. The advantage of the side-polished single mode optical fiber sensor is that only 0.1 ml of sample is sufficient to measure the pH of the fluid. This is important when the procurement of the sample in large quantity is not possible.