Fabrication and characterization of U-shaped fiber-optic pH probes

Fabrication and characterization of U-shaped fiber optic pH probes utilizing evanescent field absorption spectroscopy and dye doped sol–gel immobilization technology are presented. The U-shaped probe is used to increase the evanescent field in the film and hence its interaction with the dyes present in the film. The influences of bending radius of the probe and the numerical aperture of the fiber on the sensitivity of the sensor are studied. It has been shown that, for a given pH, as the bending radius of the U-shaped probe decreases the sensitivity of the sensor increases. Further, for a given bending radius and the fiber core diameter, increase in the numerical aperture of the fiber increases the sensitivity of the pH sensor. The response time of the sensor reported in the present study is approximately 15 s.