Fluorescent sensors based on tapered single-mode optical fibres

Abstract An optical sensor is presented that relies on the evanescent field excitation of a pH indicator in the external media. The evanescent field is made accessible through the use of an adiabatically tapered single-mode optical fibre. The level of fluorescence captured into the fibre from the excited indicator is directly related to the pH value. Theoretical calculations of the sensitivity are presented and contrasted to those of multimode fibres. The detection range of the sensor is pH 3–9, demonstrating the suitability of tapered fibre devices as sensors.