Dependence of detected intensity of fluorescence of dye on optical fiber tapered tip diameter

The measurement of pH in small objects (cells, drops of liquid etc.) using optical fluorescence-based sensors on optical fiber tapers is one of the most widely used optical techniques. In these sensors the diameter of the taper can play important role for collecting fluorescence from tested samples. This paper presents results of experimental measurements of fluorescence intensity of dye sensitive to pH in a solution that is excited by a blue laser. The fluorescence of the dye is collected by a taper tip. The fiber tips were prepared from a graded-index fiber with a core diameter of 50 m. Measurements with taper tips of different diameters have allowed us to estimated a limited tip diameter necessary for collecting any fluorescence form the dye solution on a level of about 5m.