A theoretical analysis and an experimental demonstration are presented to show the increase in collected evanescent fluorescence for a fiber-optic sensor having a high refractive-index (n<sub>r</sub>), titanium sol-gel, thin-film coating. Simulations indicated that the maximum collected fluorescence should increase and shift to smaller film thicknesses as n<sub>r</sub> increases and also predicted an interference color-filtering effect. Experimentally, collected fluorescence increased by as much as 6 over that from a bare fused-silica fiber having a numerical aperture of 0.60. Simulations and experimental data were consistent with a decrease in the effective n<sub>r</sub> as film thickness increases. Electron micrographs of the sol-gel structure supported this observation and showed that the structure differs significantly from that of films formed on a planar glass substrate. High n<sub>r</sub>, sol-gel thin films are a potentially inexpensive approach to significantly increasing the signal from fiber sensors.
© 1998 Optical Society of America
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(120.2440) Instrumentation, measurement, and metrology : Filters
(130.6010) Integrated optics : Sensors
(160.6060) Materials : Solgel
(260.2510) Physical optics : Fluorescence
H. Pin Kao, Nancy Yang, and Joseph S. Schoeniger, "Enhancement of evanescent fluorescence from fiber-optic sensors by thin-film sol-gel coatings," J. Opt. Soc. Am. A 15, 2163-2171 (1998)