Enhancement of evanescent fluorescence from fiber-optic sensors by thin-film sol-gel coatings

摘要

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↓(r)), titanium sol-gel, thin-film coating. Simulations indicated that the maximum collected fluorescence should increase and shift to smaller film thicknesses as n↓(r) 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↓(r) 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↓(r), sol-gel thin films are a potentially inexpensive approach to significantly increasing the signal from fiber sensors.# 1998 Optical Society of America [S0740-3232(98)02707-0] OCIS codes: 130.6010, 060.2370, 260.2510, 160.6060, 120.2440.