EVANESCENT-WAVE FIBER OPTIC FLUOROSENSOR - EFFECT OF TAPERING CONFIGURATION ON THE SIGNAL ACQUISITION

A comparative study of the signal acquisition from straight fiber and tapered optical fibers has been analyzed theoretically for the design of an evanescent wave fiber optic immunosensor. It has been shown that tapered optical fibers have higher sensitivity compared to straight f ibers. Among the tapered fibers combination tapered fibers were also f ound to have higher sensitivity than continuous tapered fibers. Theore tical analysis indicates that an increase in signal is a result of thr ee factors, namely, V number matching, an increase in evanescent absor ption by the fluorescent medium, and an increase in fluorescence emiss ion coupling into the fiber. Maximum sensitivity is obtained when the radius of the fiber is reduced to the V number matching radius within 1 cm from the start of the taper with rest of the fiber remaining unta pered. Also, a higher signal level is obtained when the launching ligh t fills the numerical aperture determined by the tapering ratio of the fiber. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [ S0091-3286(98)04301-3].