Trapping efficiency of fluorescent optical fibers

Fluorescent optical fibers are used in nuclear detection and other forms of fiber-optic sensors. The trapping efficiency of a fluorescent optical fiber is defined by the optical energy trapped (or guided) by the fiber divided by the total energy emitted within it by the fluorescers that dope the fiber core. This characteristic is clearly important in determining the size of signals from these devices. A calculation of the trapping efficiency has been performed under the assumption that the fluorescence radiation is emitted isotropically by the individual fluorescers that are uniformly distributed throughout the core and are equally likely to be excited by particles or shorter-wavelength light. At the price of increased complexity, nothing in the analysis precludes the lifting of these restrictions. What is included in this analysis is the contribution of skew rays, which, to the author's knowledge, is not presented elsewhere. A very simple expression for the trapping efficiency as a function of the cladding-to-core index ratio is derived. Also important in determining signal size is the transmission loss of the fluorescence radiation to either end of the fiber from the point of its generation. However, as it is a separate matter, it is not discussed here. (C) The Authors. Published by SPIE