A general theory for fiber-optic, evanescent-wave spectroscopy and sensors is presented for straight, uncladded, step-index, multimode fibers. A three-dimensional model is formulated within the framework of geometric optics. The model includes various launching conditions, input and output end-face Fresnel transmission losses, multiple Fresnel reflections, bulk absorption, and evanescent-wave absorption. An evanescent-wave sensor response is analyzed as a function of externally controlled parameters such as coupling angle, f number, fiber length, and diameter. Conclusions are drawn for several experimental apparatuses.
© 1996 Optical Society of America
Original Manuscript: July 25, 1995
Revised Manuscript: October 24, 1995
Published: May 1, 1996
A. Messica, A. Greenstein, and A. Katzir, "Theory of fiber-optic, evanescent-wave spectroscopy and sensors," Appl. Opt. 35, 2274-2284 (1996)