THEORY OF FIBEROPTIC, EVANESCENT-WAVE SPECTROSCOPY AND SENSORS

A general theory for fiber-optic, evanescent-wave spectroscopy and sen sors is presented for straight, uncladded, step-index, multimode fiber s. A three-dimensional model is formulated within the framework of geo metric optics. The model includes various launching conditions, input and output end-face Fresnel transmission losses, multiple Fresnel refl ections, bulk absorption, and evanescent-wave absorption. An evanescen t-wave sensor response is analyzed as a function of externally control led parameters such as coupling angle, f number, fiber length, and dia meter. Conclusions are drawn for several experimental apparatuses. (C) 1996 Optical Society of America