<title>Fiber Bragg grating chemical sensor</title>

Abstract

A new fiber-optic method for quasi-distributed remote chemical sensing is described. The technique is based on using a wavelength selective Bragg-grating radiation coupler for localized excitation and detection of fluorescent species on or near the surface of the fiber cladding. A grating can be formed in germanosilicate fiber by exposing the core, through the side of the cladding, to an ultraviolet, two-beam interference pattern. With a suitable choice of index modulation, the grating can be designed to couple light efficiently from a guided mode into a narrow radiation beam. The index perturbation also enhances the capture of the emitted luminescence. Since the gratings are blazed to optimize the coupling efficiency for a desired wavelength band, each sensing region can be designed for a specific measurement. An array of identical sensors can be sampled by optical time domaifl reflectometry.