Optical power transversely scattered from fiber Bragg gratings: far-field measurements and modeling

Abstract

Far-field properties of the optical power scattered from type IIA Bragg gratings photowritten within high-N.A. germanosilicate fibers have been studied under various experimental conditions. Experiments were carried out in order to measure the angular distribution of the diffracted beam intensity. The optical power detected in the far field was shown to be scattered around a cone centered on the fiber axis. The azimuthal distribution of scattered optical power was nonuniform. A theoretical model, which takes into account the LP01-mode coupling to radiation modes for wavelengths well below the Bragg wavelength, properly fits the features of the observed pattern. This theoretical model assumes the existence of a nonuniform UV-induced refractive index change across a plane perpendicular to the fiber axis.