Direct evidence of tilted Bragg grating azimuthal radiation mode coupling mechanisms

A number of useful fiber optic devices depend on being able to predict and manipulate the radiation field emitted by tilted fiber Bragg gratings. Previously we demonstrated analytically the manner in which this radiation field is directionally dependent on the phase matching characteristics of a grating's three-dimensional structure as well as the polarization dependent dipole response of the medium itself. In this paper, for the first time, experimental measurements of the out-tapped field are presented which clearly illustrate and confirm the existence of the predicted trends associated with each of these physical mechanisms. Using an infrared camera and commercially available beam profiling software, these findings were gathered from a number of tilted fiber Bragg gratings written with an ultraviolet excimer laser at a variety of blaze angles.