Cladding mode coupling in highly localized fiber Bragg gratings II: complete vectorial analysis

Abstract

Highly localized fiber Bragg gratings can be inscribed point-by-point with focused ultrashort pulses. The transverse localization of the resonant grating causes strong coupling to cladding modes of high azimuthal and radial order. In this paper, we show how the reflected cladding modes can be fully analyzed, taking their vectorial nature, orientation and degeneracies into account. The observed modes' polarization and intensity distributions are directly tied to the dispersive properties and show abrupt transitions in nature, strongly correlated with changes in the coupling strengths.