Group-velocity dispersion measurements in a photonic bandgap fiber

Spectral interferometry with a supercontinuum is used for the first experimental measurement, to our knowledge, of phase dispersion of the fundamental mode in multiple bandgaps of a photonic bandgap fiber. The dispersion data show a strong influence of the Bragg scattering from the crystal structure surrounding the core. A simple two-dimensional model that includes the effects of a wavelength-dependent angle of propagation, where the angle is determined by the Bragg-scattering condition, and the effects of thin-film-like resonant scattering planes in the fiber is found to explain the observations qualitatively.