  The waveguiding properties of two silica-based airguiding photonic bandgap
fiber designs are investigated with special emphasis on material effects. The
nonlinear coefficients are found to be 1-2 orders of magnitude smaller than
those obtained in index-guiding microstructured fibers with large mode areas.
The material dispersion of silica makes a significant contribution to the total
chromatic dispersion although less than 10% of the field energy is located in
the silica regions of the fibers. These findings suggest that dispersion
engineering through the choice of base material may be a possibility in this
type of fibers.
