  We consider photonic crystal fibers made from arbitrary base materials and
derive a unified semi-analytical approach for the dispersion and modal
properties which applies to the short-wavelength regime. In particular we
calculate the dispersion and the effective index and comparing to
fully-vectorial plane wave simulations we find excellent agreement. We also
calculate asymptotic results for the mode-field diameter and the V-parameter
and from the latter we predict that the fibers are endlessly single mode for a
normalized air-hole diameter smaller than 0.42, independently of the base
material.
