  In this report the effects of unintended deviations from ideal inverse
woodpile photonic crystals on the band gap are discussed. These deviations
occur during the nanofabrication of the crystal. By computational analyses it
is shown that the band gap of this type of crystal is robust to most types of
deviations that relate to the radii, position and angular alignment of the
pores. However, the photonic band gap is very sensitive to tapering of the
pores, i.e., conically shaped pores instead of cylindrical pores. To obtain
three-dimensional inverse woodpile photonic crystals with a large volume, our
work shows that with modern fabrication performances, tapering contributes most
significantly to a reduction in the photonic strength of inverse woodpile
photonic crystals.
