  A two-dimensional photonic crystal microcavity design supporting a
wavelength-scale volume resonant mode with a calculated quality factor (Q)
insensitive to deviations in the cavity geometry at the level of Q~2x10^4 is
presented. The robustness of the cavity design is confirmed by optical
fiber-based measurements of passive cavities fabricated in silicon. For
microcavities operating in the lambda = 1500 nm wavelength band, quality
factors between 1.3-4.0x10^4 are measured for significant variations in cavity
geometry and for resonant mode normalized frequencies shifted by as much as 10%
of the nominal value.
