Fragility of photonic band gaps in inverse-opal photonic crystals

Inverse-opal techniques provide a promising routine of fabricating photonic crystals with a full band gap in the visible and infrared regimes. Numerical simulations of band structures of such systems by means of a supercell technique demonstrate that this band gap is extremely fragile to the nonuniformity in crystals. In the presence of disorder such as variations in the radii of air spheres and their positions, the band gap reduces significantly, and closes at a fluctuation magnitude as small as under 2% of the lattice constant. This imposes a severe requirement on the uniformity of the crystal lattice. The fragility can be attributed to the creation of this band gap at high-frequency bands (eight to nine bands) in inverse-opal crystals.