Photonic band gaps in non-close-packed inverse opals

An advanced dielectric function has been designed to compute the photonic band structures of non-close-packed inverse opals fabricated using conformal infiltration and by a recently described sacrificial-layer technique. A model is proposed to correctly simulate complex dielectric structures resulting from conformal backfilled infiltrations. While large photonic band gaps (PBGs) and a reduced refractive index requirement (RIR) are predicted to occur in these inverse structures, the results also indicate a high degree of sensitivity to the dielectric/air network topology enabling fine PBG tailoring. Optimized structurally modified non-close-packed inverse opals with lower refractive indices offer enhanced optical properties compared to narrow PBGs observed in conventional inverse shell opals using high index materials such as silicon or germanium. Three-dimensional finite-difference time-domain computations predict that many experimentally achievable non-close-packed inverse structures exhibit significantly enhanced PBG properties: a RIR as low as 2.65 and PBG width of similar to 10%. Additionally, a PBG width of 14.2% is predicted for an optimized high index non-close-packed inverse structure in which the interstitial air void is smaller than in structures fabricated by conformal means. The robustness and simplicity of this technique combined with predicted adjustable PBG properties is therefore demonstrated to provide alternative fabrication routes to the synthesis of photonic crystal devices operating in the visible with lower refractive indices. (c) 2006 American Institute of Physics.