We show theoretically and experimentally that photonic band gaps can be realized using metal or metal-coated spheres as building blocks. Robust photonic gaps exist in any periodic structure built from such spheres when the filling ratio of the spheres exceeds a threshold. The frequency and the size of the photonic gap are essentially determined by the local order and they are not sensitive to the symmetry or the global long range order. These photonic crystals can withstand a large amount of disorder. For example, stacking faults cause almost no degradation. The gaps persist even in a random packing of such spheres. Good agreement between theory and experiment is obtained in the microwave regime. Calculations show that the approach can be scaled up to IR and optical frequencies.
Work done in collaboration with Z.L. Wang, W.Y. Zhang, X.Y. Lei, D.G. Zheng, W.Y. Tam and P. Sheng