Robust photonic band gap from tunable scatterers

We show theoretically and experimentally that photonic band gaps can be rea lized using metal or metal-coated spheres as building blocks. Robust photon ic gaps exist in any periodic structure built from such spheres when the fi lling ratio of the spheres exceeds a threshold. The frequency and the size of the gaps depend on the local order rather than on the symmetry or the gl obal long range order. Good agreement between theory and experiment is obta ined in the microwave regime. Calculations show that the approach can be sc aled up to optical frequencies even in the presence of absorption.