Three-dimensional light focusing in inverse opal photonic crystals

In this paper, we study negative refraction of electromagnetic waves in three-dimensional (3D) inverse opal photonic crystals (PCs). We employ the plane-wave expansion method to calculate the equifrequency surface of the PC structure, from which the frequency window where negative refraction might occur can be determined. We then investigate the propagation of electromagnetic waves radiating from a point source through a flat PC slab by means of a finite-difference time-domain method. We find that wave focusing can be achieved in such a 3D inverse opal PC structure at the negative-refraction frequency window. Because the inverse opal photonic crystal can be routinely synthesized in the optical regime by means of the self-assembly approach, our study opens a way for realization and application of 3D negative-refraction superlenses in the visible and infrared regimes.