Fano resonance of three-dimensional spiral photonic crystals: Paradoxical transmission and polarization gap

Abstract

Extraordinary Fano resonance with right handedness is present in a right-handed polarization gap of compound spiral photonic crystals. The structure is composed of unit cells with double helices of π phase shift arranged in square lattice. Such a paradoxical phenomenon is derived from mode interferences between left-handed propagating modes along spiral axis and negative group velocity modes in extended Brillouin zone. By analyzing Fourier spectra and chirality of photonic eigenmodes, intrinsic mechanism is well understood by mode coupling theory.