Light localization in chirped woodpile photonic crystals

In this article, light localization inside woodpile photonic crystal made of stacks of parallel dielectric rods is numerically and experimentally investigated. The light localization phenomena is achieved by tailoring the structural parameters in the way that a propagating beam is gradually slowed down and finally stopped at a wavelength-dependent position along the structure. In contrast to previous approaches, where light is trapped in one or two-dimensional photonic structures, the stopped light inside the proposed structure is confined in all three directions, due to the complete three-dimensional photonic bandgap enabled by the unique symmetry properties of the woodpile photonic crystal. By this means, the strict requirements of total internal reflection confinement are eliminated and in result radiation losses are minimized. The operational principle of the proposed structure is verified experimentally at the microwave regime, whose results agree well with the numerical analysis.