Experimental evidence for the mirage effect and giant dispersive phenomena in graded photonic crystals

Artificial optical materials made of graded photonic crystals or photonic metamaterials are a promising route to design versatile optical functionalities in the near-infrared. We report here the design, fabrication, and characterization of a planar gradual photonic crystal in the silicon on insulator photonics. Unusual light propagation phenomena consisting in light bending towards low long-range averaged refractive index regions are directly evidenced using an original hyperspectral scanning near-field technique. Giant dispersion properties of the gradual structure around 0.25μm/nm are reported.