Refractive index of micro/nano structured dielectric materials

The concept of refractive index has to be revisited for micro or nano structured materials. The refractive index is generally linked to the group phase velocity of the light wave traveling through a media. With such a definition it must be associated to the effective index in waveguides or in photonic crystals. This last point leads to the concept of metamaterials. The fundamental problem of the optical properties of nanostructured materials is tackled. With the progresses of nanotechnologies it becomes now possible to control the nanostructure of materials. Refractive index engineering, artificial anisotropy and antireflection structures are now possible. This paves the way to new applications concerning photonic crystals, integrated optics, micro sensors, solar cells... Some examples of applications are given.