Bragg reflection is the basic principle
Examples in nature as models
It is interesting to note that such structures have existed in nature for many millions of years. For instance, the special optical properties of the opal semiprecious gem are based on the same basic principles. The same is true for a butterfly wing or a sea mouse.
Future development will provide various optical components based on the principle of such periodic photonic structures. These could take the form of miniaturized versions of known optical elements or the implementation of totally new optical functions.
Another kind of artificial optical material is obtained if the grating period of the structure imprinted on the material has been made so small that no other than the zeroth diffraction order can occur. The grating then acts like an effective medium, i.e. a thin coating whose refractive index lies between those of the two materials involved.
Examples of applications are l/4 phase plates or anti-reflection surfaces (moth-eye structures). Metallic strip gratings with such small periods show an anisotropy of absorption and reflection (polarizing filters). The way these gratings function can be explained by means of the electric field: for parallel oscillations it is possible to imagine an effective dielectric with a parallel connection of areas of high and low dielectric constants. If the electric field oscillates perpendicular to the strip grating, it is a serial connection.
Artificial materials are the future
The application of these artificial materials will revolutionize optical technologies in the years to come. Due to the many different areas of applications, the current aim is to produce optical systems with cross or even complete functionalities. With microstructured and nanostructured optical components the basic elements are now available for an optical system technology that will allow the move from discrete components to fully integrated functional units.