Photonic Crystals in Nature

Photonic crystals have been subject of research for the last two decades. These artificial materials behave towards optical electromagnentic radiation in the same way as semiconductors behave towards electrons. A lot of materials and technologies have been tested for usefulness in this field. At the moment the most promising material is silicon processed with microelectronic technologies. It turned out however, that what people discovered a couple of years ago, Mother Nature created millions of years earlier. Examples of photonic crystals structures occur in hard minerals (opal), as well as in living creatures (butterfly wings, fur of the sea mouse). Naturally created photonic crystal structures aren't all the same, they differ in forms and functions. Two as well as three-dimensional structures are reported. That makes them even more interesting subject for research. The most interesting examples of photonic crystal structures existing in nature are presented and classified in this article.