Natural Photonic Crystal

Although Photonic Crystal architectures appear to be artificial, they are actually found in naturally occurring opal gemstones, and in many living organisms. Species that exhibit iridescent colours due to interference effects include the peacock, comb-jellyfish, the sea mouse, the rainforest beetle and the blue Morpho butterfly. Although widely cited as an example of a natural photonic crystal, the Morpho butterfly is perhaps not actually prototypical because its coloration is thought to involve both interference and diffraction effects, and dye pigmentation. Biologically, it is believed that species have evolved colour through Bragg reflections as a means of thermal regulation and signalling.


Naturally occurring periodic structures have almost exclusively 2D and 3D geometries, but are not, by the Yablonovitch criteria, genuine photonic crystal because their dielectric contrasts are not particularly large. Their activity however can be explained by the extremely large numberof periods found in these structures. This allows them to behave as essentially infinite photonic crystal which lead to perfect band gaps.