Living photonic crystals: Butterfly scales — Nanostructure and optical properties

The photonic crystal type nanostructures in the scales of male individuals of two butterfly species: Cyanophrys remus and Albulina metallica were investigated by electron microscopy and reflectance measurements. While the colors of C. remus arise from structures with rigorous long range (dorsal) or short range (ventral) three dimensional (3D) order, the colors of A. metallica are produced by quasi-ordered, layered structures. Surprisingly, the most efficient photonic band gap reflector is the quasi-ordered structure giving the shiny, yellowish green color of the ventral hind wings of A. metallica. All four investigated structures are based on a moderate refractive index contrast between chitin (n = 1.58) and air, the various structures achieve a wide range of biological functions.