Conspicuous metallic blue of Morpho butterflies is well known and attract interest because it is a brilliant luster of natural beings. The blue is produced by their proteins, which are almost transparent without pigment. The origin of the coloration with high reflectivity (>~60%) is then attributed to an interference effect based on a periodic structure. However, the interference contradicts the blue that is maintained in too wide angular range (>±40° from the normal). This mystery has recently been explained with a specific multilayer, which is a fine combination of regular and random structures at nanometer scale. We proved this hypothesis successfully by emulating the 3D structures by deposition of multilayer film on a nano-patterned substrate. Such artificial structural color can be applied to various industries, because it makes colors qualitatively impossible by pigment, and resistant to fading due to chemical change over longtime. Also we developed a high throughput nano-patterning process by use of nano-imprinting method, and succeeded in controlling the optical properties both in angular and wavelength distribution.
