Strucural color of some blue Morpho butterflies has a physically mysterious feature, because it has both high reflectivity
(>60%) and a single color in too wide angular range (>±40° from the normal), which are contradicting with each other
from viewpoint of the interference phenomena. We have recently proven the principle of the mystery by extracting the
physical essence, and emulating the nano-structures using nano-fabrication techniques. The key was exquisite
combination of regular and random structures at nanometer scale. Such artificial structural color was found to concern
wide applications, because the Morpho-color can produce a single color without pigment in wide angular range with high
reflectivity. Also it makes colors impossible by pigment, and is resistant to fading due to chemical change over longtime.
However, we must overcome several "death valleys" for wide industrial applications. A serious problem was low
throughput in the fabrication process of nano-patterning by the conventional lithography, which was solved by use of
nano-imprinting technique. Next research step is attempts at a precise control of the optical properties, in both terms of
real space and wavelength, i.e. angular distribution and spectrum. We could successfully optimize the optical properties
by controlling the parameters of nano-structures in the artificial film. In this process, optical simulations and
micro-structural observations were taken in account. The optimization was achieved both theoretically and empirically
by comparing a series of films fabricated with different nano-patterns. Also the relationship between the structural
parameters and the optical properties was analyzed. The reflective characteristics of the optimized film were found to
reproduce the optical properties closer to the natural Morpho-blue than the prototypes.