It is known that the structural colors of some beetles originate from multilayer thin-film interference. We
investigated such an example, a jewel beetle Chrysochroa fulgidissima, to quantitatively characterize the coloration mechanisms. The essential physical factors of the iridescence were elucidated by careful determinations of the structural parameters, measurements of angle and polarization-dependent reflection spectra, and theoretical modeling of the multilayer system. On the basis of the elucidated coloration mechanisms, we successfully prepared a dielectric thin film structure that reproduces the iridescence of the jewel beetle.
Multilayer interference phenomenon has been widely applied to various optical components that have highly
wavelength-selective properties in reflection and transmission. In nature, some animals also take advantage of
a similar mechanism for the coloration of their brilliant bodies. However, natural examples of multilayer thin-film
structure are often modified in some structural aspects, and the modifications have been found to cause
interesting optical effects. Recently, we found such an example, highly curved multilayer structure, in the wing
scale of the Madagascan sunset moth. In this paper, we report the extended study of this subject. First, we will
review the structural characteristics and various optical phenomena that occur on the wing of the moth. Second,
inspired by the coloration mechanism of the moth wing, we newly consider multilayer designs for the color plates
that change their colors depending on the analyzing direction of polarization.
Some of Morpho butterflies are well known with its brilliant metallic blue wings. The blue luster is produced from the butterfly's scale that is composed of almost transparent cuticle protein. The origin of the coloration is then not pigment but rather microscopic structure. The principle of this phenomenon has long been referred to as grating or multilayer that can also explain its high reflectivity. However, its optical characteristics on the scattered wavelength cannot be explained by grating or multilayer. The mystery of the lack of multi-coloration (it appears blue from wide angle) remained unnoticed for many years. This mysterious feature has recently been explained with a peculiar optical structure that includes discrete multilayers. This model is based on both of the order and disorder structures: it is not their simple medium but their delicate combination. However, a theoretical hypothesis needs a proof by experiments and we tried to fabricate the optical film by controlling the parameters. A simple fabrication process including a conventional lithography technique in the semiconductor industry was used from viewpoint of application. The result showed that the optical scattering property was basically reproduced and affected by the structure of 100-300 nanometer scales in agreement with the anticipation. A wide variety of applications are relevant to such artificial structural color.