Structural Colour in Butterfly Apatura Ilia Scales and the Microstructure Simulation of Photonic Crystal

The butterfly Apatura ilia is a species in the Northeast of China. There are billions of tiny scales on its wings, which overlap like roof tiles and completely cover the membrane, appearing as dust to people naked eye. The scales produce brilliant structural colour through their multilayer microstructure. In this paper, the microstructure and geometrical dimension of the scales were observed using a Scanning Electron Microscope (SEM). The cross section micro-configuration of the purple scales was achieved using a Transmission Electron Microscope (TEM). The reflectivity of the wing was measured by a spectrometer. The 3D multilayer microstructure of the ridges was optimized to 1D photonic crystal structure. The spectrometer experimental graph is in accord with the 1D photonic crystal simulation curves basically. In the end, the phenomenon of the purple structural colour was explained through the Snell equation.