Photonic structure in the wings of Papilio bianor ganesa

We conducted structural characterizations, reflection measurements, and theoretical simulations on the iridescent green of the wings of Papilio bianor ganesa. We found that the green iridescence originated from a stack of about 9 periodic structure composed of chitin layers and air-spacer layers. This periodic structure gave rise to a high-reflection band in yellowish-green part of the visible spectrum under normal incidence. With increasing incident angle, all reflection peaks showed a blue shift in wavelength. Based on the structural characterizations, the theoretical simulations accurately predicted the shifts in spectral reflectivity which might be observed experimentally.