Polarization-sensitive color in iridescent scales of butterfly Ornithoptera

Abstract

Diverse biological microstructures that result in advanced optical effects have been systematically investigated. However, the mechanisms of polarization-sensitive color have not been fully understood. Here, we report a combined architecture comprising upper deep grating and bottom multilayer in butterfly iridescent scales that leads to polarization-sensitive color related with scale azimuth. The polarization process is unraveled through detailed investigations on the green scales in butterfly Ornithoptera priamus poseidon and the orange scales in butterfly Ornithoptera croesus lydius. The bright green and orange scales result from the interaction between the transmitted 0th order diffraction of upper grating and the 1st order interference of the bottom multilayer. Combining experimental results with calculation, we clarify the structural origin and the mechanism of the polarization conversion. Tapered grating achieves form-birefringence rotating polarized light and the multilayer selectively reflects the incident light dominating the reflection color. The height of the grating, which determines the phase difference of the two decomposed polarized lights, is essential to polarization conversion. To our knowledge, it is the first study to provide a structural prototype comprising deep grating and multilayer for achieving polarization-sensitive color. These findings show significant promise in biosensing, anticounterfeiting and optical-material design.