Abstract

Structurally generated colour in brightly coloured animals is an exciting interdisciplinary area of research. Complex photonic bandgap (PBG) structures (which prevent the propagation of certain of wavelengths through them – causing strong coloured reflections) in Colepotera and Lepidoptera suggest broad innovation in nature’s use of materials and its manipulation of light. In certain butterflies, ultra-long-range visibility of up to one half-mile is attributed to photonic structures that are formed by discrete multilayers of cuticle and air. This contrasts, in other butterfly species, to photonic structures designed more for crypsis and which not only produce strong polarisation effects but can also create additive colour mixing using highly adapted structures. Even the existence of analogues of cholesteric liquid crystalline structures have been shown responsible for circularly polarised reflection from certain beetles’ exocuticle. Optical systems also exist that employ remarkable 2D and 3D photonic crystals of cuticle to produce partial PBGs, with the effect that bright colour is reflected, or fluorescence emission is inhibited, over specific angle ranges. From the perspective of modern optical technology, these structures indicate a significant evolutionary step, since in principle, these 2D and 3D periodicities are potentially able to manipulate the flow of light in all directions. Numerous studies, many of them very recent, have sought to discover and characterise the photonics associated with a diverse range of natural specimens. Many of them have revealed system designs that have evolved and existed naturally for millennia and that were, until their discovery in nature, thought to have been the product of recent technological innovation. This lecture will present an overview of this emerging field of study, as well as several of the exciting recent discoveries that reflect nature’s optical design ingenuity, and the technological applications to which they are currently being applied.