Photonic scales of Hoplia coerulea beetle: any colour you like

The scales covering the elytra and thorax of the male Hoplia coerulea scarab beetle are a specific case of natural photonic structure encased by a fluid-permeable envelope. These scales display several optical effects including structural colouration, fluid-induced colour changes, fluorescence emission and fluid-induced fluorescence changes. Although the photonic structure is not directly exposed to the environment, optical changes are known to be induced by liquids and vapours. These changes are controlled by the envelope that mediates exchanges with the surrounding environment. The optical system comprising the photonic structure and the envelope was previously termed 'photonic cell'. Novel possibilities to develop functional photonic materials and smart coatings are offered by such a system through a bioinspired approach. This technological potential motivated us to analyse theoretically, through numerical simulations, the water-induced changes of optical properties of light emitters embedded in a photonic structure inspired by H. coerulea beetle's scales.