The glasswing butterfly (Greta oto) has, as its name suggests, transparent wings with remarkable low haze and reflectance over the whole visible spectral range even for large view angles of 80°. This omnidirectional anti-reflection behaviour is caused by small nanopillars covering the transparent regions of its wings. In difference to other anti-reflection coatings found in nature, these pillars are irregularly arranged and feature a random height and width distribution. Here we simulate the optical properties with the effective medium theory and transfer matrix method and show that the random height distribution of pillars significantly reduces the reflection not only for normal incidence but also for high view angles.

Inspired by black butterfly scales, self-assembled phase-separated nanostructures form efficient photovoltaic absorbers.

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications.

8 pagesInternational audienceWe propose a photovoltaic solar cell design based on a 100 nm thick absorbing layer made of hydrogenated amorphous silicon and patterned as a two-dimensional planar photonic crystal (PPC). After scanning the parameters of the PPC within the patterned cell, optical simulations performed on the best configuration obtained reveal that a relative increase in the integrated absorption inside the active layer of 28% can be expected between 300 and 720 nm compared to an equivalent but nonpatterned cell under normal incidence. Besides, this integrated absorption is found to be robust toward the angle of incidence. Incident light is efficiently coupled to leaky mode resonances of the PPC provided an appropriated tuning of its parameters. The effects of the reflectance of the back contact coupled to a conductive optical spacer on the absorption are also discussed