Light guidance in photonic structures of Morpho butterfly wing scales

In this paper, we investigate the impact of the periodicity along three orthogonal axes of the blue wing scales of Morpho butterflies, whereas most of the previous studies modeled the scale structure only considering one or two photonic crystal dimensions. Moreover, the previous optical studies of these scales focused on the light reflected by the wing, whereas we investigate the light propagation along the lamellae, this direction corresponding to the third dimension of the photonic crystal structure. Simulation results obtained using the finite-element method are compared with measurements and/or literature. These calculations, performed for different scale models and orientations, show that a significant part of the non-reflected light, essentially red and infrared, is guided by the lamellae towards the base of the scales where it can be more easily absorbed and the heat more quickly transferred to the hemolymph. This new phenomenon could contribute to the thermal balance of the insect and further illustrates the multifunctionality of the wings of Lepidoptera.