Numerical Analysis on the Optical Role of Nano-Randomness on the <I>Morpho</I> Butterfly's Scale

Abstract

The blue coloration of Morpho butterflies has anomalously low angular dependence despite the production of color with a selected wavelength based on an interference effect. A key to the mechanism of the specific Morpho-color was suggested to be the randomness of its scale. Using finite-difference time-domain (FDTD) analysis, the role of different kinds of randomness in the structure of the Morpho butterfly's scale was investigated, which was impossible by conventional analytical calculations. The results revealed that incoherence in the incident light plays an essential role, which cannot be realized only by structural randomness. On the other hand, the lateral and vertical randomness, and the number of random components were found each to have an independent role to realize the specific Morpho-color preventing the sharp reflective angular dependence. The direction obtained by the numerical simulations to analyze optically complex random structures will serve not only to understand the scientific principles, but also to design the optical properties of artificial materials.

Anti-reflective surfaces: Cascading nano/microstructuring

“…This illustrates an important concept: that nanotexturing aids in the coupling of light into the substrate, but does so at the cost of the transmittance. Another possible reason for the mismatch between the results of the theory and those of the experiments is the definition of the light source in FDTD, which causes coherent addition of the fields 39 and makes the readout of the local light field intensity sensitive to minor changes in the monitoring location. To overcome this issue, it would be necessary to perform multiple simulations using different random samples of the same surface along with different placements of the light source and different average intensities; this is planned to be done as part of our future work.…”

It's Not a Bug, It's a Feature: Functional Materials in Insects

“…Anatomical allomone structures Bees, [486,491] wasps, [486] ants, [486] honeybees, [497] true bugs [473,499,607] Defense spines Lepidopteran caterpillars, [485] pine processionary caterpillars, [485,490] moths [486] Built structures Caterpillars, [608][609][610][611] moth caterpillars, [612] beetles [613][614][615] Projectile dispersal Bombardier beetles [467] Color vision and color manipulation 1D photonic structures Beetles, [289,291] butterflies [289,291] Apposition eyes Ants, [361] dragonflies [361] Bioluminescence Fireflies [616] Color vision Honeybees, [617,618] common bluebottle butterflies [619] Disorder-based color Butterflies, [320,323,324] jeweled beetles, [329][330][331] white beetles [332,333] Photonic crystals Weevils, [290,316,319,321] butterflies [290,316,…”

“…Local disorder in Morpho butterflies provides a large range of viewing angles with stable color by introducing disorder in the scale ridge reflectors (Figure 14A). [277,323,324] A certain degree of disorder can also smooth the reflectance of multilayer structures by suppressing higher-order reflections caused by perfectly ordered structures. [325] Multilayer structures can be chirped, i.e., have a varying distance between layers of refractive index, [292] or twisted, resulting in strongly circularly polarized reflected light.…”

Designing visual appearance using a structured surface

“…A regular structure with a fixed period is unfit for our purpose due to interference effects [15]. To avoid this we introduce height randomization in these repeated units [15,16]. The dominant effect of such an approach can be approximated analytically [15] and verified numerically before fabrication.…”