Theoretical and experimental analysis of the structural pattern responsible for the iridescence of Morpho butterflies

Abstract

Abstract:Morpho butterflies are well-known for their iridescence originating from nanostructures in the scales of their wings. These optical active structures integrate three design principles leading to the wide angle reflection: alternating lamellae layers, "Christmas tree" like shape, and offsets between neighboring ridges. We study their individual effects rigorously by 2D FEM simulations of the nanostructures of the Morpho sulkowskyi butterfly and show how the reflection spectrum can be controlled by the design of the nanostructures. The width of the spectrum is broad (≈ 90 nm) for alternating lamellae layers (or "brunches") of the structure while the "Christmas tree" pattern together with a height offset between neighboring ridges reduces the directionality of the reflectance. Furthermore, we fabricated the simulated structures by e-beam lithography. The resulting samples mimicked all important optical features of the original Morpho butterfly scales and feature the intense blue iridescence with a wide angular range of reflection.

The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly

“…A reflection of up to 2.2% is observed for an angle of 65°, while all the values are well below 2% for lower angles. However, due to the comparable large spot size (4 Â 4 mm 2 ) and technical constraints of this set-up for highangle measurements, we use a home-built focused laser-based angle-resolved reflectance spectroscope with an unpolarized laser light of 632.8 nm wavelength 17 . In this way, we are able to exclude the parasitic absorption on the veins of the Glasswing from the measurement because the spot size of this set-up is only 50 mm in diameter and can be easily focused on the transparent wing parts between the veins.…”

“…The universal reflectance accessory from PerkinElmer Inc. was used for automated measurements for incidence angles ranging from 8°to 65°and wavelengths from 200 to 800 nm. A stabilized He-Ne laser (632.8 nm) was used to measure reflection up to 80°using a home-built setup 17 . Here the reflectance is measured through a fibre-coupled USB spectrometer (Ocean Optics HR2000 þ with a detection range of 394-840 nm and a resolution of 0.5 nm).…”

Fabrication of hierarchical photonic nanostructures inspired by Morpho butterflies utilizing laser interference lithography

“…The fascinating phenomena of the Morpho nanostructures is their quasi-omnidirectional blue non-iridescent reflection [27][28][29]. If we use the classical equation for thin film interference m reflection peak stays in blue regime till an angle of 40 • (see Fig.…”

“…4(b)). It is mainly due to the tapered shape of the multilayer air-polymer structures [29]. The tapered or so called 'Christmas tree' shape creates an impedance matching to the blue wavelength for higher incident angle.…”

“…Frequently, these nano-and microstructures are multifunctional [26]. Evolutionary optimized scales of the famous Morpho butterfly, for example, give at the same time a strong blue coloration [27][28][29] and make the wing hydrophobic [30]. It has been demonstrated that by mimicking such structures it is possible to outperform existing photonic vapor sensors [31] and thermal sensors [32,33] in sensitivity and spatial resolution.…”