Wavelength–selective and anisotropic light–diffusing scale on the wing of the Morpho butterfly

Abstract

We have found that cover scales on the wing of the butterfly Morpho didius possess specially designed microscopic structures for wavelength-selective reflection and contribute considerably to the brilliant blue colour of the wing. In addition, the cover scale functions as an anisotropic optical diffuser which diffuses light only in one plane, while it makes the range of reflection narrower in the orthogonal plane. The quantitative analyses for the wavelength-selection mechanism and the peculiar optical diffuser are given and the role of such a special optical effect is discussed from physical and biological viewpoints.

Exaggeration and suppression of iridescence: the evolution of two-dimensional butterfly structural colours

“…In previous work, the broad-angle spectrum along the L -tilt axis of the Morpho butterflies is attributed to irregularities in the height of the adjacent ridges (Kinoshita et al 2002), and in the exact geometry of each ridge reflector (Vukusic et al 1999;Gralak et al 2001;Kinoshita et al 2002;Plattner 2004;Yoshioka & Kinoshita 2004). Re-examining the SEM image of the microrib structure (figure 1c), it is obvious that it incorporates more irregular elements than the ridgelamellae structure (figure 1b).…”

“…Extensive previous work (Vukusic et al 1999;Gralak et al 2001;Kinoshita et al 2002;Plattner 2004;Yoshioka & Kinoshita 2004) has focussed on the first type, and in particular the ridge-lamellae multi-layer found in the Morpho species. The angle-dependent absolute reflectivity and transmission of these wing scales indicates a much broader angle reflection than is typical of multi-layer systems (Vukusic et al 1999).…”

“…In the past, these structures have often been approximated as thin-film reflectors or diffraction gratings. However, recent studies of the angle-dependence of their hue and intensity (iridescence) have revealed more complex optical behaviours due to the compound effects of interference, diffraction, absorption and scattering (Vukusic et al 1999Gralak et al 2001; Kinoshita et al 2002;Lawrence et al 2002;Plattner 2004;Yoshioka & Kinoshita 2004).…”

“…Also, no study has compared the properties of all three types, or quantified the diversity within each type. This study will address these questions by examining in detail the optical properties of 10 species of butterflies, of which only two (Morpho didius (Vukusic et al 1999;Gralak et al 2001;Kinoshita et al 2002;Yoshioka & Kinoshita 2004) and Troides magellanus ) have been studied previously.…”

A dual weighted residual method applied to complex periodic gratings

“…When scattered by light, the Morpho butterfly wing produces colour and this allows a dynamical control of light flow and wavelength interaction [35] (figure 4). The scattering of the Morpho butterfly wing has inspired applications in biomimetics such as gas sensors, electronic display screens and paints for cars [2,[36][37][38]. This transmitting dielectric grating type has been studied experimentally in Vukusic et al [35] using a focused laser technique to examine the total reflectivity and transmissivity.…”