Optical Characterization of Iridescent Wings of Morpho Butterflies using a High Accuracy Nonstandard Finite-Difference Time-Domain Algorithm

In certain species of moths and butterflies iridescent colors arise from subwavelength diffractive surface corrugation of the wing-scales. The optical properties of such structures depend strongly on wavelength, incidence angle, and state of polarization of illuminating radiation, and the viewing angle. In this paper, we study the reflection spectra of the wings of the Morpho didius butterfly by simulating a double-layered model of a transverse cross-section comprised of the ground scale and the cover scale. Each layer contains a certain quasi-periodic arrangement of tree-like subwavelength microstructures. The simulation is done using a high accuracy nonstandard finite-difference time-domain (FDTD) method in two dimensions. We assume that the structure is made of a slightly lossy dielectric material. The wavelength dependence of the complex refractive index for the ground scale of Morpho didius is assumed to be similar to that of Morpho sulkowskyi. The complex refractive index in the latter case was obtained by comparing the computed reflection/transmission spectra with corresponding experimental measurements at normal incidence.

[1]  S Enoch,et al.  Morpho butterflies wings color modeled with lamellar grating theory. , 2001, Optics express.

[2]  Allen Taflove,et al.  Computational Electrodynamics the Finite-Difference Time-Domain Method , 1995 .

[3]  R. Wootton,et al.  Quantified interference and diffraction in single Morpho butterfly scales , 1999, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[4]  H. Ghiradella.  Light and color on the wing: structural colors in butterflies and moths. , 1991, Applied optics.

[5]  Peter Vukusic,et al.  Grazing-incidence iridescence from a butterfly wing. , 2002, Applied optics.

[6]  Serge Berthier,et al.  Determination of the cuticle index of the scales of the iridescent butterfly Morpho menelaus , 2003 .

[7]  Ronald E. Mickens,et al.  Advances in the Applications of Nonstandard Finite Difference Schemes , 2005 .

[8]  J. B. Cole,et al.  Calculation of Diffraction Characteristics of Sub wavelength Conducting Gratings Using a High Accuracy Nonstandard Finite-Difference Time-Domain Method , 2005 .

[9]  James B. Cole,et al.  Applications of Nonstandard Finite Difference Models to Computational Electromagnetics , 2003 .

[10]  James B. Cole,et al.  High-accuracy Yee algorithm based on nonstandard finite differences: new developments and verifications , 2002 .

[11]  J. B. Cole,et al.  Colour characterization of a Morpho butterfly wing-scale using a high accuracy nonstandard finite-difference time-domain method. , 2007, Micron.

[12]  S. Kinoshita,et al.  Mechanisms of structural colour in the Morpho butterfly: cooperation of regularity and irregularity in an iridescent scale , 2002, Proceedings of the Royal Society of London. Series B: Biological Sciences.