Abstract
The outer wing casings (elytra) of the weevil Eupholus magnificus are marked by yellow and blue bands. We have investigated the scales covering the elytra by using microspectrophotometry, imaging scatterometry, scanning electron microscopy and Fourier transform analysis. We demonstrate that the scales in the yellow elytral bands comprise highly ordered 3D photonic crystal structures, whereas the scales of the blue bands comprise quasi-ordered 3D photonic structures. Both systems, highly contrasting in their periodic order, create approximately angle-independent colour appearances in the far-field. The co-existence of these two contrasting forms of 3D structural order in the same single species is certainly uncommon in natural biological systems and has not been reported in the photonic literature.
Highlights
Photonic crystals (PCs) have been the subject of rapidly increasing interest over recent years [1]
We demonstrate that the scales in the yellow elytral bands comprise highly ordered 3D photonic crystal structures, whereas the scales of the blue bands comprise quasi-ordered 3D photonic structures
Quasi-ordered photonic crystal geometries create a more isotropic optical scattering structure due to their relatively spherical Brillouin zone boundaries [6]
Summary
Photonic crystals (PCs) have been the subject of rapidly increasing interest over recent years [1]. While the periodic structure of highly ordered photonic crystals creates strong light manipulation, the structural nature of quasi-ordered crystals that show higher orders of rotational symmetry is attracting increasing interest from the photonics community. Such quasi-ordered crystals are not limited by the same geometric constraints with which ordered structures are restricted. The possibility for complete photonic band-gap generation, using materials that have a lower refractive index contrast, becomes available, making fabrication and compatibility of complete photonic band-gap devices more accessible [6]. Many applications including LEDs can utilise the many properties associated with quasi-ordered PCs: in the case of LEDs, quasi-ordered PCs may be used to enhance the extraction efficiency by reducing the absorption of reflected light [7]
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