In recent years, structural colors have attracted great attention in a wide variety of research fields. This is because they are originated from complex interaction between light and sophisticated nanostructures generated in the natural world. In addition, their inherent regular structures are one of the most conspicuous examples of non-equilibrium order formation. Structural colors are deeply connected with recent rapidly growing fields of photonics and have been extensively studied to clarify their peculiar optical phenomena. Their mechanisms are, in principle, of a purely physical origin, which differs considerably from the ordinary coloration mechanisms such as in pigments, dyes and metals, where the colors are produced by virtue of the energy consumption of light. It is generally recognized that structural colors are mainly based on several elementary optical processes including thin-layer interference, diffraction grating, light scattering, photonic crystals and so on. However, in nature, these processes are somehow mixed together to produce complex optical phenomena. In many cases, they are combined with the irregularity of the structure to produce the diffusive nature of the reflected light, while in some cases they are accompanied by large-scale structures to generate the macroscopic effect on the coloration. Further, it is well known that structural colors cooperate with pigmentary colors to enhance or to reduce the brilliancy and to produce special effects. Thus, structure-based optical phenomena in nature appear to be quite multi-functional, the variety of which is far beyond our understanding. In this article, we overview these phenomena appearing particularly in the diversity of the animal world, to shed light on this rapidly developing research field.

https://iopscience.iop.org/article/10.1088/0034-4885/71/7/076401/pdf

Physics of structural colors

Nature's color has three main sources: pigments, structural colors and bioluminescence. Structural color is a special one, which is the color produced by micro- or nano-structures, and is bright and dazzling. The most common mechanisms of structural colors are film interference, diffraction grating, scattering and photonic crystals. Biological colors are mainly derived from film interference, which includes thin-film and multi-film interference. The diffraction grating mechanism is found in, for example, seed shrimp, mollusk Haliotis Glabra and the Hibiscus trionum flower. Scattering includes coherent and incoherent scattering. Well-known examples of coherent scattering include colors produced by brilliant iridescent butterfly wing scales and avian feather barbules, such as the peacock's tail. Examples of colors produced by photonic crystal structures include opal in beetles and iridescent spines in the sea mouse. Coloration changes occur through structural changes for camouflage, predation, signal communication and sex choice. This paper presents an overview of lessons from nature and various relevant mechanisms. Examples of bioinspired fabrication methods and applications are also presented in this paper.

Structural coloration in nature

Concentrating photovoltaic (CPV) systems are a key step in expanding the use of solar energy. Solar cells can operate at increased efficiencies under higher solar concentration and replacing solar cells with optical devices to capture light is an effective method of decreasing the cost of a system without compromising the amount of solar energy absorbed. However, CPV systems are still in a stage of development where new designs, methods and materials are still being created in order to reach a low levelled cost of energy comparable to standard silicon based PV systems. This article outlines the different types of concentration photovoltaic systems, their various design advantages and limitations, and noticeable trends. This will include comparisons on materials used, optical efficiency and optical tolerance (acceptance angle). As well as reviewing the recent development in the most commonly used and most established designs such as the Fresnel lens and parabolic trough/dish, novel optics and materials are also suggested. The aim of this review is to provide the reader with an understanding of the many types of solar concentrators and their reported advantages and disadvantages. This review should aid the development of solar concentrator optics by highlighting the successful trends and emphasising the importance of novel designs and materials in need of further research. There is a vast opportunity for solar concentrator designs to expand into other scientific fields and take advantage of these developed resources. Solar concentrator technologies have many layers and factors to be considered when designing. This review attempts to simplify and categorise these layers and stresses the significance of comparing as many of the applicable factors as possible when choosing the right design for an application. From this review, it has been ascertained that higher concentration levels are being achieved and will likely continue to increase as high performance high concentration designs are developed. Fresnel lenses have been identified as having a greater optical tolerance than reflective parabolic concentrators but more complex homogenisers are being developed for both system types which improve multiple performance factors. Trends towards higher performance solar concentrator designs include the use of micro-patterned structures and attention to detailed design such as tailoring secondary optics to primary optics and vice-versa. There is still a vast potential for what materials and surface structures could be utilised for solar concentrator designs especially if inspiration is taken from biological structures already proven to manipulate light in nature.

/pdf/optics-for-concentrating-photovoltaics-trends-limits-and-3ddbtiv50v.pdf

Optics for concentrating photovoltaics: Trends, limits and opportunities for materials and design

The photonic structures of butterfly wings are among the most anatomically diverse of all those in nature, giving rise to an unrivalled display of structural colours. These have recently become the focus of research by workers in a variety of disciplines, stimulated by their potential applications to technology (‘biomimetics’). This interest, together with the discovery of unpublished electron micrographs taken by the late Dr John Huxley (Natural History Museum, London), prompted this review of butterfly photonics in general. The current work provides a synopsis of the literature to date, covering the diversity and evolution of these optical structures and incorporating Huxley's work, which represents an important biomimetic and evolutionary database on its own. This review deals with butterfly photonic devices according to the parts of the butterfly scales on which they occur. In this way, the information is ripe for evolutionary study.

/pdf/a-review-of-the-diversity-and-evolution-of-photonic-41iei23xay.pdf

A review of the diversity and evolution of photonic structures in butterflies, incorporating the work of John Huxley (The Natural History Museum, London from 1961 to 1990).

Photonic-crystal-type nanostructures occurring in the scales of the butterfly Cyanophrys remus were investigated by optical and electron microscopy (scanning and transmission electron microscopy), reflectance measurements (specular, integrated, and goniometric), by fast Fourier transform analysis of micrographs, by modeling, and by numerical simulation of the measured reflectance data. By evaluating the collected data in a cross-correlated way, we show that the metallic blue dorsal coloration originates from scales which individually are photonic single crystals of $50\ifmmode\times\else\texttimes\fi{}120\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{2}$, while the matt pea-green coloration of the ventral side arises from the cumulative effect of randomly arranged, bright photonic crystallites (blue, green, and yellow) with typical diameters in the $3--10\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ range. Both structures are based on a very moderate refractive index contrast between air and chitin. Using a bleached specimen in which the pigment has decayed with time, we investigated the role of pigment in photonic-crystal material in the process of color generation. The possible biologic utility of the metallic blue (single-crystal) and dull green (polycrystal) textures both achieved with photonic crystals are briefly discussed. Potential applications in the field of colorants, flat panel displays, smart textiles, and smart papers are surveyed.

Gleaming and dull surface textures from photonic-crystal-type nanostructures in the butterfly Cyanophrys remus.

词法结构和 Morphidae 的 14 种类的翅膀的光性质被调查了。大多数 Morphidae (鳞翅目) 的虹彩的种类的规模介绍很特别的结构。扎根的规模，为光性质的主要部分负责，被纵的山脉的一个很常规的集合盖住。山脉被行为局部地作为 multilayered 组织的 lamellae 的重叠自己组成。这很特定的形态学导致干扰和衍射效果。Thefirst 男性的灿烂的蓝着色法是负责的，当第二使衍射时在一个很大的角度的这盏有颜色的灯。这二现象把一个很有效的远程的通讯系统给蝴蝶。各种各样的种类的规模的词法特征详细被介绍。光测量的二种类型在 Morphidae 的 14 不同种类的虹彩的翅膀上被执行：在各种各样的发生下面的分光镜的大小和为一个给定的发生角度和波长的 gonio-scopic 大小。第一允许表皮的材料的折射的索引的一颗决心。第二导致绘画空间衍射地图。它证明大多数反映的光在一个很大的角度上旁边地被使衍射(90 ° < theta < 120 °，根据不同种类) 并且这分配事件光的极化看情况。是由以前的计算预言了，山脉的不对称的结构为在各种各样的衍射订单的极化模式的分离负责。

Berthier

Papers

Morphological structure and optical properties of the wings of Morphidae