Bio-inspired Optics and Photonics – From Metamaterials to Applications

The photovoltaic energy has gained its space in the power supplying around the world, and most recently in Brazil. Aside from being a generation with a minimal impact in the environment, the photovoltaic energy brings along the expectation of electrical energy access to isolated communities, like the northeast “Sertão” in Brazil. By finding solutions to the problems in power generation, like soiling impact on power plants performance and losses by reflection of incident light, this project aims to contribute to the solar energy expansion and promote the benefits of an environmentally, socially, and economically sustainable energy. This research is proposing a solution to minimize soiling impact on photovoltaic plants performance through the development of super hydrophobic bioinspired coatings for the modules. This project tries to achieve this aim through different micro and nanostructured configurations that optimize both the hydrophobicity and the optical properties.

Pascal Freyer, Bodo D. Wilts, Doekele G. Stavenga

Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands Adolphe Merkle Institute, University of Fribourg, Fribourg, Switzerland

The peacock prides a magnificent array of feathers with a wide variety of structural colours originating from an interleaved lattice of rodlet melanosomes and air channels [H. Durrer 1962, 1965]. We have studied the spectral properties of the blue peacock feather by applying various optical methods, e.g. microspectro-photometry, imaging scatterometry and angle-resolved polarisation-dependent reflectance measurements. The blue neck feathers show a consistent colour gradient between its proximal (green) and distal (blue) barbules. The measured (angle-dependent) spectra can be explained very well by applying finite-difference time-domain (FDTD) as well as effective-medium multilayer modelling [P. Freyer et al. 2018].

Different plants, algae[1] and animals like peacocks and silverfish[2] obtain their brilliant colouration due to structural colours. Those structural colours appear as a result of the interaction between light and a periodic nanostructure, so called photonic crystals.[3] The skin of a chameleon consists of such photonic crystals based on guanine crystals embedded into cytoplasm and different pigments. Emotions of the chameleon evoke a variation in colour by changing the crystal distances, and thus the interference pattern.[4]
The processes of the chameleon skin will be mimicked with the help of polymers (biomimetic equivalent to cytoplasm) and gold nanoparticles (biomimetic equivalent to guanine crystals).[5] The gold nanoparticles are chosen because of their plasmonic behaviour. As the switching parameter polymer brushes are used due to their swelling properties. The polymer brushes can be obtained via Atom Transfer Radical Polymerization (ATRP) and combined with spherical gold nanoparticles as introduced by the von Klitzing group.[5]
The aim is to fabricate innovative biomimetic hybrid materials with the help of the above-mentioned systems to combine plasmonics with piezoelectricity.

Literature:
[1] P. Vukusic, J. R. Sambles, Nature 2003, 14, 852-855.
[2] A. R. Parker, J. Opt. A: Pure Appl. Opt. 2000, 2, R15-R28.
[3] P. Vukusic, Curr. Biol. 2011, 21(5), R187-R189.
[4] J. Teyssier, S. V. Saenko, D. van der Marel, M. C. Milinkovitch, Nat. Commun. 2015, 6, 1-7.
[5] S. Christau, T. Möller, F. Brose, J. Genzer, O. Soltwedel, R. von Klitzing, Polymer 2016, 98, 454-463.

D. Macias1 , D. Skigin2,3, M. Inchaussandague2,3 and A. Vial1

1ICD-L2n,Université de technologie de Troyes, Troyes, France
2 Grupo de Electromagnetismo Aplicado, Departamento de Física, Universidad de Buenos Aires, Buenos Aires, Argentina
3 Instituto de Física de Buenos Aires (IFIBA)- CONICET

E-mail: demetrio.macias@utt.fr

Over the past few years, the mechanisms of color generation by biological structures have attracted the attention of several research groups. This ever-growing interest lies on the great potential of bio-inspired structures for the design of optical document security holograms, lightning devices or sensors, to name some examples. Very recently a significant amount of theoretical and experimental works has been devoted to characterize the chromatic response of all-dielectric structures [1]. Nevertheless, the problem of tailoring the chromatic response of those structures through the optimization of their related opto-geometrical parameters is more complex and less well understood. This situation is a direct consequence of the nontrivial interaction between the structure’s constituent materials and geometry with the perceived color it generates. In order to solve this particular inverse problem, several approaches have been proposed [2-5]. In spite of the encouraging results, some of the optimal solutions found are either not realizable or the optimization process is computationally expensive. In this contribution, we make use of an artificial neural network (NN) to predict the spectral response of an all-dielectric structure and combine it with a meta-heuristic optimization method to manipulate, in a controlled manner, its chromatic response [6]. We show, through some examples, that the results provided by this meta-model-based optimization scheme are equivalent to those obtained when a time consuming method is used to compute the spectral response. Furthermore, our numerical experiments take into account fabrication constraints to keep the solution found close to the experimental situation. At least in principle, there are not visible restriction to extend the applicability of such approach to other research fields.

References
[1] V. Flauraud et al., ACS Photon. 4, 1913–1919 (2017).
[2] V. E. Johansen et al., J. Opt. Soc. Am. B 31, 207–217 (2014).
[3] J. Andkjær et al., J. Opt. Soc. Am. B 31, 164–174 (2014).
[4] E. Vargo, J. Opt. Soc. Am. B 34, 2250–2258 (2017).
[5] A. K. González-Alcalde et al., Appl. Opt. 57, 3959–3967 (2018).
[6] V. Kalt et al., J. Opt. Soc. Am. A 36, 79-88 (2019)

Authors: Sébastien R. Mouchet, Charlotte Verstraete, Ewan D. Finlayson, Anna M. Kaczmarek, Dimitrije Mara, Stijn Van Cleuvenbergen, Bjorn Maes, Rik Van Deun, Thierry Verbiest, Branko Kolaric, Olivier Deparis, Pete Vukusic.

Fluorescence emission occurs in the integuments of many natural species including but not limited to insects, arachnids, mammals, anthozoans (e.g., sea anemones and corals) and scyphozoans (i.e., true jellyfish). In insects, fluorophores, such as papiliochrom II and biopterin, are at the origin of such light emission. In some cases, they are naturally embedded in photonic nanostructures, which influence the emission in terms of spectral intensity, decay time and spatial distribution [1,2]. Using linear and non-linear optical and fluorescence techniques, the case of the Hoplia coerulea male beetle was investigated. The photonic structures found in the scales covering its body comprise fluorophores. These structures control both the insect’s colouration and the emission from the embedded fluorophores [2,3]. Contact with liquids gives rise to variations of the emission properties. The combination of these observations and optical modelling allows the study of the photonic confinement within the beetle’s nanostructures. Additionally, Third-Harmonic Generation and two-photon fluorescence analyses unveiled the multi-excited states character of the fluorophores and, through light polarisation effects, the role of the photonic structures’ anisotropy in the fluorescent behaviour [4]. In addition to the elaboration of new concepts and the development of technological applications through a bioinspiration approach, such investigations help the understanding of the biological functionalities behind the observed fluorescence response.

References:
1. P. Vukusic et al., Science (2005), 310, 1151.
2. S. R. Mouchet et al., Proc. R. Soc. B (2016), 283, 20162334.
3. S. R. Mouchet et al., Mater. Today Proc. (2017), 4, 4979-4986.
4. S. R. Mouchet et al., Interface Focus (2018), 9, 20180052.

Urquia G (a), Skigin D (a,b), Inchaussandague M (a,b), Barreira A (c), Tubaro P (c)

a Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, Grupo de Electromagnetismo Aplicado, Buenos Aires, Argentina
b CONICET – Universidad de Buenos Aires, Instituto de Física de Buenos Aires (IFIBA), Buenos Aires, Argentina
c División de Ornitología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” MACN-CONICET, Av. Ángel Gallardo 470 (C1405DJR),

An unusual color effect is found in certain species of birds of the family Thraupidae, which consists in the variation of the plumage coloration as a function of the relative angle between the incidence and the observation directions. The plumage of these birds exhibits attractive colors due to the interaction of the light with the three dimensional nanostructures composed of β-keratin and air present in the feathers. In this work, we investigate the generation mechanisms of structural colors in the plumage of this family, particularly in the species of the genera Dacnis and Cyanerpes. We apply an electromagnetic method called KKR (Korringa-Kohn-Rostoker), which permits the calculation of the reflectivity of a stack of layers of spheres embedded in a dielectric medium. To account for the deviations of the structure from a perfectly periodic arrangement, we introduce disorder by averaging the reflected response of many structures with different geometrical parameters. We analyze the evolution of the reflectance spectrum and calculate the color coordinates to obtain the observed color for different illumination-detection configurations.