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Bio-inspired Photonics

 

Light Propagation in Complex Structures

White is the colour that the human eye perceives when exposed to light which contains all the wavelengths in the visible spectrum with similar intensity. Typically, white colourations are produced by broadband reflection of light from randomly dispersed scattering centres. The scattering centres, or scattering particles, are regions where the refractive index is different with respect to the surrounding medium.

 

When light encounters a scattering centre embedded in the propagation medium it deviates from its straight path (also known as "ballistic path") so that the direction of propagation is eventually completely randomised after sufficient scattering events.

A striking example of this phenomenon is the white colour of the Cyphochilus beetle, which is native to South-East Asia. By investigating the optical properties of the beetle's scales we were able to demonstrate that these beetles are able to scatter light more efficiently than any other known biological tissue, which is how they are able to achieve such a bright whiteness. Our research was featured on the BBC. We further investigated the role of the anisotropy in the scales and how these have optimised under evolutionary pressure.

Studying and understanding scattering can lead to a number of interesting applications: ranging from imaging through turbid media and light trapping for energy harvesting, to the optimisation of white coatings and paints.

In our lab we mostly concentrate on the fabrication and characterisation of biocompatible white materials, for example using cellulose nanocrystals or PMMA as building blocks.

Related Publications 

Anomalous-Diffusion-Assisted Brightness in White Cellulose Nanofibril Membranes.
MS Toivonen, OD Onelli, G Jacucci, V Lovikka, OJ Rojas, O Ikkala, S Vignolini – Adv Mater (2018) 30, 1704050
Bio-inspired Highly Scattering Networks via Polymer Phase Separation
J Syurik, G Jacucci, OD Onelli, H Hölscher, S Vignolini – Advanced Functional Materials (2018) 28, 1706901
Evolutionary-Optimized Photonic Network Structure in White Beetle Wing Scales.
BD Wilts, X Sheng, M Holler, A Diaz, M Guizar-Sicairos, J Raabe, R Hoppe, S-H Liu, R Langford, OD Onelli, D Chen, S Torquato, U Steiner, CG Schroer, S Vignolini, A Sepe – Adv Mater (2017) 30, e1702057
Disordered Cellulose-Based Nanostructures for Enhanced Light Scattering.
S Caixeiro, M Peruzzo, OD Onelli, S Vignolini, R Sapienza – ACS Appl Mater Interfaces (2017) 9, 7885
Anisotropic Light Transport in White Beetle Scales
L Cortese, L Pattelli, F Utel, S Vignolini, M Burresi, DS Wiersma – Advanced Optical Materials (2015) 3, 1337
Bright-white beetle scales optimise multiple scattering of light.
M Burresi, L Cortese, L Pattelli, M Kolle, P Vukusic, DS Wiersma, U Steiner, S Vignolini – Scientific reports (2014) 4, 6075