Light in biological media is known as freely diffusing because interference is negligible. Here, we show Anderson light localization in quasi-two-dimensional protein nanostructures produced by silkworms (Bombyx mori). For transmission channels in native silk, the light flux is governed by a few localized modes. Relative spatial fluctuations in transmission quantities are proximal to the Anderson regime. The sizes of passive cavities (smaller than a single fibre) and the statistics of modes (decomposed from excitation at the gain-loss equilibrium) differentiate silk from other diffusive structures sharing microscopic morphological similarity. Because the strong reflectivity from Anderson localization is combined with the high emissivity of the biomolecules in infra-red radiation, silk radiates heat more than it absorbs for passive cooling. This collective evidence explains how a silkworm designs a nanoarchitectured optical window of resonant tunnelling in the physically closed structures, while suppressing most of transmission in the visible spectrum and emitting thermal radiation.
Bibliographical noteFunding Information:
We acknowledge Vladimir Shalaev, Hui Cao and Johannes de Boer for their insightful commentary; Chia-Ping Huang, Robert Seiler, Christopher Gilpin and Bradley Thiel for electron microscopy of silk fibres. This work was supported by Cooperative Research Program for Agriculture Science & Technology Development (PJ012089) from Rural Development Administration, Republic of Korea and Asian Office of Aerospace Research and Development (FA2386-16-1-4114 and FA2386-17-1-4072) from U.S. Air Force Office of Scientific Research, USA.
© 2018 The Author(s).
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Biochemistry, Genetics and Molecular Biology(all)