Nature offers a great diversity of well-optimized photonic engineering designs, which often represent a compromise between several potentially conflicting purposes and can maintain such a diverse array of functions as mate attraction, UV protection, water repulsion, camouflage and sensory enhancement. During the last decade, advancements in nanoscience and modern fabrication methods have enabled the detailed investigation and functional mimicry of these natural designs, especially with regards to the structural coloration effects found in biological systems. The physical phenomena responsible for structural coloration have also received considerable attention, as these structures derive their colors from a number of optical effects, such as interference, scattering, photonic crystal effects, or a combination thereof. Photonic crystals in living systems are especially notable for their iridescence and exceptionally bright coloration, which may assist in camouflage, communication, sensing and other purposes that still remain largely unexplored. The imitation of these nanostructures represents significant advances in the area of nano-optics, and promotes the design of novel photonic configurations. However, current fabrication methods cannot satisfactorily mimic the architectural complexity found in natural systems without greatly compromising control capacity, ease of fabrication and/or production costs.
We investigate and successfully imitate a peculiar 2D photonic scheme observed on the neck feathers of mallard drakes. Our bioinspired 2D photonic crystals successfully replicate not only the optical properties, but also the material features and the architectural complexity (i.e. ribbon-like flat platform) of the original structure. A novel top-down approach, called iterative size reduction (ISR) is used to avoid potential issues associated with the fabrication of solid core 2D photonic crystals and to produce a biomimetic design that displays the same structural complexity and functionality as mallard feather barbules with low fabrication costs, short processing times and minimal labor intensity. In addition to its optical properties, the barbule surface is also shown to be strongly hydrophobic, and this property is also successfully replicated in our bio-inspired 2D photonic crystals. The present work represents the first successful fabrication of an all-polymer 2D solid-core photonic crystal capable of functioning at optical frequencies. We further demonstrate that biomimetic fiber arrays displaying a great range of colors can be obtained by minor alterations in a single fabrication step, without necessitating individual process optimization procedures for each desired color.
 M. Yaman, T. Khudiyev, M. Bayindir, et al., Nature Materials 10, 494 (2011).
 T. Khudiyev, T. Dogan, M. Bayindir, Scientific Reports 4, 4718 (2014).