Research press release


Nature Photonics

Nature Photonics: Fish skin structure explains biological cloaking

今回研究された魚の皮膚がこうした優れた機能を持つのは、低屈折率細胞質層によって隔てられた高屈折率グアニン結晶層の積層体で構成されるからである。重要なのは、皮膚には光学特性の異なる2種類のグアニン結晶が含まれているため、幅広い角度にわたって反射が偏光の影響を受けないというNicholas Roberts らの発見である。


The highly effective optical means by which silvery fish, such as the European sardine and Atlantic herring, camouflage themselves from predators is explained this month in Nature Photonics. The investigation suggests that some species of fish have evolved a sophisticated skin structure that acts as a high quality reflector, regardless of the light’s wavelength, polarization or angle of incidence. This capability is not only essential for cloaking purposes but is very useful for controlling light in man-made photonic devices such as light-emitting diodes and optical waveguides.

The fish accomplish this much sought-after feat by having a skin composed of multiple layers of high-refractive-index guanine crystals separated by low-index layers of cytoplasm. Critically, Nicholas Roberts and co-workers have discovered that the skin actually contains two types of guanine crystal with different optical properties, allowing the reflection to be largely insensitive to polarization across a wide range of angles.

This polarization neutrality is thought to be especially important in the natural world, where several aquatic animals are known to have vision that can detect differences in polarization.

doi: 10.1038/nphoton.2012.260

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