The scales of white beetles strongly scatter light within a thin disordered network of chitin filaments. There is no comparable artificial material achieving such a high scattering strength within a thin layer of low refractive index material. Several analyses investigated the scattering but could not explain the underlying concept. Here a model system is described, which has the same optical properties as the white beetles’ scales in the visible wavelength range. With some modification, it also explains the behavior of the structures in the near infrared range. The comparison of the original structure and the model system is done by finite-difference time-domain calculations. The calculations show excellent agreement with the beetles’ scales with respect to the reflectance, the time-of-flight, and the intensity distribution in the far-field.
Polarization of light is essential for some living organisms and many optical applications. Here, an orientation dependent polarization conversion effect is reported for light reflected from diamond‐structure‐based photonic crystals (D‐structure) inside the scales of a beetle, the weevil Entimus imperialis. When linearly polarized light propagates along its 〈100〉 directions, the D‐structure behaves analogous to a half‐wave plate in reflection but based on a different mechanism. The D‐structure rotates the polarization direction of linearly polarized light, and reflects circularly polarized light of both handednesses without changing it. This polarization effect is different from circular dichroism occurring in chiral biological photonic structures discovered before. The structural origin of this effect is symmetry breaking inside D‐structure's unit cell. This finding demonstrates that natural photonic structures can exploit multiple functionalities inherent to the design principles of their structural organization. Aiming at transferring the inherent polarization effect of the biological D‐structure to technically realizable materials, three simplified biomimetic structural models are derived and it is theoretically demonstrated that they retain the effect. Out of these structures, functioning woodpile structure prototypes are fabricated.
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