Polarization Conversion Effect in Biological and Synthetic Photonic Diamond Structures

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.