Hiding images with multi-color THz metasurfaces

We demonstrate a novel approach for encoding images using onto a metasurface design composed of resonant dipole based unit cells. This is accomplished by varying the conductivity of individual dipole, resulting in amplitude modulation of the transmitted THz beam. However, since only a narrow regime of conductivity variation was used, the dipole array appears to be uniform visually. Thus, this offers an interesting approach for hiding information. Using one to three dipoles per unit cell, we experimentally demonstrate 9 level encoding of information using simple dipole and 64 (4
³
) color encoding per bit with RGB color metasurface as demonstrated via THz imaging.