Silicon-on-insulator based multifunctional metasurface with simultaneous polarization and geometric phase controls

Enabled with both magnetic resonance and geometric phase, dielectric nanobrick based metasurfaces have shown their unusual abilities to produce high-definition and high-efficiency holographic images. Herein, we further show that such a metasurface can not only project a holographic image in far field but also record a grayscale image right at the metasurface plane simultaneously, merely with a single-celled nanostructure design approach. Specifically, each nanobrick in a unit-cell of the metasurface acts as a half-wave plate and it can continuously rotate the polarization direction of incident linearly polarized light. Governed by Malus law, light intensity modulation is available with the help of a bulk-optic analyzer and a continuous grayscale image appears right at the metasurface plane. At the same time, the concept of orientation degeneracy of nanostructures can be utilized to generate a 4-step geometric phase, with which a holographic image is reconstructed in far field. We experimentally demonstrate this multifunctional meta-device by employing the widely used silicon-on-insulator (SOI) material and all results agree well with our theoretical prediction. With the novel features of easiness in design, high efficiency, broadband spectrum response, strong robustness, high security and high information density, the proposed SOI-based metasurfaces will have extensive applications in optical information security and multiplexing.