Active Metasurfaces for Dynamic Polarization Conversion

Polarization is an important characteristic of electromagnetic waves that has a significant impact on number of applications such as molecular analysis, and quantum communications. Here, we demonstrate that the polarization state of the reflected light can be actively controlled by using indium tin oxide (ITO)-based tunable metasurfaces. The proposed metasurfaces consist of an aluminum back reflector, a 20-nm-thick gate dielectric layer followed by a 5-nm-thick ITO layer on which we fabricate an aluminum nano-antenna array. When applying an electrical bias between the ITO layer and back reflector, the carrier concentration at the gate-dielectric/ITO interface is modulated, resulting in the change of the effective index of the ITO layer. It alters the interaction between the induced plasmonic modes, leading to the modulation of polarization state of the reflected light at telocom wavelengths. By suitably biasing the metasurface structure, the linearly-polarized incident light can be converted to a cross-polarized, circularly-polarized or elliptically-polarized light. This dynamic control of the amplitude, phase as well as the polarization state of the scattered beam provides prospects for various applications, such as adaptive wavefront control, signal monitoring and detection.