Terahertz meta-polarizers for simultaneous control of the amplitude, phase, and polarization

Terahertz (THz) waves hold immense potential for advancements in areas such as in 6G wireless communications, non-destructive testing, and biomedicine. However, the underdeveloped control level of THz devices has been a severe obstacle. Here, a THz meta-polarizer, comprising rectangular metallic holes, is proposed to achieve the simultaneous control of the amplitude, phase, and polarization. Each unit of this meta-polarizer can function as a miniature linear polarizer. The component polarized along the short side can pass through the unit, while the component polarized orthogonally is unable to do so. Leveraging the principles of the Malus' law, we can adjust the desired amplitude distribution of the transmitted x-polarized wave by modifying its polarization distribution. This adjustment is made possible by tuning the azimuth angle of each hole. The phase delay of the transmitted wave can be further manipulated by adjusting the hole dimensions perpendicular to the polarization direction. For given near-field amplitude distributions, the required phase distributions for generating far-field target holograms can be calculated using the Gerchberg–Saxton algorithm based on Fresnel diffraction theory. The meta-polarizer then realizes calculated phase distributions, enabling the creation of the required holograms. As a proof of concept, we designed THz meta-polarizers that can achieve two- and four-level amplitude holograms in the near field, respectively. Moreover, we also manipulated the phase distributions, allowing us to decouple the near- and far-field holograms. The experimental results agree well with the simulations. Owing to its ability to simultaneously control the phase, amplitude and polarization, the proposed THz meta-polarizer holds great application potential in 6G wireless communications, radar detection systems, and holography.