Terahertz multi-foci metalens with polarization-dependent/independent focal points and reconfigurable imaging

Benefiting from the unprecedented capacity in manipulating wavefront of light waves, metalens can realize unusual functions that are very difficult or impossible to achieve with conventional lenses. However, the current techniques for designing a metalens are limited to obtain polarization-dependent or polarization-independent focal points, preventing its versatile applications in modern optics. Here, we propose and experimentally demonstrate an approach that can focus the left-handed circularly polarized and/or right-handed circularly polarized components of terahertz (THz) waves to simultaneously generate polarization-dependent and polarization-independent focal points. First, a metalens is designed to obtain two focal points where the intensity of one focal point can be controlled by controlling polarization of incident THz waves, while the intensity of another focal point is fixed under the illumination of THz waves with arbitrary polarization. Second, a metalens with intensity-tunable multiple focal points and an intensity-fixed focal point is experimentally demonstrated. Third, the single to multifocal imaging (i.e., reconfigurable imaging) can be realized using the designed metalens without the aid of reconfigurable materials. In addition, a framework for mimicking logic gates is designed based on the proposed metalens. This robust approach for designing metalens with reconfigurable focal points may open a window in developing multifunctional devices with potential applications in imaging, sensing, and communications.