Helicity multiplexed terahertz multi-foci metalens

Metasurfaces have shown unprecedented capabilities in the manipulation of the light’s wavefront at subwavelength scale, enabling compact functional devices that can outperform conventional bulk components. A device with multiple functionalities is a continuing trend of device miniaturization and system integration. Here, we propose an approach to design a helicity-dependent multi-foci metalens that can independently generate longitudinally (or transversely) multiple focal points under the illumination of left-hand and right-hand circularly polarized terahertz waves. When this metalens is illuminated with linearly polarized terahertz waves, all of the helicity-dependent multiple focal points are observed simultaneously, leading to the multiplexing of helicity-dependent multiple focal spots. A dielectric metasurface consisting of micropillars with different in-plane orientations is utilized to demonstrate these characteristics. This approach for achieving a helicity multiplexed terahertz multi-foci metalens may open an avenue for designing future multifunctional devices.