A strong spin-selective asymmetric transmission metasurface usually relies on a multilayer metal frame or compound all-dielectric system. By contrast, an all-silicon metasurface has advantages of simple process, low cost, and easy optical modulation. However, there is little work to explore the spin-selective asymmetric transmission in terahertz band based on the all-silicon metasurface due to weak interaction between all-silicon materials and terahertz waves. Herein, we have achieved excellent spin-selective terahertz asymmetric transmission in the all-silicon metasurface by the ingenious chirality structure design, and the maximum circular dichroism can reach 0.4. Meanwhile, 1064 nm continuous wave optical pumping modulates the asymmetric transmission amplitude of the all-silicon metasurface to achieve circular dichroism switch between “On” and “Off.” We have also developed terahertz chiral imaging applications based on the all-silicon metasurface with spin-selective asymmetric transmission, and the chiral imaging with On and Off switching characteristics can be realized via optically active control.

Polarization is crucial in various fields such as imaging, sensing, and substance detection. A compact, fast, and accurate polarization detection device is vital for these applications. Herein, we demonstrate a multifocus metalens for terahertz polarization detection that requires only a single measurement to obtain complete polarization parameters and reconstruct the polarization state of the incident field. The individual subarrays of this metalens convert each of the six polarized components into the same polarization, which in turn links the Stokes parameters to these six foci. The incident linear polarizations and elliptical polarizations are characterized by Stokes parameters and polarization ellipses. Simulations and experimental results show that the scheme can accurately detect the incident polarization with a single measurement. The proposed metasurface polarimetry may find applications in the fields of real-time terahertz detection and integrated optics.