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.

The bound states in a continuum (BICs) are objective physical phenomena that defy conventional wisdom, and they exist in the radiating continuous spectrum but remain perfectly localized with non-radiation, which is different from the traditional bound states. In this paper, we report in theory and experiment the high thickness all-silicon terahertz (THz) metasurfaces supporting BIC and quasi-BIC, which is realized by simple pairs of elliptical pillars. Meanwhile, we used an extra optical pump to modulate the transmission amplitude difference between BIC and quasi-BIC metasurfaces, to complete the active control from “On” state to “Off” state. We utilize the abundant amplitude gradation of metasurfaces with different asymmetric degrees to develop the polarization-dependent THz near-field displaying application that can make the grayscale characteristics of a photograph reappear and also be dynamically controlled at On state to Off state.