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Vortex beam has attracted much attention for carrying orbital angular momentum (OAM). It has a helical phase structure described by exp (ilθ) and an annular intensity distribution, where l is the topological charge corresponding to the OAM of each photon, and θ is the azimuth angle. [1] Vortex beam is widely used in OAM communications, [2,3] optical tweezers, [4] and quantum information coding. [5,6] In particular, the superposition of OAM states is very significant in metrology, [7,8] quantum science, [6,9] and OAM communications. The superposition of high-order OAM modes can be used for ultra-sensitive angle measurement. [8] In Bose-Einstein condensate, multiple OAM states can also be used to generate arbitrary superpositions of atomic rotation states. [10] Vortex beam carrying OAM has shown promising prospects in increasing the data capacity of communication systems, because multiple orthogonal modes can be transmitted at the same frequency in a single communication channel simultaneously.As we all know, photons carry two different kinds of angular momentums, namely spin angular momentum (SAM) and OAM. [11] The SAM represents the polarization state of light, and the OAM is related to the spatial distribution of light. [1,12] Although mode conversion, [13] holograms, [14] spiral phase plates, [15] and spiral zone plates [16][17][18] can be used to generate vortex beam, they usually do not involve the interaction between SAM and OAM. [19] Different from the above, the geometric phase elements can establish a connection between SAM and OAM, but only two conjugate vortex states can be output. Devlin presented a method realizing arbitrary spin-to-OAM conversion, overcoming this limitation mentioned above. [20] In addition, when the paraxial beam is tightly focused, a strong longitudinal component will be generated in the focal area. [21] It is demonstrated that, in a highly focused system, a circularly polarized beam partly transfers its incident SAM to OAM and a helical phase in the longitudinal component of the electric field can be generated. [22] Due to their potential breakthroughs in optical manipulation, metasurfaces have attracted widespread attention in the scientific community. [23,24] Metasurfaces have been widely used in many applications, such as lenses, [25,26] spin Hall effect, [27] holograms, [28] and vortex generators. [29][30][31][32][33] In order to further Vortex beams, carrying orbital angular momentum (OAM), have plenty of applications ranging from particle manipulation to high-capacity data transmissions. In particular, the superpositions of OAM patterns are significant in classical physics and quantum science. The flexible control of spin angular momentum (SAM) to OAM can provide more freedom for the design of multifunctional devices. Here, a kind of dielectric metasurface is proposed that generates polarization-controllable superpositions of OAM patterns in the terahertz (THz) band, which is achieved by the interleaving of anisotropic and isotropic meta-atoms. The conversions of arbitrary S...

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Integrating independent wavefront controls into one device can meet the increasing demand for high-capacity flat electromagnetic devices. Simultaneously independent control of amplitude and phase is pivotal for completely manipulating the...

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.