As communication technology is entering the 6G era, a great demand for high-performance devices operating in the terahertz (THz) band has emerged. As an important part of 6G technology, indoor communication requires multi-beam steering and tracking to serve multi-users. In this paper, we have designed a graphene metasurface that can realize multi-beam steering for directional radiations. The designed metasurface consists of graphene ribbons, dielectric spacer, and metal substrate. By designing the graphene ribbons and controlling the applied voltage on them, we have obtained single-, double-, and triple-beam steering. In addition, we have also numerically calculated the far-field distributions of the steered multi-beam with a diffraction distance of 2 m. Our design has potential applications in future indoor directional 6G communications.

Several novel spin-selected dual-wavelength metalenses have been proposed and investigated based on the plasmonic metasurface consisting of two kinds of rotary rectangle gap nanoantennas (RGN), which are designed based on merging two or four polarity-inverse lenses corresponding to different wavelengths (765 and 1300 nm). The spin-selected dual-wavelength metalenses with two similar and two different vertical and lateral focal points have also been proposed respectively, which can focus two wavelengths with inverse spin states to arbitrary special positions. The three-dimensional metalens with four focal points have also been proposed, which can focus four beams with inverse spin states and different wavelengths to preset positions. Moreover, a spin-dependent achromatic metalens has also been proposed, which can focus left circularly polarized (LCP) incidence with different wavelengths to the same position. Our work opens up new avenues toward establishing novel spin-selected and wavelength-selected metadevices, and is significant for the development of spin-controlled photonics and particles manipulation. In addition, it provides a new idea for solving the problem of data transmission from optical fiber communication to visible light communication.

In this paper, several novel spin-selected metalenses composed of rotary silicon nanobrick array have been designed and numerically investigated at the telecommunication wavelength of 1500 nm, which can be focused at different positions along transverse or longitudinal direction for different spin light. They can not only directly distinguish the spin states but also manipulate photons with different spin states. Our optimized silicon nanobricks with varying orientation angles can achieve 98% cross-polarized transmitted efficiency, and possess Pancharatnam–Berry phase. Furthermore, a spin-independent metalens has also been designed, which can be well focused at the same spot for the light with different spin states. Our work opens up new avenues toward establishing novel spin-related metadevices, and it is significant for the development of functionality switchable optical devices and spin photonics.

In this paper, one spin-selected vortex metalens composed of silicon nanobricks is designed and numerically investigated at the mid-infrared band, which can produce vortex beams with different topological charges and achieve different spin lights simultaneously. Another type of spin-independent vortex metalens is also designed, which can focus the vortex beams with the same topological charge at the same position for different spin lights, respectively. Both of the two vortex metalenses can achieve high-efficiency focusing for different spin lights. In addition, the spin-to-orbital angular momentum conversion through the vortex metalens is also discussed in detail. Our work facilitates the establishment of high-efficiency spin-related integrated devices, which is significant for the development of vortex optics and spin optics.

Several novel spin-dependent bi-functional metasurfaces consisting of different-sized rotary silicon nanobricks have been proposed and numerically investigated based on the Pancharatnam–Berry phase and structural phase simultaneously. Here, a transmission mechanism is strictly deduced, which can avoid crosstalk from the multiplexed bi-functional metasurface. Four kinds of high-efficiency bi-functional devices have been designed successfully at infrared wavelengths, including a spin-dependent bi-functional beam deflector, a spin-dependent bi-functional metalens, a bi-functional metasurface with spin-dependent focusing and deflection function, and a spin-dependent bi-functional vortex phase plate. All of the results demonstrate the superior performances of our designed devices. Our work opens up new doors toward building novel spin-dependent bi-functional metasurfaces, and promotes the development of bi-functional devices and spin-controlled photonics.

The perfect vortex beam (PVB) possesses an annular intensity profile diameter independent of topological charge, which has attracted much attention owing to the ability of improving optical fiber transmission efficiency. The composite PVB (CPVB) is mainly based on the superposed multiple Laguerre–Gaussian beams with specific polarization states, which possesses topological charge-relevant spot shaped intensity pattern and the topological charge-irrelevant profile diameter. A series of spin-multiplexed metasurfaces have been designed to generate different PVB and CPVB under different spin light. The CPVB can also be modulated in scaling and rotating manner, which can broaden the dimensions of information. A spin-multiplexed metasurface has also been designed to generate CPVB array with different rotation angles and spot number under different spin light, and the encoding process has also been demonstrated. The uniqueness of these metasurfaces makes this design philosophy very attractive for applications in spin photonics, information encryption, optical communication, and optical information storage.