High-efficiency full-space terahertz holography with interleaved Janus metasurfaces

• This paper demonstrates a high-efficiency four-channel THz Janus metasurface for full-space orthogonal LP wave multiplexing. • The Janus meta-atom composed of a cross-shaped and central metal grating can achieve independent full-space 2π phase control in a specific polarization mode. • The highest imaging efficiencies in this paper are 43.71 % (multi-focal points) and 71.67 % (holographic images), surpassing previous reports. • The proposed high-efficiency full-space interleaved Janus metasurfaces can offer a broad spectrum of possibilities for applications in large-capacity THz wireless communications and optical encryption. Within terahertz communications, holographic imaging technology attracts significant attention due to its promising application prospects in information processing and encryption. However, conventional holographic approaches employing reflective or transmissive metasurfaces suffer from a limited number of channels and functionalities due to inefficient spatial utilization. To address these limitations, we propose a terahertz Janus metasurface that achieves full-space holographic imaging by diagonally interleaving two types of fundamental meta-atoms. In this structure, the Janus meta-atom comprises two pairs of cross-shaped metallic structures, a central metal grating, and dielectric layers sandwiched between the metallic components. Thus, rotation of the central grating selectively manipulates incident wave polarization and operational modes, enabling asymmetric transmission. By adjusting the sizes of the cross-shaped structures, moreover, the Janus meta-atom obtains full 2π phase coverage with high transmission/reflection efficiency under linearly polarized (LP) wave incidence from both front and back sides, realizing polarization-space multiplexing. Leveraging these Janus meta-atoms, we construct two metasurfaces for high-efficiency four-channel multifocal points and holographic images, respectively. The proposed scheme offers compelling merits in efficiency and channel number, showcasing strong potential for large-capacity information processing and secure encrypted terahertz communications.