Manipulating terahertz wavefront for tri-channel holograms and OAM beams based on diatomic metasurfaces

Abstract Metasurfaces possess powerful wavefront manipulation capabilities that are unattainable by traditional optical devices. They demonstrate the remarkable control over amplitude, phase, and polarization while ensuring compactness and miniaturization. This provides an innovative approach to attaining high-performance hologram and orbital angular momentum (OAM). However, most existing works can only produce a single hologram or OAM, lacking multi-channel wavefront control. To address this issue, we propose a diatomic structure capable of realizing multi-polarized wavefront modulation. The carefully designed arrangement of meta-atoms can increase the number of channels and expand the functionality of optical device. As a proof of concept, two metasurfaces are designed to implement holograms and OAM beams respectively. When the first metasurface is illuminated by x-polarized wave, it generates the hologram ‘F’ in the co-polarized channel and the hologram ‘Y’ in the cross-polarized channel. When this metasurface is illuminated by y-polarized wave, it generates the hologram ‘H’ in the co-polarized channel, thereby realizing a tri-channel hologram. Similarly, the second metasurface achieves tri-channel OAM beams with topological charges of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>l</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>l</mml:mi> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>l</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> </mml:math> , respectively. Our work offers a potential pathway for high-capacity and high-integration optical devices.