Multi-channel polarization conversion THz beam splitter based on phase gradient metasurface.

In terahertz (THz) optical systems, beam splitters are essential components. However, they still have challenges in multi-channel manipulation of THz waves. Multi-channel beam splitters are devices that simultaneously split and independently control beams through multiple channels. In this paper, multi-channel polarization conversion beam splitters are designed to achieve independent modulation of four beams. The polarization control of the beam is achieved by integrating broadband polarization conversion cells with the form of a split ring resonance (SRR). The polarization conversion rate (PCR) exceeds 90% with broadband advantages. Four independently modulated beams are generated by combining sub-metasurfaces with gradient phases. The gradient phase consisting of 2-bit cells with a phase difference of 90° enables the beam to be deflected in any direction. Furthermore, the effect of polarization conversion for far-field beams is demonstrated in simulations. Finally, four structures are fabricated and measured, and the results are in agreement with the simulations at 0.23 THz or 0.85 THz. The proposed method provides an efficient way to control THz polarization conversion beam splitters in an independent approach.