Abstract-Ultrathin freestanding terahertz vector beam generators with free phase modulation

 

Huixian Zhou, Jierong Cheng, Fei Fan, Xianghui Wang, Shengjiang Chang

Schematic of the bilayer metasurface for VBs’ generation. (b) and (c) show the structure in the top and bottom layers, respectively, where the discretized sectors and their symmetry axes are marked. (d) Schematic of the polarization conversion in each sector and the orientation of the metaatoms.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-2-1384&id=446364

Simultaneous control of phase and polarization offers a large degree of freedom to tailor the beam properties, for instance, enabling generation of structured beams such as vector beams and vector vortex beams. Here, we propose an ultrathin freestanding metasurface operating at the terahertz frequency for efficient generation of vector vortex beam with an arbitrarily defined topological charge from linearly polarized excitation. The metasurface is composed of bilayer metallic patterns separated by a thin quartz slab, with one layer determining the transmission polarization and the other controlling the transmission phase. The tightly cascaded two layers form a Fabry-Perot cavity to maximize the efficiency of the polarization and phase control. Two metasurfaces for generation of radially polarized vector beam with uniform phase and vortex phase are fabricated and tested at 0.14 THz. The experimental results successfully demonstrate the generation of high-quality vector beams with the desired phase. In the experiment, the ultrathin and freestanding properties allow the metasurface to be easily combined with other components, which shows great potential for the development of various compact terahertz systems.

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