The investigation of converged twisted beams with a helical phase structure has a remarkable impact on both fundamental physics and practical applications.Geometric metasurfaces consisting of individually orientated metal/dielectric meta-atoms provide an ultracompact platform for generating converged vortices.However,it is still challenging to simultaneously focus left-handed and right-handed circularly polarized incident beams with pure geometric phase modulation,which hinders the independent operation on topological charges between these two helical components.Here we propose and experimentally demonstrate an approach to design terahertz geo-metric metasurfaces that can generate helicity-independent converged vortices with homogeneous polarization states by the superposition of two orthogonal helical vortices with identical topological charges.Furthermore,the multiplexing of polarization-rotatable multiple vortices in multiple dimensions,i.e.,in both longitudinal and transverse directions,and a vortex with an extended focal depth is confirmed by embedding polarization modu-lation into the geometric metasurfaces.The demonstrated approach provides a new way to simultaneously manipulate orthogonal helical components and expand the design dimension,enabling new applications of geo-metric metasurface devices in polarization optics,twisted-beam related image and edge detection,high capacity optical communication,and quantum information processing,to name a few.

YANG ZHU;BINBIN LU;ZHIYUAN FAN;FUYONG YUE;XIAOFEI ZANG;ALEXEI V.BALAKIN;ALEXANDER P.SHKURINOV;YIMING ZHU;SONGLIN ZHUANG

Terahertz Technology Innovation Research Institute,Terahertz Spectrum and Imaging Technology Cooperative Innovation Center,Shanghai Key Laboratory of Modern Optical System,University of Shanghai for Science and Technology,Shanghai 200093,China;Shanghai Institute of Intelligent Science and Technology,Tongji University,Shanghai 200092,China;Department of Physics,Lomonosov Moscow State University,Moscow 119991,Russia

光子学研究（英文）

[1]YANG ZHU;BINBIN LU;ZHIYUAN FAN;FUYONG YUE;XIAOFEI ZANG;ALEXEI V.BALAKIN;ALEXANDER P.SHKURINOV;YIMING ZHU;SONGLIN ZHUANG-.Geometric metasurface for polarization synthesis and multidimensional multiplexing of terahertz converged vortices)[J].光子学研究（英文）,2022(06):1517-1532

ultracompact

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