摘要
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 geometric 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 modulation 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 geometric metasurface devices in polarization optics,twisted-beam related image and edge detection,high capacity optical communication,and quantum information processing,to name a few.
基金
National Key Research and Development Program of China(2017YFA0701005)
National Natural Science Foundation of China(61722111,61871268)
"Shuguang"Program of Shanghai Education Commission(19SG44)
Program of General Administration of Customs of the People’s Republic of China(2019HK006)
Shanghai International Joint Laboratory Project(17590750300)
111 Project(D18014)
Interdisciplinary Scientific and Educational School of Moscow University"Photonic and Quantum Technologies.Digital Medicine"。
