Abstract
Abstract Cylindrical vector beams (CVBs), being a special kind of beams with spatially variant states of polarizations, are promising in photonics applications, including high-resolution imaging, plasmon excitation, optical trapping, and laser machining. Recently, generating CVBs using metasurfaces has drawn enormous interest owing to their highly designable, multifunctional, and integratable features. However, related studies remain unexplored in the terahertz regime. Here, a generic method for efficiently generating terahertz CVBs carrying orbital angular momentums (OAMs) is proposed and experimentally demonstrated using transmission-type spatial-variant dielectric metasurfaces, which is realized by designing the interference between the two circularly polarized transmission components. This method is based on spin-decoupled phase control allowed by simultaneously manipulating the dynamic phase and geometric phase of each structure, endowing more degree of freedom in designing the vector beams. Two types of metasurfaces which respectively generate polarization-dependent terahertz vector vortex beams (VVBs) and vector Bessel beams (VBBs) are experimentally characterized. The proposed method opens a new window to generate versatile vector beams, providing new capabilities in developing novel, compact, and high-performance devices applicable to broad electromagnetic spectral regimes.
Highlights
As the vector nature of light, polarization plays an important role in light–matter interactions
We propose and experimentally investigate an approach to efficiently generate cylindrical vector beams (CVBs) using transmissiontype all-dielectric metasurfaces via spin-decoupled phase control method in the terahertz regime [32]
The pillar has a period of Pf = Ps = 150 μm and a height of h = 200 μm. Such a pillar has been demonstrated to function as an anisotropic effective truncated waveguide, whose phase responses of the two eigen orthogonally polarized waves can be freely controlled to individually cover the whole 2π range by changing the width Df and length Ds [55]
Summary
As the vector nature of light, polarization plays an important role in light–matter interactions. Among the reported metasurface-based CVB generators, geometric phase method is widely applied owing to its flexible phase control mechanism and convenient polarization reorganization ability in circular polarization basis, such as generating vector vortex beams (VVBs) [44]. Though it allows OAM of controllable value, the inter-related phase responses of the geometric phase method to some extent limit the designing and controlling freedom. The proposed method provides a new way to develop novel CVB-related compact and efficient devices essential in terahertz photonics
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