The focusing characteristics of Fresnel zone plate (FZP) on vortex beams at 1550 nm are investigated. Employing the Fresnel diffraction integral, the diffraction characteristics on different circular structures are calculated. Many calculations and measurements of the transmission light field-phase distribution demonstrate that the focusing characteristics of the vortex beam through FZP are similar to Gaussian beam. The effect of radius-dependent phase delay on the focus position is verified. At the same time, it is proved that the topological charge has nothing to do with the major focal position and the FZP will not change the topological charge of the incident vortex beam.

中文翻译：

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穿过菲涅耳波带片的光学涡旋的聚焦特性

研究了菲涅耳波带片（FZP）在1550 nm涡旋光束上的聚焦特性。利用菲涅耳衍射积分，计算出不同圆形结构的衍射特性。透射光场相位分布的许多计算和测量表明，通过FZP的涡旋光束的聚焦特性与高斯光束相似。验证了半径相关的相位延迟对焦点位置的影响。同时，证明了拓扑电荷与主焦点位置无关，FZP不会改变入射涡旋束的拓扑电荷。