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近年来，关于表面等离激元轨道角动量(Orbital Angular Momentum,OAM)态的研究主要聚焦于单一OAM态的生成及不同拓扑荷数OAM态的演化。而如何通过微纳结构的精确设计，实现具有特定相位关系的两个OAM态的相干叠加，仍面临诸多挑战。本文提出了一种新型等离激元微纳结构，以矩形缝对为结构单元，按照圆环或分段螺旋线轮廓排列。不仅能够在表面等离激元场中有效产生具有不同拓扑荷的OAM纯态，还可通过调控入射光的偏振态，实现两种OAM态以不同振幅比和相位差的灵活叠加，从而实现OAM叠加态在布洛赫球面上的演化。结合理论分析与数值模拟，本文验证了该结构在圆偏振光照射下可产生不同拓扑荷的OAM纯态；而入射光为线偏振时，则可实现两OAM态等振幅叠加，形成具有结构化分布的OAM叠加态。此外，通过调节线偏振光的偏振角，可有效控制两本征OAM态之间的相位差，从而实现叠加态场分布的规律性旋转。本研究为等离激元OAM态的相干控制提供了新的设计思路，也为多功能光场调控器件的集成设计提供了理论基础和技术路径。Recent studies on orbital angular momentum (OAM) states in the surface plasmon polariton (SPP) field have primarily focused on the generation of single OAM modes and the evolution of OAM states with various topological charges. However, achieving coherent superposition of two OAM states with well-defined phase relations through precise nanostructure design remains challenging. In this work, we propose a plasmonic nanostructure consisting of paired rectangular slits arranged along circular or segmented Archimedes spiral. The Archimedean spiral of various radii in azimuthal angle provides a geometry-dependent helical phase; coupled with a rotated nanoslit pair, it introduces a geometric phase of twice the rotated angle. By combining chiral spiral with nanoslit pair units, the design both generates plasmonic OAM eigenstates with arbitrary topological charges and enables their coherent superposition. The amplitudes of the two constituent OAM states are continuously tunable through the degree of polarization of the incident light, and their relative phase difference is controlled by the polarization angle, enabling arbitrary superposition of the plasmonic OAM states with continuously variable amplitude ratios and phase differences. Theoretical analysis and numerical simulations demonstrate that circularly polarized illumination produces distinct OAM pure states, whereas linearly polarized light leads to equal-amplitude superposition states with structured field distributions. Moreover, rotating the polarization angle continuously adjusts the relative phase between the eigenstates and produces a predictable rotation of the resultant interference pattern. These results provide a new approach for coherent control of plasmonic OAM states and offer design guidelines for multifunctional on-chip optical field manipulation devices.
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Keywords:
- Orbital angular momentum /
- Surface plasmon polaritons /
- Orbital angular momentum superposed states /
- Polarization state
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