光在Metasurface中的自旋-轨道相互作用

探讨了光在Metasurface中的自旋-轨道相互作用, 理论分析了Metasurface 对圆偏振和线偏振光的转换. 结果表明: 光与具有空间非均匀性和各向异性性的Metasurface的相互作用导致了自旋-轨道角动量的耦合. 采用Metasurface与螺旋相位片组合在一起进行了验证实验, 所得实验结果与理论分析完全一致. 这些结论有助于我们更加深入理解Metasurface 对光的操控.

Spin-orbit interaction of light in metasuface

Spin-orbit interaction of light in metasurface is investigated in this paper. We theoretically analyze the transfromation of circularly and linearly polarized light by metasurface with Jones matrix. The results indicate that the interaction of light with spatially inhomogeneous and anisotropic metasurface leads to a coupling of spin-orbital angular momentum. The nanostructrues of metasurfaces are arranged at a definite rate of rotation, which induces an additional space-variant geometrical phase (i.e., Pancharatnam-Berry phase). The Pancharatnam-Berry phase is dependent on the polarization handedness of the incident wave. This characteristic can result in spin-dependent split. A left/right-circular polarized beam is transfromed into a right/left-circular polarized vortex beam by the metasurfaces. In the convertion process, the sign of spin angular momentum of photons is inversed. At the same time, each photon can acquire orbital angular momentum from the inhomogeneous and anisotropic media. The case that a linearly polarized beam inputs the metasurfaces also is considered. A linearly polarized wave can be regarded as the linear superposition of left-circular and right-circular polarized wave. The two circularly plarized components are respectively converted into circularly polarized vortex beam with reverse polarization handedness. The coherent superposition of the two output components forms a cylindrical vector beam. Finally, we adopt the combination of a metasurface and spiral phase plate to verify the theoretical results. The vortex phase can be eliminated by the spiral phase plate when a left-circular polarized light is input, while topological charge of vortex phase will increase when a right-circular polarized light is input. For the case of inputting linearly polarized beam, one of the two outputing circularly polarized components can be eliminated by the helical phase through using the spiral phase plate, while the topological charge of another component increases. It results in the fact that the intensity pattern splits into two parts. The central part does not have helical phase, while the ambient ring-shaped intensity has helical phase. In order to judge the polarization handedness of output wave, the Stokes parameter S₃ is measured by inserting a Glan laser polarizer and a quarter wave plate behind the spiral phase plate. The experimental results are in good agreement with theoretical analyses. These results are helpful for understanding the manipulation of light with metasurface.