Generation of Perfect Vortex Beams by Dielectric Geometric Metasurface for Visible Light,Laser & Photonics Reviews

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Generation of Perfect Vortex Beams by Dielectric Geometric Metasurface for Visible Light
Laser & Photonics Reviews ( IF 9.8 ) Pub Date : 2021-10-31 , DOI: 10.1002/lpor.202100390
Qianwei Zhou _{1,

2} , Mingze Liu _{1,

2} , Wenqi Zhu _{3,

4} , Lu Chen _{3,

4} , Yongze Ren _{1,

2} , Henri J. Lezec ₃ , Yanqing Lu _{1,

2} , Amit Agrawal _{3,

4} , Ting Xu _{1,

2}

Affiliation

A perfect vortex beam (PVB) is a propagating optical field carrying orbital angular momentum (OAM) with a radial intensity profile that is independent of topological charge. PVBs can be generated through the Fourier transform of a Bessel–Gaussian beam, which typically requires a well-aligned optical setup consisting of a spiral phase plate, an axion, and a lens. Here, based on a single-layer dielectric metasurface, the broadband generation of PVBs across the entire visible spectrum is demonstrated. The metasurface is composed of TiO₂ nanopillars acting as deep-subwavelength half-waveplates, and able to provide the desired geometric phase profile to an incident circularly polarized light for the generation of PVBs. Through rigorous optimization of the nanopillars’ structural parameters, the authors experimentally generate vortex beams carrying OAM with different topological charges that exhibit constant radial intensity profiles, verifying their “perfect” characteristics. Furthermore, it is also demonstrated that the ellipticity and diameter of a PVB can be simultaneously controlled by adjusting the structural parameters of the metasurface, which further increases the flexibility in their design. These results open a new route towards creating ultra-compact, flat, multifunctional nanophotonic platforms for efficient generation of structured light beams.

中文翻译：

通过用于可见光的介电几何超表面生成完美涡旋光束

完美涡旋光束 (PVB) 是携带轨道角动量 (OAM) 的传播光场，其径向强度分布与拓扑电荷无关。PVB 可以通过 Bessel-Gaussian 光束的傅立叶变换生成，这通常需要由螺旋相位板、轴子和透镜组成的良好对准的光学装置。在这里，基于单层介电超表面，演示了整个可见光谱中 PVB 的宽带生成。超表面由TiO ₂组成纳米柱作为深亚波长半波片，能够为入射圆偏振光提供所需的几何相位分布，以产生 PVB。通过对纳米柱结构参数的严格优化，作者通过实验产生了带有不同拓扑电荷的 OAM 的涡旋光束，这些 OAM 呈现恒定的径向强度分布，验证了它们的“完美”特性。此外，还证明了通过调整超表面的结构参数可以同时控制 PVB 的椭圆度和直径，这进一步增加了其设计的灵活性。这些结果为创建超紧凑、平坦、多功能的纳米光子平台以高效生成结构光束开辟了一条新途径。

更新日期：2021-12-10

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