The control of spin electromagnetic (EM) waves is of great significance in optical communications. Although geometric metasurfaces have shown unprecedented capability to manipulate the wavefronts of spin EM waves, it is still challenging to independently manipulate each spin state and intensity distribution, which inevitably degrades metasurface-based devices for further applications. Here we propose and experimentally demonstrate an approach to designing spin-decoupled metalenses based on pure geometric phase, i.e., geometric metasurfaces with predesigned phase modulation possessing functionalities of both convex lenses and concave lenses. Under the illumination of left-/right-handed circularly polarized (LCP or RCP) terahertz (THz) waves, these metalenses can generate transversely/longitudinally distributed RCP/LCP multiple focal points. Since the helicity-dependent multiple focal points are locked to the polarization state of incident THz waves, the relative intensity between two orthogonal components can be controlled with different weights of LCP and RCP THz waves, leading to the intensity-tunable functionality. This robust approach for simultaneously manipulating orthogonal spin states and energy distributions of spin EM waves will open a new avenue for designing multifunctional devices and integrated communication systems.

中文翻译：

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具有强度可调的多焦点的自旋解耦元透镜

自旋电磁（EM）波的控制在光通信中具有重要意义。尽管几何超表面已显示出前所未有的操纵自旋电磁波波前的能力，但独立操纵每个自旋状态和强度分布仍然具有挑战性，这不可避免地降低了基于超表面的设备的进一步应用。在这里，我们提出并通过实验证明了一种基于纯几何相位设计自旋解耦超透镜的方法，即具有预设计相位调制的几何超表面，具有凸透镜和凹透镜的功能。在左/右旋圆偏振（LCP或RCP）太赫兹（THz）波的照射下，这些超透镜可以产生横向/纵向分布的RCP/LCP多焦点。由于螺旋度相关的多个焦点被锁定到入射太赫兹波的偏振态，两个正交分量之间的相对强度可以通过 LCP 和 RCP 太赫兹波的不同权重来控制，从而实现强度可调功能。这种同时操纵正交自旋状态和自旋电磁波能量分布的稳健方法将为设计多功能设备和集成通信系统开辟一条新途径。