Wavefront manipulation in metasurfaces typically relies on phase mapping with a finite number of elements. In particular, a discretized linear phase profile may be used to obtain a beam bending functionality. However, discretization limits the applicability of this approach for high angle bending due to the drastic efficiency drop when the phase is mapped by a small number of elements. In this work, we discuss a novel concept for energy redistribution in diffraction gratings and its application in the visible spectrum range, which helps overcome the constraints of ultrahigh angle (above 80°) beam bending. Arranging asymmetric dielectric nanoantennas into diffractive gratings, we show that one can efficiently redistribute the power between the grating orders at will. This is achieved by precise engineering of the scattering pattern of the nanoantennas. The concept is numerically and experimentally demonstrated at visible frequencies using several designs of TiO₂ (titanium dioxide) nanoantennas for medium (∼55°) and high (∼80°) angle light bending. Results show efficient broadband visible-light operation (blue and green range) of transmissive devices, reaching efficiencies of ∼90% and 50%, respectively, at the optimized wavelength. The presented design concept is general and can be applied for both transmission and reflection operation at any desired wavelength and polarization.

中文翻译：

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用于超高角度宽带可见光弯曲的非对称纳米天线

超表面中的波前操纵通常依赖于具有有限数量元素的相位映射。特别地，离散的线性相位轮廓可以用于获得光束弯曲功能。但是，由于相位由少量元素映射时，效率急剧下降，因此离散化限制了该方法在高角度弯曲中的适用性。在这项工作中，我们讨论了衍射光栅中能量重新分布的新概念及其在可见光谱范围中的应用，这有助于克服超高角度（大于80°）光束弯曲的限制。将不对称的介电纳米天线布置到衍射光栅中，我们证明了可以随意随意地在光栅阶次之间重新分配功率。这是通过精确设计纳米天线的散射图来实现的。使用几种设计的TiO在可见光频率下进行了数值和实验验证，_2个（二氧化钛）纳米天线，用于中等（〜55°）和大（〜80°）角光弯曲。结果表明，透射型设备可以有效地进行宽带可见光操作（蓝色和绿色范围），在最佳波长下，效率分别达到约90％和50％。提出的设计概念是一般性的，并且可以在任何所需的波长和偏振条件下用于透射和反射操作。