Fu Yangyang, Shen Chen, Cao Yanyan, Gao Lei, Chen Huanyang, Chan C T, Cummer Steven A, Xu Yadong
School of Physical Science and Technology and Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou, 215006, China.
College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing, 211106, China.
Nat Commun. 2019 May 24;10(1):2326. doi: 10.1038/s41467-019-10377-9.
Phase gradient metagratings (PGMs) have provided unprecedented opportunities for wavefront manipulation. However, this approach suffers from fundamental limits on conversion efficiency; in some cases, higher order diffraction caused by the periodicity can be observed distinctly, while the working mechanism still is not fully understood, especially in refractive-type metagratings. Here we show, analytically and experimentally, a refractive-type metagrating which can enable anomalous reflection and refraction with almost unity efficiency over a wide incident range. A simple physical picture is presented to reveal the underlying diffraction mechanism. Interestingly, it is found that the anomalous transmission and reflection through higher order diffraction can be completely reversed by changing the integer parity of the PGM design, and such phenomenon is very robust. Two refractive acoustic metagratings are designed and fabricated based on this principle and the experimental results verify the theory.
相位梯度超光栅（PGM）为波前操纵提供了前所未有的机遇。然而，这种方法在转换效率方面存在根本限制；在某些情况下，可以明显观察到由周期性引起的高阶衍射，而其工作机制仍未完全理解，尤其是在折射型超光栅中。在此，我们通过理论分析和实验展示了一种折射型超光栅，它能够在很宽的入射范围内以几乎单位效率实现异常反射和折射。我们给出了一个简单的物理图像来揭示其潜在的衍射机制。有趣的是，发现通过改变PGM设计的整数奇偶性，可以完全反转通过高阶衍射的异常透射和反射，并且这种现象非常稳定。基于这一原理设计并制作了两个折射声超光栅，实验结果验证了该理论。
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