Space‐time modulated metasurfaces enable efficient manipulations of nonlinear harmonics with more degrees of freedom than conventional materials by simply controlling the element geometries and modulation signals. The theoretical analyses reveal that a group of harmonics in reflected waves could be generated by the metasurface under the incidence of monochromatic wave with the rapid change of surface reflectivity, while the fundamental spectrum is greatly suppressed. However, it remains a great challenge to synthesize a high‐quality single‐tone signal for the reflected waves with excellent rejection ratio for higher‐order harmonics, which is highly desired for applications like wireless communications and radar detection. Here, a new scheme to overcome this limit, which experimentally realizes high‐efficiency frequency conversion from the fundamental harmonic to the $+1\mathrm{s}\mathrm{t}/-1\mathrm{s}\mathrm{t}$order harmonic of reflected waves, and beam shaping based on the space‐time joint coding strategy are proposed. The measured results show that the maximum conversion efficiency is greater than 88%. This design can also find widespread applications in THz frequencies when the active metasurface for periodical phase modulations is further developed.

中文翻译：

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基于时空编码数字超表面的空间波高效合成器

时空调制的超表面可以通过简单地控制元素的几何形状和调制信号，从而以比传统材料更大的自由度有效地操纵非线性谐波。理论分析表明，在单色波的入射下，随着反射率的快速变化，超表面可能会在反射波中产生一组谐波，同时极大地抑制了基波谱。但是，要为反射波合成高质量的单音信号并具有对高阶谐波的出色抑制比，仍然是一个巨大的挑战，这在无线通信和雷达检测等应用中是非常需要的。在这里，一个新的方案可以克服这个限制，$+\mathrm{1个}\mathrm{s}\mathrm{Ť}/-\mathrm{1个}\mathrm{s}\mathrm{Ť}$提出了反射波的二次谐波和基于时空联合编码策略的波束成形。测量结果表明，最大转换效率大于88％。当进一步开发用于周期性相位调制的有源超表面时，该设计还可在THz频率中找到广泛的应用。