Backward phase matching, which describes counterpropagating fundamental and harmonic waves in a negative‐index medium, is one of the most intriguing phenomena in nonlinear metamaterials. Predicted theoretically decades ago, however, it is still a challenging task to be applied for efficient second harmonic (SH) generation in a nonlinear metamaterial with ultrathin geometry and ultralow loss. Here, a negative‐index spoof plasmonic metamaterial is reported, which is composed of an ultrathin symmetrical corrugated metallic strips loaded with nonlinear active devices. The simulated and measured power spectra and surface near‐field distributions show that a peak SH signal can be generated at the backward phase‐matched frequency point in a 120° curved surface with high efficiency, thanks to the ultrathin flexible geometry, significant confinement effect, and large propagation length of the spoof surface plasmons. The results open new technological challenges from nano‐ and micro‐nonlinear photonics to science and engineering of compact, broadband, and efficient frequency‐mixing metamaterials and electromagnetic devices.

中文翻译：

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负折射率共形表面等离子体超材料中二次谐波产生的反向相位匹配

后向相位匹配描述了负折射率介质中反向传播的基波和谐波，是非线性超材料中最有趣的现象之一。然而，几十年前从理论上预测，在具有超薄几何形状和超低损耗的非线性超材料中高效产生二次谐波（SH）仍然是一项具有挑战性的任务。在这里，报道了一种负折射率欺骗等离子体超材料，它由装载有非线性有源器件的超薄对称波纹金属条组成。仿真和测量的功率谱和表面近场分布表明，由于超薄柔性几何结构、显着的限域效应，可以在120°曲面的反向相位匹配频点处高效地产生峰值SH信号。以及欺骗表面等离子体激元的大传播长度。这些结果提出了从纳米和微米非线性光子学到紧凑、宽带和高效混频超材料和电磁器件的科学和工程的新技术挑战。