Zhang Ziying, Kang Ming, Zhang Xueqian, Feng Xi, Xu Yuehong, Chen Xieyu, Zhang Huifang, Xu Quan, Tian Zhen, Zhang Weili, Krasnok Alex, Han Jiaguang, Alù Andrea
Center for Terahertz Waves, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronics Information and Technology, Tianjin University, Tianjin, 300072, P. R. China.
Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX, 78712, USA.
Adv Mater. 2020 Sep;32(36):e2002341. doi: 10.1002/adma.202002341. Epub 2020 Jul 23.
Metasurfaces are 2D engineered structures with subwavelength granularity, offering a wide range of opportunities to tailor the impinging wavefront. However, fundamental limitations on their efficiency in wave transformation, associated with their deeply subwavelength thickness, challenge their implementation in practical application scenarios. Here, it is shown how the coherent control of metagratings through multiple wave excitations can provide new opportunities to achieve highly reconfigurable broadband metasurfaces with large diffraction efficiency, beyond the limitations of conventional approaches. Remarkably, energy distribution between the 0th and higher diffraction orders can be continuously tuned by changing the relative phase difference between two excitation waves, enabling coherent control, with added benefits of enhanced efficiency and bandwidth. This concept is demonstrated for a thin electric metagrating operating at terahertz frequencies, showing that coherent control can overcome several of the limitations of single-layer ultrathin metastructures, and extend their feasibility in various practical scenarios.
超表面是具有亚波长粒度的二维工程结构，为定制入射波前提供了广泛的机会。然而，由于其极深的亚波长厚度，它们在波变换效率方面存在基本限制，这对其在实际应用场景中的实现构成了挑战。在此，展示了如何通过多波激发对超光栅进行相干控制，从而提供新的机会来实现具有高衍射效率的高度可重构宽带超表面，突破传统方法的限制。值得注意的是，通过改变两个激发波之间的相对相位差，可以连续调节零阶和高阶衍射级之间的能量分布，实现相干控制，同时提高效率和带宽。这一概念在太赫兹频率下工作的薄电超光栅上得到了验证，表明相干控制可以克服单层超薄超结构的一些限制，并扩展其在各种实际场景中的可行性。
