Thureja Prachi, Shirmanesh Ghazaleh Kafaie, Fountaine Katherine T, Sokhoyan Ruzan, Grajower Meir, Atwater Harry A
Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, California 91125, United States.
NG Next, Northrop Grumman Corporation, One Space Park, Redondo Beach, California 90278, United States.
ACS Nano. 2020 Nov 24;14(11):15042-15055. doi: 10.1021/acsnano.0c05026. Epub 2020 Oct 30.
We report an array-level inverse design approach to optimize the beam steering performance of active metasurfaces, thus overcoming the limitations posed by nonideal metasurface phase and amplitude tuning. In contrast to device-level topology optimization of passive metasurfaces, the outlined system-level optimization framework relies on the electrical tunability of geometrically identical nanoantennas, enabling the design of active antenna arrays with variable spatial phase and amplitude profiles. Based on this method, we demonstrate high-directivity, continuous beam steering up to 70° for phased arrays with realistic tunable antenna designs, despite nonidealities such as strong covariation of scattered light amplitude with phase. Nonintuitive array phase and amplitude profiles further facilitate beam steering with a phase modulation range as low as 180°. Furthermore, we use the device geometries presented in this work for experimental validation of the system-level inverse design approach of active beam steering metasurfaces. The proposed method offers a framework to optimize nanophotonic structures at the array level that is potentially applicable to a wide variety of objective functions and actively tunable metasurface antenna array platforms.
我们报告了一种阵列级逆设计方法，用于优化有源超表面的波束转向性能，从而克服非理想超表面相位和幅度调谐带来的限制。与无源超表面的器件级拓扑优化不同，所概述的系统级优化框架依赖于几何形状相同的纳米天线的电可调性，从而能够设计具有可变空间相位和幅度分布的有源天线阵列。基于此方法，我们展示了具有实际可调天线设计的相控阵高达70°的高指向性、连续波束转向，尽管存在诸如散射光幅度与相位的强协变等非理想情况。非直观的阵列相位和幅度分布进一步促进了低至180°相位调制范围的波束转向。此外，我们使用本工作中提出的器件几何结构对有源波束转向超表面的系统级逆设计方法进行实验验证。所提出的方法提供了一个在阵列级优化纳米光子结构的框架，该框架可能适用于各种目标函数和有源可调超表面天线阵列平台。
