Rizza Carlo, Castaldi Giuseppe, Galdi Vincenzo
Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, I-67100, Italy.
Department of Engineering, Fields & Waves Lab, University of Sannio, Benevento, I-82100, Italy.
Nanophotonics. 2022 Feb 25;11(7):1285-1295. doi: 10.1515/nanoph-2021-0605. eCollection 2022 Mar.
Nonlocality is a fundamental concept in photonics. For instance, nonlocal wave-matter interactions in spatially modulated metamaterials enable novel effects, such as giant electromagnetic chirality, artificial magnetism, and negative refraction. Here, we investigate the effects induced by spatial nonlocality in metamaterials, i.e., media with a dielectric permittivity rapidly modulated in time. Via a rigorous multiscale approach, we introduce a general and compact formalism for the nonlocal effective medium theory of temporally periodic metamaterials. In particular, we study two scenarios: (i) a periodic temporal modulation, and (ii) a temporal boundary where the permittivity is abruptly changed in time and subject to periodic modulation. We show that these configurations can give rise to peculiar nonlocal effects, and we highlight the similarities and differences with respect to the spatial-metamaterial counterparts. Interestingly, by tailoring the effective boundary wave-matter interactions, we also identify an intriguing configuration for which a temporal metamaterial can perform the first-order derivative of an incident wavepacket. Our theoretical results, backed by full-wave numerical simulations, introduce key physical ingredients that may pave the way for novel applications. By fully exploiting the time-reversal symmetry breaking, nonlocal temporal metamaterials promise a great potential for efficient, tunable optical computing devices.
非局域性是光子学中的一个基本概念。例如，空间调制超材料中的非局域波-物质相互作用能够产生新颖的效应，如巨大的电磁手性、人工磁性和负折射。在此，我们研究超材料中空间非局域性所引发的效应，即介电常数随时间快速调制的介质。通过一种严格的多尺度方法，我们为时间周期超材料的非局域有效介质理论引入了一种通用且简洁的形式体系。特别地，我们研究两种情形：（i）周期性时间调制，以及（ii）介电常数在时间上突然变化并受到周期调制的时间边界。我们表明这些构型能够产生奇特的非局域效应，并且突出了它们与空间超材料对应物的异同。有趣的是，通过调整有效的边界波-物质相互作用，我们还识别出一种引人入胜的构型，对于该构型，时间超材料能够对入射波包进行一阶导数运算。我们的理论结果得到了全波数值模拟的支持，引入了可能为新颖应用铺平道路的关键物理要素。通过充分利用时间反演对称性破缺，非局域时间超材料在高效、可调谐光学计算设备方面展现出巨大潜力。
