The advent of novel nonlinear materials has stirred unprecedented interest in exploring the use of temporal inhomogeneities to achieve novel forms of wave control, amidst the greater vision of engineering metamaterials across both space and time. When the properties of an unbounded medium are abruptly switched in time, propagating waves are efficiently converted to different frequencies, and partially coupled to their back-propagating phase-conjugate partners, through a process called time-reversal. However, in realistic materials the switching time is necessarily finite, playing a central role in the resulting temporal scattering features. By identifying and leveraging the crucial role of electromagnetic momentum conservation in time-reversal processes, here we develop a general analytical formalism to quantify time-reversal due to temporal inhomogeneities of arbitrary profile. We deploy our theory to develop a formalism, dual to spatial tapering, that enables the tailoring of a desired time-reversal spectral response, demonstrating its use for the realization of broadband frequency converters and filters.

中文翻译：

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锥形光子开关

在跨越空间和时间的工程超材料的更大视野中，新型非线性材料的出现激起了人们对探索使用时间不均匀性来实现新形式的波控制的前所未有的兴趣。当无界介质的属性在时间上突然切换时，传播的波被有效地转换为不同的频率，并通过称为时间反转的过程部分耦合到其反向传播的相位共轭伙伴。然而，在现实材料中，切换时间必然是有限的，在产生的时间散射特征中起着核心作用。通过识别和利用电磁动量守恒在时间反转过程中的关键作用，在这里，我们开发了一种通用的分析形式来量化由于任意轮廓的时间不均匀性导致的时间反转。我们部署我们的理论来开发一种形式主义，对空间逐渐变细，从而能够定制所需的时间反转光谱响应，展示其用于实现宽带频率转换器和滤波器的用途。