近日，美国纽约城市大学Andrea Alù课题组实现了对光子时间界面的时间反射和宽带频移的观测。相关研究成果已于2023年3月13日在国际学术期刊《自然—物理学》上发表。

该团队报道了在一种开关传输线上超材料中观察到光子时间反射和相关的宽带频率的平移，其有效电容通过同步开关阵列均匀地突变。研究人员将一对时间界面组合起来，演示了时间反射引起的波干涉，实现了Fabry-Pérot空腔的时间对应物。他们的研究结果为实现时间超材料和Floquet光子晶体提供了基础构建模块，并为在时空中进行极端光子操纵的机会。

据介绍，时间反射是信号时间演化的均匀反转，当主体材料的性质在空间中均匀发生突变时，就会出现这种变化。在这样的时间界面上，输入信号的一部分是时间反转的，并且其频谱由于动量守恒发生均匀平移，形成空间界面的时间对应物。时间界面的组合形成了时间超材料和弗洛凯物质，利用多重时间反射的干涉进行极端的波操纵，利用时间作为额外的自由度。

附：英文原文

Title: Observation of temporal reflection and broadband frequency translation at photonic time interfaces

Author: Moussa, Hady, Xu, Gengyu, Yin, Shixiong, Galiffi, Emanuele, Radi, Younes, Alù, Andrea

Issue&Volume: 2023-03-13

Abstract: Time reflection is a uniform inversion of the temporal evolution of a signal, which arises when an abrupt change in the properties of the host material occurs uniformly in space. At such a time interface, a portion of the input signal is time reversed, and its frequency spectrum is homogeneously translated as its momentum is conserved, forming the temporal counterpart of a spatial interface. Combinations of time interfaces, forming time metamaterials and Floquet matter, exploit the interference of multiple time reflections for extreme wave manipulation, leveraging time as an additional degree of freedom. Here we report the observation of photonic time reflection and associated broadband frequency translation in a switched transmission-line metamaterial whose effective capacitance is homogeneously and abruptly changed via a synchronized array of switches. A pair of temporal interfaces are combined to demonstrate time-reflection-induced wave interference, realizing the temporal counterpart of a Fabry–Pérot cavity. Our results establish the foundational building blocks to realize time metamaterials and Floquet photonic crystals, with opportunities for extreme photon manipulation in space and time.

DOI: 10.1038/s41567-023-01975-y

Source: https://www.nature.com/articles/s41567-023-01975-y