近日，英国伦敦帝国理工学院Riccardo Sapienza团队研究了时变介质中的光相干完全吸收和放大。这一研究成果于2026年1月26日发表在《自然—光子学》杂志上。
时不变光子结构根据其固有的材料增益或损耗来放大或吸收光。例如，在谐振腔中，可以利用空间中多束光的相干干涉来调控波与材料增益或损耗的相互作用，从而分别实现激光发射最大化或相干完美吸收。相比之下，时变系统即使在没有材料增益或损耗的情况下，也不受能量守恒的约束，并且可以通过参数现象实现探测波的放大或吸收。
研究组从理论和实验上证明了，如何通过对氧化铟锡亚波长薄膜（其体介电常数通过光泵浦进行均匀周期性调制）进行动态调谐，使其既能作为非共振放大器，也能作为完美吸收体，具体方法是通过操控两束反向传播探测光束的相对相位。这便将相干完美吸收的概念扩展到了时域。研究组将这一结果解释为在周期性调制介质的动量带隙中，增益模式与损耗模式之间的选择性切换。通过调整两束探测光的相对强度，可以实现高对比度调制，吸收率高达80%，放大率高达400%。该研究结果展示了在光频下对时变介质中增益与损耗的控制，并为在Floquet调控的复杂光子系统中实现光的相干操控铺平了道路。
附：英文原文
Title: Optical coherent perfect absorption and amplification in a time-varying medium
Author: Galiffi, Emanuele, Harwood, Anthony C., Vezzoli, Stefano, Tirole, Romain, Al, Andrea, Sapienza, Riccardo
Issue&Volume: 2026-01-26
Abstract: Time-invariant photonic structures amplify or absorb light on the basis of their intrinsic material gain or loss. The coherent interference of multiple beams in space, for example, in a resonator, can be exploited to tailor the wave interaction with material gain or loss, respectively maximizing lasing or coherent perfect absorption. By contrast, a time-varying system is not bound to conserve energy, even in the absence of material gain or loss, and can support amplification or absorption of a probe wave through parametric phenomena. Here we demonstrate theoretically and experimentally how a subwavelength film of indium tin oxide, whose bulk permittivity is homogeneously and periodically modulated via optical pumping, can be dynamically tuned to act both as a non-resonant amplifier and as a perfect absorber, by manipulating the relative phase of two counterpropagating probe beams. This extends the concept of coherent perfect absorption to the temporal domain. We interpret this result as selective switching between the gain and loss modes present in the momentum bandgap of a periodically modulated medium. By tailoring the relative intensity of the two probes, high-contrast modulation can be achieved with up to 80% absorption and 400% amplification. Our results demonstrate control of gain and loss in time-varying media at optical frequencies and pave the way towards coherent manipulation of light in Floquet-engineered complex photonic systems.
DOI: 10.1038/s41566-025-01833-8
Source: https://www.nature.com/articles/s41566-025-01833-8