Energy squeezing is attractive for its potential applications in electromagnetic (EM) energy harvesting and optical communication. However, due to the Fabry-Perot resonance, only the EM waves with discrete frequencies can be squeezed and, as far as we know, in the previous energy-squeezing devices, stringent requirements of the materials or the geometrical shape are needed. We note that the structures filled with epsilon-near-zero (ENZ) mediums as reported in some works can squeeze and tunnel EM waves at frequencies (e.g. plasma frequency). However, the group velocity is usually near zero, which means little EM information travels through the structures. In this paper, low-loss energy squeezing and tunneling (EST) based on unidirectional modes were demonstrated in YIG-based one-way waveguides at microwave frequencies. According to our theoretical analysis and the simulations using the finite element method, broadband EST was achieved and the EM EST was observed even for extremely bended structures. Besides, similar EM EST was achieved in a realistic three-dimensional remanence-based one-way waveguide as well. The unidirectional mode-based EST paves the way for ultra-subwavelength EM focusing, enhanced nonlinear optics, and the design of numerous functional devices in integrated optical circuits such as phase modulator.

中文翻译：

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基于单向模式的宽带能量压缩和隧穿

能量压缩因其在电磁 (EM) 能量收集和光通信中的潜在应用而具有吸引力。然而，由于法布里-珀罗共振，只能压缩离散频率的电磁波，据我们所知，在以前的能量压缩装置中，对材料或几何形状的要求非常严格。我们注意到，在一些工作中报告的充满 epsilon-near-zero (ENZ) 介质的结构可以挤压和隧道频率（例如等离子体频率）的 EM 波。然而，群速度通常接近于零，这意味着几乎没有电磁信息穿过结构。在本文中，基于单向模式的低损耗能量压缩和隧穿 (EST) 在基于 YIG 的单向波导中在微波频率下进行了演示。根据我们的理论分析和使用有限元方法的模拟，实现了宽带 EST，即使对于极度弯曲的结构也可以观察到 EM EST。此外，在现实的基于 3D 剩磁的单向波导中也实现了类似的 EM EST。基于单向模式的 EST 为超亚波长 EM 聚焦、增强的非线性光学以及集成光电路（如相位调制器）中的众多功能器件的设计铺平了道路。