Non-Hermitian systems can be tuned to exhibit exceptional points, where both eigenvalues and eigenstates coalesce concurrently. The inherent adaptability of photonic non-Hermitian systems in configuring gain and loss has allowed us to observe a plethora of counterintuitive phenomena, largely as a consequence of the eigenspace reduction at these exceptional points. In this work, we propose a non-Hermitian metasurface that, through the incorporation of gain, enables complete asymmetric polarization conversion at an exceptional point with a zero eigenvalue. Specifically, we provide numerical evidence for this concept by designing a non-Hermitian metasurface that facilitates polarization conversion from right to left circular polarization, while preventing conversion in the reverse direction and co-polarized transmission. Furthermore, our investigation reveals that this specific form of complete asymmetric polarization conversion results in maximum circular dichroism in transmission, thereby eliminating the need for external chirality or three-dimensional helical structures. This non-Hermitian technique offers an intriguing approach to designing polarization-sensitive optical devices and systems, further expanding their functionalities and capabilities.

中文翻译：

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在非埃尔米特超表面的零特征值异常点处完成不对称极化转换


非厄米特系统可以调整为显示异常点，其中特征值和特征状态同时合并。光子非厄米特系统在配置增益和损耗方面的固有适应性使我们能够观察到大量违反直觉的现象，这主要是由于这些异常点的特征空间缩减的结果。在这项工作中，我们提出了一种非埃尔米特超表面，通过结合增益，可以在特征值为零的异常点上实现完全不对称的极化转换。具体来说，我们通过设计一种非厄米特超表面为这一概念提供了数值证据，该超表面促进了从右圆极化到左圆极化的极化转换，同时防止反向转换和同极化传输。此外，我们的调查表明，这种特定形式的完全不对称极化转换导致传输中的最大圆二色性，从而消除了对外部手性或三维螺旋结构的需求。这种非厄米特技术为设计偏振敏感的光学器件和系统提供了一种有趣的方法，进一步扩展了它们的功能和能力。