发表机构
University of Sydney; The Australian National University（悉尼大学; 澳大利亚国立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究证明互易光波导中无法实现对所有无序的普适背向散射免疫，源于光子缺乏电子系统的自旋-1/2和费米子时间反演保护，并提出若干针对性抑制策略。
AI 中文摘要
抑制由随机缺陷、材料不均匀性、局部夹杂物以及制备引起的几何偏差等不完美因素导致的寄生背向反射，长期以来一直是光波导工程的核心目标。在本快报中，我们从理论上证明，在互易光学波导中，对任意无序的背向散射的普适免疫性从根本上是不可能的，无论底层结构是拓扑平凡的还是拓扑非平凡的。我们通过两个互补的物理上可允许的互易扰动构造来确立这一结果。第一个构造考虑有限空间范围的弱介电常数扰动，并采用一阶玻恩近似；第二个构造考虑有限对比度的光学小介电扰动。在每种构造中，都存在一个可允许的实现，能够产生非零的领先阶背向散射振幅。我们将这一限制的根本起源追溯到光子中缺乏固有的自旋-1/2和费米子时间反演结构，而这正是电子系统中Kramers保护的基础。因此，任何在指定无序类别中强制实现光子背向散射抑制的机制，必须被工程化到底层电磁结构及其本构响应中，而该结构本身可能被一般的互易扰动所修改。在代表性互易拓扑波导中的数值示例进一步说明了这些限制对随机缺陷和尖锐弯曲的影响。我们还确定了在特定无序类别中抑制背向反射的几种建设性策略。
英文摘要
Suppressing parasitic back-reflection caused by imperfections, such as random defects, material inhomogeneities, localized inclusions, and fabrication-induced geometric deviations, has long been a central objective in optical-waveguide engineering. In this Letter, we theoretically establish that universal immunity to backscattering from arbitrary disorder is fundamentally impossible in reciprocal optical waveguides, irrespective of whether the underlying structure is topologically trivial or nontrivial.We establish this result through two complementary constructions of physically admissible reciprocal perturbations. The first considers weak permittivity perturbations of finite spatial extent within the first Born approximation, whereas the second considers optically small dielectric perturbations of finite contrast. In each construction, an admissible realization exists that produces a nonzero leading-order backward-scattering amplitude. We trace the fundamental origin of this limitation to the absence in photons of the intrinsic spin-$\tfrac{1}{2}$ and fermionic time-reversal structure underlying Kramers protection in electronic systems. Consequently, any mechanism that enforces photonic backscattering suppression throughout a prescribed class of disorder must instead be engineered into the underlying electromagnetic structure and its constitutive response, which can itself be modified by generic reciprocal perturbations. Numerical examples in representative reciprocal topological waveguides further illustrate these limitations for random defects and sharp bends. We further identify several constructive strategies for suppressing back-reflection within certain prescribed classes of disorder.
Comments17 pages, 9 figures
