近周期表面中辐射模与导波模耦合的高效微扰框架
Efficient perturbative framework for coupling of radiative and guided modes in nearly periodic surfaces
AI总结：
本文提出一种半解析微扰框架，结合局部周期近似与空间耦合波理论，高效计算近周期表面中辐射模与导波模的耦合，并验证其随表面缓变而精度提升。
摘要：
我们提出了一种半解析框架，用于计算缓变（近均匀或近周期）表面中辐射波与导波之间的耦合，这对于利用大面积超表面中的非局域效应尤为重要。该框架填补了缓变表面理论中的一个空白：除了暴力数值模拟外，当前的近似方法只能分别建模导波或辐射波，却难以建模它们之间的耦合。我们通过结合两种方法来解决这一问题：局部周期近似，通过组合一组周期散射问题来近似辐射散射；以及空间耦合波理论，它允许利用本征模展开对导波进行微扰建模。我们针对近均匀和近周期表面分别推导了该框架，并针对暴力有限差分时域模拟对每种情况进行了验证，结果表明随着表面变化更缓慢，两者的一致性不断提高。
英文摘要：
We present a semi-analytical framework for computing the coupling of radiative and guided waves in slowly varying (nearly uniform or nearly periodic) surfaces, which is especially relevant to the exploitation of nonlocal effects in large-area metasurfaces. Our framework bridges a gap in the theory of slowly varying surfaces: aside from brute-force numerical simulations, current approximate methods can model either guided or radiative waves, but cannot easily model their coupling. We solve this problem by combining two methods: the locally periodic approximation, which approximates radiative scattering by composing a set of periodic scattering problems, and spatial coupled-wave theory, which allows the perturbative modeling of guided waves using an eigenmode expansion. We derive our framework for both nearly uniform and nearly periodic surfaces, and we validate each case against brute-force finite-difference time-domain simulations, which show increasing agreement as the surface varies more slowly.
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