Loulas Iridanos, Almpanis Evangelos, Kouroublakis Minas, Tsakmakidis Kosmas L, Rockstuhl Carsten, Zouros Grigorios P
Section of Condensed Matter Physics, National and Kapodistrian University of Athens, Panepistimioupolis, 157 84 Athens, Greece.
Institute of Nanoscience and Nanotechnology, NCSR "Demokritos", Patriarchou Gregoriou and Neapoleos Street, Ag. Paraskevi, 153 10 Athens, Greece.
ACS Photonics. 2025 Feb 19;12(3):1524-1534. doi: 10.1021/acsphotonics.4c02194. eCollection 2025 Mar 19.
We develop a full-wave electromagnetic (EM) theory for calculating the multipole decomposition in two-dimensional (2-D) structures consisting of isolated, arbitrarily shaped, inhomogeneous, anisotropic cylinders or a collection of such. To derive the multipole decomposition, we first solve the scattering problem by expanding the scattered electric field in divergenceless cylindrical vector wave functions (CVWFs) with unknown expansion coefficients that characterize the multipole response. These expansion coefficients are then expressed via contour integrals of the vectorial components of the scattered electric field evaluated via an electric field volume integral equation (EFVIE). The kernels of the EFVIE are the products of the tensorial 2-D Green's function (GF) expansion and the equivalent 2-D volumetric electric and magnetic current densities. We validate the theory using the commercial finite element solver COMSOL Multiphysics. In the validation, we compute the multipole decomposition of the fields scattered from various 2-D structures and compare the results with alternative formulations. Finally, we demonstrate the applicability of the theory to study an emerging photonics application on oligomer-based highly directional switching using active media. This analysis addresses a critical gap in the current literature, where multipole theories exist primarily for three-dimensional (3-D) particles of isotropic materials. Our work enhances the understanding and utilization of the optical properties of 2-D, inhomogeneous, and anisotropic cylindrical structures, contributing to advancements in photonic and meta-optics technologies.
我们开发了一种全波电磁（EM）理论，用于计算由孤立的、任意形状的、非均匀的、各向异性的圆柱体或此类圆柱体集合组成的二维（2-D）结构中的多极分解。为了推导多极分解，我们首先通过用表征多极响应的未知展开系数展开无散圆柱矢量波函数（CVWFs）来解决散射问题。然后，这些展开系数通过经由电场体积积分方程（EFVIE）评估的散射电场的矢量分量的围道积分来表示。EFVIE的核是张量二维格林函数（GF）展开与等效二维体积电和磁电流密度的乘积。我们使用商业有限元求解器COMSOL Multiphysics验证了该理论。在验证过程中，我们计算了从各种二维结构散射的场的多极分解，并将结果与替代公式进行了比较。最后，我们展示了该理论在研究基于低聚物的使用有源介质的高定向开关这一新兴光子学应用中的适用性。该分析解决了当前文献中的一个关键空白，即多极理论主要存在于各向同性材料的三维（3-D）粒子中。我们的工作增进了对二维、非均匀和各向异性圆柱结构光学特性的理解和利用，有助于光子学和超光学技术的进步。
