色散时变光子结构的全波谐波平衡框架
Full-Wave Harmonic Balance Framework for Dispersive Time-Varying Photonic Structures
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中文总结 AI 辅助
本研究提出全波谐波平衡框架，用于精确建模色散时变光子结构，经卷曲石墨烯圆柱、ITO基ENZ时空超表面验证，为相关有源光子结构设计提供通用平台。
中文摘要 AI 辅助
时变光子结构可在弗洛奎特（Floquet）谐波间重新分配电磁能量，实现频率转换、非互易性、参量增益和动态波前控制。当强色散材料中发生时间调制时，真实平台的精确建模仍具挑战性，因为各谐波会经历不同的材料响应，同时通过调制相互耦合。本研究提出一种用于色散时变光子结构的全波谐波平衡框架，该公式通过将调制分量表示为感应次级源（体介质的体积极化密度、导电片的表面电流密度），在频域求解稳态弗洛奎特响应。材料色散和辐射算子在各谐波频率处计算，而时间调制则作为弗洛奎特空间中的非对角卷积耦合项引入。该框架针对参量泵浦的卷曲石墨烯圆柱进行验证，数值结果与解析弗洛奎特散射解一致，且能解析谐波相关的散射、吸收和近场；还应用于基于氧化铟锡（ITO）的近零介电常数（ENZ）时空超表面，实现反射器件的形状优化，该器件可将光输入转换为边带并将其重定向至选定的空间衍射级。该方法为建模和设计色散型有源光子结构建立了通用平台，可获取谐波分辨的场、功率、吸收和衍射可观测量。
英文摘要
Time-varying photonic structures redistribute electromagnetic energy among Floquet harmonics, enabling frequency conversion, nonreciprocity, parametric gain, and dynamic wavefront control. Accurate modeling of realistic platforms remains challenging when temporal modulation occurs in strongly dispersive materials, because each harmonic experiences a distinct material response while remaining coupled to all others through the modulation. This work introduces a full-wave harmonic-balance framework for dispersive time-varying photonic structures. The formulation solves the steady-state Floquet response in the frequency domain by representing modulated components as induced secondary sources: volumetric polarization densities for bulk media and surface current densities for conductive sheets. Material dispersion and radiation operators are evaluated at each harmonic frequency, whereas temporal modulation enters as off-diagonal convolutional coupling in Floquet space. The framework is validated for a parametrically pumped rolled graphene cylinder, where numerical results agree with an analytical Floquet scattering solution and resolve harmonic-specific scattering, absorption, and near fields. It is further applied to an ITO-based epsilon-near-zero (ENZ) space-time metasurface, enabling shape optimization of a reflective device that converts an optical input into sidebands and redirects them into selected spatial diffraction orders. The approach establishes a general platform for modeling and designing dispersive active photonic structures with harmonic-resolved field, power, absorption, and diffraction observables.
