非线性三明治人工原子超材料的二次谐波调控研究

Nonlinear metamaterials have the unique characteristics of electromagnetic properties and the ability of optical frequency conversion and all-optical modulation. Due to these exclusive properties, nonlinear metamaterials have many potential novel applications in the fields of micro-nano photonic devices, nonlinear optics and so on, especially in all-optical integrated systems with the frequency doubling effect based on the artificial structure elements. In this project, the sandwich structure on metal/nonlinear dielectric/metal is used as the meta-atom, and nonlinear dispersion model is utilized to analyze the mode characteristic of the structure for selecting the appropriate mode to effectively excite fundamental frequency light and frequency doubling light; Nonlinear dipole moments of electric-magnetic dipole are introduced with polarizability tensor method, and therefore, the nonlinear susceptibility tensor method will be created for the model of dipole-dipole interaction. With this model, the nonlinear optical field of different sandwich structure will be studied to investigate the microcosmic mechanism of the multidimensional modulation of the artificial sandwich structure on the second harmonic generation; based on the equivalent nonlinear susceptibility tensor, the modulation characteristics of nonlinear sandwich array structure on the phase distribution of second harmonic generation can be investigated by combining analytical method with numerical simulation method, and the conversion efficiency of second harmonic generation can be improved by the phase match of fundamental frequency light and frequency doubling light, which reveal the modulation principle of the structure on the far radiation of second harmonic generation. This project will provide theoretical basis and technical support for the development of high performance nonlinear photonic devices.

非线性超材料具有奇异电磁性质和对光频转换及全光调控能力，在微纳器件、非线性光学等领域具有众多新颖应用，尤其基于人工设计结构单元的倍频效应在全光集成系统中具有重要应用。本项目以金属/非线性介质/金属三明治结构作为人工原子结构单元，基于非线性色散模型，分析该结构的模式特性，选择合适模式有效激发基频光和倍频光；借助极化率张量方法，引入电磁偶极子的非线性偶极矩，建立偶极子相互作用模型下的非线性极化率张量方法，开展不同三明治结构单元的非线性光场解析研究，阐明通过结构设计多维度调控二次谐波效应的微观机理；基于阵列结构的等效非线性极化率张量，结合解析和数值模拟方法研究非线性三明治阵列结构对二次谐波相位分布的调控特性，通过基频光和倍频光相位匹配提高二次谐波转化效率，同时揭示该结构对二次谐波远场辐射的调控规律。本项目所取得的研究成果将为发展高性能非线性纳米光子器件提供理论依据和技术支持。

由于非线性器件小型化和集成化等方面的需求，发展有效、集成且结构紧凑的表面等离激元非线性光子器件，已成为高性能非线性光子器件的研究前沿。本项目主要开展了非线性三明治阵列超材料对二次谐波调控特性的研究，为未来高性能的非线性微纳光子学器件的开发提供基础。项目执行期间，基本按照申请书上所列研究内容开展，包括：1）研究非线性三明治阵列超材料中模式分布特性及其对二次谐波效应的影响机制，通过结构设计可激发呈倍频关系的电模式和磁模式，探讨该结构内共振模式对二次谐波效应的影响机制；2）基于线性极化率张量方法，建立了一种非线性极化率张量方法，获得三明治人工原子结构单元的非线性极化率解析表达式，基于偶极子间相互作用的理论模型，利用阵列结构的等效非线性极化率张量表示入射场与感应偶极矩的关系，获得该结构的反射场、透射场等解析式，揭示通过纵向和横向设计三明治超原子阵列结构调控二次谐波转换效率的微观机制；3）研究三明治超原子结构中二次谐波远场辐射的规律及其相关的微观机理，实现亚波长尺度下定向调控二次谐波。该工作对非线性三明治阵列结构中二次谐波的产生与调控有了更加深入的理解，为亚波长非线性超材料光子器件的设计提供了全新的理论支持，在实现高效、集成倍频器件等方面有着重要的科学意义。

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