基于准正则模式的全电介质超材料宽带反射器机理

Mechanism study of all-dielectric metamaterial wideband reflector based on quasi-canonical mode

全电介质超材料宽带反射器具备损耗低、反射效率高、结构紧凑等优点,深入理解其反射带的形成机理对超材料结构和性能的优化、以及进一步设计新型光子器件均具有重要意义.本文利用离散的硅纳米柱阵列和硅膜底层连接的硅纳米柱阵列分别构造了两个全电介质超材料宽带反射器,通过求解其准正则模式,结合散射矩阵理论拟合出了超材料的反射谱.发现零频准正则模式对拟合准确性有重要影响,并提出了用色散关系分析法准确求解零频准正则模式.进一步用高Q值和低Q值准正则模式分别拟合出共振反射谱和背景反射谱.结果表明,超材料反射器的宽带反射源于低Q值的准正则模式造成的背景反射.本文提出的研究方法可进一步拓展,用于分析Mie共振、准连续域束缚态等共振现象,为超材料光谱特性的解释提供新的思路.

All-dielectric metamaterial broadband reflectors have the advantages of low loss,high reflection efficiency,and compact structure.An in-depth understanding of the formation mechanism of their reflection bands is of great significance in optimizing metamaterial structure and performance,and in further designing novel photonic devices as well.In this work,two all-dielectric metamaterial broadband reflectors are constructed by using discrete silicon nanopillar array and silicon nanopillar array connected with a silicon sublayer.The quasinormal modes of the metamaterial reflectors are solved.Combining the quasi-normal modes with the scattering matrix theory,we obtain the fitted reflection spectra of the metamaterial,and then reveal that the zerofrequency quasi-normal mode has a substantial influence on the accuracy of the fitting results.A dispersion relation analysis method is proposed to accurately solve the zero-frequency quasi-normal mode.Furthermore,the fitted resonance reflection spectrum and background reflection spectrum are obtained by using high-Q-value quasi-normal mode and low-Q-value quasi-normal mode,respectively.Our results show that the broadband reflection of the considered metamaterial reflectors should be attributed to the background reflection induced by the low-Q quasi-normal modes.The research method proposed in this paper can also be used for discussing quasi bound states in the continuum,Mie resonances,and other resonance phenomena,which provides a new way for interpreting the spectral characteristics of metamaterials.