Extended Bound States in the Continuum with Symmetry‐Broken Terahertz Dielectric Metasurfaces,Advanced Optical Materials

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Extended Bound States in the Continuum with Symmetry‐Broken Terahertz Dielectric Metasurfaces
Advanced Optical Materials ( IF 8.0 ) Pub Date : 2021-01-20 , DOI: 10.1002/adom.202002001
Song Han _{1,

2} , Prakash Pitchappa _{1,

2,

3} , Wenhao Wang _{1,

2,

4} , Yogesh Kumar Srivastava _{1,

2} , Mikhail V. Rybin _{5,

6} , Ranjan Singh _{1,

2}

Affiliation

Excitation of the non‐radiative eigenmodes in photonics and metamaterials above their light cone, that is, the bound states in the continuum (BICs), has drawn fundamental and technological interest. However, the current studies on photonic BICs are mainly restricted to the characterization of the eigenmodes with fixed point group. Here, a fourfold rotationally symmetric (C_4v) array of silicon resonators in a square lattice is investigated that reveals the traditional symmetry‐protected (Γ‐state) and accidental (off‐Γ) BICs in the momentum space. Upon symmetry‐breaking, BICs at Γ‐state transform into quasi‐states with decaying quality factors that obey the inverse‐square law α⁻² as a function of the structural asymmetry parameter α. Surprisingly, at larger asymmetries, multiple new states of extended BICs are observed beyond typical inverse‐square law behavior. The structural asymmetry of a resonator provides an important degree of freedom for exploring the Friedrich–Wintgen and new accidental BICs that are topologically protected by robust polarization vortices. The extended family of sharp BIC resonances in all‐dielectric silicon metasurfaces is extremely important for scalable applications in terahertz sensing, higher harmonic generation, and ultralow‐power switching.

中文翻译：

具有对称断裂的太赫兹介电超表面的连续谱中的扩展束缚态

激发光子和超材料中的光锥上方的非辐射本征模，即连续体中的束缚态（BIC），已经引起了基础和技术兴趣。然而，目前对光子BIC的研究主要限于定点群本征模的表征。在这里，研究了方形晶格中硅谐振器的四重旋转对称（C _4v）阵列，揭示了动量空间中传统的对称保护BIC（Γ-state）和偶然（off-Γ）BIC。对称破坏后，Γ状态的BIC转换为具有服从平方反比定律α ^-2的衰减因子的准状态作为结构不对称参数α的函数。令人惊讶的是，在更大的不对称性下，除了典型的平方反比定律行为外，还观察到了扩展BIC的多个新状态。谐振器的结构不对称性为探索Friedrich-Wintgen和受到坚固的极化涡流拓扑保护的新型偶然BIC提供了重要的自由度。全介电硅超表面中急剧的BIC共振的扩展家族对于太赫兹感测，高次谐波产生和超低功耗开关中的可扩展应用极为重要。

更新日期：2021-01-20

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