Abstract When two nonorthogonal resonances are coupled to the same radiation channel, avoided crossing arises and a bound state in the continuum (BIC) appears with appropriate conditions in parametric space. This paper presents numerical and analytical results on the properties of avoided crossing and BIC due to the coupled guided-mode resonances in one-dimensional (1D) leaky-mode photonic lattices with slab geometry. In symmetric photonic lattices with up-down mirror symmetry, Friedrich–Wintgen BICs with infinite lifetime are accompanied by avoided crossings due to the coupling between two guided modes with the same transverse parity. In asymmetric photonic lattices with broken up-down mirror symmetry, quasi-BICs with finite lifetime appear with avoided crossings because radiating waves from different modes cannot be completely eliminated. We also show that unidirectional-BICs are accompanied by avoided crossings due to guided-mode resonances with different transverse parities in asymmetric photonic lattices. The Q factor of a unidirectional-BIC is finite, but its radiation power in the upward or downward direction is significantly smaller than that in the opposite direction. Our results may be helpful in engineering BICs and avoided crossings in diverse photonic systems that support leaky modes.

中文翻译：

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连续体 (BIC) 中的束缚态伴随着漏模式光子晶格中的避免交叉

摘要 当两个非正交共振耦合到同一辐射通道时，会出现避免交叉，并在参数空间中以适当的条件出现连续介质中的束缚态（BIC）。本文介绍了由于具有平板几何形状的一维 (1D) 漏模光子晶格中的耦合导模共振而导致的避免交叉和 BIC 特性的数值和分析结果。在具有上下镜像对称性的对称光子晶格中，由于具有相同横向奇偶性的两个导模之间的耦合，具有无限寿命的 Friedrich-Wintgen BIC 伴随着避免交叉。在具有破坏的上下镜像对称性的非对称光子晶格中，由于无法完全消除来自不同模式的辐射波，因此出现具有有限寿命的准 BIC 并避免交叉。我们还表明，由于在非对称光子晶格中具有不同横向奇偶性的导模共振，单向 BIC 伴随着避免交叉。单向 BIC 的 Q 因子是有限的，但其向上或向下方向的辐射功率明显小于相反方向的辐射功率。我们的结果可能有助于设计 BIC 并避免支持泄漏模式的各种光子系统中的交叉。