漏模光子晶格中连续介质中的束缚态及其避免交叉
Bound states in the continuum accompanied by avoided crossings in leaky-mode photonic lattices
摘要：
当两个非正交共振耦合到同一个辐射通道时，避免了交叉，在参数空间中出现了连续束缚态（BIC）。本文给出了一维平板漏模光子晶格中耦合导模共振所引起的避免交叉和BIC特性的数值和解析结果。在具有上下镜像对称性的对称光子晶格中，由于具有相同横宇称的两个导模之间的耦合，具有无限寿命的Friedrich-Wintgen BIC伴随有避免的交叉。在上-下镜像对称性被破坏的非对称光子晶格中，由于不同模式的辐射波不能完全消除，因此出现了具有有限寿命的准BIC，但没有交叉。我们还表明，单向BIC伴随着避免交叉，由于导模共振与不同的横向宇称在非对称光子晶格。单向BIC的Q因子是有限的，但其在向上或向下方向上的辐射功率显著小于在相反方向上的辐射功率。我们的研究结果可能有助于工程BIC和避免交叉在不同的光子系统，支持泄漏模式。
英文摘要：
When two nonorthogonal resonances are coupled to the same radiation channel, avoided crossing arises and a bound state in the continuum (BIC) appears 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 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.
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