Bound states in the continuum (BICs) have attracted much attention in the field of nanophotonics owing to their ability to trap photons without loss. Recently, a low-refractive-index (RI) waveguide loaded on a high-RI slab structure was demonstrated to support BICs. However, strict control of structural parameters is required due to the accidental nature of those BICs. Here, we propose a novel structure consisting of two low-RI vertically coupled waveguides loaded on a high-RI slab. This structure supports symmetry-protected BICs (SP-BICs), which do not require strict control of the geometric parameters. Such SP-BICs can also possess an infinitely high quality factor in resonant structures, which can be harnessed for ultranarrow-bandwidth spatial and spectral filters. Our work opens a new way of harnessing BICs on an integrated photonic platform for realizing nanophotonic circuits and devices.

中文翻译：

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集成光子平台上连续体中对称保护的束缚态


连续体束缚态（BIC）由于其能够捕获光子而不会丢失，因此在纳米光子学领域引起了广泛关注。最近，加载在高 RI 平板结构上的低折射率 (RI) 波导被证明可以支持 BIC。然而，由于这些 BIC 的偶然性，需要严格控制结构参数。在这里，我们提出了一种新颖的结构，由加载在高 RI 板上的两个低 RI 垂直耦合波导组成。该结构支持对称保护BIC（SP-BIC），不需要严格控制几何参数。这种 SP-BIC 还可以在谐振结构中拥有无限高的品质因数，可用于超窄带宽空间和光谱滤波器。我们的工作开辟了一种在集成光子平台上利用 BIC 来实现纳米光子电路和器件的新方法。