Bound states in continuum (BICs) are believed to have the ability to achieve high quality factor (Q$Q$ factor) resonances, which is very important for plasmonics. However, the study of plasmonic BICs is not sufficient. Herein, we design and fabricate a metal−insulator−metal (MIM) metasurface and demonstrate a one-dimensional plasmonic BIC experimentally. The even-order localized surface plasmon resonance (LSPR) modes have even parity at normal incidence. The symmetry-protected BIC can be achieved at Γ$\mathrm{\Gamma }$ point. The band structure can be tuned by strong coupling between the localized plasmonic resonance and plasmonic lattice mode. Interestingly, two of the hybrid modes are also BICs. Although BICs cannot interact with the far field, we successfully demonstrate BIC splitting through far-field excitation. By further tuning the pitch of the MIM grating, the Friedrich–Wintgen BIC is also observed. Finally, we propose and preliminarily demonstrate an ultrathin bandpass spatial filter. These findings provide a new platform to study optical multipole BICs and can have applications in fields such as nano lasers, ultrasensitive sensors, filters, nonlinearity enhancement, and quantum optics.

中文翻译：

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连续体中等离子体束缚态的相互作用

连续体中的束缚态 (BIC) 被认为具有实现高质量因子（Q$Q$因子）共振的能力，这对于等离子体非常重要。然而，等离子体 BIC 的研究还不够充分。在此，我们设计并制造了一个金属-绝缘体-金属 (MIM) 超表面，并通过实验展示了一维等离子体 BIC。偶数阶局部表面等离子体共振 (LSPR) 模式在垂直入射时具有偶校验。对称保护的 BIC 可以在Γ处实现$\mathrm{\Gamma }$观点。可以通过局部等离子体共振和等离子体晶格模式之间的强耦合来调整能带结构。有趣的是，其中两种混合模式也是 BIC。尽管 BIC 无法与远场相互作用，但我们通过远场激发成功展示了 BIC 分裂。通过进一步调整 MIM 光栅的间距，还可以观察到 Friedrich-Wintgen BIC。最后，我们提出并初步展示了一种超薄带通空间滤波器。这些发现为研究光学多极 BIC 提供了一个新平台，并可在纳米激光器、超灵敏传感器、滤波器、非线性增强和量子光学等领域得到应用。