Merging Bound States in the Continuum at Off-High Symmetry Points

• Published in: Physical review letters 2021-03, Vol.126 (11), p.117402-117402, Article 117402
• Main Authors: Kang, Meng, Zhang, Shunping, Xiao, Meng, Xu, Hongxing
• Format: Article
• Language: English
• Subjects: Beam steering; Photonic crystals; Q factors
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.126.117402

Bound states in the continuum (BICs) confine resonances embedded in a continuous spectrum by eliminating radiation loss. Merging multiple BICs provides a promising approach to further reduce the scattering losses caused by fabrication imperfections. However, to date, BIC merging has been limited to only the Γ point, which constrains potential application scenarios such as beam steering and directional vector beams. Here, we propose a new scheme to construct merging BICs at almost an arbitrary point in reciprocal space. Our approach utilizes the topological features of BICs on photonic crystal slabs, and we merge a Friedrich-Wintgen BIC and an accidental BIC. The Q factors of the resulting merging BIC are enhanced for a broad wave vector range compared with both the original Friedrich-Wintgen BIC and the accidental BIC. Since Friedrich-Wintgen BICs and accidental BICs are quite common in the band structure, our proposal provides a general approach to realize off-Γ merging BICs with superhigh Q factors that can substantially enhance nonlinear and quantum effects and boost the performance of on-chip photonic devices.