Hybrid MetasurfaceBased on Si₃N₄ Nanopillar for Optical Sensingwith Dual Channels

Bound states in the continuum (BICs) are localized states decoupled from radiation, which has attracted widespread interest and found diverse applications in nanosystems. BIC can be categorized into symmetry-protected BIC (SP-BIC) and accidental BIC based on different decoupling conditions. Compared with the SP-BIC, which is realized mainly by controlling one geometry parameter called the asymmetry factor, the realization of accidental BIC is manipulated by tuning the photonic mode coupling, which has more factors that can influence its construction, larger difficulty in system design, and fewer reports in application explorations. In our study, we build an accidental BIC nanosystem, which is the metasurfaces made by the periodic Si₃N₄ nanopillars of H-shape and systematically investigated their refractive index (RI) sensing performances based on both wavelength shifting and intensity variation. We also demonstrated the great potential of our dual-channel sensor in biodetection. Experimentally, the obtained sensitivity based on wavelength shifting is 501 nm/RIU, which is larger than most of the recent works about the RI BIC sensors of the visible spectral region in the all-dielectric or dielectric–metallic nanosystems. Also, the intensity-based sensitivity of our sensor has reached 9.35 × 10⁴ counts/RIU. Our findings not only further the understanding of mode coupling in BIC systems but also introduce an innovative sensing methodology, offering perspectives for high-sensitivity optical sensing applications.