Ultrahigh-Q spin-selective dual quasi-BIC resonances in ultraviolet dielectric metasurfaces

초록

Ultraviolet (UV) dielectric metasurfaces featuring ultrahigh-quality-factor (high-Q) resonances are essential for advanced applications such as biosensing, nonlinear optics, and spectral filtering. However, achieving high-Q resonances in the UV range remains a significant challenge due to inherent material limitations and fabrication complexities. In this study, we introduce a single-layer UV metasurface comprising wide-bandgap silicon nitride (SiNx) cross-shaped nano-resonators that support spin-selective, dual quasi-bound states in the continuum (q-BICs). By breaking in-plane symmetry, a symmetry-protected mode is split into two distinct resonances-each selectively excited by left- and right-handed circularly polarized light-resulting in near-unity circular dichroism (CD) and Q-factors exceeding 103. These resonances can be tuned through geometric design, angular rotation, and modulation of the surrounding analyte's refractive index, all while preserving their high-Q characteristics. Notably, angular perturbation enhances the Q-factor from approximately 693 to 1875 by effectively controlling radiation leakage. Furthermore, analyte layers with dielectric constant ranging from 1.00 to 1.20 induce resonance shifts of approximately 10-12 nm, enabling independent tuning of both CD and Q. This fabricationcompatible platform presents a promising pathway toward next-generation UV chiral photonic technologies, including ultrasensitive biosensors, low-threshold lasers, and nonlinear optical devices.

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