Mid-infrared band multi-Fano resonance-based sensing of high-Q concave-convex arrays of metasurface with full control of Fano spectral profile

In this study, a concave-convex array metasurface with a height difference characterized structure is proposed, combining in-plane and out-of-plane asymmetry to achieve a high Q-factor, refractive index sensing, and full control of the Fano spectral profile. Notably, both the concave model and the convex model, can only produce one Fano peak. But it can yield multiple Fano resonance peaks in the mid-infrared band following a simple combination. Herein, we have performed both near-field and far-field analysis for each Fano resonance generation. The designed metasurface achieves a remarkably high Q-factor of 9.63637 × 10⁵. Moreover, it exhibits excellent reflection resonances under different polarization directions. In terms of refractive index sensing, the designed metasurface attains a sensitivity of 600 nm/RIU under TE polarization, while under TM polarization, it achieves full control of the Fano spectral profile by changing the incidence angle. The integration of periodic arrays with height differences in metasurfaces shows tremendous potential in controlling the Fano spectral profile and enhancing sensing capabilities. Additionally, this study will provide new inspirations for the sensing metasurface design with high optical performance.