Defect-insensitive bound states in the continuum in antisymmetric trapezoid metasurfaces in the visible range.

Symmetry-protected bound states in the continuum (SP-BIC) enable flexible tuning of the wavelengths and linewidths of high-Q resonances, showing great potential in high-performance photonic devices. However, the implementation of SP-BIC at shorter wavelengths, such as in the visible range, requires precise control of smaller feature sizes, which imposes stringent fabrication requirements. This trade-off between geometric accuracy and manufacturing complexity limits the practical application of SP-BIC metasurfaces. This work presents a defect-insensitive design strategy for SP-BIC metasurfaces by constructing position-detuned arrays composed of periodically arranged antisymmetric trapezoidal unit cells. Theoretical studies show that under x-polarized incidence, the dominant resonance mode is a magnetic dipole, with electric fields strongly enhanced in the inter-pillar gap rather than inside the structures body. This field distribution provides high robustness against geometric deformation. The geometric dependence of this mode under x-polarized light is approximately 1/10 to 1/20 that of the electric dipole-dominated mode under y-polarized light, and the design is demonstrating strong tolerance to typical fabrication defects encountered in nanofabrication. Experimental validation is being conducted using metasurfaces fabricated with intentional defects. Overall, this work is offering a practical, fabrication-tolerant approach to realizing high-performance dielectric BIC metasurfaces.