Spin-selective high-numerical-aperture edge detection via detuned quasi-BIC and generalized Kerker effect

Optical analog computing has garnered significant attention due to its potential in real-time, high-throughput image processing. However, existing image processing approaches are constrained by the trade-off between numerical aperture and transmission efficiency. To address this, we propose a transmissive metasurface capable of performing isotropic second-order spatial differentiation with a high numerical aperture (NA = 0.34) and over 53% peak cross-polarization conversion efficiency. By exploiting the detuned quasi-BIC and generalized Kerker effect, we intentionally introduce a spectral offset between electric and magnetic dipole resonances. This strategy smooths the phase dispersion in momentum space, ensuring resonant modes are suppressed at normal incidence (maintaining a dark background) while evolving to satisfy the first Kerker condition (|ED| ≈ |MD|) strictly at oblique incidence. Our work effectively overcomes the trade-off between numerical aperture and efficiency, laying the foundation for compact, high-performance edge detection systems in the microwave and millimeter-wave bands.