Broad-angle third-order nonlinear generation via Brillouin zone folding in an all-dielectric metasurface

Brillouin zone folding (BZF) has emerged as an effective mechanism to achieve guided-mode resonances (GMRs) with high quality (Q) factors in momentum space, offering a feasible approach for wide-angle nonlinear conversions. Nevertheless, exploring high-efficiency nonlinear effects driven by multiple pump beams across a wide angular range remains challenging. In this work, we theoretically demonstrate double ultrahigh Q GMRs via BZF in an all-dielectric metasurface and achieve high-efficiency degenerate four-wave mixing (dFWM) and third-harmonic generation (THG) across a wide angular range. The theoretical nonlinear conversion efficiencies for both THG and dFWM remain nearly constant with the incident angle changing from 0° to 10°. Moreover, the BZF-based dual GMRs system also exhibits wide-angle high-efficiency dFWM under different perturbations. This work proposes a strategy for developing high-performance wide-angle nonlinear on-chip photonic devices and offers a practical pathway for the integration and advancement of nonlinear optical components in real-world applications.