Twist-angle-engineered nonlinear optics in 3R-MoS2/BIC-metasurface heterostructures

Low-dimensional van der Waals (vdW) materials have emerged as a promising candidate for nonlinear optics due to their large nonlinear conversion efficiency. Integrating vdW materials with resonant metasurfaces can further enhance light-matter interactions and enable even stronger nonlinear optical responses. However, the pivotal role of the twist angle in determining the symmetry of vdW material/metasurface heterostructures remains illusive, which hinders the maximization of nonlinear responses, let alone the modulation of nonlinear optical fields in situ. Here we demonstrate twist-angle-engineered second harmonic generation by stacking layered 3R-MoS2 on a resonant bound state in the continuum metasurface. The interlayer coupling can be flexibly manipulated via twist angles, leading to the nonlinear conversion efficiency tuned from vanishing to the maximum (150-fold enhancement) and the second harmonic polarization modulated on the Poincaré sphere. Our work provides a general recipe for nonlinear twist-optics, paving the way towards next-generation nonlinear photonic devices.