Tunable Second Harmonic Generation by Degenerate Quasi-BIC Metasurfaces

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Resonant metasurfaces, characterized by their compact integration and strong field localization, combined with the superior nonlinear properties of low-dimensional materials, provide a promising platform for developing more efficient and integrated nonlinear devices. Enhancing nonlinear conversion efficiency is crucial; at the same time, integrating multiple functionalities into a single compact design is also urgently demanded for versatile nonlinear optical devices. In this work, we propose a polarization-independent quasi-bound state in continuum (q-BIC) metasurface integrated with a thin layer 3R-MoS2, which enables giant enhancement of second harmonic generation (SHG), as well as full-Poincaré polarization tunability of SHG emission by precisely controlling the polarization of the fundamental wave. Our work paves the way for tailoring exceptional optical nonlinearity and tunable polarization control in nonlinear light sources.