Second harmonic generation from bound-state in the continuum-hosted few-layers van der Waals metasurface

Monolayer transition metals dichalcogenides (TMDs) have been coupled to bound-state in the continuum (BIC) hosted dielectric structures to attain high second harmonic generation (SHG). However, the transvers electric modes are strongly localized in the waveguides result in fairly weak exciton-photon coupling in monolayer TMD placed on the surface. To achieve SHG in few-layers TMDs based BIC-inspired structure is a challenge. Here, we report BIC in few-layers TMDs metasurface with high quality factor (Q-factor), tunability, and modes-upholding in different environments. The metasurface sustains BIC at different thickness of the meta-atoms, which is highly desired for maintaining the accuracy in fabrications. Next, we calculate the SHG efficiency from few-layers TMD metasurface around BIC wavelengths. The high conversion efficiency in this work is 1.47 10-4 for 6 mW incident power. Moreover, our design is highly thin and can be used for various linear and non-linear applications in optics. This study will provide a new route to next generation post-silicon metasurfaces..