2D materials are promising candidates as nonlinear optical components for on-chip devices due to their ultrathin structure. In general, their nonlinear optical responses are inherently weak due to the short interaction thickness with light. Recently, there has been great interest in using quasi-bound states in the continuum (q-BICs) of dielectric metasurfaces, which are able to achieve remarkable optical near-field enhancement for elevating the second harmonic generation (SHG) emission from 2D materials. However, most studies focus on the design of combining bulk dielectric metasurfaces with unpatterned 2D materials, which suffer considerable radiation loss and limit near-field enhancement by high-quality q-BIC resonances. Here, we investigate the dielectric metasurface evolution from bulk silicon to monolayer molybdenum disulfide (MoS2${\mathrm{MoS}}_2$), and discover the critical role of meta-atom thickness design on enhancing near-field effects of two q-BIC modes. We further introduce the strong-coupling of the two q-BIC modes by oblique incidence manipulation, and enhance the localized optical field on monolayer MoS2${\mathrm{MoS}}_2$ dramatically. In the ultraviolet and visible regions, the MoS2${\mathrm{MoS}}_2$ SHG enhancement factor of our design is 105${10}^5$ times higher than that of conventional bulk metasurfaces, leading to an extremely high nonlinear conversion efficiency of 5.8%. Our research will provide an important theoretical guide for the design of high-performance nonlinear devices based on 2D materials.

中文翻译：

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通过准 BIC 的强耦合实现二次谐波增强，介电超表面从块体演化到单层

二维材料由于其超薄结构而成为片上器件非线性光学元件的有前途的候选者。一般来说，由于与光的相互作用厚度较短，它们的非线性光学响应本质上很弱。最近，人们对使用介电超表面连续体（q-BIC）中的准束缚态产生了浓厚的兴趣，它能够实现显着的光学近场增强，从而提高二维材料的二次谐波产生（SHG）发射。然而，大多数研究都集中在将体介电超表面与无图案二维材料相结合的设计上，这种材料会遭受相当大的辐射损耗，并限制高质量 q-BIC 谐振的近场增强。在这里，我们研究了从体硅到单层二硫化钼（MoS2 ）的${\mathrm{MoS}}_2$介电超表面演化，并发现了超原子厚度设计对于增强两种q-BIC模式的近场效应的关键作用。我们进一步通过斜入射操纵引入了两种q-BIC模式的强耦合，并显着增强了单层MoS 2${\mathrm{MoS}}_2$上的局域光场。在紫外和可见光区域，我们设计的MoS 2 SHG增强因子比传统体超表面高${\mathrm{MoS}}_2$10 5${10}^5$倍，从而实现5.8%的极高非线性转换效率。我们的研究将为基于二维材料的高性能非线性器件的设计提供重要的理论指导。