Giant Nonlinear Circular Dichroism from High <i>Q</i>‐Factor Asymmetric Lithium Niobate Metasurfaces
Qingsong Liu, Bo Cheng, Minghao Chao, Wenjing Zhang, Yun Xu, Guofeng Song
Abstract
Abstract Lithium niobate (LN) is a good nonlinear material with a large second‐order nonlinear polarization coefficient and low optical loss in the UV to mid‐infrared spectral regions. By combining bound states in the continuum (BICs) with chirality, a high conversion efficiency and strong second‐harmonic circular dichroism (SHG‐CD) can be achieved. The simulated results show that the SHG conversion efficiency can reach 1.35 × 10 −2 % for a peak‐pump intensity of ≈5.3 GW cm −2 in the near‐infrared, and the SHG‐CD can reach 0.98 by introducing a two‐layer structure. Quasi‐BICs are introduced to study nonlinear CD, which provide new insights for the further implementation of spin‐dependent nonlinear applications.