Chiral metasurfaces in anisotropic thin film lithium niobate and its nonlinear effect
Xianpeng Lv, Shuyao Wu, Ziping Tian, Yang Li, Tiefeng Yang, Wentao Qiu, Heyuan Guan, Huihui Lu
Abstract
Different from conventional two-dimensional photonic metasurfaces, chiral photonic metasurfaces, which are composed of a chiral pattern with subwavelength dimensions, exhibit different chiroptical physical phenomena, such as spin-preserving, nonlinear chiroptical effects, and optical vortex generation. However, the effect of symmetry in the vertical direction on the linear and nonlinear response of the chiral quasi-two-dimensional metasurface has been seldom reported. In this study, we design and simulate a chiral metasurface using topological patterns in lithium niobate (LN) thin film to obtain the optimal circular dichroism and its corresponding nonlinear effect. Triangular holes with a certain rotation constitute a quasi-two-dimensional metasurface, which possesses outstanding chirality for the spin state of light, thus allowing it to control linear and nonlinear chiralities. The nonlinear conversion efficiency η SHG reaches 2×10 −4 and 4×10 −3 on the LN structure with substrate and without substrate, respectively. Nonlinear circular dichroism CD SHG is 5.8 dB at 783 nm on a SiO 2 substrate. This tunable chiral metasurface is expected to be applicable to nonlinear chiroptical responses and chiral light modulation.