Chiral metasurfaces in anisotropic thin film lithium niobate and its nonlinear effect

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 ηSHG reaches 2×10−4 and 4×10−3 on the LN structure with substrate and without substrate, respectively. Nonlinear circular dichroism CDSHG is 5.8 dB at 783 nm on a SiO2 substrate. This tunable chiral metasurface is expected to be applicable to nonlinear chiroptical responses and chiral light modulation.