Abstract: The present application relates to a nonlinear optical crystal structure, a preparation method thereof and an optical device. The nonlinear optical crystal structure includes a plurality of material layers stacked in a direction perpendicular to a two-dimensional plane thereof. Each of the material layers has a crystal structure with y-fold rotational symmetry, and has a predetermined lattice direction parallel to the two-dimensional plane, where y is an integer in a range from 1 to 20. Adjacent material layers have a nonzero twist angle therebetween, and the twist angle is an angle between the predetermined lattice directions of the adjacent material layers.

Abstract: A nonlinear optical crystal structure is provided. The nonlinear optical crystal structure includes a plurality of two-dimensional material films, wherein the plurality of two-dimensional material films are stacked in a direction perpendicular to a two-dimensional plane thereof, and two-dimensional material films adjacent to each other are bonded by van der Waals forces, each of the plurality of two-dimensional material films is a crystal with a center-inversion-asymmetric crystal structure, and has a predetermined lattice orientation parallel to the two-dimensional plane in a direction parallel to the two-dimensional plane, there is a non-zero twist angle between the two-dimensional material films adjacent to each other, and the twist angle is an included angle between predetermined lattice orientations of the two-dimensional material films adjacent to each other in the same two-dimensional plane, and a thickness of each of the plurality of two-dimensional material films is greater than 5 nm.