Grating, preparation method thereof and optical waveguide

The invention provides a preparation method of a grating. The preparation method comprises the following steps: providing a substrate base material; and preparing a mask layer with a pattern structure complementary with the target pattern structure on the surface of the substrate base material according to the target pattern structure of the grating, wherein the pattern structure comprises a convex region and a concave region. A grating layer is deposited on the surface of the side, provided with the mask layer, of the substrate base material, the grating layer is made of semiconductor materials, the grating layer is deposited in the concave area of the pattern structure of the mask layer to form the target pattern structure, and the thickness of the grating layer is smaller than that of the mask layer. The mask layer is removed by a lift-off process. The invention also provides the grating prepared by the preparation method and the optical waveguide. The preparation method of the grating provided by the inve