Grating and optical device

An optical device, comprising a polarizer and a grating, wherein the grating is disposed at one side of the polarizer, a first grating layer is farther away from the polarizer than a second grating layer, and a polarization state of the polarizer is a transverse magnetic (TM) polarization state, wherein the grating at least comprises:

• a first grating layer comprising first grating portions and second grating portions that are alternately arranged at regular intervals, wherein a refractive index of each of the first grating portions is greater than a refractive index of each of the second grating portions, and a cross-sectional shape of each of the first grating portions is a first trapezoid;
• and
• a second grating layer disposed at one side of the first grating layer, wherein the second grating layer comprises third grating portions and fourth grating portions that are alternately arranged at regular intervals, a refractive index of each of the third grating portions is greater than a refractive index of each of the fourth grating portions, at least part of each of the third grating portions is aligned with each of the first grating portions, a cross-sectional shape of each of the third grating portions is a second trapezoid, and a long base of the second trapezoid is away from the first grating portions;
• wherein the first trapezoid and the second trapezoid each are an isosceles trapezoid, and at least one of an angle between a long base of the first trapezoid and a leg of the first trapezoid or an angle between the long base of the second trapezoid and a leg of the second trapezoid is greater than 80°, and
• wherein an orthographic projection of a long base of the first trapezoid on a plane where the long base of the second trapezoid is located at least partially overlaps the long base of the second trapezoid;
• or the orthographic projection of the long base of the first trapezoid on the plane where the long base of the second trapezoid is located is spaced apart from the long base of the second trapezoid.