Diffusion sheet and optical system

The invention discloses a diffusion sheet and an optical system, the diffusion sheet is composed of a micro-lens array, the micro-lens array comprises a plurality of periodic structures, each periodic structure comprises N * M sub-periods, N is greater than or equal to 1, M is greater than or equal to 1, and N and M are positive integers; each sub-cycle comprises a convex surface, a concave surface, a first saddle surface and a second saddle surface; in the first direction, the first saddle surface is connected with the concave surface, and the convex surface is connected with the second saddle surface; in the second direction, the convex surface is connected with the first saddle surface, the second saddle surface is connected with the concave surface, the convex surface and the concave surface are distributed diagonally, and the first saddle surface and the second saddle surface are distributed diagonally, so that a large periodic structure is used, and the brightness and color uniformity problem caused by