Patent ID: 8369016

Claim:
An optical sheet, comprising: a plurality of optical anisotropic films mutually stacked on one another, each of the optical anisotropic films having a plurality of main axis refractive indexes nx, ny and nz, wherein the main axis refractive indexes nx and ny of each optical anisotropic film are in-plane main axis refractive indexes, and the main axis refractive index nz of each optical anisotropic film is a thickness-wise refractive index, the main axis refractive index nx of each optical anisotropic film is a minimum or a maximum among the main axis refractive indexes nx, ny and nz of the optical anisotropic film, and each of the optical anisotropic films has an optical axis, and a direction of the optical axis is substantially the same to the main axis direction of the main axis refractive index nx, wherein the optical axes of the optical anisotropic films mutually stacked on one another sequentially rotate along a predetermined rotation direction in a thickness direction of the optical anisotropic films, and a total rotation angle of the stack is substantially greater than or equal to 360 degrees; an included angle is formed between the optical axes of two adjacent optical anisotropic films, and the included angle of any two adjacent optical anisotropic films is less than or equal to 90 degrees; when the total rotation angle of the optical axes rotating along a thickness direction of the optical anisotropic films is equal to 360 degrees, a sum of thicknesses of the optical anisotropic films forms a pitch, and the optical anisotropic films of the pitch are capable of reflecting a polarized light with a specific wavelength satisfying an equation of [(an extraordinary refractive index of the optical anisotropic film+an ordinary refractive index of the optical anisotropic film)/2]×the pitch; and the thicknesses of the optical anisotropic films in the optical sheet are sequentially increased or decreased along a thickness direction of the optical sheet, and the included angles between the optical anisotropic films of the optical sheet are accordingly increased or decreased.