An optical diffusion film comprises a plurality of diffraction grating
cells formed on a substrate, each cell comprising a plurality of curved
gratings disposed in parallel with each other and containing the same
profile. Such film can be manufactured by embossing, using an original
plate formed by etching a photosensitive material by means of an
electronic beam exposure system to produce gratings. When such a film is
provided with a reflection layer and exposed to light coming obliquely
from above, highly bright and diffracted light is emitted in a
predetermined direction.