Patent ID: 7502091

Claim:
An optical sheet comprising: an isotropic medium layer which is made of an optically isotropic medium and which has a first surface, a plurality of ridge-shaped projections formed on the first surface, arranged in a first direction and extending in a second direction intersecting at right angles to the first direction, and a third surface being smooth and opposed to the first surface, each of the projections having a cross section shaped like a segment of a circle; and an anisotropic medium layer which is made of an optically uniaxial medium and which has a second surface, and a plurality of groove-shaped recesses made in the second surface, arranged in the first direction and extending in the second direction, and a fourth surface being smooth and opposed to the second surface, each of the recesses having a cross section shaped like a segment of a circle; the isotropic medium layer and the anisotropic medium layer being laid one on the other, with the respective projections firmly fitted in the respective recesses, and the isotropic medium layer having a refractive index equal to a refractive index of the anisotropic medium layer in the first direction.