Patent ID: 7317572
Filing Date: 2008-01-08
Classification: G03B

Abstract:
1. A Fresnel lens sheet of total-reflection type comprising: a flat base part; a plurality of prisms formed on an entrance surface of the base part, each of the prisms having a refraction facet that refracts light rays fallen thereon and a total-reflection facet that totally reflects light rays fallen thereon; a plurality of V grooves formed in an exit surface of the base part; and a plurality of wedge-shaped light absorbing parts embedded in the V grooves, respectively, the light absorbing parts having a refractive index lower than that of the base part; wherein at least some of the light rays refracted and totally reflected by prisms are reflected by the inclined surfaces that are interfaces between the base part and the light absorbing parts embedded in the grooves of the base part, so that light rays travel outside through regions of the exit surface of the base part the regions being placed between adjacent light absorbing parts, and wherein two inclined surfaces of each of the light absorbing parts are symmetrical with respect to a direction perpendicular to the base part, and a condition expressed by: where N 1 is a refractive index of the light absorbing parts, N 2 is a refractive index of the base part, D is a depth of the light absorbing parts (length along a thickness of the base part), and W 1 is a width of the light absorbing parts (length on the exit surface of the base part along a direction perpendicular to a direction in which the light absorbing parts extend), is satisfied.