Patent ID: 7885506

Claim:
An apparatus comprising: a light source to provide an input light beam, a substrate having an input surface to form an in-coupled light beam by receiving light of said input light beam, wherein said in-coupled light beam is substantially polarized, and wherein light of said in-coupled light beam is confined to said substrate by total internal reflections, said substrate further comprising a plurality of out-coupling features to form an illuminating light beam by diffracting light of said in-coupled light beam out of said substrate, a display element having a plurality of reflective polarization-rotating pixels arranged to form reflected light beams by reflecting light of said illuminating light beam, and imaging optics to form an image by focusing or collimating light of said reflected light beams transmitted through said out-coupling features, wherein said out-coupling features form a diffractive grating having a sawtooth profile such that said out-coupling features have a first inclined surface, a second inclined surface, an edge portion between said first inclined surface and said second inclined surface, and a bottom portion adjacent to said first inclined surface, wherein the width of said edge portion is in the range of 0 to 25% of a grating period of said out-coupling features, the width of said bottom portion is in the range of 0 to 25% of the grating period of said out-coupling features, and a maximum angle between a local surface normal of said second inclined surface and a global surface normal of said out-coupling features is greater than 100°.