Patent ID: 8160411
Filing Date: 2012-04-17
Classification: G02B

Abstract:
1. A device comprising a substantially planar waveguiding substrate, an input grating to couple an input beam into said substrate to form an in-coupled light beam, a crossed grating to provide sub-beams by diffracting light of said in-coupled light beam, and an output grating to couple light of said sub-beams out of said substrate in order to provide an output beam, wherein the light of said in-coupled light beam is adapted to interact with said crossed grating two or more times, interaction at a first location providing a first sub-beam and a second sub-beam, said first sub-beam and said second sub-beam propagating in different directions, an interaction of said second sub-beam with said crossed grating at a second location providing a third sub-beam propagating in the same direction as said first sub-beam, said output beam being adapted to have substantially the same direction as said input beam, said input grating comprising substantially linear diffractive features having a grating period d 0 , said crossed grating comprising further diffractive features arranged along lines of a first set of substantially parallel lines, said further diffractive features being also arranged along lines of a second set of substantially parallel lines, the lines of said first set being perpendicular to the lines of said second set, said first set having a first grating period d 1 , said second set having a second grating period d 2 , the lines of said first set having an angle ρ with respect to the substantially linear features of said input grating, said angle ρ being in the range of 30 to 60 degrees, a constant A 0 being in the range of 1.8 to 2.2, said first grating period d 1 fulfilling a condition d 0 =A 0 d 1 sinρ, and said second grating period d 2 fulfilling a condition d 0 =A 0 d 2 cosρ.