The present invention has been disclosed to extend input light in two dimensions in an augmented reality display. The device comprises a wave guide 12 and three linear diffraction gratings H0, H1, H2. An incident beam from the projector illuminates the input grating H0 as poly chromatic light, which is coupled to a waveguide 12 . The other two gratings H1 and H2 are superimposed on top of each other. Light may be diffracted in a first diffracted order by one grating H1 and towards another grating H2 which may couple the light out of the waveguide towards a viewer. In yet another way, the crossed gratings H1, H2 may be replaced by a photonic crystal having a regular arrangement of pillars 20 creating a number of effective diffraction gratings.
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