BAE Systems PLC
OPTICAL WAVEGUIDE

Abstract:

An optical waveguide for a head up display is disclosed. The optical waveguide is configured to provide pupil expansion in two dimensions and having an input end and an output end and a first axis substantially parallel to the direction of propagation of light in the waveguide and substantially parallel with a direction from the input end to the output end. The optical waveguide comprising: an input region at the input end; a beam splitter configured to expand light received from the input region; a symmetrical diffraction grating comprising complementary first and second grating portions, wherein the second grating portion is substantially symmetrical to the first grating portion along a line of symmetry that is substantially parallel to the first axis. Light received at the symmetrical diffraction grating from the beam splitter is configured to be diffracted by the symmetrical diffraction grating towards the line of symmetry by the first grating portion or the second grating portion. Light received at the first grating portion from the second waveguide portion is configured to be diffracted out of the waveguide at the output end. Light received at the second grating portion from the first grating portion is configured to be diffracted out of the waveguide at the output end.