Optical display system and augmented reality electronic device

An optical display system, comprising:

• a waveguide,
• an input coupler, which is provided at the input end of the waveguide and couples an image light into the waveguide;
• and
• a two-dimensional grating, which is provided at the output end of the waveguide,
• wherein the waveguide delivers the image light coupled by the input coupler to the two-dimensional grating, and the two-dimensional grating performs pupil expansion on the image light and out-couples the expanded image light,
• wherein the two-dimensional grating has rhombus lattices,
• wherein a plurality of unit cells of the two-dimensional grating are un-symmetric along respective axes parallel with a propagation direction of the image light incident onto the two-dimensional grating, from a top view of the two-dimensional grating, and
• wherein the plurality of unit cells are oriented with the propagation direction of the image light and each of the plurality of unit cells has at least two vertexes at its end side.