Waveguide for augmented reality or virtual reality display

A method of manufacture of a waveguide for an augmented reality or virtual reality display, comprising steps of:

• providing a plurality of optical structures in a photonic crystal;
• arranging the plurality of optical structures in an array to provide two diffractive optical elements overlaid on one another in or on the waveguide, wherein each of the two diffractive optical elements is configured to receive light from an input direction and couple it towards the other diffractive optical element which can then act as an output diffractive optical element, providing outcoupled orders towards a viewer;
• and
• providing the plurality of optical structures with different respective cross sectional areas, for a cross section parallel to a plane of the waveguide, at different positions in the array in order to provide different diffraction efficiencies at different positions in the array, wherein the respective cross sectional areas of the plurality of optical structures are variable in the direction of a first axis which is parallel to the input direction,
• wherein each of the plurality of optical structures is a parallelogram shaped optical structure that includes a first notch at a first side of the parallelogram shaped optical structure and a second notch at a second side of the parallelogram shaped optical structure.