An optical device or display is disclosed for use in an augmented reality or virtual reality device. The display includes a waveguide (2), an output element (4) and a plurality of input diffraction gratings (6, 8, 10, 12). Light from a plurality of projectors (16, 18, 20, 22) is diffracted by the input gratings (6, 8, 10, 12) so that it is coupled into the waveguide (2) by total internal reflection. The input gratings (6, 8, 10, 12) are provided in a staggered configuration in relation to the output element (4), with respect to a y-axis. Each input grating is adjacent another input grating that has a different separation distance from the output element (4). This can improve the evenness of illumination from the output element (4).