1. A display system comprising: an optical waveguide having an incoupling grating, an intermediate grating and an exit grating; and a light engine configured to generate multiple input beams, each beam being substantially collimated and directed to the incoupling grating in a unique inward direction, whereby the multiple input beams form a virtual image image; wherein the intermediate and exit grating have widths substantially larger than the beams' diameters; wherein the incoupling grating is arranged to couple each beam into the intermediate grating, in which that beam is guided onto a splitting region of a first surface of the intermediate grating; wherein the intermediate grating comprises a second surface opposing the first surface and is arranged to split that beam at the splitting region to provide two versions of that beam which are coupled into the exit grating; whereby the two versions of that beam take respective optical paths between the splitting region before being incident on the exit grating at respective angles, said respective angles having an angular variation less than or equal to 0.5 miliradian, and beam footprints of the two versions of that beam partially overlap on the exit grating; wherein the exit grating is arranged to diffract the two versions of that beam outwardly, the multiple input beams thus causing multiple exit beams to exit the waveguide which form a version of the virtual image; and wherein the first surface and/or the second surface comprise surface variations arranged to introduce an optical path length difference between the respective optical paths such that a visible banding effect is eliminated from the version of the virtual image.