Waveguide for augmented reality or virtual reality display

A waveguide (6) for an augmented reality or virtual reality display, comprising: a waveguide substrate layer (110) having a planar surface (112); and a plurality of optical structures (120) extending into or out of the planar surface; wherein the plurality of optical structures are arranged in an array to provide at least one diffractive optical element (2) in the waveguide, and the at least one diffractive optical element is configured to receive light from an input direction (141) in the plane of the waveguide and to diffract a portion of the received light out of the waveguide towards an observer; wherein, in a plane defined by an input direction (141) and a direction (142) perpendicular to the planar surface (112), at least one of the optical structures has a cross-section comprising a top edge (121), a first side edge (122) extending from the planar surface (112) to a leading end of the top edge (121), and a second side edge (123) extending from the planar surface (112) to a leading end of the top edge (