US Patent 10156681 Waveguide grating device

An optical waveguide display comprises: a waveguide; a source of light modulated with temporally-varying angularly-distributed information; a fold grating providing a first beam expansion; an input coupler for directing light into total internal reflection paths in a first propagation direction; and an output grating for providing a second beam expansion and extracting light from the waveguide. The input light undergoes at least two diffractions within the fold grating, each diffraction directing light into a unique total internal reflection angular range along a second propagation direction.