Patent ID: 8654420

Claim:
A waveguide for a projection display for displaying an image to an observer, comprising: a substrate of light transmissive material having two opposed substantially parallel faces, the substrate of light transmissive material being arranged to transmit light within the substrate of light transmissive material, between the parallel faces, under total internal reflection, the substrate of light transmissive material having a critical angle required for total internal reflection and the substrate of light transmissive material being arranged to allow the observer to view a forward scene through the substrate of light transmissive material; an output grating element arranged within the substrate of light transmissive material to diffract a portion of light incident thereon out of the substrate of light transmissive to allow light exiting the substrate of light transmissive material to be viewed by the observer overlaid on the forward scene viewed through the substrate of light transmissive material and to allow a remainder of the light to be transmitted within the substrate of light transmissive material under total internal reflection; and an optical layer arranged on each of the parallel faces, the optical layer being arranged to reduce the critical angle required for total internal reflection of light within the substrate of light transmissive material to increase a number of interactions between light transmitted within the substrate and the output grating element.