A display (for example, a head up display (HUD)) includes a substrate waveguide. The substrate waveguide can act as a combiner. The substrate waveguide receives collimated light an input and provides the collimated light to an output. The collimated light travels from the input to the output within the substrate waveguide by total internal reflection. An input diffraction grating is disposed in the first area at the input and an output diffraction grating is disposed in the second area at the output. A plate covers at least a portion of the second area. The plate can protect the diffraction grating and reflect transmitted order light from the diffraction grating to improve efficiency.