Transparent waveguide display

An apparatus for displaying an image comprising:

• an input image node providing image modulated light, the image modulated light including image content associated with at least a portion of a display field of view;
• a beam expander comprising:
• an expander optical substrate;
• one or more first expander input Bragg gratings to couple the image modulated light into one or more waveguide layers of the expander optical substrate for propagation along a first direction;
• and
• one or more expander output Bragg gratings in the one or more waveguide layers of the expander optical substrate, wherein the one or more expander output Bragg gratings extend along the first direction to progressively extract portions of the image modulated light out of an output face of the expander optical substrate, wherein the one or more expander output Bragg gratings have increasing diffraction efficiency along the first direction to provide uniform extraction of the image modulated light out of the output face of the first expander optical substrate along the first direction;
• a display substrate comprising:
• a display optical substrate;
• one or more display input Bragg gratings in the display optical substrate configured to couple the image modulated light from the beam expander into one or more waveguide layers of the display optical substrate and to propagate the image modulated light along a third direction perpendicular to the first and second directions;
• and
• one or more display output passive-mode switchable Bragg gratings in the one or more waveguide layers of the display optical substrate, wherein the one or more display output passive-mode switchable Bragg gratings extend along the third direction to progressively extract portions of the image modulated light along the third direction out of an output face of the display optical substrate, wherein the one or more display output passive-mode switchable Bragg gratings have increasing diffraction efficiency along the third direction to provide uniform extraction of the input light out of the output face of the display optical substrate along the third direction, wherein the one or more display output passive-mode switchable Bragg gratings direct the image modulated light along angles associated with the at least a portion of the display field of view, wherein the image modulated light from the one or more display output passive-mode switchable Bragg gratings is linearly polarized.