Transparent waveguide display with passive expander input bragg gratings with different angular diffraction efficiencies

An apparatus for displaying an image comprising:

• an input image node providing image modulated light from an image plane, the image modulated light including image content associated with at least a portion of a display field of view;
• one or more projection lenses to collimate the image modulated light with different propagation directions based on position in the image plane;
• two or more beam expanders, each comprising:
• an expander optical substrate;
• two or more passive expander input Bragg gratings with different angular diffraction efficiencies to selectively couple portions of the image modulated light into one or more waveguide layers of the corresponding expander optical substrate for propagation along a first direction;
• and
• one or more passive expander output Bragg gratings in the one or more waveguide layers of the expander optical substrate, wherein the one or more passive 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 passive 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;
• and
• two or more display substrates, each comprising:
• a display optical substrate;
• one or more passive display input Bragg gratings in the display optical substrate configured to couple the image modulated light from one of the two or more beam expanders into one or more waveguide layers of the corresponding display optical substrate and to propagate the image modulated light along a second direction perpendicular to the first direction;
• and
• one or more passive display output Bragg gratings in the one or more waveguide layers of the display optical substrate, wherein the one or more passive display output Bragg gratings extend along the second direction to progressively extract portions of the image modulated light along the second direction out of an output face of the display optical substrate, wherein the one or more passive display output Bragg gratings have increasing diffraction efficiency along the second direction to provide uniform extraction of the input light out of the output face of the display optical substrate along the second direction, wherein the one or more passive display output Bragg gratings direct the image modulated light along angles associated with the at least a portion of the display field of view.