Waveguide assembly with virtual image focus

A head-mounted display (HMD) device wearable by a user and supporting a mixed-reality experience including full color holographic images from a virtual world that are represented with a color model and real-world images for objects in a real world, comprising:

• an imager generating one or more optical beams for the holographic images for each individual color in the color model;
• an optical combiner receiving the one or more optical beams from the imager as an input and having a plurality of waveguides including a waveguide for each individual color, in which the waveguides optically align in a planar stack to combine the individual colors into the full color holographic images when output from the optical combiner, wherein the stack of waveguides includes inter-waveguide spaces between adjacent waveguides in the stack that are interior to the optical combiner;
• and
• an exit pupil expander disposed on each of the waveguides for each individual color, the exit pupil expander comprising a plurality of diffractive optical elements (DOEs), in which the exit pupil expander is configured to provide one or more out-coupled optical beams as the output from the optical combiner having an expanded exit pupil relative to the input, and in which the DOEs are located within the inter-waveguide spaces,
• wherein the exit pupil expander includes an out-coupling DOE providing negative optical power using a plurality of grating features that are locally modulated to shift the grating features over an extent of the out-coupling DOE to cause a phase change in a −1 diffraction order to impart a spherical wavefront to the one or more out-coupled optical beams.

A method for assembling an optical combiner that is associated with a color model and utilized in a mixed-reality environment in which holographic images are mixed with real-world images, comprising:

• cutting a plurality of waveguide blanks from a sheet of planar optical substrate using a template so that each waveguide blank has a commonly shared shape;
• disposing an in-coupling diffractive optical element (DOE), an intermediate DOE, and a diffractive lensed out-coupling DOE on each of the plurality of cut waveguide blanks to form a respective plurality of exit pupil expanders, the in-coupling DOE configured to in-couple one or more optical beams corresponding to holographic images as an input to a respective exit pupil expander, the intermediate DOE configured for pupil expansion of the one or more optical beams in a first direction, and the diffractive lensed out-coupling DOE configured for pupil expansion of the one or more optical beams in a second direction and further configured to out-couple the one or more optical beams with a predetermined focal depth as an output from the exit pupil expander with expanded pupil relative to the input, in which the in-coupling DOE, intermediate DOE, and diffractive lensed out-coupling DOE are disposed on a common side of the waveguide blank, wherein the diffractive lensed out-coupling DOE provides negative optical power using a plurality of grating features that are locally modulated to shift the grating features over an extent of the out-coupling DOE to cause a phase change in a −1 diffraction order to impart a spherical wavefront to the out-coupled one or more optical beams;
• and
• forming a stack of a plurality of exit pupil expanders to provide an optical combiner, in which a number of exit pupil expanders in the stack corresponds to a number of colors utilized in the color model, in which the stack is formed to create at least one interior volume within the optical combiner, and in which the exit pupil expanders are oriented in the stack to place each of the plurality of DOEs within the at least one interior volume.