2D pupil expander using holographic Bragg grating

A method comprising:

• obtaining a waveguide;
• exposing the waveguide to electromagnetic radiation to create a first plurality of gratings of an output element, wherein:
• the first plurality of gratings are defined by grating vectors, and
• the grating vectors of the first plurality of gratings have an orientation in a first direction;
• and
• exposing the waveguide to electromagnetic radiation to create a second plurality of gratings of the output element, wherein:
• the second plurality of gratings are defined by grating vectors, and
• the grating vectors of the second plurality of gratings have an orientation in a second direction, different from the first direction.

A device comprising:

• a waveguide configured to guide light from an input element to an output element;
• the input element is configured to couple light from a source into the waveguide;
• and
• the output element is configured to out couple light from the waveguide, the output element comprising a super grating, wherein:
• the super grating comprises a plurality of gratings;
• the plurality of gratings are oriented in the same direction;
• and
• each grating of the plurality of gratings varies spatially so that the super grating has a first set of pitches at a first location and a second set of pitches at a second location.