Waveguide light multiplexer using crossed gratings

A waveguide comprising:

• a single substrate configured to propagate light within the waveguide by total internal reflection (TIR) as the light internally reflects off of opposite major surfaces of the single substrate;
• and
• an optical element on the substrate, the optical element arranged to multiplex, in at least a first direction and a second direction that is substantially perpendicular to the first direction, the light that is propagating in the waveguide while incoupling the light into the waveguide or outcoupling at least a portion of the light from the waveguide, the optical element comprising:
• a first arrangement of one or more first diffraction gratings disposed on a major surface of the substrate, wherein the one or more first diffraction gratings are arranged to cause the light propagating in the waveguide to be multiplexed in the first direction;
• and
• a second arrangement of one or more second diffraction gratings disposed over and overlapping the one or more first diffraction gratings on a same side of the substrate such that the one or more first diffraction gratings are substantially between the substrate and the one or more second diffraction gratings without another waveguide interposed between the one or more first diffraction gratings and the one or more second diffraction gratings,
• wherein the one or more second diffraction gratings are arranged to cause the light propagating in the waveguide to be multiplexed in the second direction that is different than the first direction, wherein the first and second directions are different lateral directions that are substantially parallel to the major surface of the waveguide and that are substantially perpendicular to each other, and
• wherein the first direction is substantially perpendicular to the second direction to cause the light propagating in the waveguide to be multiplexed in the substantially perpendicular first and second directions within the same waveguide.