1. A waveguide apparatus, comprising: a planar waveguide having a first end, a second end, a first face, and a second face; and a plurality of diffractive optical elements operatively coupled to the planar waveguide, wherein the first and second ends of the planar waveguide are opposed to each other along a length of the planar waveguide, wherein the first and the second faces of the planar waveguide form an at least partially internally reflective optical path along a portion of the length of the planar waveguide, and wherein each diffractive optical element of the plurality is configured to interrupt the at least partially internally reflective optical path to provide a respective plurality of optical paths between an exterior and an interior of the planar waveguide via the first face thereof at respective positions along a portion of the length of the planar waveguide.