A waveguide comprises a first surface and a second surface. The first surface comprises a first plurality of grating structures. The first surface other than the first plurality of grating structures comprises a first reflective layer. The second surface comprises a second reflective layer. The waveguide is configured to guide an in-coupled light beam to undergo reflections between the first reflective layer and the second reflective layer. The first plurality of grating structures are configured to disrupt the reflections to cause at least a portion of the in-coupled light beam to couple out of the waveguide and project from the first surface, the portion of the in-coupled light beam coupled out of the waveguide forming out-coupled light beams.