One example relates to an optical engine comprising an optical waveguide. The optical waveguide can comprise a total internal reflection (TIR) edge to change direction of an optical light beam to an angle parallel to a top surface and a bottom surface of the optical waveguide. The optical waveguide can also comprise a plurality of aligning holes extending from the top surface to the bottom surface of the optical waveguide. The optical engine can comprise a substantially transparent slab underlying the optical waveguide. The slab can also comprise a micro lens to collimate the optical light beam. The slab can further comprise a plurality of aligning pins extending perpendicular from a top surface and bottom surface of the slab. Each of the plurality of aligning pins can extend through a respective one of the plurality of aligning holes.