An optical waveguide extends vertically within the interior of an IC-like structure to route optical signals between horizontal waveguides in different layers of horizontal optical interconnects. A light reflecting structure is positioned at the intersection of the horizontal and vertical waveguides to reflect the light. Multiple horizontal waveguides may join the vertical waveguide at a common intersection, to form a beam splitter or a beam combiner. Optical signals from one horizontal waveguide are diverted within the IC-like structure into another horizontal or vertical waveguide. The waveguide is formed with a light reflective structure at an intersection of the horizontal and vertical waveguides, and the waveguide is completed using damascene fabrication techniques.