A method and an apparatus providing an optical interconnection in an integrated circuit die. In one embodiment, an optical interconnection is used to optically interconnect a waveguide-based optical modulator through the insulating layer and back side of the semiconductor substrate of the integrated circuit die. In one embodiment, an insulating oxide layer is disposed between a semiconductor waveguide optical modulator and the back side of the semiconductor substrate. Optical conduits are disposed in the insulating oxide layer at the locations where light enters and exits the semiconductor waveguide optical modulator. In one embodiment, the optical conduits have indexes of refraction substantially equal to the indexes of refraction of the semiconductor substrate and the semiconductor waveguide optical modulator. Thus, attenuation of the light used to optically couple the semiconductor waveguide optical modulator through the back side of the semiconductor substrate is reduced.