A process for preparing a subassembly, the process comprising (a) defining the location of one or more grooves for receiving at least one polymer waveguide in a wafer, (b) etching the grooves into the wafer, each groove having sidewalls and a first facet at the terminal end perpendicular to the side walls, the first facet having a first angle relative to the top planar surface, (c) coating the first facet with a reflective material, and (d) disposing a fluid polymer waveguide precursor into each groove, and writing a core into the polymer material by directing at least one laser beam on the first facet by directing the laser beam into the top of the polymer material such that the beam reflects off of the first facet and down the interior of the polymer material to form the core in the polymer waveguide.