Various embodiments include a silicon-based optical waveguide structure locally on a bulk silicon substrate, and systems and program products for forming such a structure by modifying an integrated circuit (IC) design structure. Embodiments include implementing processes of preparing manufacturing data for formation of the IC design structure in a computer-implemented IC formation system, wherein the preparing of the manufacturing data includes inserting instructions into the manufacturing data to convert an edge of the at least one shape from a crystallographic direction to a crystallographic direction.