We propose a new approach to physical design of optoelectronic system-on-a-package (SOP) using optical waveguide interconnect technology. The objective is to improve the performance of SOP by replacing long distance electrical interconnects with optical waveguide interconnects. A new simultaneous optimization algorithm for module placement and routing of electrical and optical interconnects is introduced in this paper. It not only improves the performance of SOP, but reduces the simulation time. Even though the small portion of electrical interconnects are replaced with optical interconnects, more than 21% improvement of the SOP performance is achieved.