A modular assembly for opto-electronic systems has a substrate on which various photonic integrated circuit (PIC) chips and electronic integrated circuit (EIC) chips are mounted. One or more waveguide (WG) chips mounted on the substrate align the optical communication between the PIC chips and fiber blocks for optical fibers. Preconfigured electrical connections in the substrate allow the PIC and EIC chips to communicate with one another and to communicate with solder bumps on the substrate for integration of the modular assembly with other electronic components.