Disclosed are multi-chip modules (MCMs) that allow for chip-to-chip transmission of light signals. The MCMs can incorporate at least two components, which are attached (e.g., by interconnects). For example, in one MCM disclosed herein, the two components can be an integrated circuit chip and an interposer to which the integrated circuit chip and one or more additional integrated circuit chips are attached by interconnects. In another MCM disclosed herein, the two components can be two integrated circuit chips that are stacked and attached to each other by interconnects. In either case, the two components can each have a waveguide and a grating coupler coupled to one end of the waveguide. The grating couplers on the different components can be approximately vertically aligned, thereby allowing light signals to be transmitted between the waveguides on those different components. Also, disclosed herein are methods of forming such MCMs.