An optoelectronic circuit having a substantially planar double-sided substrate, each side of which has a respective plurality of electrically conducting tracks and a respective plurality of planar optical waveguides. The substrate also has at least one via crossing the substrate in a manner that can be used to establish an optical path across the substrate, e.g., between optical waveguides located on different sides thereof. In an example embodiment, the electrically conducting tracks and planar optical waveguides are configured to operatively connect various optoelectronic devices and auxiliary electrical circuits attached to the two sides of the substrate using hybrid-integration technologies. In some embodiments, two or more of such double-sided substrates can be stacked and optically and electrically interconnected to create an integrated three-dimensional assembly.