Abstract: A thin-film multilayer structure on top of a substrate has three polymer layers having adapted refractive indices in which optical waveguides are formed. Signal conducting metal layers are located at these three thin-film layers. The metal is etched away at the waveguide cores so that ordinary optical waveguides of channel-type are obtained having a refractive index difference between the core and the cladding material. Holes are etched in the polymer layers in order to form electrical vias. Mirrors can be formed by laser ablating to provide connection of an optical waveguide to some component and to provide optical vias, in the case where another similar set of three polymer layers are applied on top of the layers shown. Hence, electrical and optical interconnections can be integrated in the multilayer structure using a minimum number of polymer layers and the optical waveguides can be constructed to have a low loss.