In an embodiment, a method includes: forming an interconnect including waveguides and conductive features disposed in a plurality of dielectric layers, the conductive features including conductive lines and vias, the waveguides formed of a first material having a first refractive index, the dielectric layers formed of a second material having a second refractive index less than the first refractive index; bonding a plurality of dies to a first side of the interconnect, the dies electrically connected by the conductive features, the dies optically connected by the waveguides; and forming a plurality of conductive connectors on a second side of the interconnect, the conductive connectors electrically connected to the dies by the conductive features.