An electrical waveguide transmission device accepts a differential electrical input signal (e.g., S+ and S−) propagating along two separate signal conductors with grounded electrical return paths, and outputs the differential input signal to a series push-pull traveling wave electrode Mach-Zehnder optical modulator over a pair of output conductors that act as a return path for each other and provide a desired characteristic impedance matching that of the Mach-Zehnder optical modulator.