Two low-speed electrical signals are first input to two electrical Return-to-Zero (RZ) converters to generate low-speed RZ electrical signals. After inverting one of the low-speed RZ electrical signals, the two low-speed RZ signals are then input to a dual-electrode optical modulator, e.g., a Mach-Zehnder interferometer. The dual-electrode optical modulator has a pair of electrodes driven with the pair of differential signals. This dual-electrode optical modulator has multiplexing as well as optical modulating capabilities. Within the dual-electrode optical modulator, each electrode is coupled to a different low-speed RZ electrical signal. The optical modulator also receives an optical beam from a traditional light source, e.g., a laser diode. As the electrodes of the dual-electrode modulator optically modulate independently, they effectively combine the low-speed RZ electrical signals into one Non-Return-To-Zero (NRZ) optical signal by time-division multiplexing the low-speed RZ electrical signals. The resulting output is a high-speed digital optical signal of the desired data rate, which may be greater than 40 Gb/s.