An optical communication device includes a transmitter module and a receiver module. The transmitter module includes a two laser sources, two optical modulators optically coupled to the two light sources, respectively, and an optical coupler, a semiconductor optical amplifier, an optical coupler, four optical band-pass filters or a demultiplexer, and an optical multiplexer optically coupled in series. The laser beams emitted from the two laser sources are converted into four laser beams having different frequencies due to a four-wave mixing effect occurring in the semiconductor optical amplifier. The receiver module includes a demultiplexer and four photoelectric conversion elements to receive the four laser beams respectively and convert them to electrical signals.