Abstract: An optical module includes a transmitter optical sub-assembly comprising a transmitter configured to emit a multi-longitudinal-mode (MLM) spectrum signal having an emission spectrum comprising a plurality of distinct narrow-spectrum peaks each corresponding to a longitudinal mode in the transmitter. The emission spectrum can be shifted in wavelength by a change in the transmitter temperature. The optical module also includes a heating and cooling device configured to control the temperature of the transmitter in response to a temperature-control signal and a receiver optical sub-assembly configured to output a pair of differential digital signals in response to an input optical signal.