ABSTRACT
A directly modulated photonic transmitter can consist of a single or multiple lightwave sources that can be modulated directly by manipulating the driving current of the laser diode. Alternatively, the laser source can be turned on all the time, and its output lightwaves are externally modulated via an integrated optical modulator, which is then known as an externally modulated optical transmitter. This externally modulated transmitter preserves the linewidth of the laser and hence its coherence.
