Modulation of Signals in Optical Communication Links

There are two main types of optical signals propagating in wired or wireless communication links: time continuously varied or analog, which corresponds to narrowband channels, and time discrete varied or pulse‐shaped, which corresponds to wideband channels. Therefore, there are different types of modulation that are usually used for such types of signals. This chapter defines the process of modulation and demodulation. It describes the main principle of both kinds of modulation, analog and digital, and provides some examples of the most useful types of modulation adapted for both kinds of channels, narrowband and wideband. There are three types of modulation, depending on what characteristic is time varied in the modulating signal – amplitude modulation, phase modulation, and frequency modulation. There are three kinds of digital modulation: amplitude shift keying, frequency shift keying, and phase shift keying.