5. Modulation formats

Since the invention of fiber optics, and for almost thirty years, the modulation format, i.e. the approach used to transcribe binary information onto the electric light field, had remained very simple. It involved turning a laser light on/off, depending on whether the binary information to be transmitted was a "1" or a "0", with an alphabet of just two symbols. Since then, many other modulation formats have been proposed, exploiting different levels of intensity, phase and even polarization of the electric field .