ABSTRACT

This chapter deals with the modulation of light wave sources by either direct or external modulation. For direct modulation, the generation of the light wave within the cavity of the laser is manipulated by injection or withdrawing of electrons and hence stimulating the emission process. On the other hand, in the case of external modulation the laser is turned on at all times and the generated optical continuous waves are then modulated, by frequency, phase, or amplitude through an optical modulator. The properties of modulated signals are described. The uses of these transmitters in optical communication transmissionsystems are given, especially those for long-haul transmissions at very high bit rate. MATLAB® Simulink® models are described. Further, an introduction of external modulators is given for LiNbO3, electro-absorption (EA) type, and silicon-based phase modulation devices that can then form other modulation formats on the guided light waves such as intensity, I-Q modulator, switches, and so on.