9.1 Overview of Analog Links
Figure 9.1 shows the basic elements of an analog link. The transmitter contains either an LED or a laser diode optical source. As noted in Sec. 4.5 and shown in fig. 4.39, In analog applications. one first sets a bias point on the source approximately at the midpoint of the linear output region. The analog signal can then be sent using one of several modulation techniques. The simplest form for optical fiber links is direct intensity modulation, wherein the optical output from the source is modulated simply by varying the current around the bias point in proportion to the message signal level. Thus, the information signal is transmitted directly in the baseband