ABSTRACT
This chapter provides more details on receiver sensitivity, systems with multiple channels, and multiple repeaters and some commonly used modulation techniques. Information can be transmitted from one point to another in either digital or analog form. Despite the general trend toward digital transmission, there are many potential applications where analog fiber optic transmission systems compatible with other existing analog transmission systems are needed. The transmitter usually contains an light emitting diode or laser diode as an optical source, and the electrical power driving the source is modulated in order to modulate the source output power directly. The primary advantage of the subcarrier technique is that the "demodulation gain" obtained during demodulation of the subcarrier may improve performance as compared to direct intensity modulation. A useful modulation technique for fiber optic transmissions that overcomes the potential problems created by optical source nonlinearity is either pulse duration modulation or pulse position modulation.
