The introduction to the chapter on Fiber Optic Communication Systems discusses the growing industrial manufacturing of low-loss optical fiber cables and their splicing tools, along with advancements in optoelectronic components. These developments are expected to lead to practical system installations in the 1980s. The chapter emphasizes the importance of understanding the characteristics of optoelectronic transmitters and receivers, which are similar to traditional copper pairs. It also highlights the need for protection against electromagnetic perturbations. The section on digital transmission begins with a discussion of baseband spectra, emphasizing the compatibility between the message and channel bands. Key considerations include low bandwidth for receiver bandwidth and noise reduction, and the absence of DC levels and automatic gain control. The chapter then delves into clock timing and decision circuits, using the concept of an "eye diagram" to illustrate the relationship between the message and channel bands. The transmission channel acts as a linear low-pass filter, and its characteristics can be compensated using an equalizer. The output pulse is described by a raised cosine function, and the "eye diagram" shows the superposition of such functions for all possible configurations of a binary pulse series synchronized on the same clock. A wider "eye" indicates easier decision-making.The introduction to the chapter on Fiber Optic Communication Systems discusses the growing industrial manufacturing of low-loss optical fiber cables and their splicing tools, along with advancements in optoelectronic components. These developments are expected to lead to practical system installations in the 1980s. The chapter emphasizes the importance of understanding the characteristics of optoelectronic transmitters and receivers, which are similar to traditional copper pairs. It also highlights the need for protection against electromagnetic perturbations. The section on digital transmission begins with a discussion of baseband spectra, emphasizing the compatibility between the message and channel bands. Key considerations include low bandwidth for receiver bandwidth and noise reduction, and the absence of DC levels and automatic gain control. The chapter then delves into clock timing and decision circuits, using the concept of an "eye diagram" to illustrate the relationship between the message and channel bands. The transmission channel acts as a linear low-pass filter, and its characteristics can be compensated using an equalizer. The output pulse is described by a raised cosine function, and the "eye diagram" shows the superposition of such functions for all possible configurations of a binary pulse series synchronized on the same clock. A wider "eye" indicates easier decision-making.