Chapter 5
Lightwave Systems
The preceding three chapters focused on the three main components of a fiber-optic
communication system—optical fibers, optical transmitters, and optical receivers. In
this chapter we consider the issues related to system design and performance when the
three components are put together to form a practical lightwave system. Section 5.1
provides an overview of various system architectures. The design guidelines for fiber-
optic communication systems are discussed in Section 5.2 by considering the effects
of fiber losses and group-velocity dispersion. The power and the rise-time budgets are
also described in this section. Section 5.3 focuses on long-haul systems for which the
nonlinear effects become quite important. This section also covers various terrestrial
and undersea lightwave systems that have been developed since 1977 when the first
field trial was completed in Chicago. Issues related to system performance are treated
in Section 5.4 with emphasis on performance degradation occurring as a result of signal
transmission through the optical fiber. The physical mechanisms that can lead to power
penalty in actual lightwave systems include modal noise, mode-partition noise, source
spectral width, frequency chirp, and reflection feedback; each of them is discussed in
separate subsections. In Section 5.5 we emphasize the importance of computer-aided
design for lightwave systems.
5.1 System Architectures
From an architectural standpoint, fiber-optic communication systems can be classified
into three broad categories—point-to-point links, distribution networks, and local-area
networks [1]–[7]. This section focuses on the main characteristics of these three system
architectures.
5.1.1 Point-to-Point Links
Point-to-point links constitute the simplest kind of lightwave systems. Their role is to
transport information, available in the form of a digital bit stream, from one place to
another as accurately as possible. The link length can vary from less than a kilometer