Page 31 - Optical Communications Essentials

Source: Optical Communications Essentials

Chapter
2

Optical Communication

Systems Overview

Telecommunications network organizations started using optical fiber commu-
nication links just over 25 years ago. Since then, researchers have devised and
developed a truly impressive collection of sophisticated passive and active opti-
cal components, transmission techniques that are unique to optical links, and
software-based modeling tools for components, links, and networks. These
developments enabled optical networks to deliver increasingly higher data rates
over longer and longer distances for both terrestrial and transoceanic links.
The purpose of this chapter is to get an appreciation of this growth and to set
the basis for understanding the material in the rest of the book. First we present
the motivations for using optical communication, such as the physical differences
and capacity advantages between electrical and optical signaling formats. Then
we will review the evolution of optical fiber transmission systems, starting with
the quest to create a viable optical fiber. This will lead us to present-day imple-
mentations. The chapter ends with an overview of the general concepts and
issues of current transmission equipment, links, and networks. This includes the
process of combining many independent wavelengths onto the same fiber, signal
routing and switching, and standards for optical communications.

2.1. Motivations for Using Optical Fiber Systems
The motivation for developing optical fiber communication systems started with
the invention of the laser in the early 1960s. The operational characteristics of
this device encouraged researchers to examine the optical spectrum as an exten-
sion of the radio and microwave spectrum to provide transmission links with
extremely high capacities. As research progressed, it became clear that many
complex problems stood in the way of achieving such a super broadband com-
munication system. However, it also was noted that other properties of optical
fibers gave them a number of inherent cost and operational advantages over
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