ABSTRACT
The enormous potential of optical waves for high-rate transmission of information was recognized as
early as the 1960s. Because of their very high frequency, it was predicted that lightwaves could be
ultimately modulated at extremely large bit rates, well in excess of 100Gbit s
and orders of magnitudes
faster than possible with standard microwave-based communication systems. The promise of optical
waves for high-speed communication became a reality starting in the late 1980s and culminated with the
telecommunication boom of the late 1990s, during which time a worldwide communication network
involving many tens of millions of miles of fibre was deployed in many countries and across many
oceans. In fact, much of the material covered in this handbook was generated to a large extent as a result
of the extensive optoelectronics research that was carried out in support of this burgeoning industry. The
purpose of this chapter is to provide a brief overview of the basic architectures and properties of the most
widely used type of optical transmission line, which exploit the enormous bandwidth of optical fibre by a
general technique called wavelength-division multiplexing (WDM). After a brief history of optical
network development, this chapter examines the various physical mechanisms that limit the
performance of WDM systems, in particular, their output power (which affects the output signal-
to-noise ratio (SNR)), capacity (bit rate times number of channels), optical reach (maximum distance
between electronic regeneration) and cost. The emphasis is placed on the main performance-limiting
effects, namely fibre optical nonlinearities, fibre chromatic and group velocity dispersions, optical
amplifier noise and noise accumulation, and receiver noise. Means of reducing these effects, including
fibre design, dispersion management, modulation schemes, and error-correcting codes, are also reviewed
briefly. The text is abundantly illustrated with examples of both laboratory and commercial optical
communication systems to give the reader a flavour of the kinds of system performance that are
available. This chapter is not meant to be exhaustive, but to serve as a broad introduction and to supply
background material for the following two chapters (Optical network architecture and Optical switching
and multiplexed architectures), which dwell more deeply into details of system architectures. We also
refer the reader to the abundant literature for a more in-depth description of these and many other
aspects of optical communication systems (see, for example [1, 17, 32, 34]).
