Page 227 - Optical Communications Essentials

Source: Optical Communications Essentials

Chapter
13

Constructing the WDM

Network Puzzle

In the early days of optical fiber communications, optical link design engineers
only needed to be concerned with the operation of a few component types.
Mainly these included light sources, optical fibers, photodetectors, connectors,
splices, and couplers. The links carried a single wavelength, and the data rates
were low enough that the design did not require a great deal of special signal
processing to compensate for distortion effects. However, the push to increase
the data rate, provide longer transmission distances, and send many wave-
lengths simultaneously over the same fiber has resulted in the development of
numerous, highly sophisticated passive and active optical components to meet
the new and ever-increasing link performance demands. The design, installa-
tion, and operation of WDM links now have become more complex with the use
of these new components.
This chapter describes the major modules of a typical WDM link and explains
their functions. The first part outlines performance requirements for wideband
long-distance networks (known as long-haul networks), for metro networks,
and for local-area networks (LANs). Section 13.2 gives a top-level view of how
various optical devices and modular components fit into a WDM system and
what their functions and impacts are on system operation. Next, Sec. 13.3 gives
some examples of coarse WDM (CWDM) and dense WDM (DWDM) networks.
Finally, Sec. 13.4 introduces the concepts of monitoring the performance and
health of WDM links. Chapter 18 presents further details on this last topic.

13.1. Network Requirements

Figure 13.1 shows the major parts of a generic WDM link. The start of a link
(shown on the left) has a series of fixed or tunable laser sources and a multi-
plexing device for combining the independent light signals from the sources

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