
8.1 ROADMs—A KEY COMPONENT IN THE
EVOLUTION OF OPTICAL SYSTEMS
Since optical transmission systems were first deployed there has been a constant push
to improve system reach and capacity. A high-level overview of the evolution of
optical transmission systems is shown in Figure 8.1. The development of wave length-
division multiplexing (WDM) and optical amplifiers, such as the erbium-doped
fiber amplifier (EDFA), has led to cost-effective long-haul, high-capacity systems.
Optical t ransmission has been realized over distances greater than the longest
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