Page 37 - Optical Communications Essentials

Optical Communication Systems Overview

Optical Communication Systems Overview 27

Figure 2.5. The key sections of an optical fiber communications link.

it to an electric signal. The receiver also contains amplification devices and
circuitry to restore signal fidelity. Chapter 7 gives details on this topic.
■ Passive devices. As Chap. 9 describes, passive devices are optical components
that require no electronic control for their operation. Among these are optical
connectors for connecting cables, splices for attaching one bare fiber to
another, optical isolators that prevent unwanted light from flowing in a back-
ward direction, optical filters that select only a narrow spectrum of desired
light, and couplers used to tap off a certain percentage of light, usually for per-
formance monitoring purposes.
■ Optical amplifiers. After an optical signal has traveled a certain distance along
a fiber, it becomes weakened due to power loss along the fiber. At that point
the optical signal needs to get a power boost. Traditionally the optical signal
was converted to an electric signal, amplified electrically, and then converted
back to an optical signal. The invention of an optical amplifier that boosts the
power level completely in the optical domain circumvented these transmission
bottlenecks, as Chap. 11 describes.

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