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FIBER OPTIC SYSTEMS
System design has centered on long-haul communications and the subscriber-loop plant.
The subscriber-loop plant is the part of a system that connects a subscriber to the
nearest switching center. Cable television is an example. Limited work has also been done
on short-distance applications and some military systems.
Initially, central office trunking required multimode optical fibers with moderate to
good performance. Fiber performance depends on the amount of loss and signal distortion
introduced by the fiber when it is operating at a specific wavelength. Long-haul systems
require single mode optical fibers with very high performance. Single mode fibers tend to
have lower loss and produce less signal distortion.
In contrast, short-distance and military systems tend to use only multimode technology.
Examples of short-distance systems include process control and local area networks (LANs).
Short-distance and military systems have many connections. The larger fiber core and
higher fiber numerical aperture (NA) of multimode fibers reduce losses at these
connections. Chapter 4 explains fiber connection properties in more detail. Chapter 2
provides more detail on multimode and single mode fibers.
In military and subscriber-loop applications, system design and parts selection are
related. Designers consider trade-offs in the following areas:
Fiber properties
Types of connections
Optical sources
Detector types
Designers develop systems to meet stringent working requirements, while trying to
maintain economic performance. It is quite difficult to identify a standard system design
approach. This module identifies the types of components chosen by the Navy for shipboard
applications.
Future system design improvements depend on continued research. Researchers expect
fiber optic product improvements to upgrade performance and lower costs for short-distance
applications. Future systems center on broadband services that will allow transmission of
voice, video, and data. Services will include television, data retrieval, video word
processing, electronic mail, banking, and shopping.
Q.10 Which type of optical fiber (multimode or single mode) tends to have lower loss
and produces less signal distortion?
Q.11 What optical fiber properties reduce connection loss in short-distance systems?
Q.12 In fiber optic systems, designers consider what trade-offs?
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