System design has centered on long-haul communications and the subscriber-loop plants. The subscriber-loop plant is the part of a system that connects a subscriber to the nearest switching center. Cable television is an example. Also, limited work has 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. Two basic types of optical fibers are used in industry: multimode fibers and single mode fibers.
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.
Fiber-optic systems have many attractive features that are superior to electrical systems. These include improved system performance, immunity to electrical noise, signal security, and improved safety and electrical isolation. Other advantages include reduced size and weight, environmental protection, and overall system economy. Table 6-1 details the main advantages of fiber-optic systems.
Despite the many advantages of fiber-optic systems, there are some disadvantages. Because of the relative newness of the technology, fiber-optic components are expensive. Fiber-optic transmitters and receivers are still relatively expensive compared to electrical interfaces. The lack of standardization in the industry has also limited the acceptance of fiber optics. Many industries are more comfortable with the use of electrical systems and are reluctant to switch to fiber optics; however, industry researchers are eliminating these disadvantages.
Standards committees are addressing fiber-optic part and test standardization. The cost to install fiber- optic systems is falling because of an increase in the use of fiber-optic technology. Published articles, conferences, and lectures on fiber optics have begun to System Performance Greatly increased band. width and capacity Immunity to Electrical I m m u n e t o noise Noise (electromagnetic interference [EMI] and radio-frequency interference [RFI]) Signal Security Electrical Isolation educate managers and technicians. As the technology matures, the use of fiber optics will increase because of its many advantages over electrical systems.
Table 6-1. - Advantages of Fiber Optics
Lower signal attenuatior (loss)
No cross talk
Low bit error rates
Difficult to tap
Nonconductive (does no radiate signals)
No common ground required
Freedom from short circuit and sparks
Size and Weight Reduced size and weigh cables
Environmental Protection Resistant to radiation and corrosion
Resistant to temperature variations
Improved ruggedness and flexibility
Less restrictive in harsh environments
Overall System Economy Low per-channel cost
Lower installation cost
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