Fiber optics systems 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.
In military and subscriber-loop applications, system design and parts selection are related. Designers consider trade-offs in the following areas:
1. Fiber properties
2. Types of connections
3. Optical sources
4. 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.
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.
ADVANTAGES AND DISADVANTAGES OF FIBER OPTICS
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. The list below details the main advantages of fiber optic systems.
1. System Performance
2. Greatly increased bandwidth and capacity
3. Lower signal attenuation (loss)
4. Immunity to Electrical Noise
5. Immune to noise (electromagnetic interference [EMI] and
6. radio-frequency interference [RFI]
7. No crosstalk
8. Lower bit error rates
9. Signal Security
10. Difficult to tap
11. Nonconductive (does not radiate signals)Electrical Isolation
12. No common ground required
13. Freedom from short circuit and sparks
14. Size and Weight
15. Reduced size and weight cables
16. Environmental Protection
17. Resistant to radiation and corrosion
18. Resistant to temperature variations
19. Improved ruggedness and flexibility
20. Less restrictive in harsh environments
21. Overall System Economy
22. Low per-channel cost
23. Lower installation cost
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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 educate managers and technicians. As the technology matures, the use of fiber optics will increase because of its many advantages over electrical systems.