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This chapter is from the book

Optical Fiber—The Bedrock for SONET

It is likely you understand and appreciate the advantages of using optical fiber as the transmission medium for a telecommunications system. This section summarizes the major aspects of optical fiber, and Appendix A explains these aspects in more detail. Optical fiber is widely used as the physical medium in SONET for the following reasons:

  • Optical transmission has a very large information capacity. Gigabit/s rates are easily obtainable in today's systems.

  • Optical fibers have electrically nonconducting photons instead of the electrons found in metallic cables such as wires or coaxial cables. This characteristic is attractive for applications in which the transmission path traverses hostile environments. For example, optical cables are not subject to electrical sparks or interference from electrical components in a building or computer machine room.

  • Optical fibers suffer less loss of signal strength than copper wire or coaxial cables. The strength of a light signal is reduced only slightly after propagation through several miles of the glass cable.

  • Optical fibers are more secure than copper cable transmission methods. Transmission of light does not yield residual intelligence that is found in electrical transmission.

  • Optical cables are very small (roughly the size of a hair) and weigh very little. For example, 900 copper wire pairs pulled through 1000 feet in a building would weigh approximately 4800 pounds. Two optical fibers, with protective covers pulled the same distance, weigh only 80 pounds and yet yield greater capacity.

  • Optical fibers are relatively easy to install and operate in high and low temperatures.

  • Due to the low signal loss, the error rate for optical fibers is very low. Some systems operate with a bit error rate (BER) or 10-12, which is several orders of magnitude better than copper media.

Figure 1–3 shows the progress made in transmission capacity of single-mode fibers since 1980 [CHAR99]. The top line represents experimental systems, and the bottom line represents commercial systems. The commercial results have lagged behind experimental results by about six years. The dramatic growth in the experimental capacity was due to improved laboratory techniques and the progress made in optical signal management.

Figure 6-3Figure 1–3 Progress in optical fiber technology.

While optical fiber is an excellent medium for the transport of SONET traffic, it is by no means the only alternative. Other cable-based systems, such as twisted pair, and wireless systems, such as microwave, are applicable as well.

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