Fiber Optic Wiki

Cross Section of a Fiber-Optic Cable

September 3, 2011

The index of refraction is calculated by dividing the speed of light in a vacuum by the speed of light in another medium, as shown in the following formula Refractive index of the medium = [Speed of light in a vacuum/Speed of light in the medium]The refractive index of the core, n1, is always greater than the index of the cladding, n2. Light is guided through the core, and the fiber acts as an optical waveguide.

Performance Considerations

September 3, 2011

The amount of light that can be coupled into the core through the external acceptance angle is directly proportional to the efficiency of the fiber-optic cable. The greater the amount of light that can be coupled into the core, the lower the bit error rate (BER), because more light reaches the receiver.

SEMICONDUCTOR LASERS

September 1, 2011

Transistors make use of the special properties of a class of materials known as semiconductors. Electric current is carried by moving electrons, and ordinary metals, such as copper, are good conductors of electricity because their electrons are not tightly bound to the nucleus of the atom and are freely attracted to a positive charge. Other substances, such as rubber, are insulators--poor conductors of electricity--because their electrons do not move freely. Semiconductors, as their name implies, fall somewhere in between; they ordinarily behave more like insulators, but under some conditions they can be made to conduct electricity.

OPTICAL FIBERS EMERGE

September 1, 2011

Optical fibers offered one approach, although in the mid-1960s it was by no means certain that the answer lay in this direction and other possibilities were seriously considered. Light is channeled in glass fibers by a property known as total internal reflection. The equations governing the trapping of light inside a flat glass plate were known to Augustine-Jean Fresnel as early as 1820, and their extension to what were then known as glass wires was achieved by D. Hondros and Peter Debye in 1910. It was not until 1964, however, that Stewart Miller at Bell Laboratories deduced detailed ways to probe the potential of glass as an efficient long-distance transmission medium.

PRACTICAL SYSTEMS TAKE SHAPE

September 1, 2011

Still, it would take more than good fiber to build commercial-grade communication systems. Lasers--which would require lifetimes of up to 1,000,000 hours--were still coming up short in reliability, failing after no more than a few hours of operation. Moreover, there was as yet no economical method of producing reliable lasers in the quantities that would be needed.

FIBER OPTICS TO THE FORE

September 1, 2011

The prospect of widespread installation of fiber-optics systems was exhilarating. In the United States, railroad rights-of-way offered convenient paths for long-distance fiber cables, which were so robust that even the strong vibrations of heavy trains did not disturb them. Work proceeded slowly at first. In 1978, the total of all fiber-optic installations in the world came to only 600 miles. In 1980, AT&T filed plans with the Federal Communications Commission for a 611-mile system that would connect major cities in the Boston-Washington corridor. Four years later, when the system entered service, its cable, less than 1 inch across, provided 80,000 voice channels for simultaneous telephone conversations. By then, the total length of fiber cables in the United States alone approached 250,000 miles--enough to stretch to the moon.

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