what is optical fiber

what is fiber optic cable

An optical fiber is a thin, flexible medium capable of conducting an optical ray. An optical fiber cable has a cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket. The core is the innermost section and consists of one or more very thin strands, or fibers, made of glass or plastic. Each fiber is surrounded by its own cladding, a glass or plastic coating that has optical properties different from those of the core. The outermost layer, surrounding one or a bundle of cladded fibers, is the jacket. The jacket is composed of plastic and other materials layered to protect against moisture, abrasion, crushing, and other environmental dangers.

Uses
The following characteristics distinguish optical fiber from twisted pair and coaxial cable:
♦ Greater bandwidth
♦ Smaller size and higher weight
♦ Lower attenuation
♦ Electromagnetic isolation
♦ Greater repeater spacing.

Five basic categories of applications have become important for optical fiber:
♦ Long-haul trunks
♦ Metropolitan trunks
♦ Rural exchange trunks
♦ Local loops
♦ Local area networks.

Optical fiber transmit a signal-encoded beam of light by means of total internal reflection. In effect, the optical fiber acts as a waveguide for frequencies in the range 1014 to 1015 Hz, which covers the visible spectrum and part of the infrared spectrum. Light from a source enters the cylindrical glass or plastic core. Rays at shallow angles are reflected and propagated along the fiber; other rays are absorbed by the surrounding material. Two different types of light source are used in fiber optic systems: the light emitting diode (LED) and the injection laser diode (ILD). Both are semiconductor devices that emit a beam of light when a voltage is applied. The detector used at the receiving end to convert the light into electrical energy is a photodiode. In optical fiber, light propagates best in three distinct wavelength “windows”, centered on 850, 1300, and 1500 nanometers (nm). These are all in the infrared portion of the frequency spectrum. Most local application today use 850 nm LED light sources. It is generally limited to data rates under 100 Mbps and distance of a few km. To achieve higher data rates and longer distances, a 1300 nm LED or laser source is needed. The highest data rates and longest distances require 1500 nm laser sources.

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