A fiber optic (or optical fiber) cable transmits photons (light) instead of electrons. Depending on the diameter of the cable, the light is guided either by total internal reflection or as a waveguide (manipulating refraction). These principles were known as early as the mid-19th century and began to be used in the 20th century for such applications as dental and medical illumination and in experiments in transmitting images for television.
Development
Optical fiber in its modern form was developed in the 1950s. The glass fiber through which the light passes is surrounded by a transparent cladding designed to provide the needed refractive index to keep the light confined. The cladding, in turn, is surrounded by a resin buffer layer and often an outer jacket and plastic cover. The fiber used for communication is flexible, allowing it to bend if necessary. Early optical fiber could not be used for practical communication because of progressive attenuation (weakening) of the light as it traveled. However, by the 1970s the attenuation was being reduced to acceptable levels by removing impurities from the fibers. Today the light signals can travel hundreds of miles without the need for repeaters or amplifiers. In the 1990s a new type of optical fiber (photonic crystal) using diffraction became available. This kind of fiber is particularly useful in applications that require higher power signals.
Communications and Network Applications
Optical fiber has several advantages over ordinary electric cable for communications and networking. The signals can travel much farther without the need for a repeater to boost the signal. Also, the ability to modulate wavelengths allows optical fiber to carry many separate channels, greatly increasing the total data throughput. Optical fiber does not emit RF (radio frequency) energy, a source of “cross-talk” (interference) in electrical cable. Fiber is also more secure than electrical cable because it is hard for an eavesdropper to tap. Today fiber is used for most long-distance phone lines and Internet connections. many cable television systems are upgrading from video cable to fiber because of its greater reliability and ability to carry more bandwidth and enhanced data services. The last area where electrical (copper) cable predominates is in the “last mile” between main lines and houses or buildings and within local networks. However, new buildings and higher-end homes often include built-in fiber. Increasingly, phone companies are upgrading service by bridging the last mile through fiber-to-the-home (FTTH) networks. While requiring a considerable investment, FITH allows phone companies to replace relatively slow DSL with faster (higher bandwidth) service better suited to deliver video, data, and phone service simultaneously (see bandWidth, cable modem, and dsl). As of 2008, 3.3 million American homes had fiber connections, mainly through Verizon’s FIOS service. It is expected that FTTH will be built into many new housing developments. In 2007 Corning announced the development of “nanostructured” optical fibers that can be bent more sharply (such as around corners) without loss of signal. Corning is working with Verizon to develop easier and cheaper ways to provide FTTH.
0 Comments