Fiber Cable Tutorial

Due to its high speed, large carrying capacity and smaller maintenance costs, fiber optic cable is gradually replacing the traditional copper wire. Fiber optic cable provides greater resistance to electromagnetic noise from motors, radios and the neighboring cables, especially power cables.

Fiber optic cables are suitable for carrying transmission at both long and short distances for connecting local phone systems, cable television networks, industrial plants, university campuses, electric companies and office buildings.

Although the fiber optic cable system is very analogous to the copper wire system, the primary difference is the use of light as a transmission medium in fiber optic cables. Fiber optic cable systems can work in conjunction with copper wire systems. A transmitter is used at one end of the fiber optic cable system to originate data coming onto the fiber optic lines. The transmitter accepts the information as coded electronic pulses from copper wire, it then processes and translates them into equivalent light pulses using ILD injection-laser diode or LED light-emitting diode. The light pulses will be funneled into the fiber optic medium by a lens. A light source near to infrared wavelength of 850nm is used for shorter lengths and 1300nm for longer distances on multi mode fiber. While on single-mode fiber, light of about 1300nm is used for shorter distances and 1500nm for longer distances.

A principle called “total internal reflection” states that when the angle of incidence exceeds a critical value, light can not get out of the glass and instead it bounces back in. This principle makes possible the transmission of information using light pulses in the fiber optic lines.

The core of the fiber optic cable is made of very pure and clear material for the easy reflection of light. Mostly glass is used as the core of the fiber optic cable. However plastic may also be used as the core for short distance transmission. The glass of the fiber optic cable is almost always made from pure silica along with other materials like chalcogenide, fluorozirconate and fluoroaluminate which are suitable for longer wavelength infrared applications.

Fiber optic cable acts as a guide to the light from one end of the cable to the other. The transmitter transmits the light source as ON and OFF pulses and are converted to digital 0s and 1s by the light sensitive receiver at the other end. The strength of the light may become weaker after traveling a certain distance and can be strengthened by using repeaters.

The only disadvantage of fiber optic cable is the high costs as compared to the copper wire. However with advancement in technologies it is becoming cheaper over time. Fiber cable is categorized into single-mode, multi-mode and plastic optical fiber POF.

Single-mode cable is also known by the names single-mode optical wavelength, mono-mode optical fiber and uni-mode fiber. It is composed of single strand glass fiber with diameter ranging from 8.3 to 10 microns and one mode of transmission. The comparatively narrow diameter allows only one mode to propagate typically 1310nm or 1550nm. Single-mode cables are carriers for higher bandwidths than multi mode fiber, but need the light to be of narrow spectral width. It is widely used in applications where data is needed to be sent at different frequencies.

Although single-mode cable is more expensive than multi mode cables, however it provides a higher transmission rate and a distance 50 times larger than the multi mode cables. The distortion resulting from the overlapping of light pulses is almost eliminated in single-mode fiber optic cables due to its small core and single light wave. The lowest mode can propagate at a wavelength typically in the range of 1300nm to 1320nm in single-mode fiber optic cables.

Multi-mode cable has a diameter larger than the single-mode cables ranging from 50 microns to 100 microns. It transmits data at speeds (10Mbps to 100Mbps) at (275m to 2000m) distances. Dispersed light waves travel at numerous paths in the core of Fiber optic cable of typically 850nm or 1300nm. The typical diameters of the core are 50, 62.5 and 100 microns. The disadvantage of multi-mode cable is the distortion of signal at longer distances due to multiple paths of light, resulting in loss of information.

The use of fiber-optics was made possible after 1970 when Corning was able to produce a glass fiber with 20dB/km loss of data. It was decided then that the optical fiber could be used for telecommunication transmission if the glass in the fiber optic cable is so pure that the attenuation would be less than 20dB/km. Fiber optic cable was commercially installed in 1977.

The usage of fiber optics has increased rapidly with time and is considered the backbone of telecommunication industry. Fiber optic cable is quickly replacing the copper wire in almost all parts of the world. Various organizations like cable television companies have integrated their cable system with fiber-optics while some have developed a fiber/coaxial hybrid, which allow the integration of fiber optic cable with coaxial cable at the neighboring locations. Industrial plants, office buildings, schools, colleges and universities are the few names that widely use fiber optic cable in their LAN systems. Fiber optic cable is becoming more popular in power companies for monitoring their power grid and communication systems.