Fibre Optic Glossary and Terms:

Absorption: One cause of attenuation where light signal is absorbed into the glass during transmission.

Adapter: A device used to interconnect two different connector types.

Attenuation: Optical loss of power. Attenuation is measured in dB loss per length of cable. Attenuation is usually caused by absorption and scattering.

Attenuator: A device used to attenuate an optical signal.

Back Reflection: A measure of the light reflected off the polished end of a fibre connector. Measured in negative dB relative to incident power.

Bandwidth: The range of signal frequencies that a fibre optic cable will transmit.

Buffer: The protective coating over the fibre

Coupler: A device used to connect two similar connector types.

Fusion Splice: A permanent splice where the two fibre ends are welded together.

Graded-index multimode fibre contains a core in which the refractive index diminishes gradually from the centre axis out toward the cladding. The higher refractive index at the centre makes the light rays moving down the axis advance more slowly than those near the cladding. Also, rather than zigzagging off the cladding, light in the core curves helically because of the graded index, reducing its travel distance. The shortened path and the higher speed allow light at the periphery to arrive at a receiver at about the same time as the slow but straight rays in the core axis. The result: a digital pulse suffers less dispersion.

Insertion Loss: The attenuation caused by the insertion of a device (such as a splice or connection point) to a cable.

Link: The entire span between two optical devices. Includes all cable, connections, and splices.

Loss Budget: The maximum amount of power that is allowed to be lost per optical link.

Jack: The female receptacle - usually found on equipment.

Mandrel: A fibre wrapping device used to cause attenuation within a fibre cable.

Mechanical Splice: A mechanical means of connecting two fibres.

Multimode: A type of fibre optic cable where the core diameter is much larger than the wavelength of light transmitted. Two common multimode fibre types are 50/125 and 62.5/125.

Multimode cable is made of of glass fibres, with a common diameters in the 50-to-100 micron range for the light carry component (the most common size is 62.5). POF is a newer plastic-based cable which promises performance similar to glass cable on very short runs, but at a lower cost.

Multimode fibre gives you high bandwidth at high speeds over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable core typically 850 or 1300nm. Typical multimode fibre core diameters are 50, 62.5, and 100 micrometers. However, in long cable runs (greater than 3000 feet [914.4 ml), multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.

The use of fibre optics was generally not available until 1970 when Corning Glass Works was able to produce a fibre with a loss of 20 dB/km. It was recognised that optical fibre would be feasible for telecommunication transmission only if glass could be developed so pure that attenuation would be 20dB/km or less. That is, 1% of the light would remain after travelling 1 km. Today, optical fibre attenuation ranges from 0.5dB/km to 1000dB/km depending on the optical fibre used. Attenuation limits are based on intended application.

The applications of optical fibre communications have increased at a rapid rate, since the first commercial installation of a fibre optic system in 1977. Telephone companies began early on, replacing their old copper wire systems with optical fibre lines. Today telephone companies use optical fibre throughout their system as the backbone architecture and as the long-distance connection between city phone systems.

Cable television companies have also began integrating fibre optics into their cable systems. The trunk lines that connect central offices have generally been replaced with optical fibre Some providers have begun experimenting with fibre to the curb using a fibre/coaxial hybrid. Such a hybrid allows for the integration of fibre and coaxial at a neighbourhood location. This location, called a node, would provide the optical receiver that converts the light impulses back to electronic signals. The signals could then be fed to individual homes via coaxial cable.

Local Area Networks (LAN) is a collective group of computers, or computer systems, connected to each other allowing for shared program software or data bases. Colleges, universities, office buildings, and industrial plants, just to name a few, all make use of optical fibre within their LAN systems.

Power companies are an emerging group that have begun to utilise fibre optics in their communication systems. Most power utilities already have fibre optic communication systems in use for monitoring their power grid systems.

Plug: The male connector.

Return Loss: The ratio of the power launched into a cable and the power of the light returned down the fibre This measurement is expressed in positive decibel units (dB). A higher number is better. Return Loss = 10 log (incident power / returned power).

Scattering: A second cause of attenuation. Scattering occurs when light collides with individual atoms in the glass.

Singlemode: A type of fibre with a small core that allows only one mode of light to propagate. Single Mode cable is a single stand of glass fibre with a diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fibre with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550nm. Carries higher bandwidth than multimode fibre, but requires a light source with a narrow spectral width. Synonyms mono-mode optical fibre, single-mode fibre, single-mode optical waveguide, uni-mode fibre

Single-mode fibre gives you a higher transmission rate and up to 50 times more distance than multimode, but it also costs more. Single-mode fibre has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fibre cable type.

Single-mode optical fibre is an optical fibre in which only the lowest order bound mode can propagate at the wavelength of interest typically 1300 to 1320nm.

Step-index multimode fibre has a large core, up to 100 microns in diameter. As a result, some of the light rays that make up the digital pulse may travel a direct route, whereas others zigzag as they bounce off the cladding. These alternative pathways cause the different groupings of light rays, referred to as modes, to arrive separately at a receiving point. The pulse, an aggregate of different modes, begins to spread out, losing its well-defined shape. The need to leave spacing between pulses to prevent overlapping limits bandwidth that is, the amount of information that can be sent. Consequently, this type of fibre is best suited for transmission over short distances, in an endoscope, for instance.

Termination: The process of mechanically installing a connector onto a fibre cable.

Wavelength: A means of measuring light colour. Expressed in nanometers (nm).