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Glossary

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Term Definition
Average wavelength (l)
The average of the two wavelengths for which the peak optical power has dropped to half.
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Axial ray
In fiber-optic transmissions, a light ray that travels along the axis of a fiber-optic filament.
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Backbone
A cable connection between telecommunications or wiring closets, floor distribution terminals, entrance facilities, and equipment rooms either within or between buildings. This cable can service voice communications or data communications. In star-topology data networks, the backbone cable interconnects hubs and similar devices, as opposed to cables running between hub and station. In a bus topology data network, it is the bus cable. Backbone is also called riser cable, vertical cable, or trunk cable.
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Backbone wiring
The physical/electrical interconnections between telecommunications rooms and equipment rooms. See also backbone.
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Backscatter
Usually a very small portion of an overall optical signal, backscatter occurs when a portion of scattered light returns to the input end of the fiber; the scattering of light in the direction opposite to its original propagation. Light that propagates back toward the transmitter. Also known as back reflection or backscattering.
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Bait
The mold or form on which silicon dioxide soot is deposited to create the optical fiber preform.
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Balance
An indication of signal voltage equality and phase polarity on a conductor pair. Perfect balance occurs when the signals across a twisted-pair cable are equal in magnitude and opposite in phase with respect to ground.
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Balanced cable
A cable that has pairs made up of two identical conductors that carry voltages of opposite polarities and equal magnitude with respect to ground. The conductors are twisted to maintain balance over a distance.
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Balanced coupler
A coupler whose output has balanced splits; for example, one by two is 50/50, or one by four is 25/25/25/25.
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Balanced signal transmission
Two voltages, commonly referred to as tip and ring, equal and opposite in phase with respect to each other across the conductors of a twisted-pair cable.
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Balun
A device that is generally used to connect balanced twisted-pair cabling with unbalanced coaxial cabling. The balun is an impedance-matching transformer that converts the impedance of one transmission media to the impedance of another transmission media. For example, a balun would be required to connect 100 ohm UTP to 120 ohm STP. Balun is short for balanced/unbalanced.
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Bandpass
A range of wavelengths over which a component will meet specifications.
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Bandwidth
Indicates the transmission capacity of media. For copper cables, bandwidth is defined using signal frequency and specified in hertz (Hz). For optical fiber, wavelength in nanometers (nm) defines bandwidth. Also refers to the amount of data that can be sent through a given channel and is measured in bits per second.
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Bandwidth-limited operation
Systems can be limited by power output or bandwidth; bandwidth-limited operation is condition when the total system bandwidth is the limiting factor (as opposed to signal amplitude).
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Barrier layer
A layer of glass deposited on the optical core to prevent diffusion of impurities into the core.
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