Backbone
The cabling used to connect entrance facilities, crossconnects, telecommunications closets, and equipment rooms. The backbone may consist of either interbuilding and/or intrabuilding cabling.
Backreflection
The loosely-used term covers optical return loss (ORL) for spans, reflectance for components, and Fresnel reflectance.
Backscatter coefficient
The ratio of the optical pulse power (not energy) at the OTDR output to the backscatter power at the near end of the fiber (z=0). This ratio is inversely proportional to the pulse width, because the optical pulse power is independent. It is expressed in dB.
Backscattering
See Rayleigh scattering.
Band
A range of optical spectrum allocated based on optical amplifiers. Six bands are specified by the ITU: O (original), E (enhanced), S (short), C (conventional), L (long), and U (ultra). These cover the optical spectrum from 1260 nm to 1675 nm.
Bandwidth
A measure of the maximum frequency by which light intensity can be modulated before the signal experiences 3 dB of excess attenuation. The difference between the highest and the lowest frequencies of a transmission channel or path; identifies the amount of data that can be sent through a given channel. The greater the bandwidth, the greater the information carrying capacity. Multimode fiber bandwidth is expressed in Megahertz per kilometer (MHz-km).
Baseband
A transmission media where the entire capacity of the cable is used for one signal.
Bayonet
A locking prong and slot interconnect device. The mechanical latching mechanism for the ST-type connector.
Bayonet fiber-optic connector (BFOC)
The formal name for the ST connector, a specific slotted twistlock connector with 2.5-mm ferrule.
Beam splitter
A passive device that uses optical lenses with reflective coatings to control the split ratio and divide an optical beam into two or more beams.
Bend insensitive fiber (BIF)
Single-mode fibers that have been modified to demonstrate reduced bend radius characteristics without attenuation changes. Specified in the ITU-T G.657 standard.
Bend loss
Increased attenuation due to macrobends (curvature of fiber) or microbends (small distortions in the fiber) coupling light energy from the fiber core to the cladding.
Bend radius
The minimum radius that fiber or cable can bend and still maintain its optical and physical qualities.
Bias current
The steady current applied to a laser diode to overcome its threshold current.
Biconic
A phenolic-bodied, threaded, spring-loaded, nonkeyed connector with a cone-shaped alignment area.
Bidirectional (Bidi)
Operating in both directions over a single fiber.
Bidirectional transceiver
A device that sends information in one direction and receivesinformation from the opposite direction.
Binder
A tape or thread used for holding assembled cable components in place within loose tube cables.
Bit
An electrical or optical pulse whose presence or absence indicates data. The capacity of the optical waveguide to transmit information without error is expressed in bits per second per unit length.
Bit error rate (BER)
A measurement of transmission accuracy. It is a ratio of bits received in error versus bits sent. Fiber optic communication systems normally have a BER value of 10(-9) or 10(-12).
Bit error rate tester (BERT)
Test equipment that measures the bit error rate (BER) of digital transmission systems.
Bit rate
A unit of measure for digital transmission speeds expressed in bit per second (b/s).
Blocking
Creating a physical barrier to keep moisture-repellent gel in loose tube cables from migrating or flowing out of the buffer tubes into splice trays.
Bonding
A method where all conductive cables and messengers are continuously connected to the grounding network. May also be referred to as continuity bonding.
Boot
Strain relief device consisting of a flexible material on the rear end of a fiber optic connector that protects the cable-toconnector interface from bending damage.
Braid
Textile or metallic filaments that are interwoven to form a flexible tube structure that may be applied over one or more wires, or flattened to form a strap. Kevlar® is also braided into cables for additional strength.
Breakout cable
A tight buffered cable with 900-micron coated fibers and aramid yarn surrounding each fiber. Jumper cordage is a breakout structure. Available in simplex and duplex variations for jumpers and in large fiber counts. Normally used for indoor installations and for tactical cables.
Breakout kit
A kit that provides a breakout cable structure for non breakout structures (with one fiber per tube).
Bridge
A data communications device that connects two or more network segments and forwards packets between them.
Brillouin scattering
In stimulated Brillouin backscattering (SBS), the laser signal creates periodic regions of altered refractive index; that is, a periodic grating that travels as an acoustic wave away from the signal. This effect can result in a noisy and unstable forward-propagating signal, since much of the optical energy is backscattered.
Broadband PON (B-PON)
The first FTTx standard issued as ITU-T G.983, the B-PON standard was designed for the bidirectional transmission of ATM cells over G.652 single-mode fiber at a distance of 20 kilometers using wavelength independent couplers (splitters) with split rates of up to 1:32. Originally defined by the FSAN S652 document.
Bubble splice
An air bubble in a splice that can cause high loss.
Buffer coating
A protective material with no optical function that covers and protects a fiber. A secondary plastic coating adhered around the coating of the optical fiber to provide additional protection against damage. Normally 250 or 900 microns.
Buffer tube
Part of a loose tube cable structure, buffer tubes accommodate 250-micron coated fibers in a loose configuration. The buffer tubes can be filled with gel, powder, or tapes to resist moisture intrusion.
Building local exchange carrier (BLEC)
A network service provider that contracts with real estate, property owners, and building managers to provide broadband services within multiple tenant units or multiple dwelling units.
Bulge splice
Slight overfeed results in bulging at the splice point. Bulging is not always lossy. Splice strength requires a solid fusion joint; monitor splice strength if you are reducing feed to eliminate bulging. Also known as a fat splice.
Buried
Cable placed by trenching, direct burial, plowing, boring, or installation into underground ducts.
Butt closure
Closure with cable ports located at one end of the closure.
Bypass switch
A high-speed switch that transfers an optical signal to an alternate fiber.
Byte
One segment of digital information; usually 8, 16, or 32 bits equal to a single character. Defined with a capital “B” as opposed to “bits”, which uses a lowercase “b”.
