The following terms are defined within the context of the fiber optic industry.


A mechanical media termination device designed to align and join fiber optic connectors. Often referred to as coupling, bulkhead, or interconnect sleeve.

Aramid Yarn

Strength elements that provide tensile strength, support and additional protection of the fiber bundles. Kevlar is a particular brand of aramid yarn.


Additional protective element beneath outer jacket to provide protection against severe outdoor environments. Usually made of plastic-coated steel, it may be corrugated for flexibility.


The decrease in magnitude of power of a signal in transmission between points. A term used for expressing the total loss of an optical system, normally measured in decibels (dB) at a specific wavelength.

Attenuation Coefficient

The rate of optical power loss with respect to distance along the fiber, usually measured in decibels per kilometer (dB/km) at a specific wavelength. The lower the number, the better the fiber’s attenuation. Typical multimode wavelengths are 850 and 1300 nanometers (nm); single mode wavelengths are 1310 and 1550 nm.

Backbone Cabling

The portion of premises telecommunications cabling that provides connections between telecommunications closets, equipment rooms, and entrance facilities. The backbone cabling consists of the transmission media (optical fiber cable), main and internediate cross-connects, and terminations for the horizontal cross-connect, equipment rooms, and entrance facilities. The backbone cabling can further be classified as interbuilding backbone (cabling between buildings), or intrabuilding backbone (cabling within a building).


Measure of the information-carrying capacity of an optical fiber. Note: This term is often used to specify the normalized modal bandwidth (MHz-km) of a multimode fiber.

Bandwidth Distance Product

The information-carrying capacity of a transmission medium is normally referred to in units of MHz-km. This is called the bandwidth-distance product or, more commonly, bandwidth. The amount of information that can be transmitted over any medium changes according to distance.


A protective material extruded directly on the fiber coating to protect it from the environment (tight-buffered).

Buffer Tubes

Extruded cylindrical tubes covering optical fiber(s) used for protection and isolation. See Loose Tube.


Many individual fibers contained within a single jacket or buffer tube. Also, a group of buffered fibers distinguished in some fashion from another group in the same cable core.


An assembly of optical fibers and other material providing mechanical and environmental protection.

Cable Assembly

Optical fiber cable that has connectors installed on one or both ends. General use of these cable assemblies includes the interconnection of optical fiber cable systems and opto-electronic equipment. If connectors are attached to only one end of a cable, it is known as a pigtail. If connectors are attached to both ends, it is known as a jumper or patchcord.

Cable Bend Radius

Cable bend radius during installation infers that the cable is experiencing a tensile load. Free bend infers a smaller allowable bend radius since it is at a condition of no load.

Central Member

The center component of a cable. It serves as an antibuckling element to resist temperature-induced stresses. Sometimes serves as a strength element. The central member material is either steel, fiberglass, or glass-reinforced plastic.


The material surrounding the core of an optical waveguide. The cladding must have a lower index of refraction to keep the light in the core.


A material put on a fiber during the drawing process to protect it from the environment and handling.

Composite Cable

A cable containing both fiber and copper media per article 770 of the National Electrical Code (NEC).

Connecting Hardware

A device, used to terminate an optical fiber cable with connectors and adapters, that provides an administration point for cross-connecting between cabling segments or interconnecting to electronic equipment.


A mechanical device used to align and join two fibers together to provide a means for attaching to and decoupling from a transmitter, receiver, or another fiber (patch panel).

Connector Panel

A panel designed for use with patch panels; it contains either 6, 8 or 12 adapters pre-installed for use when field-connectorizing fibers.

Connector Panel Module

A module designed for use with patch panels; it contains either 6, 8 or 12 connectorized fibers that are spliced to backbone cable fibers.


The central region of an optical fiber through which light is transmitted.


Unit for measuring the relative strength of ight signals. Normally expressed in dB, it is equal to one-tenth the common logarithm of the ratio of two levels. Expressed in dBm when a power level is compared to a milliwatt.


Non-metallic and therefore, non-conductive. Glass fibers are considered dielectric. A dielectric cable contains no metallic components.


The cause of bandwidth limitations in a fiber. Dispersion causes a broadening of input pulses along the length of the fiber. Three major types are (1) modal dispersion caused by differential optical path lengths in a multimode fiber; (2) chromatic dispersion caused by a differential delay of various wavelengths of light in a waveguide material; and (3) waveguide dispersion caused by light traveling in both the core and cladding materials in single mode fibers.


Fiber Optic Test Procedures. Defined in TIA / EIA Publication Series 455.


Multi-fiber cable constructed in the tight-buffered design. Designed for ease of connectorization and rugged applications for intra-or inter-building requirements.


A mechanical fixture, generally a ceramic tube, used to protect and align a fiber in a connector. Generally associated with fiber optic connectors.


Thin filament of glass. An optical waveguide consisting of a core and a cladding that is capable of carrying information in the form of light. Radius for a fiber can bend before the risk of breakage or increase in attenuation.

Fiber Distributed Data Interface (FDDI)

A standard for a 100 Mbit/s fiber optic local area network.

Fiber Optics

Light transmission through optical fibers for communication signaling.

Fusion Splice

A permanent joint produced by the application of localized heat sufficient to fuse or melt the ends of the optical fiber, forming a continuous single fiber.

Gigahertz (GHz)

A unit of frequency that is equal to one billion cycles per second, 10 Hertz.

Horizontal Cabling

The portion of telecommunications cabling that provides connectivity between the horizontal cross-connect and the work-area telecommunications outlet. The horizontal cabling consists of transmission media, the outlet, the terminations of the horizontal cables, and horizontal cross-connect.

Horizontal Cross-Connect (HC)

A cross-connect of horizontal cabling to other cabling, e.g., horizontal, backbone equipment.

Hybrid Cable

A fiber optic cable containing two or more different types of fiber, such as 62.5 um multimode and single mode.

Jumper (Patchcord)

Optical fiber cable that has connectors installed on both ends.


A unit of force per area expressed in thousands of pounds per square inch. Usually used as the specification for a fiber proof test, e.g., 100 kpsi.


One thousand meters, or approximately 3,281 feet. The kilometer is a standard unit of length measurement in fiber optics. Conversions is 1 ft. = 0.3048 m.


See Local Area Network.


Light Amplification by Stimulated Emission of Radiation. An electro-optic device that produces coherent light with a narrow range of wavelengths, typically centered around 780 nm, 1310 nm, or 1550 nm. Lasers with wavelengths centered around 780 nm are commonly referred to as CD Lasers.

Light Emitting Diode (LED)

A semiconductor device used to transmit light into a fiber in response to an electrical signal. It typically has a broad spectral width.

Local Area Network (LAN)

A geographically limited communications network intended for the local transport of voice, data, and video. Often referred to as a customer premises network.

Loose Tube Cable

Type of cable design whereby coated fibers are encased in buffer tubes offering excellent fiber protection and segregation.


Abbreviation used to denote medium density polyethylene. A type of plastic material used to make cable jacketing.

Main Cross-Connect (MC)

The centralized portion of the backbone cabling used to mechanically terminate and administer the backbone cabling, providing connectivity between equipment rooms entrance facilities, horizontal cross-connects, and intermediate cross-connects.

Mechanical Splicing

Joining two fibers together by permanent or temporary mechanical means (vs. fusion splicing or connectors) to enable a continuous signal. The CamSplice is a good example of a mechanical splice.

Megahertz (MHz)

A unit of frequency that is equal to one million cycles per second.

Micrometer (um)

One millionth of a meter; 10 -6 meter. Typically used to express the geometric dimension of fibers, e.g., 62.5 um.

Mini Bundle Cable

Siecor loose tube cable in which the buffer tube contains two or more fibers, typically 6 or 12 fibers.


A term used to describe an independent light path through a fiber, as in multimode or single mode.

Mode Field Diameter

The diameter of the one mode of light propagating in a single mode fiber. The mode field diameter replaces core diameter as the practical parameter in single mode fiber.

Multi-Fiber Cable

An optical fiber cable that contains two or more fibers.

Multimode Fiber

An optical waveguide in which light travels in multiple modes. Typical core/cladding size (measured in micrometers) is 62.5/125.


Combining two or more signals into a single bit stream that can be individually recovered.

National Electrical Code (NEC)

Defines building flammability requirements for indoor cables. Note: Local codes take precedence but may refer to or require compliance to the NEC.

Nanometer (nm)

A unit of measurement equal to one billionth of a meter; 10 -9 meters. Typically used to express the wavelength of light, e.g., 1300 nm.

Numerical Aperture (NA)

The number that expresses the light gathering ability of a fiber. Related to acceptance angle.

Optical Time Domain Reflectometer (OTDR)

An instrument that measures transmission characteristics by sending a series of short pulses of light down a fiber and providing a graphic representation of the back-scattered light.


Abbreviation used to denote polyethylene. A type of plastic material used for outside plant cable jackets.


Abbreviation used to denote polyvinyl-chloride. A type of plastic material used for cable jacketing. Typically used in flame-retardant cables.


Abbreviation used to denote polyvinyldifluoride. A type of material used for cable jacketing. Often used in plenum-rated cables.


Optical fiber cable that has a connector installed on one end. See Cable Assembly .

PIN Diode

A semiconductor device used to convert optical signals to electrical signals in a receiver.


An air-handling space such as that found above drop-ceiling tiles or in raised floors. Also, a fire-code rating for indoor cable.


An electronic package that converts optical signals to electrical signals.


Reflectance is the ratio of power reflected to the incident power at a connector junction or other component or device, usually measured in decibels or dB. Reflectance is stated as a negative value, e.g., -30 dB. A connector that has a better reflectance performance would be a -40 dB connector or a value less than -30 dB. The terms return loss, back reflection, and reflectivity are also used synonymously in the industry to describe device reflections, but stated as positive values.


A device used to regenerate an optical signal to allow an increase in the system length.


Pathways for indoor cables that pass between floors. It is normally a vertical shaft or space. Also a fire code rating for indoor cable.


A property of glass that causes light to deflect from the fiber and contributes to optical attenuation.

Single Mode Fiber

An optical waveguide (or fiber) in which the signal travels in one mode. The fiber has a small core diameter, typically 9 um.

Splice Closure

A container used to organize and protect splice trays. Typically used in outside plant environments.

Splice Tray

A container used to secure, organize, and protect spliced fibers.


The permanent joining of bare fiber ends to another fiber.

Telecommunications Closet (TC)

An enclosed space for housing telecommunications equipment, cable terminations, and cross-connects. The closet is the recognized cross-connect between the backbone and horizontal cabling. Type of cable construction whereby each glass fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900 micrometers. Increased buffering provides ease of handling and connectorization.


An electronic package used to convert an electrical information-carrying signal to a corresponding optical signal for transmission by fiber. The transmitter is usually a Light Emitting Diode (LED) or Laser Diode.


Underwriters Laboratories, Inc.


The distance between two successive points of an electromagnetic waveform, usually measured in nanometers (nm).

Zero-Dispersion Wavelength

Wavelength at which the chromatic dispersion of an optical fiber is zero. Occurs when waveguide dispersion cancels out material dispersion.