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ITS Networking & Telecommunications

Fiber Optic Cable Glossary

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

Acceptance Angle
The half-angle of the cone within which incident light is totally internally reflected by the fiber core. It is equal to Arcsin (NA).

Amplitude Modulation
A transmission technique in which the amplitude of the carrier is varied in accordance with the signal. A means of signal transmission whereby transmitter (light source) signal intensity is varied in relation to the amplitude of the input signal.

Analog
A format that uses continuous physical variables such as voltage amplitude or frequency variations to transmit information.

Angle of Incidence
The angle between an incident ray and the normal to a reflecting surface.

Aramid Yarn
Strength element used in Siecor cable to provide support and additional protection of the fiber bundles. Kevlar is a particular brand of aramid yarn.

Armoring
Additional protection between jacket layers that provides protection against severe outdoor environments. Usually made of plastic­coated steel, and may be corrugated for flexibility.

Attenuation
(1) Limited Operation The condition in a fiber optic link when operation is limited by the power of the received signal (rather than by bandwidth or by distortion). (2) The decrease in magnitude of power of a signal in transmission between points. A term used for expressing the total losses on an optical fiber consisting of the ratio of light output to light input. Attenuation is usually measured in decibels per kilometer (dB/km) at a specific wavelength. The lower the number, the better the fiber. Typical multi-mode wavelengths are 850 and 1300 nanometers (nm); singlemode, at 1300 and 1500 nm. NOTE: When specifying attenuation, it is important to note if it is nominal or average, room temperature, value or maximum over operating range.

Attenuator
A passive optical component that intentionally reduces the optical power propagating in a fiber.

APD (Avalanche Photodiode)
A photodiode designed to take advantage of avalanche multiplication of photocurrent. As the reverse-bias voltage approaches the break-down voltage, hole-electron pairs created by absorbed photons acquire sufficient energy to create additional hole-electron pairs when they collide with ions; thus a multiplication or signal gain is achieved.

Average Power
The average level of power in a signal that varies with time.

Axial Ray
A light ray that travels along the axis of an optical fiber.

B.P.S. (Bits Per Second)
The number of energy pulses passing a given point in a transmission medium in one second.

Backscattering
A small fraction of light that is reflected out of the original direction of propagation by scattering suffers a reversal of direction. In other words, it propagates in the optical waveguide towards the transmitter.

Bandpass
A range of wavelengths over which a component will meet specifications.

Bandwidth Limited Operation
The condition prevailing when the system bandwidth, rather than the amplitude of the signal, limits performance. The condition is reached when modal dispersion distorts the shape of the waveform beyond specified limits.

Bandwidth
Information carrying capacity of an optical fiber. Expressed in MHz-km, specifies the analog bandwidth capability or number of digital transitions per second the fiber can sustain over a 1 km distance. Bandwidth is dependent upon wavelength and type of light source.

Baseband
A method of communication in which a signal is transmitted at its original frequency without being impressed on a carrier.

BAUD
A unit of signaling speed equal to the number of signal intervals per second, which may or may not be equal to the data rate in bits per second. In some encoding schemes, such as Non Return to Zero (NRZ). baud rate equals the data rate. In others, such as Manchester encoding, two transitions per bit are required per baud.

Beamsplitter
A device used to divide an optical beam into two or more separate beams.

Bend Radius
Radius a fiber can bend before the risk of breakage or increase in attenuation. Also can refer to cable bend radius.

Bend Loss
A form of increased attenuation in a fiber that results from bending a fiber around a restrictive curvature (a macrobend) or from minute microbends.

BEND RADIUS The lower limit below which fiber or cable should not be bent for reasons of optical and mechanical performance. BER
Bit error rate. Specifies expected frequency of errors. The ratio of incorrectly transmitted bits to correctly transmitted bits.

Bit
A binary digit, the smallest element of information in binary system. A 1 or 0 of binary data.

Break-Out Cable
See Fan-Out Cable.

Broadband
The ability of a system to carry a multitude of signals simultaneously. In data transmission, it denotes transmission facilities capable of handling frequencies greater than those required for high-grade voice communications. The higher frequency allows the carrying of several simultaneous channels. Broadband infers the use of a carrier signal rather than direct modulation (i.e., baseband).

BUFFER
The protective coating over a fiber. The primary buffer (i.e., next to the cladding) is 250 microns in diameter. A secondary buffer of 900 micron diameter is used on indoor cables.

Buffered Fiber
Fiber protected with an additional material (hytrel or nylon) to provide ease in handling, connectorization and increased tensile strength.

Building Entrance
Terminal Cable entrance point where typically a trunk cable between buildings is terminated and fiber is then distributed through the building.

Bundle
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.

Bus Network
A network topology in which all terminals are attached to a transmission medium serving as a bus.

BUS
Commonly called "data bus", term used to describe the physical linkage between stations on a network sharing some common communication.

Byte
A unit of 8 bits (Digital Data).

Cable
An assembly of optical fibers and other material providing mechanical and environmental protection and optical insulation of the waveguides.

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

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

Carrier Sense Multiple Access With Collision Detection (CSMA/CD)
A technique used to control the transmission channel of a local area network to ensure that there is no conflict between terminals that wish to transmit.

Center Wavelength(s)
The nominal operating wavelength(s).

Central Member
The center component of a cable. It serves as an anti-buckling element to resist temperature-induced stresses. Sometimes serves as a strength element. The central member is composed of steel, fiberglass, or glassreinforced plastic.

Central Office (CO)
The place where communications common carriers terminate customer lines and locate switching equipment that interconnects those lines.

Channel
A communications path or the signal sent over that channel. Through multiplexing several channels, voice channels can be transmitted over an optical channel.

Chromatic Dispersion
Spreading of a light pulse caused by the difference in refractive indices at different wavelengths.

Cladding
The material surrounding the core of an optical fiber. The cladding must have a lower index of refraction in order to steer the light in the core.

Cladding Mode
A mode confined to the cladding; a light ray that propagates in the cladding.

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

Conduit
Pipe or tubing through which cables can be pulled or housed.

Connector
A mechanical device used to align and join two fibers together to provide a means for attaching and decoupling it to a transmitter, receiver or another fiber. Commonly used connectors include the FC, FCPC, Biconic, ST Connector-Compatible, D4, SMA 905 or 906.

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

Core Eccentricity
A measure of the displacement of the center of the core relative to the cladding center.

Coupler
(1) A passive device that distributes optical power among two or more ports. (Can be in various ratios.) Commonly called a splitlet. (2) A multipod device used to distribute optical power.

COUPLER
An optical device that coupes (or splits) light in accordance with its number of input and output legs.

Coupling Efficiency
The efficiency of optical power transfer between two components.

Coupling Ratio
The percentage of light transferred to a receiving output port with respect to the total power of all output ports.

Coupling Loss
The power loss suffered when coupling light from one optical device to another.

CPC
Customer Premises Communication

CPE
Customer Premises Equipment

Critical Angle
The smallest angle from the fiber axis at which a ray may be totally reflected at the core/cladding interface.

Cutoff Wavelength
The shortest wavelength at which only the fundamental mode of an optical waveguide is capable of propagation.

Data Rate
The maximum number of bits of information which can be transmitted per second, as in a data transmission link. Typically expressed as megabits per second (mb/s). dbm Decibel referenced to a milliwatt. dbp Decibei referenced to a microwatt.

Decibel (dB)
Unit for measuring the relative strength of a signal. Power level referenced in decibels to a microwatt.

Demultiplex
The process of separating optical channels.

Detector
(1) A transducer that provides an electrical output signal in response to an incident optical signal. The current is dependent on the amount of light received and the type of device. (2)A semiconductor device which converts optical energy to electrical energy.

Diameter-Mismatch Loss
The loss of power at a joint that occurs when the transmitting half has a diameter greater than the diameter of the receiving half. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.

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

Digital
A data format that uses two physical levels to transmit information. A discrete or discontinuous signal.

Direetivity
Also referred to as near-end crosstalk, it is the amount of power observed at a given input port with respect to an initial input power.

Dispersion
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: (a) mode dispersion caused by differential optical path lengths in a multimode fiber; (b) material dispersion caused by a differential delay of various wavelengths of light in a waveguide material; and (c) waveguide dispersion caused by light traveling in both the core and cladding materials in single­mode fibers.

Distortion-Limited Operation
Generally synonymous with bandwidth­limited operation.

Duplex Cable
A two-fiber cable suitable for duplex transmission.

Duplex Transmission
Transmission in both directions, either one direction at a time (half duplex) or both directions simultaneously (full duplex).

Duty Cycle
In a digital transmission, the ratio of high levels to low levels.

EIA
Electronic Industries Association. A standards association that publishes test procedures. See FOTP.

Electromagnetic Interference (EMI)
Any electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.

EMD
Equilibrium Mode Distribution.

ENCODING
A scheme to represent digital ones and zeros through combining high and low signal voltage states.

Excess Loss
(1) In a fiber-optic coupler, the optical loss from that portion of light that does not emerge from the nominally operational pods of the device. (2)The ratio of the total output power of a passive component with respect to the input power.

Extrinsic Loss
In a fiber interconnection, that portion of loss that is not intrinsic to the fiber but is related to imperfect joining, which may be caused by the connector or splice.

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

Ferrule
A small alignment tube attached to the end of the fiber and used in connectors. Generally made of stainless steel, alumina, or zirconia, used to confine and align the stripped end of a fiber.

Fiber Optic Link
Any optical fiber transmission channel designed to connect two end terminals or to be connected in series with other channels.

Fiber
Thin filament of glass. An optical waveguide consisting of a core and a cladding which is capable of carrying information in the form of light.

Fiber Optics
Light transmission through optical fibers for communication or signalling.

FOTP
Fiber Optic Test Procedures

FOTS
Fiber Optic Transmission System

FREQUENCY MODULATION (FM)
Transmission scheme whereby information is sent by varying the frequency of an optical carrier. A method of transmission in which the carrier frequency varies in accordance with the signal.

Fresnel Reflection
The reflection of a portion of the light incident on a planar surface between two homogeneous media having different refractive indices. Fresnel reflection occurs at the air/glass interfaces at entrance and exit ends of an optical fiber.

Fundamental Mode
The lowest order mode of a waveguide.

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

FUSION SPLICE
A joining of two fibers by physically fusing through heat the two fiber ends.

Gap Loss
Loss resulting from the end separation of two axially aligned fibers.

Graded-Index
Fiber design in which the refractive index of the core is lower toward the outside of the fiber core and increases toward the center of the core; thus it bends the rays inward and allows them to travel faster in the lower index of refraction region. This type of fiber provides high bandwidth capabilities.

Ground-Loop Noise
Noise that results when equipment is grounded at ground points having different potentials and thereby created an unintended current path. The dielectric of optical fibers provide electrical isolation that eliminates ground loops.

Hard Clad Silica
A fiber with a hard plastic cladding surrounding a silica glass core.

IEEE
Institute of Electrical and Electronics Engineering.

Index Matching Material
A material, often a liquid or cement whose refractive index is nearly equal to the core index, used to reduce Fresnel reflections from a fiber end face.

Index Profile
Curve of the refractive index over the cross section of an optical waveguide.

Index of Refraction
The ratio of light velocity in a vacuum to its velocity in a given transmitting medium.

INDEX OF REFRACTION
An optical characteristic (n) of a material, referencing the speed of light in that material to a vacuum.

Insertion Loss
The attenuation caused by the insertion of an optical component; in other words, a connector or coupler in an optical transmission system.

Isolation
Also referred to as far-end cross-talk or far-end isolation. Predominantly used in reference to WDM products, it is a measure of light at an undesired wavelength at any given port.

Jumper
Fiber optic cable that has connectors installed on both ends. See also cable assembly.

JUMPER
A section of cable with a connector an both ends.

Kevlar
See
Aramid Yarn

Kilometer
One thousand meters or 3,281 feet. The kilometer is a unit of measurement for fiber optics.

KPSI
A unit of tensile strength expressed in thousands of pounds per square inch.

LASER Light
Amplification by Stimulated Emission of Radiation. A device which produces coherent light with a narrow range of wavelengths.

Lateral Displacement Loss
The loss of power that results from lateral displacement from optimum alignment between two fibers or between a fiber and an active device.

Launch Angle
Angle between the propagation direction of the incident light and the optical axis of an opticat waveguide.

Launching Fiber
A fiber used in conjunction with a source to excite the modes of another fiber in a particular way. Launching fibers are most often used in test systems to improved the precision of measurements.

Light
In the laser and optical communication fields, the portion of the electromagnetic spectrum that can be handled by the basic optical techniques used for the visible spectrum extending from the near ultraviolet region of approximately 0.3 micron, through the visible region and into the mid­infrared region of about 30 microns.

LED (Light Emitting Diode)
A device used in a transmitter to convert information from electric to optical form. It typically has a large spectral width.LIGHT EMITTING DIODE (LED) A semiconductor diode which emits light when forward biased to an optical signal.

Lightguide Cable
An optical fiber, multiple fiber, or fiber bundle which includes a cable jacket and strength.

Lightwaves
Electromagnetic waves in the region of optical frequencies. The term "light" was originally restricted to radiation visible to the human eye, with wavelengths between 400 and 700 nanometers (nm). However, it has become customary to refer to radiation in the spectral regions adjacent to visible light (in the near infrared from 700 to about 2000 nm) as "light" to emphasize the physical and technical characteristics they have in common with visible light.

Link
A fiber optic cable with connectors attached to a transmitter (source) and receiver (detector).

LLDPE
Linear Low Density Polyethylene jacketing.

Local Area Network (LAN)
A geographically limited communications network intended for the local transport of data, video and voice.

Loose Tube
A protective tube loosely surrounding a cabled fiber, often filled with a water blocking gel.

LOOSE TUBE
Type of cable design, primarily for outdoor use, where one or more fibers are enclosed in hard plastic tubes. Fibers are usually buffered to 250 microns.

Loss
Attenuation of optical signal, normally measured in decibels.

Macrobending
Macroscopic axial deviations of a fiber from a straight line, in contrast to microbending.

Material Dispersion
The dispersion associated with a non-monochromatic light source due to the wavelength dependence of the refractive index of a material or of the light velocity in this material.

MDPE
Medium Density Polyetheylene jacketing.

Mechanical Splicing
Joining two fibers together by mechanical means to enable a continuous signal. Elastomeric splicing is one example of mechanical splicing.

Megahedz (MHz)
A unit of frequency that is equal to one million hertz.

Microbending
Curvatures of the fiber which involve axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Microbends cause loss of light and consequently increase the attenuation of the fiber.

Micron (um)
Another term for micrometer. One millionth of a meter. 10exp-6 meter.

Misalignment Loss
The loss of power resulting from angular misalignment, lateral displacement, and end separation.

Modal Dispersion
Pulse spreading due to multiple light rays traveling different distances and speeds through an optical fiber.

Mode Field Diameter (MFD)
The diameter of optical energy in a singlemode fiber. Because the MFD is greater than the core diameter, MFD replaces core diameter as a practical parameter.

Mode Filter
A device used to remove high-order modes from a fiber and thereby simulate EMD.

Mode Scrambler
A device composed of one or more optical fibers in which strong mode coupling occurs. Frequently used to provide a mode distribution that is independent of source characteristics.

Mode
A term used to describe a light path through a fiber, as in multi­mode or single­mode.

Mode Mixing
The numerous modes of a multi-mode fiber differ in their propagation velocities. As long as they propagate independently of each other, the fiber bandwidth varies inversely with the fiber length due to multi-mode distortion. As a result of inhomogenejties of the fiber geometry and of the index profile, a gradual energy exchange occurs between modes with differing velocities. Due to this mode mixing, the bandwidth of long multimode fibers is greater than the value obtained by linear extrapolation from measurements on shod fibers.

Modulation
Coding of information onto the carrier frequency. This includes amplitude, frequency, or phase modulation techniques.

Monochromatic
Consisting of a single wavelength. In practice, radiation is never perfectly monochromatic but, at best, displays a narrow band of wavelengths.

Multi-Mode Fiber
An optical waveguide in which light travels in multiple modes. Typical core/cladding sizes (measured in microns) are 50/125, 62.5/125, and 100/140.

MULTIMODE FIBER
A fiber type which supports multiple light paths through its core.

MULTIPLEX
The combination of several signals onto a single communications channel.

Multiplexing
The process by which two or more signals are transmitted over a single communications channel. Examples include time-division multipiexing and wavelength-division multiplexing.

NA-Mismatch Loss
The loss of power at a joint that occurs when the transmitting half has an NA greater than the NA of the receiving half. The loss occurs when coupling light from a soume to fiber, from fiber to fiber, or from fiber to detector.

Nanometer
A unit of measurement equal to one billionth of a meter. 10exp-9 meter.

NANOMETER Common unit of measure for wavelength One billionth of a meter.

NEC
National Electrical Code. Defines building flammatory requirements for indoor cables.

Numerical Aperture A numerical value that expresses the light gathering ability of a fiber.

Numerical Aperture (NA)
The number that expresses the light gathering power of a fiber.

NUMERICAL APERTURE
The imaginary cone which defines the acceptance area for the fiber core to accept rays of light.

Optical Time Domain Reflectometer (OTDR)
A method for characterizing a fiber wherein an optical pulse is transmitted through the fiber and the resulting backscatter and reflections to the input are measured as a function of time. Useful in estimating attenuation coefficient as a function of distance and identifying defects and other localized losses.

Optical Fiber
See
Fiber.

Optical Waveguide
Dielectric waveguide with a core consisting of optically transparent material of low attenuation (usually silica glass) and with cladding consisting of optically transparent material of lower refractive index than that of the core. It is used for the transmission of signals with lightwaves and is frequently referred to as fiber. In addition, there are planar dielectric waveguide structures in some optical components, such as laser diodes, which are also referred to as optical waveguides.

Optical Waveguide
See Fiber.

Optoelectronic
Pertaining to a device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electricalto-optical or optical-to-electrical transducer.

OTDR
Optical time domain Reflectometer. A test instrument, working on the principal of continuous energy backscatter, which provides a complete characterization of fiber loss along its length.

PCM
Pulse-Coded Modulation.

PCS
Plastic-Clad Silica.

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

Peak Wavelength
The wavelength at which the optical power of a source is at a maximum.

Photocurrent
The current that flows through a photosensitive device, such as a photodiode, as the result of exposure to radiant power.

Photodetector
An optoelectronic transducer, such as a pin photodiode or avalanche photodiode.

Photodiode
A diode designed to produce photocurrent by absorbing light. Photodiodes are used for the detection of optical power and for the conversion of optical power into electrical power.

Photon
A quantum of electromagnetic energy.

Pigtail
Fiber optic cable that has connectors installed on one end. See also
Cable Assembly.

PIN Photodiode
A diode with a large intrinsic region sandwiched between pdoped and n­doped semiconducting regions. Photons in this region create electron hole pairs that are separated by an electric field thus generating an electric current in the load circuit.

Plastic Fiber
An optical fiber having a plastic core and plastic cladding.

Plastic-Clad Silica Fiber
An optical fiber having a glass core and plastic cladding.

Plenum
Air duct inside buildings through which cable can be pulled or housed.

Plenum Cable
A cable whose flammability and smoke characteristics allow it to be routed in a plenum area without being enclosed in a conduit. Point-to-Point A connection established between two specific locations, as between two buildings.

Polarization Stability
The variation in insertion loss as the polarization state of the input light is varied.

Preform
A glass structure from which an optical fiber waveguide may be drawn.

Prefusing
Fusing with a low current to clean the fiber end. Precedes fusion splicing.

Primary Coating
The plastic coating applied directly to the cladding surface of the fiber during manufacture to preserve the integrity of the surface.

Pulse Spreading
The dispersion of an optical signal with time as it propagates through an optical fiber.

PUR
Polyurethane. Material used in manufacture of a type of jacketing material.

PVC
Polyvinyl Chloride. Material used in manufacture of a type of jacketing material.

Receiver
An electronic package which converts optical signals to electrical signals.

Receiver Sensitivity
The optical power required by a receiver for low error signal transmission. In the case of digital signal transmission, the mean optical power is usually quoted in Watts or dbm (decibels referred to 1 milliwatt).

Reflectance
Light that is reflected back along the path of transmission, from either the coupling region, the connector or a tertninated fiber.

Reflection
The abrupt change In direction of a light beam at an interface between two dissimilar media so that the light beam returns into the media from which it originated.

Refraction
The bending of a beam of light at an interface between two dissimilar media or a medium whose refractive index is a continuous function of position (graded index medium).

Refractive Index
See
Index of Refraction.

Regenerative Repeater
A repeater designed for digital transmission that both amplifies and reshapes the signal.

Repeater
A device which consists of a transmitter and a receiver or transceiver, used to regenerate a signal to increase the system length.

Return Loss
See reflectance.

Ring Network
A network topology in which terminals are connected in a point-to-point serial fashion in an unbroken circular configuration.

Rise Time
The time it takes the signal output to rise from low levels to peak value. Usually measured from 10% to 90% of max. output.

Riser
Application for indoor cables that pass between floors. It is normally a. vertical shaft or space.

Scattering
A property of glass which causes light to deflect from the fiber and contributes to losses.

Sensitivity
For a fiber-optic receiver, the minimum optical power required to achieve a specified level of performance, such as a BER.

Signal-to-Noise Ratio (SNR)
The ratio of signal power to noise power.

SIGNAL-NOISE RATIO
The ratio of signal power to noise power. Measured in dB.

Simplex Cable
A term sometimes used for a single­fiber cable.

Simplex Transmission
Transmission in one direction only.

Single-Mode Fiber
An optical waveguide (or fiber) in which the signal travels in one "mode". The fiber has a small core diameter.

SINGLE-MODE FIBER
A fiber type which supports a single path through its core, Wavelength dependent.

SMA
A connector type with screw threads,

Source
The means used to convert an electrical information carrying signal to a corresponding optical signal for transmission by fiber. The source is usually a Light Emitting Diode (LED) or Laser.

Spectral Width
A measure of the extent of a spectrum. For a source, the width of wavelengths contained in the output at one half of the wavelength of peak power. Typical spectral widths are 20 to 60 nm for an LED and 2 to 5 nm for a laser diode.

SPECTRAL WIDTH
The width of wavelengths in a light pulse, based on 50% intensity.

Splice
(1)A permanent joint between two optical waveguides. (2)Means for joining two fiber ends.

Splicing
The permanent joining of fiber ends to identical or similar fibers, without the use of a connector. See also Fusion Splicing and Mechanical Splicing.

Splice Closure
A container used to organize and protect splice trays.

Splice Tray
A container used to organize and protect spliced fibers.

Splitting Loss
See coupling ratio.

ST
A connector type with a bayonet housing which is spring loaded "ST" stands for "straight tip".

Star Coupler
An active or passive device where energy presented at an input port is distributed through several output ports.

Star Network
A network in which all terminals are connected through a single point, such as a star coupler.

Step-Index
Fiber Optical fiber which has an abrupt ("step") change in its refractive index, due to a core and cladding that have different indices or refraction. Typically used for single mode.

Strength Member
That part of a fiber optic cable composed of Kevlar aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.

Tap Port
In a coupler in which the splitting ratio between output pods is not equal, the output port containing the lesser power.

Tap Loss
In a fiber optic coupler, the ratio of power at the tap port to the power at the input port.

Tee Coupler
A Three-Pod Optical Coupler.

Thermal Stability
A measure of insertion loss variation as the device undergoes various environmental changes.

Tight Buffer
Type of cable construction whereby each glass fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900 microns. High tensile strength rating achieved, providing durability, ease of handling and ease of connectorization.

Time-Division Multiplexing (TDM)
A transmission technique whereby several low-speed channels are multiplexed into a high­speed channel for transmission.

Topology
The physical layout of a network.

Total Internal Reflection
Total reflection of light back into a material when it strikes the interface of a material having a lower index at an angle below the critical angle.

Transceiver
An electronic device which has both transmit and receive capabilities.

Transducer
A device for converting energy from one form to another, such as optical energy to electrical energy.

Transmission Loss
Total loss encountered in transmission through a system.

Transmitter
An electronic package which converts an electrical signal to an optical signal.

Tree Coupler
A passive fiber optical component in which power from one input is distributed to more than two output fibers.

UL
Underwriters Laboratories, Inc.

Uniformity
The maximum insertion loss difference between ports of a coupler.

Waveguide
Structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide.

Wavelength
The distance between two peaks of an electromagnetic waveform.

Wavelength Dependence
The variation in an optical parameter caused by a change in the operating wavelength.

Wavelength Division Multiplexing (WDM)
Simultaneous transmission of several signals in an optical waveguide at differing wavelengths.

WDM
Wavelength Division Multiplexer - a passive fiber optical device used to separate signals of different wavelengths carried on one fiber.

WIC
Wavelength Independent Coupler.