Industry Glossary

Click on a letter to view the terms and definitions:
A  B  C  D  E  F  G  H  I   J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

— A —


Abbreviation for AC power.  An electric current which periodically reverses direction

APC Polishing

The angled physical contact (APC) polish adds an 8 degree angle to a flat polish. Back reflection can be reduced to about —70 dB with this technique.


Loss of power in an optical fiber, resulting from conversion of optical power into heat and caused principally by impurities, such as transition metals and hydroxyl ions, and also by exposure to nuclear radiation.


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).

Active Branching Devices

A device which converts an optical input into two or more optical outputs with gain or regeneration.

Adjustable Attenuator

An attenuator in which the level of attenuation is varied with an internal adjustment. Also known as variable Attenuator.

Angular Misalignment

The loss of optical power caused by deviation from optimum alignment of fiber to fiber or fiber to waveguide.


A general term indicating a decrease in power from one point to another. In optical fibers, it is measured in decibels per kilometer at a specified wavelength.

Avalanche Photodiode (APD)

A photodiode that exhibits internal amplification of photo current through avalanche multiplication of carriers in the junction region.

Average Wavelength (l)

The average of the two wavelengths for which the peak optical power has dropped to half.


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—B —


The return of a portion of scattered light to the input end of a fiber; the scattering of light in the direction opposite to its original propagation.


A range of frequencies.

Bandwidth-Limited Operation

The condition in a fiber optic link when bandwidth, rather than received optical power, limits performance. This condition is reached when the signal becomes distorted, principally by dispersion, beyond specified limits.

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 distortions in the fiber (microbend).


A method of communication in which the signal is transmitted by being impressed on a higher-frequency carrier.

Buffer Coating

A protective layer, such as an acrylic polymer, applied over the fiber cladding for protective purposes.

Buffer Tube

A hard plastic tube, having an inside diameter several times that of a fiber, that holds one or more fibers.


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—C —

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 singlemode fiber optical cable systems and optoelectronics equipment. If connectors are attached to only one end of the cable, it is known as a pigtail. It’s 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.

Center Wavelength (Laser)

The nominal value central operating wavelength. It is the wavelength defined by a peak mode measurement where the effective optical power resides.

Center Wavelength (LED)

The average of the two wavelengths measured at the half amplitude points of the power spectrum.

Chromatic Dispersion

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


The outer concentric layer that surrounds the fiber core and has a lower index of refraction.

Cladding Mode

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


The process of separating an optical fiber by a controlled fracture of the glass, for the purpose of obtaining a fiber end, which is flat, smooth, and perpendicular to the fiber axis.


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


A device for making connectable/disconnectable connections of a fiber to another fiber, source, detector, or other devices.

Connector Plug

A device used to terminate an optical conductor cable.

Connector Receptacle

The fixed or stationary half of a connection that is mounted on a panel/bulkhead. Receptacles mate with plugs.

Connector Variation

The maximum value in dB of the difference in insertion loss between mating optical connectors (e.g., with remating, temperature cycling, etc.). Also known as Optical Connector Variation.


The central, light-carrying part of an optical fiber; it has an index of refraction higher than that of the surrounding cladding.

Core Eccentricity

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

Core Ellipticity (non-circularity)

A measure of the departure of the core from roundness.


A multiport device used to distribute optical power.

Coupling Efficiency

The efficiency of optical power transfer between two components.

Coupling Ratio/Loss (CR, CL)

The ratio/loss of optical power from one output port to the total output power, expressed as a percent. For a 1* 2 WDM or coupler with output powers 01 and 02, and Oi representing both output powers.

Critical Angle

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

Cut-off  Wavelength

For a singlemode fiber, the wavelength above which the fiber exhibits singlemode operation.


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—D —




Decibel referenced to a milliwatt.


Decibel referenced to a microwatt.


A standard logarithimic unit for the ratio of two powers, voltages or currents. In fiberoptics, the ratio is power.


An optoelectronics transducer used in fiberoptics for converting optical power to electric current. In fiberoptics, usually a photodiode.

Dichroic Filter

An optical filter that transmits light selectively according to wavelength.

Diffraction Grating

An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhance the effects of diffraction to concentrate the diffracted light in a few directions determined by the spacing of the lines and by the wavelength of the light.


See Near-end Crosstalk.


A general term for those phenomena that cause a broadening or spreading of light as it propagates through an optical fiber.The three types are model, material and waveguide.

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).


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—E —

Excess Loss

In a fiberoptic coupler, the optic loss from that portion of light that does not emerge from the nominally operational ports of the device.

Extinction Ratio

The ratio of the low, or off optical power level (PL) to the high, or on optical power level (PH) when the station is transmitting a stream of Halt symbols. Extinction Ratio (%) = (PL/PH) * 100

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.


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—F —


Fiber Distributed Data Interface.


A mechanical fixture, generally a rigid tube, used to confine and align the stripped end of a fiber.

Fiberoptic Attenuator

A component that is installed in a fiberoptic transmission system to reduce the power in the optical signal. It is often used to limit the optical power received by the photodetector to within the limits of the optical receiver.

Fiberoptic Communication System

The transfer of modulated or unmodulated optical energy through optical fiber media which terminates in the same or different media.

Fiberoptic Link

A combination of fiberoptic spans and repeaters which are concentrated to form a transmission path.


Dielectric material the guides light; waveguide.

Fiberoptic Cable

A cable containing one or more optical fibers.

Fiber Optic Test Procedure (FOPT)

Standards developed and published by the Electronic Industrials Association (EIA) under the EIA-RS-455 series of standards.

Flat Polishing

A flat polish of the endface results in back reflection of about —14 dB (4%).


Abbreviation for Fiber-to-the-Home.

Fusion Splicing

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


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—G —

Graded-index Fiber

An optics fiber whose core has a nonuniform index of refraction. The core is composed on concentric rings if glass whose refractive ineices decrease from the center axis. The purpose is to reduce model dispersion and thereby increase fiber bandwidth.


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—I —

Index of Refraction

The ratio of the velocity of light in free space to the velocity of light in a given material. Symbolized by n.

Index-Matching Material

A material, used at optical interconnection, having a refractive index close to that of the fiber core and used to reduce Fresnel reflections.

Insertion Loss

The loss of power that results from inserting a component, such as a connector or splice, into a previously continuous path.


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— J —


Fiberoptic cable that has connectors installed on both ends.


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— L —


A light source producing, through simulated emission, coherent, near monochromatic light. Lasers in fiberoptics are usually solid-state semiconductor types.

Launch Angle

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

Launch Fiber

An optical fiber used to couple and condition light from an optical source into an optical fiber. Often the launch fiber is used to create an equilibrium model distribution in multimode fiber. Also referred to as launching Fiber.


In the laser and optical communication fields, the portion of the electrode 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 mid-infrared region of about 30 microns.

Light-Emitting Diode (LED)

A semiconductor diode that spontaneously emits light from the pn junction when forward current is applied.


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 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.


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— M —

Mechanical Splicing

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

Megahertz (Mhz)

A unit of frequency that is equal to one million hertz.


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.


Another term for micrometer. One millionth of a meter. 10epx-6 meter.

Misalignment Loss

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

Modal Dispersion

Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber.


In guided wave propagation, such as through a waveguide or optical fiber, a distribution of electromagnetic energy that satisfies Maxwell’s equations and boundary conditions. Loosely, a possible path followed by light rays.

Mode Field Diameter (MFD)

The diameter of optical energy in a singlemode fiber. Because the MFD is greater than the core diameter, MFD laser core diameter as a practical parameter.

Mode Filter

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

Multimode Fiber

A type of optical fiber that supports more than one propagating mode.


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


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— N —


A unit of measurement equal to one billionth of a meter.

Near-end Crosstalk

The optical power reflected from one or more input ports, back to another input port.

Numeric Aperture (NA)

The “lightgathering ability” of a fiber, defining the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA=sinq, where q is the acceptance angle. NA also is used to describe the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.


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— O —


Original Equipment Manufacturer.

Optical Bandpass

The range of optical wavelengths which can be transmitted through a component.

Optical Channel Spacing

The wavelength range of a channel.

Optical Channel Width

The optical wavelength range of a channel.

Optical Fiber

Dielectric material that guides light; optical waveguide.

Optical Isolator

A component used to block out reflected and other unwanted light.

Optical Return Loss (ORL)

The ratio (expressed in units of dB) of optical power reflected by a component or an assembly to the optical power incident on a component port when that component or assembly is introduced into a link or system.


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— P —

PC Polishing

The physical contact (PC) polish produces a slightly curved endface that forces the fibers in the mating connectors into contact. This reduces back reflection to about —40dB.

Passive Branching Device

A device which divides and optical input into two or more optical outputs.

Peak Wavelength

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


An optoelectronic tansducer, such as a pin photodiode or avalanche photodiode.


A short length of fiber permanently attached to a component, such as a source, detector, coupler or connector.

Pin Photodiode

A photodiode having a large intrinsic layer sandwiched between p-type and n-type layers.


The direction of the electric field in the lightwave.


Hardware entity at each end of the link.


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 manufacturing to preserve the integrity of the surface.


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— S —

SPC Polishing

The super physical contact (SPC) polish includes an extended polishing cycle for a better surface finish, resulting in back reflection as low as —55 dB.


For a fiberoptic receiver, the minimum optical power required to achieve a specified level of performance, such as BER.

Signal-to-Noise Ration (SNR, S/N)

The ratio (usually expressed in dB) of the dominant mode power Pd, to the power of the largest side mode, Ps.

Simplex Cable

A term sometimes used for a single-fiber cable.

Simplex Transmission

Transmission in one direction only.

Singlemode Fiber

An optical fiber that supports only one mode of light propagation above the cutoff wavelength.


The light emitter, either an LED or laser diode, in a fiberoptic link.

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.

Splice Closure

A container used to organize and protect splice trays.

Splice Tray

A container used to organize and protect spliced fibers.


The permanent joining of fiber ends to identical or similar fibers, without the use of a connector.

Stabilized Light Source

An LED or laser diode that emits light with a controlled and constant spectral width, central wavelength, and peak power with respect to time and temperature.

Star Coupler

A fiberoptic coupler in which power at any input port is distributed to all output ports.

Step-Index Fiber

An optical fiber, either multimode or singlemode, in which the core refractive index is uniform throughout so that a sharp step in refractive index occurs at the core-to-cladding interface. It usually refers to a multimode fiber.


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— T —

Tee Coupler

A three-port optical coupler.

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.

Transmission Loss

Total loss encountered in transmission through a system.


A physical topology consisting of a hierarchy of master-slave connections between a concentrator and other FDDE nodes (including subordinate concentrators).


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— U —

UPC Polishing

The ultra physical contact (UPC) polish includes an extended polishing cycle for a better surface finish, resulting in back reflection as low as —55 dB.


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— W —

Wavelength-Division Multiplexers (WDMs)

Passive fiberoptic components which combine or separate optical channels.

Wavelength-Division Multiplexers

A transmission technique by which separate optical channels, distinguished by wavelength, are multiplexed onto an optical fiber for transmission.

Wavelength Isolation

A WDM’s isolation of light signal in the desired optical channel from the unwanted channels. Synonym: Far-end Crosstalk.