Industry Terms

Industry Terms


Fiber Information

APC Connector

APC ConnectorAn “angled physical contact” connector is polished on an 8o angle. When compared with a normal “physical contact” (PC) connector, an APC connector exhibits better reflectance properties, because the angled polish reduces the amount of light reflected at the connector interface. Connector types available with an angled polish include: SC, ST, FC, LC, MU, MT, MTP™

See also: fiber optic connectorPC connectorpolishingreflectance, UPC

Apex offset

The apex of the polished dome does not always coincide with the fiber core. Apex offset measures the lateral displacement between the actual placement of the apex and the ideal placement directly on the fiber core. Apex offset should be less than 50μm; otherwise, physical contact between fiber cores of the mated connectors might be prevented.


Attenuation is the measure of the reduction in signal magnitude, or loss, along a length of fiber. Attenuation in fiber optic cabling is usually expressed in decibels per unit length of cable (i.e. dB/km) at a specified wavelength.

See also: reflectanceinsertion loss

Bend insensitive fiber

Fibers that are designed for improved bend performance in reduced radius applications.

Biconic Connector

The biconic connector features a cone-shaped tip, which holds a single fiber. The dual conical faces ensure proper mating of the fibers in a connection. The ferrule can be made with either ceramic or stainless steel. Its rugged design allows the biconic connector to be used in military applications.


Breakouts refer to a multiple-fiber cable connectorized with either many single connectors or one or more multiple-fiber connectors on either end. A breakout assembly makes use of the fact that fiber optic cable can be separated into multiple fibers that are easily distributed and terminated individually or in groups. Also called “fanouts.”

See also: fiber optic cable


The cladding of an optical fiber surrounds the core and has a lower index of refraction than the core. This difference in refractive index allows total internal reflection to occur within the fiber core. Total internal reflection is the mechanism by which an optical fiber guides light.

See also: fibercoreindex of refractiontotal internal reflection


Corning’s line of bend insensitive optical fiber


A connector is an intervening device used to fasten or join. In fiber optics, connectors provide impermanent links between two optical cables, or a fiber optic cable and another optical component. Connectors must also maintain good optical contact between fibers at the connector interfaces.

See also: fiber optic connector


The core of an optical fiber denotes the central part of the fiber where the majority of the light propagates. In single mode fiber, the core is small in diameter (~8 μm), so that only one mode will propagate along its length. By contrast, the core of multimode fibers is larger (50 or 62.5 μm).

See also: fibercladdingsingle mode fibermultimode fiber

Duplex cable

A duplex cable consists of two separately buffered fibers, joined together into one fiber optic cable. A duplex cable resembles two simplex cables fused together along their length, like a lamp wire. Duplex cable ends may be distributed and terminated separately, or they might be connectorized with one duplex connector, such as the MT-RJ. Duplex cables are most useful as a two-way communication channel, such as a transmit/receive pair running to a computer.

See also: Simplex cablefiber optic cable

D4 Connector

The D4 connector holds a single fiber in a 2.0 mm ceramic ferrule. The D4 connector’s body is similar in design to the FC connector, except for the smaller ferrule, and a longer coupling nut. Properties and applications of the D4 are likewise comparable to the FC.

E2000 Connector

The E2000 connector holds a single fiber in a ceramic ferrule. E2000’s are small form factor connectors with a moulded plastic body similar to that of an LC. The E2000 also exhibits a push- pull latching mechanism, and integrates a protective cap over the ferrule, which acts as a dust shield and shields users from laser emissions. The protective cap is loaded with an integrated spring to ensure proper closing of the cap. Like other small form factor connectors, the E-2000 connector is suited for high-density applications.


Enclosures are wall-mounting or ceiling-mounting devices containing fiber and fiber optic connectors in high density. An enclosure provides a system with modularity, security, and organisation. One common application for such enclosures is use in a telecommunications closet or patch panel.

See also: fiber optic assemblies


Usually refers to a single filament made of a dielectric material such as glass or plastic, which is used to guide optical signals. A fiber consists of a core, and cladding with slightly lower index of refraction. In addition, the fiber is protected by a buffer layer, and often also covered in Kevlar (aramid yarn) and more buffer tubing. Optical fibers may be used as a channel to guide light for purposes of illumination or for data and communications applications. Multiple fibers may be grouped together in fiber optic cables. The diameter of the fiber is usually expressed in microns, with the core diameter shown first, followed by the total fiber diameter (core and cladding together). For instance, a 62.5/125 multimode fiber has a core 62.5μm in diameter, and is 125μm in diameter in total.

See also: corecladdingfiber optic cablesingle mode fibermultimode fiberpolarization maintaining fiberribbon fiberindex of refraction


The endface of a connector refers to the circular cross-section of the filament where light is emitted and received, and the surrounding ferrule. The endface is often polished to improve upon the endface geometrical properties, which in turn provide better optical coupling. The fiber endface undergoes a visual inspection for defects, as well as testing on an interferometer, for endface geometry that will encourage good mating between connectors. Three main properties are examined on the interferometer:

Fiber protrusion or undercut

The distance between the fitted domed surface of the ferrule and the polished fiber end is called fiber undercut or fiber protrusion. If the fiber end is cut beneath the surface of the ferrule, it is said to be undercut. If the fiber end extends above the ferrule surface, it is said to protrude. Proper undercut or protrusion allows the fibers to maintain physical contact, while avoiding damage to the fiber itself. For a UPC connector, the protrusion ranges from +50 to ¬125 nm, depending on the radius of curvature. For the APC connector, the range is from +100 to ¬100 nm.

See also: polishingfiberinterferometerferruleUPCAPC

FC Connector (Fiber Connector)

The FC connector holds a single fiber in a standard-sized (2.5 mm) ceramic ferrule. The connector body is made of nickel-plated brass, and features a key-aligned, threaded locking coupling nut for repeatable, reliable coupling. The threaded coupling nut provides a secure connector even in high-vibration environments, although it takes slightly longer to connect, since it requires turning the connector instead of a simple push and click. Some FC style connectors exhibit tunable keying, which means the connector key can be tuned to obtain the best insertion loss, or to otherwise align the fiber.

See more: FC Connectors

* FC-PM assemblies are available, with the FC key aligned to either the fast or slow polarization axis.
Key-aligned FC-PM assemblies are available in either wide or narrow key varieties.


A ferrule is a precision ceramic or metal tube within a fiber optic connector that holds and aligns the fiber. Some fiber optic connectors, such as the MTP™ connector, have a single, monolithic ferrule, which consists of a single solid component that holds several fibers in a row. Ceramic ferrules offer the best thermal and mechanical performance, and are preferred for most single-fiber connectors.

See also: fiber optic connectorfiberMTP™ connector

Fiber distribution module (FDM)

Fiber distribution modules contain pre-connectorized and pre-tested fiber optic cables. These assemblies mount easily into traditional patch panels. FDM’s provide a modular, compact, and organised fiber optic solution.

See also: fiber optic assemblies

Fiber optics Abbreviated “FO”

Fiber optics refers in general to the use of flexible glass or plastic fibers in controlling the propagation of light for illumination or data communications purposes. A light beam is produced at a source, such as a laser or LED, and propagates through the channel provided by the fiber optic cable to a receiver. Along the length of the fiber channel, different fiber optic components and cables will be connected together; for instance, the light source must be coupled into the first fiber to transmit any signal. At these interfaces between components, fiber optic connectors are often used.

See also: fiber optic connector,  fiber optic cable,  fiber optic assemblies,  fiber

Fiber optic assemblies

A fiber optic assembly generally contains pre-connectorized and pre-tested fiber optic connectors and cabling in a modular attachment that mounts into standard patch panels. Fiber optic assemblies come in many shapes and sizes, including custom-sized assemblies.

See also: Gator patch™,  fiber distribution module,  enclosure,  Polarization maintaining fiberoptical circuit assemblies

Fiber optic cable

A fiber optic cable consists of a package of one or more optical fibers. Packaging of the fragile glass fiber offers protection from the elements and additional tensile strength. Fiber optic cabling provides many arrangements of optical fibers. A single fiber may be buffered by tight or loose tubing. Multiple fibers may be contained in a single fiber optic cable, which might then be fanned out in a distribution cable. Fiber optic cables also offer many variations in the connectorization of the cord. A connector on one end is called a pigtail, a cable with connectors on each end is called a patch cord or jumper, and a multi-fiber cable with a single connector on one end and multiple connectors on the
other can be called a breakout.

See also: fiber,  patch cord,  breakout,  pigtail

Fiber optic connector

A device mounted to the end of a fiber optic cable, light source, or optical receiver, which mates to a similar device to couple light into and out of optical fibers. Fiber optic connectors provide an impermanent connection between two fiber optic components, and can be removed and reconnected in a new configuration if desired. Unlike an electrical connector, where contact of conductors is enough to pass the signal, an optical connection must be precision-aligned to permit the light to pass from one optical fiber to another with minimal loss.

Fiber optic connectors are joined to fiber optic cables by a process called termination. The connector endfaces are then polished to lessen the amount of light lost at the interface between two connectors. The polished connectors then undergo a series of tests that certify the optical performance of the connector.

Types of fiber optic connector include: SC, ST, FC, LC, MU, MTRJ, D4, E2000, Biconic, MT, MTP™, MPO, SMC, SMA

See also: connectorfiber optic cableterminationpolishinginsertion lossreflectanceinterferometersmall form factor connectorUPCAPCPC

Gator PatchTM

Fiber distribution modules contain pre-connectorized and pre-tested fiber optic cables. These assemblies mount easily into traditional patch panels. FDM’s provide a modular, compact, and organised fiber optic solution.

See also: fiber optic assemblies

Index of refraction

The index of refraction of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium. Also called “refractive index.”

See also: fibercorecladdingtotal internal reflection

Industrial wiring

Industrial wiring involves the use of fiber optic cable in an industrial application, such as communication or lighting. Also called “industrial cabling.”

See also: fiber optic cablepremise wiring

Insertion loss

Insertion loss is the measure of reduction in signal magnitude caused by inserting a component, such as a connector, into a previously connected optical path. This measurement allows for analysis of the impact of inserting a single optical component into a system, sometimes called “calculating a loss budget.” Insertion loss is measured in decibels (dB).

See also: attenuationreflectance


In reference to testing fiber optic cable assemblies, an interferometer is used to measure the endface geometry of the connector after polishing. An interferometer measures the differences in path length of light reflected off the connector endface. Interferometer measurements are accurate to within one wavelength of the light used in measurement.

See also: endfacepolishing

LC Connector

The LC connector holds a single fiber in a 1.25 mm ceramic ferrule, half the size of the standard SC ferrule. LC connectors are examples of small form factor connectors. The connector body is made of moulded plastic, and features a square front profile. An RJ-style latch (like that on a phone jack) on the top of the connector provides easy, repeatable connections. Two LC connectors may be clipped together to form a duplex LC. The small size and push-in connections of LC connectors make them an excellent choice for high-density fiber applications, or for cross connects.

See more: LC Connectors

* LC-PM assemblies are available, with the LC key aligned to either the fast or slow polarization axis


A mode of light is a distribution of the electromagnetic field that satisfies boundary conditions for a waveguide, such as an optical fiber. A mode can be visualized as the path of a single ray of light in the fiber. In multimode fibers, where the core is larger, more paths are available for rays of light to propagate.

See also: single mode fibermultimode fiber

MPO connector

The MPO connector houses an MT ferrule, and so can provide for upwards of twelve fibers in a single connector. Like an MTP™, MPO connectors operate with a simple push-pull latching mechanism and intuitive insertion. MPO’s may be polished flat or at an 8o angle. See more

See more: MPO connector

MTP™ connector

An MTP™ connector can house up to twelve and sometimes more optical fibers in a single, monolithic ferrule. The same style of monolithic ferrule provides a basis for other connectors, such as the MPO. The MT-style connectors save space by providing at least twelve potential connections with a single ferrule, replacing up to twelve single-fiber connectors. MTP™ connectors provide an intuitive push-pull latching mechanism for easy insertion. MTP is a trade mark of USConec.

See more: MTP Connectors

MTRJ connector

The MTRJ connector holds a pair of fibers in a monolithic ferrule made of a plastic composite. The ferrule is held inside a plastic body that clips into a coupler with an intuitive push and click motion, much like the copper RJ-45 jack. The fibers are aligned by the pair of metal guide pins in the end of the ferrule of a male connector, which join into guide pinholes on the female connector inside the coupler. The MT-RJ connector is an example of a duplex small form factor connector. Having the pair of fibers held by a monolithic ferrule makes it easy to maintain the polarity of connections, and renders the MT-RJ ideal for applications such as horizontal fiber runs in facility cabling.
See more: MTRJ connectors

MU Connector (Miniature Unit)

The MU connector holds a single fiber in a ceramic ferrule. MU connectors are small form factor connectors that emulate the design           of the larger SC connector. The MU exhibits a square front profile and a moulded plastic body that provides simple push-pull latching         connections. The MU connector is well suited for high-density applications.

See more: MU Connectors

Multimode fiber

Multimode fiber allows multiple modes of light to propagate along its length at various angles and orientations to the central axis. Conventional sizes of multimode fiber are 62.5/125μm or 50/125μm.

See also: fibersingle mode fiber,


Stands for Open Device Vendor Association – specifies cables and connectors for Industrial Ethernet/IP Networks

OM1, OM2, OM3, OM4

OMx fiber classifications refer to different types/grades of multimode fiber in terms of bandwidth as specified in ISO/IEC 11801

Optical circuit assemblies.

An optical circuit assembly may contain many connectors joined by fiber and mounted onto a circuit board.

Optical circuits come in custom configurations

See also: fiber optic assemblies

OS1, OS2

References for cabled single mode optical fiber specifications. OS1 is standard SM fiber while OS2 is low water peak, enhanced performance.

Patch cord

A patch cord is a fiber optic cable with a single connector on each end. Patch cords are useful in cross connects in a system, or for connecting a patch panel to another optical component or device. Also called a “jumper.”

See also: fiber optic cable

PC connector

A “physical contact” connector is polished in a dome-shaped geometry to maximize the signal transmitted at the connection.

See also: fiber optic connectorAPC connectorpolishingUPC


A pigtail refers to a fiber optic cable with a connector at one end. The end without a connector is often permanently connected to a device, such as a testing apparatus, or a light source.
See also: fiber optic cable

Polarization Maintaining Fiber

Polarization maintaining fiber (also called “PM fiber”) places stresses on the fiber core, creating two perpendicular transmission axes. If linearly polarized light is input to the fiber along one of these axes, the polarization state is maintained for the length of the fiber. Common types of PM fiber include “PANDA Fiber” and “TIGER fiber” type fibers.

See also: fiber, polarization maintaining fiber assembly

Polarization maintaining fiber assembly

Polarization maintaining fiber assemblies are manufactured with polarization maintaining (PM) fiber. The connectors on either end can be aligned using the connector key to the fast axis, the slow axis, or to a customer-specified angular offset from one of these axes. Connector keying allows easy, repeatable alignment of the fiber axes to the input polarized light.

See also: fiber optic assembliespolarization maintaining fiber


Fiber optic connectors are often polished after termination to remove surface defects and to improve optical qualities such as insertion loss and backreflection. PC and UPC connectors are polished flat (perpendicular to the length of the straight fiber), whereas APC connectors are polished on an 8o angle from the flat. In all these cases, the ferrule endface adopts a dome-shaped geometry that yields good mating properties in the conenctor.

See also: PCAPCfiber optic connectorendface

Premise wiring

Premise cabling involves the manufacture, installation, and maintenance of fiber optic cabling in a building network or campus network (for a group of buildings). Also known as “building wiring,” “building cabling,” “facility wiring,” or “facility cabling.”

See also: fiber optic cableindustrial wiring

Radius of curvature

Nominally, a polished ferrule will have a dome-shaped surface, permitting two coupled ferrules to come into contact over a small surface area in the region of the fiber. A small radius of curvature indicates a smaller contact area between the ferrules. Radius of curvature for a UPC connector should fall between 7 and 25mm, whereas for an APC connector, the range of acceptable radii is from 5 to 12mm.


Reflectance is a measure of the light reflected from the cleaved or polished fiber end at the glass/air interface. Reflectance is expressed in dB relative to the incident signal. Reflectance is important in optical systems because some active optical components are sensitive to light reflected into them. Reflected light is also a source of loss. Also known as “backreflection,” and “optical return loss.”

See also: insertion lossattenuation

Ribbon fiber

Ribbon fiber consists of multiple fibers (usually 6, 8, or 12) bound together in a flat ribbon. Fibers are colour-coded for easy identification. Ribbon fiber may be either single mode or multimode and may be contained within a buffer tube. A single multi-fiber connector, such as an MTP™, may terminate one ribbon fiber, or the ribbon fiber could be fanned out into many single-fiber connectors.

See also: fiberfiber optic cable

SC Connector (Subscriber Connector)

The SC connector holds a single fiber in a standard-sized (2.5 mm) ceramic ferrule. The connector body has a square front profile, and is made of moulded plastic. Clips on either side of the body and the connector key allow for easy push-in connections. This push-pull latching mechanism makes the SC connector preferred in high-density interconnect applications such as telecommunications closets and premise wiring. Two SC connectors may be mounted side by side on duplex cable. SC connectors have been preferred by the TIA/EIA-568-A industry standard for premise cabling because it is felt to be easier to maintain the polarity of duplex cables with this type of connector.

See more: SC Connectors

* SC-PM assemblies are available, with the SC key aligned to either the fast or slow polarization axis

Simplex cable

A Simplex cable carries a single optical fiber within a buffer tube. Simplex cable is often used in jumper and pigtail assemblies.

See also: Duplex cablefiber optic cable

Single mode fiber

Single mode fiber allows a single mode of light to propagate along its core efficiently. Conventional sizes of single mode fiber are 8/125μm, 8.3/125μm or 9/125μm. Single mode fiber allows very high-speed transmission, and a single mode system is usually only limited in signal transmission by the electronic components on either the transmitting or receiving end.Single mode fiber allows a single mode of light to propagate along its core efficiently. Conventional sizes of single mode fiber are 8/125μm, 8.3/125μm or 9/125μm. Single mode fiber allows very high-speed transmission, and a single mode system is usually only limited in signal transmission by the electronic components on either the transmitting or receiving end.

See also: fibermultimode fiber,

Small form factor connector

The small form factor connectors improve upon the larger traditional connector styles (like the ST, SC, and FC connectors) with their smaller size, while using proven connector design ideas. These smaller styles of connector were developed to meet the need for high-density connections in fiber optic components. Most small form factor connectors also provide easy “push-in” connectivity. Many of the small form factor connectors emulate the copper RJ-45 jack’s intuitive operation and design. Small form factor fiber optic connectors include: LC, MU, MTRJ, E2000

See also: fiber optic connector

ST Connector (Straight Tip connector)

The ST connector holds a single fiber in a standard-sized (2.5 mm) ceramic ferrule. The connector body is made of a plastic composite, and the connector couples using a twist-lock mechanism. This connector type is often found in data communications applications. The ST is versatile, and very popular, as well as comparably cheaper than some other
connector styles.

See more: ST Connectors


The SMC connector holds multiple fibers in an MT ferrule. The SMC has been submitted for review as an industry standard connector. SMC connectors easily terminate buffered or non-buffered ribbon fiber. A variety of connector configurations exist, depending on the needs of the application. For instance, the SMC has three different body lengths available, depending on size considerations. The plastic molded body uses side-mounted locking clips to hold the connector in place.


Termination is the act of attaching the fiber optic connector to the end of an optical fiber or fiber optic cable. Terminating an optical assembly with connectors allows for easy, repeatable use of the assembly in the field. Also called “connectorization.”

See also: fiber optic connectorfiberfiber optic cable

Total internal reflection

Total internal reflection is the mechanism by which an optical fiber guides light. At the interface between the core and cladding (which have different indices of refraction), there exists a critical angle such that light incident at any smaller angle will be entirely reflected (none is transmitted into the cladding where it is lost). The critical angle depends on both the index of refraction in the core and in the cladding.

See also: index of refraction corecladdingfiber


UPC, or “Ultra Physical Contact,” describes connectors that undergo extended polishing to render the fiber endface more suitable for optical contact with another fiber than an ordinary PC connector. UPC connectors, for example, exhibit better reflectance properties (< -55dB).

See also: PCpolishingreflectanceAPC

Visual inspection

After termination and polishing, a fiber optic connector undergoes visual inspection to ensure the endface of the fiber does not contain any faults, such as scratches or pitting. The visual inspection stage ensures that the polished fibers are of consistent quality. A clean fiber endface, without scratches or pits, provides better optical properties and improves the connector’s re-mateability as well as the overall lifetime of the connector.