Friday, June 11, 2010

How It's Made: Fiber Optic Cable

Corning has been a leading manufacturer of fiber optic cables since the beginning. State of the art test equipment and highly trained professionals ensure top quality fiber optic products. Take a look at the process involved in making, testing, and the history of fiber optic cable.

For more information, visit Fiber Optic Cable

Related Fiber Posts:
Loose Tube vs Tight Buffer Fiber - What's the Difference?
10 Gigabit Ethernet Technology Overview
Glossary of Common Fiber Optic Terms
How To Make Fiber Optic Patch Cables... Kinda

Monday, June 7, 2010

What is Plenum Cable/Innerduct and When Do I Use it?

What is Plenum?

According to the National Electric Code (NEC) a plenum is a "compartment or chamber to which one or more air ducts are connected and [which] forms part of the air distribution system." To qualify as a plenum, the space above an acoustic tile ceiling would have to extend above other rooms in the same building or be open to ducts connecting it to other parts of the building. The concern is that during a fire, if there is burning material in a plenum air space, smoke and fumes can travel through air ducts to the whole building. For this reason, there are codes to restrict the types of materials (such as wiring) that can be placed in the plenum.

It's quite common to have an acoustic tile ceiling without having a plenum. If your room-dividing walls extend above the dropped ceiling and seal off the space above, you do not have a plenum air space and so may not require plenum-rated wires. You can lift up an acoustical tile in your room and peek in to see if your room has a plenum.

What is the code?

According to the National Electric Code (NEC), in plenum air spaces you must use plenum rated cables, also called Communications Plenum Cable (CMP). Plenum cable is only required when cable is installed in a plenum air space. Materials kept below the ceiling — including speaker wire, computer cables, telephone cords, etc. — do not need to be plenum rated according to the NEC.

Remember that even though the National Electric Code may allow non- plenum cable, the final decision is up to your local Fire Marshall. Most cities adopt the national codes as their own without revision, but some cities modify or expand them and require plenum-rated cable in all situations. Regardless of the code or its interpretation, your Fire Marshall makes the final decision. We recommend that you contact your Fire Marshall if you have questions.

Why is the regulation for plenum air spaces but not for inside the classroom?

It's dangerous to inhale fumes from any burning material. Communications cable is no more dangerous than any other plastic item you would find below the ceiling in a typical classroom — computers, carpet, power cords, etc. Therefore, requiring the use of plenum wires within the classroom itself would have little impact. The regulation covers the area where it's most critical.

How is plenum cable and innerduct different from CRM/PVC?

The Plenum rated coating on wire burns at a much higher temperature and emits fewer fumes.

What does plenum wire look like?

Identifying this cable just by looking at it is hard to tell. It is very similar in look and feel, so you'll want to check the print on the jacket for the letters "CMP"

Who sets the guidelines?

The National Electrical Code (NEC) is a set of guidelines recommending procedures to reduce the risk of fires, electric shock and other hazards associated with electrical installations. The code is advisory in nature, but most state and local building departments across the country use the NEC as the basis for their own electrical codes. Some local codes may be more restrictive, so please check with your local Fire Marshall if you're unsure.

Is compliance with the locally-adopted code mandatory?

Yes. City, county or state codes are mandatory and enforceable as law.

Make sure you and your contractor are on the same page. When life has been lost in a fire a lawsuit is not out of the question if plenum wire has not been installed when it should have been.

Friday, June 4, 2010

Glossary of Common Fiber Optic Terms: R - Z

Common Fiber Terms A-E

Common Fiber Terms F-L

Common Fiber Terms M-P

Common Fiber Terms: R-Z


Rack Panels
Framework or boxes to hold patch panels and other cable management devices.

Rayleigh Scattering
Scattering by refractive index fluctuations (inhomogeneities in material density or composition) that are small with respect to wavelength. Referred to as backscatter.

A device which detects an optical signal, converts into an electronic form, then processes it further so it can be used by electronic equipment. From the standpoints of components, it can be viewed as a combination of detector and single processing electronics.

Receiver I.C.
Consists of photodiode which converts the signal to an elec­tronic one which feeds into an amplifier bringing the signal back to a level.

Receiver Sensitivity (expressed in dBm)
This tells how much optical power the photo-detector must receive to achieve a specified base band per­formance, such as a specified bit-error rate of signal-to-noise ratio.

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.

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

Repeater (fiber optic)
A device which detects a weak signal in a fiber optic communication system, amplifies it, cleans it up, and retransmits it in optical form. Also known as a regenerator.

Return Loss
Expressed in negative value (-dB), this refers to the amount of back reflection. The lower the dB value, the better the connector and polish finish on the connector ferrule.

RF (Radio Frequency)
The frequency spectrum from 15kHz to 100GHz.

RFI (Radio Frequency Interference)
Electromagnetic radiation in the radio frequency spectrum fiom 15kHz to 100GHz. The best shielding material against RFI is copper and aluminum alloys. The term "EMI" should not be used in place of RFI since shielding materials for the entire electromagnetic frequency spectrum are not available.

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.

Scribe Tool
Also called a cutting tool or breaking tool, consisting of cut­ting blade usually made from tungsten carbide or a diamond. Application is to break/scribe fiber @90? without lips or hackles or angular irregularities.

Selco Lenses
Segments of optical fibers specially designed to function as lenses.

Semi-Graded Index
An optical fiber with refractive index profile interme­diate between step-index and graded index. Strictly speaking, this might be considered a type of graded-index fiber with refractive index profile some­what steeper than normal.

Signal-to-Noise Ratio
The ratio of the power of the signal to that of background noise, usually measured in decibels. This is a common measure of the quality of analog electronics or transmission systems.

Simplex Cable
A single cable structure with a single fiber.

One type of low-loss optical waveguide with a very small Core (2-9 microns). It requires a laser source for input signals becauuse of the very small entrance aperture. The core diameter of a single-mode is designed to accept a one mode(wavelength) from the light source .

Skew Rate
A ray somethimes refered to as a dominant ray, that never intersects the axis of fiber while being internally reflected (in contrast with a meridional ray).

A permanent junction between two optical-fiber ends.

Splice Housing (Fiber Optics)
A housing designed to protect a splice in an optical fiber from damage by the environment, such as from the applica­tion of stress on the fiber. It also can seal the splice fiom environmental agents such as water which could cause it to deteriorate.

Star Coupler (fiber optics)
A coupler in which many fibers are brought together to a single optical element in which their signals are mixed. The mixed signals are then transmitted back through all the fibers. The name comes from the geometric arrangement

An optical fiber in which there is a discontinuous (step-function) change in refractive index at the boundary between fiber core and cladding. Such fibers have a large numerical aperture (light accepting angle), and are simple to connect. but have lower bandwidth than other types of optical fibers.

Mechanical tool used to remove buffer coatings from fibers.

Standard TTL (see TTL)

To displace metal by pressure.

Switch (fiber optics)
A device for rerouting signals from one optical fiber into others.


Tap (fiber optic)
A coupler in which part of the light carried by one fiber is split off and inserted into another fiber, essentially the same as a Tee coupler.

Tee Coupler (fiber optic)
A fiber optic coupler in which three fiber ends are joined together, and a signal transmitted from one fiber is split between the other two. A conceptual drawing looks like the letter T, which accounts for the name.

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.

Termination tools
Tools used in preparing optical fibers for spliciug and/or installation of connectors.

Tight Buffered Cable
a protective coating extruded tightly over fiber for mechanical and environmental protection. The coating material is either nylon or PVC. This buffering offers excellent physical and flexing properties, but higher micro-bending sensitivity.

Time-Division multiplexing
A digital technique for combining two or more signals into a single stream of data by interleaving bits from each signal. Bit one might be from signal one, bit two from signal two, etc.

Total Internal Reflection
The total reflection that occurs when light strikes an interface at angles of incidence greater than the critical angle.

Transmitter (fiber optics)
A light source (LED or diode laser) which is combined with electronic circuitry to drive it. A transmitter operates directly from the signal generated by other electronic equipment to produce the drive current needed for LED or diode laser.


Wavelength-Division Multiplexing
Combination of two or more signals so they can be transmitted over a common optical path, usually over a single fiber; by a technique in which the signals are generated by light sources having different wavelengths. For example, one signal might be transmitted at 850 nanometers and a second at 1300 nanometers.

Wave Division Multiplexing. Multiplexing is done by combining different wavelengths over one optical fiber simultaneously. Each wavelength is capable of carrying a certain amount of information.

White Light
A mixture of colors of visible light that appears white to the eye. In theory, a mixture of three colors is sufficient to product white light.


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

Glossary of Common Fiber Optic Terms: M - P

Common Fiber Terms A-E

Common Fiber Terms F-L

Common Fiber Terms: M-P


In an optical fiber, all macro deviations of the axis from a straight line.

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.

Mating Sleeve
A mechanical media termination device designed to align and join fiber optic connectors of the same type. Often referred to as a coupling, bulkhead, or interconnect sleeve.

Mechanical Splicing
Joining two fibers together by permanent or temporary mechanical means (vs. fusion splicing or connectors)

Megahertz (MHz)
A unit of frequency that is equal to one million cycles per second.

Meridional Ray
A ray that passes through the axis of a fiber while being internally reflected (in contrast with a skew ray) and is confined to a single plane.

Microbending Loss
In an optical fiber, loss caused by sharp curvatures involving local axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Such bends may result from fiber coating, cabling, packaging, installation, etc.

A unit of length equal to one-millionth (10 E-6) of a meter (same as a micrometer).

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

A stable condition of oscillation in a laser. A laser can operate in one mode (singlemode) or in many modes (multimode). The theoretical underpinnings are extremely complex; the main practical implications are in beam quality.

Mode Changing
In a optical fiber, the exchange of power among modes.

Mode Conditioning Patchcord
a duplex multimode cord that has a small length of singlemode fiber at the start of the transmission leg. The basic principle behind the cord is that you launch your laser into the small section of single mode fiber. The other end of the singlemode fiber is cou­pled to multimode section of the cable with the core offset from the center of the multimode fiber. The laser light thus misses the "dip" and this new launch condition more closely mimics a standard LED launch. The bonus is that you still retain the speed advantages of using a laser.

Mode Filter
A device to remove high order modes to simulate equilibrium mode distribution in a short length of optical fiber.

Mode Scrambler
A device for inducing mode coupling in an optical fiber.

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

See Singlemode

Multifiber Cable
In general usage, a fiber optic cable which containsmany fibers which transmit signals independently and are housed in separate substructures within the cable or otherwise isolated from one another. This term is usually not applied to bundles of fibers which together transmit single signal.

An optical waveguide with a relatively much larger core (commonly 50 to 62.5 micron) than the singlemode waveguide core (2 to 9 microns) and which permits approximately 1000 modes to propagate through the core compared to only one mode through a singlemode fiber.

A device which combines two or more separate signals for transmission through a single fiber. Optical multiplexers combine signals at different wavelengths. Electronic multiplexers combine signals electronically before being converted into optical form.


One-Billionth of a meter (10 E-9) (same as a millimicrometer).

Non-Silica Glasses
A glass in which the primary constituent is a material other than silica (silicon dioxide). The term is sometimes applied to mean non-oxide glasses, those which do not contain oxide compounds. In fiber optics, some of these materials are used for fibers transmitting mid-infrared wavelengths.

Numerical Aperture
NA The numerical aperture of an optical fiber defines a characteristic of the fiber in terms of it's acceptance of light. The "degree of openess", "light gathering ability" and "acceptance cone" are all terms describing this characteristic.


Optical Fiber, Non-conductive, Plenum rated.

Optical Fiber, Non-conductive, Riser rated.

OM1 Fiber Classification (FDDI)
OM1 is legacy (FDDI) grade fiber originally designed for use with LEDs and tend to be 62.5/125 types.  OFL Bandwidth (LED) 850/1300nm ( is 200 / 500.  

OM2 Fiber Classification (50/125)
OM2 fibers enable maintenance and extension to existing 50/125 cabling.  OFL Bandwidth (LED) 850/1300nm ( is 500 / 500

OM3 Fiber Classification (10Gb/s)
OM3 fibers can support 10 Gb/s over 300 meters and are recommended for all new network builds for link distances up to 300 meters. OFL Bandwidth (LED) 850/1300nm ( is 1500 / 500, and Effective Laser Launch Bandwidth at 850nm is 2000  

Optical Attenuation Meter (Attenuator)
Device which measures the loss or Attenuation of an optical fiber, fiber optic cable, or a fiber optic system. Measurements generally are made in decibels.

Optical Break
The breaking of an optical fiber in such a way which predictably produces flattened surfaces that are perpendicular to the longitudinal axis of the fiber. Sometimes referred to as a mirror-like surface across the entire end surface.

Optical Return Loss (ORL)
a reflection that travels down the fiber back to the source. In high speed systems this is undesirable because it can interfere with the transmission. Also referred to as “back reflection”.

Optical Time Domain Refectometer (OTDR)
A method for characterizing a fiber via an optical pulse transmitted through the fiber. The resulting backscatter and reflections are measured as a function of time. The OTDR is useful in measuring attenuation, in distance and identification of defects and other losses.

Output Power (LED)
Radiant power expressed in watts.


Patch Panel
Flat strip of material with adapters for interconnections. Generally 6, 8, or 12 per panel. See Rack Panels

A length of cable with connectors at both ends. Also known as jumpers.

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

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.

A short length of optical fiber with one connector on one end and no connector on the other end.

Pin Photodiode
A semiconductor diode light detector in which a region of intrinsic silicon separates the p and n materials. It offers particularly fast response and is often used in optic systems.

Plastic Clad SiIica (PCS)
A step index optical fiber in which a silica core is covered by a transparent plastic cladding of lower refractive index that of the core. The plastic cladding is usually a soft material, although hard-clad versions have recently been introduced. Offers good radiation resistance.

Plastic Fibers
Optical fibers in which both core and cladding are made of plastic material. Typically their transmission is much poorer than that of glass fibers, and their lowest losses are in the visible region.

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

Polarization-Maintaining Fiber
A singlemode optical fiber which maintains the polarization of the light which entered it, normally by including some birefringence within the fiber itself. Normal singlemode fibers, and all other types, allow polarization to be scrambled in light transmitted through them.

A step in the connectorization process that creates a flat even surface on the ferrule face. Quality is measured in terms of back reflection reduction. Also referred to as “finish”

Polyethylene (PE)
A type of plastic material used for outside plant cable jackets.

Polyvinyl-chloride (PVC)
A type of plastic material used for cable jacketing. Typically used in flame-retardant cables.

Pulse Dispersion (pulse spreading)
The separation or spreading of the input characteristics of the optical signal that appears along the length of the optical fiber and limits the useful transmission bandwidth of the fiber. Expressed in time and distance a nanoseconds per kilometer. Three basic mechanisms for dispersion are the material effect, the waveguide effect, and the multimode effect.

Pulse Suppressor
A launching fiber used to take up the unmeasurable beginning (dead zone) of an OTDR.

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 polyvinyldiflouride. A type of material used for cable jacketing. Often used in plenum-rated cables.

Common Fiber Terms R-Z

Glossary of Common Fiber Optic Terms: F - L

Common Fiber Terms A-E

Common Fiber Terms: F-L


A multi-fiber cable constructed in a tight buffered tube design. At a termination point, cable fibers must be separated from the cable to their separate connection positions.

A component of fiber optic connections that holds a fiber in place and aids in it's alignment. It is the protruding portion of the connector, made of Ceramic, Stainless Steel, or Polymer, and is polished during the connection process to form a smooth finish.

Fiber Buffer
Material used to protect an optical fiber or cable from physical damage. providing mechanical isolation or protection. Fabrication techniques include both tight jacket, or loose tube buffering, as well as multiple buffer layers.

Fiber Optic Cable
A sub-assembly made up of several optical fibers incorporated into an assembly of organic materials arranged for providing the necessary tensile strength, external protection, and handling properties comparable to those of equivalent diameter coaxial cables.

Fiber Optics
The technique of conveying light or images through a particular configuration of glass or plastic fibers. Fiber optics can be categorized roughly into three groups: incoherent, coherent and specialties.

   1. Incoherent fiber optics will transmit light|like a pipe will water|but not an image.
   2. Coherent fiber optics can transmit an image through the perfectly aligned small (12 micron) clad optical fibers (image carrying).
   3. Specialty fiber optics combines some aspects of a and b.

Fiber Sensor
A sensing device in which the active sensing element is in an optical fiber or an element attached directly to an optical fiber. The quantity being measured changes the optical properties of the fiber in way that can be detected and measured. For example, pressure changes induced in a fiber by acoustics can change the amount of light transmitted by a fiber.

Field Installable (fiberoptics)
Nominally, a fiber optic splice or cable is field installable if it can be mounted by technicians working in the field without a lab-full of equipment at hand. Different manufacturers define the term differently.

Refers to the polish results on the end of the ferrule. Better the Finish, the less the back reflectance.

Frequency-Division Multiplexing
The combination of two or more signals at different frequencies so they can be transmitted as one signal. This can be done electronically, or it can be done optically by using two or more light sources of different wavelengths. The optical version is better known as wavelength division multiplexing.

Fresnel Relflection
Reflection losses that are incurred at the input and output faces of the fiber and are due to the difference in refractive index between the core glass and the immersion medium.

“Fiber to the Home" FTTH is where fiber will be brought directly to the side of your home to support your cable TV, telephone service and internet needs. It looks much like the utility box that you currently have on the side of your home, only with fiber jumpers inside.

Furcation Tubing
A protective tubing used to protect exposed fiber. Commonly used in terminating multi-fiber cable or “fan out” situations.

Fusion splicer
A high precision piece of equipment that allows the user to 'melt' or fuse the ends of two optical fibers together to create one continous fiber. There is typically very low loss at this junction. Alignment of fibers can be by manual or automatic manipulation. The fusing takes place by electrical discharge between two electrodes.


Gigahertz (GHz)
A unit of frequency that is equal to one billion cycles per second.

Graded Index Fiber
An optical fiber in which the refractive index changes gradually between the core and cladding, in a way designed to refract light so it stays in the fiber core. Such fibers have lower dispersion and hence broader bandwidth than step-index fibers.


Hard-Clad Silica Fluid
A liquid with refractive index that matches that of the core or cladding of an optical fiber. It is used in coupling light into or out of optical fibers and can help in suppressing reflections at glass surfaces.

Hybrid Cable
A fiber optic cable containing two or more different types of fiber, such as 62.5um multimode and singlemode.


Index Matching Gel
A gel material with an index of refraction close to that of glass that reduces reflections caused by refractive-index differences.

Index of refraction
The ratio of light velocity in a vacuum to its velocity in a given transmission medium.

Those wavelengths that extend beyond 770 nanometers. Infrared is used extensively in the transmission of light through optical waveguides. These light wavelengths are invisible and harmful to the naked eye.

Insertion Loss
Total optical power loss caused by insertion of an optical component such as a connector, splice, or coupler into a previously continuous path.

Interconnect Sleeve
A mechanical media termination device designed to align and join fiber optic connectors, designed to be mounted on a panel. Often referred to as a coupling, bulkhead, or mating sleeve.

Interferometer Test
A test used to determine the quality of the ferrule surface using three measurements.

   1. The angle of the cut or radius on the end of a connector which determines actual back reflection values or characteristics.
   2. The undercut or protrusion of the fiber. This is mea­sured against the ferrule end face determining how well the physical contact will be.
   3. The position of the fiber in relation to cut or curve, called the apex.

Intrinsic Joint Loss
Loss caused by fiber parameter (e.g.: core dimensions, profile parameter) mismatches when two non identical fibers are joined.


A length of cable with connectors at both ends. Also known as patchcords.


Strands of aramid yarn used to provide strain relief in cable assemblies.

Kilometer (km)
One thousand meters, or approximately 3281 feet. The kilometer is a standard unit of length measurement in fiber optics. Conversion is 1 ft. = 0.3048


A Local Area Network. A network which does not utilize outside telco company lines.

Large-Core Fiber
An optical fiber with a comparatively large core, usually a step-index type. Usually, 400 micrometers or more (see Step Index).

An acronym for Light Amplification by the Stimluated Emission of Radiation, applied to a wide range of devices which produce light by that principle. Compared other light sources, laser light covers a narrow range of wavelengths. tends to be coherent, and is emitted in a directional beam.

Launch 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 improve the precision of measurements. See “Pulse Suppressor”

LED (Light-Emitting Diode)
A semiconductor device in which light is produced when current carriers combine at a p-n junction. The emission is spontaneous and there are no feedback mirrors, unlike diode lasers. Output is lower in power than from diode lasers, reflecting the use lower operating currents. Generally LEDs are less expensive than diode lasers, and can operate at shorter wavelengths without the rapid degradation that occurs with visible-wavelength diodes.

Loose Buffer Cable
Loose buffered designs Consist of a loose tube surrounding a coated fiber. It also includes a Kevlar? braid as the strength member for improved flexibility.

LSTTL (Low Power Schottky TTL)
Utilizes a diode-clamped transistor to lower power requirememts.

Common Fiber Terms M-P

Common Fiber Terms R-Z

Glossary of Common Fiber Optic Terms: A - E

Common Fiber Terms: A-E


A.T.C. (Automatic Threshold Control)
Electric control circuit which regulates the input current to an LED to prevent it from being overdriven.

Absorption Losses
Losses caused by impurities principally transition metals and neighboring elements (Cr, Mn, Fe, Co, Ni), and also by water as well as intrinsic material absorption.

Acceptance Angle
Any angle measured from the longitudinal center line up to the maximum acceptance angle of an incident ray that will be accepted by the waveguide. The maximum acceptance angle is depend­ent on the indices of refraction of the two mediums.

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

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

Aramid Yarn
Fibers, yellow, that provide cable tensile strength, support, and additional protection of the optical fiber bundles. KevlarĂ’ is a particular brand of aramid yarn. Often refered to as central strength member.

Protective material in cable made of corrugated steel.

A method of data multiplexing that can provide large, instantaneous bandwidths for busy traffic while permitting slow traffic to use that bandwidth between bursts. Very short, fixed-length packets or cells are used to transmit information. Its basic cell is 53 bytes long.

a measure of the decrease in energy transmission (loss of light) expressed in dB/Km. When in optical wave guides it is primarily due to absorption losses and scattering losses.

Avalanche photodiode (APD)
A type of semiconductor detector operated at high voltages. When incident light generates photoelectron from the material, the high voltage across the device accelerates the elec­tron enough to cause avalanche of other electrons, effectively amplifying the signal. An avalanche photodiode could be seen as similar to a solid state photo-multiplier.

Axial Ray
A ray passing through the axis of the optical waveguide without any internal reflection.


Back Reflection
An undesirable characteristic in singlemode fiber transmission. Reflectance of light pulse back towards the transmitted source. Also referred to as Optical Return Loss (ORL).

See “Back Reflection”

The capacity of an optical fiber to transmit information expressed in bits of information transmitted in a specific time period for a specific length of optical wave guide. (Usually expressed in megabits/sec./km.) Bandwidth is limited by pulse spreading or broadening due to dispersion, so that adjacent pulses overlap and cannot be distinguished. (see Pulse Dispersion)

A device which divides a beam of light passing through it into separate beams going in two different directions. Some types affect polarization of the beam, while others do not. Various splitting ratios are possible. (eg., 90-10, 70-30, 50-50, etc.)

Bend Radius
Maximum bend allowed before physical damage is incurred. Generally expressed for two conditions, loaded (under tensile load) or unloaded.

An electrical light pulse whose presence or absence indicates data. The capacity of the optical waveguide to transmit information through the waveguide without error is expressed in bits per second per unit length.

Bragg Gratings, Fiber
Fiber that is treated to back reflect a particular wavelength, called the Bragg Wavelenth. See technical notes: Fiber Bragg Gratings

Material used to protect an optical fiber or cable from physical damage and providing mechanical isolation or protection. Fabrication techniques include both tight jacket, or loose tube buffering, as well as multiple buffer layers.

Bulkhead Attenuator
A mechanical media termination device designed to align and join fiber optic connectors, designed to be mounted on a panel, and that contains an attenuation device.

Bulkhead Connector
A mechanical media termination device designed to align and join fiber optic connectors, designed to be mounted on a panel. Often referred to as a coupling, bulkhead, interconnect or mating sleeve.


Card-Edge Connector
Designed for printed circuit boards for blind mating of connectors.

Central Member
The center component of a cable used to provide strength. Commonly referred to as “Central Strength Member”

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

A low refractive index, glass or plastic that surrounds the core of a fiber. Optical cladding promotes total internal reflection for the propagation of light in a fiber.

A process in which a divergent or convergent beam of radiation is converted into a beam with the minimum divergence as possible, preferably parallel.

Composite Cable
A cable containing both fiber and copper conductors.

A junction which allows users to connect / disconnect cables or devices.

The light conducting portion of a fiber, defined by its high refraction index. The core is the center of a fiber, surrounded by concen­tric cladding of lower refractive index.

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.

Coupler (fiber optic)
A coupler is a device which joins together three or more fiber ends, for example, splitting the signal from one fiber so it can be transmitted to two or more other fibers. Directional , star, and tee couplers are the most common varieties.

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


Dark Current
The output current that a photodiode emits in the absence of light.

Data Link (fiber optic)
A fiber optic signal transmission system which carries information in digital or (sometimes) analog form. Usually this term refers to short-distance communications, spanning distances of less than a kilometer.

Data Rate
The maximum number of bits of information that can be transmitted per second, as in a data transmission link. Typically expressed as megabits per second (Mbps)

Decibels relative to one milliwatt. A positive number indicates the power is above one milliwatt; a negative number indicates the power is below. This unit has become common in fiber optic communication sys­tems because the power of light sources used with optical fibers is on the order of one milliwatt.

The standard unit used to express the ratio of two power 1evels. It is used in communications to express either a gain or loss in power between the input and output devices.

A device which separates two or more signals that have been multiplexed together for transmission through a single fiber. (See multiplexer.)

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.

A device in which an optical detector is packaged together with electronic amplification circuitry.

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

Diode Adapter Receptacle
Designed to house LED or PlN/APD diodes in a receptacle which allows the mating plug to position the fiber for an optimum coupling efficiency.

Directional Coupler (fiber optics)
A fiber coupler is directional if it preferentially transmits light in one direction.

Spread of the signal delay in an optical waveguide. It consists of various components: modal dispersion, material dispersion, and waveguide dispersion. As a result of its dispersion, an optical waveguide acts as a low-pass filter for the transmitted signals.

The spreading out of a laser beam with Distance, measured as an angle.

Doppler Shift
A change in the wavelength of light caused by the motion of an object emitting (or reflecting) the light. Motion toward the observer causes a shift toward shorter wavelengths, while motion away causes a shift toward longer wavelegths.

Driver I.C
An amplifier in an integrated circuit used to increase signal current to the LED for greater transmission distance.

Duplex Cable (fiber optics)
A cable which contains two optical fibers in a single cable structure. Light is not coupled between the two fibers: typically one is used to transmit signals in one direction and the other used to transmit in the opposite direction.

Duplex Connector (Fiber optics)
A connector which simultaneously makes two connections, joining one pair of optical fibers with another.


E.C.L. (Emitted-Coupled Logic)
Method of data transmission which uses negative logic. -0.8V is "1" and -1.6V is "0".

Electromagnetic Interference (EMI)
The frequency spectrum of electromagnetic radiation extending from subsonic frequency to X-rays. This term should not be used instead of the term "RFI" (see RFI) (Shielding materials for the entire EMI spectrum are not readily available.)

EMP (Electromagnetic Pulse)
An extremely strong short lived magnetic field resulting from a nuclear explosion could cause a damaging magnetic field at a distance of 1500-3000 miles.

End Finish
Quality of the surface of an optical fiber's end, commonly described as mirror, mist, hackle, chipped, cracked or specified by final grit size in polishing. (1um, .3um, etc.). See “Polish”

End Separation Loss
The optical power loss of a fiber and source, detector or another fiber (see Frensel Reflection).

Extinction ratio
a performance standard measurement of polarization maintaining (PM) fiber. The measurement of light entering and exiting a fiber indicates how well the fiber maintains polarization.

Extrinsic joint Loss
Loss caused by imperfect alignment of fibers in a connector or splice. Contributors include angular misalignment, lateral offset, end separation and end finish. Generally synonymous with Insertion loss.

Common Fiber Terms F-L

Common Fiber Terms M-P

Common Fiber Terms R-Z