fiber optics glossary
fiber optics glossary
The following terms were defined with the assistance of Panduit Corporation, a leading manufacturer of wiring and network cabling products (www.panduit.com) and Jeff Hecht, noted optical networking consultant and author.adapter
A mechanical device designed to align fiber-optic connectors. It contains the split sleeve (interconnect sleeve) that holds the two ferrules together.
adapter sleeve
A mechanical fixture within the adapter body that aligns and holds two terminated fiber connectors. Adapter sleeve material is typically phosphor bronze, ceramic or polymer.
absorption
The absorbing of light energy within an optical fiber due to natural impurities in the glass. Absorption and scattering are the main cause of attenuation (signal loss) in an optical fiber.
acceptance angle
The angle at which the core of the fiber will take in light. See numerical aperture.
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add/drop multiplexer
A device that includes or removes one or more optical channels to a signal passing through it. See add/drop multiplexer.
aramid yarn
An ingredient in optical fiber cable that provides support, protection and tensile strength. Also referred to as KEVLAR, which is a brand of aramid yarn.
ATM (asynchronous transfer mode)
A network technology that switches optical and electronic signals that are broken into 53-byte cells (see ATM).
attenuation
The loss of signal strength (optical power) during transmission between two points. It expresses the total loss of an optical system, measured in decibels per kilometer (dB/km) at specific wavelengths. See "intrinsic loss" and "extrinsic loss" in this glossary.
axis
The center of an optical fiber.
backbone cabling
The interbuilding and intrabuilding cable connections between entrance facilities, equipment rooms and the telecommunications closets. It consists of the transmission media, main and intermediate cross-connects and terminations at these locations.
bandwidth
The information-carrying capacity of an optical fiber. It is measured in MHz-km and GHz-km, as distance plays an important role.
birefringent
A property of a material that causes the polarizations of light to travel at different speeds.
Bragg scattering
A distribution of light that is caused by a change in the refractive index of a material. See fiber Bragg grating.
buffer
The protective layer that surrounds the fiber cladding. Fabrication techniques include tight or loose tube buffering.
cable assembly
An optical fiber cable that has connectors installed on one or both ends. See "pigtail" and "patch cord" in this glossary.
C band
A range of wavelengths from 1530 to 1565 nm. In this region, erbium-doped amplifiers (EDFAs) have highest gain. See EDFA and optical bands.
chirped pulse
A pulse in which the wavelength changes during the duration of the pulse. See chirped pulse.
channel spacing
The amount of bandwidth allotted to each channel. See channel spacing.
chromatic dispersion
The spreading of light pulses caused by the difference in refractive indices at different wavelengths. See dispersion.
cladding
The material surrounding the core of an optical fiber. The cladding has a lower refractive index (faster speed) in order to keep the light in the core. The cladding and core make up an optical waveguide.
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cleave
The process of scoring and breaking the optical fiber end in order to terminate a connector.
coarse WDM (CWDM)
A WDM technology that spaces wavelengths widely apart. See CWDM.
coating
A protective layer applied over the fiber cladding during the drawing process to protect it from the environment.
connector
A mechanical device used on a fiber to provide a means for aligning, attaching and decoupling the fiber to a transmitter, receiver or other fiber. Commonly used connections include 568SC (Duplex SC), ST, FDDI, FC, D4 and Biconic.
core
The central region of an optical fiber through which light is transmitted. It has a higher refractive index (slower speed) than the surrounding cladding.
coupler
A device that combines two or more fiber inputs into one fiber output or divides one fiber input into two or more fiber outputs. See "directional coupler" in this glossary.
coupling
The transferring of light going into and coming out of a fiber. This term does not imply that a coupler is used.
critical angle
The maximum angle from the axis at which light can be confined within the core. See critical angle.
cutoff wavelength
The shortest wavelength at which a singlemode fiber transmits only one mode. At shorter wavelengths, it transmits two or more modes.
dark fiber
Fiber lines that are supplied without any electronic or optical signaling equipment in its path.
dBm (decibels milliwatt)
A measurement of decibels (dB) at one milliwatt.
dBµ (decibels microwatt)
A measurement of decibels (dB) at one microwatt.
decibel
A unit of measure used to express the relative strength of a signal.
dielectric
A material such as a glass fiber, which is not metallic and is not conductive.
diode laser
See "laser diode" in this glossary or see laser diode.
diffraction
The bending of light rays as they pass around corners or through holes smaller than their own wavelengths.
diffraction grating
A series of scored lines that separates light into its various colors. See fiber Bragg grating.
directional coupler
A coupler in which light is transmitted differently depending on the direction of transmission. See "coupler" in this glossary.
dispersion
The spreading or broadening of light pulses as they travel through a fiber. The fiber property that causes this effect is also called dispersion. The three principal types are modal dispersion, chromatic dispersion and polarization mode dispersion. See dispersion.
dispersion compensation
Reducing dispersion in a fiber in order to reduce total dispersion. Different methods are used for chromatic dispersion and polarization mode dispersion.
dispersion-shifted fiber
An optical fiber that has lower chromatic dispersion in the 1550 nm range. See dispersion-shifted fiber.
duplex cord
A two-fiber cable used for bi-directional transmission.
DWDM (dense WDM)
Another term for closely spaced WDM. DWDM and WDM are used synonymously.
EDFA (erbium-doped fiber amplifier)
An optical amplifier that boosts all channels in the optical signal at the same time. See EDFA.
EDWA (erbium-doped waveguide amplifier)
An optical amplifier similar to an EDFA, but derives a higher gain through a small waveguide rather than several meters of fiber.
electro-absorption modulator
A semiconductor diode that modulates light from a separate laser, but that may be fabricated on the same wafer. Turning current on causes light absorption.
EMI (electromagnetic interference)
The interference in signal transmission or reception resulting from radiation of electrical or magnetic fields. Optical fibers are not susceptible to EMI.
enclosure
A cabinet used to organize and enclose cable terminations and splices for use within main equipment rooms, entrance facilities, main or intermediate cross-connects and telecommunications closets.
epoxy
A thermosetting resin used to secure the fiber with the connector ferrule.
etalon
A passive filter that uses a Fabry-Perot cavity. See Fabry-Perot.
evanescent waves
The light that passes into the cladding from the core.
extrinsic loss
The loss that is induced in an optical transmission system by an external source. In a fiber-optic link, this can be caused by improper alignment of connectors or splices.
Fabry-Perot
A cavity with mirrors at opposite ends. It is a foundation component of certain lasers and passive filters. See Fabry-Perot.
ferrule
The rigid prong in a fiber-optic plug that aligns the fiber with the socket. Ferrule materials are ceramic, plastic and stainless steel.
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fiber
A thin filament of glass or plastic consisting of a core (inner region) and a cladding (outer region) and a protective coating.
fiber Bragg grating
A series of periodically spaced zones in a short length of fiber with a higher refractive index used to filter out wavelengths. See fiber Bragg grating.
fiber laser
An alternate way of building a laser. The laser is built into the fiber itself.
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fiber optics
Information transmitted through optical fibers in the form of light.
fusion splice
The joining of two fiber ends by applying enough heat to fuse or melt the ends together to form a continuous single fiber.
graded-index fiber
A multimode fiber designed to compensate for modal dispersion by allowing light to travel increasingly faster from the center of the core to its outer edge. See graded-index fiber.
index of refraction
See "refractive index" in this glossary or refractive index.
infrared
A range of light from approximately 700 to 1000 nm. Fiber-optic systems transmit between 700 and 1700 nm.
injection loss, insertion loss
The amount of light that leaks out or is otherwise lost after being inserted into a fiber either from a light source or another fiber.
interference
The combination of light waves in which the wave amplitudes add together. Constructive interference produces bright light when the peaks are in phase with each other. Destructive interference produces dark zones when the peaks of one wave align with the valley of the second.
intrinsic loss
The loss due to inherent traits within the fiber; for example, absorption (light energy is absorbed in the glass) and splice loss (mismatched numerical aperture).
L band
A range of wavelengths from 1565 to 1625 nm. In this region, erbium-doped amplifiers (EDFAs) can be used, but have less gain than in C band. See EDFA and optical bands.
laser
A device that generates a coherent beam of light all in phase and of a single (or nearly single) wavelength. A cavity with mirrors at each end causes a chain reaction that stimulates the emission of photons. See laser.
laser diode
A laser made of semiconductor materials widely used to transmit light into optical fibers. It is always used for singlemode fiber and certain high-bandwidth multimode fiber such as used with Gigabit Ethernet.
LED (light emitting diode)
A device that produces light with a wide range of wavelengths. LEDs are typically used with lower-bandwidth multimode fiber.
loose tube
The protective tube surrounding one or more fibers. This is usually found in cables used for outdoor installations.
macrobending
The loss due to large scale bending (extrinsic loss). Bending causes imperfect guiding of light which will exceed the critical angle of reflection. Macrobending loss can be reversed once the bend is corrected.
mechanical splice
Joining two fiber ends together by a temporary or permanent mechanical method in order to maintain continuous signal transmission.
MEMS (microelectromechanical systems)
Tiny components etched from a semiconductor material that can move under the control of electronic signals. MEMS devices include movable mirrors that can switch or redirect the path of light.
microbending
The loss of light due to small distortions in the fiber, not usually visible to the naked eye.
micron (µm)
One micrometer or one millionth of a meter. Used to express the geometric dimension of fibers.
modal dispersion
The spreading of light pulses along the length of the fiber caused by differential optical paths taken in multimode fiber. See dispersion.
mode
A reflective path that the light takes in a fiber. Each mode has its own pattern of electromagnetic fields as it propagates through the fiber. There is only one mode in singlemode fiber. In multimode fiber, multiple modes are generated, causing pulse dispersion at the receiving end. See dispersion.
mode field diameter
In singlemode fiber, the diameter of the zone where the single mode propagates down the center of the fiber. It is slightly larger than the core diameter.
multimode
An optical fiber in which light travels in multiple modes. Multimode fiber is used in shorter-distance applications than singlemode fiber. See multimode fiber, graded-index fiber and step-index fiber.
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multiplex
Combining two or more signals into a single bit stream that can be individually recovered.
nanometer
One billionth of a meter.
numerical aperture (NA)
See "acceptance angle" in this glossary.
OC-1, OC-3, OC-12, OC-48, OC-192, OC-786
An optical carrier rate in the SONET hierarchy. See OC.
OEO (Optical Electrical Optical)
Devices that convert light back to electricity for manipulation and then back out to light. Contrast with OOO.
OFNR (Optical Fiber Non-conductive Riser)
A type of fiber-optic cable.
OFNP (Optical Fiber Non-conductive Plenum)
A type of fiber-optic cable.
OOO (Optical Optical Optical)
Devices that maintain the transmission signal as light throughout. Contrast with OEO.
optical amplifier
A device that boosts signals in an optical fiber. The EDFA was the first successful optical amplifier. See EDFA.
optical channel
A signal transmitted at one wavelength in a fiber-optic system.
optical network
A network that processes and switches signals in optical form.
optical switch
A device that routes optical signals to their appropriate destination. All-optical switches (OOO) do not have to convert light back to electricity for processing. See optical switch.
optical waveguide
An optical fiber, planar waveguide or other structure that guides light along its length.
OTDR (Optical Time Domain Reflectometer)
An instrument that measures optical transmission characteristics by sending a short pulse of light down a fiber and observing backscattered light. Used to measure fiber attenuation and evaluate optical transmission at splices and connectors.
passive optical network
A fiber-optic system with no active components between its distribution point and remote receiver nodes.
photodiode
A device that receives optical power and changes it to electrical power. See photoelectric.
PC (Physical Contacting)
A type of fiber-optic connector that causes two terminated fiber ends to contact each other, keeping signal losses to a minimum.
patch cord
A specific length of optical fiber cable with terminated connectors on each end. Used for connecting patch panels or optoelectronic devices.
photon
A particle of light.
photonic
Having to do with light or photons.
pigtail
A short length of fiber in which one end is attached to a component and the other is free to be spliced to another fiber.
planar waveguide
A flat waveguide on the surface of a substrate with a lower refractive index. It confines light similar to an optical fiber. Used in waveguide arrays.
polarization
The alignment of the perpendicular electrical and magnetic fields that make up a light wave.
polarization mode dispersion
The dispersion that arises from slight asymmetries in optical fibers. The speed of light varies with polarization.
polishing paper
Also known as lapping film, it is a paper with a fine grit used to remove any imperfections in the fiber end surface that may exist after cleaving. Fiber ends terminated within a connector are polished flush with the end of the ferrule.
polishing puck
A device used to hold the connector during the polishing of the fiber.
population inversion
The state of atoms that have been excited. See population inversion.
Raman amplifier
A device that boosts the signal in an optical fiber by transferring energy from a powerful pump beam to a weaker signal beam. See Raman amplifier.
receiver (RX)
An optoelectronic device that converts optical signals into electrical signals.
reflection
The process that occurs when a light ray traveling in one material hits a different material and reflects back into the original material without loss of light. See refractive index.
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refraction
The bending of light rays as they pass through a transmission medium of one refractive index into a medium with a different refractive index. See refractive index.
refractive index
The ratio of the velocity of light in a vacuum to the velocity of light in a specific material. Using 1.0 as the base reference, the higher the number, the slower light travels. See refractive index.
repeater
A transceiver that converts optical signals to electronic and back out to optical.
riser
A pathway for indoor cables that pass between floors.
S band
A range of wavelengths from 1460 to 1530 nm. See optical bands.
scattering
A property of glass that causes light to deflect from the fiber and contribute to losses (intrinsic attenuation).
SDH (Synchronous Digital Hierarchy)
A scale of standard data rates for fiber-optic systems defined by the ITU. See SONET.
singlemode
An optical fiber in which the signal travels in one mode (path). It typically has an 8-10 µm core within a 125 µm cladding. See singlemode fiber.
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soliton
A laser pulse that retains its shape in a fiber over long distances. See soliton.
SONET (Synchronous Optical Network)
A scale of standard data rates for fiber-optic systems used in North American systems. See SONET.
splice
A method for joining two optical fiber ends. Fusion splicing and mechanical splicing are the two types.
splice closure
A container used to hold and protect splice trays.
splice tray
A container used to hold, organize and protect spliced fibers.
split sleeve
The part of a fiber-optic adapter that aligns the ferrules of two terminated connectors.
splitter
A device that takes the light from one fiber and injects it into the cores of several other fibers.
step-index fiber
A fiber in which the core and cladding each have a uniform, but different, refractive index. See step-index fiber.
threshold current
The mimimum current required to cause a diode laser to generate a beam of light.
tight buffer
A protective coating (typically 900 µm) that is extruded directly over the primary coating of fibers. Provides high tensile strength, durability, ease of handling and termination.
transceiver
A transmitter and receiver combined in one device.
transmitter (TX)
An optoelectronic device that converts an electrical signal to an optical signal. It is usually an LED or laser diode.
transparent network
A fiber-optic network that is entirely light based with optical switches and other optical-only devices.
tunable laser
A laser that can change its frequency over a given range.
VCSEL (vertical cavity surface-emitting laser)
Pronounced "vixel." A semiconductor laser that emits a beam from its surface rather than its edge. See VCSEL.
VOA (variable optical attenuator)
A device that can be adjusted to block different fractions of light passing through it.
waveguide
A structure that guides electromagnetic waves. An optical fiber is an optical waveguide.
waveguide array
A device that separates wavelengths by passing them through an array of curved waveguides running between a pair of mixing regions.
wavelength
The length of a wave measured from any point on one wave to the corresponding point on the next. The wavelengths of light used in optical fibers are measured in nanometers. Common wavelengths are 850, 1300 and 1350 nm.
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WDM (wavelength division multiplexing)
Transmitting several wavelengths of light (colors) in one fiber. See WDM.