Glossary of Optical Fiber Terms
A/D — Analog to Digital
Absorption — A physical mechanism in fibers
that attenuates light by converting it into heat—thereby raising the fiber’s
temperature. In practice the temperature increase is slight and difficult to measure.
Absorption arises from tails of the ultraviolet and infrared absorption bands, from
impurities such as the OH – ion, and from defects in the glass structure.
Acceptance Angle – The maximum angle at
which a light ray entering the core will be guided through the fiber.
Access Coupler — A device to insert or
withdraw a signal from a fiber from between two ends. Many couplers require connectors on
either end, and for many applications they must be APC.
Active Coupler — A coupler that includes a
receiver and one or more transmitters. The idea is to regenerate the input signal and then
send them on.
Active Splicing — In this process, the
splicing is done with an alignment device, using the light in the core of one fiber to
measure the transmittance to the other, to assure optimal alignment before splicing is
completed.
Actives — Components that handle signals and
that require power. Examples are line amplifiers and nodes.
Adapter — A mechanical media termination
device designed to align and join fiber optic connectors. Often referred to as a coupling,
bulkhead, or interconnect sleeve.
Adapter Efficiency — The efficiency of
optical power transfer between two components.
Adapter Loss — The power loss suffered when
coupling light from one optical device to another.
Add/Drop Devices and Multiplexing — The ability to add or
drop specific portions of a signal from a stream without multiplexing or demultiplexing
the entire signal.
ADSL — Asymmetrical Digital Subscriber line.
AGC — Automatic gain control. Circuitry in
an amplifier that senses the level of a signal at the output and adjusts the gain such
that the signal level is constant regardless of input level.
AM — (Amplitude Modulation) Modulation by
varying the amplitude of a light wave, common in analog/RF applications.
Angle of Incidence — The angle between an
incident ray and the normal to a reflecting surface.
Angled End — A fiber whose end is polished
with purpose to an angle to reduce reflectance.
Angular Misalignment Loss — This is the loss
of optical power due to an angular deviation from the optimal angle and alignment between
the source to another fiber, or to a detector for instance.
APC — Angled Polished Connector or Angled
Physical Contact Connector. A connector whose angled endface assures low-mated reflectance
and low unmated reflectance.
APD — Avalanche Photo Diode.
Aramid Yarn — Strength elements that provide
tensile strength and provide support and additional protection for fibers in a cable.
Kevlar is a brand name for aramid yarn.
Armor — Protective elements added to fiber
optic cable jackets to provide protection against severe outdoor environments. Usually
made of plastic- coated steel, it may be corrugated for flexibility.
ATM — Asynchronous Transfer Mode.
Attenuation — The decrease in magnitude of
power of a signal in transmission between points. A term used for expressing the total
loss of an optical system, normally measured in decibels (dB) at a specific wavelength.
Attenuation Coefficient — The rate of
optical power loss with respect to distance along the fiber, usually measured in decibels
per kilometer (dB/km) at a specific wavelength.
Avalanche Photodiode (APD) — A photodiode
designed to take advantage of avalanche multiplication of photocurrent.
Axial Ray — A light ray that travels along
the axis of an optical fiber.
Backbone — Point-to-point or ring
connections between or linking equipment buildings communications network.
Back Reflection – Occurs when light
propagating through the fiber is mirrored back into the fiber at the end face, instead of
continuing through to the receiving source.
Backscattering — The scattering of light in
a direction opposite the original one.
Balanced Coupler — A coupler whose output
has balanced splits, for example 1 by two: 50/50 or 1 by 4: 25/25/25/25.
Bandwidth — The lowest frequency at which
the magnitude of the waveguide transfer function decreases to 3 dB (optical power) below
its zero frequency value. The bandwidth will be a function of the length of the waveguide,
but may not be directly proportional to the length.
Bandwidth-Distance Product — The
information-carrying capacity of a transmission medium is normally referred to in units of
MHz-km. This is called the bandwidth-distance product or more commonly bandwidth.
Bandwidth Limited Operation — The condition
prevailing when the system bandwidth, rather than the amplitude of the signal, limits
performance. The condition is reached when modal dispersion distorts the shape of the
waveform beyond specified limits.
Barrier Layer — A layer of glass deposited
on the core to prevent diffusion of impurities into the core.
Baud — The number of signal-level
transitions per second in digital data transfer. Often described in bits per second.
Beamsplitter — A device used to divide an
optical beam into two or more separate beams.
Beamwidth — The distance between two
diametrically opposed points at which the irradiance is a specified fraction of the beam’s
peak irradiance; most often applied to beams that are circular in cross section.
Beat Length – The length of fiber over which
signals propagating in two perpendicular (or orthogonal) polarization orientations become
out of phase by 2p.
Bend Loss – Attenuation due to (1)
microscopic imperfections in the fiber (microbending) or (2) bending the fiber in a tight
radius curve (macrobending).
Bend Radius – The minimum radius of
curvature in which a fiber can bend without breakage, other adverse mechanical effects, or
increased attenuation beyond an acceptable threshold.
BER (Bit Error Rate) — In digital
applications, the ratio of bits received in error to bits sent. BERs of one error bit per
billion (1×10-9) sent are typical.
Biconic — Fiber optic connector developed by
AT&T used in early fiber optic systems.
Bi-directional couplers — Couplers that
operate in the same way in both directions.
Bi-directional transmission — Signals are
passed and carried in both directions along a single fiber or device.
Biocompatibility – A characteristic of fiber
and cable designed for medical uses, having been tested to various classifications for
direct use within the human body.
Birefringence – A condition in an
anisotropic medium in which two perpendicular polarizations in a fiber have different
refractive indices and thus provide different group velocities.
BISDN — Broadband integrated services
digital networks.
Bi-stable Optics — Optical devices with two
stable transmission states.
Bit — A binary digit, either 1 or 0, which
is the smallest element of data in a binary system.
Black body — A body or material that absorbs
100% of the energy incident upon it. Blown Fiber — A method for installing fiber in
which fibers are blown through a vessel, such as a tube.
BNC — Bayonet connector.
BPON — Broadband passive optical network.
Brewster’s Angle — For light incident upon a
plane boundary between two regions having different refractive indexes, the Brewster’s
angle is that angle of incidence at which reflectance should be zero.
Broadband — Transmission facilities capable
of handling a wide range of frequencies simultaneously.
Buffer or Buffering — Material used to
protect an optical fiber from the environment, providing mechanical isolation and/or
protection.
Buffer Coating — A material applied to the
fiber in layers, usually measured in microns, which increases the diameter of the fiber
and protects and enhances the fiber performance.
Buffer Tubes — Extruded cylindrical tubes
covering optical fibers(s) used for protection and isolation. (See Loose Tube.)
Bundle — Many individual fibers contained
within a single jacket or buffer tube. Also a group of buffered fibers distinguished in
some fashion from another group in the same cable core.
Bypass — The capability of a station to be
isolated from the network while maintaining the integrity of the ring.
Byte — A unit of 8 bits.
Cable — An assembly of optical fibers and
other material providing mechanical and environmental protection.
Cable Assembly — Optical fiber cable that
has connectors installed on one or both ends.
Cable Bend Radius — The radius at which a
cable is bent during installation.
Cable Plant — This is the installed
infrastructure including the cable, fiber, connectors, splices, WDMs etc. that exist
between the transmitter and the detector or receiver.
CableLabs — Cable Television Laboratories;
the research consortium of the cable television operating companies.
Cabling – The process of extruding various
buffers and jackets onto fiber and incorporating strength members or armoring as needed
after the draw process.
CAN — Cable area network.
CATV — Community antenna television (Cable
TV).
CBR — Constant bit rate; an adjective
describing a service or communications channel that carries a constant number of bits per
second.
CCD — Change coupled devices.
Central Member — The center component of a
cable. It serves as an antibuckling element to resist temperature-induced stresses.
Sometimes serves as a strength element. The central member material is steel, fiberglass,
or glass-reinforced plastic.
Centralized Cabling — A cabling topology
used with centralized electronics connecting the optical horizontal cabling with
intra-building backbone cabling passively in the telecommunications closet.
CEV — A below ground vault, Controlled
Environment Vault, whose humidity and temperature are controlled.
Channel — A range of frequencies assigned to
a signal in an FDM transmission system.
Chromatic Dispersion — Spreading of a light
pulse caused by the difference in refractive indices at different wavelengths.
Cladding — The dielectric material
surrounding the core of an optical fiber.
CO — Central Office: The building containing
communications switching and transmission equipment.
Coating — A material put on a fiber during
the drawing process to protect it from the environment and handling.
Coherence — Characterized in light forms as
a consistent fixed relationship between points on the wave.
Coherence length or time — The distance time
over which a light form may be considered coherent.
Coherent Communications — Where the light
from a laser oscillator is mixed with the received signal and the difference frequency is
detected and amplified.
Coherent light — Light in which all
parameters are predictable and correlated at any point in time or space, particularly over
an area in a lane perpendicular to the direction of propagation or over time at a
particular point in space.
Composite Cable — A cable containing both
fiber and copper media or containing two different fiber types simultaneously.
Concatenation — Joining several fibers
together end to end.
Concatenation Gamma — The coefficient used
to scale bandwidth when several fibers are joined together.
Concentricity – The degree to which the
geometric centerpoints—particularly of the core and cladding of a
fiber—coincide.
Concentricity error — The tolerance errors
describing the lack of concentricity between the core in position to its cladding, as well
as the distribution of concentricity errors between the distribution of the fiber cladding
and the ID of the ferrule capillary diameter; also the concentricity between the ID
capillary diameter and the OD of the ferrule. All of these cumulatively create the basis
for the insertion loss.
Conduit — Pipe or tubing through which
cables can be pulled or housed.
Connecting Hardware — A device used to
terminate an optical fiber cable with connectors and adapters that provide an
administration point for cross- connecting between cabling segments or interconnecting to
electronic equipment.
Connector — A mechanical device used to
align and join two fibers together or to provide a means for attaching to and decoupling
from a transmitter, receiver, or another fiber (patch panel).
Connector-Induced Optical Fiber Loss — That
part of connector insertion loss due to impurities or structural changes to the optical
fiber caused by the termination within the connector.
Connector Panel — A panel designed for use
with patch panels containing a multiple of adapters pre-installed for use when
field-connectorizing fibers.
Connector Panel Module — A module designed
for use with patch panels, it contains either 6 or 12 connectorized fibers that are
spliced to backbone cable fibers.
Core — The central region of an optical
fiber through which light is transmitted.
Core Eccentricity — A measure of the
displacement of the center of the core relative to the cladding center.
Core Ellipticity (non-circularity) — A
measure of the departure of the core from roundness.
Coupling — Transferring light into or out of
an optical fiber.
Coupler — A device that connects three or
more fiber ends.
Coupling Efficiency — The efficiency of
optical power transfer between two optical components.
Coupling loss — The power loss experienced
at a coupling of light from one optical device to another.
Counter-rotating Ring — A ring in which two
signal paths with opposing direction of travel exist in a ring topology.
CPE — Customer Premises Equipment.
Crimp and Cleave – A process of finishing an
end of fiber, allowing it to be terminated.
Critical Angle — The smallest angle from the
fiber axis at which a ray may be totally reflected at the core/cladding interface.
Crosstalk – In polarization-maintaining
fiber, this measurement indicates the degree to which the light in two orthogonal
polarization modes is isolated. This measurement is stated in terms of decibels per
kilometer.
CSU — Channel service unit.
Curvature Loss — Macro-bending loss.
Cutback Gamma — The coefficient used to
scale bandwidth when a long fiber is shortened.
Cutback Measurement of Technique — A method
for measuring the attenuation or bandwidth in a fiber by measuring from the end, and then
from a shorter length and comparing the difference.
Cutoff Wavelength — The shortest wavelength
at which only the fundamental mode of an optical waveguide is capable of propagation.
CW — Continuous wave.
Cycles per second — The count of
oscillations in a wave. Once cycle per second equals a hertz.
D/A — Digital to Analog.
Dark Current — The external current that,
under specified biasing conditions, flows in a photodetector when there is no incident
radiation.
Dark Fiber — Unused fiber; a fiber carrying
no light.
Data Link — A fiber optic transmitter,
cable, and receiver that transmits, detects and converts digital data between two points.
Data Rate — The maximum number of bits of
information which can be transmitted per second, as in a data transmission link. Typically
expressed as megabits per second (Mbps).
Decibel (dB) — The standard unit used to
express gain or loss of optical power.
dB Loss Budget —Each system is defined by
the dB loss budget of three parameters: the power required for successful detection, the
attenuation extant in the fiber plant, and the amount of power available from the
modulator.
DBR — Distributed Bragg Reflector.
DCC — Data Communication Channel: A three
byte, 192 kbps portion of the SONET signal that contains information about the system
performance, performs surveillance, and carries alarms when there is a problem.
DD — Direct detection.
Degenerate Waveguides — A set of waveguides
having the same propagation constant for all specified frequencies.
Degree of Coherence — The visibility, V, of
the fringes of a two-beam interference test, where V = Imax-Imin/Imax + Imin, where Imax
is the intensity of a maximum of the interference pattern, and Imin is the intensity at a
minimum. Light is considered highly coherent when the degree of coherence exceeds 0.88,
incoherent for small values, and partial coherent for intermediate values.
Delta — Equal to the “delta” between the
indices of refraction of the core and the cladding divided by the index of the core.
Demux — Demultiplexer; a device that
separates a multiplexed signal into its original components.
Detector — 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.
Detem — A single device that operates as
both an optical detector and as an emitter. Can be useful in ring architecture.
DF — The Radia fiber optic connector.
DFA — Doped fiber amplifier. Erbium doped
fiber amplifiers are the most common: DFA.
DFB Laser — Distributed Feedback Laser: An
injection laser diode using a Bragg reflection diode in the active region so to suppress
multiple longitudinal modes and enhance a single-longitudinal mode.
Diameter mismatch loss — The loss of power
that occurs when one fiber transmits to another and the transmitting fiber has a diameter
greater than the receiving fiber.
Dichromic Filter or mirror — One that
selectively transmits or reflects light according to selected wavelengths.
Dielectric — Non-metallic and, therefore,
non-conductive. Glass fibers are considered dielectric. A dielectric cable contains no
metallic components.
Differential Mode Attenuation – Variation in
attenuation in and among modes carried in a fiber.
Diffraction — The deviation of a wavefront
from the path predicted by geometric optics when an opening or an edge of an object
restricts a wavefront.
Digital — A data format that uses two
physical levels to transmit information corresponding to 0s and 1s. A discrete or
discontinuous signal.
Dispersion — 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.
Dispersion flattened fiber — A single mode
fiber that has a low chromatic dispersion throughout the range from 1300 to 1600
nanometers.
Dispersion Limited Operation — Describes
cases where the dispersion of the pulse rather than loss of amplitude limits the distance
a signal can be carried in a fiber.
Dispersion shifted fiber — A single mode
fiber that has zero dispersion wavelength at 1550 nanometers.
Dispersion unshifted fiber — A single mode
fiber that has zero dispersion wavelength at 1300 nanometers. Often called conventional or
unshifted fiber.
Dope(d) (ing) – The process of using any of
a number of different chemical elements to alter the properties of glass, such as its
refractive index.
Double Reflection — Re-reflection: Whenever
there is a reflection, for instance one caused by a connector or a splice, the reflected
light will travel back towards the source and meet new reflective planes.
Draw Process – The process of heating a
glass preform rod to the appropriate temperature for its composition on a fiber-draw tower
and letting controlled tension and gravity reduce the diameter of the rod to the desired
measurement, resulting in an optical fiber. The draw process includes application of one
or more protective coatings and sometimes also the application of a buffer. Drawing fiber
in this manner preserves all the geometries of the original preform rod and reduces them
such that their proportions remain the same in the finished fiber.
Drive Circuit — The electrical circuit that
drives the light emitting source, controls the modulator, and thereby causes the
intelligence bearing signal to be inserted optically upon the waveform.
Drop Cable —A cable either in coax or fiber
that connects an incoming or feeder to the customer premise.
DU — Fiber Optic Connector developed by the
Nippon Electric Group.
Dual Ring — A pair of counter rotating
logical rings.
Dual-window Fiber – Graded-index fiber in
which the refractive index profile is designed to give low modal dispersion at both 850
and 1300 nm.
Duplex Cable – Two, side-by-side simplex
cable sub-units surrounded by a single polymer jacket.
Duplex Transmission — Transmits in both
directions. When one direction at a time it is called half duplex, when it can do both
direction at a time it is called full duplex.
E/O — Electrical to Optical.
EDF — Erbium doped fiber.
EDFA — Erbium doped fiber amplifier. The
components in an EDFA include an erbium doped fiber, a laser pump diode, couplers, and
isolators.
Emitter — A source of Optical power, or
other electromagnetic energy.
End Finish — The quality of a fiber’s end
surface.
End Separation — The distance between the
ends of two joined fibers; the degree of separation causes an extrinsic loss, depending on
the configuration of the connection.
End to End Loss — This is the loss
experienced and measured between the transmitter and the detector due to fiber quality,
splices, connectors, bends etc.
Energy Density — Expressed in joules per
square meter. Often called irradiance.
Entrance Facility — An entrance to a
building for both public and private network service cables including the entrance point
at the building wall and continuing to the entrance room or space.
Epoxy/Polish – A process of finishing a
fiber end, allowing it to be terminated. Equilibrium length — Applies to multimode
fiber: the length required to produce equilibrium mode distribution.
Equipment Room — A centralized space for
telecommunications equipment that serves the occupants of a building.
Error Correction — In data transmission, the
technique of adding extra bits to a transmitted signal, with the extra bits being used to
detect and correct errors in the transmission.
ETFE – Ethylene tetrafluoroethylene. A
polymer commonly used to buffer fiber. Sold under the brand name, Tefzel, for example.
Ethernet — A baseband local area network
(LAN) developed by Xerox, Intel, and DEC.
Extrinsic Joint Loss — Optical loss caused
by end separation, (unmated connection, open) angular misalignments and lateral offsets.
Extrinsic Loss — These are losses caused by
defects and imperfections that cause the loss to exceed the theoretical minimum loss that
is intrinsic, and called intrinsic loss. Examples of causes of extrinsic losses include
lateral or axial offset between mating fibers that causes higher insertion loss, lack of
physical contact, lack of an angle on fiber ends, imperfections on the fiber’s surface as
well as many others that can cause higher reflectance losses.
Fan-Out — Multifiber cable constructed in
the tightbuffered design. Designed for ease of connectorization and rugged applications
for intra- or interbuilding requirements.
FC — Fiber optic connector developed by NTT.
FC-PC — FC connector with a physical contact
end finish.
FDM — Frequency Division Multiplex: While
WDM (Wavelength division multiplex) uses several discrete laser sources each having a
distinct center frequency, FDM can be used with any and all of those sources.
FDMA — Frequency Division Multiplex Access.
FEC — Forward Error Correction.
Feeder Cable — The cable running from a
central office to a remote terminal, hub, headend, node, etc.
Ferrule — A mechanical fixture, generally a
rigid tube, used to protect and align a fiber in a connector. Generally associated with
fiber optic connectors.
FET Photodetector — A photodetector using
photoregeneration of carriers in the channel region of a FET (field effect transistor) to
provide the photodetection with gain.
Fiber — Any filament or fiber, made of
dielectric materials, that guides light.
Fiber axis — The line connecting the centers
of the diameters that describe and circumscribe the core.
Fiber Bend Radius — Radius a fiber can bend
before the risk of breakage or increase in attenuation.
Fiber Bragg Gratings (FBGs) – a
photosensitive optical fiber that contains a periodic grating written into the core of the
fiber by exposure to UV radiation; used as filters for specific wavelengths or bands of
light.
Fiber Curl — This is a term that has become
useful for describing what happens to a fiber when there is misalignment in a mass or
ribbon splicing joint. In this case the fiber(s) curl away from the joint to take up the
slack or stress caused by misalignment of fiber lengths at the joint.
Fiber Distributed Data Interface (FDDI) — A
standard for a 100 Mbit/s fiber optic area network
Fiber loss — Attenuation of light in an
optical fiber transmission.
Fiber Optic Attenuator — An active device
designed to reduce the power of an optical signal, often used to limit the optical power
received by a photodetector so that it is received within the limits of the optical
receiver.
Fiber Optic Cable — An optical fiber,
multiple fiber, or fiber bundle which includes a cable jacket and strength members,
fabricated to meet optical, mechanical, and environmental specifications.
Fiber Optic Link — Any optical fiber
transmission channel designed to connect two end terminals or to be connected in series
with other channels.
Fiber optic waveguide — A long thin strand
of transparent material, usually glass but sometimes plastic, which can convey
electromagnetic energy in the optical waveform longitudinally by means of internal
reflection.
Fiber Optics — The branch of optical
technology concerned with the transmission of radiant power through fibers made of
transparent materials such as glass, fused silica, or plastic.
Field-Effect Transistor (FET) Photodetector
— A photodetector employing photogeneration of carriers in the channel region of an
FET structure to provide photodetection with current gain.
Filler – A non-optical cabling material used
to keep a cable round for handling purposes. Fillers run the length of the cable in place
of an actual optical fiber.
FIR — Finite Impulse Response.
FIT Rate — The number of device failures per
one billion device hours. A statistically derived value.
FITL — Fiber-in-the-loop. See also, FTTx
FM — Frequency Modulation, different from
amplitude modulation.
FOTP — Fiber Optic Test Procedures. Defined
in TIA/EIA Publication Series 455.
FOX — Fiber optic extension.
Frame — A frame equals a variable number of
bytes, typically not more than 4,500, including x bytes of header information. It is
defined by MAC (media access control) PDU (protocol data unit) and is normally transmitted
between MAC entities on a ring. See also SONET
FOXI — Fiber optic transparent synchronous
transmitter-receiver interface.
Frequency — The number of cycles per second
at which a waveform alternates, expressed in Hertz.
Frequency response — Transfer function.
Fresnel Reflection — The reflection of a
portion of the light incident, between two homogeneous media having different refractive
indices. Fresnel reflection occurs at the air/glass interfaces at entrance and exit ends
of an optical fiber.
Fresnel Reflection Losses — Reflection
losses that are incurred at the input and output of optical fibers due to the differences
in refraction index between the core glass and immersion medium.
Fresnel Reflection Method — The method for
measuring the index profile of an optical fiber by measuring reflectance as a function of
position on the endface. This position can be influenced by angling.
FSA — Fixed Shroud Duplex Fiber Optic
Connector.
FTF — Fiber trunk feeder.
FTM — Fiber telecommunications module.
FTTx — Fiber-To-The-x that includes: FTMB:
Fiber to major business. FTTB: Fiber to the business. FTTC: Fiber to the curb. FTTD: Fiber
to the desk. FTTH: Fiber to the home. FTTS: Fiber to the school.
Fundamental Mode — The lowest order mode
that will travel in a waveguide.
Fusing — The actual operation of joining
fibers together by fusion or by melting.
Fusion Splice — A permanent joint produced
by the application of localized heat sufficient to fuse or melt the ends of the optical
fiber, forming a continuous single fiber.
FUT — Fiber under test.
GaAlAs — Gallium Aluminum Arsinide.
GaAs — Gallium Arsinide.
Gain Bandwidth — In an avalanche photodiode
the gain multiplied by the frequency of measurement when the device is biased for maximum
obtainable gain.
Gamma — The coefficient used to scale
bandwidth with fiber length.
Gap Loss — Also called loss from open or
unmated condition. The loss, often most significant in reflectance, resulting when two
axially aligned fibers are separated by an air gap.
Gigahertz (GHz) — A unit of frequency that
is equal to one billion cycles per second, 109 Hertz.
Gigabit — Transmissions of billions of bits
per second; Gbps.
Glass-Reinforced Plastic – Also GRP. Also
Epoxy Rod. A cabling material used to provide strength and rigidity over the length of a
cable.
GOSIP — Government Open System Interconnect
Protocol.
Graded-Index — Fiber design in which the
refractive index of the core is lower toward the outside of the fiber core and increases
toward the center of the core, thus, it bends the rays inward and allows them to travel
faster in the lower index of refraction region.
Guided Ray — A ray that is completely
confined to the core.
Handhole — A buried access box containing
splice or patch panels together with associated active and passive equipment that may be
required to maintain the operation of the system whose lid is even with the surface of the
substrate.
HDSL — High Bit Rate Digital Subscriber
Line.
HDT — Host digital terminal.
Headend — That position in the ring where
the signals are captured, often by microwave or by from the backbone, and entered into the
CATV system.
HFC — Hybrid fiber-coax. A network for
transmitting signals modulated onto RF carriers that includes a linearly amplitude
modulated optical link followed by a coaxial distribution network.
Horizontal Cabling — That portion of the
telecommunications cabling that provides connectivity between the horizontal cross-connect
and the work-area telecommunications outlet. The horizontal cabling consists of
transmission media, the outlet, the terminations of the horizontal cables, and horizontal
cross-connect.
Horizontal Cross-Connect (HC) — A
cross-connect of horizontal cabling to other cabling, e.g., horizontal, backbone,
equipment.
Horizontal Distribution Frame — A physical
structure, usually constructed of steel and lying on the floor, which contains the
components that provide interconnection between inter and intra building cabling.
Hybrid Cable — A fiber optic cable
containing two or more different types of fiber, such as 62.5 µm multimode and
single-mode.
Hybrid Connector — A connector containing
both fiber and electrical connectivity.
Hydrogen loss — Hydrogen in glass absorbs
light and turns it into heat and thus attenuates the light.
Hydroxyl Ion Absorption — When water enters
the process of making the glass it remains as the hydroxyl ion, and also absorbs the
energy of the light and converts it to heat and thus attenuates the height passing through
the hydroxyl bearing glass.
I/O — Input and output.
IC — Integrated circuit.
IDP — Integrated detector/preamplifier.
IEEE — Institute of Electrical and
Electronics Engineers.
IF — Intermediate Frequency.
ILD — Injection laser diode. In this case
the “lasing” takes place within the actual semiconductor junction, often called a P-N
junction, and the light is emitted from the edge of the diode.
Incident Angle — The angle between the
subject light wave and a plane perpendicular to the subject optical surface.
Incoherent Light — Random light forms
whereby the phase of the light is unpredictable.
Index Matching Material — A material, often
a liquid or cement whose refractive index is nearly equal to the core index. Used to
reduce Fresnel reflections from a fiber end face.
Index of Refraction — The ratio of light
velocity in a vacuum to its velocity in a given transmission medium.
Index Profile — Curve of the refractive
index over the cross section of an optical waveguide.
InGaAs — Indium Gallium Arsinide.
InGaAsP — Indium Gallium Arsinide Phosphide.
Injection Laser Diode (ILD) — Laser diode.
InP — Indium Phosphide.
Insertion Loss — The attenuation caused by
the insertion of an optical component; in other words, a connector or coupler in an
optical transmission system.
Inside Plant, Inside the plant — (IP, ITP)
the portion of the cable network inside buildings, where cable lengths are usually shorter
than 100 meters.
Integrated Detector/Preamplifier — A
detector containing both a pin photodiode and a trans-impedance amplifier.
Integrated Optics — Device(s) integrated on
a single substrate that perform two or more functions.
Integrated Optoelectronics — Similar concept
to Integrated Optics, except one of the integrated devices on the semiconductor chip is
optical and the other electronic. Intensity — Irradiance.
Interbuilding Backbone — The portion of the
backbone cabling between buildings. (See Backbone Cabling.)
Interconnect Cabinet — Cabinets containing
connector panels and connectors and patch cords to interface from inside the plant to
outside the plant.
Interference — The interaction of two or
more beams of coherent or partially coherent light.
Interferometer — The application of light
waves and the characterization of their patterns of interference to make physical
measurements.
Intermediate Cross-Connect (IC) — A
secondary cross-connect in the backbone cabling used to mechanically terminate and
administer backbone cabling between the main cross-connect and horizontal cross-connect.
Intermodal Distortion — Multimode
distortion.
Intrabuilding Backbone — The portion of the
backbone cabling within a building. (See Backbone Cabling.)
Intrinsic Joint Loss — This is the
theoretical minimum loss that a given joint or device will have as a function of its
nature.
IOC — Integrated optical circuit: This is an
optical circuit that is used for coupling between optoelectronic devices and providing
signal processing functions. It can be monolithic or hybrid, and is composed of both
active and passive components.
IOF — Interoffice trunks: used to describe
both copper and fiber.
Ion Exchange Techniques — A method for
making and doping glass by ion exchange.
IP — Internet Protocol.
IPF — Intrinsic Performance Factor
IR — Infrared: This is the band of
electromagnetic radiation beyond the red wavelength, whose wavelength is between 750 and
1,000 nanometers.
Irradiance — Power density at a surface
through which radiation passes at the radiating surface of a light source or at the cross
section of an optical waveguide. ISDN — Integrated Services Digital Network. This is
a network in which a single digital bit stream can carry a great variety of services.
Isolator — These are usually installed to
protect the source from interference by unacceptable noise to signal ratios caused by
reflectance, mostly caused by EDFA systems, and/or the cumulative effect of the passive
plant.
Jacket – A protective layer of polymer
material extruded outside the buffered fibers as part of the cabling process.
Joint — Any joining or mating of a fiber by
splicing, both by fusion and by physical contact, or by connecting.
Jumper — Optical fiber cable that has
connectors installed on both ends. (See Cable Assembly.)
Kevlar — (See Aramid Yarn.)
KHz — Kilo Hertz, or 1,000 hertz.
Kilometer (km) — One thousand meters, or
approximately 3,281 feet. The kilometer is a standard unit of length measurement in fiber
optics. Conversion is 1 ft. = 0.3048 m
kpsi — A unit of force per area expressed in
thousands of pounds per square inch. Usually used as the specification for fiber
prooftest. e.g., 100 kpsi.
LAN — (See Local Area Network.)
Laser — An acronym for Light Amplification
by Stimulated Emission Radiation.
Laser Diode (LD) — An electro-optic device
that produces coherent light with a narrow range of wavelengths, typically centered around
780 nm, 1320 nm, or 1550 nm.
Lasing Threshold — The lowest excitation
level at which a laser’s output is dominated by stimulated emission rather than
spontaneous emission.
Launch Angle — Angle between the propagation
direction of the incident light and the optical axis of an optical waveguide.
Launching Fiber — A fiber used in
conjunction with a source to excite the modes of another fiber in a particular way.
Launching fibers are most often used in test systems to improve the precision of
measurements.
LED – See Light Emitting Diode
Leaky Modes — In the boundary region between
the guided modes of an optical waveguide and the light waves, which are not capable of
propagation, there are so-called leaky modes which are not guided but are capable of
limited propagation with increased attenuation.
LID — Local Injection Detection: This is a
method for injecting a signal and detecting it within a discrete segment of fiber.
Light — In the laser and optical
communication fields, the portion of the electromagnetic spectrum that can be handled by
the basic optical techniques used for the visible spectrum extending from the near
ultraviolet region of approximately 0.3 micron, through the visible region and into the
mid- infrared region of about 30 microns.
Light Emitting Diode (LED) — A semiconductor
device that emits incoherent light from a p-n junction when biased with an electrical
current in the forward direction. Lightwaves — Electromagnetic waves in the region
of optical frequencies.
Linear Low-Density Polyethylene (LLDPE) – A
cable jacketing material.
Linear Polarization – A state in which the
electric field of a light wave is oriented in only one direction.
Link — A telecommunications circuit between
any two telecommunications devices, not including the equipment connector.
LO — Local Oscillator
Local Area Network (LAN) — A LAN is a data
communications system that enables users to access common data processing (PCs,
minicomputers, and mainframe computers) and peripheral equipment (printers and fax
machines.
Local Loop — The loop or circuit between
receivers, (and in two way systems receivers and senders) who are normally the customers
or subscribers to the systems products, and the terminating equipment at the central
office.
Long wavelength — Light whose wavelength is
greater than 1,000 nanometers. (longer than one micron or 1 um.)
Longitudinal Modes — The oscillation of
light along the length of the laser’s cavity are normally such that two times the length
of the cavity will equal an integral number of wavelengths.
Loose Tube — A protective tubular
encapsulant, often filled with a gel, used to contain one or multiple fibers.
Loss — Attenuation and loss of power
measured in decibels. The opposite of loss is gain.
Loss Budget — A calculation and allowance
for total attenuation in a system that is required in order to assure that the detectors
and receivers can make intelligent decisions about the pulses they receive.
Low Smoke Zero Halogen (LSZH) – An
environmental cable specification indicated primarily for indoor applications to reduce
toxicity in case of fire.
LUCAS — Line Utilization Cable Assignment
System.
LXE — Fiber Optic Express Entry.
MAC — Media Access Control. This is the data
link sublayer that manages the scheduling and routing of data transmissions on a shared
LAN (Local area network), for instance in the case of FDDI, (Fiber Distributed Data
Interface.)
Macrobending — Macroscopic axial deviations
of a fiber from a straight line, in contrast to microbending.
Macrobending Loss — Loss due to large bends
in the fiber.
Main Cross-Connect (MC) — The centralized
portion of the backbone cabling used to mechanically terminate and administer the backbone
cabling, providing connectivity between equipment rooms, entrance facilities, horizontal
cross-connects, and intermediate cross-connects.
Mass Splicing — This is the concurrent and
simultaneous splicing of multiple fibers at one time.
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.
MBE — Molecular Beam Epitaxy.
Mbps — Megabit: Millions of bits of data per
second.
MCVD — Modified chemical vapor deposition.
MDPE — Abbreviation used to denote medium
density polyethylene. A type of plastic material used to make cable jacketing.
MDU — Multiple Dwelling Unit.
Mechanical Splicing — Joining two fibers
together by permanent or temporary mechanical means (vs. fusion splicing or connectors) to
enable a continuous signal.
Megahertz (MHz) — A unit of frequency that
is equal to one million cycles per second.
Meridian Plane — Any plane that includes or
contains the optical axis.
Meridinal Ray — A ray that passes through
the optical axis of an optical fiber.
MFD — Mode Field Diameter: The measure of
the width of a guided optical power’s intensity in a single mode laser.
MHz — Megahertz: or millions of hertz.
MIC — Media Interface Connector: This is a
pair of fiber optic connectors that link the fiber media to the FDDI or other cable. The
MIC consists of both the MIC plug termination of an optical cable, and the MIC receptacle
is joined with the FDDI node.
Microbending — Curvatures of the fiber which
involve axial displacements of a few micrometers and spatial wavelengths of a few
millimeters. Microbends cause loss of light and consequently increase the attenuation of
the fiber.
— Loss due to microscopic bends in the fiber.
Micrometer (µm) — One millionth of a meter;
10-6 meter. Typically used to express the geometric dimension of fibers, for example, 62.5
µm.
Mid span meet — When a SONET architecture is
able to mix the terminal, multiplexing and mixing and cross connecting equipment from
different vendors.
Mini Bundle Cable — Loose tube cable in
which the buffer tube contains two or more fibers, typically 6 or 12 fibers.
MLM — Multilongitudinal mode.
MMF — Multimode fiber.
MOCVD — Metal organic chemical vapor
deposition.
Modal Bandwidth, or Intermodal Distortion —
The bandwidth limiting characteristic of multimode fiber systems caused by the variable
arrival times of various modes.
Modal Dispersion — Pulse spreading due to
multiple light rays traveling different distances and speeds through an optical fiber.
Modal Noise — Disturbance in multimode
fibers fed by laser diodes. It occurs when the fibers contain elements with mode-dependent
attenuation, such as imperfect splices, and is more severe the better the coherence of the
laser light.
Mode — A term used to describe an
independent light path through a fiber, as in multimode or single-mode.
Mode Field Diameter — The diameter of the
one mode of light propagating in a single-mode fiber. The mode field diameter replaces
core diameter as the practical parameter in single-mode fiber.
Mode Filter — A device that can select,
attenuate, or reject a mode.
Mode Mixing — The numerous modes of a
multimode fiber differ in their propagation velocities.
Modes — Discrete optical waves that can
propagate in optical waveguides.
Mode Scrambler — A device composed of one or
more optical fibers in which strong mode coupling occurs. Frequently used to provide a
mode distribution that is independent of source characteristics.
Modified Chemical Vapor Deposition (MCVD)
Technique — A process in which deposits are produced by heterogeneous gas/solid and
gas/liquid chemical reactions at the surface of a substrate. The MCVD method is often used
in fabricating optical waveguide preforms by causing gaseous material to react and deposit
glass oxides. Modulation — Coding of information onto the carrier frequency. This
includes amplitude, frequency, or phase modulation techniques.
Monochromatic — Consisting of a single wavelength.
MOVPE — Metal organic vapor phase epitaxy.
MPEG — Motion Pictures Experts Group.
Multifiber Cable — An optical fiber cable
that contains two or more fibers.
MRN — Multiple Reflection Noise: This is
noise at the receiver caused by the interface of delayed signals form two or more
reflection points in an optical fiber span.
MTBF — Mean time before failures.
Multimode Distortion — The signal distortion
in an optical waveguide resulting from the superposition of modes with differing delays.
Multimode Fiber — An optical waveguide in
which light travels in multiple modes. Multi-mode Laser — A laser that produces
emissions in two or more transverse or longitudinal modes.
Multiplexing — Combining two or more signals
into a single bit stream that can be individually recovered.
Multiplexer — A device or protocol that
combines discrete signals, two or more, into a single output.
Multi-User Outlet — A telecommunications
outlet used to serve more that one work area, typically in open-systems furniture
applications.
MUX — See Multiplexer.
Mw — Milliwatt.
MZI — Mach Zehnder Interferometer.
NA — Nano-amp.
Nanometer (nm) — A unit of measurement equal
to one billionth of a meter; 10-9 meters. Typically used to express the wavelength of
light, for example, 1300 nm.
National Electrical Code (NEC) — Defines
building flammability requirements for indoor cables.
NDFA — Neodymium doped fiber amplifier.
Near Field Radiation Pattern — Distribution
of the irradiance over an emitting surface; in other words, over the cross section of an
optical waveguide.
NEP — Noise equivalent power: The radiant
power that provides a noise to signal ratio of one at the output of a given detector,
within defined parameters for modulation, frequency, wavelength, and a given effective
noise bandwidth.
Node — The term for any FDDI network
attachment, such as a station, concentrator or bridge. A branching, exchange of
distribution element.
Normal Angle — One that is perpendicular to
a surface.
NTSC — National Television Standards Code.
Numerical Aperture — A measure of the range
of angles of incident light transmitted through a fiber.
O/E — Optical to electrical.
OAM&P — Operations, Administration,
Maintenance, and Provisioning. A generic term for software suites that allow centralized
administering of a communications network.
OC-1 — Optical carrier level one, equal to
51.84 Mbps. This is a SONET channel, which format measures 90 bytes and is composed of the
transport overhead and the synchronous payload envelope.
OC-3 — A SONET channel of 155.52 Mbps.
OC-12 — A SONET channel of 622.08 Mbps.
OC-48 — SONET channel of 2.4 Gbps.
OC-192 — SONET channel of 10 Gbps, currently
the highest level now commonly implemented.
OC-768 — SONET channel of 40 Gbps, the
highest level becoming available for field deployment.
ODC — Optical Directional Coupler: used to
combine or separate optical power.
OEIC — Optoelectronic integrated chip.
OFDM — Orthogonal Frequency Division
Multiplexing.
OIU — Optical interface unit.
ONU — Optical Node Unit, or Optical Network
Unit (PON or DLC Term).
Open — An open fiber connection, or a broken
fiber. In the case of a connector this condition is also called unmated, open,
unterminated etc.
Operating Wavelength – The wavelength in
nanometers at which an optical fiber is designed to operate optimally.
Optical Amplifier — Optical amplifiers
increase the power of an optical signal without converting any of the signals from optical
to electrical energy and then back to optical.
Optical Attenuator — The optical attenuator
reduces the intensity of light waves, usually so that the power is within the capacity of
the detector.
Optical Cavity — A region bounded by two or
more mirrors or other reflecting surfaces that are aligned so to provide multiple
reflections. An example of an optical cavity would include the resonator in a laser.
Optical Channel — A wavelength band for WDM
(wavelength division multiplexers) optical communications.
Optical Channel Spacing — The wavelength
separation between adjacent WDM channels.
Optical Channel Width — The optical
wavelength range of a channel.
Optical contact — Also called the terminus.
Optical detector — A transducer that
generates an electronic signal when excited by an optical power source.
Optical Fiber — See Fiber.
Optical Polarization — The term used to
describe the orientation in space of time varying field vector of an optical signal.
Optical receiver — An optoelectronic circuit
that converts an incoming signal to an electronic signal.
Optical reference plane — The plane that
defines the optical boundary between the MIC plug (Media Interface Connector) and the MIC
receptacle.
Optical Repeater — This optoelectronic
device, which could include an amplifier, receives a signal, amplifies it, especially in
the case of analog signals, or in the case of a digital signal reshapes it or re-times it,
and then retransmits it.
Optical Spectrum — “Colors” of light, each
of which represents a wavelength, or frequency of electromagnetic energy.
Optical Time Domain Reflectometer (OTDR) — A
method for characterizing a fiber wherein an optical pulse is transmitted through the
fiber and the resulting backscatter and reflections to the input are measured as a
function of time. Useful in estimating attenuation coefficient as a function of distance
and identifying defects and other localized losses.
Optical Transmitter — This is an
optoelectronic circuit that converts an electronic signal into an optical signal, the
later bearing the same intelligence as the earlier.
Optical Waveguide — Dielectric waveguide
with a core consisting of optically transparent material of low attenuation (usually
silica glass) and with cladding consisting of optically transparent material of lower
refractive index than that of the core.
Optoelectronic — Pertaining to a device that
responds to optical power, emits or modifies optical radiation, or utilizes optical
radiation for its internal operation.
Orthogonal — Literally, at right angles.
Often used by the engineering community to describe two functions that are independent of
each other.
Packet — A group of binary digits, including
data and call control signals, which are switched as a composite whole. The data are
arranged in a specific format.
PAD — Packet assembler/dissembler.
PAMA — Pulse address multiple access: In
this case carriers are characterized by their temporal and special characteristics at the
same time.
PAS — Profile Alignment System:This is a
technique for using non electro- optical linked access technology for aligning fibers for
splicing.
Passive — A component that handles signals
but that requires no power of its own. Examples are taps and power inserters.
Passive coupler — Divides light without
generating new light.
Patch cords — Jumper cords: Interconnect
cables: Short distance cables, usually with connectors pre-installed on both ends, used to
connect between equipment, and generally between two and ten meters long.
Path Layer — The highest of four layers of
SONET, which generates signaling pointers and overseas transport.
PBS — Polarizing Beam Splitter.
PDN — Passive distribution network.
PE — Abbreviation used to denote
polyethylene. A type of plastic material used for outside plant cable jackets.
Peak Power — Highest instantaneous power in
a pulse.
Peak Wavelength — The wavelength at which
the optical power of a source is at a maximum.
PFA – Perfluoro alkoxy fluorocarbon. A
thermoplastic used as both a buffer and cable jacket material. Sold under the brand name,
Teflon, for example.
Phase — The position of a wave in its
oscillation cycle.
Photo-bleaching — A reduction in added loss
that occurs when a fiber is exposed to light.
Photocurrent — The current that flows
through a photosensitive device, such as a photodiode, as the result of exposure to
radiant power.
Photo-darlington — A light detector in which
a photo-transistor is combined in a circuit with a second transistor in order to amplify
its output. Not known for speed but for sensitivity.
Photodiode — A diode designed to produce
photocurrent by absorbing light. Photodiodes are used for the detection of optical power
and for the conversion of optical power into electrical power.
Photon — A quantum of electromagnetic
energy.
Photonic Layer — The lowest of the four
layers of SONET that determines the type and sensitivity of fiber and laser that must be
used.
Photovoltaic effect — This is the effect
caused when a photon is absorbed by a semiconductor detector and it generates an
electrical charge, measured as voltage, across an =n junction of that semiconductor.
PIC — Photo-optic Integrated Circuit.
Pigtail — A short length of optical fiber
for coupling optical components, with a connector on one end.
PIN Device — Positive Intrinsic Negative
Device.
PIN Diode — A semiconductor device used to
convert optical signals to electrical signals in a receiver.
PIN-FET Receiver — Optical receiver with a
PIN photodiode and low noise amplifier with a high impedance input, whose first stage
incorporates a Field- Effect Transistor (FET).
PIN Photodiode — A diode with a large
intrinsic region sandwiched between p-doped and n-doped semiconducting regions. Photons in
this region create electron hole pairs that are separated by an electric field, thus
generating an electric current in the load circuit.
Plenum — An air-handling space such as that
found above drop-ceiling tiles or in raised floors. Also, a fire-code rating for indoor
cable.
Plenum Cable — A cable used in plenum spaces
with tight controls and specifications with regard to fire retardance, low smoke evolution
in fire etc. Generally controlled by UL910 and other specifications such as the NEC
(National Electrical Code).
POFFDI — Plastic optical fiber/Fiber
Distributed Interface.
Point-to-Point — A connection established
between two specific locations as between two buildings.
Polarization-Maintaining Fiber – An
internally-stressed fiber designed to keep two signals propagating in perpendicular
orientations throughout the length of fiber.
POLSK — Polarization shift keying.
PON — Passive Optical network.
Port — The hardware elements at each end of
a link.
POTS — Plain Old Telephone Service.
PPS — Packets per second.
Preform — A glass structure from which an
optical fiber waveguide may be drawn.
Prefusing — Fusing with a low current to
clean the fiber end. Precedes fusion splicing.
Primary Coating — The plastic coating
applied directly to the cladding surface of the fiber during manufacture to preserve the
integrity of the surface.
Propagation – The movement of light through
a fiber from transmitter to receiver, usually constrained to the core of the fiber, but
sometimes utilizing the cladding as a portion of the waveguide.
Protocol — In data transmission, a set of
rules defining how various pieces of equipment or software will interact cooperatively.
PS — Picosecond. One trillionth of a second.
PSK — Phase shifted key.
PVC — Abbreviation used to denote
polyvinyl-chloride. A type of plastic material used for cable jacketing. Typically used in
flame-retardant cables.
PVDF — Abbreviation used to denote
polyvinyl-difluoride. A type of material used for cable jacketing. Often used in
plenum-rated cables.
QAM — Quadrature Amplitude Modulation. This
is modulation of two separate signals onto carriers at one frequency and kept separate by
having two signals 90 degrees out of phase.
QPSK — Quadrature Phase Shift Keying. A
digital modulation method in which the state of a two-bit symbol is represented by one of
four possible phase states.
Quantization Noise — The noise-like
uncertainty imparted to an analog signal when it is digitized.
Radial Refractive Index Profile — The
refractive index measured in a fiber as a function of the distance from the axial core or
center.
Radian Flux — The time rate in watts of flow
of radiant energy.
Radiance — The radiant flux as Watts per
unit soled angle per unit of projected area of the source in units described as
watts/m2/steradian.
Radiant Emission — Expressed in watts per
square meter and equal to the power emitted into a full sphere by a unit area of source.
Ray — A geometric representation of a light
path through an optical medium; a line normal to the wave front indicating the direction
of radiant energy flow.
Rayleigh Scattering — Scattering by
refractive index fluctuations (inhomogeneities in material density or composition) that
are small with respect to wavelength.
RBOC — Regional Bell Operating Company.
Receiver — A detector and electronic
circuitry to change optical signals into electrical signals.
Receiver Sensitivity — The optical power
required by a receiver for low error signal transmission. In the case of digital signal
transmission, the mean optical power is usually quoted in Watts or dBm (decibels referred
to 1 milliwatt).
Reflection — The abrupt change in direction
of a light beam at an interface between two dissimilar media so that the light beam
returns into the media from which it originated.
Refraction — The bending of a beam of light
at an interface between two dissimilar media or in a medium whose refractive index is a
continuous function of position (graded index medium).
Refractive Index — The ratio of the velocity
of light in vacuum to that in an optically dense medium.
Refractive Index Profile – A graphical
representation showing the refractive index of the core and cladding of a fiber.
Regenerative Repeater — A repeater designed
specifically for digital operations.
REM — Remote Electronic Maintenance.
Repeater — In a lightwave system, an
optoelectronic device or module that receives an optical signal, converts it to electrical
form, amplifies or reconstructs it, and retransmits it in optical form.
Return Loss — Also reflectance: The ratio of
reflected power to inserted power; expressed in decibels.
RH — Relative humidity.
Ribbon — Multiple fibers organized in a flat
array
Ring — Two or more stations in which data
are passed sequentially between active stations, each in turn examining or copying the
information, before finally returning it to the source.
Ring Architecture — A network design in
which a transmission line forms a complete ring.
Ring Network — A network topology in which
terminals are connected in a point-to-point serial manner in an unbroken circular
configuration.
Ripcord – A string-like material embedded in
the length of a multi-fiber cable which, when pulled, splits the outer jacket of the cable
lengthwise, revealing the individual fiber sub-units within and allowing them to be routed
or connectorized separately from a single cable.
Rise time — The time it takes for output to
rise from low values, say 10%, to high values, say 90% of peak power.
Riser — Pathways for indoor cables that pass
between floors. It is normally a vertical shaft or space. Also a firecode rating for
indoor cable.
Riser Cable — Cable used to reach between
floors in vertical spaces.
Rod – (1) Another term for “Preform.” (2) A
strength member inserted under the outer jacket along the length of a cable to provide
rigidity.
Router — In data communications, a device
used to switch packets from any number of input ports to any one of a number of output
ports.
RSU — Remote service unit.
SAS — Single attach station.
SBS — Stimulated Brillouin Scattering. A
mechanism that limits the amount of optical power at a single wavelength that can be
transmitted through an optical fiber.
SC — Fiber optic connector made from molded
plastic, using push-pull mechanics for joining to a fiber adapter.
Scattering — A property of glass that causes
light to deflect from the fiber and contributes to optical attenuation.
SCDMA — Synchronous Code Division Multiplex
Access.
SCM — Sub-carrier multiplex.
SDH — Synchronous Digital Hierarchy: Term
used by ITU for SONET-like technology (interoperable technologies).
SDSL — Symmetrical Digital Subscriber Line.
Semiconductor diode laser — A laser in which
injection of current into a semiconductor diode produces light by way of recombination of
holes and electrons at the junction of the p-doped and n-doped materials.
Semiconductor laser — A laser in which
coherent light is generated at the junction of the n-type and p-type semi-conducting
materials.
Short wavelength — Light whose wavelength is
shorter than 1,000 nanometers. (shorter than one micron or 1 um.)
Side Mode — Any observable mode of an
optical devices spectrum that is not the dominant mode.
Signal – A generic term for light launched
from a source, intended for receipt at the other end of an optical fiber.
Simplex — A component or element in units of
one. For instance a simplex connector would only have one fiber attached.
Simplex Cable – A single fiber with at least
one layer of protective jacketing for environmental protection and ease of handling. May
also include strength members or external armoring.
Single-mode Fiber (SMF)— Optical fiber with
a small core diameter (typically 9 µm) in which only a single-mode, the fundamental mode,
is capable of propagation. This type of fiber is particularly suitable for wideband
transmission over large distances, since its bandwidth is limited only by chromatic
dispersion.
SLA — Semiconductor laser amplifier.
SLC — Subscriber loop carrier.
SLED — Surface emitting light emitting
diode.
SLM — Single longitudinal mode.
SMA – Surface mount assembly. A connector
type commonly used in the military and medical markets.
SMDS — Switched multi-megabit digital
service: a 1.544-155 Mbps data service with IEEE 802.6 standard user interface. It can
support Ethernet, Token ring, and FDDI (OC-3c) LAN to LAN connections.
SMF — See Single-mode fiber.
SMOLTS — Single mode optical lost test set.
SMSR — Side mode suppression ration: The
relationship, expressed in dB, of the dominant mode power, P, to the power of the largest
side mode, P(s) .
SNMP — Simple Network Management Protocol.
SNR — Signal To Noise Ratio.
Solid state laser — A laser whose active
medium is a glass or crystal.
SONET — Synchronous Optical Network: This is
the underlying architecture in most systems and uses frames of fixed length.
SOP — State of Polarization.
Source — A device that emits light. Usually
a laser or LED.
SPE — Synchronous payload envelope.
Spectral Radiance — Radiance per unit
wavelength interval: W/sr/m2/meter. (See Steradian = sr, which is the unit solid angular
measure.)
Speed of light in a vacuum — 299 x 106
meters per second. Reference for calculating the index of refraction.
Splice — A permanent joint between two
optical waveguides.
Splice Closure — A container used to
organize and protect splice trays. Typically used in outside plant environments.
Splice Bushing – A connector accessory used
to attach two connectorized cables end to end, keep them held in place, and protect them
from disconnecting under normal use.
Splice Tray — A container used to secure,
organize, and protect spliced fibers.
Spontaneous Emission — This occurs when
there are too many electrons in the conduction band of a semiconductor. These electrons
drop spontaneously into vacant locations in the valence band, a photon being emitted for
each electron. The emitted light is incoherent.
S-SEED — Symmetric self-electrooptic device.
ST — A connector type invented by OFS
featuring a bayonet-style nut and commonly used in telecommunications.
Star Network — A network in which all
terminals are connected through a central point.
Station — An addressable node on an FDDI
(fiber distributed data interface) cable of transmitting, receiving and repeating data.
Has one each instance of SMT, MAC, PHY and PMD.
Step Index Fiber — A fiber having a uniform
refractive index within the core and a sharp decrease in refractive index at the
core/cladding interface.
Stimulated Emission — This occurs when
photons in a semiconductor stimulate available excess charge carriers to the emission of
photons. The emitted light is identical in wavelength and phase with the incident coherent
light.
Strength Member – A rigid or flexible
element, such as a glass-reinforced plastic rod or aramid yarn, used in cabling fiber to
achieve increased tensile strength.
STS-1 — Synchronous transport level one. An
electrical signal that is converted to or from SONET’s optically based signal; equivalent
to the OC-1 signal of 51.84 Mbps. STS-1 was designed to allow mapping in a DS3 channel of
45 Mbps.
STS-Synchronous Payload Envelope — The
payload portion of the SONET signal that uses 50.11 Mbps of the total OC-1 signal. It
measures 87 bytes wide and 9 bytes deep.
Supertrunk — A cable that carries several
video channels between the facilities of a cable television company.
Surface Emitting Diode — Emits from its
surface instead of its edge. Emissions are spread over a wider angle.
T1 — Transmission system that operates at
1.544 Mbps.
T2 — Transmission system that operates at
6.176 Mbps. Multiplexed signal comprised of four (4) T1 signals.
T3 — Telecommunications transmissions at 45
Mbps. Multiplexed signal comprised of seven (7) T2 signals (28-T1s).
Tap — A device for extracting a portion of
the optical fiber.
Tapered fiber — An optical fiber whose
transverse dimensions vary monotonically with length.
Tb/s — Terabits per second.
TDM — Time division multiplexing: digital
multiplexing by taking one pulse at a time from separate signals and combining them in a
single bit stream.
TDMA — Time division multiplexing access.
TE — Transverse electric.
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.
Tensile Strength – A measure of the maximum
resistance a fiber can sustain before breaking under a stretching load.
Termination – The process of connectorizing
one or both ends of a fiber or cable.
Theoretical Cutoff Wavelength — The shortest
wavelength at which a single mode can be propagated in a single-mode fiber. Below the
cutoff several modes will propagate and the fiber is no longer single, but multimode.
Threshold Current — The driving current
above which the amplification of the lightwave in a laser diode becomes greater than the
optical losses, so that stimulated emission commences. The threshold current is strongly
temperature dependent.
Tight-Buffered Cable — Type of cable
construction whereby each glass fiber is tightly buffered by a protective thermoplastic
coating to a diameter of 900 micrometers. Increased buffering provides ease of handling
and connectorization.
Tolerance – The accuracy of a specification
to within a certain degree of error.
Total Bandwidth — The combined modal and
chromatic bandwidth.
Total Internal Reflection — The total
reflection that occurs when light strikes an interface at angles of incidence greater than
the critical angle.
Tower (Draw) – A multi-story structure at
the top of which is affixed a high- temperature furnace through which preforms are drawn
into fiber.
TPE – Thermoplastic elastomer. Sold under
the brand name, Hytrel, for example.
TPON — Telephone passive optical network.
Transceiver — A device that combines both
functions of the transmitter and receiver, thereby providing both output and input
interfaces.
Transmission Loss — Total loss encountered
in transmission through a system.
Transmitter — A driver and a source used to
change electrical signals into optical signals.
Transverse Modes — In this case modes across
the width of the waveguide are considered.
Trunk Cable — The cable connecting central
offices to each other.
Trunk line — The transmission line running
between telephone switching offices.
TSI — Time slot interchanger.
TVRO — Television receive only.
Unmated — Unterminated: Open:These are
descriptors for connectors in a system whose end-faces are not in contact with another
connector resulting in a fiber which is launching light from the surface of the glass in
to air.
Upjacket – A layer of fiber protection in
any of a variety of materials extruded outside the buffered fibers as part of the cabling
process—usually refers to a second-or-higher-order after a primary jacket or buffer
layer.
VBR — Variable Bit Rate. A signal or
communications channel that generates or accommodates a digital signal whose bit rate
varies with time.
VCSE — Vertical cavity emitting surface.
Example is VCSEL (Vertical Cavity Surface Emitting Laser).
VHDSL — Very High-Rate Digital Subscriber
Line.
Visible light — Electromagnetic radiation
between 400 and 700 nm.
VT — Virtual Tributary: A unit of sub-SONET
bandwidth that can be combined or concatenated for transmission through the network; VT1.5
is equal to 1.544 Mbps; VT2 is equal to 2.048 Mbps; VT3 is equal to 3 Mbps, and VT6 equals
6 Mbps.
WAN — Wide area network.
Water Peak – The point or points on the
optical attenuation spectrum where water in a particular fiber design causes a spike.
Waveguide – The center portion of an optical
fiber where light travels— usually limited to the core but sometimes including a
fraction of the cladding as well.
Waveguide Couplers — Couples light between
planner waveguides.
Waveguide Dispersion – A cause of dispersion
due to the geometry of the fiber.
Waveguide Scattering — Caused by variations
in geometry as well as by the index profile of the fiber or waveguide.
Wavelength – The distance between successive
peaks or nodes of a light wave, measured in nanometers (nm).
Wavelength Dispersion — In an optical fiber,
the variation in transmission time as a function of the wavelength of the light.
Wavelength Division Multiplexing (WDM) —
Simultaneous transmission of several signals in an optical waveguide at differing
wavelengths.
Work-Area Telecommunications Outlet — A
connecting device located in a work area at which the horizontal cabling terminates and
provides connectivity for work-area patch cords.
Zero Dispersion Slope — The value of the
chromatic dispersion slope at the fiber’s zero dispersion wavelength.
Zero-Dispersion Wavelength — Wavelength at
which the chromatic dispersion of an optical fiber is zero. Occurs when waveguide
dispersion cancels out material dispersion.
Zipcord – A cable constructed of two simplex
cables connected by a bridge or web of jacketing material. The webbing is designed to
split lengthwise to allow the individual simplex cable units to be separated for
connectorizing or routing.