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Absorption
That portion of optical
attenuation in optical fiber resulting from the
conversion of optical power to heat. Caused by
impurities in the fiber such as hydroxyl ions.
Abrasive
A material such as silicon carbide, aluminum oxide,
silica, cerium oxide, emery or rouge that is used to
figure, shape, or finish optical elements. Abrasives
differ from polishing materials mainly in particle size.
A/B Switch
A device that accepts inputs (optical or electrical)
from a primary path and a secondary path to provide
automatic or manual switching in the event that the
primary path signal is broken or otherwise disrupted. In
optical A/B switches, optical signal power thresholds
dictate whether the primary path is functioning and
signals a switch to the secondary path until optical
power is restored to the primary path.
Active Device
A device that requires a source of energy for its
operation and has an output that is a function of
present and past input signals. Examples include
controlled power supplies, transistors, LEDs,
amplifiers, and transmitters.
Add/Drop Multiplexing
A multiplexing function offered in connection with SONET
that allows lower level signals to be added or dropped
from a high-speed optical carrier in a wire center. The
connection to the add/drop multiplexer is via a channel
to a central office port at a specific digital speed
(DS3, DS1, etc.)
ADM
Abbreviation for add-drop multiplexer. A device which
adds or drops signals from a communications network.
ADSL
Abbreviation for asynchronous digital subscriber line.
See DSL.
Aramid Yarn
Yellow fibers that provide cable tensile strength,
support, and additional protection for the optical fiber
bundle. Kevlar® is a particular brand of aramid yarn.
Acceptance Angle
The angle over which the core of an optical fiber
accepts incoming light; usually measured from the fiber
axis. Related to numerical aperture (NA).
Access Network
Part of the telecommunication network that connects to
individual and corporate users.
Adapter
An adapter is a mechanical device designed to align
fiber-optic connectors. It contains the split sleeve,
also known as the interconnect sleeve, that holds the
two ferrules together. Adapters can help mate or connect
a variety of fiber optic cables together.
Adapter Sleeve
A mechanical fixture within an adapter body that aligns
and holds two terminated fiber connectors. Adapter
sleeve material is typically phosphor bronze, ceramic or
polymer.
Add-drop multiplexer
A device that drops and/or add one or more optical
channels to a signal.
All-Dieletric Cable
Cable made entirely of dielectric (insulating) materials
without any metal conductors, armor, or strength
members.
All Silica Fiber
Also known as all-glass fiber. A fiber with both a
silica core and a silica cladding, regardless of the
presence of a polymer overcoat or buffer.
Analog
A signal that varies continuously (e.g., sound wavers).
Analog signals have frequency and bandwidth measured in
hertz.
Angle of Incidence
The angle between an incident ray and the normal to a
reflecting or refracting surface.
Aerial Plant
Cable that is suspended in the air on telephone or
electric utility poles.
AGC
Abbreviation for automatic gain control. A process or
means by which gain is automatically adjusted in a
specified manner as a function of input level or another
specified parameter.
AM
Abbreviation for amplitude modulation. A transmission
technique in which the amplitude of the carrier varies
in accordance with the signal.
Amplifier
A device, inserted within a transmission path, that
boosts the strength of an electronic or optical signal.
Amplifiers may be placed just after the transmitter
(power booster), at a distance between the transmitter
and the receiver (in-line amplifier), or just before the
receiver (preamplifier).
Angular Misalignment
Loss at a connector due to fiber end face angles being
misaligned.
ANSI
Abbreviation for American National Standards Institute.
An organization that administers and coordinates the
U.S. voluntary standardization and conformity assessment
system.
APC (Angled Physical Contact)
Abbreviation for angled physical contact. A style of
fiber optic connector with a 5°-15° angle on the
connector tip for the minimum possible backreflection.
AR Coating
Antireflection coating. A thin, dielectric or metallic
film applied to an optical surface to reduce its
reflectance and thereby increase its transmittance.
Armor
A protective layer, usually metal, wrapped around a
cable.
Asynchronous
Data that is transmitted without an associated clock
signal. The time spacing between data characters or
blocks may be of arbitrary duration. Opposite of
synchronous.
Attenuation
Reduction of signal magnitude, or loss, normally
measured in decibels. Fiber attenuation is normally
measured per unit length in decibels per kilometer. The
decrease in signal strength along a fiber optic
waveguide caused by absorption and scattering.
Attenuation is usually expressed in dB/km.
Attenuation Meter
A device used to measure power loss in fiber optic
connectors, cables, or systems.
Attenuator
1) In electrical systems, a usually passive network for
reducing the amplitude of a signal without appreciably
distorting the waveform. 2) In optical systems, a
passive device for reducing the amplitude of a signal
without appreciably distorting the waveform.
Attenuation-Limited Operation
The condition in a fiber optic link when operation is
limited by the power of the received signal (rather than
by bandwidth or distortion).
Avalanche Photodiode (APD)
A semiconductor photodetector with integral detection
and amplification stages. Electrons generated at a p/n
junction are accelerated in a region where they free an
avalanche of other electrons. APDs can detect faint
signals but require higher voltages than other
semiconductor electronics.
Average Power
The average level of power in a signal that varies with
time.
AWG (Arrayed Waveguide Grating)
An array of curved planar waveguides that separates many
optical channels at once. Also called Waveguide Array. A
device, built with silicon planar lightwave circuits
(PLC), that allows multiple wavelengths to be combined
and separated in a dense wavelength-division
multiplexing (DWDM) system.
Axial Propagation Constant
For an optical fiber, the propagation constant evaluated
along the axis of a fiber in the direction of
transmission.
Axis
The center of an optical fiber.
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Backbone
A transmission network that carries high speed
telecommunications between locations. This is normally
the main portion of a telecommunication network, with
branches going to individual buildings. In a local area
network, this is usually the link between routers,
switches, and bridges.
Backbone Cabling
The inter-building and intra-building cable connections
between entrance facilities, equipment rooms and
telecommunications closets. Backbone cabling consists of
the transmission media, main and intermediate
cross-connects and terminations at these locations.
Backbone System
A transmission network that carries high-speed
telecommunications between regions (e.g., a nationwide
long-distance telephone system). Sometimes used to
describe the part of a local area network that carries
signals between branching points.
Backscattering
Scattering of light in the direction opposite to that in
which it was originally traveling. The return of a
portion of scattered light to the input end of a fiber;
the scattering of light in the direction opposite to its
original propagation.
BR (Backreflection)
A term applied to any process in the cable plant that
causes light to change directions in a fiber and return
to the source. Occurs most often at connector interfaces
where a glass-air interface causes a reflection.
Bandwidth
The highest frequency that can be transmitted by an
analog system.. Also, the information-carrying capacity
of a system (especially for digital systems). The range
of frequencies within which a fiber optic waveguide or
terminal device can transmit data or information.
Bandwidth-limited Operation
The condition in a fiber optic link when bandwidth,
rather than received optical power, limits performance.
This condition is reached when the signal becomes
distorted, principally by dispersion, beyond specified
limits.
Baseband
A method of communication in which a signal is
transmitted at its original frequency without being
impressed on a carrier. The number of signal level
transitions per second in digital data. The term is
often confused with bits per second. Telecommunications
specialists prefer to use "bits-per-second" to provide
an accurate description.
Baud
The number of signal-level transitions per second in a
digital data. For some common coding schemes, this
equals bits per second, but this is not true for more
complex coding. Bits per second is less ambiguous. A
unit of signaling speed equal to the number of signal
symbols per second, which may or may not be equal to the
data rate in bits per second.
Beamsplitter
A device that divides incident light into two separate
beams. An optical device, such as a partially reflecting
mirror, that splits a beam of light into two or more
beams. Used in fiber optics for directional couplers.
Bending Loss
Attenuation caused by high-order modes radiating from
the outside of a fiber optic waveguide which occur when
the fiber is bent around a small radius. See also
macrobending, microbending.
Bend Radius
The smallest radius an optical fiber or fiber cable can
bend before excessive attenuation or breakage occurs.
Biconic Connector
A type of fiber optic connector consisting of two
cone-shaped ferrules aligned by a mating sleeve.
Bidirectional
Operating in both directions. Bidirectional couplers
split or combine light the same way when it passes
through them in either direction. Bidirectional
transmission sends signals in both directions, sometimes
through the same fiber.
Birefringent
Having a refractive index that differs for light of
different polarizations.
Bit
The smallest unit of information upon which digital
communications are based; also an electrical or optical
pulse that carries this information.
Bit Depth
The number of levels that a pixel might have, such as
256 with an 8-bit depth or 1,024 with a 10-bit depth.
Bit Period (T)
The amount of time required to transmit a logical one or
a logical zero.
Bit Error Rate (BER)
The fraction of bits transmitted incorrectly. The
fraction of bits transmitted that are received
incorrectly.
BNC
Popular coax bayonet style connector, Often used for
baseband video.
BPON
An abbreviation for broadband on passive optical
network.
Bragg Grating
A technique for building optical filtering functions
directly into a piece of optical fiber based on
interferometric techniques. Usually this is accomplished
by making the fiber photosensitive and exposing the
fiber to deep UV light through a grating. This forms
regions of higher and lower refractive indices in the
fiber core.
Bragg Scattering
Scattering of light caused by a change in refractive
index, as used in Fiber Bragg Gratings and
Distributed Bragg Reflectors.
Braid
An essential part of many fiber-optic cable designs,
consisting of a layer of woven yarn. Note: In the case
of single-fiber loose-buffered or two-fiber "zip-cord"
loose-buffered fiber-optic cables, the braid is situated
between the buffer tube and jacket. In the case of
cables having multiple buffer tubes, the braid is
usually situated between the inner jacket and outer
jacket.
Break Out
To separate the individual fibers or buffer tubes of a
fiber-optic cable for the purpose of splicing or
installing optical connectors.
Breakout Cable
A type of fiber optic cable containing several fibers,
each with its own jacket and all of them surrounded by
one common jacket. Breakout cables are designed for
convenient installation of fiber optic connectors but
tend to have high transmission losses due to bends in
the fibers.
Broadband
Covering a wide range of frequencies or having a high
data rate. The broadband label is sometimes used for a
network that carries many different services or for
video transmission.
Broadcast Transmission
Sending the same signal to many different places, like a
television broadcasting station. Broadcast transmission
can be over optical fibers if the same signal is
delivered to many subscribers.
Bundle of Fibers
A rigid or flexible group of fibers assembled in a unit.
Coherent fiber bundles have fibers arranged in the same
way on each end and can transmit images.
Buffer
Material that is used to protect an optical fiber or
cable from physical damage and to provide mechanical
isolation or protection. Fabrication techniques include
both tight jacket or loose tube buffering, as well as
multiple buffer layers.
Buffer Tubes
A protective tubing used to protect exposed fiber.
Commonly used in terminating multi-fiber cable or
"fan-out" situations. Also known as furcation tubing.
Burn In
The operation of a laser diode or other component prior
to its use in its intended application, as a means of
testing and stabilizing it.
Bus Network
A network topology in which all terminals are attached
to a transmission medium serving as a bus. Also called a
daisy-chain configuration.
Butt Splice
A joining of two fibers without optical connectors
arranged end-to-end by means of a coupling. Fusion
splicing is an example.
Byte
Eight bits of digital data. (Sometimes parity and check
bits are included, so one "byte" may include 10 bits,
but only 8 of them are data.)
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Cable
One or more optical fibers enclosed, with strength
members, in a protective covering.
Cable Assembly
A cable that is connector terminated and ready for
installation.
Cable Plant
The cable plant consists of all the optical elements
including fiber, connectors, splices, etc. between a
transmitter and a receiver.
Cable Television
Communications system that distributes broadcast and
non-broadcast signals as well as a multiplicity of
satellite signals, original programming and other
signals by means of a coaxial cable and/or optical
fiber.
Carrier
In technology, the wave that is modulated with a signal
carrying information. In business, a company that
provides telecommunication services.
Carrier-to-Noise Ratio (CNR)
The ratio, in decibels, of the level of the carrier to
that of the noise in a receiver's IF bandwidth before
any nonlinear process such as amplitude limiting and
detection takes place.
Category 5e
Category 5 (CAT5) cable is a popular twisted pair copper
cable. It is used for Ethernet cable applications.
Category 5e (CAT5e) can support short-run Gigabit
Ethernet (1000 Mbps) networking, unlike CAT5 which
supports Fast Ethernet (100 Mbps).
CATV
An acronym for cable television, derived from Community
Antenna TeleVision.
C-Band
Wavelengths of about 1530 to 1565 nm, where erbium-doped
fiber amplifiers have their strongest gain. Normally
erbium-fiber amplifiers operate in either C- or L-band.
The wavelength range between 1530 nm and 1562 nm used in
some CWDM and DWDM applications.
CCIR
Abbreviation for Consultative Committee on Radio.
Replaced by ITU-R.
CCITT
Abbreviation for Consultative Committee on Telephony and
Telegraphy. Replaced by ITU-T.
CDMA
Abbreviation for code-division multiple access. A coding
scheme in which multiple channels are independently
coded for transmission over a single wideband channel
using an individual modulation scheme for each channel.
Cell
A fixed-length data packet transmitted in certain
digital systems such as ATM.
Center Wavelength
In a laser, the nominal value central operating
wavelength. It is the wavelength defined by a peak mode
measurement where the effective optical power resides
(see illustration). In an LED, the average of the two
wavelengths measured at the half amplitude points of the
power spectrum.
Central Office
A telephone company facility for switching signals among
local telephone circuits; connects to subscriber
telephones. Also called a switching office.
Central Memeber
The center component of a cable that provides strength.
Commonly referred to as "Central Strength Member."
Channel
A communications path or the signal sent over that path.
Through multiplexing several channels, voice channels
can be transmitted over an optical channel.
Channel Coding
Data encoding and error correction techniques used to
protect the integrity of data. Typically used in
channels with high bit error rates such as terrestrial
and satellite broadcast and videotape recording.
Channel Markers
A/B Markers easily identify the TX and RX connector on
each end of a fiber optic cable assembly. These channel
markers assure that the proper connections are made
between the transmitting and receiving ports of a
transceiver.
Channel Spacing
The amount of bandwidth allocated per channel.
Chirp
In laser diodes, the shift of the laser's center
wavelength during single pulse durations.
Chirped Pulse
A pulse in which the wavelength changes during the
duration of the pulse.
Chromatic Dispersion
Wavelength-dependent pulse spreading in optical fibers,
measured in pico seconds (of pulse spreading) per
nanometer (of source bandwidth) per kilometer (of fiber
length). It is the sum of waveguide and material
dispersion. Reduced fiber bandwidth caused by different
wavelengths of light traveling at different speeds down
the optical fiber. Chromatic dispersion occurs because
the speed at which an optical pulse travels depends on
its wavelength, a property inherent to all optical
fiber. May be caused by material dispersion, waveguide
dispersion, and profile dispersion.
Circulator
Passive three-port devices that couple light from Port 1
to 2 and Port 2 to 3 and have high isolation in other
directions.
Circuit
Originally a physical connection that transmits
electricity or signals. Now also a communication channel
that guarantees a fixed transmission capacity.
Circuit Switching
making temporary physical or virtual connections between
two points, which guarantees a fixed transmission
capacity.
Cladding
The layer of glass or other transparent material
surrounding the light-carrying core of an optical fiber.
It has a lower refractive index than the core and thus
confines light in the core. Coatings may be applied over
the cladding. Material that surrounds the core of an
optical fiber. Its lower index of refraction, compared
to that of the core, causes the transmitted light to
travel down the core. This is glass or plastic, having a
low refractive index, that surrounds the core of a
fiber. Optical cladding promotes total internal
reflection for the propagation of light in a fiber.
Cladding Mode
A mode confined to the cladding; a light ray that
propagates in the cladding.
Cleave
The process of separating an optical fiber by a
controlled fracture of the glass, for the purpose of
obtaining a fiber end, which is flat, smooth, and
perpendicular to the fiber axis.
CLEC (Competitive Local
Exchange Carrier)
A company that offers local telephone service in
competition against dominant phone companies.
CMTS
Abbreviation for cable modem termination system.
Coarse Wavelength-Division
Multiplexing (CWDM)
Transmitting signals at multiple wavelengths through the
same fiber with wide spacing between optical channels.
Typical spacing is several nanometers or more. Also
called wide wavelength multiplexing. CWDM allows
eight or fewer channels to be stacked in the 1550 nm
region of optical fiber, the C-Band.
Coating
An outer plastic layer applied over the cladding of a
fiber for mechanical protection. The material
surrounding the cladding of a fiber. Generally a soft
plastic material that protects the fiber from damage.
Coax
Coaxial cable - cable with a central metallic conductor
surrounded by an insulator that is covered by a metallic
sheath that runs the leg nth of the cable. 1) A cable
consisting of a center conductor surrounded by an
insulating material and a concentric outer conductor and
optional protective covering. 2) A cable consisting of
multiple tubes under a single protective sheath. This
type of cable is typically used for CATV, wideband,
video, or RF applications.
Coder
A device, also called an encoder that converts data by
the use of a code, frequently one consisting of binary
numbers, in such a manner that reconversion to the
original form is possible.
Coherent Bundle of Fibers
Fibers packaged together in a bundle so they retain a
fixed arrangement at the two ends and can transmit an
image.
Coherent Communications
In fiber optics, a communication system where the output
of local laser oscillator is mixed with the received
signal, and the difference frequency is detected and
amplified.
Coherence Length
That length over which energy in two separate waves
remains constant. With respect to a laser, the greatest
distance between two arms of an interferometric system
for which suficient interferometric effects can be
obtained.
Collimation
1. The process of aligning the optical axes of optical
systems to the reference mechanical axes or surfaces of
an instrument.
2. The adjustment of two or more optical axes with
respect to each other.
Collimator
An optical instrument consisting of a well-corrected
objective lens with an illuminated slit or reticle at
its focal plane. Collimators are used in lens testing to
determine focal lengths, and in other metrological
applications where a distant object at a known location
is required.
Compression
Reducing the number of bits needed to encode a digital
signal, typically by eliminating long strings of
identical bits or bits that do not change in successive
sampling intervals (e.g., video frames).
Composite Cable
A cable containing both fiber and copper conductors.
Also known as hybrid cable.
Concatenation
The process of connecting pieces of fiber together.
Connector
A device mounted on the end of a fiber-optic cable,
light source, receiver, or housing that mates to a
similar device to couple light into and out of optical
fibers. A connector joins two fiber ends, or one fiber
end and a light source or detector. A mechanical or
optical device that provides a demountable connection
between two fibers or a fiber and a source or detector.
Connector Variation
The maximum value in dB of the difference in insertion
loss between mating optical connectors (e.g., with
remating, temperature cycling, etc.). Also called
optical connector variation.
Concentricity
The measurement of how well-centered the core is within
the cladding.
Constructive Interference
Any interference that increases amplitude of the
resultant signal. For example, when the wave forms are
in phase, they can create a resultant wave equal to the
sum of multiple light waves.
Copper
Industry slang for metal wire, either twisted-pair or
coaxial cable.
Copper vs Fiber
In general, fiber has many advantages over copper. In
copper networks, loss increases with signal frequency-
High data rates increase power loss and therefore
decrease transmission distances. In fiber optic
networks, loss does not change with signal frequency.
Core
The central part of an optical fiber that carries light.
The light-conducting portion of a fiber, defined by its
higher refraction index. The core is the center of a
fiber, surrounded by concentric cladding of lower
refractive index.
Coupled Modes
In fiber optics, a mode that shares energy among one or
more other modes, all of which propagate together. Note:
The distribution of energy among the coupled modes
changes with propagation distance.
Coupler
A device that connectors three or more fiber ends,
dividing one input between two or more outputs or
combining two or more inputs into one output.
Coupling
Transfer of light into or out of an optical fiber. (Note
that coupling does not require a coupler).
Coupling Efficiency
The fraction of available output from a radiant source
that is coupled and transmitted by an optical fiber.
Crimp Sleeve
A crimped metal cylinder that holds the connector to the
cable through the cable's strength member.
Critical Angle
The angle at which light in a high-refractive-index
material undergoes total internal reflection. In
geometric optics, at a refractive boundary, the smallest
angle of incidence at which total internal reflection
occurs.
Cross-connect
Connections between terminal blocks on the two sides of
a distribution frame or between terminals on a terminal
block (also called straps). Also called cross-connection
or jumper.
Cross-gain Modulation (XGM)
A technique used in wavelength converters where gain
saturation effects in an active optical device, such as
a semiconductor optical amplifier (SOA), allow the
conversion of the optical wavelength. Better at shorter
wavelengths (e.g. 780 nm or 850 nm).
Cross-phase Modulation (XPM)
A fiber nonlinearity caused by the nonlinear index of
refraction of glass. The index of refraction varies with
optical power level which causes different optical
signals to interact.
Crosstalk (XT)
1) Undesired coupling from one circuit, part of a
circuit, or channel to another. 2) Any phenomenon by
which a signal transmitted on one circuit or channel of
a transmission system creates and undesired effect in
another circuit or channel.
CSMA/CD
Abbreviation for carrier sense multiple access with
collision detection. A network control protocol in which
(a) a carrier sensing is used and (b) while a
transmitting data station that detects another signal
while transmitting a frame, stops transmitting that
frame, waits for a jam signal, and then waits for a
random time interval before trying to send that frame
again.
Customer Premises Equipment
(CPE)
Terminal, associated equipment, and inside wiring
located at a subscriber's premises and connected with a
carrier's communication channel(s) at the demarcation
point (demarc), a point established in a building or
complex to separate customer equipment from telephone
company equipment.
Cut-Back Measurements
Measurement of optical loss made by cutting a fiber to
compare loss of a short segment with loss of a longer
one.
Cutback Technique
A destructive technique for determining certain optical
fiber transmission characteristics, such as attenuation
and bandwidth, by (a) performing the desired
measurements on a long length of the fiber under test,
(b) cutting the fiber under test at a point near the
launching end, (c) repeating the measurements on the
short length of fiber, and (d) subtracting the results
obtained on the short length to determine the results
for the residual long length.
Cutoff Mode
The highest order mode that will propagate in a given
waveguide at a given frequency.
Cutoff Wavelength
The longest wavelength at which a single mode fiber can
transmit two modes, or (equivalently) the shortest
wavelength at which a single mode fiber carries only one
more.
CW
Abbreviation for continuous wave. Usually refers to the
constant optical output from an optical source when it
is biased (i.e., turned on) but not modulated with a
signal.
Cycles per Second
The frequency of a wave, or number of oscillations it
makes per seconds. One cycle per second equals one
hertz.
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D1
A format for component digital video tape recording
working to the ITU-R 601, 4:2:2 standard using 8-bit
sampling.
D2
The VTR standard for digital composite (coded) NTSC or
PAL signals that uses data conforming to SMPTE 244M.
D3
A composite digital video recording format that uses
data conforming to SMPTE 244M.
D5
An uncompressed tape format for component digital video
which has provisions for HDTV recording by use of 4:1
compression.
Dark Current
The noise current generated by a photodiode in the dark.
Dark Fiber
Optical fiber installed without transmitter and
receiver, usually to provide expansion capacity. Some
carries lease dark fibers to other companies that add
equipment to transmit signals through them.
Data Dependent Jitter
Also called data dependent distortion. Jitter related to
the transmitted symbol sequence. DDJ is caused by the
limited bandwidth characteristics, non-ideal individual
pulse responses, and imperfections in the optical
channel components.
Data Rate
The number of bits of information in a transmission
system, expressed in bits per second (b/s or bps), and
which may or may not be equal to the signal or baud
rate.
dBc
Abbreviation for decibel relative to a carrier level.
dBm
Decibels relative to 1mW.
dBµ
Decibels relative to 1 µW.
DBR
Reflection of light caused by periodic changes in
refractive index in a stack of layers of different
composition or-equivalently-by a corrugation at the
boundary between two semiconductor layers. The period
and the refractive index select one wavelength.
DCE
Abbreviation for data circuit-terminating equipment. 1)
In a data station, the equipment that performs functions
such as signal conversion and coding, at the network end
of the line between the data terminal equipment (DTE)
and the line, and may be a separate or an integral part
of the DTE or of intermediate equipment. 2) The
interfacing equipment that may be required to couple the
data terminal equipment (DTE) into a transmission
circuit or channel and from a transmission circuit of a
channel into the DTE.
Decibel (dB)
A logarithmic comparison of power levels, defined as ten
times the base-10 logarithm of the ratio of the two
power levels. One-tenth of a bel.
Delay Line
A device used to delay transmission of a signal for
functions such as memory loops, sequential processing or
built-in testing. The delay can be achieved by coiling
long lengths of coaxial cable or optical fiber.
Demultiplexer
A device that separates a multiplexed signal into its
original components; the inverse of a multiplexer.
Dense Wavelength-Division
Multiplexing (DWDM)
Transmitting signals at multiple wavelengths through the
same fiber with close spacing. Channel spacing usually
is 200GHz or less in frequency units, corresponding to
1.6nm in wavelength units at 1550nm. The transmission of
many of closely spaced wavelengths in the 1550 nm region
over a single optical fiber. Wavelength spacings are
usually 100 GHz or 200 GHz which corresponds to 0.8 nm
or 1.6 nm. DWDM bands include the C-Band, the S-Band,
and the L-Band.
Destructive Interference
Any interference that decreases the desired signal. For
example, two light waves that are equal in amplitude and
frequency, and out of phase by 180°, will negate one
another.
Detector
A device that generates an electrical signal when
illuminated by light. The most common fiber-optic
detectors are photodiodes.
DFB
Feedback arising from reflection distributed through a
structure.
Diameter-mismatch Loss
The loss of power at a joint that occurs when the
transmitting fiber has a diameter greater than the
diameter of the receiving fiber. The loss occurs when
coupling light from a source to fiber, from fiber to
fiber, or from fiber to detector.
Dielectric Filter
An optical fiber that selectively transmits one
wavelength and reflects others based on interference
effects inside the structure. Also called
interference filter.
Diffraction Grating
An array of fine, parallel, equally spaced reflecting or
transmitting lines that mutually enhance the effects of
diffraction to concentrate the diffracted light in a few
directions determined by the spacing of the lines and by
the wavelength of the light.
Digital Subscriber Line (DSL)
A service that transmits digital signals to homes at
speeds of hundreds of kilobits to tens of metabits per
second over twisted-pair wires at higher frequencies
than voice telephone signals. There are several
variations.
Diode
An electronic device that lets current flow in only one
direction. Semiconductor diodes used in fiber optics
contain a junction between regions of different doping.
They include light emitters (LEDs and laser diodes) and
detectors (photodiodes).
Diode Laser
A semiconductor diode that generates laser light. A
current flowing through the diode causes electrons and
holes to recombine at the junction layer between p- and
n-doped regions, producing excited states that can
release energy in the form of light.
DIP
Abbreviation for dual in-line package. An electronic
package with a rectangular housing and a row of pins
along each of two opposite sides.
Diplexer
A device that combines two or more types of signals into
a single output. Usually incorporates a multiplexer at
the transmit end and a demultiplexer at the receiver
end.
Directional Coupler
A coupler in which light is transmitted differently when
it goes in different directions.
Dispersion
The stretching of light pulses as they travel in an
optical fiber, which increases their duration. The
temporal spreading of a light signal in an optical
waveguide caused by light signals traveling at different
speeds through a fiber either due to modal or chromatic
effects.
Dispersion Compensation
Offsetting the dispersion of one fiber by using
different fibers or other components that have
dispersion of the opposite sign. Usually done for
chromatic dispersion; compensation for polarization-mode
dispersion is in development.
Dispersion-compensating Fiber
(DCF)
A fiber that has the opposite dispersion of the fiber
being used in a transmission system. It is used to
nullify the dispersion caused by that fiber.
Dispersion-compensating Module
(DCM)
This module has the opposite dispersion of the fiber
being used in a transmission system. It is used to
nullify the dispersion caused by that fiber. It can be
either a spool of a special fiber or a grating based
module.
Dispersion-Shifted Fiber (DSF)
Optical fiber with nominal wavelength of zero chromatic
dispersion shifted away from 1310nm. Often used for zero
dispersion-shifted fiber, which has zero chromatic
dispersion at 1550nm and is not used in DWDM system.
Dispersion Management
A technique used in a fiber optic system design to cope
with the dispersion introduced by the optical fiber. A
dispersion slope compensator (illustrated) is one
dispersion management technique.
Dispersion Penalty
The result of dispersion in which pulses and edges smear
making it difficult for the receiver to distinguish
between ones and zeros. This results in a loss of
receiver sensitivity compared to a short fiber and
measured in dB. The equations for calculating dispersion
penalty are as follows:
Dispersion Slope
The change in dispersion with wavelength
Distributed Bragg Reflection
Reflection of light caused by periodic changes in
refractive index in a stack of layers of different
composition or-equivalently-by a corrugation at the
boundary between two semiconductor layers. The period
and the refractive index select one wavelength.
Distributed Feedback Laser (DFB
Laser)
A diode laser with a corrugation in the electrically
pumped part of the laser, which selects the laser
wavelength by reflecting that wavelength back into the
active layer.
Distribution System
Part of a cable system consisting of trunk and feeder
cables used to carry signals from headend to customer
terminals.
Dominant Mode
The mode in an optical device spectrum with the most
power.
Dope
Thick liquid or paste used to prepare a surface or a
varnish-like substance used for waterproofing or
strengthening a material.
Dopant
An impurity added to an optical medium to change its
optical properties. EDFAs use erbium as a dopant for
optical fiber.
Double-window Fiber (Dual
Window Fiber)
1) Multimode fibers optimized for 850 nm and 1300 nm
operation.
2) Single-mode fibers optimized for 1310 nm and 1550 nm
operation.
Doubly Clad Fiber
Optical fiber that exhibits wide transmission bandwidth
and low bending loss to reduction of guided modes as a
result of the high-refractive index external cladding
and the tight confinement within the core regions.
Drawing Tower
A system for fabricating optical fiber, consisting of a
furnace that heats the materials, a polymer coating
stage, a capstan-pulling apparatus that free-draws the
preform into a fiber and a drum on which the finished
product is wound.
DSR
Abbreviation for data signaling rate. The aggregate rate
at which data pass a point in the transmission path of a
data transmission system expressed in bits per second
(bps or b/s).
Drop
A cable that delivers service to an individual customer.
DSx
A transmission rate in the North American digital
telephone hierarchy. Also called T-carrier.
DTE
Abbreviation for data terminal equipment.
1) An end instrument that converts user information into
signals for transmission or reconverts the received
signals into user information.
2) The functional unit of a data station that serves as
a data source or a data sink and provides for the data
communication control function to be performed in
accordance with link protocol.
DTR
Abbreviation for data terminal ready. In a
communications network, a signal from a remote
transmitter that the transmitter is clear to receive
data.
DTV
Abbreviation for digital television. Any technology,
using any of several digital encoding schemes, used in
connection with the transmission and reception of
television signals. Depending on the transmission
medium, DTV often uses some type of digital compression
to reduce the required digital data rate. Except for
artifacts of the compression, DTV is more immune (than
analog television) to degradation in transmission,
resulting in a higher quality of both audio and video,
to the limits of signal reception.
Dual Attachment Concentrator
A concentrator that offers two attachments to the FDDI
network which are capable of accommodating a dual
(counter-rotating) ring.
Dual Ring (FDDI Dual Ring)
A pair of counter-rotating logical rings.
Duplex
In cables, one that contains two fibers. For connectors,
one that connects two pairs of fibers. For data
transmission, full-duplex transmitters and receivers
simultaneously send and receive signals in both
directions, but half-duplex cannot do both at the same
time.
Duplex Cable
A two-fiber cable suitable for duplex transmission.
Duplex Transmission
Transmission in both directions, either one direction at
a time (half-duplex) or both directions simultaneously
(full-duplex).
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E2000 Connector
The E2000/LX-5 is like a LC but with a shutter over the
end of the fiber.Edge-Emitting Diode (ELED)
An LED that emits light from its edge, producing more
directional output than LEDs that emit from their top
surface.
Edge-Emitting Laser
A semiconductor laser that emits light in the plane of
its junction from the edge of the chip.
Effective Area
The area of a single-mode fiber that carries the light.
EIA
An acronym for Electronic Industries Alliance.
Ellipticity
Describes the fact that the core or cladding may be
elliptical rather than circular.
Electro-Absorption Modulator
A semiconductor diode reverse-modulated so it modulates
light passing through it.
Electromagnetic Interference
(EMI)
Noise generated when stray electromagnetic fields induce
currents in electrical conductors.
Electromagnetic Radiation
Waves made up of oscillating electrical and magnetic
fields perpendicular to one another and traveling at the
speed of light. Can also be viewed as photons or quanta
of energy. Electromagnetic radiation includes radio
waves, microwaves, infrared, visible light, ultraviolet
radiation, X rays, and gamma rays.
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.
Encoding
A means of combining clock and data information into a
self synchronizing stream of signals.
Endscope
A fiber-optic bundle used for imaging and viewing inside
the human body.
End Face
Term often used to describe the end of a ferrule. The
end face is finished or polished to have a smooth end,
which can minimize connector loss or backreflection.
Typical polish types are PC, UPC, and APC.
End finish
The quality of the end surface of a fiber prepared for
splicing or terminated in a connector. For an optical
fiber, the optical quality of the surface at the end of
the fiber.
E/O
Abbreviation for electrical-to-optical converter. A
device that converts electrical signals to optical
signals, such as a laser diode.
Equilibrium Mode Distribution
(EMD)
The steady modal state of a multimode fiber in which the
relative power distribution among modes is independent
of fiber length.
Erbium-Doped Fiber Amplifier
(EDFA)
Optical fiber doped with the rare earth element erbium,
which can amplify light at 1530 to 1610nm when pumped by
an external light source.
Error Correction
In digital transmission systems, a scheme that adds
overhead to the data to permit a certain level of errors
to be detected and corrected.
Error Detection
Checking for errors in data transmission. A calculation
based on the data being sent; the results of the
calculation are sent along with the data. The receiver
then performs the same calculation and compares its
results with those sent. If the receiver detects an
error, it can be corrected, or it can simply be
reported.
ESCON
Abbreviation for enterprise systems connection. A duplex
optical connector used for computer-to-computer data
exchange.
Ethernet
A local-area network standard. The original Ethernet
transmits 10 Mbit/s. Other version are Fast Ethernet at
100 Mbit/s, Gigabit Ethernet at 1Gbit/s, and 10 Gigabit
Ethernet. A standard protocol (IEEE 802.3) for a 10-Mb/s
baseband local area network (LAN) bus using carrier
sense multiple access with collision detection (CSMA/CD)
as the access method. Ethernet is a standard for using
various transmission media, such as coaxial cables,
unshielded twisted pairs, and optical fibers.
Evanescent Wave
Guided light waves that extend beyond the boundary of a
fiber core into the cladding. Evanescent waves can
transfer energy between waveguides. Light guided in the
inner part of an optical fiber's cladding rather than in
the core, i.e. the portion of the light wave in the core
that penetrates into the cladding.
Excess Loss
Loss of a passive coupler above that inherent in
dividing light among the output ports. In a fiber optic
coupler, the optical loss from that portion of light
that does not emerge from the nominal operation ports of
the device.
External Modulation
Modulation of output of a light source by an external
device.
Extrinsic Loss
Splice losses arising from the splicing process itself.
Extinction Ratio
The ratio of the low, or OFF optical power level (PL) to
the high, or ON optical power level (PH).
Extinction Ratio
The ratio of the power of a plane-polarized beam that is
transmitted through a polarizer placed in its path with
its polarizing axis parallel to the beam's plane, as
compared with the transmitted power when the polarizer's
axis is perpendicular to the beam's plane.
Eye Pattern
A pattern formed by overlaying traces of a series of
transmitted pulses in a visual display. The more open
the eye, the sharper the distinction between on and off
pulses. A diagram that shows the proper function of a
digital system. The "openness" of the eye relates to the
BER that can be achieved.
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Fabry Perot Laser
A laser oscillator in which two mirrors are separated by
an amplifying medium with an inverted population, making
a Fabry-Perot cavity. Standard diode lasers are
Fabry-Perot lasers.
Fall Time
Also called turn-off time. The time required for the
trailing edge of a pulse to fall from 90% to 10% of its
amplitude; the time required for a component to produce
such a result. Typically measured between the 90% and
10% points or alternately the 80% and 20% points.
Fast Axis
In a birefringent material, the index of refraction
varies with the direction of vibration of a lightwave.
That direction having a low refractive index is the fast
axis; at right angles to it is the slow axis, with a
high index of refraction.
Faraday Effect
A phenomenon that causes some materials to rotate the
polarization of light in the presence of a magnetic
field parallel to the direction of propagation. Also
called magneto-optic effect.
Fan-Out
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.
FC Connector
FC stands for Fixed Connection. It is fixed by way of a
threaded barrel housing. FC connectors are typical in
test environments and for singlemode applications.
FCC
Abbreviation for Federal Communications Commission. The
U.S. Government board of five presidential appointees
that has the authority to regulate all non-Federal
Government interstate telecommunications as well as all
international communications that originate or terminate
in the United States.
FC/PC
See FC. A threaded optical connector that uses a special
curved polish on the connector for very low
backreflection. Good for single-mode or multimode fiber.
FCS
Abbreviation for frame check sequence. An
error-detection scheme that (a) uses parity bits
generated by polynomial encoding of digital signals, (b)
appends those parity bits to a digital signal, and (c)
uses decoding algorithms that detect errors in the
received digital signal.
FDA
Abbreviation for Food and Drug Administration.
Organization responsible for, among other things, laser
safety.
Frequency-division Multiplexing
(FDM)
A method of deriving two or more simultaneous,
continuous channels from a transmission medium by
assigning separate portions of the available frequency
spectrum to each of the individual channels.
Ferrule
A tube within a connector with a central hole that
contains and aligns a fiber.
Fiber Amplifier
An optical fiber doped to amplify light from an external
source. The most important type is the erbium-doped
fiber amplifier.
Fiber Bandwidth
The lowest frequency at which the magnitude of the fiber
transfer function decreases to a specified fraction of
the zero frequency value. Often, the specified value is
one-half the optical power at zero frequency.
Fiber Bragg Grating (FBG)
An optical fiber in which the core refractive index
varies periodically, causing Bragg scatting at
wavelengths selected by the period and refractive index.
A fiber Bragg grating reflects the selected wavelength
and transmits others.
Fiber Distributed Data
Interface (FDDI)
A standard for a 100 Mbit/s fiber optic local-area
network. Abbreviation for fiber distributed data
interface.
1) A dual counter-rotating ring local area network.
2) A connector used in a dual counter-rotating ring
local area network (illustrated).
Fiber Fuse
A mechanism whereby the core of a single-mode fiber can
be destroyed at high optical power levels.
Fiber Grating
An optical fiber in which the refractive index of the
core varies periodically along its length, scattering
light in a way similar to a diffraction grating, and
transmitting or reflecting certain wavelengths
selectively.
Fiber Optic Attenuator
A component installed in a fiber optic transmission
system that reduces the power in the optical signal. It
is often used to limit the optical power received by the
photodetector to within the limits of the optical
receiver.
Fiber-Optic Gyroscope
A coil of optical fiber that can detect rotation about
its axis.
Fiber Optic Cable
A cable containing one or more optical fibers.
Fiber Optic Communication
System
The transfer of modulated or unmodulated optical energy
through optical fiber media which terminates in the same
or different media.
Fiber Optic Link
A transmitter, receiver, and cable assembly that can
transmit information between two points.
Fiber Optic Modems
Fiber optic modems are used in fiber optic networks for
sending and receiving data.
Fiber Optic Ribbon
A coherent optical fiber bundle in which the
configuration is flat rather than round, giving an
output in a line.
Fiber Optic Sensor
Any device in which variations in the transmitted power
or the rate of transmission of light in optical fiber
are the means of measurement or control. Fibers can be
used to measure temperature, pressure, strain, voltage,
current, liquid level, rotation and particle velocity
Fiber Optic Span
An optical fiber/cable terminated at both ends which may
include devices that add, subtract, or attenuate optical
signals.
Fiber Optic Subsystem
A functional entity with defined bounds and interfaces
which is part of a system. It contains solid state
and/or other components and is specified as a subsystem
for the purpose of trade and commerce.
Fiberscope
An optical instrument consisting of an objective lens, a
coherent (usually flexible) fiber bundle and an eyepiece
to examine the output of the fiber bundle.
Fiber to the Curb (FTTC)
Fiber optic service to a node that is connected by wires
to several nearby homes, typically on a block.
Fiber to the Home (FTTH)
A network in which optical fibers bring signals all the
way to homes.
Fibre Channel
A standard for transmitting signals at 100 Mbit/s to
4.25 Gbit/s over fiber or (at slower speeds) copper. An
industry-standard specification that originated in Great
Britain which details computer channel communications
over fiber optics at transmission speeds from 132 Mb/s
to 1062.5 Mb/s at distances of up to 10 kilometers.
Fiber Tracer
An instrument that couples visible light into the fiber
to allow visual checking of continuity and tracing for
correct connections.
Fiber Identifier
A device that clamps onto a fiber and couples light from
the fiber by bending, to identify the fiber and detect
high speed traffic of an operating link or a 2 kHz tone
injected by a test source.
Figure 8 Cable
An aerial cable configuration in which the conductors
and the steel strand which supports the cable are
integrally jacketed. A cross section of the finished
cable approximates the figure 8.
Filter
A device which transmits only part of the incident
energy and may thereby change the spectral distribution
of energy.
Filled Cable
A cable construction in which the cable core is filled
with a gel material that will prevent moisture from
entering or passing through the cable.
FITL
Fiber in the loop. Fiber-in-the-loop (FITL): Fiber optic
service to a node that is located in a neighborhood.
Flooding Compound
A substance surrounding the buffer tubes of a
fiber-optic cable, to prevent water intrusion into the
interstices in the event of a breach of the jacket.
Fluoride Glasses
Materials that have the amorphous structure of glass but
are made of fluoride compounds (e.g., zirconium fluoride
) rather than oxide compounds (e.g., silica). Suitable
for very long wavelength transmission. This material
tends to be destroyed by water, limiting its use.
FM (Frequency Modulation)
A method of transmission in which the carrier frequency
varies in accordance with the signal.
Forward Error Correcting (FEC)
A communication technique used to compensate for a noisy
transmission channel. Extra information is sent along
with the primary data payload to correct for errors that
occur in transmission.
FOTP (Fiber Optic Test
Procedure)
Standards developed and published by the Electronic
Industries Association (EIA) under the EIA-RS-455 series
of standards.
FWM - Four Wave Mixing (FWM)
A nonlinearity common in DWDM systems where multiple
wavelengths mix together to form new wavelengths, called
interfering products. Interfering products that fall on
the original signal wavelength become mixed with the
signal, mudding the signal, and causing attenuation.
Interfering products on either side of the original
wavelength can be filtered out. FWM is most prevalent
near the zero-dispersion wavelength and at close
wavelength spacings.
FP
Abbreviation for Fabry-Perot. Generally refers to any
device, such as a type of laser diode, that uses mirrors
in an internal cavity to produce multiple reflections.
Free-Space Optics
Also called free-space photonics. The transmission of
modulated visible or infrared (IR) beams through the
atmosphere via lasers, LEDs, or IR-emitting diodes
(IREDs) to obtain broadband communications.
Frame
A fixed-length block of data transmitted as a unit;
SONET transmits frames. In video, one of a series of
images shown in sequence.
Frequency
The number of times an electromagnetic wave oscillates
in a second, or the number of wave peaks that pass a
point in second; measured in hertz.
FDM - Frequency-Division
Multiplexing (FDM)
Combining analog signals by assigning each a different
carrier frequency and merging them in a single signal
with a broad range of frequencies
Frequency-shift Keying (FSK)
Frequency modulation in which the modulating signal
shifts the output frequency between predetermined
values. Also called frequency-shift modulation,
frequency-shift signaling.
Fresnel Reflection Loss
Reflection losses at the ends of fibers caused by
differences in the refractive index between glass and
air. The maximum reflection caused by a perpendicular
air-glass interface is about 4% or about -14 dB.
FSAN
Abbreviation for full service access network. A forum
for the world's largest telecommunications services
providers and equipment suppliers to work define
broadband access networks based primarily on the ATM
passive optical network structure.
FTTB
Fiber to the Building. This is in reference to fiber
optic cable, carrying network data, connected all the
way from an Internet service provider to a customer's
physical building.
FTTC
An abbreviation for fiber to the curb.
FTTD
An abbreviation for fiber to the desk.
FTTH
An abbreviation for fiber to the home.
FTTP
Stands for Fiber to the Premises.
FTTx
An abbreviation for 'Fiber to the x'. The 'x' is a
variable which can mean fiber to the: premises, curb,
home, business, or desk, for example.
Full Duplex
In data transmission, transmitters and receivers that
simultaneously send and receive signals in both
directions.
Fundamental Mode
The lowest order mode of a waveguide. Note: In optical
fibers, the fundamental mode is designated LP01 or HE11.
Fused Fibers
A bundle of fibers melted together so they maintain a
fixed alignment with respect to each other in a rigid
rod.
Fused Coupler
A method of making a multimode or single-mode coupler by
wrapping fibers together, heating them, and pulling them
to form a central unified mass so that light on any
input fiber is coupled to all output fibers.
Fusion Splice
A splice made by melting the tips of two fibers together
so they form a solid junction.
Fusion Splicer
An instrument that permanently bonds two fibers together
by heating and fusing them.
Furcation Tubing
A protective tubing that protects exposed fiber.
Commonly used in terminating multi-fiber cable or
"fan-out" situations. Also referred to as buffer tubing.
FUT
Abbreviation for fiber under test. Refers to the fiber
being measured by some type of test equipment.
FWHM
Abbreviation for full width half maximum. Used to
describe the width of a spectral emission at the 50%
amplitude points. Also known as FWHP (full width half
power).
Gallium Aluminum Arsenide
(GaAlAs)
A semiconductor compound used in LEDs, diode lasers, and
certain detectors.
Gallium Arsenide (GaAs)
A semiconductor compound used in LEDs, diode lasers,
detectors and electronic components.
Gap Loss
Loss resulting from the end separation of two axially
aligned fibers.
Gap Loss Attenuator
An optical attenuator that exploits the principle of gap
loss to reduce the optical power level when inserted
in-line in the fiber path. e.g., to prevent saturation
of the receiver.
Gaussian Beam
A beam pattern used to approximate the distribution of
energy in a fiber core. It can also be used to describe
emission patterns from surface-emitting LEDs. Most
people would recognize it as the bell curve
(illustrated).
GBE
An abbreviation for Gigabit Ethernet. Gigabit
networking, or commonly called 10-Gigabit Ethernet
(10GBASE-T), is a communications technology that offers
data speeds up to 10 billion bits per second.
Gbit/s
Gigabits (billion bits ) per second
Ge
Abbreviation for germanium. Generally used in detectors.
Good for most fiber optic wavelengths (e.g., 800-1600
nm). Performance is inferior to InGaAs
Gel
A substance, resembling petroleum jelly in viscosity,
that surrounds a fiber, or multiple fibers, enclosed in
a loose buffer tube.
GHz
Abbreviation for gigahertz. One billion Hertz (cycles
per second) or 109 Hertz.
Graded-Index Fiber
A fiber in which the refractive index changes gradually
with distance from the fiber axis, rather than abruptly
at the core-cladding interface.
Graded-Index Fiber Lens
A short segment of a graded-index fiber that focuses
light passing through it.
GRIN
Abbreviation for gradient index. Generally refers to the
SELFOC lens often used in fiber optics.
Group Delay
The rate of change of the total phase shift with respect
to angular frequency, d /d , through a device or
transmission medium, where is the total phase shift, and
is the angular frequency equal to 2f , where f is the
frequency.
Group Delay Time
The difference in travel time through a fiber for light
of different wavelengths.
Group Index
Also called group refractive index. In fiber optics, for
a given mode propagating in a medium of refractive index
(n), the group index (N), is the velocity of light in a
vacuum (c), divided by the group velocity of the mode.
Group Velocity
1) The velocity of propagation of an envelope produced
when an electromagnetic wave is modulated by, or mixed
with, other waves of different frequencies.
2) For a particular mode, the reciprocal of the rate of
change of the phase constant with respect to angular
frequency.
3) The velocity of the modulated optical power.
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H
Half-Duplex
In data transmission, a system in which transmitters and
receivers cannot simultaneously send and receive
signals.
Hard-Clad Silica Fiber
A fiber with a hard plastic cladding surrounding a
step-index silica core. (Other plastic-clad silica
fibers have a soft plastic cladding.)
HDSL
Abbreviation for high data-rate digital subscriber line.
A DSL operating at a high data rate compared to the data
rates specified for ISDN.
HDTV
Abbreviation for high-definition television. Television
that has approximately twice the horizontal and twice
the vertical emitted resolution specified by the NTSC
standard.
Head-End
1) A central control device required within some LAN and
MAN systems to provide such centralized functions as
remodulation, retiming, message accountability,
contention control, diagnostic control, and access to a
gateway.
2) A central control device within CATV systems to
provide such centralized functions as remodulation
(illustrated). See also local area network (LAN).
Helium Neon Laser
The most commonly used gas laser. The HeNe laser has an
emission that is determined by neon atoms by virtue of a
resonant transfer of excitation of helium. It operates
continuously in the red, infrared and far-infrared
regions and emits highly monochromatic radiation.
HFC - Hybrid Fiber/Coax (HFC)
The use of fiber to distribute cable-television signals
to nodes, which in turn distribute them to homes over
coaxial cable.
HFC Network
A telecommunication technology in which optical fiber
and coaxial cable are used in different sections of the
network to carry broadband content. The network allows a
CATV company to install fiber from the cable headend to
serve nodes located close to business and homes, and
then from these fiber nodes, use coaxial cable to
individual businesses and homes.
Hierarchy
A set of transmission speeds arranged to multiplex
signals at successively higher data rates.
High Loss Fiber
Optical fiber in which the attenuation exceeds the
normally acceptable level for long-haul or data
communications use.
HIPPI
Abbreviation for high performance parallel interface as
defined by the ANSI X3T9.3 document, a standard
technology for physically connecting devices at short
distances and high speeds. Primarily to connect
supercomputers and to provide high-speed backbones for
local area networks (LANs).
Hockey Puck
A polishing fixture used to facilitate the manual
finishing of the endfaces of certain types of optical
fiber connectors.
Hybrid Cable
1. A fiber optic cable containing two or more different
types of fiber, such as 62.5µm multimode and singlemode.
2. A cable containing both optical fiber and copper
wire. Also known as composite cable.
Hydrogen Losses
Increases in fiber connector attenuation that occur when
hydrogen diffuses into the glass matrix and absorbs some
light.
ICEA Abbreviation for Insulated Cable Engineers Association.
A technical professional organization that contributes
to the standards of insulated cable in these four areas:
power cables, communication cables, portable cables, and
control and instrumentation. Within this organization
there are subcommittees that concentrate on one of the
four areas.
IEEE
Abbreviation for Institute of Electrical and Electronic
Engineers. A technical professional association that
contributes to voluntary standards in technical areas
ranging from computer engineering, biomedical technology
and telecommunications, to electric power, aerospace and
consumer electronics, among others.
IF
Abbreviation for Intermediate Frequency. A frequency to
which a carrier frequency is shifted as an intermediate
step in transmission or reception.
Index-Matching Gel
(Index-Matching Fluid)
A gel or fluid with refractive index close to glass that
reduces refractive-index discontinuities that can cause
reflective losses.
Index Matching Material
A substance, usually a liquid, cement (adhesive), or
gel, which has an index of refraction that closely
approximates that of an optical fiber, and is used to
reduce Fresnel reflection at the fiber endface.
Index Dip
In an optical fiber, an undesired decrease in the
refractive index at the center of the core.
Index of Refraction
The speed of light in a vacuum divided by the speed of
light in a material, abbreviated n, which measures how
materials refract light.
Index Profile
The refractive index of a fiber as a function of cross
section.
Indium Gallium Arsenide
(InGaAs)
A semiconductor material used in lasers, LEDs, and
detectors.
Indium Gallium Arsenide
Phosphide (InGaAsP)
A semiconductor material used in lasers, LEDs, and
detectors.
Infrared (IR)
Light with wavelengths longer than 700nm and shorter
than about 1mm, invisible to the human eye, which we can
feel as heat. Glass optical fibers transmit infrared
signals at 700 to about 1650nm in the infrared.
Infrared Emitting Diodes
LEDs that emit infrared energy (830 nm or longer).
Infrared Fiber
Colloquially, optical fibers with best transmission at
wavelengths of 2µm or longer, made of materials other
than silica glass.
Integrated Services Digital
Network (ISDN)
Originally a standard to transmit two digital voice
lines at 64 kbit/s and one 16 kbit/s data channel. Now
repackaged as IDSL, a form of DSL, transmitting 128
kbit/s over distances beyond the reach of DSL.
In-line Amplifier
An EDFA or other type of amplifier placed in a
transmission line to strengthen the attenuated signal
for transmission onto the next, distant site. In-line
amplifiers are all-optical devices.
Integrated Optics
Optical devices that perform two or more functions and
are integrated on a single substrate; analogous to
integrated electronic circuits.
Intensity
Power per unit solid angle.
InP
Indium Phosphide. A semiconductor material used to make
optical amplifiers and HBTs.
Insertion Loss
The loss of power that results from inserting a
component, such as a connector, coupler (illustrated),
or splice, into a previously continuous path.
Inside Plant
Telecommunications facilities placed inside a building.
Insulation
A material having high resistance to the flow of
electric current. Often called a dielectric.
Integrated
Detector/Preamplifier (IDP)
A detector package containing a PIN photodiode and
transimpedance amplifier.
Intensity
The square of the electric field strength of an
electromagnetic wave. Intensity is proportional to
irradiance and may get used in place of the term
"irradiance" when only relative values are important.
Intensity Modulation (IM)
In optical communications, a form of modulation in which
the optical power output of a source varies in
accordance with some characteristic of the modulating
signal.
Interchannel Isolation
The ability to prevent undesired optical energy from
appearing in one signal path as a result of coupling
from another signal path. Also called crosstalk.
Interference
For light, the way that waves add together, depending on
their phase. Constructive interference occurs when the
waves are in phase and their amplitudes add. Destructive
interference occurs when the waves are 180 degree out of
phase and their amplitudes cancel.
Interference Filter
An optical filter that selectively transmits one
wavelength and reflects others based on interference
effects inside the structure. Also called dielectric
filter.
Interferometer
An instrument that employs the interference of
lightwaves to measure the accuracy of optical surfaces;
it can measure a length in terms of the length of a wave
of light by using interference phenomena based on the
wave characteristics of light. Interferometers are used
extensively for testing optical elements during
manufacture. Typical designs include the Michelson,
Twyman-Green and Fizeau interferometers.
Interleaver
An optical device that separates a series of optical
channels so alternating wavelengths emerge out its two
ports. The best known type is a Mach-Zehnder
interferometer.
Intermodulation (Mixing)
A fiber nonlinearity mechanism caused by the power
dependant refractive index of glass. Causes signals to
beat together and generate interfering components at
different frequencies. Very similar to four wave mixing.
Internet Protocol (IP)
Standard packet-switched transmission format for the
Internet; uses variable-length packets.
International
Telecommunications Union (ITU)
A civil international organization, headquartered in
Geneva, Switzerland, established to promote standardized
telecommunications on a worldwide basis. The ITU-R and
the ITU-T are committees under the ITU, which is
recognized by the United Nations as the specialized
agency for telecommunications.
Intrinsic Losses
Loss due to inherent traits within the fiber; for
example, absorption, scattering, and splice loss.
IP
Abbreviation for Internet protocol. A standard protocol,
developed by the DOD, for use in interconnected systems
of packet-switched computer communications networks.
IRE Unit
An arbitrary unit created by the Institute of Radio
Engineers to describe the amplitude characteristic of a
video signal, where pure white is defined as 100 IRE
with a corresponding voltage of 0.714 Volts and the
blanking level is 0 IRE with a corresponding voltage of
0.286 Volts.
ISA
Abbreviation for Instrumentation, Systems, and
Automation Society. An international, non-profit,
technical organization. The society fosters advancement
of the use of sensors, instruments, computers, and
systems for measurement and control in variety of
applications
ISO
Abbreviation for International Standards Organization.
Established in 1947, ISO is a worldwide federation of
national standards committees from 140 countries. The
organization promotes the development of standardization
throughout the world with a focus on facilitating the
international exchange of goods and services, and
developing the cooperation of intellectual, scientific,
technological, and economical activities.
ISP
Abbreviation for Internet service provider. A company or
organization that provides Internet connections to
individuals or companies via dial-up, ISDN, T1, or some
other connection.
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Jacket
The outer, protective covering of the cable. Also called
the cable sheath.
Jitter
Small and rapid variations in the timing of a waveform
due to noise, changes in component characteristics,
supply voltages, imperfect synchronizing circuits, etc.
See also DDJ, DCD, and RJ. Also called phase jitter,
timing distortion, or inter-symbol interference. The
slight movement of a transmission signal in time or
phase that can introduce errors and loss of
synchronization. The amount of jitter will increase with
longer cables, cables with higher attenuation, and
signals at higher data rates.
Jumper Cable
A short single fiber cable with connectors on both ends
used for interconnecting other cables or testing.
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Kevlar®
A very strong, very light, synthetic compound developed
by DuPont which is used to strengthen optical cables.kHz
One thousand cycles per second.
km
Abbreviation for kilometer. 1 km = 3,280 feet or 0.62
miles.
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Lambertian Emitter
An emitter that radiates according to Lambert's cosine
law, which states that the radiance of certain idealized
surfaces depends on the viewing angle of the surface.
The radiant intensity of such a surface is maximum
normal to the surface and decreases in proportion to the
cosine of the angle from the normal. Given by:
Large-Core Fiber
Usually, a fiber with a core of 200µm or more.
Large Effective Area Fiber
(LEAF)
An optical fiber, developed by Corning, designed to have
a large area in the core, which carries the light.
Laser
From Light Amplification by Stimulated
Emission of Radiation, one of the wide
range of devices that generates light by that principle.
Laser light is directional, covers a narrow range of
wavelengths, and is more coherent than ordinary light.
Semiconductor diode lasers are the usual light sources
in fiber optic systems.
Laser Diode (LD)
A semiconductor that emits coherent light when forward
biased.
Lateral Displacement Loss
(Lateral Offset Loss)
The loss of power that results from lateral displacement
of optimum alignment between two fibers or between a
fiber and an active device.
Launch Fiber (Launch cable)
An optical fiber used to couple and condition light from
an optical source into an optical fiber. Often the
launch fiber is used to create an equilibrium mode
distribution in multimode fiber. Also called launching
fiber.
Layer
A standard or protocol for signal transmission or
processing to perform certain functions. It includes
standard interfaces with other layers, which perform
other functions.
LC Connector
LC stands for Lucent Connector. The LC is a small
form-factor fiber optic connector.
L-Band
Wavelengths of about 1570 to 1625nm where some
erbium-doped fiber amplifiers operate. Separate from
C-Band.
Leaky Mode
In an optical fiber, a mode having a field that decays
monotonically for a finite distance in the transverse
direction but becomes oscillatory everywhere beyond that
finite distance.
LEC (Local Exchange Carrier)
A local telephone company, i.e., a communications common
carrier that provides ordinary local voice-grade
telecommunications service under regulation within a
specified service area.
LEX
Abbreviation for local exchange. Synonym for central
office.
L-I Curve
The plot of optical output (L) as a function of current
(I) which characterizes an electrical-to-optical
converter. A typical L-I curve is shown at right.
Light ARMOR Cable
A fiber optic cable assembly with ruggedized plastic
jacketing providing fiber protection for semi-harsh
environment, commercial, or industrial applications.
Light Emitting Diode (LED)
A semiconductor diode that emits incoherent light at the
junction between p- and n-doped materials.
Lightguide
An optical fiber or fiber bundle.
Light Piping
Use of fibers to illuminates.
Lightwave
An adjective, a synonym for optical, often (but not
always) meaning fiber-optic. The path of a point on a
wavefront. The direction of the lightwave is generally
normal (perpendicular) to the wavefront.
Linearity
The basic measurement of how well analog-to-digital and
digital-to-analog conversions are performed. To test for
linearity, a mathematically perfect diagonal line is
converted and then compared to a copy of itself. The
difference between the two lines is calculated to show
linearity of the system and is given as a percentage or
range of least significant bits.
Linewidth
The rang of wavelengths in an optical signal, sometimes
called spectral width.
Lip
A defect in the cleaved end face of an optical fiber, in
the form of a sharp protrusion at the edge of the fiber.
Local-Area-Network (LAN)
A network that transmits data among many nodes in a
small area (e.g., a building or campus). A communication
link between two or more points within a small
geographic area, such as between buildings. Smaller than
a metropolitan area network (MAN) or a wide area
network(WAN).
Local Loop
The part of the telephone network extending from the
central (switching) office to the subscriber.
LH - Long Haul (LH)
Abbreviation for long-haul. A classification of video
performance under RS-250C. Lower performance than
medium-haul or short-haul.
LOMMF Laser Optimized Multimode
Fiber
LOMMF is the highest capacity medium for 10-gig optical
transmission. LOMMF was developed for use with VCSEL
lasers. With laser optimized multimode fiber no special
terminations or connectors are necessary.
Long-haul Telecommunications
1. In public switched networks, regarding circuits that
span long distances, such as the circuits in inter-LANA,
interstate, and international communications.
2. In military use, communications among users on a
national or worldwide basis. Long-haul communications
are characterized by a higher level of users, more
rigorous performance requirements, longer distances
between users, including world wide distances, higher
traffic volumes and densities, larger switches and trunk
cross sections, and fixed and recoverable assets.
Usually pertains to the U.S. Defense Communications
System.
Long Wavelength
A commonly used term for light in the 1300 and 1550 nm
ranges.
Longitudinal Modes
Oscillation modes of a laser along the length of its
cavity. Each longitudinal mode contains only a narrow
range of wavelengths, so a laser emitting a single
longitudinal mode has a narrow bandwidth. Distinct from
transverse modes.
Loose Tube
A protective tube loosely surrounding a cabled fiber,
often filled with gel. A type of fiber optic cable
construction where the fiber is contained within a loose
tube in the cable jacket.
Loose Tube vs Tight Buffered
Fiber optic cables are constructed in two ways: loose
tube and tight buffered. Both contain a type of
strengthening member, such as aramid yarn, stainless
steel wire strands, or gel-filled sleeves. Each,
however, is designed for very different environments.
Loss
Attenuation of optical signal, normally measured in
decibels. The amount of a signal's power, expressed in
dB, that is lost in connectors, splices, or fiber
defects.
Loss Budget
An accounting of overall attenuation in a system.
LSZH
Primarily used for indoor applications, Low Smoke Zero
Halogen (LSZH) cable is designed to reduce toxic
emissions in event of fire.
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Mach-Zehnder Interferometer
An optical device that separates a series of optical
channels so alternating wavelengths emerge out its two
ports, sometimes called an interleaver.
Macrobending
In a fiber, all macroscopic deviations of the fiber's
axis from a straight line, that will cause light to leak
out of the fiber, causing signal attenuation.
Mandrel Wrapping
In multimode fiber optics, a technique used to modify
the modal distribution of a propagating optical signal.
Metropolitan Area Network (MAN)
A telecommunication system serving a metropolitan area,
typically with cable lengths to 200km. A network
covering an area larger than a local area network. A
series of local area networks, usually two or more, that
cover a metropolitan area.
Margin
Allowance for attenuation in addition to that explicitly
accounted for in a system design.
Mass Splicing
Splicing of many fibers in a cable.
Material Dispersion
Pulse dispersion caused by variation of a material's
refractive index with wavelength.
Mechanical Splice
A splice in which fibers are joined mechanically (e.g.,
glued or crimped in place) but not fused together. An
optical fiber splice accomplished by fixtures or
materials, rather than by thermal fusion. The capillary
splice, illustrated, is one example of a mechanical
splice.
Mean Launched Power
The average power for a continuous valid symbol sequence
coupled into a fiber.
Medium Access Control (MAC)
1) A service feature or technique used to permit or deny
use of the components of a communication system.
2) A technique used to define or restrict the rights of
individuals or application programs to obtain data from,
or place data onto, a storage device, or the definition
derived from that technique.
MEMS (Micro-electro-mechanical
systems)
Tiny moving mirrors fabricated from semiconductor
materials.
Mesh
A network that makes multiple interconnections between
different points.
Messenger Cable
The linear supporting member, usually a high strength
steel wire, used as the supporting element of a
suspended aerial cable. The messenger may be an integral
part of the cable, or exterior to it.
Microbending
Tiny bends in a fiber that allow light to leak out and
increase loss. Mechanical stress on a fiber that
introduces local discontinuities, which results in
light leaking from the core to the cladding by a process
called mode coupling.
Micrometer
One millionth of a meter or 10-6 meters.
Abbreviated µm.
Microscope Fiber Optic
Inspection
A microscope used to inspect the end surface of a
connector for flaws or contamination or a fiber for
cleave quality.
Microsecond
One millionth of a second or 10-6 seconds.
Abbreviated µs.
Microwatt
One millionth of a Watt or 10-6 Watts.
Abbreviated µW.
MIL-SPEC
Abbreviation for military specification. Performance
specifications issued by the Department of Defense that
must be met in order to pass a MIL-STD.
MIL-STD
Abbreviation for military standard. Standards issued by
the Department of Defense.
Minimum Bend Radius
The smallest radius an optical fiber or fiber cable can
bend before increased attenuation or breakage occurs.
Misalignment Loss
The loss of power resulting from angular misalignment,
lateral displacement, and fiber end separation.
Modal Dispersion
Dispersion arising from differences in the times that
different modes take to travel through multimode fiber.
Modal Noise
Noise that occurs whenever the optical power propagates
through mode-selective devices. It is usually only a
factor with laser light sources.
Mode
An electromagnetic field distribution that satisfied
theoretical requirements for propagation in a waveguide
or oscillation in a cavity (e.g., a laser). Light has
modes in a fiber or laser. A single electromagnetic wave
traveling in a fiber.
Mode Coupling
The transfer of energy between modes. In a fiber, mode
coupling occurs until equilibrium mode distribution
(EMD) is reached.
Mode Evolution
The dynamic process a multilongitudinal mode laser
undergoes whereby the changing distribution of power
among the modes creates a continuously changing envelope
of the laser's spectrum.
Mode-Field Diameter (MFD)
The diameter of the one mode of light propagating in a
single mode fiber, slightly larger than core diameter.
Mode Filter
A device that removes higher-order modes to simulate
equilibrium mode distribution. A mode filter is most
easily constructed.
Modem
Acronym for modulator/demodulator. 1) In general, a
device that both modulates and demodulates signals. 2)
In computer communications, a device used for converting
digital signals into, and recovering them from,
quasi-analog signals suitable for transmission over
analog communications channels such as telephone lines.
Mode Scrambler
A device that mixes modes to uniform power distribution.
MH - Medium Haul (MH)
Abbreviation for medium-haul. A classification of video
performance under RS-250C. Higher performance than
long-haul and lower performance than short-haul.
Mode Stripper
A device that removes high-order modes in a multimode
fiber to give standard measurement conditions. A device
that removes cladding modes.
Modulation
The process by which the characteristic of one wave (the
carrier) modifies another wave (the signal). Examples
include amplitude modulation (AM), frequency modulation
(FM), and pulse-coded modulation (PCM).
Modulation Index
In an intensity-based system, the modulation index is a
measure of how much the modulation signal affects the
light output.
Modulator
A device that imposes a signal on a carrier.
MSO
Abbreviation for multiple service operator. A
telecommunications company that offers more than one
service, e.g. telephone service, Internet access,
satellite service, etc.
MT Connector
Multi-fiber connector housing up to 24 fibers in a
single ferrule.
MT RJ Connector
MT-RJ stands for Mechanical Transfer Registered Jack.
MT-RJ is a fiber-optic cable connector that is very
popular for small form factor devices due to its small
size. Housing two fibers and mating together with
locating pins on the plug, the MT-RJ comes from the MT
connector, which can contain up to 12 fibers.
MU Connector
MU is a small form factor SC. It has the same push/pull
style, but can fit 2 channels in the same footprint of a
single SC. MU was developed by NTT.
Multilongitudinal Mode (MLM)
Laser
An injection laser diode which has a number of
longitudinal modes.
Multimode (Multi Mode)
Transmits or emits multiple modes of light. An optical
waveguide with a much larger core (50µm +) than the
singlemode waveguide core (2µm to 9µm) and which permits
approximately 1,000 modes to propagate through the core
compared to only one mode through a singlemode fiber.
Multimode Dispersion
Dispersion resulting from the different transit lengths
of different propagating modes in a multimode optical
fiber. Also called modal dispersion.
Multimode Fiber - MM
An optical fiber that has a core large enough to
propagate more than one mode of light The typical
diameter is 62.5 micrometers or 50 micrometers.
Multiple Reflection Noise (MRN)
The fiber optic receiver noise resulting from the
interference of delayed signals from two or more
reflection points in a fiber optic span. Also known as
multipath interference.
Multiplexer
A device that combines two or more signals into a single
output.
Multiplexing
The process by which two or more signals are transmitted
over a single communications channel. Examples include
time-division multiplexing (TDM) and wavelength-division
multiplexing (WDM).
MZ
Abbreviation for Mach-Zehnder, a structure used in fiber
Bragg gratings and interferometers. Named for the two
men who developed the underlying principles of the
structure.
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NA Mismatch Loss
The loss of power at a joint that occurs when the
transmitting half has a numerical aperture greater than
the NA of the receiving half. The loss occurs when
coupling light from a source to fiber, from fiber to
fiber, or from fiber to detector.
National Electric Code® (NEC)
A standard governing the use of electrical wire, cable
and fixtures installed in buildings; developed by the
American National Standards Institute (ANSI), sponsored
by the National Fire Protection Association (NFPA),
identified by the description ANSI/NFPA 70-1990.
NCTA
Abbreviation for National Cable Television Association.
The major trade association for the cable television
industry.
NDSF - Non Dispersion-Shifted
Fiber
The most popular type of single-mode fiber deployed. It
is designed to have a zero-dispersion wavelength near
1310 nm.
NEXT , RN - Near-end Crosstalk
(NEXT, RN)
The optical power reflected from one or more input
ports, back to another input port. Also known as
isolation directivity.
Near-Infrared
The part of the infrared near the visible spectrum,
typically from 700 to 1500 or 2000nm; it is not rigidly
defined.
NEMA
Abbreviation for National Electrical Manufacturers
Association. Organization responsible for the
standardization of electrical equipment, enabling
consumers to select from a range of safe, effective, and
compatible electrical products.
Near Field Scanning
A technique for measuring the refractive-index profile
of an optical fiber by using an extended source to
illuminate an endface and measuring the point-by-point
radiance at the exit face.
Network
A system of cables or other connections that links many
terminals or devices, all of which can communicate with
each other through the system.
Network Topology
The specific physical, i.e., real, logical, or virtual,
arrangement of the elements of a network. Common network
topologies include a bus (or linear) topology, a ring
topology, and a hybrid topology, which can be a
combination of any two or more network topologies.
Illustrated to the right is a bus topology utilizing tee
couplers to connect a series of stations that listen to
a single backbone of cable.
Neutral Density Coating
A coating that appears gray to the eye and has a flat
absorption curve throughout the visible spectrum. Metals
are generally used for this purpose.
Neutral Density Filter
Also known as a gray filter. A light filter that
decreases the intensity of the light without altering
the relative spectral distribution of the energy.
NF - Noise Figure (NF)
The ratio of the output signal-to-noise ratio to the
input signal-to-noise ratio for a given element in a
transmission system. Used for optical and electrical
components.
NFPA
Abbreviation for National Fire Protection Association.
Publisher of the National Electrical Code®, and 300
other codes and standards through a full, open-consensus
process.
NIST
An acronym for National Institute of Standards and
Technology.
Node
1) A terminal of any branch in network topology or an
interconnection common to two or more branches in a
network.
2) One of the switches forming the network backbone in a
switch network.
3) A point in a standing or stationary wave at which the
amplitude is a minimum.
Noise
1) An undesired disturbance within the frequency band of
interest; the summation of unwanted or disturbing energy
introduced into a communications system from man-made
and natural sources.
2) A disturbance that affects a signal and that may
distort the information carried by the signal.
3) Random variations of one or more characteristics of
any entity such as voltage, current, or data.
Noise Equivalent Power (NEP)
The optical input power to a detector needed to generate
an electrical signal equal to the inherent electrical
noise.
No Return to Zero (NRZ)
A digital code in which the signal level is low for a 0
bit and high for a 1 bit and does not return to 0
between successive 1 bits.
Nonlinearity
The deviation from linearity in an electronic circuit,
an electro-optic device or a fiber that generates
undesired components in a signal. Examples of fiber
nonlinearities include SBS, SRS, FWM, SPM, XPM, and
Intermodulation.
Normal (angle)
Perpendicular to a surface.
NRZ
Abbreviation for nonreturn to zero. A common means of
encoding data that has two states termed €śzero€ť and
€śone€ť and no neutral or rest position.
NTSC
The analog video broadcast standard used in North
America, set by the National Television System
Committee.
Numerical Aperture (NA)
The sine of half the angle over which a fiber can accept
light. Strictly speaking, this is multiplied by the
refractive index of the medium containing the light, but
for air the index is almost equal to 1. The
light-gathering ability of a fiber; the maximum angle to
the fiber axis at which light will be accepted and
propagated through the fiber. NA = sin a, where a is the
acceptance angle. NA also describes the angular spread
of light from a central axis, as in exiting a fiber,
emitting from a source, or entering a detector.
NZ-DSF - Nonzero
Dispersion-Shifted Fiber (NZ-DSF)
Single mode fiber with the wavelength of zero chromatic
dispersion shifted to just outside of the erbium-fiber
amplifier region. Some types have zero dispersion near
1500nm, others near 1625nm. Types with zero dispersion
at 1580nm are not usable in the L-band of erbium-doped
fiber amplifiers.
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OADM - Optical Add/Drop
Multiplexer
A device which adds or drops individual wavelengths from
a DWDM system.
OAM
Abbreviation for operation, administration, and
maintenance. Refers to telecommunications networks.
OAN
Abbreviation for optical access network. A network
technology, based on passive optical networks (PONs),
that includes an optical switch at the central office,
an intelligent optical terminal at the customer's
premises, and a passive optical network between the two,
allowing services providers to deliver fiber-to-the-home
while eliminating the expensive electronics located
outside the central office.
OCH - Optical Channel
An optical wavelength band for WDM optical
communications.
OCx
Optical Carrier, a carrier rate specified in the SONET
standard.
ODN
Abbreviation for optical distribution network. Term for
optical networks being developed for interactive video,
audio, and data distribution.
O/E
Abbreviation for optical-to-electrical converter. A
device used to convert optical signals to electrical
signals. Also known as OEC.
OEIC
Abbreviation for opto-electronic integrated circuit. An
integrated circuit that includes both optical and
electrical elements.
OEM
Abbreviation for original equipment manufacturer. The
manufacturer of any device that is designed and built to
be distributed under the label of another company.
OFNG
Optical Fiber Nonconductive General Purpose. Type OFNG
cable must be resistant to the spread of fire and
suitable for general-purpose use, with the exception of
risers and plenums.
OFNP
Optical Fiber Nonconductive Plenum. Cable installed in
ducts, plenums, and other spaces used for environmental
air must be listed as having adequate fire-resistant and
low-smoke producing characteristics.
OFNR
Optical Fiber Nonconductive Riser. Optical fiber cable
used in vertical shafts, or in runs between floors, must
have fire-resistant characteristics capable of
preventing the spread of fire from floor-to-floor.
OLT
Abbreviation for optical line termination. Optical
network elements that terminate a line signal.
OLTS
Abbreviation for optical loss test set. A source and
optical power meter combined used to measure optical
loss.
OMS
Abbreviation for optical multiplex section. A section of
a DWDM system that incorporates an optical add/drop
multiplexer.
ONI
Abbreviation for optical network interface. A device
used in an optical distribution network to connect two
parts of that network.
ONT
Abbreviation for optical network termination. Optical
network element that terminates a line signal in
installations where the fiber extends into the customer
premises.
ONU
Abbreviation for optical network unit. A network element
that is part of a fiber-in-the-loop system.
OOI
Abbreviation for open optical interface. A point at
which an optical signal is passed from one equipment
medium to another without conversion to an electrical
signal.
Open Systems Interconnection
(OSI)
Pertaining to the logical structure for communications
networks standardized by the International Organization
for Standardization (ISO).
Optical Amplifier
A device that amplifies an input optical signal without
converting it into electrical form. The best developed
are optical fibers doped with the rare-earth element
erbium.
Optical Bandpass
The range of optical wavelengths which can be
transmitted through a component.
Optical Channel
An optical signal transmitted at one wavelength. WDM
systems transmit multiple channels at separate
wavelengths.
Optical Channel Spacing
The wavelength separation between adjacent WDM channels.
Optical Channel Width
The optical wavelength range of a channel.
Optical Continuous Wave
Reflectometer (OCWR)
An instrument used to characterize a fiber optic link
wherein an unmodulated signal is transmitted through the
link, and the resulting light scattered and reflected
back to the input is measured. Useful in estimating
component reflectance and link optical return loss.
Optical Circulator
A device that transmits light only in one direction
through a series of ports, so light can go from port 1
to port 2 and port 2 to port 3, but not from port 2 to
port 1.
Optical Directional Coupler
(ODC)
A component used to combine and separate optical power.
Optical Fall Time
The time interval for the falling edge of an optical
pulse to transition from 90% to 10% of the pulse
amplitude. Alternatively, values of 80% and 20% may be
used.
Optical Fiber
A glass or plastic fiber that has the ability to guide
light along its axis. The three parts of an optical
fiber are the core, the cladding, and the coating or
buffer.
Optical Isolator
A component used to block out reflected and unwanted
light. Also called an isolator.
Optical Link Loss Budget
The range of optical loss over which a fiber optic link
will operate and meet all specifications. The loss is
relative to the transmitter output power and affects the
required receiver input power.
Optical Networking
Processing and switching signals in optical form as well
as transmitting them optically.
Optical Node
The point where signals are transferred from optical
fibers to other transmission media, typically
twisted-pair wires or coaxial cable.
Optical Path Power Penalty
The additional loss budget required to account for
degradations due to reflections, and the combined
effects of dispersion resulting from intersymbol
interference, mode-partition noise, and laser chirp.
Optical Performance Monitor
A device installed in a WDM system to monitor signals at
the transmitted wavelengths.
Optical Power Meter
An instrument that measures the amount of optical power
present at the end of a fiber or cable.
Optical Pump Laser
A shorter wavelength laser used to pump a length of
fiber with energy to provide amplification at one or
more longer wavelengths. See also EDFA.
Optical Return Loss (ORL)
The ratio (expressed in dB) of optical power reflected
by a component or an assembly to the optical power
incident on a component port when that component or
assembly is introduced into a link or system.
Optical Rise Time
The time interval for the rising edge of an optical
pulse to transition from 10% to 90% of the pulse
amplitude. Alternatively, values of 20% and 80% may be
used.
Optical Spectrum Analyzer (OSA)
An instrument that scans the spectrum to record power as
a function of wavelength.
Optical Signal-to-Noise-Ratio
(OSNR)
The optical equivalent of SNR.
Optical Time-Domain
Reflectometer (OTDR)
An instrument that measures transmission characteristics
by sending a short pulse of light down a fiber and
observing back-scattered light.
Optical Waveguide
Technically, any structure that can guide light.
Sometimes used as a synonym for optical fiber, it can
also apply to planar light waveguides.
Outside Plant (OSP)
In telephony, all cables, conduits, ducts, poles,
towers, repeaters, repeater huts, and other equipment
located between a demarcation point in a switching
facility and a demarcation point in another switching
facility or customer premises.
Overfilled Launch
A condition for launching light into the fiber where the
incoming light has a spot size and NA larger than
accepted by the fiber, filling all modes in the fiber.
OXC
Abbreviation for optical cross-connect. See
cross-connect.
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PABX
Abbreviation for private automatic branch exchange. See
PBX.
Packet
In data communications, a sequence of binary digits,
including data and control signals, that is transmitted
and switched as a composite whole. The packet contains
data, control signals, and possibly error control
information, arranged in a specific format.
Packet Switching
Organizing signals by dividing then into data packets,
each containing a header that specifies its destination
and a packet of data intended for that destination.
Separate data packets then are directed to their
destinations.
PAL
Abbreviation for phase alternation by line. A composite
color standard used in many parts of the world for TV
broadcast. The phase alternation makes the signal
relatively immune to certain distortions (compared to
NTSC). Delivers 625 lines at 50 frames per second.
PAL-plus is an enhanced-definition version.
Panda Fiber
Panda is a common style of PM fiber, using round and
symetrical stress rods on either side of the core to
induce polarization.
Parabolic Profile
In an optical fiber, a power-law index profile with the
profile parameter, g, equal to. Synonym: quadratic
profile.
Passband
The region of usable frequency in electronics or
wavelength in optics.
Passive Branching Device
A device which divides an optical input into two or more
optical outputs.
Passive Component
A component that doesn't require outside power.
Passive Device
Any device that does not require a source of energy for
its operation. Examples include electrical resistors or
capacitors, diodes, optical fiber (photo), cable, wires,
glass, lenses, and filters.
Pay-Per-View (PPV)
An event that has an associated viewing cost, and which
may be purchased separately from any package or
subscription. The ordered events could include movies,
special events, such as sporting, or adult programming.
The event could be purchased by either impulse PPV by
using a television remote (this application requires a
continuous land line phone based connection), or over
the phone PPV (this application may have additional
costs for processing).
Passive Optical Network
A fiber-optic distribution network with no active
components between the switching point and the customer.
PBX
Abbreviation for private branch exchange. A
subscriber-owned telecommunications exchange that
usually includes access to public switched networks.
PC (Fiber Connector Polish)
Abbreviation for physical contact. Refers to an optical
connector that allows the fiber ends to physically
touch. Used to minimize backreflection and insertion
loss.
PCS Fiber - Plastic Clad Silica
Also called hard clad silica (HCS). A step-index fiber
with a glass core and plastic or polymer cladding
instead of glass.
Peak Power
Highest instantaneous power level in a pulse.
Peak Wavelength
In optical emitters, the spectral line having the
greatest output power. Also called peak emission
wavelength.
PFM
Abbreviation for pulse-frequency modulation. Also
referred to as square wave FM.
Phase
The position of a wave in its oscillation cycle.
Phase Constant
The imaginary part of the axial propagation constant for
a particular mode, usually expressed in radians per unit
length. See also attenuation.
Phase Noise
Rapid, short-term, random fluctuations in the phase of a
wave caused by time-domain instabilities in an
oscillator.
Phase-shift Keying (PSK)
1) In digital transmission, angle modulation in which
the phase of the carrier discretely varies in relation,
either to a reference phase or to the phase of the
immediately preceding signal element, in accordance with
data being transmitted.
2) In a communications system, the representation of
characters, such as bits or quaternary digits, by a
shift in the phase of an electromagnetic carrier wave
with respect to a reference, by an amount corresponding
to the symbol being encoded. Also called biphase
modulation, phase-shift signaling.
Photoconductive
Losing an electrical charge on exposure to light.
Photodetector
An optoelectronic transducer such as a PIN photodiode or
avalanche photodiode. In the case of the PIN diode, it
is so named because it is constructed from materials
layered by their positive, intrinsic, and negative
electron regions.
Photodiode - PD
A diode that can produce an electrical signal
proportional to light falling upon it.
Photonic
A term coined for devices that work using photons or
light, analogous to "electronic" for devices working
with electrons.
Photovoltaic
Providing an electric current under the influence of
light or similar radiation.
Photons
Quanta of electromagnetic radiation. Light can be viewed
as either a wave or a series of photons.
Pigtail
A short optical fiber permanently attached to a source,
detector, or other fiber optic device at one end and an
optical connector at the other.
pin Photodiode
A semiconductor detector with an intrinsic (i) region
separating the p- and n-doped regions. It has fast
linear response an is used in fiber-optic receivers.
Planar Waveguide
A flat waveguide formed on the surface of a flat
material. The zone of high refractive index is
rectangular in cross-section and guides light in the
same way as the core of an optical fiber.
Plastic-Clad Silica (PCS) Fiber
A step-index multimode fiber in which a silica core is
surrounded by a lower-index plastic cladding.
Plastic Optical Fiber (POF)
An optical fiber made entirely of plastic compounds.
Optical fibers in which both the 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.
PLC
Abbreviation for planar lightwave circuit. A device
which incorporates a planar waveguide.
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
Cable made of fire-retardent material that meets
electrical code requirements (UL 910) for low smoke
generation and installation in air spaces.
Plesiochronous Digital
Hierarchy (PDH)
The North American Digital Hierarchy of time-division
multiplexing rates.
Point-to-Point Transmission
Carrying a signal between two points, without branching
to other points.
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.
PVDF (Kynar®)
Abbreviation used to denote polyvinyldifluoride. A type
of material used for cable jacketing.
Polarization
Alignment of the electric and magnetic fields that make
up an electromagnetic wave; normally refers to the
electric field. If all light waves have the same
alignment, the light is polarized.
Polarization Maintaining Fiber
(PM Fiber)
Fibers that maintains the polarization of light that
enters it.
Polarization Dependent Loss
In passive optical components, loss that varies as the
polarization state of the propagating wave changes.
Expressed as the difference between the maximum and
minimum loss in decibels.
Polarization Mode Dispersion
(PMD)
Dispersion arising from random fluctuations in how
fibers transmit light in vertical and horizontal
polarizations.
Polishing
The optical process, following grinding, that puts a
highly finished, smooth and apparently amorphous surface
on a lens or a mirror.
Polishing and Abrasive Material
Any of the numerous powders used for grinding and
polishing glass, crystal or metal, the chief material
being emery and carborundum for grinding, and rouge or
the oxides of tin, cerium or other metals for polishing.
Polishing Jig
In fiber optics, a device used to polish a biconic plug
to a specified length and surface finish. Also called a
polishing disc.
PON
Abbreviation for passive optical network. A broadband
fiber optic access network that uses a means of sharing
fiber to the home without running individual fiber optic
lines from an exchange point, telco CO, or a CATV
headend and the subscriber's home.
POP (Point of Presence)
POTS (Plain Old Telephone
Service)
Analog voice telephone line.
p-p
Abbreviation for peak-to-peak. The algebraic difference
between extreme values of a varying quantity.
Preform
A cylindrical rod of specially prepared and purified
glass from which an optical fiber is drawn.
Precision Sleeve Splicing
Optical fiber splicing that uses a capillary tube, of
suitable material, to align the mating fibers.
Profile Dispersion
Dispersion attributed to the variation of refractive
index contrast with wavelength.
ps
Abbreviation for picosecond. One trillionth of a second
or 10-12 seconds.
Pulling Eye
A pulling eye is a device fastened to a fiber cable to
which a hook may be attached in order to pull the cable
through a duct or small space.
Pulse
A current or voltage which changes abruptly from one
value to another and back to the original value in a
finite length of time. Used to describe one particular
variation in a series of wave motions. The parts of the
pulse include the rise time, fall time, and pulse width,
pulse amplitude. The period of a pulse refers to the
amount of time between pulses.
Pulse-code Modulation (PCM)
A technique in which an analog signal, such as a voice,
is converted into a digital signal by sampling the
signal's amplitude and expressing the different
amplitudes as a binary number. The sampling rate must be
at least twice the highest frequency in the signal.
Pulse Dispersion
The Spreading out of pulses as they travel along an
optical fiber.
Public Switched Networks (PSN)
1. Any common carrier network that provides circuit
switching among public users.
2. A switched network accessible to the public for
originating and terminating telecommunications messages.
3. Any common carrier switched network, whether by wire
or radio, including local exchange carriers,
interexchange carriers, and mobile service providers,
that use the North American Numbering Plan in common
with provision of switched services.
Pump Laser
The semiconductor laser that provides the light that
excites atoms in a fiber amplifier, putting them in the
right state to amplify light. A power source for signal
amplification, typically a 980 nm or 1480 nm laser, used
in EDFA applications.
pW
Abbreviation for picowatt. One trillionth of a Watt or
10-12 Watts.
QAM
- Quadrature Amplitude Modulation.
A coding technique that uses many discrete digital
levels to transmit data with minimum bandwidth. QAM256
uses 256 discrete levels to transmit digitized video.
QDST
Abbreviation for quaternary dispersion supported
transmission. See DST.
QoS
- Quality of Service
1. The performance specification of a communications
channel or system which may be quantitatively indicated
by channel or system performance parameters such as
signal-to-noise ratio, bit error rate, message
throughput rate, and call blocking probability.
2. A subjective rating of telephone communications
quality in which listeners judge transmissions by
qualifiers such as excellent, good, fair, poor, or
unsatisfactory.
Quadrature Phase-shift Keying
(QPSK)
Phase-shift keying uses
four different phase angles out of phase by 90°. Also
called quadriphase or quaternary phase-shift keying.
Quantization
The process of converting
the voltage level of a signal into digital data before
or after the signal has been sampled.
Quantizing Error
Inaccuracies in the
digital representation of an analog signal. These errors
occur because of limitations in the resolution of the
digitizing process.
Quantizing Noise
Noise which results from
the quantization process. In serial digital video, a
granular type of noise that occurs only in the presence
of a signal.
Quantum Efficiency
The fraction of photons
that strike a detector that produces electron-hole paris
in the output current.
Quaternary
A semiconductor compound made of four elements. (e.g.,
InGaAsP).
Quaternary Signal
A digital signal having
four significant conditions.
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Radiation-hardened Fiber
An optical fiber made with core and cladding materials
that are designed to recover their intrinsic value of
attenuation coefficient, within an acceptable time
period, after exposure to a radiation pulse.
Radiometer
An instrument, distinct from a photometer, to measure
power (watts) of electromagnetic radiation.
Raman Amplifier
A fiber that transfers energy from a strong pump beam to
amplify a weaker signal at a longer wavelength, using
stimulated Raman scattering.
Random Jitter (RJ)
Random jitter is due to thermal noise and may be modeled
as a Gaussian process. The peak-to-peak value of RJ is
of a probabilistic nature, and thus any specific value
requires an associated probability.
Rare Earth Doped Fiber
An optical fiber in which ions of a rare-earth element,
such as neodymium, erbium or holmium, have been
incorporated into the glass core matrix, yielding high
absorption with low loss in the visible and
near-infrared spectral regions.
Rayleigh Scattering
The scattering of light that results from small
inhomogeneities of material density or composition.
Rays
Lines that represent the path taken by light.
Receiver
A device that detects an optical signal and converts it
into an electrical form usable by other devices.
Receive Cable
A known good fiber optic jumper cable attached to a
power meter used as a reference cable for loss testing.
This cable must be made of fiber and connectors of a
matching type to the cables to be tested.
Receiver Overload
The maximum acceptable value of average received power
for an acceptable BER or performance.
Receiver Sensitivity
The minimum acceptable value of received power needed to
achieve an acceptable BER or performance. It takes into
account power penalties caused by use of a transmitter
with worst-case values of extinction ratio, jitter,
pulse rise times and fall times, optical return loss,
receiver connector degradations, and measurement
tolerances. The receiver sensitivity does not include
power penalties associated with dispersion, or
backreflections from the optical path; these effects are
specified separately in the allocation of maximum
optical path penalty. Sensitivity usually takes into
account worst-case operating and end-of-life (EOL)
conditions.
Recombination
Combination of an electron and a hole in a semiconductor
that releases energy, sometimes leading to light
emission.
Refraction
The bending of light as it passes between materials of
different refractive index.
Refractive Index
The speed of light in a vacuum divided by the speed of
light in a material, abbreviated n, which measures how
materials refract light.
Refractive-Index Gradient
The change of refractive index with distance from the
axis of an optical fiber. Also called refractive index
profile.
Regenerator
A receiver-transmitter pair that detects a weak signal,
cleans it up, then sends the regenerated signal through
another length of fiber.
Repeater
A receiver-transmitter pair that detects and amplifies a
weak signal for retransmission through another length of
optical fiber.
Responsivity
The ratio of detector output to input, usually measured
in units of amperes per watt (or microampers per
microwatt).
Residual Loss
The loss of the attenuator at the minimum setting of the
attenuator.
Return Loss
See optical return loss.
Return Path
A communications connection that carries signals from
the subscriber back to the operator. The return path
allows for interactive television and on-demand
services, such as pay-per-view, video on demand, and
interactive games.
Return to Zero (RZ)
A digital coding scheme where signal level is low for a
0 bit and high for a 1 bit during the first half of a
bit interval and then in either case returns to zero for
the second half of the bit interval.
RF
Abbreviation for radio frequency. Any frequency within
the electromagnetic spectrum normally associated with
radio wave propagation.
RF Carrier
An AM technique wherein a carrier, with a frequency much
higher than the encoded information, varies according to
the amplitude of the information being encoded.
RFI
Abbreviation for radio frequency interference. Synonym
for electromagnetic interference.
Ribbon Cables
Cables in which many parallel fibers are embedded in a
plastic material, forming a flat ribbon-like structure.
RIN
Abbreviation for relative intensity noise. Often used to
quantify the noise characteristics of a laser.
Ring
A cable that forms a closed loop connecting two or more
points, so all points remain connected if the cable
breaks at one point.
Ring Network
A network topology in which terminals are connected in a
point-to-point serial fashion in an unbroken circular
configuration.
Rip Cord
Of an optical cable, a parallel cord of strong yarn that
is situated under the jacket(s) of the cable for the
purpose of facilitating jacket removal preparatory to
splicing or breaking out.
Riser
A pathway for indoor cables that pass between floors,
normally a vertical shaft or space. Also a fire-code
rating for indoor cable.
Rise Time
The time it takes output to rise from low levels to peak
value. Typically measured as the time to rise from 10%
to 90% of maximum output.
RJ 45
RJ-45 is the 8-conductor version of an RJ-11. It looks
like a regular modular phone connector, only it's wider.
You need to use RJ-45 for Ethernet, because the
connection standard puts the Ethernet on some of the
outer connectors not in RJ-11. RJ-11 plugs will fit into
an RJ-45 socket, but because the plastic plug is
smaller, some of the contacts will get bend back a
little more.
Router
A device that directs data packets to their destinations
using information in their headers to pick the best
path. Distinct from wavelength router.
RTS
Abbreviation for request to send. In a communications
network, a signal from a remote receiver to a
transmitter for data to be sent to that receiver.
Ruby Laser
The optically pumped, solid-state laser that uses
sapphire as the host lattice and chromium as the active
ion. The emission takes place in the red portion of the
spectrum.
RZ
Abbreviation for return to zero. A common means of
encoding data that has two information states called
€śzero€ť and €śone€ť in which the signal returns to a
rest state during a portion of the bit period.
Sampling Rate
The number of discrete sample measurements made in a
given period of time. Often expressed in megahertz (MHz)
for video.
SAN (Storage Area Network)
Connects a group of computers to high-capacity storage
devices. May be incorporated into local area networks
(LAN), metropolitan area networks (MAN), and wide area
networks (WAN).
Saturation
1) In a communications system, the condition in which a
component of the system has reached its maximum traffic
handling capacity.
2) The point at which the output of a linear device,
such as a linear amplifier, deviates significantly from
being a linear function of the input when the input
signal is increased.
3) The degree of the chroma or purity of a color.
S-Band
A proposed designation for wavelengths of 1460 to
1530nm, where optical amplifiers based on thulium-doped
fibers are in development.
SC Connector
Abbreviation for subscription channel connector. A
push-pull type of optical connector that features high
packing density, low loss, low backreflection, and low
cost.
Scattering
Loss of light that is scattered off atoms in different
directions, so it escapes from the fiber core. A major
component of fiber attenuation.
S-CDMA
Abbreviation for synchronous code division multiple
access. A synchronized version of CDMA.
Scoring
The cutting of pitch tooling surfaces by an optical
technician to permit polishing compounds to flow across
the surface of the tool.
Scrambler
1) A device that transposes or inverts signals or
otherwise encodes a message at the transmitter to make
the message unintelligible at a receiver not equipped
with an appropriately set descrambling device.
Scramblers usually use a fixed algorithm or mechanism.
2) A device intended to normalize the duty cycle of a
data stream to be close to 50%.
Scratch
A defect on a polished optical surface whose length is
many times its width. Block reek is a chainlike scratch
formed in polishing. A runner cut is a curved scratch
caused by grinding. A sleek is a hairline scratch. A
crush or rub is a surface scratch or scratches usually
caused by mishandling.
Self-phase modulation (SPM)
A fiber nonlinearity caused by the nonlinear index of
refraction of glass. The index of refraction varies with
optical power level causing a frequency chirp which
interacts with the fiber's dispersion to broaden the
pulse.
Semiconductor Optical Amplifier
(SOA)
A laser diode without end mirrors coupled to the fibers
on both ends. Light coming in either fiber is amplified
by a single pass through the laser diode. An alternative
to EDFAs.
SFP Loopback
An small form factor test fixture used loop an
electrical signal from the Tx side of a port to the Rx
side of a port, prior to population with an optical
transceiver.
Synchronous Digital Hierarchy
(SDH)
The international version of SONET, the Synchronous
Optical Network Standard. The biggest difference is in
the names of the transmission rates.
Selfoc Lens
A trade name used by Nippon Sheet Glass Company (NSG)
for a graded-index fiber lens; a segment of graded-index
fibers made to serve as lens.
Semiconductor Laser
A laser in which injection of current into a
semiconductor diode produces light by recombination of
holes and electrons at the junction between p- and
n-doped regions.
SH
Abbreviation for short-haul. A classification of video
performance under RS-250B/C. Higher performance than
long-haul or medium-haul.
Sheath
An outer protective layer of a fiber optic cable. Also
called the cable jacket.
Short Wavelength
A commonly used term for light in the 665, 790, and 850
nm ranges.
Si
Abbreviation for silicon. Generally used in detectors.
Good for short wavelengths only (e.g., < 1000 nm).
Silica
Silicon dioxide (SiO2).
SI Units
The standard international system of metric units.
Signal-to-Noise Ratio (SNR)
The ratio of signal to noise, measured in decibels; an
indication of analog signal quality.
Simple Network Management
Protocol (SNMP)
The Internet standard protocol for network management
software. It monitors devices on the network, and
gathers device performance data for management
information data bases (MIB).
Silica Glass
Glass made mostly of silicon dioxide, SiO2, used in
conventional optical fibers.
Simplex
Single element (e.g., a simplex connector is a
single-fiber connector).
Simplex Cable
A term sometimes used for a single-fiber cable.
Single-Frequency Laser
A laser that emits a range of wavelengths small enough
to be considered a single frequency.
Single-longitudinal Mode Laser
(SLM)
An injection laser diode which has a single dominant
longitudinal mode. A single-mode laser with a side mode
suppression ratio (SMSR)< 25 dB.
Single Mode
Containing only one mode. When dealing with lasers,
beware of ambiguities because of the difference between
transverse and longitudinal modes. A laser operating in
a single transverse mode typically does not operate in a
single longitudinal mode. A type of low-loss optical
waveguide with a very small core (2-9 microns). It
requires a laser source for input signals because of the
very small entrance aperture. The smallest of the core
radius approaches the wavelength of the source.
Consequently, only a singlemode is propagated.
Single Mode Fiber (SMF)
A small-core optical fiber through which only one mode
will propagate. The typical diameter is 8-9 microns.
Single Polarization Fiber
Optical fibers capable of carrying light in only one
polarization.
Slab Dielectric Waveguide
An electromagnetic waveguide (a) that consists solely of
dielectric materials, (b) in which the dielectric
propagation medium has a rectangular cross section, (c)
that has a width, thickness, and refractive indices that
determine the operating wavelength and the modes the
guide will support beyond the equilibrium length, (d)
that may be cladded, protected, distributed, and
electronically controllable, and (e) that may be used in
various applications, such as in integrated optical
circuits (IOCs) in which their shape is geometrically
more convenient than the optical fibers that are
circular in cross section, that are used in fiber optic
cables for long-distance transmission.
Slurry
The name of the mixture of liquid and grinding or
polishing compounds used in processing optical
materials.
SMA
A threaded type of optical connector. One of the
earliest optical connectors to be widely used. Offers
poor repeatability and performance.
SM Zipcord Fiber
Zipcord (or zip-cord) is a two fiber cable essentially
with two single-fiber cables conjoined by their jackets.
The jacket strip can be easily separated from one
another for the installation of optical connectors. Zip
cord cables may include both loose-buffer and
tight-buffer designs.
Soliton
An optical pulse that naturally retains its original
shape as it travels along an optical fiber.
Synchronous Optical Network
(SONET)
A standard for fiber-optic transmission. Abbreviation
for synchronous optical network transport system. An
interface standard widely used by the telecom industry
where OC-3 is the lowest current rate (155.5 Mb/s), and
OC-768 is the highest rate being contemplated (39.808
Gb/s). Valid rates increase by a factor of four from the
OC-3 rate up to OC-768.
Source
In fiber optics, a transmitting LED or laser diode, or
an instrument that injects test signals into fibers.
Span Engineering
The process of designing a DWDM transmission span to
achieve the required performance based on fiber type,
the transmission distance, amplifier spacing, noise,
power, and channel count.
Spectral Efficiency
The number of data bits per second that can be
transmitted in a one Hertz bandwidth range.
Spectral Width
A measure of the extent of a spectrum. For a source, the
width of wavelengths contained in the output at one half
of the wavelength of peak power. Typical spectral widths
are 50 to 160 nm for an LED and less than 5 nm for a
laser diode.
Spectral Width, Full Width,
Half Maximum (FWHM)
The absolute difference between the wavelengths at which
the spectral radiant intensity is 50 percent of the
maximum power.
Splice
A permanent junction between two fiber ends.
Splice Organizer
In optical communication, a device that facilitates the
splicing or breaking out of fiber optic cables.
Splice Tray
A container that prevents spliced fibers from becoming
damaged or being misplaced.
Splitter
see Coupler.
Splitting Ratio
The ratio of power emerging from output ports of a
coupler.
ST Connector
Abbreviation for straight tip connector. Popular fiber
optic connector originally developed by AT&T.
Stainless Steel Cable
A fiber optic cable with flexible stainless steel
jacketing for increased fiber protection
Standard Single Mode Fiber
Step-index single mode fiber with zero dispersion at
1310nm; the first type used in fiber optic
communications, still widely used.
Star Coupler
A coupler with more than three or four ports.
Star Network
A network in which all terminals are connected through a
single point, such as a star coupler or concentrator.
Steady State Modal Distribution
Equilibrium modal distribution (EMD) in multimode fiber,
achieved some distance from the source, where the
relative power in the modes becomes stable with
increasing distance.
Strain Relief
A Method of controlling the bend of a fiber as it exits
the connector. Available in various sized depending on
the cable size. 900um, 1.6mm, 2.0mm, and 3.0mm, or even
the Timbercon Armadillo cable (custom integrated boot
shell design).
Strength Member
The part of a fiber optic cable composed of aramid yarn,
steel strands, or fiberglass filaments that increase the
tensile strength of the cable.
Step-Index
An optical fiber, either multimode or singlemode, in
which the core refractive index is uniform throughout so
that a sharp step in refractive index occurs at the
core-to-cladding interface. It usually refers to a
multimode fiber. Such fibers have a large numerical
aperture, are simple to connect, but have lower
bandwidth than other types of optical fibers.
Step-Index Multimode Fiber
A step-index fiber with a core large enough to carry
light in multiple modes.
Step-Index Single-Mode Fiber
A step-index fiber with a small core capable of carrying
light in only one mode; this type has zero dispersion at
1310nm.
Stimulated Raman Scattering
Interactions between light and atoms in a transparent
material that convert energy from one wavelength to
another.
Subscriber Loop
The part of the telephone network from a central office
to individual subscribers.
Submarine Cable
A cable designed to be laid underwater.
Surface-Emitting Diode (SLED)
An LED that emits light from its flat surface rather
than its side. Simple and inexpensive, with emission
spread of a wide angle.
Surface-Emitting Laser
A semiconductor laser that emits light from the wafer
surface.
Switch
A device that directs light or electricity along
different paths, such as fibers or wires.
Switched Network
A network that routes signals to their destinations by
switching circuits, such as the telephone system.
Synchronous
A data signal that is sent along with a clock signal. A
system in which events, such as signals, occur at evenly
spaced time durations. Opposite of asynchronous.
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T1
In telecommunications, the cable used to transport DS1
service.
Talkset (fiber optic)
A communication device that allows conversation over
unused fibers.
Tap Loss
In a fiber optic coupler, the ratio of power at the tap
port to the power at the input port.
Tap Port
In a coupler where the splitting ratio between output
ports is not equal, the output port containing the
lesser power.
Tbit/s
Terabits (trillion, or 1012 bits) per second.
T Carrier
A system transmitting signals at one of the standard
levels in the North American digital hierarchy.
TCP/IP
Abbreviation for transmission control protocol/Internet
protocol. Two interrelated protocols that are part of
the Internet protocol suite. TCP operates on the OSI
transport layer and breaks data into packets. IP
operates on the OSI network layer and routes packets.
Originally developed by the U.S. Department of Defense.
T Coupler
A coupler with three ports.
TEC (TE Cooler)
Abbreviation for thermoelectric cooler. A device used to
dissipate heat in electronic assemblies.
Telecommunications Management
Network (TMN)
A network that interfaces with a telecommunications
network at several points in order to receive
information from, and to control the operation of, the
telecommunications network.
Termination
Preparation of the end of a fiber to allow connection to
another fiber or an active device, sometimes also called
"connectorization".
Termination and Splicing
Termination and splicing equipment for fiber optics
include tools or kits for cutting, finishing,
positioning, aligning and joining fiber optic cables.
Terminating
Terminating a fiber is accomplished through preparing
the fiber for connection to another fiber or device such
as a connector. The goal when terminating is to produce
a perfect end to the fiber. The end should be cleanly
cut, clear and physically connected to the receiving
optical device. This can be accomplished through two
means; permanently joining the fibers by welding or
gluing the ends of the fiber together, or mechanically
aligning the fibers and joining them with transparent
gel.
Test Cable
A short single fiber jumper cable with connectors on
both ends used for testing. This cable must be made of
fiber and connectors of a matching type to the cables to
be tested.
Test Kit
A kit of fiber optic instruments, typically including a
power meter, source and test accessories used for
measuring loss and power.
Test Source
A laser diode or LED used to inject an optical signal
into fiber for testing loss of the fiber or other
components.
Thermal Noise
Noise resulting from thermally induced random
fluctuation in current in the receiver's load
resistance.
Thermo-Optic Switches
Optical switches controlled by temperature-induced
changes in refractive index.
Threshold Current
The minimum current needed to sustain laser action in a
diode laser.
Throughput Loss
In a fiber optic coupler, the ratio of power at the
throughput port to the power at the input port.
Throughput Port
In a coupler where the splitting ratio between output
ports is not equal, the output port containing the
greater power.
TIA
An acronym for Telecommunications Industry Association.
TICL
Abbreviation for temperature induced cable loss. Optical
loss as a result of extreme temperatures outside a fiber
optic cable's environmental specifications.
Tight Buffer
A material tightly surrounding a fiber in a cable,
holding it rigidly in place.
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
(TDM)
Digital multiplexing by taking one bit or byte of data
at a time from separate signals and combining them in a
single bit stream.
Token Ring
A ring-based network scheme in which a token is used to
control access to a network. Used by IEEE 802.5 and
FDDI.
Total Internal Reflection
Total reflection of light back into a material when it
strikes the interface with a material having a lower
refractive index at an angle below a critical value.
Transceiver
A combination of transmitter and receiver providing both
output and input interfaces with a device.
Transverse Modes
Modes across the width of a waveguide, fiber or laser.
Distinct from longitudinal modes, which are along he
length of a laser.
Transducer
A device that converts energy from one form to another,
such as optical energy to electrical energy.
Transmitter
A device that includes a source and driving electronics.
It functions as an electrical-to-optical converter.
Transponder
The part of a satellite that receives and transmits a
signal.
Traveling Wave
A wave that (a) propagates in a transmission medium, (b)
has a velocity determined by the launching conditions
and the physical properties of the medium, and (c) may
be a longitudinal or transverse wave.
Tray
A unit or assembly of units or sections, and associated
fittings, made of metal or other noncombustible
materials forming a rigid structural system used to
support cables. Includes ladders, troughs, channels,
solid bottom trays, and similar structures.
Tree
A network architecture in which transmission routes
branch out from a central point.
Trunk
1) In a communications network, a single transmission
channel between two switching centers or nodes, or both.
2) A circuit between switchboards or other switching
equipment, as distinguished from circuits which extend
between central office switching equipment and
information origination/termination equipment. Trunks
may be used to interconnect switches, such as major,
minor, public and private switches, to form networks.
Trunk Line
A transmission line running between telephone switching
offices or from a cable-TV head end to a distribution
node.
Twisted-Pair
Pair of copper wires twisted around each other. The
standard way to connect individual voice telephones,
widely used for other low-speed communications.
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UL
Abbreviation for Underwriter's Laboratory. An
organization that tests product safety for a wide
variety of products. UL approved products carry UL
symbol.
Ultraviolet (UV)
Electromagnetic waves invisible to the human eye, with
wavelengths about 10 to 400nm, shorter than visible
light.
Unidirectional
Operating in one direction only.
UPC (Ultra Physical Contact)
Specific to singlemode applications, referring to the
endface geometry of a connector ferrule as well as
performance characteristics (-55dB Return Loss).
UTP
Unshielded Twisted Pair.
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VCSEL (Vertical Cavity Surface
Emitting Laser)
A semiconductor laser in which light oscillate
vertically (perpendicular to the junction plane) and
light emerges from the surface of the waver rather than
from the edge of the chip.VDSL
Abbreviation for very high data rate digital subscriber
line. A DSL operating at a data rate higher than that of
HDSL. See also DSL.
Visible Light
Electromagnetic radiation visible to the human eye at
wavelengths of 400 to 700nm.
Visual Fault Locator
A device that couples visible light into the fiber to
allow visual tracing and testing of continuity. Some are
bright enough to allow finding breaks in fiber through
the cable jacket.
Virtual Circuit (VC)
A communications arrangement in which data from a source
user may be passed to a destination user over various
real circuit configurations during a single period of
communication, usually on a per call basis, although
permanent connections can be established.
VOA (Variable Optical
Attenuator)
An attenuator in which the attenuation can be varied.
Voice Circuit
A circuit capable of carrying one telephone conversation
or its equivalent; the standard subunit in which
telecommunication is counted. The US analog equivalent
is 4kHz, the digital equivalent is 64 kbit/s.
VPN
Abbreviation for virtual private network. A protected
information-system link utilizing tunneling, security
controls, and end-point address translation giving the
end user the impression that a dedicated line exists
between nodes.
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WAN
Wide area network. A wide area network (WAN) is a
geographically dispersed telecommunications network. The
term distinguishes a broader telecommunication structure
from a local area network (LAN). A wide area network may
be privately owned or rented, but the term usually
connotes the inclusion of public (shared user) networks.
An intermediate form of network in terms of geography is
a metropolitan area network (MAN).
Waveguide
A structure that guides electromagnetic waves along its
length. An optical fiber is an optical waveguide.
Waveguide Array
An array of curved planar waveguides that separates many
optical channels at once. Also called Array Waveguide
(AWG).
Waveguide Coupler
A coupler in which light gets transferred between planar
waveguides.
Waveguide Dispersion
The part of chromatic dispersion arising from the
different speeds light travels in the core and cladding
of a single mode fiber (i.e., from the fiber's waveguide
structure).
Wavelength
The distance an electromagnetic wave travels in the time
it takes to oscillate through a complete cycle.
Wavelengths of light are measured in nanometers (10-9
m) or micrometers (10-6m).
Wavelength Division
Multiplexing(WDM)
Multiplexing of signals by transmitting them at
different wavelengths through the same fiber.
Wavelength Adapter
A device which receives one wavelength and outputs a
second wavelength, usually to take a standard signal and
convert it to an ITU wavelength.
Wavelength Isolation
A WDM's isolation of a light signal in the desired
optical channel from the unwanted optical channels. Also
called far-end crosstalk.
Wavelength Router
An optical device that directs input signals according
to their wavelength.
Wavelength Routing Switch (WRS)
A switch, used in optical networks, that routes
wavelengths as required to specific terminals in the
network.
Wavelength Selective Coupler
A device which couples the pump laser wavelength to the
optical fiber while filtering out all other unwanted
wavelengths. Used in erbium-doped fiber amplifiers.
Wideband
Possessing large bandwidth.
Window
A wavelength region where fibers have low attenuation,
used for transmitting signals.
Working Margin
The difference (in dB) between the power budget and the
loss budget (i.e. the excess power margin).
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X-Band
The frequency range between 8.0 and 8.4 GHz.
X-Series Recommendations
Sets of data telecommunications protocols and interfaces
defined by the ITU.
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Y Coupler
A variation on the tee coupler in which input light is
split between two channels (typically planar waveguide)
that branch out like a Y from the input.
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Zero Dispersion-Shifted Fiber
Fiber with zero chromatic dispersion shifted to 1550nm,
used before the advent of DWDM.
Zero-Dispersion Wavelength
Wavelength at which net chromatic dispersion of an
optical fiber is nominally zero. Arises where waveguide
dispersion cancels out material dispersion.
Zipcord (Zip Cord)
A two-fiber cable consisting of two single fiber cables
having conjoined jackets. A zipcord cable can be easily
divided by slitting and pulling the conjoined jackets
apart.
Zip Cord Fiber
Two-fiber cable with two single fiber cables having
conjoined jackets. The zipcord cable can be easily
divided by slitting and pulling the conjoined jackets
apart. Zip cord cables include both loose-buffer a
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