A
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.
APD (Avalanche Photodiode)
A photodiode that exhibits
internal amplification of photocurrent through avalanche multiplication of
carriers in the junction region.
AR Coating
Antireflection coating. A thin, dielectric or
metallic film applied to an optical surface to reduce its reflectance and
thereby increase its transmittance.
Armadillo Loopback
A ruggedized fiber optic test adapter
designed to loop a signal from the Tx side of a port to the Rx side, simulating
a complete connection.
Armor
A protective layer, usually metal, wrapped around a
cable.
ASE (Amplified Spontaneous Emission)
A background noise
mechanism common to all types of erbium-doped fiber amplifiers (EDFAs). It
contributes to the noise figure of the EDFA which causes loss of signal-to-noise
ratio (SNR).
ASIC
Abbreviation for application-specific integrated
circuit. A custom-designed integrated circuit.
ASTM
Abbreviation for American Society for Testing and
Materials. An organization that provides a forum for the development and
publication of voluntary consensus standards for materials, products, systems,
and services that serve as a basis for manufacturing, procurement, and
regulatory activities.
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.
ATM (Asynchronous Transfer Mode)
A digital transmission
switching format, with cells containing 5 bytes of header information followed
by 48 data types. A transmission standard widely used by the telecom industry. A
digital transmission switching format with cells containing 5 bytes of header
information followed by 48 data bytes. Part of the B-ISDN standard.
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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B
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.)
C
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).
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.
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.
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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.
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.
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.
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.
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 €œzero€Â and €œone€Â 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.
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.
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.
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 €œzero€Â and €œone€Â 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-On Connector
A fiber optic connector that is formed by fusion splicing the "field fiber" to an internal fiber stub within a connector assembly.
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.
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.
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.
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.
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.
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.
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
