of Fiber Optic Terms
an alphabetical glossary of fiber optic terms. You can
search the list using the alphabetical index below.
Absorption: That portion of fiber optic attenuation
resulting of conversion of optical power to heat.
Analog: Signals that are continually changing, as opposed to
being digitally encoded.
Angled Physical Contact, APC Connector
Attenuation Coefficient: Characteristic of the attenuation
of an optical fiber per unit length, in dB/km.
Attenuation: The reduction in optical power as it passes
along a fiber, usually expressed in decibels (dB). See
Attenuator: A device that reduces signal power in a fiber
optic link by inducing loss.
Average power: The average over time of a modulated signal.
Back reflection (obsolete term), reflectance, optical return
loss: Light reflected from the cleaved or polished end of a
fiber caused by the difference of refractive indices of air
and glass. Typically 4% of the incident light. Expressed in
dB relative to incident power.
Backscattering: The scattering of light in a fiber back
toward the source, used to make OTDR measurements.
The range of signal frequencies or bit rate within which a
fiber optic component, link or network will operate.
Bend-Insensitive Multimode Fiber: Multimode fiber that is
designed to provide decreased macrobend loss.
Radius: The minimal radius below which a cable should not
be bent. For fiber optic cables, the normal limit is 20
times the cable diameter under tension (e.g. while being
pulled) and 10 times when not under stress.
loss, microbending loss: Loss in fiber caused by stress on
the fiber bent around a restrictive radius.
Abbreviation for bend-insensitive multimode fiber
rate (BER): The fraction of data bits transmitted that are
received in error.
Bit: An electrical or optical pulse that carries
Buffer: A protective coating applied directly on the fiber.
Cable: One or more fibers enclosed in protective coverings
and in some constructions, additional components that act as
strength members, stiffeners, water blocking compounds, etc.
Cable Plant, Fiber Optic: The combination of fiber optic
cable sections, connectors and splices forming the optical
path between two terminal devices.
Calibration: The process of comparing a
measurement system or instrument of unverified accuracy with
a measurement system of known accuracy. The measurement
system of known and better accuracy is commonly referred to
as a calibration standard.
An abbreviation for Community Antenna Television or cable
Chromatic dispersion: The temporal spreading of a pulse in
an optical waveguide caused by the wavelength dependence of
the velocities of light.
Cladding: The lower refractive index optical coating over
the core of the fiber that "traps" light into the core.
A device that provides for a demountable connection between
two fibers or a fiber and an active device and provides
protection for the fiber.
the joining of two optical fibers made by mating two fiber
optic connectors with a mating adapter if required.
The center of the optical fiber through which light is
Coupler: An optical device that splits or combines light
from more than one fiber.
Cutback method: A technique for measuring the loss of bare
fiber by measuring the optical power transmitted through a
long length then cutting back to the source and measuring
the initial coupled power.
Cutoff wavelength: The wavelength beyond which singlemode
fiber only supports one mode of propagation.
Coarse wavelength division multiplexing using lasers spaced
widely over the range of 1260 to 1670 nm.
dBm: Optical power referenced to 1 milliwatt.
Decibel (dB): A unit of measurement of optical power which
indicates relative power on a logarithmic scale, sometimes
called dBr. dB=10 log ( power ratio)
Detector: A photodiode that converts optical signals to
Digital: Signals encoded into discrete bits.
Dispersion: The temporal spreading of a pulse in an optical
waveguide. May be caused by modal or chromatic effects.
EDFA: Erbium-doped fiber amplifier, an all optical amplifier
for 1550 nm SM transmissionsystems.
Edge-emitting diode (E-LED): A LED that emits from the edge
of the semiconductor chip, producing higher power and
narrower spectral width.
Encircled Flux: The total optical power, as a function of
radius, emanating from a source. Encircled flux has been
applied to measuring the power distribution within
graded-index multimode fiber.
finish: The quality of the end surface of a fiber prepared
for splicing or terminated in a connector.
Equilibrium modal distribution (EMD): Steady state modal
distribution in multimode fiber, achieved some distance from
the source, where the relative power in the modes becomes
stable with increasing distance.
Excess loss: The amount of light lost in a coupler, beyond
that inherent in the splitting to multiple output fibers.
Beam Connector: A connector in which the diameter of
the light beam and the launch angle are increased by a lens,
so that the losses caused by longitudinal off-set and
lateral off-set are reduced to a minimum.
Fiber Amplifier: an all optical amplifier using erbium or
other doped fibers and pump lasers to increase signal output
power without electronic conversion.
Ferrule: A precision tube which holds a fiber for alignment
for interconnection or termination. A ferrule may be part of
a connector or mechanical splice.
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.
Fiber optics: Light transmission through flexible
transmissive fibers for communications or lighting.
FO: Common abbreviation for "fiber optic."
Fresnel reflection, back reflection, optical return loss:
Light reflected from the cleaved or polished end of a fiber
caused by the difference of refractive indices of air and
glass. Typically 4% of the incident light.
fiber to the home
Fusion splicer: An instrument that splices fibers by fusing
or welding them, typically by electrical arc.
Graded index (GI): A type of multimode fiber which used a
graded profile of refractive index in the core material to
correct for dispersion.
Index of refraction: A measure of the speed of light in a
Index matching fluid: A liquid used of refractive index
similar to glass used to match the materials at the ends of
two fibers to reduce loss and back reflection.
Index profile: The refractive index of a fiber as a function
of cross section.
Insertion loss: The loss caused by the insertion of a
component such as a splice or connector in an optical fiber.
Jacket: The protective outer coating of the cable.
Jumper cable: A short single fiber cable with connectors on
both ends used for interconnecting other cables or testing.
Laser diode, ILD: A semiconductor device that emits high
powered, coherent light when stimulated by an electrical
current. Used in transmitters for singlemode fiber links.
Laser Optimized Multimode Fiber: A high bandwidth optical
fiber optimized for enhanced performance with laser sources
at a particular wavelength, e.g. an 850 nm laser optimized
cable: A known good fiber optic jumper cable attached to a
source and calibrated for output power used 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
Light-emitting diode, LED: A semiconductor device that emits
light when stimulated by an electrical current. Used in
transmitters for multimode fiber links.
Link, fiber optic: A combination of transmitter, receiver
and fiber optic cable connecting them capable of
transmitting data. May be analog or digital.
Long wavelength: A commonly used term for light in the 1300
and 1550 nm ranges.
Loss,optical: The amount of optical power lost as light is
transmitted through fiber, splices, couplers, etc.
Loss budget: The amount of power lost in the link. Often
used in terms of the maximum amount of loss that can be
tolerated by a given link.
Margin: The additional amount of loss that can be tolerated
in a link.
Mechanical splice: A semi-permanent connection between two
fibers made with an alignment device and index matching
fluid or adhesive.
Micron (Ám): A unit of measure, 10-6 m, used to measure
wavelength of light.
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.
Small diameter fiber optic cable made with
A method of installing fiber optic cable using narrow
trenches sawed in dirt, pavement or sidewalks.
dispersion: The temporal spreading of a pulse in an optical
waveguide caused by modal effects.
Mode field diameter: A measure of the core size in
Mode filter: A device that removes optical power in higher
order modes in fiber.
Mode scrambler: A device that mixes optical power in fiber
to achieve equal power distribution in all modes. Mode
stripper: A device that removes light in the cladding of an
Mode: A single electromagnetic field pattern that travels in
Multimode fiber: A fiber with core diameter much larger than
the wavelength of light transmitted that allows many modes
of light to propagate. Commonly used with LED sources for
lower speed, short distance links.
Nanometer (nm): A unit of measure , 10-9 m, used to measure
the wavelength of light.
Network: A system of cables, hardware and equipment used for
Numerical aperture (NA): A measure of the light acceptance
angle of the fiber.
Optical amplifier: A device that amplifies light without
converting it to an electrical signal.
Optical fiber: An optical waveguide, comprised of a light
carrying core and cladding which traps light in the core.
Optical loss test set (OLTS): An measurement instrument for
optical loss that includes both a meter and source.
Optical power: The amount of radiant energy per unit time,
expressed in linear units of Watts or on a logarithmic
scale, in dBm (where 0 dB = 1 mW) or dB* (where 0 dB*=1
Optical return loss, back reflection, reflectance: Light
reflected from the cleaved or polished end of a fiber caused
by the difference of refractive indices of air and glass.
Typically 4% of the incident light at a cleaved fiber end.
Expressed in dB relative to incident power. May also refer
to the total of relfectance from components and backscatter
from the optical fiber on an entire cable.
Optical switch: A device that routes an optical signal from
one or more input ports to one or more output ports.
Optical time domain reflectometer (OTDR): An instruments
that used backscattered light to find faults in optical
fiber and infer loss.
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.
Physical Contact, PC Connector
Photodiode: A semiconductor that converts light to an
electrical signal, used in fiber optic receivers.
Pigtail: A short length of fiber attached to a fiber optic
component such as a connector, laser or coupler.
Plastic optical fiber (POF): An optical fiber made of
Plastic-clad silica (PCS) fiber: A fiber made with a glass
core and plastic cladding.
a male fiber optic connector that mates to a female
POF: Plastic optical fiber, optical fiber made from polymer
budget: The difference (in dB) between the transmitted
optical power (in dBm) and the receiver sensitivity (in
Power meter, fiber optic: An instrument that measures
optical power emanating form the end of a fiber.
Preform: The large diameter glass rod from which fiber is
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: A device containing a photodiode and signal
conditioning circuitry that converts light to an electrical
signal in fiber optic links.
a female fiber optic connector, mates to a plug. Also known
as a jack.
cable: A known good fiber optic jumper cable attached
to a light source or power meter used as a reference cable
for loss testing.
Light reflected from the cleaved or polished end of a fiber
caused by the difference of refractive indices of air and
index: A property of optical materials that relates to the
velocity of light in the material.
Repeater, regenerator: A device that receives a fiber optic
signal and regenerates it for retransmission, used in very
long fiber optic links.
Scattering: The change of direction of light after striking
small particles that causes loss in optical fibers.
Short wavelength: A commonly used term for light in the 665,
790, and 850 nm ranges.
Singlemode fiber: A fiber with a small core, only a few
times the wavelength of light transmitted, that only allows
one mode of light to propagate. Commonly used with laser
sources for high speed, long distance links.
Source: A laser diode or LED used to inject an optical
signal into fiber.
splice-on connector, termination with a factory made
connector attached with a fusion splicer Splice
(fusion or mechanical): A device that provides for a
connection between two fibers, typically intended to be
Splitting ratio: The distribution of power among the output
fibers of a coupler.
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.
Step index fiber: A multimode fiber where the core is all
the same index of refraction.
Surface emitter LED: A LED that emits light perpendicular to
the semiconductor chip. Most LEDs used in datacommunications
are surface emitters.
Talkset, fiber optic: A communication device that allows
conversation over unused fibers.
Termination: Preparation of the end of a fiber to allow
connection to another fiber or an active device, sometimes
also called "connectorization".
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
Total internal reflection: Confinement of light into the
core of a fiber by the reflection off the core-cladding
Transmitter: A device which includes a LED or laser source
and signal conditioning electronics that is used to inject a
signal into fiber.
VCSEL: vertical cavity surface emitting laser, a type of
laser that emits light vertically out of the chip, not out
the edge, widely used in fast multimode networks.
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.
Watts: A linear measure of optical power, usually expressed
in milliwatts (mW), microwatts (*W) or nanowatts (nW).
Wavelength: A measure of the color of light, usually
expressed in nanometers (nm) or microns (*m).
Wavelength division multiplexing (WDM): A technique of
sending signals of several different wavelengths of light
into the fiber simultaneously.
Working margin: The difference (in dB) between the power
budget and the loss budget (i.e. the excess power margin).
FOA Reference Guide to Outside Plant Fiber Optics
The FOA OSP Civil Works Guide can
be downloaded free from the FOA Website.
FOA Online Reference Guide to Fiber Optics
You can buy the printed version of the The
FOA Reference Guide to Outside Plant Fiber Optics from the
eStore or Amazon.