- Here's an alphabetical glossary
of fiber optic terms. You can search the list using the alphabetical
index below.
A, B,
C, D, E, F, G, I, J, L, M, N, O, P, R, S, T, V, W
A
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.
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 Loss, optical.
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.
B
Back reflection, 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. - Bandwidth: The range
of signal frequencies or bit rate within which a fiber optic
component, link or network will operate.
Bending loss, microbending loss: Loss in fiber caused by stress
on the fiber bent around a restrictive radius. - Bit-error rate
(BER): The fraction of data bits transmitted that are received
in error.
Bit: An electrical or optical pulse that carries information.
Buffer: A protective coating applied directly on the fiber.
C
Cable: One or more fibers enclosed in protective coverings and in some
cable constructions, strength members, stiffeners, water blocking
compounds or other components.
Cable Plant, Fiber Optic: The combination of fiber optic cable
sections, connectors and splices forming the optical path between
two terminal devices.
CATV: An abbreviation for Community Antenna Television or cable
TV.
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.
Connector: A device that provides for a demountable connection
between two fibers or a fiber and an active device and provides
protection for the fiber.
- Connector: A device which terminates an optical fiber and allows temporary joining of fibers with like terminations.
- Core: The center of the optical fiber through which light is
transmitted.
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.
D
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 electrical
signals.
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.
E
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.
End 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.
ESCON: IBM standard for connecting peripherals to a computer
over fiber optics. Acronym for Enterprise System Connection.
Excess loss: The amount of light lost in a coupler, beyond that
inherent in the splitting to multiple output fibers.
F
Fiber: see Optical Fiber. - Fiber Amplifier: an all optical amplifier using erbium or other
doped fibers and pump lasers to increase signal output power
without electronic conversion.
Fiber Distributed Data Interface, FDDI: 100 Mb/s ring architecture
data network.
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, 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. - FTTH: fiber to the home
Fusion splicer: An instrument that splices fibers by fusing or
welding them, typically by electrical arc.
G
Graded index (GI): A type of multimode fiber which used a graded
profile of refractive index in the core material to correct for
dispersion.
I
Index of refraction: A measure of the speed of light in a material.
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.
J
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.
L
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.
Launch 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 tested.
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.
M
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 (*m): 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.
Modal 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 singlemode
fiber.
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 optical fiber.
Mode: A single electromagnetic field pattern that travels in
fiber.
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.
N
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
communications.
Numerical aperture (NA): A measure of the light acceptance angle
of the fiber.
O
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 microWatt).
Optical return loss, back reflection: 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.
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.
P
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 laser or coupler.
Plastic optical fiber (POF): An optical fiber made of plastic.
Plastic-clad silica (PCS) fiber: A fiber made with a glass core
and plastic cladding.
POF: plastic optical fiber, optical fiber made from polymer materials. - Power budget: The difference (in dB) between the transmitted
optical power (in dBm) and the receiver sensitivity (in dBm).
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 drawn.
R
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. - Reference cable: A known good fiber optic jumper cable attached
to a light source or power meter used as a reference cable for loss testing.
- Reflectance: Light reflected from the
cleaved or polished end of a fiber caused by the difference of
refractive indices of air and glass.
- Refractive 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.
-
S
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 (fusion or mechanical): A device that provides for a connection
between two fibers, typically intended to be permanent.
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.
T
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 components.
Total internal reflection: Confinement of light into the core
of a fiber by the reflection off the core-cladding boundary.
Transmitter: A device which includes a LED or laser source and
signal conditioning electronics that is used to inject a signal
into fiber.
V
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.
W
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).
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