Glossary
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APC
Polishing
The angled physical contact (APC) polish adds an 8 degree angle to
a flat polish. Back reflection can be reduced to about —70 dB with
this technique.
Absorption
Loss of power in an optical fiber, resulting from conversion of
optical power into heat and caused principally by impurities, such
as transition metals and hydroxyl ions, and also by exposure to
nuclear radiation.
Acceptance
Angle the half-angle of the cone within which incident light is
totally internally reflected by the fiber core. It is equal to arcsin
(NA).
Active
Branching Devices
A device which converts an optical input into two or more optical
outputs with gain or regeneration.
Adjustable
Attenuator
An attenuator in which the level of attenuation is varied with an
internal adjustment. Also known as variable Attenuator.
Angular
Misalignment
The loss of optical power caused by deviation from optimum alignment
of fiber to fiber or fiber to waveguide.
Attenuation
A general term indicating a decrease in power from one point to
another. In optical fibers, it is measured in decibels per kilometer
at a specified wavelength.
Avalanche
Photodiode (APD)
A photodiode that exhibits internal amplification of photo current
through avalanche multiplication of carriers in the junction region.
Average
Wavelength (l)
The average of the two wavelengths for which the peak optical power
has dropped to half.
"sBackscattering
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.
Bandwidth
A range of frequencies.
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.
Bend
Loss
A form of increased attenuation in a fiber that results from bending
a fiber around a restrictive curvature (a macrobend) or from minute
distortions in the fiber (microbend).
Broadband
A method of communication in which the signal is transmitted by being
impressed on a higher-frequency carrier.
Buffer
Coating
A protective layer, such as an acrylic polymer, applied over the fiber
cladding for protective purposes.
Buffer
Tube
A hard plastic tube, having an inside diameter several times that
of a fiber, that holds one or more fibers.
Cable
Assembly
Fiber optic cable that has connectors installed on one or both ends.
General use of these cable assemblies includes the interconnection
of multimode and singlemode fiber optical cable systems and optoelectronics
equipment. If connectors are attached to only one end of the cable,
it is known as a pigtail. It's connectors are attached to both ends,
it is known as a jumper.
Cable
Bend Radius
Cable bend radius during installation infers that the cable is experiencing
a tensile load. Free bend infers a lower allowable bend radius since
it is at a condition of no load.
Center
Wavelength (Laser)
The nominal value central operating wavelength. It is the wavelength
defined by a peak mode measurement where the effective optical power
resides.
Center
Wavelength (LED)
The average of the two wavelengths measured at the half amplitude
points of the power spectrum.
Chromatic
Dispersion
Spreading of a light pulse caused by the difference in refractive
indices at different wavelengths.
Cladding
The outer concentric layer that surrounds the fiber core and has a
lower index of refraction.
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.
Coating
A material put on a fiber during the drawing process to protect it
from the environment.
Connector
A device for making connectable/disconnectable connections of a fiber
to another fiber, source, detector, or other devices.
Connector
Plug
A device used to terminate an optical conductor cable.
Connector
Receptacle
The fixed or stationary half of a connection that is mounted on a
panel/bulkhead. Receptacles mate with plugs.
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 known as Optical Connector Variation.
Core
The central, light-carrying part of an optical fiber; it has an index
of refraction higher than that of the surrounding cladding.
Core
Eccentricity
A measure of the displacement of the center of the core relative to
the cladding center.
Core
Ellipticity (non-circularity)
A measure of the departure of the core from roundness.
Coupler
A multiport device used to distribute optical power.
Coupling
Efficiency
The efficiency of optical power transfer between two components.
Coupling
Ratio/Loss (CR, CL)
The ratio/loss of optical power from one output port to the total
output power, expressed as a percent. For a 1* 2 WDM or coupler with
output powers 01 and 02, and Oi representing both output powers.
Critical
Angle
The smallest angle from the fiber axis at which a ray may be totally
reflected at the core/cladding interface.
Cut-off
Wavelength
For a singlemode fiber, the wavelength above which the fiber exhibits
singlemode operation.
DB
Decibel.
Dbm
Decibel referenced to a milliwatt.
DBµ
Decibel referenced to a microwatt.
Decibel
A standard logarithimic unit for the ratio of two powers, voltages
or currents. In fiberoptics, the ratio is power.
Detector
An optoelectronics transducer used in fiberoptics for converting optical
power to electric current. In fiberoptics, usually a photodiode.
Dichroic
Filter
An optical filter that transmits light selectively according to wavelength.
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.
Directivity
See Near-end Crosstalk.
Dispersion
A general term for those phenomena that cause a broadening or spreading
of light as it propagates through an optical fiber.The three types
are model, material and waveguide.
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).
Excess
Loss
In a fiberoptic coupler, the optic loss from that portion of light
that does not emerge from the nominally operational ports of the device.
Extinction
Ratio
The ratio of the low, or off optical power level (PL) to the high,
or on optical power level (PH) when the station is transmitting a
stream of Halt symbols. Extinction Ratio (%) = (PL/PH) * 100
Extrinsic
Loss
In a fiber interconnection, that portion of loss that is not intrinsic
to the fiber but is related to imperfect joining, which may be caused
by the connector or splice.
FDDI
Fiber Distributed Data Interface.
Ferrule
A mechanical fixture, generally a rigid tube, used to confine and
align the stripped end of a fiber.
Fiberoptic
Attenuator
A component that is installed in a fiberoptic transmission system
to reduce 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.
Fiberoptic
Communication System
The transfer of modulated or unmodulated optical energy through optical
fiber media which terminates in the same or different media.
Fiberoptic
Link
A combination of fiberoptic spans and repeaters which are concentrated
to form a transmission path.
Fiber
Dielectric material the guides light; waveguide.
Fiberoptic
Cable
A cable containing one or more optical fibers.
Fiber
Optic Test Procedure (FOPT)
Standards developed and published by the Electronic Industrials Association
(EIA) under the EIA-RS-455 series of standards.
Flat
Polishing
A flat polish of the endface results in back reflection of about —14
dB (4%).
FTTH
Abbreviation for Fiber-to-the-Home.
Fusion
Splicing
A permanent joint accomplished by the application of localized heat
sufficient to fuse or melt the ends of the optical fiber, forming
continuous single fiber.
Graded-index
Fiber
An optics fiber whose core has a nonuniform index of refraction. The
core is composed on concentric rings if glass whose refractive ineices
decrease from the center axis. The purpose is to reduce model dispersion
and thereby increase fiber bandwidth.
Index
of Refraction
The ratio of the velocity of light in free space to the velocity of
light in a given material. Symbolized by n.
Index-Matching
Material
A material, used at optical interconnection, having a refractive index
close to that of the fiber core and used to reduce Fresnel reflections.
>Insertion
Loss
The loss of power that results from inserting a component, such as
a connector or splice, into a previously continuous path.
Jumper
Fiberoptic cable that has connectors installed on both ends.
Laser
A light source producing, through simulated emission, coherent, near
monochromatic light. Lasers in fiberoptics are usually solid-state
semiconductor types.
Launch
Angle
Angle between the propagation direction of the incident light and
the optical axis of an optical waveguide.
Launch
Fiber
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 model distribution in multimode fiber. Also referred
to as launching Fiber.
Light
In the laser and optical communication fields, the portion of the
electrode by the basic optical techniques used for the visible spectrum
extending from the near ultraviolet region of approximately 0.3 micron,
through the visible region and into the mid-infrared region of about
30 microns.
Light-Emitting
Diode (LED)
A semiconductor diode that spontaneously emits light from the pn junction
when forward current is applied.
Lightwaves
Electromagnetic waves in the region of optical frequencies. The term
"light" was originally restricted to radiation visible to the human
eye, with wavelengths between 400 and 700 nm. However, it has become
customary to refer to radiation in the spectral regions adjacent to
visible light (in the near infrared from 700 to about 2000 nm)as "light"
to emphasize the physical and technical characteristics they have
in common with visible light.
Mechanical
Splicing
Joining two fibers together by mechanical means to enable a continuos
signal. Elastomeric splicing is one example of mechanical splicing.
Megahertz
(Mhz)
A unit of frequency that is equal to one million hertz.
Microbending
Curvatures of the fiber which involve axial displacements of a few
micrometers and spatial wavelengths of a few millimeters. Microbends
cause loss of light and consequently increase the attenuation of the
fiber.
Micromn>
Another term for micrometer. One millionth of a meter. 10epx-6 meter.
Misalignment
Loss
The loss of power resulting from angular misalignment, lateral displacement
and end separation.
Modal
Dispersion
Dispersion resulting from the different transit lengths of different
propagating modes in a multimode optical fiber.
Mode
In guided wave propagation, such as through a waveguide or optical
fiber, a distribution of electromagnetic energy that satisfies Maxwell's
equations and boundary conditions. Loosely, a possible path followed
by light rays.
Mode
Field Diameter (MFD)
The diameter of optical energy in a singlemode fiber. Because the
MFD is greater than the core diameter, MFD laser core diameter as
a practical parameter.
Mode
Filter
A device used to remove high-order modes from a fiber and thereby
simulate EMD.
Multimode
Fiber
A type of optical fiber that supports more than one propagating mode.
Multiplexing
The process by which two or more signals are transmitted over a single
communications channel. Examples include time-division multiplexing
and wavelength-division multiplexing.
Nanometer
A unit of measurement equal to one billionth of a meter.
Near-end
Crosstalk
The optical power reflected from one or more input ports, back to
another input port.
Numeric
Aperture (NA)
The "lightgathering ability" of a fiber, defining the maximum angle
to the fiber axis at which light will be accepted and propagated through
the fiber. NA=sinq, where q is the acceptance angle. NA also is used
to describe the angular spread of light from a central axis, as in
exiting a fiber, emitting from a source, or entering a detector.
OEM
Original Equipment Manufacturer.
Optical
Bandpass
The range of optical wavelengths which can be transmitted through
a component.
Optical
Channel Spacing
The wavelength range of a channel.
Optical
Channel Width
The optical wavelength range of a channel.
Optical
Fiber
Dielectric material that guides light; optical waveguide.
Optical
Isolator
A component used to block out reflected and other unwanted light.
Optical
Return Loss (ORL)
The ratio (expressed in units of 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.
PC
Polishing
The physical contact (PC) polish produces a slightly curved endface
that forces the fibers in the mating connectors into contact. This
reduces back reflection to about —40dB.
Passive Branching Device
A device which divides and optical input into two or more optical
outputs.
Peak Wavelength
The wavelength at which the optical power of a source is at a maximum.
Photodetector
An optoelectronic tansducer, such as a pin photodiode or avalanche
photodiode.
Pigtail
A short length of fiber permanently attached to a component, such
as a source, detector, coupler or connector.
Pin
Photodiode
A photodiode having a large intrinsic layer sandwiched between p-type
and n-type layers.
Polarization
The direction of the electric field in the lightwave.
>Port
Hardware entity at each end of the link.
Prefusing
Fusing with a low current to clean the fiber end. Precedes fusion
splicing.
Primary
Coating
The plastic coating applied directly to the cladding surface of the
fiber during manufacturing to preserve the integrity of the surface.
SPC
Polishing
The super physical contact (SPC) polish includes an extended polishing
cycle for a better surface finish, resulting in back reflection as
low as —55 dB.
Sensitivity
For a fiberoptic receiver, the minimum optical power required to achieve
a specified level of performance, such as BER.
Signal-to-Noise
Ration (SNR, S/N)
The ratio (usually expressed in dB) of the dominant mode power Pd,
to the power of the largest side mode, Ps.
Simplex
Cable
A term sometimes used for a single-fiber cable.
Simplex
Transmission
Transmission in one direction only.
Singlemode
Fiber
An optical fiber that supports only one mode of light propagation
above the cutoff wavelength.
Source
The light emitter, either an LED or laser diode, in a fiberoptic link.
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 20 to 60 nm for an LED
and 2 to 5 nm for a laser diode.
Splice
Closure
A container used to organize and protect splice trays.
Splice
Tray
A container used to organize and protect spliced fibers.
Splicing
The permanent joining of fiber ends to identical or similar fibers,
without the use of a connector.
Stabilized
Light Source
An LED or laser diode that emits light with a controlled and constant
spectral width, central wavelength, and peak power with respect to
time and temperature.
Star
Coupler
A fiberoptic coupler in which power at any input port is distributed
to all output ports.
Step-Index
Fiber
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.
Tee
Coupler
A three-port optical coupler.
Tight
Buffer
Type of cable construction whereby each glass fiber is tightly buffered
by a protective thermoplastic coating to a diameter of 900 microns.
High tensile strength rating achieved, providing durability, ease
of handling and ease of connectorization.
Transmission
Loss
Total loss encountered in transmission through a system.
Tree
A physical topology consisting of a hierarchy of master-slave connections
between a concentrator and other FDDE nodes (including subordinate
concentrators).
Wavelength-Division
Multiplexers (WDMs)
Passive fiberoptic components which combine or separate optical channels.
Wavelength-Division
Multiplexers
A transmission technique by which separate optical channels, distinguished
by wavelength, are multiplexed onto an optical fiber for transmission.
Wavelength
Isolation
A WDM's isolation of light signal in the desired optical channel from
the unwanted channels. Synonym: Far-end Crosstalk.
