Friday, June 4, 2010

Glossary of Common Fiber Optic Terms: A - E

Common Fiber Terms: A-E


A.T.C. (Automatic Threshold Control)
Electric control circuit which regulates the input current to an LED to prevent it from being overdriven.

Absorption Losses
Losses caused by impurities principally transition metals and neighboring elements (Cr, Mn, Fe, Co, Ni), and also by water as well as intrinsic material absorption.

Acceptance Angle
Any angle measured from the longitudinal center line up to the maximum acceptance angle of an incident ray that will be accepted by the waveguide. The maximum acceptance angle is depend­ent on the indices of refraction of the two mediums.

A mechanical media termination device designed to align and join fiber optic connectors. Often referred to as a coupling, bulkhead, or interconnect sleeve.

Angle on Incidence
The angle between an incident ray and the normal to a reflecting surface.

Aramid Yarn
Fibers, yellow, that provide cable tensile strength, support, and additional protection of the optical fiber bundles. KevlarĂ’ is a particular brand of aramid yarn. Often refered to as central strength member.

Protective material in cable made of corrugated steel.

A method of data multiplexing that can provide large, instantaneous bandwidths for busy traffic while permitting slow traffic to use that bandwidth between bursts. Very short, fixed-length packets or cells are used to transmit information. Its basic cell is 53 bytes long.

a measure of the decrease in energy transmission (loss of light) expressed in dB/Km. When in optical wave guides it is primarily due to absorption losses and scattering losses.

Avalanche photodiode (APD)
A type of semiconductor detector operated at high voltages. When incident light generates photoelectron from the material, the high voltage across the device accelerates the elec­tron enough to cause avalanche of other electrons, effectively amplifying the signal. An avalanche photodiode could be seen as similar to a solid state photo-multiplier.

Axial Ray
A ray passing through the axis of the optical waveguide without any internal reflection.


Back Reflection
An undesirable characteristic in singlemode fiber transmission. Reflectance of light pulse back towards the transmitted source. Also referred to as Optical Return Loss (ORL).

See “Back Reflection”

The capacity of an optical fiber to transmit information expressed in bits of information transmitted in a specific time period for a specific length of optical wave guide. (Usually expressed in megabits/sec./km.) Bandwidth is limited by pulse spreading or broadening due to dispersion, so that adjacent pulses overlap and cannot be distinguished. (see Pulse Dispersion)

A device which divides a beam of light passing through it into separate beams going in two different directions. Some types affect polarization of the beam, while others do not. Various splitting ratios are possible. (eg., 90-10, 70-30, 50-50, etc.)

Bend Radius
Maximum bend allowed before physical damage is incurred. Generally expressed for two conditions, loaded (under tensile load) or unloaded.

An electrical light pulse whose presence or absence indicates data. The capacity of the optical waveguide to transmit information through the waveguide without error is expressed in bits per second per unit length.

Bragg Gratings, Fiber
Fiber that is treated to back reflect a particular wavelength, called the Bragg Wavelenth. See technical notes: Fiber Bragg Gratings

Material used to protect an optical fiber or cable from physical damage and providing mechanical isolation or protection. Fabrication techniques include both tight jacket, or loose tube buffering, as well as multiple buffer layers.

Bulkhead Attenuator
A mechanical media termination device designed to align and join fiber optic connectors, designed to be mounted on a panel, and that contains an attenuation device.

Bulkhead Connector
A mechanical media termination device designed to align and join fiber optic connectors, designed to be mounted on a panel. Often referred to as a coupling, bulkhead, interconnect or mating sleeve.


Card-Edge Connector
Designed for printed circuit boards for blind mating of connectors.

Central Member
The center component of a cable used to provide strength. Commonly referred to as “Central Strength Member”

Chromatic Dispersion
Spreading of a light pulse caused by the difference in refractive indices at different wavelengths.

A low refractive index, glass or plastic that surrounds the core of a fiber. Optical cladding promotes total internal reflection for the propagation of light in a fiber.

A process in which a divergent or convergent beam of radiation is converted into a beam with the minimum divergence as possible, preferably parallel.

Composite Cable
A cable containing both fiber and copper conductors.

A junction which allows users to connect / disconnect cables or devices.

The light conducting portion of a fiber, defined by its high refraction index. The core is the center of a fiber, surrounded by concen­tric cladding of lower refractive index.

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 (fiber optic)
A coupler is a device which joins together three or more fiber ends, for example, splitting the signal from one fiber so it can be transmitted to two or more other fibers. Directional , star, and tee couplers are the most common varieties.

Coupling Loss
The power loss suffered when coupling light from one optical device to another.


Dark Current
The output current that a photodiode emits in the absence of light.

Data Link (fiber optic)
A fiber optic signal transmission system which carries information in digital or (sometimes) analog form. Usually this term refers to short-distance communications, spanning distances of less than a kilometer.

Data Rate
The maximum number of bits of information that can be transmitted per second, as in a data transmission link. Typically expressed as megabits per second (Mbps)

Decibels relative to one milliwatt. A positive number indicates the power is above one milliwatt; a negative number indicates the power is below. This unit has become common in fiber optic communication sys­tems because the power of light sources used with optical fibers is on the order of one milliwatt.

The standard unit used to express the ratio of two power 1evels. It is used in communications to express either a gain or loss in power between the input and output devices.

A device which separates two or more signals that have been multiplexed together for transmission through a single fiber. (See multiplexer.)

A transducer that provides an electrical output signal in response to an incident optical signal. The current is dependent on the amount of light received and the type of device.

A device in which an optical detector is packaged together with electronic amplification circuitry.

Non-metallic, and therefore, non-conductive. Glass fibers are considered dielectric. A dielectric cable contains no metallic components.

Diode Adapter Receptacle
Designed to house LED or PlN/APD diodes in a receptacle which allows the mating plug to position the fiber for an optimum coupling efficiency.

Directional Coupler (fiber optics)
A fiber coupler is directional if it preferentially transmits light in one direction.

Spread of the signal delay in an optical waveguide. It consists of various components: modal dispersion, material dispersion, and waveguide dispersion. As a result of its dispersion, an optical waveguide acts as a low-pass filter for the transmitted signals.

The spreading out of a laser beam with Distance, measured as an angle.

Doppler Shift
A change in the wavelength of light caused by the motion of an object emitting (or reflecting) the light. Motion toward the observer causes a shift toward shorter wavelengths, while motion away causes a shift toward longer wavelegths.

Driver I.C
An amplifier in an integrated circuit used to increase signal current to the LED for greater transmission distance.

Duplex Cable (fiber optics)
A cable which contains two optical fibers in a single cable structure. Light is not coupled between the two fibers: typically one is used to transmit signals in one direction and the other used to transmit in the opposite direction.

Duplex Connector (Fiber optics)
A connector which simultaneously makes two connections, joining one pair of optical fibers with another.


E.C.L. (Emitted-Coupled Logic)
Method of data transmission which uses negative logic. -0.8V is "1" and -1.6V is "0".

Electromagnetic Interference (EMI)
The frequency spectrum of electromagnetic radiation extending from subsonic frequency to X-rays. This term should not be used instead of the term "RFI" (see RFI) (Shielding materials for the entire EMI spectrum are not readily available.)

EMP (Electromagnetic Pulse)
An extremely strong short lived magnetic field resulting from a nuclear explosion could cause a damaging magnetic field at a distance of 1500-3000 miles.

End Finish
Quality of the surface of an optical fiber's end, commonly described as mirror, mist, hackle, chipped, cracked or specified by final grit size in polishing. (1um, .3um, etc.). See “Polish”

End Separation Loss
The optical power loss of a fiber and source, detector or another fiber (see Frensel Reflection).

Extinction ratio
a performance standard measurement of polarization maintaining (PM) fiber. The measurement of light entering and exiting a fiber indicates how well the fiber maintains polarization.

Extrinsic joint Loss
Loss caused by imperfect alignment of fibers in a connector or splice. Contributors include angular misalignment, lateral offset, end separation and end finish. Generally synonymous with Insertion loss.

Common Fiber Terms F-L

Common Fiber Terms M-P

Common Fiber Terms R-Z