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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 thecore, thecladding, and thecoatingor buffer.

Core

The light-conducting central portion of an optical fiber, composed of material with a higherindex of refraction than the cladding. The portion of the fiber that transmits light.

Cladding

Material that surrounds thecoreof an optical fiber. Its lowerindex of refraction, compared tothat of the core, causes the transmitted light to travel down the core.

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Coating

The material surrounding thecladdingof a fiber. Generally a soft plastic material that protects

the fiber from damage.

Single-mode (SM) Fiber

A small-coreoptical fiberthrough which only onemodewill propagate. The typical diameter is

8-9 microns.

Multimode (MM) Fiber

Anoptical fiberthat has a core large enough to propagate more than one mode of light Thetypical diameter is 62.5 micrometers.

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Index of Refraction

The ratio of the velocity of light in free space to the velocity of light in a fiber material. Always

greater than or equal to one. Also called refractive index.

n = C/V

Where:

C = The speed of light in a vacuum.

V = The speed of the same wavelength in the fiber material.

Attenuation

The decrease in signal strength along a fiber optic waveguide caused by absorption and

scattering. Attenuation is usually expressed in dB/km

Absorption

That portion of optical attenuation in optical fiber resulting from the conversion of optical powerto heat. Caused by impurities in the fiber such as hydroxyl ions.

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Backreflection (BR)

A term applied to any process in thecable plantthat causes light to change directions in a fiberand return to the source. Occurs most often at connector interfaces where a glass-air interface

causes a reflection.

Backscattering

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.

Bend Radius

The smallest radius an optical fiber or fiber cable can bend before excessive attenuation or

breakage occurs.

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BER (Bit Error Rate)

The fraction of bits transmitted that are received incorrectly. Thebiterror rate of a system can beestimated as follows:

Where N0 = Noise power spectral density (A2/Hz).

IMIN = Minimum effective signal amplitude (Amps).

B = Bandwidth (Hz).

Q(x) = Cumulative distribution function (Gaussian distribution).

Bending Loss

Attenuation caused by high-order modes radiating from the outside of a fiber opticwaveguide

which occur when the fiber is bent around a small radius. See alsomacrobending,microbending.

Macrobending

In a fiber, all macroscopic deviations of the fibersaxisfrom a straight line, that will cause lightto leak out of the fiber, causing signalattenuation.

Microbending

Mechanical stress on afiberthat introduces local discontinuities, which results in light leakingfrom thecoreto thecladdingby a process calledmode coupling.

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Binary

Base two numbers with only two possible values, 0, or 1. Primarily used by communication andcomputer systems.

Bit

The smallest unit of information upon which digital communications are based; also an electrical

or opticalpulsethat carries this information.

Pulse

A current or voltage which changes abruptly from one value to another and back to the originalvalue in a finite length of time. Used to describe one particular variation in a series of wave

motions. Th