fiber optic


fiber optic
FIBER OPTIC CABLE
Glossary of Terms


Attenuation
Loss of signal power between points. In optical cables, attenuation is a ratio of input power vs. output power, measured in decibels per unit length, usually dB/km.

Backbone
A high-speed transmission system used to connect relatively distant points. Backbone networks can be used to join autonomous networks within buildings or between different buildings.

Bandwidth
The information carrying capacity of a fiber. The bandwidth for a given wavelength is the lowest frequency at which optical power has decreased by 3 dB and is expressed in MHz-km.

Bend Radius
The radius of curvature that an optical fiber cable can bend without causing harmful effects on the optical or mechanical performance of the cable.

Chromatic Dispersion
Different wavelengths travel along an optical medium at different speeds. Wavelengths reach the end of the medium at different times, causing the light pulse to spread. This chromatic dispersion is expressed in picoseconds (of dispersion) per kilometer (of length) per nanometer (of source bandwidth). It is the sum of material and waveguide dispersion.

Cladding
The layer of material, usually glass, that immediately surrounds the fiber core. The cladding is usually coated with another material to provide protection when handling.

Core
The central part of the glass construction through which light is transmitted.

Cut-off Wavelength
The wavelength at which a single-mode fiber transmits a single mode of light.

Dielectric
Non-metallic. All-dielectric de-signs are inherently non-conductive; all-dielectric cables contain no metal and are lightning resistant.

Graded Index
A core refractive index profile that varies with the radius of the core.

Loss Budget
The total acceptable loss for a given system from transmitter to receiver. Includes cables, splices and connectors.

Material Dispersion
Pulse dispersion due to the variations in a material’s refractive index as a function of wavelength.

Microbending
Minute but severe bends in fiber that result in light displacement and increased loss. Most microbending can be avoided by the correct selection of materials and proper cabling, handling, and installation techniques.

Mode
A path of light through a fiber.

Mode Field Diameter
In single-mode fiber, the region in which light propagates is larger than the glass core diameter. This mode field diameter is a measured value and often listed as a requirement with core diameter in fiber specifications.

Numerical Aperture
In fiber optics, the sine of half the angle over which a fiber can accept light, it is a function of the relationship between the refractive index of the core and that of the cladding.

Optical Time Domain Reflectometer (DTDR)
An instrument that measures transmission characteristics of fiber by sending a pulse of light down the fiber and measuring the light scattered across the length and reflected back from the end as a function of time. Used to measure attenuation, point discontinuities and fiber length, as well as to find breaks.

Refractive Index
The ratio of the speed of light in a vacuum to the speed of light in a material. Also called Index of Refraction.

Step Index
A refractive index profile characterized by a uniform refractive index within the core and a sharp decrease at the core-cladding interface.

Waveguide Dispersion
Dispersion caused by the fact that light travels at different speeds in the core and cladding of single-mode fibers.

Zero Dispersion Wavelength
In single-mode fibers, the wavelength at which the effects of chromatic dispersion and waveguide dispersion are lowest, thus providing the greatest information carrying capacity.