Fiber Sizes and Types

Fiber comes in two types, singlemode and multimode. Except for fibers used in specialty applications, singlemode fiber can be considered as one size and type. If you deal with long haul telecom or submarine cables, you may have to work with specialty singlemode fibers.

Multimode fibers originally came in several sizes, optimized for various networks and sources, but the data industry standardized on 62.5 core fiber in the mid-80s (62.5/125 fiber has a 62.5 micron core and a 125 micron cladding. It's now called OM1 standard fiber.) Recently, as gigabit and 10 gigabit networks have become widely used, an old fiber design has been revived. 50/125 fiber was used from the late 70s with lasers for telecom applications before singlemode fiber became available. 50/125 fiber (OM2 standard) offers higher bandwidth with the laser sources used in the gigabit LANs and can allow gigabit links to go longer distances. Newer OM3 or laser-optimized 50/125 fiber today is considered by most to be the best choice for multimode applications.

To identify the types of fiber in a cable, there are standardized color codes for the cable jacket covered under TIA-598. Here is more information on color codes for cables and connectors.

Fiber Specifications

The usual fiber specifications are size (core/cladding diameter in microns), attenuation coefficient (dB/km at appropriate wavelengths) and bandwidth (MHz-km) for multimode fiber and chromatic and polarization-mode dispersion for singlemode fiber. While manufacturers have other specs for designing and manufacturing the fiber to industry standards, like numerical aperture (the acceptance angle of light into the fiber), ovality (how round the fiber is), concentricity of the core and cladding, etc., these specs do not generally affect users who specify fibers for purchase or installation. Here is more information on testing fiber specifications.

Some fibers have been designed to be much less sensitive to bend-induced losses. These "bend-insensitive" fibers are designed for use as patchcords or in tight premises appplications where regular fibers would suffer losses. Here is more information on bend-insensitive fibers.

November 9, 2011

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