Optical fiber sizes

One of the major ways of specifying optical fibre cables is by the diameters of the inner core and the external cladding. As may be expected there are industry standards for these and this helps in reducing the variety of fittings needed for connectors, splices and the tools needed for fitting.

The standard for most optical fibres is 125 microns (um) for the cladding and 245 microns (um) for the outer protective coating. Multimode optical fibres have core sizes of either 50 or 62.5 microns whereas the standards for single mode fibres is approximately 8 to 10 microns.

When specifying optical fibre cables, the diameters usually form the major part of the cable specification. A multimode fibre with a core diameter of 50 microns and a cladding diameter of 125 microns would be referred to as a 50/125 fibre.

In addition to the specification of the diameter, other parameters such as the loss, etc are also required, but these elements do not form part of the cable type in the same way as the diameter.