Fan-out Cable
Multi fibre cable designed for easy connectorization. Often sold with connectors installed, or as part of a splice pig tail, with one end carrying many connectors and the other installed in a splice cabinet or panel ready for splicing or patching. An important added value product, it is often called a drop cable, an intra facility cable, or an inter-facility cable. It is often sold packaged as installed in a patch panel, ready to splice on one side, ready to connect to equipment with jumpers on the other.

FDDI
Fibre Distribution Data Interface.

Ferrule
The component with a precise capillary which holds a fibre in place and aids in its alignment. The standard ferrule has an OD of 2.499 mm, and a capillary of about 126 microns. The single mode versions normally carry tolerances on OD, ID and concentricity of a micron or less.

Fibre
The dielectric waveguide that guides and conveys the light along a desired path with minimal or managed loss. The fibre is composed of several glass (silica: SiO2) components: The Core is the central diameter, and in single mode has a diameter of 8.3 microns, 50 or 62.5 microns or more in multimode. The Cladding builds the diameter to 125 microns. Between the core and the cladding exists the mode field, which in single mode begins at the core diameter and ranges 2-4 microns larger. The index of refraction between the core and the cladding is mismatched by about .01 (1.46/1.45), and this provides the basis for light being contained in the core, so long as the incident angle is less than 8 degrees. This mismatch is created and managed by doping of the silica with a family of "glass formers" which include sodium, potassium, boron, gallium etc..

Fibre Channel
Fibre Channel is an industry standard technology for transmitting data between computer devices at up to 1.0625 Gbps and over 10 km in distance.

Fiber Bragg Gratings (FBGs)
A photosensitive optical fiber that contains a periodic grating written into the core of the fiber by exposure to UV radiation; used as filters for specific wavelengths or bands of light.

Fibre bundle
A group of parallel optical fibres over which a loose fitting jacket has been extruded.

Filter, optical
A device or element that selectively transmits or blocks a range of wavelength.

Fresnel Loss
The loss at a joint due to a portion of the light being reflected. Some is always present, and its limit is a 100% unmated PC connector where the reflectance will reach a high of -14.8 dB. For instance in the case of 1300 NM the Fresnel loss is 3.16%, and in the case of 1550 the loss is 3.37%. The Fresnel loss in dB is 10 log .0316 and 10 log .0337 respectively, or 15 dB and 14.7 dB respectively.

Fusion splice
As opposed to a mechanical splice. Two fibre ends are butted and then joined by permanently bonding the glass endfaces through the softening of the glass which is fused together.